One-, two-, and three-electron bonding: An 'in vitro' theoretical study using noninteger nuclear charges evidences the crucial role of electronegativity in the strength of symmetrical bonds

摘要

Fictitious hydrogen atoms H _A of variable nuclear charge 0.5 ≤ Z _A ≤ 2 (and thus of variable electronegativity) are used to study the intrinsic dependency of chemical bonding on electronegativity. Dissociation energy and equilibrium distance are reported for symmetrical 1-, 2- and 3-electron H _AH _A systems and 2-electron dissymmetrical H _A-H ones. Dealing with symmetrical systems, the strongest two-electron bonds are found for Z _A ≈ 1.2. Oneelectron and three-electron strongest bonds occur respectively with low (ca. 0.7) and high (ca. 1.7) Z _A values and can become stronger than the corresponding 2-electron system. Comparison with data on real systems leads to conclude that electronegativity is a prevailing atomic property in the control of the dissociation energy of symmetrical 1-, 2- and 3-electron bonds. A simplified mathematical model at Hartree-Fock or Heitler-London level with a minimal basis set reproduces these trends semi-quantitatively and provides the overall shape of the dissociation curves. Finally some points are qualitatively discussed from MO analysis, which emphasize the dependence of the bonding/antibonding properties on the nucleus charge Z _A and their occupancy number.