Portrait of Dr Helena Shepherd

Dr Helena Shepherd

Senior Lecturer in Chemistry


Helena graduated from the University of Bath in 2006 with an MChem (first class honours), before moving to Durham University to study for a PhD in the Department of Chemistry under the supervision of Dr Andrés E. Goeta and Professor Judith A. K. Howard (CBE, FRS). Helena's thesis described detailed structure-property correlations in switchable molecular materials using in-situ light irradiation, high-pressure and variable-temperature crystallographic investigations. 

In 2010 Helena moved to the Laboratoire de Chimie de Coordination in Toulouse (LCC-CNRS) for a two-year post-doctoral appointment under the supervision of Dr Gábor Molnár and Dr Azzedine Bousseksou in the Switchable Molecular Materials group.  During that time Helena investigated the physics of the spin crossover phenomenon under pressure, in collaboration with Professor Philippe Guionneau at the Institut de Chimie de la Matière Condensée de Bordeaux (ICMCB-CNRS), and initiated a project concerned with novel applications for molecular materials as actuator devices.  In 2013, Helena returned to the University of Bath for a post-doctoral position under the supervision of Professor Paul R. Raithby, before taking up the position of Lecturer in Chemistry at the University of Kent in 2015.  

Research interests

Dr Shepherd's principal research interests are concerned with the development of new smart materials with useful properties (colour, size, magnetism, etc.) that can change in response to an external influence (e.g. temperature, pH, stress). She conducts both fundamental studies aimed at rationalisation of the underlying physical phenomena giving rise to the switchable properties, and also seeks to develop these materials towards useful real-world applications.


Showing 50 of 59 total publications in the Kent Academic Repository. View all publications.


  • Lord, R. et al. (2019). ?-Ketoiminato iridium(III) organometallic complexes: Selective cytotoxicity towards colorectal cancer cells HCT116 p53-/-. Chemistry - A European Journal [Online] 25:495-500. Available at: https://doi.org/10.1002/chem.201804901?
    This report presents a new library of organometallic iridium(III) compounds of the type [Cp*IrCl(N,O)] (Cp* = pentamethylcyclopentadienyl and N,O = a functionalized ??ketoiminato ligand) showing moderate to high cytotoxicity against a range of cancer cell lines. All compounds show increased activity towards colorectal cancer, with preferential activity observed against the immortalized p53?null colorectal cell line, HCT116 p53?/?, with sensitivity factors (SF) up to 26.7. Additionally, the compounds have excellent selectivity for cancerous cells when tested against normal cell types, with selectivity ratios (SR) up to 35.6, contrary to that of cisplatin which is neither selective nor specific for cancerous cells (SF = 0.43 and SR = 0.7?2.3). This work provides a preliminary understanding of the cytotoxicity of iridium compounds in the absence of p53 and has potential applications in treatment of cancers for which the p53 gene is absent or mutant.
  • Saunders, L. et al. (2018). Tuning charge-assisted and weak hydrogen bonds in molecular complexes of the proton sponge DMAN by acid co-former substitution. CrystEngComm [Online] 20:3074-3083. Available at: https://doi.org/10.1039/C8CE00443A.
    Nine new molecular complexes of the proton sponge 1,8-bis(dimethylamino)naphthalene (DMAN) with substituted benzoic acid co-formers have been engineered with varying component stoichiometries (1?:?1, 1?:?2 or 1?:?3). These complexes are all ionic in nature, following proton transfer between the acid co-former and DMAN; the extracted proton is held by DMAN in all instances in an intramolecular [N–H?N]+ hydrogen bond. A number of structural features are common to all complexes and are found to be tunable in a predictable way using systematic acid co-former substitution. These features include charge-assisted hydrogen bonds formed between acid co-formers in hydrogen bonding motifs consistent with complex stoichiometry, and weak hydrogen bonds which facilitate the crystal packing of DMAN and acid co-former components into a regular motif. Possible crystal structure tuning by co-former substitution can aid the rational design of such materials, offering the potential to target solid-state properties that may be influenced by these interactions.
  • Tyuleva, S. et al. (2018). A Symbiotic Supramolecular Approach to the Design of Novel Amphiphiles with Antibacterial Properties Against MSRA. Chemical Communications [Online] 55. Available at: http://dx.doi.org/10.1039/C8CC08485H.
    Herein, we identify Supramolecular Self-associating Amphiphiles (SSAs) as a novel class of antibacterials with activity towards Methicillin-resistant Staphylococcus aureus. Structure-activity relationships have been identified in the solid, solution and gas phases. Finally, we show that when supplied in combination, SSAs exhibit increased antibacterial efficacy against these clinically relevant microbes.
  • Gaspar, A. et al. (2018). Pressure effect investigations on spin-crossover coordination compounds. Comptes Rendus Chimie [Online] 21:1095-1120. Available at: https://doi.org/10.1016/j.crci.2018.07.010.
    The piezochromic properties of spin-crossover complexes have been recognized for a long time, with increasing pressure favouring the low spin state due to its smaller volume and therefore shifting the spin equilibrium towards higher temperatures and accelerating the relaxation at a given temperature. However, the interpretation and quantification of pressure-induced changes have been several times compromised by the relatively poor and incomplete spectral and structural information provided by the detection methods or due to the experimental difficulties related to the need for hydrostatic conditions at low temperatures. The present review is therefore primarily focused on these experimental aspects of high-pressure spin crossover research providing an overview of methods of pressure generation and associated detection methods as well as on selected recent results
  • Mikolasek, M. et al. (2018). Complete Set of Elastic Moduli of a Spin-Crossover Solid: Spin-State Dependence and Mechanical Actuation. Journal of the American Chemical Society [Online] 140:8970-8979. Available at: http://dx.doi.org/10.1021/jacs.8b05347.
    Molecular spin crossover complexes are promising candidates for mechanical
    actuation purposes. The relationships between their crystal structure and mechanical properties
    remain, however, not well understood. In this study, combining high pressure synchrotron Xray
    diffraction and nuclear inelastic scattering measurements, we assessed the effective
    macroscopic bulk modulus (11.5 ± 2.0 GPa), Young’s modulus (10.9 ± 1.0 GPa) and Poisson’s
    ratio (0.34 ± 0.04) of the spin crossover complex [FeII(HB(tz)3)2] (tz = 1,2,4-triazol-1-yl) in its
    low spin state. Crystal structure analysis revealed a pronounced anisotropy of the lattice
    compressibility, which was correlated with the difference in spacing between the molecules in
    different crystallographic directions. Switching the molecules from the low spin to the high spin
    state leads to a remarkable drop of the Young’s modulus to 7.1 ± 0.5 GPa, which was also
    assessed in thin film samples by means of micromechanical measurements. These results are in
    agreement with the high cooperativity of the spin crossover in this compound and highlight its
    application potential in terms of recoverable stress (21 ± 1 MPa) and work density (15 ± 6
  • Félix, G. et al. (2018). Elasticity of Prussian-Blue-Analogue Nanoparticles. European Journal of Inorganic Chemistry [Online]. Available at: http://dx.doi.org/10.1002/ejic.201700796.
