Spin-Crossover Behavior in Two New Supramolecular Isomers

Two spin-crossover (SCO) supramolecular isomers formulated as [Fe­(Mebpt)­{Au­(CN)2}]n·xH2O (1, x = 0, and 2·H2O, x = n, MebptH = 3-(5-methyl-2-pyridyl)-5-(2-pyridyl)-1,2,4-triazole) have been successfully isolated and characterized by single-crystal X-ray crystallography, thermogravimetric analysis, differential scanning calorimetry, variable-temperature powder X-ray diffraction, and magnetic measurements. Structural analysis reveals that 1 is a two-dimensional coordination layer and 2·H2O is a one-dimensional coordination ladder structure, in which the Mebpt– ligands are coordinated in trans and cis bridging mode in 1 and 2·H2O, respectively. Dramatically, their SCO properties are further influenced by the octahedral coordination configuration of Fe­(II). In 1, only the Fe­(II) centers in trans configuration exhibit spin transition (Tc = 303 K), while in 2·H2O and the dehydrated 2, gradual two-step SCO (Tc1 = 235 K, Tc2 = 313 K) and one-step SCO behaviors (Tc = 315 K) occur, respectively.