structure of Cu 4 SiP 8 contains Cu 2 pairs and a three-dimen-The title compounds were prepared in well-crystallized form sionally infinite silicon phosphorus polyanion. In CeSiP 3 from a tin flux and their crystal structure was determined (3) the cerium atoms are coordinated by nine phosphorus from single-crystal diffractometer data of LaSi 2 P 6 : Cmc2 1 , a β«Ψβ¬ atoms, the silicon atoms have tetrahedral phosphorus coor-1012.9(3) pm, b β«Ψβ¬ 2817.5(7) pm, c β«Ψβ¬ 1037.4(5) pm, Z β«Ψβ¬ 16, dination, and some phosphorus atoms have-in addition to R β«Ψβ¬ 0.034 for 3303 structure factors and 181 variable paramecerium and silicon neighbors-also phosphorus neighbors, ters. The structure of the isotypic compound CeSi 2 P 6 was also thus forming infinite phosphorus chains. refined from single-crystal X-ray data: a β«Ψβ¬ 1011.8(4) pm, b β«Ψβ¬ Ono et al. (2) have reported on the preparation of the 2803.1(8) pm, c β«Ψβ¬ 1031.1(4) pm, R β«Ψβ¬ 0.035 for 2132 F values compounds LnSi 2 P 6 (Ln Ο La, Ce, Pr). Their X-ray powder and 181 variables. The silicon and the phosphorus atoms could patterns were indexed on the basis of a C centered orthobe distinguished by comparing their occupancy parameters obrhombic cell. We have been successful in growing single tained from both structure refinements. The assignments agree crystals of the lanthanum and cerium compounds of these with those deduced by structure-chemical arguments. These atoms form a three-dimensionally infinite framework polyseries from a tin flux, and we now report their structure, anion, which accommodates four different kinds of rare earth which is notable for the presence of four different phosphoatoms: three with nine and one with ten phosphorus neighbors. rus polyanions. In addition, we have prepared the new The silicon atoms are all in tetrahedral phosphorus coordinaisotypic compound NdSi 2 P 6 .
tion. There are phosphorus atoms which have only two rare earth and two silicon neighbors, but most phosphorus atoms SAMPLE PREPARATION AND LATTICE CONSTANTS have-in addition to the rare earth and silicon atomsphosphorus neighbors, thus forming P 3 , P 4 , P 5 , and P 6 units.
The samples were prepared by the tin flux technique. Using oxidation numbers, the compounds can be rationalized Starting materials were filings of the rare earth metals with the formulas Ln 3Ψ (Si 2 P 6 ) 3Ψ and Ln 3Ψ (Si 4Ψ ) 2 (P 6 ) 11Ψ , where the (Kelpin, 99.9 %), silicon powder (Υ99.9%), red phosphorus octet rule is obeyed for the silicon and phosphorus atoms and (Hoechst, ''ultrapure''), and granules of tin (Merck, two electrons are counted for each Si-P and P-P 99.9%). The elements, in the atomic ratio Ln : Si : P : interaction.