Fe-II Spin crossover materials based on dissymmetrical N-4 Schiff bases including 2-pyridyl and 2R-imidazol-4-yl rings: Synthesis, crystal structure and magnetic and Modssbauer properties

摘要

The synthesis and characterization of new symmetrical Fe-II complexes, [FeLA (NCS)(2)] (1), and [FeLBx (NCS)(2)] (2-4), are reported (L-A is the tetradentate Schiff base N,N'-bis(1-pyridin-2-ylethylidene)-2,2-dimethylpropane-1,3-diamine, and L-Bx stands for the family of tetradentate Schiff bases N,N'-bis[(2-R-1H-imidazol-4-yl)methylene]-2,2-dimethylpropane-1,3-diamine, with: R=H for L-B1 in 2, R = Me for L-B2 in 3, and R=Ph for L-B3 in 4). Single-crystal X-ray structures have been determined for 1 (low-spin state at 293 K), 2 (high-spin (HS) state at 200 K),. and 3 (HS state at 180 K). These complexes remain in the same spin-state over the whole temperature range (80-400 K]. The dissymmetrical tetradentate Schiff base ligands L-Cx, N-[(2-R-2-1H-imidazol-4-yl)methylene]-N'-(1-pyridin-2-ylethylidene)-2,2-R-1 -propane-1,3-diamine (R-1 = H, Me; R-2 = H, Me, Ph), containing both pyridine and imidazole rings were obtained as their [FeLCx(NCS)(2)] complexes, 5-10, through reaction of the isolated aminal type ligands 2-methyl-2-pyridin-2-ylhexahydropyrimidine (R-1 = H, 5-7) or 2,5,.5-trimethyl-2-pyridin-2-ylhexahydropyrimidine (R-1 = Me, 8-10) with imidazole-4-carboxaldehyde (R-2 = H: 5, 8), 2-methylimidazole-4-carboxaldehyde (R-2 = Me: 6, 9), and 2-phenyl-imidazole-4-carboxaldehyde (R-2 = Ph: 7, 10) in the presence of iron(II) thiocyanate. Together with the single-crystal X-ray structures of 7 and 9, variable-temperature magnetic susceptibility and Mossbauer studies of 5-10 showed that it is possible to tune the spin crossover properties in the [FeLCx(NCS)(2)] series by changing the 2-imidazole and/or C2-propylene susbtituent of L-Cx. (c) 2006 Elsevier Ltd. All rights reserved.