The effect of the counter ion on M–H···H–X (X=O, N) interactions in crystalline transition metal hydrides

Abstract

The relationship between molecular and crystal structures of organometallic complexes showing intramolecular interactions of the M–H···H–X type (M=transition metal, X=O, N, and S) has been investigated by a combined use of molecular orbital calculations and crystal packing analysis. Molecular and crystal structures determined by neutron and/or X-ray diffraction data of coordination complexes and clusters showing intramolecular (M–H···H–X) interactions within the range 1.5–2.5 Å have been retrieved from the Cambridge Structural Database. DFT calculations were performed for the majority of compounds in order to determine the nature of the H···H interaction. The optimized geometries obtained by DFT are usually in good agreement with the experimentally determined ones, short H···H distances being also found. Most of the systems analysed, such as cis-[IrH(OH)(PMe₃)₄][PF₆], involve cationic complexes. It has been found that the counter ion exerts a strong influence in bringing together the two hydrogens. When it is included in the calculations, the agreement between the observed and the calculated structures is much better.