Synthesis, structure and properties of new chain cuprates, Na3Cu2O4 and Na8Cu5O10

Na3Cu2O4 and Na8Cu5O10 were prepared via the azide/nitrate route from stoichiometric mixtures of the precursors CuO, NaN3 and NaNO3. Single crystals have been grown by subsequent annealing of the as prepared powders at 500 degrees C for 2000 h in silver crucibles, which were sealed in glass ampoules under dried Ar. According to the X-ray analysis of the crystal structures (Na3Cu2O4: P2(1)/n, Z = 4, a = 5.7046(2) b = 11.0591(4), c = 8.0261(3) angstrom, beta = 108.389(1)degrees 2516 independent reflections, R-1(all) = 0.0813, wR(2) (all) 0.1223; Na8Cu5O10: Cm, Z = 2, a = 8.228(1), b = 13.929(2), c = 5.707(1) angstrom, beta = 111.718(2)degrees, 2949 independent reflections, R-1(all) = 0.0349, wR(2) (all) = 0.0850), the main feature of both crystal structures are CuO2 chains built up from planar, edge-sharing CuO4 squares. From the analysis of the Cu-O bond lengths, the valence states of either + 2 or + 3 can be unambiguously assigned to each copper atom. In Na3Cu2O4 these ions alternate in the chains, in Na8Cu5O10 the periodically repeated part consists of five atoms according to Cu-II-Cu-II-Cu-III-Cu-II-Cu-III. The magnetic susceptibilities show the dominance of antiferromagnetic interactions. At high temperatures the compounds exhibit Curie-Weiss behaviour (Na3Cu2O4: mu = 1.7 mu(B), Theta = - 160 K, Na8Cu5O10: mu = 1.8 mu(B), Theta = -58 K, magnetic moments per divalent copper ion). Antiferromagnetic ordering is observed to Occur in these compounds below 13 K (Na3Cu2O4) and 24 K (Na8Cu5O10). (C) 2005 Elsevier Inc. All rights reserved.