A mixed-ligand homodinuclear copper(II) complex with weak disulfide-metal interactions: synthesis, properties and molecular and crystal structure of μ-( N,N,N′, N′-Tetrakis(carboxymethyl)cystaminato(4−))-bis(imidazole)diaquodicopper(II) dihydrate, [Cu 2(TTC)(ImH) 2(H 2O) 2]·2H 2O

Abstract

μ-( N,N,N′, N′-Tetrakis(carboxymethyl)cystaminato (4−))-bis(imidazole)diaquodicopper dihydrate, [Cu2- (TCC)(ImH) 2(H 2O) 2]·2H 2O ( I) (where TCC = (O 2- CCH 2) 2NC 2H 4SSC 2H 4N(CH 2CO 2) 2 4−), has been obtained in good yield by reaction of [Cu 2 (TCC)(H 2O) 2]·4H 2O ( II) with excess of imidazole (ImH) in water. The new product I has been characterized by chemical analysis, TG-DTA diagram, infrared, reflectance and ESR spectra and the single- crystal X-ray diffraction method. The compound crystallizes in the monoclinic system, space group P2 1/ n ( a = 20.800(2), b = 10.191(2), c = 13.419(2) Å, β = 92.41(1)°). Final R = 0.036 and R w, = 0.035 for 2784 independent observed reflections. Instead of the polynuclear layered crystal structure of II, the crystal of I consists of hydrogen bonded water molecules and discrete dinuclear units [Cu 2(TCC)- (ImH) 2(H 2O) 2] linked together in a tridimensional hydrogen bonding network. Both crystallographic independent copper atoms of the mixed dinuclear unit show analogous distorted elongated octahedral coordination (of the type 4 + 1 + 1). The two CuN(ImH) bonds are shorter than the homologous bond in a variety of copper(II)imidazole derivatives, lying in the lowest limit of the corresponding bond lengths in Cu(II)(ImH)aminoacidato (or peptide) complexes (1.95–1.98 Å). However, the ImH ligands do not play any π acceptor role (the CuN(ImH) bonds are tilted with respect to the ImH planes, which are twisted with respect to the mean equatorial coordination planes of the copper(II) atoms). By reacting ImH with II to give I, the copper coordinated water molecule in the equatorial position in II is replaced by an ImH molecule in I and moves to an apical position; this results in the lengthening of the CuS(disulfide) bonds, from 2.721(3) Å in II to 2.959(2) Å, average in I.