RELATIVISTIC EFFECTS IN PHYSICS AND CHEMISTRY OF ELEMENT 105 .4. THEIR INFLUENCE ON THE ELECTRONIC-STRUCTURE AND RELATED PROPERTIES

Results of relativistic (Dirac-Slater and Dirac-Fock) and nonrelativis tic (Hartree-Fock-Slater) atomic and molecular calculations have been compared for the group 5 elements Nb, Ta, and Ha and their compounds M Cl5 to elucidate the influence of relativistic effects on their proper ties especially in going from the 5d element Ta to the 6d element Ha. The analysis of the radial distribution of the valence electrons of th e metals for electronic configurations obtained as a result of the mol ecular calculations and their overlap with ligands show opposite trend s in behavior for ns1/2, np1/2, and (n - 1)d5/2 orbitals for Ta and Ha in the relativistic and nonrelativistic cases. Relativistic contracti on and energetic stabilization of the ns1/2 and np1/2 wave functions a nd expansion and destabilization of the (n - 1)d5/2 orbitals make hahn ium pentahalide more covalent than tantalum pentahalide and increase t he bond strength. The nonrelativistic treatment of the wave functions results in an increase in ionicity of the MCl5 molecules in going from Nb to Ha making element Ha an analog of V. Different trends for the r elativistic and nonrelativistic cases are also found for ionization po tentials, electronic affinities, and energies of charge-transfer trans itions as well as the stability of the maximum oxidation state.