    We report on the elastic properties of Ni/[Fe(CN)6] Prussian-blue-analogue nanoparticles investigated by high-pressure synchrotron X-ray diffraction and nuclear inelastic scattering. For 3 nm and 115 nm particles, we have obtained bulk moduli of (30.3?±?3.8) GPa and (24.5?±?3.2) GPa, with Debye sound velocities of (2496?±?46) m?s–1 and (2407?±?38) m?s–1, respectively. Combining these results, Poisson's ratio, Young's modulus, the shear modulus, and the transversal/longitudinal sound velocities have been calculated for each particle size. All of these physical quantities suggest a stiffening of the lattice when the particle size decreases, which is mainly attributed to the reduction of iron ions on the particle surface.
  • Balónová, B. et al. (2018). Influencing the Optoelectronic Properties of a Heteroleptic Iridium Complex by Second-Sphere H-Bonding Interactions. Inorganic Chemistry [Online]. Available at: https://doi.org/10.1021/acs.inorgchem.8b01326.
    The use of a new second-sphere coordination methodology for emission color
    tuning of iridium complexes is presented. We demonstrate that a complimentary H-bonding guest
    molecule binding through contiguous triple H-bonding interactions can induce a shift in the
    emission of the iridium complex from green to blue without the need to alter the ligand structure
    around the metal centre, while simultaneously increasing the photoluminescence quantum yield in
    solution. The association constant for this host-guest interaction was determined to be Ka = 4.3 x
    103 M-1 in a solution of 2% dimethylsulfoxide in chloroform by UV-Vis titration analysis and the
    impact of the hydrogen bonding interaction further probed by photoluminescence, electrochemical, and computational methods. Our findings suggest that directed self-assemblies are an effective approach to influencing emission properties of phosphorescent iridium (III)
  • Pearce, K. et al. (2018). Exploring the reactivity of donor-stabilised phosphenium cations: Lewis acid catalysed reduction of chlorophosphanes by silanes. Inorganic Chemistry [Online] 57:11530-11536. Available at: http://dx.doi.org/10.1021/acs.inorgchem.8b01578.
    Phosphane-stabilised phosphenium cations react with silanes to effect either reduction to primary or secondary
    phosphanes, or formation of P-P bonded species depending upon counter-anion. This operates for in situ generated phosphenium
    cations, allowing catalytic reduction of P(III)-Cl bonds in the absence of strong reducing agents. Anion and substituent dependence
    studies have allowed insight into the competing mechanisms involved.
  • White, L. et al. (2018). Towards the prediction of global solution state properties for hydrogen bonded, self-associating amphiphiles. Chemistry - A European Journal [Online] 24:7761-7773. Available at: https://doi.org/10.1002/chem.201801280.
    Through this extensive structure-property study we show
    that critical micelle concentration correlates with self-associative
    hydrogen bond complex formation constant, when combined with
    outputs from low level, widely accessible, computational models.
    Herein, we bring together a series of 39 structurally related
    molecules obtained through stepwise variation of a hydrogen bond
    donor-acceptor amphiphilic salt. The self-associative and
    corresponding global properties for this family of compounds have
    been studied in the gas, solid and solution states. Within the solution
    state we have shown the type of self-associated structure present to
    be solvent dependent. In DMSO, this class of compound show a
    preference for hydrogen bonded dimer formation, however moving
    into aqueous solutions the same compounds are found to form
    larger self-associated aggregates. This observation has allowed us
    the unique opportunity to investigate and begin to predict selfassociation
    events at both the molecular and extended aggregate
  • Gumbs, T. et al. (2018). 'Frustrated' hydrogen bonded self-associated systems as templates towards DNA incorporated nanostructure formation. Supramolecular Chemistry [Online] 30:42-51. Available at: http://dx.doi.org/10.1080/10610278.2017.1351613.
    Herein, we present the synthesis of a thymine nucleobase appended ‘frustrated’ monomer, which exhibits self-association in DMSO solutions through the formation of hydrogen bonds. This self-association process has been explored in both competitive DMSO solutions and the solid state, using a combination of NMR and single crystal X-ray diffraction techniques. The self-associative equilibria within the solution state are balanced in such a way that the hydrogen bond donating (HBD) and accepting (HBA) thymine residue present within the monomeric structure is free to coordinate further guest species such as the complimentary DNA base adenine. The adenine simulants, 2-aminopyridine and 2,6-diaminopyridine have been used to explore the potential of these self-associated structures towards the coordination of complimentary DNA base pairs.
  • Laisney, J. et al. (2018). Pressure-induced switching properties of the iron(iii) spin-transition complex [FeIII(3-OMeSalEen)2]PF6. Physical Chemistry Chemical Physics [Online] 20:15951-15959. Available at: https://doi.org/10.1039/C8CP02376J.
    We investigated the effect of an externally applied pressure on the iron(III) Schiff-base compound [Fe(3-OMeSalEen)2]PF6 (H-3-OMeSalEen, condensation product of 3-methoxy-substituted salicylaldehyde and N-ethylethylenediamine), which at ambient pressure displays a thermal spin transition with a 3 K wide hysteresis loop centered at 164 K. Raman spectrometry revealed the occurrence of a complete spin-state switching process for a pressure of P1/2 = 8–9 kbar at room temperature. The evolution of lattice parameters as a function of pressure was followed by X-ray diffraction measurements on single crystals, highlighting the important microscopic aspects at the origin of the pressure-induced transition, i.e. an anisotropic response and a high compressibility of the HS molecular lattice. Variable temperature magnetic susceptibility measurements at different applied pressures revealed the smoothening of the spin transition curves and a linear increase of the transition temperatures by ca. 16.4 (1.0) K kbar?1, in good agreement with the Clausius–Clapeyron law. The non-negligible influence of the pressure transmitting oils on the intrinsic transition properties was also evidenced and attributed to mechanical interactions between the particles and the solidified matrix.
  • Basri, A. et al. (2017). Bis-picolinamide Ruthenium(III) Dihalide Complexes: Dichloride-to-Diiodide Exchange Generates Single trans Isomers with High Potency and Cancer Cell Selectivity. Chemistry - A European Journal [Online] 23:6341-6356. Available at: https://doi.org/10.1002/chem.201605960.
