Synthesis, Crystal Structure, and Magnetic Properties of a Ferromagnetically Coupled Difluoro-Bridged Dinuclear Chromium(III) Complex with a Substituted Tetrahydrosalen Derivative as Ligand

Abstract

A novel difluoro-bridged dinuclear chromium(III) complex has been synthesized by the reaction of trans-[Cr(py)4F2]ClO4 in 2-methoxyethanol with a substituted tetrahydrosalen derivative L8 (L8 means the negatively charged ligand obtained by dissociation of two protons from H2L8 = N,N‘-bis(2-hydroxy-3,5-di-tert-butylbenzyl)-1,2-ethanediamine). The crystal structure of [CrL8F]2·2C3H8O2 has been determined. The crystal system is triclinic, and the lattice constants are a = 9.604(2) Å, b = 13.346(2) Å, c = 15.751(2) Å, α = 74.00(1)°, β = 87.94(1)°, and γ = 70.55(1)°. Z = 1 and the volume of the unit cell is 1826.40(49) Å3. The space group is P̄1 (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)°, and the Cr−F(bridge) distances are 2.0172(8) and 1.9754(9) Å, and the Cr−Cr distance is 3.0787(4) Å. The configuration of the dinuclear molecule is cis,cis-O,O‘-Δ,Λ, where cis refers to the position of the two oxygen donors and Δ and Λ refer to the configuration of the two N,O chelates of the tetradentate ligand L8 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, De = 0.008 cm-1, Ee = −0.015 cm-1, Da = Db = −0.658 cm-1, Ea = Eb = 0.133 cm-1, gxa = gxb = gya = gyb = 1.98, and gza = gzb = 2.00.