TRIGONAL-BIPYRAMIDAL CLUSTERS WITH INTERS TITIAL C-2-UNITS IN THE CHLORIDES K[M(5)(C2)]CL-10 (M=LA, CE, PR) AND RB[M(5)(C-2)]CL-10 (M=PR, ND)

The chlorides K[M(5)(C-2)]Cl-10 (M = La, Ce, Pr) and Rb[M(5)(C-2)]Cl-1 0 (M = Pr, Nd) are obtained via metallothermic reduction of the trichl orides MCl(3) with potassium and rubidium, respectively, in the presen ce of metal M and carbon in sealed niobium containers at temperatures between 700 and 900 degrees C. They contain trigonal bipyramids, inter stitially stabilized by a C-2 unit, [M(5)(C-2)], and crystallize with the hexagonal (K[Pr-5(C-2)]Cl-10, Rb[M(5)(C-2)]Cl-10 with M = Pr, Nd) or monoclinic (K[M(5)(C-2)]Cl-10 with M = La, Ce) crystal system. The trigonal bipyramids are surrounded by nine inner Cl- ligands (capping the nine edges) and by 12 (hexagonal) or 13 (monoclinic) outer ligands and are connected via all of the 21 and 22 ligands, respectively. Spe cial features are Cl-a-a-a (hexagonal) and Cl-a-a-a-a (monoclinic) bri dges.