    A library of new bis-picolinamide ruthenium(III) dihalide complexes of the type [RuX2L2] (X=Cl or I, L=picolinamide) have been synthesised and characterised. The complexes exhibit different picolinamide ligand binding modes, whereby one ligand is bound (N,N) and the other bound (N,O). Structural studies revealed a mixture of cis and trans isomers for the [RuCl2L2] complexes but upon a halide exchange reaction to yield [RuI2L2], only single trans isomers were detected. High cytotoxic activity against human cancer cell lines was observed, with the potencies of some complexes similar to or better than cisplatin. The conversion to [RuI2L2] substantially increased the activity towards cancer cell lines by more than twelvefold. The [RuI2L2] complexes displayed potent activity against the A2780cis (cisplatin-resistant human ovarian cancer) cell line, with a more than fourfold higher potency than cisplatin. Equitoxic activity was observed against normoxic and hypoxic cancer cells, which indicates the potential to eradicate both the hypoxic and aerobic fractions of solid tumours with similar efficiency. The activity of selected complexes against non-cancer ARPE-19 cells was also tested. The [RuI2L2] complexes were found to be more potent than the [RuCl2L2] analogues and also more selective towards cancer cells with a selectivity factor in excess of sevenfold.
  • Francisco, T. et al. (2017). Hard X-ray-Induced Valence Tautomeric Interconversion in Cobalt-o-Dioxolene Complexes. The Journal of Physical Chemistry Letters [Online] 8:4774-4778. Available at: http://dx.doi.org/10.1021/acs.jpclett.7b01794.
    Valence tautomeric interconversion (VTI) is a reversible process occurring in metal complexes in which an intramolecular metal–ligand electron transfer is accompanied by a change of metal ion spin state, creating two switchable electronic states (redox isomers). Herein, we describe the low-temperature, 30–100 K, single-crystal study of the [Co(diox)2(4-CN-py)2]·benzene complex (1) (diox = 3,5-di-t-butylsemiquinonate (SQ•-) and/or 3,5-di-t-butylcatecholate (Cat2–) radical; 4-CN-py = 4-cyano-pyridine) using hard synchrotron X-ray radiation with different intensities. We demonstrate for the first time that hard X-rays can induce VTI, and that the interconversion molar fraction is dependent on both intensity and exposure time. This in turn shows that X-rays, as a probe, might be altering the very nature of many structures under investigation at low temperatures, and consequently their properties. Our findings add new perspectives to VTI studies and might be of significant interest to the entire community investigating photoresponsive complexes.
  • Askew, J. and Shepherd, H. (2017). Mechanochemical synthesis of cooperative spin crossover materials. Chemical Communications [Online] 54:180-183. Available at: https://doi.org/10.1039/C7CC06651A.
    We describe the synthesis of switchable spin crossover materials via mechanochemistry for the first time. Three chemically diverse spin crossover materials have been produced using solvent-free grinding. Crucially, cooperative spin transition behavior and crystallinity is retained, presenting exciting opportunities for the discovery of new materials with switchable magnetic, optical and structural properties.
  • Ridier, K. et al. (2017). Spatiotemporal dynamics of the spin transition in [Fe(HB(tz)3)2] single crystals. Physical Review B [Online] 96. Available at: http://dx.doi.org/10.1103/PhysRevB.96.134106.
    The spatiotemporal dynamics of the spin transition have been thoroughly investigated in single crystals of the mononuclear spin-crossover (SCO) complex [Fe(HB(tz)3)2] (tz=1,2,4-triazol-1-yl) by optical microscopy. This compound exhibits an abrupt spin transition centered at 334 K with a narrow thermal hysteresis loop of
    ?1 K (first-order transition). Most single crystals of this compound reveal exceptional resilience upon repeated switching (several hundred cycles), which allowed repeatable and quantitative measurements of the spatiotemporal dynamics of the nucleation and growth processes to be carried out. These experiments revealed remarkable properties of the thermally induced spin transition: high stability of the thermal hysteresis loop, unprecedented large velocities of the macroscopic low-spin/high-spin phase boundaries up to 500 µm/s, and no visible dependency on the temperature scan rate. We have also studied the dynamics of the low-spin ? high-spin transition induced by a local photothermal excitation generated by a spatially localized (Ø=2?m) continuous laser beam. Interesting phenomena have been evidenced both in quasistatic and dynamic conditions (e.g., threshold effects and long incubation periods, thermal activation of the phase boundary propagation, stabilization of the crystal in a stationary biphasic state, and thermal cutoff frequency). These measurements demonstrated the importance of thermal effects in the transition dynamics, and they enabled an accurate determination of the thermal properties of the SCO compound in the framework of a simple theoretical model.
  • Robertson, K. et al. (2017). [Fe(Htrz)2(trz)](BF4) nanoparticle production in a milliscale segmented flow crystalliser. Chimica Oggi [Online] 35:19-22. Available at: http://www.teknoscienze.com/tks_article/fehtrz2trzbf4-nanoparticle-production-in-a-milli-scale-segmented-flow-crystalliser/.
    Microfluidics has become well established as the benchmark method of nanoparticle production but the need for special equipment and the challenge of scale-up can make it prohibitive for many laboratories. In contrast, the larger scale millifluidics methodology provides a platform for controlled nanoparticle production in a simple set-up without risk of blockages, increasing the volume of material produced while continuing to offer control over particle attributes. Nanoparticle size can have a profound effect on the properties exhibited, in the case of spin-crossover materials the size of nanoparticles can have a direct correspondence with the hysteresis of magnetic susceptibility vs temperature. Nanoparticle synthesis of the spin-crossover coordination polymer [Fe(Htrz)2(trz)](BF4) (Htrz = 1,2,4-1H-triazole) has hitherto been reported through batch methods alone. Here we present the first flow synthesis of [Fe(Htrz)2(trz)](BF4) in a milli-scale segmented flow crystalliser (the Kinetically Regulated Automated Input Crystalliser, KRAIC).
  • Knichal, J. et al. (2016). An Iodine-Vapor-Induced Cyclization in a Crystalline Molecular Flask. Angewandte Chemie International Edition [Online] 55:5943-5946. Available at: http://dx.doi.org/10.1002/anie.201601525.
    A vapor-induced cyclization has been observed in
    the host environment of a crystalline molecular flask (CMF),
    within which 1,8-bis(2-phenylethynyl)naphthalene (bpen),
    a diarenynyl system primed for cyclization, was exposed to
    iodine vapor to yield the corresponding indeno[2,1-a]phenalene
    species. The cyclization process, unique in its vaporinduced,
    solvent-free nature, was followed spectroscopically,
    and found to occur concurrently with the displacement
    of lattice solvent for molecular iodine in
    CMF·0.75bpen·2.25CHCl3·H2O. The cyclization occurred
    under mild conditions and without the need to suspend the
    crystals in solvent. The ability of CMFs to host purely gasinduced
    reactions is further highlighted by the subsequent
    sequential oxidation reaction of cyclized 7-iodo-12-
    phenylindeno[2,1-a]phenalene (ipp) with molecular oxygen
    derived from air, yielding 12-hydroxy-7-iodo-2-phenylindeno-
    [2,1-a]phenalen-1(12H)-one (hipp).
  • Blackholly, L., Shepherd, H. and Hiscock, J. (2016). 'Frustrated' hydrogen bond mediated amphiphile self-assembly - a solid state study. CrystEngComm [Online] 18:7021-7028. Available at: http://dx.doi.org/10.1039/C6CE01493C.
