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.