An ‘atoms in molecules’ (AIM) analysis of the dihydrogen bond in organometallic compounds

The interactions of the IrH⋯HX type (X=O, N) were studied theoretically in models of the neutral complex [Ir(H)3(PPh3)(C5H4NHR] and the two cationic derivatives cis-[IrH(OH)(PMe)4][PF6] and [IrH2(CO)(PPh3)2(pzHN)][BF4]. The geometries were optimized using both RHF and MP2 calculations and an analysis of the charge density was carried out with the atom in molecules (AIM) procedure. The conclusion was that a hydrogen bond between the hydride and the protonic hydrogen is found only in the neutral complex. In the cationic species, the counterion is determining in order to get a good agreement between the optimized and the X-ray determined structures, and the short H⋯H distance is a consequence. The only hydrogen bonds appear to be formed between hydrogen atoms and fluorine atoms of the anion.