PREPARATION AND CRYSTAL-STRUCTURE OF NA7CU12S10, A MIXED-VALENT THIOCUPRATE WITH A PSEUDO-ONE-DIMENSIONAL STRUCTURE

The novel mixed valent thiocuprate Na7Cu12S10 was prepared by a fusion reaction of the binary sulphides Na2S and Cu2S and sulphur at 800-deg rees-C. Na7Cu12S10 is monoclinic, space group P2/m, with a = 16.074(9) angstrom, b = 3.847(1) angstrom, c = 16.222(8) angstrom, beta = 91.94 (3)-degrees and Z = 2. The crystal structure was determined from singl e-crystal data and refined to a conventional R of 0.052 for 1976 obser ved reflections with F(o)2 greater-than-or-equal-to 4sigma(F(o)2) and 178 variables. The structure is pseudo-one-dimensional, characterized by a novel type of infinite triple chains 1 infinity-[Cu12S10]7- which are formed by condensation of 1 infinity-[Cu4S4] units via common sul phur atoms. The unit cell contains two crystallographically independen t moieties. The Na ions occupy octahedral voids in the h.c.p. arrangem ent of the chalcogen atoms.