Complex salt and heterobimetallic complexes derived from bis(1-ethoxycarbonyl-1-cyanoethylene-2,2-dithiolato) diargentate(I) ion: preparation, spectroscopic investigation and electrical conductance properties

Abstract

The reaction between K 2[Ag 2(ecda) 2] (generated in situ by the reaction of AgNO 3 and K 2ecda) and R 4NX (R=Et 4 or n-Pr 4; X=Br − or I −) as well as metal(II) salt leads to the formation of the complex salt, [R 4N] 2[Ag 2(ecda) 2] and heterobimetallic complexes, M[Ag 2(ecda) 2] [M=Co(II), Ni(II), Cu(II), Pd(II), Cd(II), or Hg(II); ecda 2−=1-ethoxycarbonyl-1-cyanoethylene-2,2-dithiolate 2−]. They were characterized by elemental analysis, molar conductance, magnetic susceptibility, X-ray powder diffraction, IR and Raman, 1H and 13C NMR, UV-visible and EPR spectroscopies. The molar conductance value ∼50 Ω −1 cm 2 mol −1 in 10 −3 M DMSO solution indicates 2:1 electrolytic behaviour of the complex salts [R 4N] 2[Ag 2(ecda) 2] while low conductivity/insolubility of heterobimetallic complexes in common organic solvents indicate their polymeric nature. Diamagnetism and powder room temperature EPR spectrum with A ‖=66.6 G indicate strong antiferromagnetic interaction between spins of two adjacent copper(II) atoms in Cu[Ag 2(ecda) 2]. The g values together with electronic spectral bands are consistent with square planar geometry around copper(II) in this complex. The magnetic moment value, a feature of the EPR spectrum and parameters derived from this and UV-visible absorption bands suggest square planar geometry around cobalt(II) with CoS 4 chromophore in Co[Ag 2(ecda) 2]. The UV-visible bands and unusual magnetic moment for Ni[Ag 2(ecda) 2] indicate square planar coordination around nickel(II). Slightly paramagnetic behaviour of this complex shows some sort of solid state interaction bringing some of the nickel(II) ions into a high spin octahedral environment. Pd[Ag 2(ecda) 2] is diamagnetic and possesses square planar coordination around palladium(II). IR and Raman, 1H and 13C NMR spectral studies indicate identical chemical environment around the metal ions with a bidentate/bridging coordination mode of ecda 2− in all the complexes. The temperature dependent (313–373 K) conductivity and activation energy calculated from the plot of ln σ versus 1/ T shows their semiconducting behaviour. The higher activation energy (0.78–1.59 eV) for [Et 4N] 2[Ag 2(ecda) 2], [ n-Pr 4N] 2[Ag 2(ecda) 2] and Hg[Ag 2(ecda) 2] indicate their potential to be used as semiconductors for practical applications.