Microscopic model for superexchange interactions and photomagnetism in binuclear transition metal complexes

摘要: Recent experiments show that the superexchange interaction in molecular clusters containing transition metal ions $A = Ni^{II}$ and $B = W^V, Nb^{IV} or Mo^V$ some cases is antiferromagnetic, contrary to conventional rules. To understand this anomaly, we develop a quantum many-body model Hamiltonian solve it exactly using valence bond (VB) approach. We identify various parameters which control ground state spin different of A-B system. present phase diagrams delineate high low-spin states parameter space. fit gap extract effective exchange constant within experimentally observed range, for reasonable values. also find region intermediate space, larger size. The spectrum microscopic cannot be reproduced by simple Heisenberg Hamiltonian. above generic can employed explain photomagnetism $MoCu_6$ degenerate spanned S = 0, 1, 2 3 manifolds with doubly occupied Mo site corresponding Mo(IV) singly Cu sites Cu(II) configurations. In each these spaces, observe there exist charge-transfer (CT) at \approx 3 eV are dipole coupled state. S = 3 manifold largest CT excitations. Coupled fact density sparse, compared other manifolds, expect excited long-lived, thereby explaining