Abstract

A new synthesis of (8-quinolyl)-5-methoxysalicylaldimine (Hqsal-5-OMe) is reported and its crystal structure is presented. Two Fe^III complexes, [Fe(qsal-5-OMe)<inf>2</inf>]Cl×solvent (solvent=2 MeOH×0.5 H <inf>2</inf>O (1) and MeCN×H<inf>2</inf>O (2)) have been prepared and their structural, electronic and magnetic properties studied. [Fe(qsal-5-OMe)<inf>2</inf>] Cl×2 MeOH×0.5 H<inf>2</inf>O (1) exhibits rare crystallographically independent high-spin and low-spin Fe ^III centres at 150K, whereas [Fe(qsal-5-OMe)<inf>2</inf>]Cl× MeCN×H<inf>2</inf>O (2) is low spin at 100K. In both structures there are extensive π-π and C-H×××π interactions. SQUID magnetometry of 2 reveals an unusual abrupt stepped-spin crossover with T <inf>1/2</inf>=245K and 275K for steps1 and 2, respectively, with a slight hysteresis of 5K in the first step and a plateau of 15K between the steps. In contrast, 1 is found to undergo an abrupt half-spin crossover also with a hysteresis of 10K. The two compounds are the first Fe^III complexes of a substituted qsal ligand to exhibit abrupt spin crossover. These conclusions are supported by ⁵⁷Fe Mössbauer spectroscopy. Both complexes exhibit reversible reduction to Fe^II at -0.18V and irreversible oxidation of the coordinated qsal-5-OMe ligand at +1.10V. Time to step up! Two novel Fe^III complexes, [Fe(qsal-5-OMe)<inf>2</inf>]Cl×solvent {qsal-5-OMe=5-methoxy-N-(8-quinolyl) salicylaldiminate, solvent=2 MeOH×0.5 H<inf>2</inf>O (1) and MeCN×H<inf>2</inf>O (2)} are reported. The structure of 1 reveals crystallographically independent high-spin and low-spin Fe^III centres, with 1 and 2 undergoing abrupt half-spin crossover and spin crossover in two steps, respectively (see figure). Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.