The Series of Rare Earth Zinc Phosphides RZn3P3 (R=Y, La–Nd, Sm, Gd–Er) and the Corresponding Cadmium ompound PrCd3P3

The 12 title compounds were prepared by reaction of the elemental components in a NaCl/KCl flux. Their isotypic crystal structures were determined for the two praseodymium compounds from single-crystal X-ray data in the space group P63/mmc with Z=2 formula units per cell; PrZn3P3: a=404.0(1) pm, c=1997.9(6) pm, R=0.064 for 253 structure factors; PrCd3P3: a=426.5(1) pm, c=2090.6(6) pm, R=0.020 for 309 F values and 14 variables each. Large displacement parameters for one-third of the zinc, cadmium, and phosphorus sites of both structures indicate distortions. Hence, the true symmetry of both compounds may be lower, as is known for the closely related structure of ScAl3C3. The cadmium and phosphorus atoms of PrCd3P3 form triple-layers similar to the layers in the wurtzite-type structure of ZnS. These nets are separated from each other by the praseodymium atoms. The praseodymium and cadmium atoms form close-packed layers of the stacking sequence (hccc)2 corresponding to the atomic layers (CdCdPrCd)2. The phosphorus atoms occupy octahedral and trigonal bipyramidal voids of the kind Pr3Cd3 and Cd5, respectively. Chemical bonding is briefly discussed. The praseodymium and cadmium atoms obtain their usual oxidation numbers corresponding to the formula Pr3+(Cd2+)3(P3-)3.