A UNIQUE BROMO-BRIDGED AND THIOETHER-BRIDGED TETRANUCLEAR MIXED-VALENCE COPPER(I) COPPER(II) COMPOUND WITH THE N,S-DONOR LIGAND 4-((ETHYLTHIO)METHYL)-5-METHYLIMIDAZOLE

The mixed-valence compound tribromo|4-((ethylthio)methyl)-5-methylimidazole)copper(II)copper(I), Cu2(C7H12N2S)Br3, forms spontaneously from an ethanol solution of copper(II) bromide and the ligand. The complex crystallizes as dark brown needles in the monoclinic space group 12/a: a = 13.6953 (15) Å b = 12.4347 (5) Å, c = 15.7589 (7) Å, 0 = 91.960 (11)°, Z = 8, R = 0,038. and Rw = 0.045 for 1902 observed reflections. Each copper(Il) ion is surrounded by a nitrogen atom at 1.964 (5) Å, a thioether sulfur at 2.350 (2) Å. and two bromide ions at 2.439 (1) and 2.394 (1) Å, in a square-planar geometry. The copper(I) ion is surrounded by three bromide ions at 2.360 (I), 2.483 (1), and 2.573 (1) Å and one thioether sulfur at 2.321 (2) Å in a distorted tetrahedral geometry. The dinuclcar asymmetric unit is held together by a double bromide bridge between the Cu(I) and Cu(ll) ion; the third bromide is terminally bonded to the Cu(I) at 2.360 (I) Å. The Cu(l) ion in each asymmetric unit is eonnectcd to the Cu(ll) ion in another dinuclear unit through the bridging thioether sulfur of the ligand, thereby forming a unique tetranuclear species. The bromide, which is terminally bonded to the Cu(I), is a distance of 3.073 (1) Å from the nearest Cu(II), which is regarded as semicoordinating. Through this bond all tetranuclear species are bromide bridged to one another, forming a polymer with the copper(ll) in a square-pyramidal environment. In confirmation of its mixed-valence nature, the title compound undergoes one-electron oxidation as well as one-electron reduction in DMSO at rather positive, coincident potential values (EÅ‧ = +0.19 V vs SCE). X-ray, electrochemical, and EPR techniques point to an electron-localized Cu11Cu1 species. © 1990, American Chemical Society. All rights reserved.