Dimerization processes of square planar [PtII(tbpy)(dithiolato•)]+ radicals

The preparation and structural characterization of the neutral, square planar complexes [Pt-II((t)bpy)(A)] (1), [Pt-II((t)bpy)(B)] (2), and [Pt-II(PPh3)(2)(B)] (3) have been accomplished, where ((t)bpy) = 4,4'-di-tert-butylpyridine, (A)(2-) = 3,6-bis(trimethylsilyl)-1,2-benzenedithiolate(2-), and (B)(2-) = 1,2-bis(4-tert-butylphenyl)ethylene-1,2-dithiolate(2-) and (A(center dot))(1-) and (B-center dot)(1-) represent the corresponding monoanionic radicals. Electrochemical and chemical one-electron oxidation of 1 and 2 in CH2Cl2 solution affords the monomeric monocations [Pt-II((t)bpy)(A(center dot))](+) (1a) and [Pt-II((t)bpy)(B-center dot)](+) (2a), both of which possess an S = (1)/(2) ground state. The corresponding spin doublet monocationic dimers [Pt-2(II)((t)bpy)(2)(A)(A(center dot))](+) (1b) and [Pt-2(II)((t)bpy)(2)(B)(B-center dot)](+) (2b) were electrochemically generated in solution (50% oxidation) and identified by X-band EPR spectroscopy. Complete one-electron oxidation of 1 and 2 yielded the diamagnetic dimers [Pt-2(II)((t)bpy)(2)(A(center dot))(2)](2+) (1c) and [Pt-2(II)((t)bpy)(2)(B-center dot)(2)](2+) (2c) which are in equilibrium with the corresponding paramagnetic monomers 1a and 2a in solution. The crystal structure of [Pt-2(II)((t)bpy)(2)(B-center dot)(2)](PF6)(2)center dot 3CH(2)Cl(2) (2c) revealed a centrosymmetric, lateral dimer whose bridging part is a Pt-2(II)(mu(2)-S)(2) rhomb; the metal ions possess a square based pyramidal geometry. Solid-state sulfur K-edge X-ray absorption spectra of 1, 2, 2a, 2c, and [Pt-II(B-center dot)(2)](0) (4) have been recorded, which clearly show that a sulfur-centered radical (B-center dot)(1-) is present in 2a, 2c, and 4. The absence of ligand-based radicals in 1 and 2 is also clearly established. One-electron oxidation of [Pt(PPh3)(2)(B)] (3) afforded only the spin doublet species [Pt-II(PPh3)(2)(B-center dot)](+) (3a); no dimer formation was detected. Synthesis and crystal structure of square planar [Pt-II(B-center dot)(2)](0)center dot thf are also reported.