Mössbauer spectra and bonding in four-co-ordinate tin compounds containing a tin–cobalt bond

Abstract

¹¹⁹ Sn Mössbauer spectra are reported for organometallic tin compounds of the type R_lX_mSn[Co(CO)₄]_n(R = Me or Ph; X = Cl or Br; l+m+n= 4). From the quadrupole splitting of the compound ClSn[Co(CO)₄]₃(1·42 mm s^–1), we have derived a partial quadrupole-splitting value for the Co(CO)₄ moiety of –0·71 mm s^–1. Using this value, signs and magnitudes of the quadrupole splittings for 25 compounds containing tin–cobalt bonds have been predicted. Except for two compounds, the observed magnitudes of the quadrupole-splitting parameters are in good agreement (within ± 0·4 mm s^–1) of these predicted values. The partial quadrupole-splitting value for Co(CO)₄ indicates that the moiety is an appreciably poorer donor ligand than Mn(CO)₅ or Fe(CO)₂(cp)(cp =π-cyclopentadienyl). Centre-shift trends are rationalized by considering that the Sn–Co bond has a large amount of s character. This treatment is consistent with known X-ray structural information, and with correlations of the centre shift with both ⁵⁹Co n.q.r. data, and 2J(¹¹⁹Sn–CH₃) for compounds containing methyl groups.