材料期刊网

A covalent magnetic exchange interaction formula for describing the transition-metal ion pairs in strong covalent complex molecules has been derived in terms of the Girerd-Journaux-Kahn's magnetic theory and the Cuire-Barth-Canny's covalent theory. By this formula the relationship between the magnetic exchange coupling parameter J and the covalent parameter N has been studied. It is shown that the exchange interaction depends sensitively on the covalent effect, i.e., \J\ increases rapidly with decreasing N. For the diiron(III) core in the active site of ribonucleotide reductase as well as in its TPA model molecules, our calculations revealed that: (1) about 40% of the antiferromagnetic contribution comes from the covalent effect; (2) the theoretical values J = -98.6 similar to -103.9 cm(-1) of diiron(III) core for N = 0.89 and R = 3.58-3.60 A (R = R-1 + R-2 is the sum of the two bond lengths of Fe-III(1)-O and Fe-III(2)-O in Fe-III(1)-O-Fe-III (2) cluster) are in good agreement with the experimental findings J = -108 cm(-1) for Fe(III) pairs in the active site of ribonucleotide reductase and J = -101 similar to -119 cm(-1) in its TPA series model molecules, respectively. (C) 2002 Published by Elsevier Science B.V.