Pyridazine-Supported Polymeric Cyanometallates with Spin Transitions

Heterometallic cyano-bridged spin-crossover complexes form a large family of switchable compounds with different structural motives and diverse transition characteristics. Here we report on the hysteretic water-dependent spin transitions found in the family of [Fe(pyridazine)2M(CN)4] frameworks (M = Ni, Pd, Pt). The structure of three new spin-crossover compounds is built of cyanometallic layers supported by pyridazine ligands. The frameworks contain water guest molecules that can be removed upon heating. Spin transition was found in both hydrated and dehydrated compounds, while the removal of water stimulated a complete spin state switch. Mössbauer spectroscopy revealed two different high-spin centers in hydrated frameworks, and only one of them is switchable. The compounds display a pronounceable thermochromism, changing their color from red in low-spin to yellow in high-spin. The work shows a perspective of 1,2-diazine application for the design of switchable complexes