The influence of the lattice on the spin transition in solids. Investigations of the high spin ag low spin transition in mixed crystals of [FexM1−x(2−pic)3]C12·MeOH☆

Abstract The spin transition behaviour in the iron(II) complex [ Fe (2− pic ) 3 ] Cl 2 · MeOH (2− pic = 2− aminomethylpyridine ) is discussed within a previously developed model which describes the High Spin (HS) ag Low Spin (LS) transition on the grounds of the elasticity theory. For this purpose, the relative HS fraction γ as a function of temperature was determined for mixed crystals of [Fe x M 1- x (2-pic) 3 ]Cl 2 ·MeOH ( M = Co , Zn, 0 x ⩽ 1) employing 57 Fe Mossbauer spectroscopy. In addition, the temperature dependence of the lattice constants of the pure iron compound was derived from X-ray diffraction measurements and the Lamb Mossbauer factors for [Fe(2-pic) 3 ]Cl 2 ·Sol (Sol = EtOH, MeOH) were determined at room temperature. It is shown that essential features of the spin transition behaviour of the title system can be explained within the λ model. The quantitative agreement of the predicted elastic interaction energy with the experimental data, however, is not yet satisfactory.