Intermolecular 119Sn,31P Through-Space Spin-Spin Coupling in a Solid Bivalent Tin Phosphido Complex

A bivalent tin complex [Sn(NP)(2)] (NP = [(2-Me2NC6H4)P(C6H5)](-)) was prepared and characterized by X-ray diffraction and solution and solid-state nuclear magnetic resonance (NMR) spectroscopy. In agreement with the X-ray structures of two polymorphs of the molecule, P-31 and Sn-119 CP/MAS NMR spectra revealed one crystallographic phosphorus and tin site with through-bond (1)J(Sn-117/119,P-31) and through-space (TS)J(Sn-117/119,P-31) spin-spin couplings. Density functional theory (DFT) calculations of the NMR parameters confirm the experimental data. The observation of through-space (TS)J(Sn-117/119,P-31) couplings was unexpected, as the distances of the phosphorus atoms of one molecule and the tin atom of the neighboring molecule (>4.6 angstrom) are outside the sum of the van der Waals radii of the atoms P and Sn (4.32 angstrom). The intermolecular Sn...P separations are clearly too large for bonding interactions, as supported by a natural bond orbital (NBO) analysis.