Qualitative Guest Sensing via Iron(II) Triazole Complexes.

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 variable-temperature 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'.