    Herein, we present the synthesis of ten structurally related ‘frustrated’ amphiphiles, from which were obtained eleven single crystal X-ray structures, allowing observation of the hydrogen bonding modes present in the solid state. We previously reported the synthesis of a novel amphiphilic salt which contains both hydrogen bond donating (HBD) and hydrogen bond accepting (HBA) functionalities. This amphiphilic salt was shown to self-associate in the solution state, aided by the formation of hydrogen bonds. The exact nature of the hydrogen bonding modes involved in this self-association process remains unclear due to the combination of HBD and HBA groups present in the amphiphile structure. This results in a ‘frustrated’ system with access to a variety of possible hydrogen bonding modes.
  • Shepherd, H. et al. (2016). A High Pressure Investigation of the Order-Disorder Phase Transition and Accompanying Spin Crossover in [FeL12](ClO4)2 (L1 = 2,6-bis{3-methylpyrazol-1-yl}-pyrazine). Magnetochemistry [Online] 2:9. Available at: http://doi.org/10.3390/magnetochemistry2010009.
    A high pressure single crystal X-ray diffraction and Raman spectroscopy study has revealed a similar mechanism for both thermal and pressure-induced spin crossover in [FeL12](ClO4)2 (L1 = 2,6-bis{3-methylpyrazol-1-yl}-pyrazine) and the concomitant anion order-disorder transition.
  • Hernández, E. et al. (2016). Spatially Resolved Investigation and Control of the Bistability in Single Crystals of the [Fe(bbpya) (NCS)2] Spin Crossover Complex. The Journal of Physical Chemistry C [Online] 120:27608-27617. Available at: http://doi.org/10.1021/acs.jpcc.6b10258.
    The spin transition in single crystals of the [FeII(bbpya) (NCS)2] (bbpya = N,N-bis(2–2?-bipyrid-6-yl)amine) mononuclear complex was investigated by a combination of X-ray diffraction, Raman spectroscopy, as well as optical and atomic force microscopy (AFM) methods. These studies, performed around 440 K, revealed an extremely abrupt spin transition associated with a structural phase transition from a triclinic (low spin) to a monoclinic (mixed low spin/high spin) structure. Spatially resolved observations of this transition evidenced a clear phase separation associated with heterogeneous nucleation and the formation of a moving macroscopic interface whose velocity reached in some cases 300 ?m s–1. Using photothermal control it was possible to stabilize biphasic states of the crystal and then acquire AFM images of the phase boundary. A “sawtooth” like topography was repeatedly observed, which most likely emerges so as to minimize the elastic strain. Remarkably, a fine spatial control of the phase boundary could be also achieved using the AFM probe itself, through probe–sample convective heat exchange.
  • Hiscock, J., Shepherd, H. and Blackholly, L. (2016). ‘Frustrated’ hydrogen bond mediated amphiphile self-assembly – a solid state study. CrystEngComm [Online] 18:7021-7028. Available at: http://dx.doi.org/10.1039/C6CE01493C.
    Herein, we present the synthesis of ten structurally related ‘frustrated’ amphiphiles, from which were obtained eleven single crystal X-ray structures, allowing observation of the hydrogen bonding modes present in the solid state. We previously reported the synthesis of a novel amphiphilic salt which contains both hydrogen bond donating (HBD) and hydrogen bond accepting (HBA) functionalities. This amphiphilic salt was shown to self-associate in the solution state, aided by the formation of hydrogen bonds. The exact nature of the hydrogen bonding modes involved in this self-association process remains unclear due to the combination of HBD and HBA groups present in the amphiphile structure. This results in a ‘frustrated’ system with access to a variety of possible hydrogen bonding modes.
  • Shepherd, H. et al. (2016). Cooperative High-Temperature Spin Crossover Accompanied by a Highly Anisotropic Structural Distortion. European Journal of Inorganic Chemistry [Online]:1-5. Available at: http://www.dx.doi.org/10.1002/ejic.201600406.
    Spin transitions are a spectacular example of molecular switching that can provoke extreme electronic and structural reorganizations in coordination compounds. A new 3D cyanoheterometallic framework, [Fe(pz){Au(CN)2}2], has been synthesized in which a highly cooperative spin crossover has been observed at 367 and 349 K in heating and cooling modes, respectively. Mössbauer spectroscopy revealed a complete transition between the diamagnetic and paramagnetic states of the iron centres. The low-spin-to-high-spin transition induced a drastic structural distortion involving a large one-directional expansion (ca. 10.6?%) and contraction (ca. 9.6?%) of the lattice. Negative thermal expansion along the c axis was detected below and above the transition temperature.
  • Rodriguez-Marin, S. et al. (2015). Design, synthesis and conformational analyses of bifacial benzamide based foldamers. RSC Advances [Online] 5:104187-104192. Available at: http://doi.org/10.1039/c5ra20451h.
    The design, synthesis and conformational analyses of novel backbones represents a key focus of research that underpins efforts to exploit foldamers (i) in a biological setting e.g. as inhibitors of protein–protein interactions (PPIs) and (ii) for the purposes of constructing functional architectures that adopt defined tertiary and quaternary folds. The current manuscript addresses a need to develop aromatic oligoamide backbones that are regioisomeric in terms of backbone connectivity and/or functionalized on more than one face. We describe the design, synthesis and comparative conformational analyses of foldamers derived from 2-, 3- and 2,5-O-alkylated derivatives of para-aminobenzoic acid, and, derived from 2-,3- and 2,5-O-alkylated derivatives of 1,4-diaminobenzene/terephthalic acid monomers. Analysis of the accessible conformational space for these oligomers indicates that despite different connectivity they can adopt conformations that position side chains in a manner that mimic the i, i + 3, i + 4 of an ?-helix.
  • Manrique-Juárez, M. et al. (2015). Switchable molecule-based materials for micro- and nanoscale actuating applications: Achievements and prospects. Coordination Chemistry Reviews [Online] 308:395-408. Available at: http://www.dx.doi.org/10.1016/j.ccr.2015.04.005.
    Molecular switches rely on various physico-chemical phenomena, and in most cases the switching event is accompanied by a significant rearrangement of atomic positions. At the macroscopic level the long range order of switching molecules usually results in a collective, or even cooperative, volume change, which can be readily exploited for actuating purposes. These molecular (or molecule-based) systems can provide multiple advantages for this type of application due, primarily, to their intrinsic chemical and functional versatility and the small size of their functional units. This review provides an overview of advances and presents the prospects for integrating switchable molecular materials as active elements into actuator devices, with particular emphasis on micro- and nanoscale systems.
  • Cook, L. et al. (2015). Decoupled spin crossover and structural phase transition in a molecular iron(II) complex. Chemistry - A European Journal [Online] 21:4805-4816. Available at: http://dx.doi.org/10.1002/chem.201406307.
