Qualitative Guest Sensing via Iron(II) Triazole Complexes

Abstract

The pyridazine-pyridine triazole-based Rat ligand, Lpydzpy [4-(4-methylphenyl)-3-(3-pyridazinyl)-5-(2-pyridinyl)-1,2,4-triazole], is potentially ditopic. Nevertheless, Lpydzpy is shown herein to exclusively form mononuclear iron(II) complexes, [FeII(Lpydzpy)2(NCE)2]·solvent, in the presence of coordinating NCE anions (E = S or Se). Specifically, a new family of 10 mononuclear complexes, in which Lpydzpy binds in a monotopic bidentate manner, has been made: two solvent-free complexes, [FeII(Lpydzpy)2(NCS)2] (1) and [FeII(Lpydzpy)2(NCSe)2] (2); six solvatomorphs, 1·4CH3CN, 2·4CH3CN, 1·2.25CH3CN, 2·3CH3CN, 2·tetrahydrofuran, and 2·CHCl3; and a pair of desolvated polymorphs, 1′ and 2′. Seven of them are spin crossover-active, the exceptions being 1, 2, and 2′. This is confirmed by single-crystal X-ray diffraction (XRD) for 1, 2, 1·4CH3CN, and 2·4CH3CN and is consistent with variableerature optical microscopy observations on single crystals of 1·4CH3CN and 2·4CH3CN and on samples of 1′ and 2′. Powder XRD, thermogravimetric analysis, and solid-state magnetometry reveal that desolvated 1′ and 2′ are capable of absorbing and desorbing a range of volatile guests: CH3CN in both cases and also tetrahydrofuran and CHCl3 in the case of 2′.