Spin density and structure of aquabis(2,2′-bipyridine)di-µ-hydroxosulphatodicopper(II) tetrahydrate at 4.2 K

Abstract

The spin density distribution in the metal–ligand framework of the title compound has been determined from two-dimensional polarised neutron diffraction data. A qualitative picture of the superexchange pathway between copper atoms in the dimeric molecule emerges, and the importance of spin polarisation effects is indicated by the presence of significant regions of negative spin density on the sides of the bridging oxygen atoms away from the copper atoms. The important role played by the spin polarisation phenomenon in the exchange process indicates the need for a full unconstrained Hartree–Fock calculation in any theoretical treatment of the CuO₂Cu system. As a necessary corollary to the spin density study, the molecular structure of [(H₂O)(bipy)Cu(OH)₂Cu(bipy)(OSO₃)]·4H₂O (bipy = 2,2′-bipyridine) has been determined at 4.2 K by single-crystal neutron diffraction methods from limited three-dimensional intensity data. Crystals are monoclinic, space group P2₁/c, with a= 9.658(12), b= 34.29(3), c= 7.626(10)Å, β= 103.3(1)°, and Z= 4.