    Crystalline [Fe(bppSMe) 2][BF4]2 (1 ; bppSMe = 4-(methylsulfanyl)-2,6-di(pyrazol-1-yl)pyridine) undergoes an abrupt spin-crossover (SCO) event at 265 ±5 K. The crystals also undergo a separate phase transition near 205 K, involving a contraction of the unit-cell a axis to one-third of its original value (high-temperature phase 1; Pbcn, Z = 12; lowtemperature phase 2; Pbcn, Z = 4). The SCO-active phase 1 contains two unique molecular environments, one of which appears to undergo SCO more gradually than the other. In contrast, powder samples of 1 retain phase 1 between 140-300 K, although their SCO behaviour is essentially identical to the single crystals. The compounds [Fe(bppBr)2][BF4]2 (2; bppBr = 4-bromo-2,6-di(pyrazol-1-yl)pyridine) and [Fe(bppI)2] [BF4]2 (3 ; bppI = 4-iodo-2,6-di(pyrazol-1-yl)-pyridine) exhibit more gradual SCO near room temperature, and adopt phase 2 in both spin states. Comparison of 1-3 reveals that the more cooperative spin transition in 1, and its separate crystallographic phase transition, can both be attributed to an intermolecular steric interaction involving the methylsulfanyl substituents. All three compounds exhibit the lightinduced excited-spin-state trapping (LIESST) effect with T(LIESST = 70-80 K), but show complicated LIESST relaxation kinetics involving both weakly cooperative (exponential) and strongly cooperative (sigmoidal) components. ©2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
  • Gural'Skiy, I. et al. (2014). Spin crossover composite materials for electrothermomechanical actuators. Journal of Materials Chemistry C [Online] 2:2949-2955. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-84897131493&partnerID=40&md5=a9b7b279abedc2eb14067d9b6a484957.
    Composites of the spin crossover complex [Fe(trz)(H-trz) 2](BF4) (H-trz = 1,2,4-4H-triazole and trz = 1,2,4-triazolato) dispersed in a poly(methylmethacrylate) (PMMA) matrix were synthesized and investigated for their spin crossover properties by optical reflectivity, Raman spectroscopy and calorimetry. These composite films were used to fabricate bilayer cantilevers that can perform efficient and tuneable mechanical actuation based on the spin transition. A prototype device that uses the spin transition phenomenon to convert electrical energy into mechanical motion through Joule heating is described. This device is used to perform oscillatory actuation driven by a modulated current. The ability to tune the performance of this electromechanical system is demonstrated by varying the working temperature, the applied ac current and its frequency. © 2014 the Partner Organisations.
  • Craig, G. et al. (2014). High-temperature photo-induced switching and pressure-induced transition in a cooperative molecular spin-crossover material. Dalton Transactions [Online] 43:729-737. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-84890085882&partnerID=40&md5=1eb5d45511a17fbb47974dd31e9c144b.
    The thermal and photo-induced switching properties of the recently published molecular spin crossover complex [Fe(H4L) 2](ClO4)2·H2O· 2(CH3)2CO (1) have been investigated in detail through Raman spectroscopy. Magnetometric and single crystal X-ray diffraction kinetic studies within the hysteresis loop have proven its metastable character, which allowed establishing the shape of the true, quasi-static hysteresis loop. This is related to the proximity of the temperatures of the thermal high to low spin SCO (T1/2â??) to those of the relaxation of the thermally or photo-generated metastable states (T(TIESST) and T(LIESST), respectively). Green light irradiation within the hysteresis loop results in a complete low to high spin photo-switch. In addition, the SCO of 1 at room temperature can be induced by applying pressure, as followed by Raman spectroscopy. © 2014 The Royal Society of Chemistry.
  • Gültekin, Z. et al. (2014). Participation of compact planar 1,3,5-tri(buta-2,3-dien-1-yl)-1,3,5- triazinane-2,4,6-trione in Pd(0) catalysed seven component cascade reactions delivers novel tunable molecular architecture. Tetrahedron [Online] 70:4934-4941. Available at: http://www.dx.doi.org/10.1016/j.tet.2014.05.025.
    We report the spatially controlled, protecting group free, catalytic assembly of a library of nineteen 7-component cascade products generated from a novel planar trisallenyl 1,3,5-triazinane-2,4,6-trione core in combination with aryl iodides and amines with excellent regio and good stereoaselectivity for Z,Z,Z-isomers. © 2014 Elsevier Ltd. All rights reserved.
  • Tate, D. et al. (2014). A simple route to derivatives of benzo[j]fluoranthene. Tetrahedron [Online] 70:67-74. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-84889681677&partnerID=40&md5=2235087959a4d53c003fcdbac6ef46d8.
    3,6,8,11-Tetramethoxybenzo[j]fluoranthene can be made from 1,6-dimethoxynaphthalene in a one-pot ferric chloride oxidation/methanol reduction procedure. The reaction is tolerant of the presence of substituents in the 7-position of the naphthalene nucleus and provides a quick and easy route to these particular benzo[j]fluoranthenes. The reactions presumably proceed through initial formation of a bond between the 4-positions of two naphthalene molecules followed by closure of the five-membered ring. Indeed in one case some 4,4�-binaphthyl was isolated from the reaction mixture and it was generally found that better yields of the benzo[j]fluoranthrenes were obtained starting from the 4,4�-binaphthyl rather than by using the naphthalene as the starting material. In an analogous manner to the ring-closure of the 4,4�-binaphthyls, starting from a hexakisalkoxyphenylnaphthalene, a hexakisalkoxyfluoranthene could be obtained. © 2013 Elsevier Ltd. All rights reserved.
  • Woodall, C. et al. (2014). Tunable trimers: Using temperature and pressure to control luminescent emission in gold(i) pyrazolate-based trimers. Chemistry - A European Journal [Online] 20:16933-16942. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-84915747957&partnerID=40&md5=997a5dc61e33d41b0debc79ad5b7861f.
    A systematic investigation into the relationship between the solid-state luminescence and the intermolecular AuAu interactions in a series of pyrazolate-based gold(I) trimers; tris(μ2-pyrazolato-N,N')-tri-gold(I) (1), tris(μ2-3,4,5- trimethylpyrazolato-N,N')-tri-gold(I) (2), tris(μ2-3-methyl-5- phenylpyrazolato-N,N')-tri-gold(I) (3) and tris(μ2-3,5-diphenylpyrazolato- N,N')-tri-gold(I) (4) has been carried out using variable temperature and high pressure X-ray crystallography, solid-state emission spectroscopy, Raman spectroscopy and computational techniques. Single-crystal X-ray studies show that there is a significant reduction in the intertrimer AuAu distances both with decreasing temperature and increasing pressure. In the four complexes, the reduction in temperature from 293 to 100 K is accompanied by a reduction in the shortest intermolecular AuAu contacts of between 0.04 and 0.08 The solid-state luminescent emission spectra of 1 and 2 display a red shift with decreasing temperature or increasing pressure. Compound 3 does not emit under ambient conditions but displays increasingly red-shifted luminescence upon cooling or compression. Compound 4 remains emissionless, consistent with the absence of intermolecular AuAu interactions. The largest pressure induced shift in emission is observed in 2 with a red shift of approximately 630 cm-1 per GPa between ambient and 3.80 GPa. The shifts in all the complexes can be correlated with changes in AuAu distance observed by diffraction. © 2014 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
  • Kulmaczewski, R. et al. (2014). A homologous series of [Fe(H2Bpz2)2(L)] spin-crossover complexes with annelated bipyridyl co-ligands. Inorganic Chemistry [Online] 53:9809-9817. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-84919754545&partnerID=40&md5=c1d0556064bd3bf4e27d192ba322e94a.
