Mössbauer spectra of four-co-ordinate tin compounds containing a tin–iron or tin–manganese bond

Abstract

Tin-119 Mössbauer spectra are reported for 15 Sn-organometallic compounds which contain Sn–Fe or Sn–Mn bonds. Using recently derived partial quadrupole splitting (p.q.s.) values for Ph, R (Me, Et, etc.) and X (F, Cl, Br), we have derived new p.q.s. values for C₆F₅, Mn(CO)₅, and Fe(CO)₂(cp) and have predicted the magnitude of ½e₂qQ(q.s.) and η, and the sign of the q.s. for 40 compounds containing Sn–Fe or Sn–Mn bonds. Except for four compounds, agreement between predicted and observed q.s. values is within 0·4 mm s^–1, and the signs of the q.s. agree with the known signs, and those determined in this study for Me₂ClSnMn(CO)₅(–ve) and MeCl₂SnMn(CO)₅(+ve). The predicted η value for Me₂ClSnMn(CO)₅(0·41) agrees well with that determined (0·35) from magnetic spectra, whereas for MeCl₂SnMn(CO)₅ the predicted (0·89) and observed (0·46) values of η are not in good agreement. Calculations indicate that η should be much more sensitive than the q.s. to variations in p.q.s. values. The derived p.q.s. values show that the p donor capacity of the ligands increase in the order Cl, Br < C₆F₅ < Mn(CO)₅ < Fe(CO)₂(cp) < Ph < R.

The centre shifts for the compounds X_nR_{3 –n}SnM [X = Cl, Br, or C₆F₅; R = Me or Ph; M = Mn(CO)₅ or Fe(CO)₂(cp)] generally increase as n increases. This trend is largely due to the concentration of s electron density in the Sn–M bond, and the high p character in the Sn–X bonds. The s character in Sn–L bonds increases in the order L = Cl, Br < C₆F₅ < Ph < Me < Mn(CO)₅ < Fe(CO)₂(cp). The known tetrahedral distortions about Sn can be rationalized using this series.