Polymorphism and its effects on the magnetic behaviour of the [Fe(sal2-trien)][Ni(dmit)2] spin-crossover complex

Abstract

The syntheses, structural characterisation, and magnetic and spectroscopic properties of three new polymorphs of the spin-crossover complex [Fe(sal 2 -trien)][Ni(dmit) 2 ] are reported. The results are discussed as a function of their intra-and intermolecular arrangement. Correlation of their crystal structures and magnetic properties suggest that some torsion angles play a significant role in the magnetic properties of this class of compounds. Intermolecular contacts are also of importance, and the nature of the short contacts between molecular species seems to be more crucial than their number in the allowance of spin-crossover.

A Sequential Method to Prepare Polymorphs and Solvatomorphs of [Fe(1,3‐bpp)2](ClO4)2⋅nH2O (n=0, 1, 2) with Varying Spin‐Crossover Behaviour

“…The vast majority of them are obtained serendipitously, as mixtures of crystals. As a result, some of them cannot be accumulated in sufficient amount for bulk studies, do not form systematically or even cannot be reproduced . In one exceptional case, the sequential interconversion of polymorphs over long periods of time within the reaction system was described, presumably driven by the formation of systems of increasing thermodynamic stability .…”

Structure:function relationships in molecular spin-crossover complexes

“…Sections 2.1, 2.2 and 2.3.1),39,40,47,58 but in other cases there are only small differences in molecular structure between the polymorphs.…”

Spin-crossover Compounds with Wide Thermal Hysteresis

“…The true thermodynamic hysteresis of 5, after its phase change has been induced by annealing at 200 K, is only ¦T = 12 K. 20 Compound 7 and a polymorph of 8 also undergo crystallographic phase changes during their spin transitions with ¦T = 4256 K for 7, depending on the preparation of the sample, 18 and ¦T = 30 K for 8. 42,43 Crystal structures of 8 were obtained in both spin states and show that the conformation of the hexadentate saltrien ligand changes substantially during spin crossover. 42 Since the ligand conformation has a strong influence on the steric environment of neighboring molecules in the lattice, this provides an alternative mechanism for the propagation of structural cooperativity through the sample.…”