Structure and Bonding in a Diamond-Shaped Tin Cluster Possessing a cyclo-Sn4 Core.

A tetrameric cluster composed entirely of (aryl)Sn units, [DMPSn] 4 (DMP = 2,6-dimesitylphenyl), has been prepared by reduction of [DMPSnCl] 2 with a variety of reductants. This cluster was characterized in solution by multinuclear NMR spectroscopies, as well as in the solid-state by single crystal X-ray diffraction analysis. This species is stereochemically nonrigid in solution and possesses a folded cyclo -Sn 4 core that undergoes rapid ring-flipping at higher temperatures. The solid-state molecular structure is remarkably unsymmetrical and possesses a nearly planar cyclo -Sn 4 core. The DMP substituents are arranged such that three are approximately coplanar, while one is nearly perpendicular to the cyclo -Sn 4 core. Density functional theory calculations for a [PhSn] 4 model system show that this distorted geometry about the cyclo -Sn 4 core maximizes sigma-bonding between the Sn centers in a manner reminiscent of trans -bent bonding in the heavy group 14 analogues of alkenes and alkynes.