Charge density in [Ru(ND3)6][SCN]3 by X-ray diffraction at 92 K

Abstract

High quality X-ray data were collected on a [Ru(ND₃)₆][SCN]₃ crystal at 92 K. All 7531 unique data were analysed with multipole and with valence-orbital population models of the charge density to give R(I) as low as 0.017 with χ² 0.88. The model suggests substantial σ donation from the ammonia molecules [0.65(7) e] to the ruthenium atom, but almost negligible π donation [0.09(7) e], as expected. The 4d charge distribution on the ruthenium atom is essentially cubic in symmetry [4d_xy^1.61(5)4d_xz^1.63(5)4d_yz^1.67(5)]. A general ligand-field model, derived from the highly anisotropic magnetic data on crystals, predicts just such an almost cubic 4d-electron distribution. The hole in the Ru^III t_2g⁵ configuration (²T_2g ground state) is not in this case localised into a non-cubic t_2g orbital population because the spin-orbit coupling dominates the rhombic components of the ligand field. Charge transfers are also found from the thiocyanate anion to the ammonia molecules. As contact distances from ND₃ to NCS decrease, substantial charge is transferred from SCN to ND₃. In addition the ND₃ molecule becomes more polarised, with charge migrating from D to N and the SCN group becomes polarised, with charge migrating towards the centre. These ‘intermolecular’ or crystal effects result, as judged by agreement factors, in very significant differences in the charge distributions on the three crystallographically distinct ammonia groups and the two distinct thiocyanate ions.