Spectroscopic and electrical properties of [Cu(C3Se5)2]2– and [Ni(C3Se5)2]2– anion complexes and X-ray crystal structures of [NMe4]2[Cu(C3Se5)2]·2MeCN and[NBun4][Ni(C3Se5)2]

Abstract

The complexes [epy]₂[Cu(C₃Se₅)₂]·MeCN (1)[epy =N-ethylpyridinium; C₃Se₅^2–= 4,5-di(hydroseleno)-1,3-diselenole-2-selonate], [NMe₄]₂[Cu(C₃Se₅)₂]·2MeCN (2), [NMe₄][Cu(C₃Se₅)₂](3) and [ttf]_0.4[Cu(C₃Se₅)₂](4)[ttf˙⁺= radical cation of tetrathiafulvalene, 2-(1′,3′-dithiol-2′-ylidene)-1,3-dithiole] have been prepared. Complexes [NBuⁿ₄]₂[Ni(C₃Se₅)₂](5) and [NMe₄]₂[Ni-(C₃Se₅)₂]·0.5MeCN (6) have been oxidized electrochemically under a controlled current in acetonitrile or acetone to afford [NBuⁿ₄][Ni(C₃Se₅)₂][7), [NBuⁿ₄]_0.25[Ni(C₃Se₅)₂](8), and [NMe₄]_0.33[Ni(C₃Se₅)₂](9). All the complexes behave as semiconductors. Although complexes (1)–(3), (5), and (6) exhibit electrical conductivities of 1 × 10^–7–1 × 10^–8 S cm^–1 for compacted pellets at 25 °C, conductivities of 1.4 × 10^–5 for (4)(compacted pellet), 2.0 × 10^–4 for (7)(crystal), 0.21 for (8), and 0.056 S cm^–1 for (9)(compacted pellets) were observed. A single-crystal X-ray structure analysis of (2) reveals that the CuSe₄ geometry around the copper(II) ion is substantially distorted from square planar, with a dihedral angle of 53.7° between the two diselenolate ligand planes. Additionally the anionic moieties form a two-dimensional molecular sheet through some interligand selenium–selenium contacts in the crystal phase. The orthorhombic crystal, space group lbam, has cell dimensions a= 10.289(3), b= 23.367(6), c= 15.519(7)Å, and Z= 4. Block-diagonal least-squares refinement, based on 704 reflections [|F_o| > 3σ(F)], converged at R= 0.065. An X-ray structure analysis of (7) reveals an almost square-planar geometry of the [Ni(C₃Se₅)₂]^– anion, which forms a one-dimensional arrangement through several selenium–selenium contacts. The crystals are monoclinic, space group P2₁/c, with a= 21.088(3), b= 13.494(1), c= 12.3818(9)Å, β= 106.17(1)°, and Z= 4. The refinement, based on 3 127 reflections [|F_o| > 3σ(F)], converged at R= 0.067. Electronic absorption, i.r., e.s.r., and X-ray photoelectron spectra of these complexes are described.