He(I) and He(II) Photoelectron Spectra and Pseudopotential ab Initio Calculations of Some Tetracoordinated Tin(IV) Derivatives

T h e gas-phase UV photoelectron (PE) spectra of Sn(CH3),C14-, ( n = 0-4) and of Sn(CH3),(NCS)4-, ( m = 2,3) are discussed with the aid of the results of pseudopotential a b initio calculations (extended basis sets with inclusion of 5d polarization functions and relativistic corrections for tin). The excellent numerical agreement between experimental and computed (Koopmans) ionization energies has allowed a reassignment of some published PE da t a and t h e discussion of t h e new spectra. T h e actual involvement of tin 5s ,5p, and 5d atomic orbitals into the valence MOs is also discussed. Both the theoretical and experimental data suggest t h e presence of strong xs,-cl interactions with significant contribution from Sn 5d AOs. As far as the NCS derivatives are concerned, both PE and theoretical da t a are in agreement with a largely ionic bond