Synthesis, crystal structure, and magnetic properties of a ferromagnetically coupled difluoro-bridged dinuclear chromium(III) complex with a substituted tetrahydrosalen derivative as ligand

A novel difluoro-bridged dinuclear chromium(III) complex has been synthesized by the reaction of trans-[Cr-(py)(4)F-2]ClO4 in 2-methoxyethanol with a substituted tetrahydrosalen derivative L(8) (L(8) means the negatively charged ligand obtained by dissociation of two protons from H(2)L(8) = N,N'-bis(2-hydroxy-3,5-di-tert-butylbenzyl)-1,2-ethanediamine), The crystal structure of [CrL(8)F](2) . 2C(3)H(8)O(2) has been determined. The crystal system is triclinic, and the lattice constants are a 9.604(2) Angstrom, b = 13.346(2) Angstrom, c 15.751(2) Angstrom, alpha = 74.00(1)degrees, beta = 87.94(1)degrees, and gamma = 70.55(1)degrees. Z = 1 and the volume of the unit cell is 1826.40(49) Angstrom(3). The space group is <(P)over bar 1> (No. 2). The refinement of 456 variables includes 6279 of the 7631 independent reflections, The final residual is 4.08%. The centrosymmetric dinuclear molecule consists of two slightly distorted octahedrally cis coordinated chromium centers bound together by two fluoride bridges. The Cr-F-Cr angle is 100.90(4)degrees, and the Cr-F(bridge) distances are 2.0172(8) and 1.9754(9) Angstrom, and the Cr-Cr distance is 3.0787(4) Angstrom. The configuration of the dinuclear molecule is cis, cis-O, O'-Delta, Lambda, where cis refers to the position of the two oxygen donors and Delta and Lambda refer to the configuration of the two N, O chelates of the tetradentate ligand L(8) at each of the two chromium(III) centers. The two chromium-(III) centers in the complex are ferromagnetically coupled. On basis of measurements of the field-dependent magnetization and the magnetic susceptibility, respectively, it has been shown unambiguously that the ground state is a septet state. It has not been possible to determine the monoatomic zero field splitting parameter D from the magnetic susceptibility measurements, but the parameter has been determined from the EPR spectra measured at 4 and 21 K. From simulation of the EPR spectra the following parameters have been obtained: J = -1.4 cm(-1), D-e = 0.008 cm(-1), E(e) = -0.015 cm(-1), D-a = D-b = -0.658 cm(-1), E(a) = E(b) = 0.133 cm(-1), g(xa) = g(xb) = g(ya) = g(yb) = 1.98 and g(za) = g(zb) = 2.00.