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Structural and thermodynamic characteristics of adducts of silicon tetrahalides with 2,2'-bipyridine and 1,10-phenanthroline were calculated by the DFT B3LYP method. The enthalpies of sublimation of SiCl4·2,2'-bipyridine, reconstruction energies for donor and acceptor fragments, and energies of Si-N bonds in the complexes under consideration were estimated using the data obtained. These characteristics were compared with similar data for pyridine complexes. The chelate effect on the energy of Si-N bonds upon replacement of pyridine by 2,2'-bipyridine and 1,10-phenanthroline was discussed. The significant reconstruction of the bidentate donor upon the complex formation levels off the chelate effect. [ABSTRACT FROM AUTHOR]

The structural and thermodynamic characteristics of SiX4·Py and SiX4·2Py adducts (X = H, F, Cl, Br) were calculated by ab initio and DFT methods (RHF and B3LYP). The resulting data were used to estimate for the first time the enthalpies of sublimation of trans-SiX4·2Py complexes. The distortion energies of the donor and acceptor fragments and the energies of the Si-N bonds in the 1:1 and 1:2 halide complexes were calculated. The high distortion energy makes thermodynamically unfavorable equatorial monopyridine adducts with Si-N bond energies of 150-200 kJ/mol. In trans 1:2 complexes, pyridine acts as a weaker donor than ammonia with respect to silicon tetrahalides. [ABSTRACT FROM AUTHOR]