Magnetic structure and covalence in tetrachlorobis(N-phenylacetamidinato)rhenium(IV) by neutron diffraction

Powder neutron diffraction measurements have been made at 2 and 20 K for the complex cis-[ReCl₄(NH=CMe-NHPh)₂]. The changes in diffracted intensities on magnetic ordering at 9.7(1) K were fitted in the Shubnikov group Pc′c′n to an antiferromagnetically ordered magnetic structure in which the spins are aligned along c in this orthorhombic crystal. A moment of 2.58(6) μ_B resides on the rhenium site in each molecule, while each chlorine site has a spin population of 1.03(8) μ_B due to covalent spin delocalisation. The N-C-N region of the other two ligands each has a spin population of -1.86(10) μ_B, indicating a substantial spin polarisation resulting from electron correlation effects. The antiferromagnetic structure is consistent with a reinterpretation of earlier single crystal magnetisation data. The very large amounts of spin transfer observed within the molecule are not unexpected in this heavy metal complex, and qualitatively reasonable given a synergistic interaction between the two ligand types. The previous observation of a metamagnetic transition in this crystal is explained as being driven by a change in canting angles within the molecule, from alignment closely along c to an arrangement in which opposite halves of the molecule are differently canted, with small but significant +b and -b components. The direction of magnetisation within the molecule is thus not all parallel.