SE-17[NBCL6](2) AND SE-17[TABR6](2) - 2 N EW COMPOUNDS IN THE STRUCTURE TYPE SE-17[MX6](2)

The reaction of Se, SeCl4 and NbCl5 in SnCl4 in a sealed glass ampoule at 150 degrees C yields Se-17[NbCl6](2) and from Se, SeBr4 and TaBr5 in SiBr4 under the same conditions Se-17[TaBr6](2) is formed. Both com pounds crystallize triclinic in form of black moisture sensitive cryst als, space group P (1) over bar, Z = 2 (Se-17[NbCl6](2): a = 1322.3(5) pm, b = 1309.0(6) pm, c = 1144.9(4) pm, alpha = 99.18(3)degrees, beta = 99.55(3)degrees, gamma = 112.17(3)degrees; Se-17[TaBr6](2): 1354.5( 7) pm, b = 1346.0(9) pm c = 1179.5(6) pm, alpha = 99.26(5)degrees, bet a = 97.81(4)degrees, gamma = 112.52(5)degrees). Both are isotypic to t he previously reported Se-17[WCl6](2). The structures are built of oct ahedral [NbCl6](-) and [TaBr6](-) ions, respectively, and of (Se-17)(2 +) ions. The cations consist of two Se-7 rings which are connected by a Se-3 chain, and thus contain two three-coordinate Se atoms which car ry formally the positive charge.