Iron(II) Spin Crossover Complex with the 1,2,3-Triazole-Containing Linear Pentadentate Schiff-Base Ligand and the MeCN Monodentate Ligand

A mononuclear iron(II) complex bearing the linear pentadentate N-5 Schiff-base ligand containing two 1,2,3-triazole moieties and the MeCN monodentate ligand, [(FeMeCN)-Me-II(L-3-Me-3(Ph))](BPh4)(2)MeCNH2O (1), have been prepared (L-3-Me-3(Ph) = bis(N,N '-1-Phenyl-1H-1,2,3-triazol-4-yl-methylideneaminopropyl)methylamine). Variable-temperature magnetic susceptibility measurements revealed an incomplete one-step spin crossover (SCO) from the room-temperature low-spin (LS, S = 0) state to a mixture of the LS and high-spin (HS, S = 2) species at the higher temperature of around 400 K upon first heating, which is irreversible on the consecutive cooling mode. The magnetic modulation at around 400 K was induced by the crystal-to-amorphous transformation accompanied by the loss of lattice MeCN solvent, which was evident from powder X-ray diffraction (PXRD) studies and themogravimetry. The single-crystal X-ray diffraction studies showed that the complex is in the LS state (S = 0) between 296 and 387 K. In the crystal lattice, the complex-cations and B(1)Ph-4(-) ions are alternately connected by intermolecular CH pi interactions between the methyl group of the MeCN ligand and phenyl groups of B(1)Ph-4(-) ions, forming a 1D chain structure. The 1D chains are further connected by P4AE (parallel fourfold aryl embrace) interactions between two neighboring complex-cations, constructing a 2D extended structure. B(2)Ph-4(-) ions and MeCN lattice solvents exist in the spaces of the 2D layer. DFT calculations verified that the 1,2,3-triazole-containing ligand L-3-Me-3(Ph) gives a stronger ligand field around the octahedral coordination environment of the iron(II) ion than the analogous imidazole-containing ligand H2L2Me (= bis(N,N '-2-methylimidazol-4-yl-methylideneaminopropyl)methylamine) of the known compound [(FeMeCN)-Me-II(H2L2Me)](BPh4)(1.5)Cl(0.5)0.5MeCN (2) reported by Matsumoto et al. (Nishi, K.; Fujinami, T.; Kitabayashi, A.; Matsumoto, N. Tetrameric spin crossover iron(II) complex constructed by imidazolechloride hydrogen bonds. Inorg. Chem. Commun. 2011, 14, 1073-1076), resulting in the much higher spin transition temperature of 1 than that of 2.