The electron density of bridging hydrides observed via experimental and theoretical investigations on [Cr-2(mu(2)-H)(Co)(10)](-)

The accurate experimental electron density distribution of [Cr-2(mu(2)-H)(CO)(10)](-) has been determined through X-ray diffraction at T = 28 K and gas phase theoretical calculations. The nature of the Cr-H-Cr bond has been investigated by means of the quantum theory of atoms in molecules, including the analysis of the Fermi hole distribution and the delocalization indicators from the pair density distribution. We were able to clarify not only the delocalization mechanism inside the three-center system but also the unexpected role of the equatorial carbonyls. In addition, the comparative study of a few Cr-H-X three center interactions has provided more insight into the nature of the M-H-M bond itself and has shed light on its peculiar stereochemical flexibility.