TRIGONAL BIPYRAMIDAL CLUSTERS WITH ONE FACE-CAPPING BROMIDE LIGAND IN[LA-5(C-2)]BR-9 AND [CE-5(C-2)]BR-9

Red single crystals of the isotypic bromides [La-5(C-2)]Br-9 and [Ce-5 (C-2)]Br-9 (space group: Pnma; La: a = 1130.90(8) pm, b = 994.77(7) pm , c = 1649.11(11) pm; Ce: a = 1121.5(2) pm, b = 985.43(12) pm, c = 163 9.5(2) pm) have been obtained by reaction of the respective rare earth metal, tribromide and graphite in sealed tantalum containers at 750 d egrees C (La) and 800 degrees C (Ce), respectively. The structure cont ains [M(5)(C-2)] cluster units. The nine edges of the trigonal bipyram id are capped by nine Br-i ligands (mu(2)) in an irregular fashion. El even ligands (mu(1)) are in terminal positions. For the first time in interstitially stabilized rare earth cluster chemistry, a face-capping ligand (mu(3)) is observed. Therefore, the cluster units can be descr ibed as [M(5)(C-2)](Br10Br11a)-Br-i with bridging Br-i-a Br-i-i, Br-i- a-a Br-a-a-a and Br-a-a-i ligands leading to a three-dimensional struc ture.