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

Treatment of cis-[Mn(CN)(CO)(2){P(OEt)(3)}(dppm)] with SbCl5 gave paramagne tic trans-[Mn(CNSbCl5)(CO)(2){P(OEt)(3)}(dppm)][SbCl6] the crystal structur e of which shows the geometry of the [Mn(CN)(CO)(2){P(OEt)(3)}(dppm)] fragm ent 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 Angstrom compa red with those in analogous manganese(I) species while the Mn-C distances a re little changed. A Cambridge Structural Database study of octahedral L . SbCl5 species indicated that the Sb-Cl distances (cis and trans to the liga nd 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. T he geometry variations were analysed using a qualitative molecular orbital model for the bonding in L . SbCl5 species.