Characterization and decomposition mechanism of an unusual nickel, thiocyanate and 4-methylpyridine polymeric complex

Abstract

The synthesis, characterization, and thermal decomposition of the [Ni(SCN) 2(H +SCN) 2(4-mepy) 2] compound with an octahedral structure in polymeric chain were reported, in which SCN groups form bridges among Ni(II) ions. The compound decomposes in water resulting in a pH<4 solution. The FT-IR spectrum presented doublet bands at 2117; 2128 cm −1, 788; 773 cm −1 assigned to ν(CN) and ν(CS) stretching modes, respectively, and δ(SCN) deformation modes at 468; 476 cm −1. The Raman spectrum of the compound presented the ν(CN) stretching as a strong doublet at 2122; 2128 cm −1, ν(CS) at 783; 770 cm −1, and δ(SCN) at 468; 477 cm −1. No significant changes were observed in the 4-mepy ligand bands compared with the vibrational frequencies of the pure compound or the compound in aqueous solution 0.2 mol l −1. The crystal UV–vis reflectance spectrum presented two bands centered in 626 and 424 nm tentatively assigned to the d→d type transitions, 3A 2g→ 3T 1g and 3A 2g→ 3T 1g, for a symmetry close to O h. The TG curve showed a mass loss between 120 and 200 °C assigned to the loss of the two 4-mepy molecules; from 200 to 265 °C, the loss of the two H +SCN groups; and from 265 to 450 °C, the loss of the two SCN groups that formed the bridges among the nickel atoms. Based on these mass loss data, a mechanism of thermal decomposition for the compound was proposed.