All That Glitters Is Not Gold: A Computational Study of Covalent vs Metallophilic Bonding in Bimetallic Complexes of d(10) Metal CentersA Tribute to Al Cotton on the Tenth Anniversary of His Passing

As the tenth year that follows the premature passing of the inorganic chemistry legend F. Albert (Al) Cotton comes to a close, we provide some soul food that we believe Al would have enjoyed as he looks down upon two generations of disciples, a grandchild and two great grandchildren, in his scientific family tree. This article also represents a new tradition by which the editors of Comments on Inorganic Chemistry wish to lead by example, whereby we start publishing original research content that nonetheless preserves the journal's identity as a niche for critical discussion of the current literature of inorganic chemistry. Thus, we show novel demonstrations of a posteriori validation and a priori prediction of possible counterintuitive covalent M-M' bondsafter and before synthesis, respectivelycontrasted with non-covalent MM interactions of the metallophilic type in bridge-dimeric systems of d(10) metal centers. Mixing of (n+1)s(0)/p(0) orbitals with (n)d(10) orbitals in the former heterobimetallics caseand lack thereof in the latter homobimetallics caseis hypothesized to be responsible for the presence or absence of covalency, respectively. However, we also demonstrate that the consequent d-s' and/or d-p' orbital mixing/hybridization can occur even in homobimetallic complexes that contain asymmetric bridging ligands (e.g., with -S<^>C- donor atoms that lead to orbital interactions between M-S and M-C fragments). Hence, the control metallophilic case for the hypothesized d(10)-d(10) polar-covalent bonding herein is best manifest by M-2(P<^>P)(2) homobimetallics vis-a-vis M-2(S<^>C)(2) embodiments. Finally, we also offer a point/counterpoint commentary to the readers to contrast factors that argue for covalency vs metallophilicity and forewarn against exaggerating the extent of covalent bonding in such d(10)-d(10) species. Thus, scrutinizing the various theoretical parameters has pointed to M-M' and M-M partially bonded S<^>C-bridge dinuclear d(10) complexes vis-a-vis the classic Cotton-type multiple metal-metal bond description in d(0