title: Stacked nickelocenes: synthesis, structural characterization, and magnetic properties.
abstract: The disubstitution of 1,8-diiodonaphthalene (1) with cyclopentadienyl nucleophiles reveals 1,8-(dicyclopentadienyl)-naphthalene, which rapidly undergoes Diels-Alder reaction forming 1,8-(3a',4',7',7a'-tetrahydro-4',7'-methanoindene-7a',8'-diyl)-naphthalene (2). A subsequent retro-Diels-Alder reaction in the presence of sodium hydride yields the disodium salt of 1,8-(dicyclopentadiendiyl)-naphthalene 3. The disodium salt 3 was the starting material to obtain the paramagnetic bisnickelocene derivative 4, which structure was obtained by X-ray structure analysis, revealing two nickelocenes kept together in a stacked fashion by a 1,8-naphthalene clamp. An electronic interaction between the two nickel atoms is found as a result of cyclic voltammetry, indicating five different oxidation states +4, +3, +2, +1, and 0. The magnetic properties of 4 in solution were studied by variable temperature paramagnetic (1)H NMR spectroscopy and Evans method and revealed Curie behavior between 213 and 293 K. The magnetic susceptibility of a powdered sample of 4 was measured, and an antiferromagnetic interaction with an exchange coupling of J(12) = -31.49 cm(-1) is found. In accord with experimental data, broken symmetry density functional theory (DFT) calculations revealed four antiferromagnetically coupled electrons resulting in an open shell singlet ground state.
authors.affiliation: Institute of Inorganic and Analytical Chemistry, University of Hamburg, Martin-Luther-King-Platz 6, 20146 Hamburg, Germany.
authors.forename: Sabrina
authors.initials: S
authors.lastname: Trtica
authors.forename: Marc Heinrich
authors.initials: MH
authors.lastname: Prosenc
authors.forename: Michael
authors.initials: M
authors.lastname: Schmidt
authors.forename: Jürgen
authors.initials: J
authors.lastname: Heck
authors.forename: Ole
authors.initials: O
authors.lastname: Albrecht
authors.forename: Detlef
authors.initials: D
authors.lastname: Görlitz
authors.forename: Frank
authors.initials: F
authors.lastname: Reuter
authors.forename: Eva
authors.initials: E
authors.lastname: Rentschler