    Four new iron(II) complexes [Fe- (H2Bpz2)2(L)] were prepared (pz = pyrazolyl), where L is dipyrido[3,2-f:2',3'-h]quinoxaline (dpq), dipyrido[3,2-a:2'3'- c]phenazine (dppz), dipyrido[3,2-a:2'3'-c]benzo[i]-phenazine (dppn), and dipyrido[3,2-a:2',3'-c](6,7,8,9-tetrahydro)- phenazine (dppc). Crystal structures of [Fe(H2Bpz2)2(dpq)], [Fe(H2Bpz2)2(dppz)], and [Fe(H2Bpz2)2(dppn)] all reveal stacks of complex molecules formed through Ï?-Ï? stacking between interdigitated bipyridyl chelate ligands, often with additional intercalated toluene or uncoordinated bipyridyl ligand (dpq). Molecules of [Fe(H2Bpz2)2(dppc)] form a different stacking motif in the crystal, with weaker contacts between individual molecules. Many of the structures also contain channels of disordered solvent, running between the molecular stacks. Despite their different stacking motifs, all these compounds exhibit very gradual thermal spin-crossover (SCO) on cooling, which occur over different temperature ranges but are otherwise quite similar in form. Weak thermal hysteresis in one of these spin equilibria can be attributed to the effects of a change in bipyridyl ligand conformation in the molecular stacks around 150 K, which was observed crystallographically. These results demonstrate that strong mechanical coupling between molecules in a crystal is not sufficient to engineer cooperative SCO switching, if other regions of the lattice are less densely packed.
  • Windle, J. et al. (2014). Sequential one-pot three component rhodium-catalysed isomerisation/1,3- dipolar cycloaddition cascades to fused-ring heterocycles. RSC Advances [Online] 4:2624-2627. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-84890662236&partnerID=40&md5=37736c5af6d0607f12abcb64c512f332.
    One-pot three component rhodium-catalysed isomerisation/1,3-dipolar cycloaddition cascades to fused ring heterocycles with formation of three new bonds and four stereo centres occurred in good yields. © 2014 The Royal Society of Chemistry.
  • Shepherd, H. et al. (2013). Spin crossover at the nanometre scale. European Journal of Inorganic Chemistry [Online]:653-661. Available at: https://doi.org/10.1002/ejic.201201205.
    From the development of new methods for the synthesis and patterning of nanometre-scale thin films and particles, to the first investigations of charge transport and photonic properties, there has been a proliferation of research concerning spin crossover nanomaterials in recent years. Studies have aimed at addressing fundamental questions concerning sizereduction effects, as well as striving towards practical applications in this important class of bistable molecular materials. This microreview describes the most recent achievements and highlights possible future directions in this field. © 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
  • Bao, X. et al. (2013). The effect of an active guest on the spin crossover phenomenon. Angewandte Chemie - International Edition [Online] 52:1198-1202. Available at: https://doi.org/10.1002/anie.201207218.
    Throw the switch: A new strategy for regulating spin crossover (SCO) properties by the control of an active guest molecule is proposed. As a proof of concept, maleic anhydride was incorporated into a microporous {Fe(pyrazine)[Pt(CN)4]} framework material and chemically switched to maleic acid, thus modifying the SCO properties (see picture). Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
  • Hung, T. et al. (2013). Room temperature magnetic detection of spin switching in nanosized spin-crossover materials. Angewandte Chemie - International Edition [Online] 52:1185-1188. Available at: https://doi.org/10.1002/anie.201205952.
    Building a better SQUID: A prototype for a SQUID-like magnetometry device for the indirect detection of room-temperature switching in spin-crossover nanoparticles has been developed and used in the study of [Fe(hptrz) 3](OTs)2 (hptrz=4-heptyl-1,2,4-triazole, OTs=p-toluenesulfonyl) nanoparticles, as a proof of concept for this novel micromagnetometry approach. The method provides significant benefits over conventional SQUID and nano-SQUID techniques. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
  • Bartual-Murgui, C. et al. (2013). Tunable spin-crossover behavior of the hofmann-like network {Fe(bpac)[Pt(CN)4]} through host-guest chemistry. Chemistry - A European Journal [Online] 19:15036-15043. Available at: https://doi.org/10.1002/chem.201300227.
    A study of the spin-crossover (SCO) behavior of the tridimensional porous coordination polymer {Fe(bpac)[Pt(CN)4]} (bpac=bis(4-pyridyl) acetylene) on adsorption of different mono- and polyhalobenzene guest molecules is presented. The resolution of the crystal structure of {Fe(bpac)[Pt(CN) 4]}Ã?G (G=1,2,4-trichlorobenzene) shows preferential guest sites establishing Ï?Ã?Ã?Ã?Ï? stacking interactions with the host framework. These host-guest interactions may explain the relationship between the modification of the SCO behavior and both the chemical nature of the guest molecule (electronic factors) and the number of adsorbed molecules (steric factors). Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
  • Shepherd, H. et al. (2013). Molecular actuators driven by cooperative spin-state switching. Nature Communications [Online] 4:3607. Available at: http://www.scopus.com/inward/record.url?eid=2-s2.0-84886668965&partnerID=40&md5=0e7ecf0b7c25d20466fb787fffaab519.
    Molecular switches have great potential to convert different forms of energy into mechanical motion; however, their use is often limited by the narrow range of operating conditions. Here we report on the development of bilayer actuator devices using molecular spin crossover materials. Motion of the bilayer cantilever architecture results from the huge spontaneous strain accompanying the spin-state switching. The advantages of using spin crossover complexes here are substantial. The operating conditions used to switch the device can be manipulated through chemical modification, and there are many existing compounds to choose from. Spin crossover materials may be switched by diverse stimuli including light, temperature, pressure, guest molecules and magnetic field, allowing complex input combinations or highly specific operation. We demonstrate the versatility of this approach by fabricating actuators from four different spin crossover materials and by using both thermal variation and light to induce motion in a controlled direction. © 2013 Macmillan Publishers Limited. All rights reserved.
  • Tissot, A. et al. (2013). Temperature- and pressure-induced switching of the molecular spin state of an orthorhombic iron(III) spin-crossover salt. European Journal of Inorganic Chemistry [Online]:1001-1008. Available at: https://doi.org/10.1002/ejic.201201059.
