Synthesis and Structure of Di-n-Butyltin Pyridine-2-phosphonate-6-carboxylate

The crystal structure of di- n -butyltin pyridine-2-phosphonate-6-carboxylate, [C 14 H 24 NO 6 PSn] 2, features centrosymmetric dimers disposed about a central Sn 2 O 2 core. The phosphonate carboxylate dianion is μ 2 -tetradentate, coordinating one tin atom via one of the phosphonate oxygen atoms, the pyridine nitrogen atom, and one of the carboxylate oxygen atoms; the latter atom also coordinates the second tin atom of the dimer. The remaining positions in the seven-coordinate, distorted pentagonal bipyramidal geometry are occupied by a water molecule and two n -butyl groups that occupy axial positions. The lattice is stabilized by hydrogen-bonding contacts leading to an arrangement of parallel, orthogonally related chains of dimeric units. In methanol solution, the dimer is involved in a dissociation equilibrium that is fast on the NMR time scale.