The Nature of Bond Critical Points in Dinuclear Copper(I) Complexes

Abstract

Closed-shell contacts between two copper(I) ions are expected to be repulsive. However, such contacts are quite frequent and are well documented. Crystallographic characterization of such contacts in unsupported and bridged multinuclear copper(I) complexes has repeatedly invited debates on the existence of cuprophilicity. Recent developments in the application of Bader's theory of atoms-in-molecules (AIM) to systems in which weak hydrogen bonds are involved suggests that the copper(I)-copper(I) contacts would benefit from a similar analysis. Thus the nature of electron-density distributions in copper(I) dimers that are unsupported, and those that are bridged, have been examined. A comparison of complexes that are dimers of symmetrical monomers and those that are dimers of two copper(I) monomers with different coordination spheres has also been made. AIM analysis shows that a bond critical point (BCP) between two Cu atoms is present in most cases. The nature of the BCP in terms of the electron density, ρ, and its Laplacian is quite similar to the nature of critical points observed in hydrogen bonds in the same systems. The ρ is inversely correlated to Cu-Cu distance. It is higher in asymmetrical systems than what is observed in corresponding symmetrical systems. By examining the ratio of the local electron potential-energy density (V(c)) to the kinetic energy density (G(c)), |V(c)|/G(c) at the critical point suggests that these interactions are not perfectly ionic but have some shared nature. Thus an analysis of critical points by using AIM theory points to the presence of an attractive metallophilic interaction similar to other well-documented weak interactions like hydrogen bonding.

Preparations of a series of coinage metal complexes with pyridine-based bis(N-heterocyclic carbene) ligands including transmetalation to palladium complexes

“…This distance is shorter than those of two similar pyridine-bridged bis(carbene) silver complexes (3.1585(9) [8a] and 3.7848(2) [8b] Å). The Cu•••Cu distance of 2 (2.9431(8) Å), suggesting a cuprophilic interaction [6,9], is similar to those of the previously reported C-N-C copper complexes (7) and 114.49 (9) and the length of the four sides is 2.720(3) Å. Thus, there may be very weak interaction between the middle pyridyl nitrogen atoms and the copper atoms.…”

Cuprophilic Interactions in and between Molecular Entities

“…In addition to “aurophilicity” and “argentophilicity”, the term “cuprophilicity” was coined to denote the closed‐shell d 10 –d 10 Cu I –Cu I interactions. Relativistic effects are more prominent for the heavier elements with high atomic numbers, so Cu I –Cu I closed‐shell d 10 –d 10 interactions were expected to be insignificant, and sometimes controversial . It, however, should be noted that cuprophilic interactions have been implicated to play important roles in unexpected photophysical properties and conductivity of copper(I) compounds.…”

Highly Luminescent Linear Complex Arrays of up to Eight Cuprous Centers

“…The formation of complex 2 is in agreement with an increased number of Cu I ⋅⋅⋅Cu I cuprophilic interactions in complex 2 (by three, if compared with 2 equiv of complex 1 ) and their combined contribution to the central Cu I 4 cluster formation. It has been demonstrated in comprehensive computational studies that in neutral Cu I dimeric complexes Cu I ⋅⋅⋅Cu I contacts are considered as bonding interactions, even though they are very weak (in the range of weak hydrogen bonds) and the major contribution of stabilization originates from the ligand framework . Overall, the subtle interplay between the bis(amindinates) and cuprophilic interactions results in a rearrangement of (at least) two substantially strong Cu−N bonds from two equivalents of complex 1 to complex 2 .…”

“…Au I ⋅⋅⋅Au I aurophilic interactions, which generally originate from relativistic and correlation effects, are comparably strong as hydrogen bonds . Because of the decrease of relativistic effects with a decreasing nuclear charge, Ag I ⋅⋅⋅Ag I argentophilic bonding is less pronounced and Cu I ⋅⋅⋅Cu I cuprophilic interactions are considered to be very weak or not significant at all . Except for rare examples of unsupported Cu I ⋅⋅⋅Cu I contacts, multinuclear Cu I complexes exhibiting cuprophilic interactions usually require a suitable ligand framework to incorporate the cuprous ions in close proximity to each other.…”