title: Synthesis of paramagnetic tetranuclear rhodium and iridium complexes with the 2,6-pyridinedithiolate ligand. Redox-induced degradation to diamagnetic triiridium compounds.
abstract: The tetranuclear complexes [M4(mu-PyS2)2(diolefin)4] [PyS2 = 2,6-pyridinedithiolate; M = Rh, diolefin = cod (1,5-cyclooctadiene) (1), tfbb (tetrafluorobenzo[5,6]bicyclo[2.2.2]octa-2,5,7-triene) (2); M = Ir, diolefin = cod (3), tfbb (4)] exhibit two one-electron oxidations at a platinum disk electrode in dichloromethane at potentials accessible by chemical reagents. The rhodium tetranuclear complexes were selectively oxidized to the monocationic complexes [Rh4(mu-PyS2)2(diolefin)4](+) (1(+), 2(+)) by mild one-electron oxidants such as [Cp2Fe](+) or [N(C6H4Br-4)3](+) and isolated as the PF6(-), BF4(-), and ClO4(-) salts. Silver salts behave as noninnocent one-electron oxidants for the reactions with the rhodium complexes 1 and 2 since they give sparingly soluble coordination polymers. The complex [Ir4(mu-PyS2)2(cod)4](+) (3(+)) was obtained as the tetrafluoroborate salt by reaction of 3 with 1 molar equiv of AgBF4, but the related complex 4(+) could not be isolated from the chemical oxidation of [Ir4(mu-PyS2)2(tfbb)4] (4) with AgBF4. Oxidation of 3 and 4 with 2 molar equiv of common silver salts resulted in the fragmentation of the complexes to give the diamagnetic triiridium cations [Ir3(mu-PyS2)2(diolefin)3](+). The molecular structure of [Ir3(mu-PyS2)2(cod)3]BF4, determined by X-ray diffraction methods, showed the three metal atoms within an angular arrangement. Both 2,6-pyridinedithiolate tridentate ligands bridge two metal-metal bonded d(7) centers in pseudo octahedral environments and one d(8) square-planar iridium center. An interpretation of the EPR spectra of the 63-electron mixed-valence paramagnetic tetranuclear complexes suggests that the unpaired electron is delocalized over two of the metal atoms in the complexes 1(+)-3(+).
authors.affiliation: Departamento de Química Inorgánica, Instituto de Ciencia de Materiales de Aragón, Universidad de Zaragoza-CSIC, E-50009 Zaragoza, Spain.
authors.forename: M A
authors.initials: MA
authors.lastname: Casado
authors.forename: J J
authors.initials: JJ
authors.lastname: Pérez-Torrente
authors.forename: J A
authors.initials: JA
authors.lastname: López
authors.forename: M A
authors.initials: MA
authors.lastname: Ciriano
authors.forename: P J
authors.initials: PJ
authors.lastname: Alonso
authors.forename: F J
authors.initials: FJ
authors.lastname: Lahoz
authors.forename: L A
authors.initials: LA
authors.lastname: Oro
mesh_terms: D002614:Chelating Agents / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004563:Electrochemistry; D004578:Electron Spin Resonance Spectroscopy; D007202:Indicators and Reagents; D007495:Iridium / Q000737:chemistry*; D008280:Magnetics; D010084:Oxidation-Reduction; D011725:Pyridines / Q000737:chemistry*; D012238:Rhodium / Q000737:chemistry*; D013055:Spectrophotometry, Infrared
chemical_list: C436500:2,6-pyridinedithiolate; D002614:Chelating Agents; D007202:Indicators and Reagents; D011725:Pyridines; D007495:Iridium; D012238:Rhodium