An Xα ab initio Calculation of the Charge and Spin-Density in Cs3Mo(NCS)6 Crystals Compared With Experiment

We have performed ab initio discrete variational Xα calculations on a Cs18[Mo(NCS)6]15+ cluster, with the external electric field appropriate for a Cs3Mo(NCS)6 crystal. The calculations show both σ and π bonding, and also the participation of diffuse molybdenum- centred orbitals . Compared with the charge density experiment these effects are qualitatively correct but are underestimated. We performed further calculations successively removing the external electric field and the 18 Cs+ neighbours . The effects on the calculated metal- ligand bonding in the complex ion are negligible. This is not in agreement with experiment, so that these calculations which invoke only electrostatic effects and orthogonality with neighbouring ions and which also use only simple basis sets are not adequate. Further calculations on the Cr(NCS)63- and W(NCS)63- ions show increasing covalence from chromium to tungsten as expected. The spin transfer to the ligand is calculated to triple, but charge transfer is almost constant.