title: Pi*-pi* bonding interactions generated by halogen oxidation of zirconium(IV) redox-active ligand complexes.
abstract: The new complex, [Zr(pda)2]n (1, pda2- = N,N'-bis(neo-pentyl)-ortho-phenylenediamide, n = 1 or 2), prepared by the reaction of 2 equiv of pdaLi2 with ZrCl4, reacts rapidly with halogen oxidants to afford 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 have been structurally characterized and display an unusual parallel stacked arrangement of the disq- ligands in the solid state, with a separation of approximately 3 A. Density functional calculations show a bonding-type interaction between the SOMOs of the disq- ligands to form a unique HOMO while the antibonding linear combination forms a unique LUMO. This orbital configuration leads to a closed-shell-singlet ground-state electron configuration (S = 0). Temperature-dependent magnetism measurements indicate a low-lying triplet excited state at approximately 750 cm-1. In solution, 3a-c show strong disq--based absorption bands that are invariant across the halide series. Taken together these spectroscopic measurements provide experimental values for the one- and two-electron energies that characterize the pi-stacked bonding interaction between the two disq- ligands.
authors.affiliation: Department of Chemistry, University of California, Irvine, California 92697, USA.
authors.forename: Nicole A
authors.initials: NA
authors.lastname: Ketterer
authors.forename: Hongjun
authors.initials: H
authors.lastname: Fan
authors.forename: Karen J
authors.initials: KJ
authors.lastname: Blackmore
authors.forename: Xiaofan
authors.initials: X
authors.lastname: Yang
authors.forename: Joseph W
authors.initials: JW
authors.lastname: Ziller
authors.forename: Mu-Hyun
authors.initials: MH
authors.lastname: Baik
authors.forename: Alan F
authors.initials: AF
authors.lastname: Heyduk
mesh_terms: D018360:Crystallography, X-Ray; D006219:Halogens / Q000737:chemistry*; D008024:Ligands; D008956:Models, Chemical; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D010084:Oxidation-Reduction; D011789:Quantum Theory; D013696:Temperature; D015040:Zirconium / Q000737:chemistry*
chemical_list: D006219:Halogens; D008024:Ligands; D009942:Organometallic Compounds; D015040:Zirconium