Vibrational Spectra and Crystal Structures of Tris- and Tetrakis(ethylenethiourea)copper(I) Systems

Abstract

A room-temperature redetermination of the crystal structure of [Cu(SC(NHCH₂)₂)₃]₂ (SO₄) has been carried out. The original determination, recorded in communication format in space group Ic , Z = 4, seemingly with the full formula as the asymmetric unit, is at variance with our findings which describe the structure in space group R3c, a 12.741(7), c 35.59(1) Ǻ (hexagonal setting), Z = 6, with one-third of each of two independent cations , each lying on a threefold axis, comprising the asymmetric unit. The sulfate ion also lies on a threefold axis in proximity to only one of the two cations , the S-O axial bond approaching the copper atom normal to the planar CuS₃ array [Cu-S, O 2.269(2), 2.834(8)Ǻ]; in the other cation, unperturbed by any sulfate approach, Cu-S is appreciably shorter [2.246(2)Ǻ]. R was 0.029 for 905 'observed' reflections. A redetermination of the structure of tetrakis ( ethylenethiourea )copper(I) nitrate is also recorded; crystals are triclinic, Pī , a 13.211(2), b 11.2167(4), c 7.566(3) Ǻ, α 81.93(2), β 78.35(3), γ 87.22(1)°, Z = 2, R being 0.031 for 3861 independent 'observed' reflections. The copper environment is quasi-tetrahedral, Cu-S ranging between 2.3322(9) and 2.3658(12) Ǻ, and S-Cu-S 98.76(3)-117.83(3)°. The vibrational (far-infrared and Raman) spectra are recorded for these CuS_n systems, and discussed and assigned in the light of the structural results.