CHAIN-LIKE CRYSTAL-STRUCTURE AND MAGNETIC-PROPERTIES OF )COPPER(II)-MU-DICYANO-ARGENTATE]-DICYANOARGENTATE

Cu(en)(2)Ag-2(CN)(4) (en = 1,2-diaminoethane) crystallizes in the orth orhombic space group Pnnm with cell parameters a = 6.316(1), b = 9.018 (2), c = 13.199(3) Angstrom, Z = 2. The structure is formed of free li near [Ag(CN)(2)](-) anions and infinite cationic chains [-Cu(en)(2)-NC AgCN-](+) containing paramagnetic copper atoms bridged by a second kin d of linear dicyanoargentate species. The coordination geometry of the copper atoms corresponds to an elongated tetragonal bipyramid with tw o chelating en molecules in the equatorial positions and N-bonded brid ging cyano groups in the axial positions. The Ag ... Ag distances exhi bit short value of 3.1580(5) Angstrom. Weak bifurcated hydrogen bonds of the N(3)-H(2)... N(2)(equivalent to C(2))... H(2)-N(3) type, symmet rical about twofold axis, are present (N(3)... N(2) 3.195(3) Angstrom) . These hydrogen bonds form two symmetrically related infinite 2D patt erns in the xz plane at y = 0 and y = 1/2 connecting free dicyanoargen tate anions and Cu(en)(2)(2+) cations, The phase identity between sing le crystal and bulk sample was evidenced by powder X-ray diffractometr y and Rietveld profile refinement. The study of magnetic properties by magnetization and specific heat measurements reveals that despite the chain structure the title compound may represent an S = 1/2 3D magnet ic system characterized by a low value of the exchange coupling consta nt, \J/k(b)\ much less than 60mK. (C) 1998 Elsevier Science S.A. All r ights reserved.