Coordination geometry determination of stannane compounds with phosphinoyldithioformate ligands using multinuclear NMR, Sn Mössbauer and DFT methods

A series of tin(IV) phosphinoyldithioformate compounds were prepared from metathesis reaction of [R2P(O)CS2]- anion and aliphatic organotin: R′nSnX4-n (R = Ph, Bz; R′ = Me, Et; X = Cl, Br). The compounds are formulated as [SnR′2X{S2CP(O)R2}] (1), [SnR′2{S2CP(O)R2}2] (2), and [SnR′3{S2CP(O)R2}] (3). Structural analysis using a combination of IR, UV and multinuclear NMR (1H, 13C, 31P and 119Sn) spectroscopy showed the ligand prefers S,O bidentate coordination mode in these series for (1), and (2), while monodentate coordination is preferred by (3). Geometries of compounds were determined using 119Sn and 13C NMR coupling constants. The spectroscopic data is consistent with (S,O)-bidentate coordination of the ligands in (1) and (2) in solution, while a monodentate coordination through sulfur is observed in (3). Mössbauer measurements confirmed formal oxidation state of Sn, and shows comparable isomer shifts and quadrupole splitting for compounds (2) and (3) in the solid state. DFT structure optimizations and vibrational frequency calculations were performed for all compounds. The optimized structures and computed shifts of PO and CS vibrations are in excellent agreement with the conclusions of the spectroscopic structural analysis.