ic070130+_si_002.cif (86.9 kB)

Dimerization Processes of Square Planar [PtII(tbpy)(dithiolato)]+ Radicals

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posted on 02.04.2020 by József Sándor Pap, Flávio Luiz Benedito, Eberhard Bothe, Eckhard Bill, Serena DeBeer George, Thomas Weyhermüller, Karl Wieghardt
The preparation and structural characterization of the neutral, square planar complexes [PtII(tbpy)(A)] (1), [PtII(tbpy)(B)] (2), and [PtII(PPh3)2(B)] (3) have been accomplished, where (tbpy) = 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)1- and (B)1- represent the corresponding monoanionic radicals. Electrochemical and chemical one-electron oxidation of 1 and 2 in CH2Cl2 solution affords the monomeric monocations [PtII(tbpy)(A)]+ (1a) and [PtII(tbpy)(B)]+ (2a), both of which possess an S = 1/2 ground state. The corresponding spin doublet monocationic dimers [PtII2(tbpy)2(A)(A)]+ (1b) and [PtII2(tbpy)2(B)(B)]+ (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 [PtII2(tbpy)2(A)2]2+ (1c) and [PtII2(tbpy)2(B)2]2+ (2c) which are in equilibrium with the corresponding paramagnetic monomers 1a and 2a in solution. The crystal structure of [PtII2(tbpy)2(B)2](PF6)2·3CH2Cl2 (2c) revealed a centrosymmetric, lateral dimer whose bridging part is a PtII22-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 [PtII(B)2]0 (4) have been recorded, which clearly show that a sulfur-centered radical (B)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 [PtII(PPh3)2(B)]+ (3a); no dimer formation was detected. Synthesis and crystal structure of square planar [PtII(B)2]0·thf are also reported.