π Acceptor Abilities of Anionic Ligands: Comparisons Involving Anionic Ligands Incorporated into Linear d 10 [(NH 3 )Pd(A)] - , Square Planar d 8 [(NN 2 )Ru(A)] - , and Octahedral d 6 [(AsN 4 )Tc(A)] - Complexes.

Extended transition state-natural orbitals for chemical valence (ETS-NOCV)] data were used to rank electron acceptor capacities for several potentially synergistic anionic ligands incorporated into linear d 10 [(NH 3 )Pd(A)] - , square planar d 8 [(NN 2 )Ru(A)] - , and octahedral d 6 [(AsN 4 )Tc(A)] - complexes [A = anionic ligand, NN 2 = HN(CH 2 CH 2 CH 2 NH 2 ) 2 , and AsN 4 = [As(CH 2 CH 2 CH 2 NH 2 ) 4 ] - ]. It was possible to differentiate between the best acceptors, among them BI 2 - and B(CF 3 ) 2 - , and the poorest ones. A sizable fraction of the anionic ligands studied exhibit similar acceptor capacities (backbonding), mostly regardless of d electron count. A number of trends were discerned, including the fact that acceptor capacity decreases down families and across rows but increases down families of the peripheral substituents. The latter appears tied to the ability of the peripheral ligands to compete with the metal in donating electrons to the ligand-binding atom.