Impact of ligand spacer and counter-anion in selected 1D iron(II) spin crossover coordination polymers

摘要

A new ID coordination polymer [Fe(βAlatrz)_3](ClO_4)_2·H_2O(1) with aneutral bidentate ligand, βAlatrz = 4H-1,2,4-triazol-4-yl-propionate, was preparedand its magnetic behavior was investigated by temperature dependent magneticsusceptibility measurements and ~(57)Fe Mossbauer spectroscopy. The temperature de-pendence of the high-spin molar fraction derived from ~(57)Fe Mossbauer spectroscopyrecorded on cooling below room temperature reveals a gradual single step transitionwith T_(1/2) =173 Kbetween high-spin and low-states in agreement with magneticsusceptibility measurements. 1 presents striking reversible thermochromism fromwhite, at room temperature, to pink on quench cooling to liquid nitrogen. The phasetransition is of first order as deduced from differential scanning calorimetry, with T_(1/2)matching the one determined by both SQUID and ~(57)Fe Mossbauer spectroscopy. Abrief assessment has been made among closely related 1D coordination polymersto perceive the effect of ligand spacer length and anion effect on the spin crossoverbehavior of these new materials.