Single crystal E.P.R. study of fluoride-bridged copper(II) dimers
- 20 April 1986
- journal article
- research article
- Published by Taylor & Francis in Molecular Physics
- Vol. 57 (6), 1283-1296
- https://doi.org/10.1080/00268978600100911
Abstract
The first single-crystal E.P.R. spectra of fluoride-bridged copper(II) dimers are reported. The g- and the Zero Field Splitting (ZFS) tensors of the triplet systems [Cu2F2(dmpz)2(mpz)4](BF4)2 and [Cu2F2(mpz)2(dmpz)4](BF4)2 differ appreciably from previous results obtained from powder spectra. The ZFS-tensor is rhombic and identical for both systems: D 1 = ± 411, D 2 = ∓ 101, D 3 = ∓ 310 × 10-4cm-1 (spin hamiltonian S. D. S). D 1 is in the Cu2F2 plane but, as in many other bridged copper(II) dimers, perpendicular to the Cu-Cu direction; D 3 is along the Cu-Cu′ direction and D 2 perpendicular to the Cu2F2 plane. A semiempirical molecular orbital calculation results in the location of the unpaired electrons in the copper 3d x 2 - y 2 orbitals (the z-axis is the longer Cu-F vector), with a small admixture of copper 4pz and fluorine 2s, 2px and 2pz orbitals. The calculated g-tensor is in good agreement with the experiment: it is axial with g‖ > g⊥ and the axial axis is oriented along the z-axis. The dipolar interaction between the two unpaired electrons is calculated exactly, but it cannot account for the ZFS-tensor. The fit of the theoretically calculated E.P.R. intensities to the experimentally obtained intensities between 1·3 K and 14K of the first system leads to an isotropic exchange constant of + 0·375 ± 0·125 cm-1 (spin hamiltonian 2J S 1. S 2), in accord with earlier magnetic susceptibility measurements.Keywords
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