X-ray constrained unrestricted Hartree-Fock and Douglas-Kroll-Hess wavefunctions.

The extension of the X-ray constrained (XC) wavefunction approach to open-shell systems using the unrestricted Hartree-Fock formalism is reported. The XC method is also extended to include relativistic effects using the scalar second-order Douglas-Kroll-Hess approach. The relativistic effects on the charge and spin density on two model compounds containing the copper and iron atom are reported.

Disodium tetra-aqua-bis(sulfato)iron(II).

In the title compound, [FeNa(2)(SO(4))(2)(H(2)O)(4)], the Fe(2+) cation is situated on a centre of inversion and is hexa-coordinated by four O atoms from water mol-ecules and two O atoms from two sulfate anions in an octa-hedral geometry. The coordination environment of Na(+) comprises six O atoms in a more distorted octa-hedral arrangement, with Na-O distances between 2.368 (1) and 2.