Browsing by Author "Powell, BJ"
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- ItemDual-supramolecular contacts induce extreme Hofmann framework distortion and multi-stepped spin-crossover(Royal Society of Chemistry, 2021-01-13) Ahmed, M; Brand, HEA; Peterson, VK; Clegg, JK; Kepert, CJ; Price, JR; Powell, BJ; Neville, SMAn extended nitro-functionalised 1,2,4-triazole ligand has been used to induce considerable lattice distortion in a 2-D Hofmann framework material via competing supramolecular interactions. Single crystal X-ray diffraction analyses on [Fe3(N-cintrz)6(Pd(CN)4)3]·6H2O (N-cintrz: (E)-3-(2-nitrophenyl)acrylaldehyde) reveal a substantial deviation from a regular Hofmann structure, in particular as the intra- and inter-layer contacts are dominated by hydrogen-bonding interactions rather than the typical π-stacking arrays. Also, the 2-D Hofmann layers show an assortment of ligand conformations and local FeII coordination environments driven by the optimisation of competing supramolecular contacts. Temperature-dependent magnetic susceptibility measurements reveal a two-step spin crossover (SCO) transition. Variable temperature structural analyses show that the two crystallographically distinct FeII centres, which are arranged in stripes (2[thin space (1/6-em)]:[thin space (1/6-em)]1 ratio) within each Hofmann layer, undergo a cooperative HS ↔ HS/LS ↔ LS (HS = high spin, LS = low spin) transition without periodic spin-state ordering. The mismatch between crystallographic (2[thin space (1/6-em)]:[thin space (1/6-em)]1) and spin-state (1[thin space (1/6-em)]:[thin space (1/6-em)]1) periodicity at the HS[thin space (1/6-em)]:[thin space (1/6-em)]LS step provides key insight into the competition (frustration) between elastic interactions and crystallographically driven order. © The Royal Society of Chemistry 2021
- ItemHierarchical spin-crossover cooperativity in hybrid 1D chains of Fe(II)-1,2,4-triazole trimers linked by [Au(CN)2]− bridges(John Wiley & Sons, Inc, 2021-02-04) Ezzedinloo, L; Zenere, KA; Xie, Z; Ahmed, M; Scottwell, S; Bhadbhade, MM; Brand, HEA; Clegg, JK; Hua, C; Sciortino, NF; Parker, LC; Powell, BJ; Kepert, CJ; Neville, SMForemost, practical applications of spin-crossover (SCO) materials require control of the nature of the spin-state coupling. In existing SCO materials, there is a single, well-defined dimensionality relevant to the switching behavior. A new material, consisting of 1,2,4-triazole-based trimers coordinated into 1D chains by [Au(CN)2]− and spaced by anions and exchangeable guests, underwent SCO defined by elastic coupling across multiple dimensional hierarchies. Detailed structural, vibrational, and theoretical studies conclusively confirmed that intra-trimer coupling was an order of magnitude greater than the intramolecular coupling, which was an order of magnitude greater than intermolecular coupling. As such, a clear hierarchy on the nature of elastic coupling in SCO materials was ascertained for the first time, which is a necessary step for the technological development of molecular switching materials. © 2021 Wiley-VCH GmbH