Ternary phosphides and arsenides of rhodium and iridium:: Synthesis and crystal structures

Single crystals of eight new compounds were prepared by heating mixtures of the elements in a lead flux. They were investigated by X-ray methods. Ca2Ir12P7 (a = 9.512(1), c = 3.923(l) Angstrom) is an additional representative of the Zr2Rh12P7 type structure, micro domains required refinements of the structural parameters in space group P6(3)/m. Ca5Rh19P12 (a = 12.592(1), c = 3.882(1) Angstrom) and Ca5Ir19P12 (a = 12.577(2), c = 3.954(1) Angstrom) crystallize with the Ho5Ni19P12 type structure (P (6) over bar 2m: Z = 1), whereas the compounds A(6)Rh(30)X(19) form a slightly modified structure of the Yb6Co30P19 type. The lattice constants are: Ca6Rh30P19: a = 15.532(l) Angstrom c = 3.784(1) Angstrom Sr6Rh30As19: a = 16.135(2) Angstrom c = 3.916(1) Angstrom Eu6Rh30P19: a = 15.566(1)Angstrom c = 3.821(1) Angstrom Eu6Rh30As19: a = 16.124(1) Angstrom c = 3.903(3) Angstrom Yb6Rh30P19: a = 15.508(1) Angstrom c = 3.770(1) Angstrom Because one of the four non-metal atoms, located on different crystallographic sites, is disordered along [001] micro domains are formed. Therefore the parameters were not refined in space group P (6) over bar (Yb6Rh30P19 type). but in space group P6(3)/m. The metalmon-metal ratio of all compounds is in the range of 2:1. Accordingly most of the non-metal atoms are coordinated by nine metal atoms. which form tricapped trigonal prisms. These polyhedra are combined with each other in a different way.