New Hofmann-like spin crossover compound with 3,5-lutidine

A new type III of 3,5-lutidine spin crossover coordination compound with formula Fe(3,5-lutidine)₂Ni(CN)₄·2[(H₂O)(3,5-lutidine)] 2c has been obtained. The ratio of the high spin state (HS) iron (II) changing to the low spin state (LS) iron (II) in 2c is higher than that of type I and type II 3,5-lutidine coordination polymer 2a and 2b previously reported. ⁵⁷Fe Mössbauer spectra of 2c show two different doublets which correspond to HS1 (inner doublet lines) and HS2 (outer doublet lines). The intensity of the HS1 doublet decreases on cooling to 80 K while the intensity of another component, the LS singlet, increases. The 90 % of the HS1 doublet change to the LS singlet is probably due to suitable environments of octahedral iron (II) ions coordinated by four nitrogen atoms of cyano groups and two nitrogen atoms of 3,5-lutidine ligands. We also prepared the Hofmann-like 3,5-dichloropyridine coordination compound Fe(3,5-dichloropyridine)₂Ni(CN)₄ ·2[(3,5-dichloropyridine)(H₂O)] 2d to compare it with 2c. ⁵⁷Fe Mössbauer spectra of 2d show that 2d is not a spin crossover coordination compound.