Spin crossover in the Fe(3PyMe)2[M(CN)4] series with M = Ni, Pd, Pt, and 3PyMe = 3-pyridinemethanol. The role of the intermolecular OH---OH interaction.

Abstract

Pillared ferrous 2D tetracyanometallates, Fe(L)2[M(CN)4] where M = Ni, Pd, Pt, and L is pyridine and its derivative, form a family of Hofmann-type 2D coordination polymers. This family includes members with spin crossover (SCO) behavior. The geometry for the coordination polyhedron of the iron atom determines the possibility of observing such an effect in these solids. A highly distorted coordination geometry for the iron atom inhibits the high spin (HS) to low spin (LS) transition. In these SCO materials, the temperature where the HS  LS transition is observed usually follows Ni < Pd < Pt. The electron density available at the CN5 orbital of the equatorial CNs ligand mainly determines the strength of the formed CN-Fe coordination bond and, consequently, that order. This contribution discusses the role of the hydrogen bonding OHOH interaction in the interlayer region on the possibility of observing the SCO. The observed SCO effect in the titled series of 2D Hofmann-like coordination polymers deviates from the regular behavior reported for this family of 2D pillared solids. The probability of observing the effect follows the order Ni (53%)  Pd (23%)  Pt (11%), with a narrow hysteresis of about 2 K. This contribution discusses the nature of such a deviation, from magnetic (SQUID) measurements, Raman, IR, and Mössbauer spectroscopic information, and structural (XRD) data.