    The [(TPA)FeIII(TCC)]+ complex [TPA = tris(2-pyridylmethyl) amine, TCC2- = 3,4,5,6-tetrachlorocatecholate dianion] forms a molecular solid with the SbF6 - anion, which exhibits an incomplete S = 1/2 â?? S = 5/2 thermal spin-crossover process centered at 250 K. Single-crystal X-ray diffraction, Raman spectroscopy, and magnetic measurements of this orthorhombic polymorph were performed to delineate the spinstate thermo- and piezoswitching in relation to the structural and elastic properties. Indeed, a pressure-induced spin cross- over (centered at P1/2 â?? 1.65 kbar, T = 294 K) concomitant with unit-cell contraction was observed by applying a hydrostatic pressure to the single crystal. Under ambient conditions, the piezo-induced transition, like that induced thermally, is relatively gradual, which probably reflects a similar mechanism in response to both stimuli. Except for a 47 K shift, the spin-crossover curves of the isostructural SbF6 - and PF6 - salts compare well. They are discussed with respect to structural anisotropy and pressure effects. © 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
  • Pillet, S. et al. (2012). Multimetastability, phototrapping, and thermal trapping of a metastable commensurate superstructure in a FeII spin-crossover compound. Physical Review B - Condensed Matter and Materials Physics [Online] 86:64106-64106. Available at: https://doi.org/10.1103/PhysRevB.86.064106.
    The photoinduced switching and subsequent relaxation regime at cryogenic temperatures of the two-step spin-crossover compound [Fe(bapbpy)(NCS) 2] has been investigated by time-dependent photocrystallography. Upon photoexcitation from the low-spin (LS) state, a direct population of the metastable high-spin (HS) state occurs, without involving any intermediate structural state. The relaxation from the metastable HS state in isothermal conditions at 40K proceeds in two successive steps associated with two symmetry breaking processes. The first step corresponds to the cooperative transformation to an intermediate superstructure, characterized by a long-range-ordered [HS-LS-LS] motif coupled to a commensurate displacive modulation, and concomitant with a tripling of the c axis of the unit cell (C2/c space group). The stabilization of the intermediate state is driven by strong molecule-lattice coupling. In the second stage, the intermediate state undergoes a transformation twinning triggered by lattice strain towards the LS state. The two-step relaxation is reminiscent of the two-step thermal transition of [Fe(bapbpy)(NCS) 2] and evidences multimetastability in the light-induced or relaxation regime. The long-range-ordered [HS-LS-LS] superstructure has also been trapped by rapid quench cooling to very low temperature, and has been structurally characterized. © 2012 American Physical Society.
  • Létard, J. et al. (2012). Photomagnetism of a sym-cis-dithiocyanato iron(II) complex with a tetradentate N,N'-bis(2-pyridylmethyl)1,2-ethanediamine ligand. Chemistry - A European Journal [Online] 18:5924-5934. Available at: https://doi.org/10.1002/chem.201102637.
    A comprehensive study of the magnetic and photomagnetic behaviors of cis-[Fe(picen)(NCS) 2] (picen=N,N'-bis(2-pyridylmethyl)1,2- ethanediamine) was carried out. The spin-equilibration was extremely slow in the vicinity of the thermal spin-transition. When the cooling speed was slower than 0.1 K min -1, this complex was characterized by an abrupt thermal spin-transition at about 70 K. Measurement of the kinetics in the range 60-70 K was performed to approach the quasi-static hysteresis loop. At low temperatures, the metastable HS state was quenched by a rapid freezing process and the critical T(TIESST) temperature, which was associated with the thermally induced excited spin-state-trapping (TIESST) effect, was measured. At 10 K, this complex also exhibited the well-known light-induced excited spin-state-trapping (LIESST) effect and the T(LIESST) temperature was determined. The kinetics of the metastable HS states, which were generated from the freezing effect and from the light-induced excitation, was studied. Single-crystal X-ray diffraction as a function of speed-cooling and light conditions at 30 K revealed the mechanism of the spin-crossover in this complex as well as some direct relationships between its structural properties and its spin state. This spin-crossover (SCO) material represents a fascinating example in which the metastability of the HS state is in close vicinity to the thermal spin-transition region. Moreover, it is a beautiful example of a complex in which the metastable HS states can be generated, and then compared, either by the freezing effect or by the LIESST effect. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
  • Bashforth, R. et al. (2012). The relative stabilities of cyclic dicationic derivatives of diphosphanes with three (3P) or four (4P) linked phosphorus atoms. Dalton Transactions [Online] 41:1165-1172. Available at: http://dx.doi.org/10.1039/c1dt11549a.
    Reaction of a diphosphane with a chlorophosphane in the presence of SnCl 2 or AlCl 3 leads to the formation of dicationic heterocycles with three (3P) or four (4P) linked phosphorus atoms. Some 3P derivatives with small alkyl substituents may also be prepared by direct alkylation of cyclic triphosphenium ions. Several new species were prepared in solution, some of which were isolated and characterised by single-crystal X-ray diffraction. Investigations into the factors favouring formation of 3P or 4P species are described. © 2012 The Royal Society of Chemistry.
  • Shepherd, H. et al. (2012). Antagonism between extreme negative linear compression and spin crossover in [Fe(dpp) 2(NCS) 2]·py. Angewandte Chemie - International Edition [Online] 51:3910-3914. Available at: https://doi.org/10.1002/anie.201108919.
    A scissor-like geometric mechanism is responsible for the strongest negative linear compression effect yet observed in a molecular material, [Fe(dpp) 2(NCS) 2]·py (see picture; dpp=dipyrido[3,2-a:2�3�-c]phenazine), C gray, N blue, S yellow, Fe red). The same mechanism is also responsible for suppressing the high-spin to low-spin transition under pressure. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
  • Shepherd, H. et al. (2012). Structural origin of the gradual spin transition in a mononuclear iron(II) complex. Journal of Physics and Chemistry of Solids [Online] 73:193-197. Available at: https://doi.org/10.1016/j.jpcs.2011.11.003.
    Variable temperature single crystal X-ray diffraction and SQUID magnetometry experiments have revealed a gradual spin transition in [Fe II(L)](ClO4)2 (where L=1,4,7-tris(2- aminophenyl)-1,4,7-triazacyclononane), centred around room temperature. The gradual nature of the spin transition has been attributed to the lack of significant intermolecular interactions between iron centres and the propensity of the counter ions to accommodate the internal strain in the crystal caused by spin crossover. © 2011 Elsevier Ltd. All rights reserved.
  • Bartual-Murgui, C. et al. (2012). Synergetic effect of host-guest chemistry and spin crossover in 3D hofmann-like metal-organic frameworks [Fe(bpac)M(CN) 4] (M=Pt, Pd, Ni). Chemistry - A European Journal [Online] 18:507-516. Available at: https://doi.org/10.1002/chem.201102357.
