Interpretations of the magnetic properties of the trinuclear oxo-centered
metal carboxilates of general composition [M3O(OOCR)6(L)3]X continue to
present the difficulties due to the lack of the well founded theoretical model
of the exchange interactions in polynuclear molecular systems. The wide
used phenomenological Heisenberg model needs in many cases additional
assumptions for the theoretical description of the magnetic experimental data.
Therefore it is important to perform the systematic rigorous investigations of the
magnetic properties using quantum chemical methods.
In this work the geometry and electronic structure of the [Cr3O(OOCH)6(H2O)3]+
molecular system in the ground and lowest excited states are studied quantum
chemically. The calculations were carried out by ab initio MO LCAO Hartree – Fock
(HF) - Roothaan self-consistent field method in restricted HF approximations,
using STO-6G base for atomic orbitals and taking into consideration the
configuration interaction. To determine the optimal geometric configuration it
was supposed that the [Cr3O(OOCH)6(H2O)3]+ system has the symmetry D3h.
The configurational interaction was considered taking into account 52920
determinants corresponding to 27720 electron configurations with total spin
value S=1/2, 19800 configurations with S= 3/2, 4950 configurations with S= 5/2,
440 configurations with S= 7/2 and 10 configurations with S= 9/2.
As the result of the performed calculations it was obtained that the total
energy of considered system in ground electronic states 2E is equal to -4543.9307
atomic units of energy (a.u.e.). First excited term with total energy -4543.9299
a.u.e. is of the 4A type. Calculated value of the gap between the ground and first
excited terms exceeds twice the experimental value.