Quantum-chemical study of intramolecular spin-forbidden rearrangements of the transition metal chelate complexes

An overview of quantum-chemical methods of studying the spin-forbidden reactions is presented. It was shown that HF and MP2 methods overestimate stabilization of the high-spin states whereas DFT methods with the use of LSDA and CGA functionals underestimate these states. Hybrid exchange-correlation density functionals B3P86 and B3LYP give the best agreement with the experimental data. The intramolecular spin-forbidden rearrangement of bis-chelate Ni(II) and Co(II) complexes was studied using the B3LYP/6-311++G (d,p) method.