Spin crossover in iron(ii) Hofmann clathrates analogues with 1,2,3-triazole

Abstract

Hofmann-like cyanometallic complexes represent one of the biggest and well-known classes of Fe^II spin-crossover compounds. In this paper, we report on the first Fe^II Hofmann clathrate analogues with unsubstituted 1,2,3-triazole, which exhibit temperature induced spin transition. Two new coordination polymers with the general formula [Fe^II(1,2,3-triazole)₂M^II(CN)₄] (M = Pt, Pd) undergo abrupt hysteretic spin crossover in the range of 190–225 K as revealed by magnetic susceptibility measurements. Two compounds are isostructural and are built of infinite cyanometallic layers which are supported by 1,2,3-triazole ligands. The thermal hysteresis loop is very stable at different scan rates from 0.5 to 10 K min⁻¹. The compounds display strong thermochromic effect, changing their colour from pink in the low-spin state to white in the high-spin state. Our findings show that 1,2,3-triazole is suitable for elaboration of spin-crossover Hofmann clathrate analogues, and its use instead of more classical azines can advantageously expand this family of complexes.