CRYSTAL-STRUCTURE AND MAGNETIC-PROPERTIES OF DI-MU-AQUA-BIS[MU-[N,N'-BIS(2-HYDROXYETHYL)DITHIOOXAMIDATO(2-)-N,O,S-N',O',S']]-BIS[AQUACOPPER(II)SULFATOCOPPER(II)] - NEW EXAMPLE OF VERY STRONG ANTI-FERROMAGNETIC COUPLING BETWEEN COPPER(II) IONS FAR AWAY FROM EACH OTHER

The title compound, [(Cu2[S2C2(NCH2CH2OH)2](H2O)(SO4))(H2O)]2, was synthesized and its crystal structure solved at room temperature. It crystallizes in the monoclinic system, space group C2/c. The lattice constants are a = 24.211 (6) Å, b = 8.173 (5) Å, c = 15.179 (6) Å, and β = 110.68 (2)°. Least-squares refinement of the structure has led to a conventional R factor of 0.038. The structure is made of binuclear units [Cu2[S2C2(NCH2CH2OH)2](H2O)(SO4)) doubly bridged by water molecules making tetrameric entities. The coordination of each copper is 4 + 1 in the form of a square pyramid, the apex of which is occupied by a more weakly bonded oxygen atom of the bridging water molecule. This compound (noted B) is isomeric with catena- μ-sulfato- μ-[N, N‘-bis(2-hydroxyethyl)dithiooxamidato(2-)-N, O, S:N, O‘, S‘]-bis[aqua-copper(II)] (noted A) the structure of which has been recently reported. The difference between both isomers essentially concerns the positions of H2O and SO42- ligands. The mechanism of the isomerization is discussed. It could involve as an intermediate step a binuclear unit in which one of the Cu(II) ions would be coordinated in the form of a trigonal bipyramid. The temperature dependence of the molar magnetic susceptibility, studied in the range 15-300 K, reveals a large anti-ferromagnetic coupling characterized by a 523-cm-1 singlet-triplet separation. This coupling is however slightly smaller than that found for the A isomer. The difference is interpreted as resulting from the distortion of the binuclear unit due to the bridging water molecules and from the correlated lengthening of the S-N distances in B with regard to A. © 1979, American Chemical Society. All rights reserved.