The 13-vertex stannacarborane 1,6-Me2-4,1,6-closo-SnC2B10H10 reacts with the Lewis bases 2,2′-bipyridine, 1,10-phenanthroline, 4,4′-dimethybipyridine and 4,4′-diphenylbipyridine, in toluene, to precipitate bright-yellow adducts 1,6-Me2-4-(L2)-4,1,6-closo-SnC2B10H10 (1–4, respectively) in good yield. Compounds 1–3 have been characterised by NMR spectroscopy and single-crystal X-ray diffraction. Compound 4 is somewhat less stable in solution but has also been studied crystallographically. Adduct formation retains the docosahedral structure of 1,6-Me2-4,1,6-closo-SnC2B10H10 but is accompanied by polyhedral distortion arising from significant increases in Sn-C and Sn-B2 distances. This distortion is described in terms of either a slipping or hinging of the {SnL2} fragment. In the molecular structures of 1–4 it is evident that the Sn lone pair of electrons is stereochemically active since the L2 ligand is clearly inclined with respect to the polyhedron. Both the inclination and orientation of L2 are rationalised by the results of DFT calculations on 4,1,6-closo-SnC2B10H12. Calculations on models of the adducts 1, 3 and 4 reproduce the structural distortion that accompanies adduct formation, but appear to underestimate somewhat the strength of Sn-L2 bonding.