    The synthesis and characterization of a series of three-dimensional (3D) Hofmann-like clathrate porous metal-organic framework (MOF) materials [Fe(bpac)M(CN) 4] (M=Pt, Pd, and Ni; bpac=bis(4-pyridyl)acetylene) that exhibit spin-crossover behavior is reported. The rigid bpac ligand is longer than the previously used azopyridine and pyrazine and has been selected with the aim to improve both the spin-crossover properties and the porosity of the corresponding porous coordination polymers (PCPs). The 3D network is composed of successive {Fe[M(CN) 4]} n planar layers bridged by the bis-monodentate bpac ligand linked in the apical positions of the iron center. The large void between the layers, which represents 41.7% of the unit cell, can accommodate solvent molecules or free bpac ligand. Different synthetic strategies were used to obtain a range of spin-crossover behaviors with hysteresis loops around room temperature; the samples were characterized by magnetic susceptibility, calorimetric, Mössbauer, and Raman measurements. The complete physical study reveals a clear relationship between the quantity of included bpac molecules and the completeness of the spin transition, thereby underlining the key role of the Ï?-Ï? stacking interactions operating between the host and guest bpac molecules within the network. Although the inclusion of the bpac molecules tends to increase the amount of active iron centers, no variation of the transition temperature was measured. We have also investigated the ability of the network to accommodate the inclusion of molecules other than water and bpac and studied the synergy between the host-guest interaction and the spin-crossover behavior. In fact, the clathration of various aromatic molecules revealed specific modifications of the transition temperature. Finally, the transition temperature and the completeness of the transition are related to the nature of the metal associated with the iron center (Ni, Pt, or Pd) and also to the nature and the amount of guest molecules in the lattice. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
  • Shepherd, H. et al. (2012). High-pressure spin-crossover in a dinuclear Fe(ii) complex. Physical Chemistry Chemical Physics [Online] 14:5265-5271. Available at: https://doi.org/10.1039/c2cp23940j.
    The effect of pressure on the dinuclear spin crossover material [{Fe(bpp)(NCS) 2} 2(4,4�-bipy)]·2MeOH (where bpp = 2,6-bis(pyrazol-3-yl)pyridine and 4,4�-bipy = 4,4�-bipyridine, 1) has been investigated with single crystal X-ray diffraction and Raman spectroscopy using diamond anvil cell techniques. The very gradual pressure-induced spin crossover occurs between 7 and 25 kbar, and shows no evidence of crystallographic phase transitions. The pressure-induced spin transition leads to a complete LS state which is not thermally accessible. This structural evolution under pressure is in stark contrast to the previously reported thermal spin crossover behaviour, in which a symmetry-breaking, purely structural phase transition results in only partial conversion to the low spin state. This observation is attributed to the symmetry-breaking phase transition becoming unfavourable under pressure. © 2012 the Owner Societies.
  • Griffin, M. et al. (2011). A symmetry-breaking spin-state transition in iron(III). Angewandte Chemie - International Edition [Online] 50:896-900. Available at: https://doi.org/10.1002/anie.201005545.
    Stepping up: A two-step magnetic spin transition with accompanying structural phase transitions is reported for the first time for Fe III. The transitions are observed at 187 K and 90 K on cooling with a hysteretic transition recorded upon heating during the first crossover at 106 K. The intermediate phase persists over 97 K and contains an unprecedented [HS-HS-LS] motif with tripling of the unit cell. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
  • Shepherd, H. et al. (2011). Thermal and pressure-induced spin crossover in a novel three-dimensional Hoffman-like clathrate complex. New Journal of Chemistry [Online] 35:1205-1210. Available at: https://doi.org/10.1039/c0nj00845a.
    The synthesis and crystal structure of the interpenetrated metal-organic framework material Fe(bpac) 2[Ag(CN) 2] 2 (bpac = 4,4�-bis(pyridyl)acetylene) are reported along with the characterization of its spin crossover properties by variable temperature magnetometry and Mössbauer spectroscopy. The complex presents an incomplete stepped spin transition as a function of temperature that is modified upon successive thermal cycling. The pressure-induced transition has also been investigated by means of high pressure Raman spectroscopy using a diamond anvil cell. The results show that it is possible to reach the thermally-inaccessible fully low spin state at room temperature by applying hydrostatic pressure to the sample. © 2011 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.
  • Shepherd, H. et al. (2011). Pressure-induced two-step spin transition with structural symmetry breaking: X-ray diffraction, magnetic, and Raman studies. Physical Review B - Condensed Matter and Materials Physics [Online] 84:144107-144107. Available at: https://doi.org/10.1103/PhysRevB.84.144107.
    We have used single-crystal x-ray diffraction, Raman spectroscopy, and magnetometry to investigate the effect of hydrostatic pressures up to 16 kbar on the molecular spin crossover complex [FeII(bapbpy)(NCS)2]. A stepped first-order transition from the high-spin (HS) to low-spin (LS) phase was observed upon compression of single-crystal samples. The intermediate phase (IP) is stable between 4 and 11 kbar at room temperature. This phase is characterized by supercell reflections and tripling of the c-axis of the unit cell (C2/c) due to the formation of a periodic [HS-LS-LS] structural motif, as seen in the thermal stepped transition. The pressure-temperature phase diagram reveals an anomalous increase of the thermal hysteresis widths with increasing pressure and the stabilization of the IP across the investigated P-T space. © 2011 American Physical Society.
  • Bartual-Murgui, C. et al. (2011). Enhanced porosity in a new 3D Hofmann-like network exhibiting humidity sensitive cooperative spin transitions at room temperature. Journal of Materials Chemistry [Online] 21:7217-7222. Available at: https://doi.org/10.1039/c0jm04387g.
    The porous coordination polymers (PCPs) of general formula {Fe(bpac)[M(CN) 4]}·guest (M = Pt, Pd) exhibit larger channels than previously synthesised 3D-Hofmann-like PCP. The channels are partially occupied by uncoordinated guest bpac ligands and labile H 2O molecules. These PCPs exhibit very scarce cooperative spin crossover behaviour around room temperature with a large hysteresis loop (up to 49 K) and also display sensitivity to humidity and guest molecules. The inclusion of bpac molecules in the 3D network can be avoided by adding competitive volatile molecules during the crystallization process, affording the guest-free material. The spin crossover behavior of different guest and guest-free materials is also presented. © 2011 The Royal Society of Chemistry.

Book section

  • Shepherd, H. et al. (2013). Luminescent Spin-Crossover Materials. in: Spin-Crossover Materials: Properties and Applications. John Wiley and Sons, pp. 347-373. Available at: https://doi.org/10.1002/9781118519301.ch13.
    This chapter begins with a general introduction to luminescent spin-crossover (SCO) materials and luminescence energy transfer. It provides a brief overview of electronic transitions and optical properties of SCO complexes. The chapter brings together only those ingredients which are the most important for the design and application of multifunctional luminescent SCO entities. The second part of the chapter reviews the existing literature concerning materials that combine SCO and luminescence properties using examples of luminescent SCO compounds (ligands, counterions), and concludes with a discussion on the perspectives in this area of research. This edition first published 2013 © 2013 John Wiley & Sons, Ltd.
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