Contrasting Behavior of the Z Bonds in X–Z···Y Weak Interactions: Z = Main Group Elements Versus the Transition Metals

Abstract

In contrast to the increasing family of weak intermolecular interactions in main-group compounds (X-Z···Y, Z = main-group elements), an analysis of the Cambridge Structural Database indicates that electron-saturated (18-electron) transition-metal complexes show reluctance toward weak M bond formation (X-M···Y, M = transition metal). In particular, weak M bonds involving electron-saturated (18-electron) complexes of transition metals with partially filled d-orbitals are not found. We propose that the nature of valence electron density distribution in transition-metal complexes is the primary reason for this reluctance. A survey of the interaction of selected electron-saturated transition-metal complexes with electron-rich molecules (Y) demonstrates the following: shielding the possible σ-hole on the metal center by the core electron density in 3d series, and enhanced electronegativity and relativistic effects in 4d and 5d series, hinders the formation of the M bond. A balance in all the destabilizing effects has been found in the 4d series due to its moderate polarizability and primogenic repulsion from inner core d-electrons. A changeover in the donor-acceptor nature of the metal center toward different types of incoming molecules is also unveiled here. The present study confirms the possibility of M bond as a new supramolecular force in designing the crystal structures of electron-saturated transition-metal complexes by invoking extreme ligand conditions.

Not Only Hydrogen Bonds: Other Noncovalent Interactions

“…We propose herein to name these bonds "spodium bonds" because a derivative of the first element of the group (ZnO) is called spodium in Latin. It is important to emphasize that the interesting and remarkable work of Joy and Jemmis [76] anticipated that metals of the twelfth group might also participate in noncovalent interactions as Lewis acids. Moreover, these authors also showed that for groups 3-10, this type of interaction (denoted generically as metal bonding) is very scarce.…”

Intramolecular Spodium Bonds in Zn(II) Complexes: Insights from Theory and Experiment

“…Among the great deal of noncovalent forces, investigations on σ-hole interactions [ 4 , 5 ] are growing very fast and are definitively recognized by the scientific community as an alternative to the ubiquitous hydrogen bonding [ 6 ]. Very recently, the attractive interaction between elements of Group 12 of the Periodic Table and any electron rich ‘accepting’ atom (:A) [ 7 , 8 ] has been termed as a spodium bond (SpB) [ 9 ]. Therefore, the SpB has become a new member of the σ-hole family of interactions and it is adequate to differentiate the coordination bond (high covalent character) typical of transition metals from the noncovalent contact.…”

Regium–π bonds: An Unexplored Link between Noble Metal Nanoparticles and Aromatic Surfaces

“…They also concluded that the location of the σ‐holes in Pt and Au NPs seemed to be correlated with their catalytic activity. Recently, inspection of the CSD by Joy et al., backed up by theoretical calculations, revealed the participation of pentacoordinate transition metal complexes in noncovalent Cl−M ⋅⋅⋅ Y (M=Co, Rh, Ir; Y=electron‐rich atom) interactions. In addition, Stenlid et al.…”