RbCu1.2Ag3.8Se3 and CsCu2Sb2Se5:: Novel quaternary intermetallics synthesized from superheated organic medial

Reactions in superheated ethylenediamine (en) solutions at 160 degrees C resulted in two novel quaternary intermetallic copper selenides, RbCu1.2Ag3.8Se3(I) and Cs2Cu2Sb2Se5(II). Both I and II are metal rich and represent new layered structure types. Compound I crystallizes in the tetragonal crystal system, space group P4/nbm (No. 125) with a 5.991(1) Angstrom, c=10.918(2) Angstrom, Z= 2, V=391.9(1) Angstrom(3), R1/wR2 = 0.0373/0.0458 for all reflections. Compound II belongs to the triclinic crystal system, space group P (1) over bar (No. 2), a 7.645(1) Angstrom, b = 8.768(2) Angstrom, 10.264(1) A, a = 91.97(2)degrees, beta = 92.07(2)degrees, gamma = 103.05(1)degrees Z= 2, V= 669.2(3) Angstrom(3), R1/wR2= 0.0685/0.0740 for all reflections. I consists of (2)(infinity)[(Cu1.2Ag3.8Se3)(-)] layers and Rb+ counterions located between these layers. There are two types of metal-to-selenium coordination, a square planar (Ag) and a trigonal pyramidal(Cu/Ag). The Se(1) atom displays an unusual eight coordination with Ag and Cu. II contains alternating (2)(infinity)[(Cu2Sb2Se5)(2-)] anionic and Cs+ cationic layers. Each copper atom has a distorted tetrahedral coordination to four Se atoms, and each antimony atom bonds to three Se atoms to result in a trigonal pyramidal geometry. Both I and II are semiconductors with estimated band gaps of 0.7-0.8 and 1.2-1.3 eV, respectively. (C) 1999 Academic Press.