Hydrogen bonding in organometallic crystals .6. X-H---M hydrogen bonds and M---(H-X) pseudo-agostic bonds

The intermolecular interactions between X-H groups (X = C, N, and O) and metal atoms in crystalline organometallic complexes have been investigated. Molecular and crystal structures determined by neutron and/or X-ray diffraction data have been retrieved from the Cambridge Structural Database. The comparative analysis of intermolecular H ... M and X ... M distances as well as that of the X-H ... M angles allows a discrimination between the behavior of electrophilic and nucleophilic metal centers. Two novel types of interactions have been characterized: (i) the intermolecular multicenter hetero-acceptor (IMH) hydrogen bond formed when the X-H donor group interacts with M-X'(n) systems where M is an electron-rich metal and X' a metal-coordinated electronegative atom (X' = S, N, O, Cl); (ii) the intermolecular pseudo-agostic (IPA) interaction in which the X-H bond can donate electron density to electron deficient metal atoms M ...(H-X) as observed in intramolecular agostic interactions. Hydrogen bonding to metal centers in neutral complexes (X-H ... M) have been compared with charge assisted (X-H+... M-) hydrogen bonds involving electron-rich anionic complexes.