Mossbauer Study of an Intramolecular Antiferromagnet

Mossbauer measurements at 4.2sTs22 K and OsHosBO kOe are + reported in (Fe Salen Cl);a' a molecular complex containing two coupled Fe3 ions bridged by oxygen atoms. At 4.2 K only the ground state with effective spin S ;::: 0 is appreciably populated. Analysis of the magnetic field and temperature dependence of the magnetic hyperfine field yields an exchange constant J ;::: 6.7 cmI and a hyperfine field of 192 kOe per unit spin at each Fe3+ nucleus. In certain transition metal complexes, the paramagnetic ions are situated so that two or more of them cluster close to each other, but the clusters are relatively well isolated from each other. Such systems are found in nature, for example, in certain biologically important enzymes. 1, 2 The paramagnetic ions within such clusters can interact strongly with each other' and the interactions between clusters will be relatively very weak. We may speak then, of intramolecular magnetism. 3 Such situations are also of interest because they provide the possibility of studying exchange inter­ actions in finite systems. The simplest model for such a system is to consider the paramagnetic ions to interact via the classical exchange Hamiltonian