| Abstract
| - The new complex, [Zr(pda)2]n (1, pda2- = N,N‘-bis(neo-pentyl)-ortho-phenylenediamide, n = 1or 2), prepared by the reaction of 2 equiv of pdaLi2 with ZrCl4, reacts rapidly with halogen oxidants toafford the new product ZrX2(disq)2 (3, X = Cl, Br, I; disq- = N,N‘-bis(neo-pentyl)-ortho-diiminosemiquinonate)in which each redox-active ligand has been oxidized by one electron. The oxidation products 3a−c havebeen structurally characterized and display an unusual parallel stacked arrangement of the disq- ligandsin the solid state, with a separation of ∼3 Å. Density functional calculations show a bonding-type interactionbetween the SOMOs of the disq- ligands to form a unique HOMO while the antibonding linear combinationforms a unique LUMO. This orbital configuration leads to a closed-shell-singlet ground-state electronconfiguration (S = 0). Temperature-dependent magnetism measurements indicate a low-lying triplet excitedstate at ∼750 cm-1. In solution, 3a−c show strong disq--based absorption bands that are invariant acrossthe halide series. Taken together these spectroscopic measurements provide experimental values for theone- and two-electron energies that characterize the π-stacked bonding interaction between the two disq-ligands.
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