Mössbauer effect and susceptibility studies of a dimeric Schiff-base iron(III) adduct

Abstract

Variable-temperature susceptibility and Mössabauer effect measurements of the nitromethane adduct Fe(salen) Cl,-½MeNO₂ are reported. The susceptibility from 13 to 300°K is well explained by the assumption that the molecules are dimeric with an antiferromagnetic exchange (J–6·3 cm.^–1) between the two S= 5/2 iron ions. The zero-field Mössbauer spectrum is a quadrupole doublet with an integral asymmetry which is attributed to anisotropy in the recoil-free fraction. There is also an additional peak-height asymmetry which is accounted for by a theoretical study of the spin-spin relaxation caused by magnetic dipolar interaction between pairs of the dimeric molecules. At 4·2°K the Mössbauer spectra obtained in applied fields of up to 60 kOe show that there is no appreciable hyper = fine field so that the ground state of the molecules is predominantly spin zero. These spectra also show that the electric field gradient is positive (V_zz < O) with its principal axis perpendicular to the hyperfine magnetic fields.