OXAMIDATO COMPLEXES .6. COMPLEX-FORMATION BETWEEN COPPER(II) AND N,N'-BIS[2-(DIMETHYLAMINO)ETHYL]OXAMIDE (H-2DMAEOXD) - PREPARATION, CRYSTAL-STRUCTURE, AND MAGNETIC-PROPERTIES OF [CU2(DMAEOXD)(NCO)2(H2O)2]

The protonation and deprotonation of N,N'-bis[2-(dimethylamino)ethyl]o xamide (H-2dmaeoxd, H-2L) and its complex formation with Cu(II) have b een investigated by potentiometry in aqueous solution at 25-degrees-C and 0.1 mol dm-3 NaNO3. The proton association constants beta(j) corre sponding to the equilibria L2- + jH+ half arrow right over half arrow left H(j)L(j-2)+ were found to be log beta2 = 24.0(2), log beta3 = 32. 63(1) and log beta4 = 40.46(1). The values of the stability constants beta(pqr) concerning the equilibria pCu2+ + qL2- + rH+ half arrow righ t over half arrow left [Cu(p)L(q)H(r)][2(p-q)+r]+ were log beta212 = 3 4.11 (8), log beta211 = 29.52(8), log beta210 = 24.74(2), log beta320 = 44.87(5), log beta430 = 64.09(7) and log beta110 = 16.92(2). The com pound of formula [Cu2(dmaeoxd)(NCO)2(H2O)2] has been synthesised and i ts crystal structure determined by single-crystal X-ray diffraction me thods at room temperature. It crystallizes in the monoclinic system, s pace group P2(1)/a and Z = 2, with a = 11.589(3), b = 12.456(1), c = 6 .771 (2) angstrom, and beta = 102.39(2)degrees. Least-squares refineme nt gave a final R (R') factor of 0.038 (0.045) for 2249 unique reflect ions having I greater-than-or-equal-to 3sigma(I). The structure consis ts of neutral centrosymmetric oxamidato-bridged dinuclear copper(II) u nits. The co-ordination geometry around each copper(II) ion is distort ed square pyramidal: the equatorial plane comprises the oxygen and nit rogen atoms of the amide, the nitrogen atom of the amine group and the nitrogen atom of the cyanate ligand, whereas the apical position is f illed by a water molecule. The intramolecular copper-copper separation is 5.306(1) angstrom. Variable-temperature magnetic susceptibility me asurements (50-300 K) of this complex reveal a strong antiferromagneti c coupling through the oxamidate, the relevant parameters being g = 2. 12 and J (singlet-triplet energy gap) = -560 cm-1. The chelating abili ty of dmaeoxd2- and its ability to transmit electronic effects are dis cussed and compared to those of related N,N'-dialkyloxamidate ligands.