. Can. J. Chem. 62, 27 (1984). Ab initio minimal basis set STO-6G calculations show axial-SiF4. NH3 and trans-SiF4. 2NH3 to be energetically more stable with respect to SiF, and ammonia. All other geometrical isomers are 1 .O-2.0 eV higher.Our calculation results rule out the steric hindrance between ligands as the reason S F 4 . 2NH3 is, according to experimental evidences, cis while complexes of bulkier ligands are trans.Since the cis-SiF,. 2NH, has a large electric dipole moment and a suitable charge arrangement it is conceivably the favoured form in the solid phase. The cis + trans rearrangement may take place under conditions where the advantages of the cis are not operative.Although there is some degree of covalency in the Si-N bond it remains largely electrostatic, with the lone pair of ammonia attracted to the positively charged Si atom. The lone pair does not appear to be extensively altered by the complex formation.

Formulas are given for those two-center one-electron integrals, over Slater basis functions, of the type 〈χA|1/rAirB j|χB〉, 〈χB|1/rAirB j|χB〉, and one-center two-electron integrals 〈χχ′|1/r122|χ″χ″′〉, which arise in the application of the generalized variational method.

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CNDO calculations have been carried out for the molecule InC5H5 of C5υ symmetry. Overlap populations were calculated and compared with those for related species. The bonding between In and the organic moiety can be described as essentially a covalent interaction involving mainly indium 5s and 5p orbitals with ring pπ orbitals. A lone pair on indium is a dominant feature of the structure, and is largely responsible for a (calculated) dipole moment of 4.75 D. The calculated orbital energies are compared with experimental photoelectron spectra.