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Theoretical Chemistry of The 7p Series of Superheavy Elements II. The Relativistic Molecular Orbital and Kappa Valence Methods

N. C. Pyper
Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences
Vol. 304, No. 1488 (Apr. 30, 1982), pp. 567-642
Published by: Royal Society
Stable URL: http://www.jstor.org/stable/37101
Page Count: 76
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Theoretical Chemistry of The 7p Series of Superheavy Elements II. The Relativistic Molecular Orbital and Kappa Valence Methods
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Abstract

The relativistic generalizations of both molecular orbital and spin-valence (the Kappa valence method) theories are used to investigate the covalent bonds that can be formed by the ground relativistic configuration of a heavy element containing a non-closed subshell of p̄ or p valence electrons. Both theories predict that p̄-H and p-H bonds are not greatly weakened compared with normal covalent σ bonds and that covalent compounds based on the p2 relativistic configuration will be bent with an equilibrium interbond angle of 90°. Both p̄-H and p-H bonds are predicted by the Kappa valence method to be a mixture of a normal covalent σ bond and the triplet bond formed by the interaction of two electrons occupying orthogonal orbitals. This method predicts that the bond formed between a heavy element and a group of rather different electronegativity may be weakened by relativity more than a p̄-H or p-H bond because only the non-orthogonal Heitler-London singlet portion of such a bond can be stabilized by ionic-covalent resonance. The Kappa valence method is used to show that a closed p̄2 subshell cannot form a stable covalent bond. Both Kappa valence and relativistic molecular orbital methods are used to investigate the bonding between an element having a single p̄ or p valence electron and a group containing both a closed shell of π electrons and a single electron in the σ orbital. It is shown by the Kappa valence method that the presence of the π electrons introduces destabilizing anti-bonding terms unless the π -σ excitation energy is small as for a halogen. The destabilizing term is predicted to inhibit the formation of a normal covalent bond between a p̄ orbital and such a group while in the p case the bond is merely predicted to be greatly weakened. In the case for which the π -σ excitation energy is small both Kappa valence and relativistic molecular orbital theories predict that the bond is not weakened because the group adopts a valence state that eliminates the anti-bonding terms to yield a bond of unit order containing both σ and π character. It is shown by the Kappa valence method that the ionic-covalent resonance stabilizations of p̄-Halogen and p-Halogen bonds are not qualitatively dissimilar to that of the corresponding non-relativistic bond. Relativistic molecular orbital theory is used to show that the ground manifold of an element having two valence electrons occupying Dirac-Fock p orbitals can covalently bind two halogens and that the potential energy curve for inter-bond angle bending is shallow. The bonding between the j-j coupled ground states of two heavy elements each containing a single valence electron occupying a p̄ or a p Dirac-Fock atomic orbital is investigated by both the Kappa valence and relativistic molecular orbital methods. It is shown that p̄-p̄ but not p̄-p bonds are greatly weakened by relativity and that p-p bonds are entirely π in character. These results are used to comment on the cohesive energies of elemental E113 and E115.

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