Subvalent Group 4B metal alkyls and amides. Part III Mössbauer spectroscopy studies of bis[bis(trimethylsilyl)methyl]tin(II) and its derivatives
Mössbauer spectra of SnR2[R = CH(SiMe3)2] and of 16 of its derivatives have been recorded. The latter fall into two classes: (i) the dialkylstannylene complexes such as [Cr(CO)5(SnR2)] in which bivalent Sn is three-co-ordinate: and (ii) dialkylstannylene insertion products into C–X, M–H, M–Cl, M–Me, or M–M bonds (M = a transition metal, X = halogen) such as [Fe(η-C5H5)(CO)2(SnR2Cl)], in which quadrivalent tin is four-co-ordinate. The compound SnR2 and class (i) complexes are characterised by isomer shifts of 2.15 ± 0.1 mm s–1 relative to BaSnO3 and large quadrupole splittings [2.31 (for SnR2) or 4.25 ± 0.2 mm s–1 for class (i)]. Class (ii) complexes show lower isomer shifts (1.49 ± 0.25 mm s–1) and quadrupole splittings (<2.37 mm s–1). Magnetic Mössbauer measurements on SnR2 and [Cr(CO)5(SnR2)] show that for both complexes the sign of the quadrupole coupling constant eQVzz, is negative and hence Vzz the principal component of the field gradient tensor, is positive.