The synthesis and structure of a paramagnetic Lewis base adduct of antimony pentachloride, trans-[MnII(CNSbCl5)(CO)2{P(OEt)3}(dppm)][SbCl6]†

Abstract

Treatment of cis-[Mn(CN)(CO)₂{P(OEt)₃}(dppm)] with SbCl₅ gave paramagnetic trans-[Mn(CNSbCl₅)(CO)₂{P(OEt)₃}(dppm)][SbCl₆] the crystal structure of which shows the geometry of the [Mn(CN)(CO)₂{P(OEt)₃}(dppm)] fragment to be characteristic of a low-spin manganese(II) centre. The Mn–P(OEt)₃ and Mn–P_dppm bond lengths are increased by 0.10 and 0.07 Å compared with those in analogous manganese(I) species while the Mn–C distances are little changed. A Cambridge Structural Database study of octahedral L·SbCl₅ species indicated that the Sb–Cl distances (cis and trans to the ligand L) and the average L–Sb–Cl_cis angle are strongly correlated and appear to reflect the donor ability of the ligand L. A comparison of the geometry of the Mn(CNSbCl₅) moiety with those of other L·SbCl₅ species showed that the manganese ligand is a donor comparable with a range of other nitrogen and oxygen ligands but much weaker than ligands such as the phenyl anion. The geometry variations were analysed using a qualitative molecular orbital model for the bonding in L·SbCl₅ species.