The relationship between molecular and crystal structures of organometallic complexes showing intermolecular interactions of the M-H- - -H-M and M-H- - -H-C type has been investigated by a combined use of extended Huckel and DFT calculations, and crystal packing analysis. Molecular and crystal structures determined by neutron and/or X-ray diffraction experiments of coordination complexes and clusters showing intermolecular M-H-- -H-M and M-H- - -H-C interactions below 2.6 Angstrom have been retrieved from the Cambridge Structural Database. Molecular orbital analysis has been carried out by means of extended Huckeland DFT calculations on selected compounds. For the HMn(CO)(5) dimer, where the 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 weakened. A very small binding energy of ca. 5 kJ mol(-1) has been determined using DFT calculations. This simple interpretation does not hold in the cases of M-H- - -H-C short contacts, which are more appropriately described as arising from a special type of hydrogen bond associated with opposite charges on the two hydrogen atoms.