Theoretical study of the complexes of first-row transition metals with SiH2

The HF/6-311+G* basis set was used to study the characteristics of molecula r orbitals and bond dissociation energies of the complexes, MSiH2, of the f irst-row transition metals with SiH2. The atoms in MSiH2 are all coplanar, and M-Si bonds of ground state (TiSiH2)-Ti-3 and (CoSiH2)-Co-4 show obvious ly the double bond characteristic. In (VSiH2)-V-4 and (CrSiH2)-Cr-5 there i s the week single occupied pi bond. The (MnSiH2)-Mn-8 with a high-spin eigh tet ground state has both of single occupied sigma and pi bonds, and chief component of its sigma and pi orbital are the Mn 4s and the Si 3p(x) orbita ls, respectively. Other ground state MSiH2 have only a double occupied a si ngle bond. The most of M-Si bonds are quite covalent. The formation of M-SI sigma bonds can be considered as the interaction between one electron in 4 s or 4p(z), or 3d orbital of M and other electron in Si sp hybrid orbital. The double occupied pi bonds are also considered as the pairing of one pi e lectron of SiH2(B-3(1)) With one 3d electron of M. All of the HSiH bond ang les in MSiH2 are closed to that in SiH2(B-3(1)). It means that the Si in MS iH2 still keeps a sp hybrid orbital similar to Si in SiH2(B-3(1) states). T he Sc-Si, V-Si and Ni-Si bonds are longer because their formation involves mainly the 4s orbitals of M. On the contrary, the Cu-Si bond is shorter sin ce its a bond would involve primarily the M 3d(Z)(2) obitals. The (TiSiH2)- Ti-3 and (CoSiH2)-Co-4 have much shorter bond lengths and larger bond disso ciation energies because of their double bond character. From Sc to Cu, the bond dissociation energies of M-Si change in periodic trend. There is an a pproximate linear relationship between the bond dissociation energies and t he metal ion promotion energy.