CRYSTAL-STRUCTURES OF THE POLYSELENIDES [CS(18-CROWN-6]2SE5.DMF, [RB(222-CRYPT)]2SE6, [BA(15-CROWN-5)2]SE6.DMF, AND [NA(12-CROWN-4)2]SE7

The title compounds have been prepared by reactions of the correspondi ng diselenides with excess selenium in the presence of crown ethers in dimethylformamide solutions, forming black crystals. [Cs(18-Crown-6)] 2Se5 . DMF: Space group P2(1)/m, Z = 2, 2 194 observed unique reflecti ons, R = 0.119. Lattice dimensions at 20-degrees-C: a = 1041.2; b = 1 496.3; c = 1 459.7 pm; beta = 100.39-degrees. The compound forms an io nic triple with Cs ... Se-contacts between 374 and 381 pm. [Rb(222-Cry pt)]2Se6: Space group P1BAR, Z = 2, 7405 observed unique reflections, R = 0.056. Lattice dimensions at -70-degrees-C: a = 1 106.8; b = 1 460 .8; c = 1 718.8 pm; alpha = 89.22-degrees; beta = 86.65-degrees; gamma = 71.53-degrees. The compound contains Se-6(2-) chains without direct contact with each other. [Ba(15-Crown-5)2]Se6 . DMF: Space group P2(1 )/n, Z = 4, 2680 observed unique reflections, R = 0.055. Lattice dimen sions at -80-degrees-C: a = 1 051.9; b = 1 322.4; c = 2729.9 pm; beta = 100.93-degrees. The compound contains Se-6(2-) chains, which are iso lated from each other by the cations and the included DMF molecules. [ Na(12-Crown-4)2]2Se7: Space group P1BAR, Z = 2, 7313 observed unique r eflections, R = 0.042. Lattice dimensions at -70-degrees-C: a = 1 260. 9; b = 1 433.6; c = 1 462.9 pm; alpha = 80.27-degrees; beta = 78.60-de grees; gamma = 69.34-degrees. The compound contains Se-7(2-) chains wi thout direct contacts with each other.