Synthesis and molecular structure of the polar, binuclear complex, monochlorotetra-(6-fluoro-2-oxopyridine)diruthenium(II,III)

Abstract

The dark purple title compound was prepared by reaction of Ru₂Cl(O₂CCH₃)₄ with molten 6-fluoro-2-hydroxypyrine (Hfhp) in quantitative yield. Crystals of composition Ru₂Cl(fhp)₄ were obtained by slow diffusion of hexane into a CH₂Cl₂ solution of the compound. The crystals belong to the tetragonal space group I4mm with the following unit-cell dimensions: a = b = 10.890(2) Å, c = 13.178(4) Å, α = β = γ = 90.0°, V = 1562.8(6) ų, and Z = 2. The Ru₂Cl(fhp)₄ molecule, which has crystallographic 4mm (C4c) symmetry, contains a diruthenium(II,III) unit with a metal---metal bond order of 2.5. The four bridging fhp ligands across the Ru₂ unit are oriented in one direction to form a polar molecule. The coordinatioin spheres of the two ruthenium atoms [Ru(1) and Ru(2)] are Ru(2)N(I)4 and Ru(1)Cl(1)O(1)4, respectively. The axial site on Ru(1) is blocked by four F(1) atoms. The Ru(1)---Ru(2), Ru(2)---Cl(1), Ru(2)---O(1) and Ru(1)---N(1) distances are 2.284(1), 2.427(3), 1.971(2) and 2.089(4) Å, respectively. The electronic spectrum of the compound in CH2Cl2 shows two strong bands at 552 nm ( = 4720 M^-1 cm^-1) and 355 nm = 3770 M^-1 cm^-1). Cyclic voltammetry of Ru2Cl(fhp)4 in CH2Cl2 in the presence of 0.1 M [N(C2H5)4]ClO4 at 100 mV s^-1 shows two quasireversible metal-centered one-electron oxication and reduction processes at +1.68 (ΔE_p = 120 mV) and -0.01 V (ΔE_p = 126 mV), respectively, vs an Ag---AgCl reference electrode.