Homoleptic platinum(II) and palladium(II) organothiolates and phenylselenolates: Solvothermal synthesis, structural determination, optical properties, and single-source precursors for PdSe and PdS nanocrystals

Homoleptic d8-metal organothiolates and phenylselenolates [M-(EC ₆H₅)₂]λ (E = S, M = Pt 1, M = Pd 2, M = Ni 5 ;E = Se, M = Pt 3, M = Pd 4) were prepared as crystalline solids under solvothermal conditions. Their structures were solved using powder X-ray diffraction data. In each case, the EC₆H₅ (E = S, Se) ligand binds to two metal ions (M = Pt, Pd, and Ni) to form chain-like structures with planar (in 1) or zig-zag (in 2-5) conformations. The [M(SR) ₂]λ complexes (M = Pt, R = 4-tert-butylphenyl 6 ;R = 2-naphthyl 8; R= 4-nitrophenyl 10 and M = Pd, R= 4-tert-butylphenyl 7;R = 2-naphthyl 9; R= 4-nitrophenyl 11) were prepared under similar solvothermal conditions. Based on the XPS binding energies and elemental analyses, complexes 6-11 have the same [M(SR)₂]λ formulation as 1 and 2. The cyclic complex [Pd₆ (SCH₃)₁₂] 12 was prepared as a crystalline solid by solvothermal annealing treatment of the amorphous precipitate. A chain-like polymer structure is proposed for both [Pd(SC ₁₂H₂₅)₂]λ 13 and [Pd(SC ₁₆H₃₃)₂]λ 14; these polymeric chains self-assemble to give layerlike structures. Solid-state diffuse reflectance spectra reveal that the optical band gap E_g (eV) of complexes 1, 6, 8, 10 and of 2, 7, 9, 11 are in the range of 2.10-3.00 eV and 2.10-2.63 eV, respectively, and 5 has the lowest E_g value (1.72 eV). Heating solid samples of 4 and 13 under solvothermal conditions afforded phase-pure Pd ₁₇Se₁₅ and PdS nanocrystals, respectively. Field-effect transistors fabricated with a drop-cast thin film made from Pd ₁₇Se₁₅ nanocrystals prior treated with an ethanolic solution of 1-hexadecanethiol displayed ambipolar charge transporting properties with hole and electron mobility being 7 × 10^-2 cm² V^-1S^-1 and 6 × 10^-2 cm² V ^-1s^-1, respectively.