MOLECULAR STRUCTURE OF MANGANESE TRIS-ACETYLACETONATE IN DIFFERENT SPIN STATES

Abstract

Quantum chemical calculations of the geometric structure, force fields and harmonic vibration frequencies of the molecule Mn(acac)3 for electronic states with multiplicities M = 1, 3 and 5 were performed using the GAUSSIAN 09 program in the framework of density functional theory (DFT/UB3LYP) with correlation-consistent valence three-exponential basis functions cc-pVTZ. The structure with high-spin state S=2 (symmetry of electronic state 5B) possesses the lowest energy and it is characterized by C2 symmetry. The coordination polyhedron MnO6 possesses the shape of “elongated octahedron”. The high-spin state 5A is characterized by structure of compressed octahedron. The distortion of octahedral structure of coordination polyhedron in the states 5A and 5B is significant, and this fact testifies to the strong Jahn-Teller effect, or vibronic effect, in 5E electronic state. The calculations for low-spin state S=0 are notable for some specifics. The optimization resulted in C2 symmetry of molecule having the symmetry of electronic state 1B. The bond distances Mn-O within 0.001 Å were equal to values obtained for structure with D3 symmetry with S=1. This result corresponds to the situation if two electrons occupy different 1e orbitals possessing opposite spins. The spin states 3A2 and 1B lie higher than the high-spin state by 5.2 and 17.3 kcal/mol, respectively. The structural features are explained well in a framework of simple crystal field theory indicating that d-orbitals of Mn3+ ion undergo the significant influence of ligand field.Forcitation:Berger R.J.F., Girichev G.V., Giricheva N.I., Petrova A.A., Sliznev V.V., Tverdova N.V. Molecular structure of manganese tris-acetylacetonate in different spin states. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2017. V. 60. N 4. P. 47-53.