Synthesis and Mössbauer Spectroscopy of Formal Tin(II) Dichloride and Dihydride Species Supported by Lewis Acids and Bases

119Sn Mössbauer spectroscopy was performed on a series of formal Sn­(II) dichloride and dihydride adducts bound by either carbon- or phosphorus-based electron pair donors. Upon binding electron-withdrawing metal pentacarbonyl units to the tin centers in LB·SnCl2·M­(CO)5 (LB = Lewis base; M = Cr or W), a significant decrease in isomer shift (IS) was noted relative to the unbound Sn­(II) complexes, LB·SnCl2, consistent with removal of nonbonding s-electron density from tin upon forming Sn-M linkages (M = Cr and W). Interestingly, when the nature of the Lewis base in the series LB·SnCl2·W­(CO)5 was altered, very little change in the IS values was noted, implying that the LB-Sn bonds were constructed with tin-based orbitals of large p-character (as supported by prior theoretical studies). In addition, variable temperature Mössbauer measurements were used to determine the mean displacement of the tin atoms in the solid state, a parameter that can be correlated with the degree of covalent bonding involving tin in these species.