Equiatomic quaternary rare earth element zinc pnictide oxides RZnPO and RZnAsO

The twelve phosphide oxides RZnPO (R = Y, La-Nd, Sm, Gd-Tm) and the nine arsenide oxides (R = Y, La-Nd, Sm, Gd-Dy) have been prepared by reaction of the rare earth elements, ZnO, and phosphorus or arsenic, respectively, in a NaCYKC1 flux. The compounds RZnPO (R Y, Pr, Nd, Sm, Gd-Tm) crystallize with a new trigonal rhombohedral structure type, determined from single-crystal X-ray diffractometer data of NdZnPO: R (3) over bar m, a = 397.7(1) pm, c = 3097.5(5) pm, Z = 6. The other eleven compounds are isotypic with ZrCuSiAs (P4/nmm, Z = 2). This tetragonal structure was refined from single-crystal X-ray data of LaZnPO (a = 404.0(1) pm, c = 890.8(2) pm) and NdZnAsO (a = 403.0(1) pm, c = 894.9(4) pm). In both structure types rare earth element-oxygen layers alternate with zinc-pnictogen layers. The ran earth element atoms have four oxygen and three (NdZnPO) or four (LaZnPO, NdZnAsO) pnictogen neighbors. The zinc atoms have tetrahedral pnictogen coordination. The arsenide oxides as well as the tetragonal phosphide oxides LaZnPO and CeZnPO are black, while the other (trigonal) phosphide oxides are transparent. The more metallic character of the tetragonal compounds is ascribed to their more delocalized chemical bonding, as is indicated by their higher coordination numbers, which in part also result through significant Zn-Zn bonding.