X-Ray crystal structure of (2,2′-bipyrimidine)[1,2-dicyanoethylene-1,2-dithiolato(2–)]platinum(II)–N,N-dimethylformamide and properties of PtS2N2-type complexes

Abstract

PtS₂N₂-type complexes containing both an electron-donor dithiolate ligand, 1,2-dicyanoethylene-1,2-dithiolate(2–)(maleonitriledithiolate, mnt) or 4,5-dimercapto-1,3-dithiole-2-thionate(2–)(dmit), and a π-electron acceptor nitrogen ligand, 2,2′-bipyrimidine (bipym) or N-ethyl-2-methylpyridine-2-carbaldimine (epa), were isolated. The complexes are polarized in their ground states, exhibiting intense electronic absorption bands due to ligand-to-lignad charge-transfer transitions at 490–580 nm. On doping iodine into the dmit complexes they were partially oxidized to afford [Pt(dmit)L]I_x(L = bipym or epa; x= 1.6–3.4) containing I₃^– or I₅^– ions, which behave as semiconductors with electrical conductivities of 1 × 10^–4–1 × 10^–7 S cm^–1 at 25 °C as compacted pellets. A single-crystal X-ray analysis of [Pt(mnt)(bipym)]·dmf (dmf =N,N-dimethylformamide) revealed a one-dimensional columnar packing of [Pt(mnt)(bipym)] molecules. The crystals are triclinic, space group P, with cell dimensions a= 9.811(1), b= 12.792(1), c= 7.5367(9)Å, α= 100.73(1), β= 93.37(1), γ= 91.03(1)°, and Z= 2. Least-squares refinement, based on 3 765 independent reflections with |F_o| > 3σ(F), converged at R= 0.062. Electronic states and molecular interactions of the PtS₂N₂-type complexes and their iodine-doped analogues are discussed on the basis of electronic, e.s.r., and X-ray photoelectron spectra.