Qualitative Guest Sensing via Iron(II) Triazole Complexes

The pyridazine-pyridine triazole-based Rat ligand, L-pydzpy [4-(4-methylphenyl)-3-(3-pyridazinyl)-5-(2-pyridinyl)-1,2,4-triazole], is potentially ditopic. Nevertheless, L-pydzpuy is shown herein to exclusively form mononuclear iron(II) complexes, [Fe-II(L-pydzpy)(2) (NCE)(2)]center dot solvent, in the presence of coordinating NCE anions (E = S or Se). Specifically, a new family of 10 mononuclear complexes, in which L-pydzpy binds in a monotopic bidentate manner, has been made: two solvent-free complexes, [Fe-II(L-pydzphy)(2)(NCS)(2)] (1) and [Fe-II(L-pydzpy)(2)(NCSe)(2)] (2); six solvatomorphs, 1 center dot 4CH(3) CN, 2 center dot 4CH(3)CN, 1 center dot 2.25CH(3)CN, 2 center dot 3CH(3)CN, 2 center dot tetrahydrofuran, and 2 center dot 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 center dot 4CH(3)CN, and 2 center dot 4CH(3)CN and is consistent with variable-temperature optical microscopy observations on single crystals of 1 center dot 4CH(3)CN and 2 center dot 4CH(3)CN 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'.