Nucleophilicity of diatomic Lewis bases MA in hydrogen-bonded complexes MA⋯HX: influence of the group and row of M in the periodic table

Nucleophilicities <i>N</i>_MA of diatomic Lewis bases MA acting as hydrogen-bond acceptors in complexes MA⋯HX are reported. The molecules MA were chosen so that the atom M adjacent to the atoms A directly involved in the hydrogen bonds belongs to Groups 13, 14, 15, 16 and 17 of the periodic table. The effects of changing atom M from rows 1 to 4 within a given group were also investigated. The hydrogen-bond donors HX involved in the complexes were HF, HCl, HBr, HI, HCCH, and HCP. Nucleophilicities <i>N</i>_MA were determined from dissociation energies <i>D</i>_e for the process MA⋯HX = MA + HX by using <i>D</i>_e = <i>cN</i>_MA·<i>E</i>_HX + <i>d</i>, where <i>E</i>_HX are electrophilicities of the Lewis acids HX, and <i>c</i> and <i>d</i> are constants. The order of <i>N</i>_MA values was found to be Row 4 > Row 3 ∼ Row 2 ≫ Row 1 in each of the Groups 13, 15, 15, 16 and 17. The effect of adding an H atom to MA to give linear triatomic molecules HMA were considered. The reduced nucleophilicities <i>И</i>_MA = <i>N</i>_MA/<i>σ</i>_min (<i>σ</i>_min is the minimum value of the molecular electrostatic surface potential of MA) as a function of the group and row of atom M were also discussed for diatomic molecules MA.