Covalent versus Dative Bonds to Main Group Metals, a Useful Distinction

TLDR: The difference between the covalent and the dative bond becomes apparent only after the orbital coefficients have been analyzed as discussed by the authors, which may explain why many structural chemists seem reluctant to distinguish between the two types of bonds.

Abstract: Textbooks of inorganic chemistry describe the formation of adducts by coordination of an electron donor to an electron acceptor, often using the amine-boranes, X3N → BY3, as examples. In the Lewis (electron dot) formulas of the compounds, the dative bond in H3N → BH3 and the covalent bond in H3CCH3 are both represented by a shared electron pair. In the simple molecular orbital or valence bond models the wave functions of both electron pairs would be constructed in the same manner from the appropriate sp3 type atomic orbitals on the bonded atoms; the difference between the covalent and the dative bond becomes apparent only after the orbital coefficients have been analyzed. This may be the reason why many structural chemists seem reluctant to distinguish between the two types of bonds. The object of this article is to remind the reader that the physiocochemical properties of covalent and dative bonds may be – and often are – quite different, and to show that a distinction between the two provides a basis for understanding the structures of a wide range of main group metal compounds.