STRUCTURAL AND THEORETICAL-ANALYSIS OF M-H-CENTER-DOT-CENTER-DOT-CENTER-DOT-H-M AND M-H-CENTER-DOT-CENTER-DOT-CENTER-DOT-H-C INTERMOLECULARINTERACTIONS

The relationship between molecular and crystal structures of organomet allic complexes showing intermolecular interactions of the M-H- - -H-M and M-H- - -H-C type has been investigated by a combined use of exten ded Huckel and DFT calculations, and crystal packing analysis. Molecul ar and crystal structures determined by neutron and/or X-ray diffracti on experiments of coordination complexes and clusters showing intermol ecular M-H- - -H-M and M-H- - -H-C interactions below 2.6 Angstrom hav e been retrieved from the Cambridge Structural Database. Molecular orb ital analysis has been carried out by means of extended Huckeland DFT calculations on selected compounds. For the HMn(CO)(5) dimer, where th e interaction is of the M-H- - -H-M type, the system is reminiscent of a bound hydrogen molecule where the H-H bond has been greatly weakene d. A very small binding energy of ca. 5 kJ mol(-1) has been determined using DFT calculations. This simple interpretation does not hold in t he cases of M-H- - -H-C short contacts, which are more appropriately d escribed as arising from a special type of hydrogen bond associated wi th opposite charges on the two hydrogen atoms.