Theoretical investigation of optical and paramagnetic resonance spectra of [NiF6](4-) clusters with orthorhombic symmetry.

The ground state absorption spectra of [NiF6](4-) clusters with orthorhombic symmetry (Ni(2+) in NiF2 crystal and Ni(2+)-doped ZnF2 crystal, D2h point group) are theoretically calculated and assigned by diagonalization of 45×45 complete energy matrix for 3d(8) configuration and the spin-Hamiltonian (SH) parameters (zero-field splitting D and E, and g factors gx, gy, gz) are studied by use of high-order perturbation method, in the frame of semi-empirical molecular orbital (MO) scheme based on strong crystal field framework. In those energy matrix, all the configuration interactions though the cubic crystal field (CF), the orthorhombic crystal field, the Coulomb interaction are taken into account. The calculated results are in good agreement with the experimental data. The local structure (bond length and bond angle) of [NiF6](4-) clusters are determined, and the results shows that the structure data given by Stout are more plausible than those given by Baur.