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 th e complex cis-[ReCl4(NH=CMeNHPh)(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) mu(B) resides on the rhenium site in each molecule, while each chlorine site has a spin population of 1.03(8) mu(B) due to covalent spin delocalisation. Th e N-C-N region of the other two ligands each has a spin population of -1.86 (10) mu(B), indicating a substantial spin polarisation resulting from elect ron 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 unexpec ted in this heavy metal complex, and qualitatively reasonable given a syner gistic interaction between the two ligand types. The previous observation o f a metamagnetic transition in this crystal is explained as being driven by a change in canting angles within the molecule, from alignment closely alo ng c to an arrangement in which opposite halves of the molecule are differe ntly canted, with small but significant +b and -b components. The direction of magnetisation within the molecule is thus not all parallel.