THE FIRST BROMIDE WITH TRIGONAL-BIPYRAMID AL [M(5)(C-2)] CLUSTERS - [PR-5(C-2)]BR-9

The bromide [Pr-5(C-2)]Br-9 is obtained via metallothermic reduction o f PrBr3 with rubidium in the presence of praseodymium and carbon in a sealed niobium container at 730 degrees C as dark red single crystals. [Pr-5(C-2)]Br-9 crystallizes in the monoclinic crystal system [P2(t)/ n; Z = 4; a = 1006.9(1); b = 1886.1(1); c = 1045.9(1)pm; beta = 108.13 0(1)degrees; R(int) = 0.059; R1 = 0.038; wR2 = 0.077]. One edge in the base of the trigonal bipyramid in [Pr-5(C-2)]Br-9 is unusually long ( 440 pm). It is not brigded by a Br-i ligand. In addition to the eight Br-i, the cluster is coordinated by 12 terminal ligands (Br-a). Except for the known Br-a-a-a and Br-i-a connections, Br-i-a-a brigdes are o bserved for the first time for trigonal-bipyramidal clusters.