CS-2[PR-6(C-2)I-12 - THE 1ST QUATERNARY REDUCED HALIDE WITH ISOLATED [M-6(C-2)] CLUSTERS

CS2[Pr6(C2)]I12 is obtained as one of the major products from the reaction of PrI3, cesium and carbon in sealed tantalum containers at 850-degrees-C. The crystal structure (triclinic, P1BAR; a = 948.1(2), b = 953.6(3), c = 1005.2(3) pm; alpha = 71.01(2); beta = 84,68(3), gamma = 89.37(2)-degrees; Z = 1) contains discrete Pr6I12-type clusters elongated along the pseudo-four-fold axis to accommodate the C2 units (d(C-C) = 139 pm). The clusters are connected through common (i-a)I and (a-i)I linkages at metal vertices and edges according to CS2[Pr6(C2)(i)I6(i-aI6/2](a-i)I6/2. The cesium cations occupy interstices within the (distorted) iodide layers in a way that ''Cs2I18'' dimers are formed, in which Cs' is surrounded by eleven I-. On the basis of the MO scheme of [SC6(C2]I11, the bonding of the C2 unit is discussed and compared with other cluster compounds containing C2 units.