A valence bond description of coordinate covalent bonding

作者：Fiorillo AA; Galbraith JM^*

来源：Journal of Physical Chemistry A, 2004, 108(23): 5126-5130.

DOI：10.1021/jp049632o

The coordinate covalent (dative) bonded molecules H3N-BH3, H3N-BF3, F3N-BH3, H3N-BMe3, and Me3N-BH3 have been studied using valence bond theory (VB). The classic three-structure VB picture changes slightly to account for the increased importance of the VB configuration with both electrons on the donor fragment. When the effects of geometric distortion upon molecule formation are removed, the expected trends in bond energies emerge. Addition of electron-withdrawing (F) substitutents increases bond energy in H3N-BF3 and decreases bond energy in F3N-BH3. Likewise, addition of electron-donating methyl groups (Me) decreases bond energy in H3N-BMe3 and increases bond energy in Me3N-BH3. In addition, the effects of adding fluorines stepwise in the series H3N-BH3, H3N-BHZF, H3N-BHF2, H3N-BF3 has been determined. Bond energies are due to the opposing factors of electron withdrawal due to the high fluorine electronegativity and donation into the N-B bonding region by F p lone pairs. VB weights obtained by the method of Chirgwin and Coulson were unstable for coordinate covalently bonded molecules whereas no such problems were found for inverse overlap weights. VB weights in conjunction with bond energy partitioning show that the coordinate covalent bonds studied herein are predominantly charge shift bonds which owe their stability to VB structure mixing rather than any one structure alone.

• 出版日期2004-6-10