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The crystal structure of the known compound HgSnP 14 (HgPbP 14 -type, Pnma, Z ϭ 4) was refined from single-crystal X-ray diffractometer data to a residual of R ϭ 0.067 for 1470 structure factors and 83 variable parameters. This polyphosphide has a smaller cell volume than the isotypic compound CdSnP 14 . For that reason it had been suggested earlier that the mercury atoms in HgSnP 14 will show a tendency for linear PϪHgϪP coordination. This is not supported by the present structure refinement, which shows a distorted tetrahedral phosphorus coordination for the mercury atoms, very similar to that of the cadmium atoms in CdSnP 14 . A brief literature survey shows that quite generally the mercury atoms have a smaller volume requirement than the cadmium atoms in intermetallics and more or less covalent compositions, in contrast to more ionic compounds, where the inverse relationship is observed. Chemical bonding in HgSnP 14 can be rationalized on the basis of the Zintl-Klemm concept, resulting in the formula Hg ϩ2 Sn ϩ2 (P 14 ) Ϫ4 . Accordingly, the environment of the tin atoms shows the lone pair effect. Reactions of the elemental components

The title compounds were prepared by reacting powders of the binary transition metal alloys with phosphorus in a tin melt. They crystallize with a monoclinic structure of space group C 2/c, which was determined from single-crystal X-ray data; VNi4P16: a = 1956.0(3), b = 565.9(1), c = 1106.6(2) pm, ß = 100.99(1)°, R -0.020 for 1904 structure factors and 97 variable parameters; NbNi4P16: a = 1973.0(3), b = 571.2(3), c = 1117.2(2) pm, ß = 100.74(1)°, R = 0.023 for 2431 F-values and 97 variables; WNi4P16: a = 1964.2(3), b = 568.3(2), c = 1109.3(2) pm,/? = 101.04(2)°, R = 0.031 for 371 F-values and 43 variables. The T atoms (T = V, Nb, W) have eight P neighbors, which form a slightly distorted square antiprism, and the Ni atoms have appro ximately octahedral P coordination. The P atoms form novel P8 units, which consist of 6 -membered rings with a P2 side chain. Chemical bonding is discussed on the basis of classical twoelectron bonds. A comparison of the interatomic distances suggests that the Fermi level cuts through a band formed by antibonding nickel-phosphorus states. A band structure is propos ed, which also rationalizes the metallic conductivity and the Pauli paramagnetism of the com pounds.The transition metals (T) form numerous poly phosphides with the composition TP4 [1]. Ternary compounds with a T : P ratio of 1:4 are also known, e.g. M oFe2P 12 and W Fe2P 12 [2], TiMn2P 12 [3], NbMn2P12, MoMn2P12, and WMn2P12 [4], VFe2P 12 [5], NbFe2P12 [6 ,7], MoNiP8 and WNiP8 [8 ]. In these polyphosphides the early transition metals have mostly square-antiprismatic or cubic (MoNiP8 and WNiP8) phosphorus coordination, while the late transition metals are surrounded octahedrally by phosphorus atoms. In VP4 • 4 NiP3 = VNi4P 16 and the isotypic compounds NbNi4P 16 and WNi4P16 report ed here the T : P ratio is 1:3.2 and thus these com pounds form an entirely new structure type. How ever, the near-neighbor coordinations of the tran sition metals are very similar to those of the struc tures with the composition T T '2P12. Again the chemical bonding in the TNi4P 16 polyphosphides can be rationalized on the basis of classical twoelectron bonds. A preliminary account of the struc ture of VNi4P 16 has been given earlier [5].* Reprint requests to W. Jeitschko. PreparationThe title compounds can be prepared in wellcrystallized form by reacting a T-nickel alloy (T = V, Nb, W) with red phosphorus in a tin melt. This preparation m ethod has been used with good results in the past for the preparation of Ti2NiP5 [9], Mo(W )NiP8 [8 ] and VFe2P 12 [5]. Starting materials were powders of vanadium, niobium, tungsten and nickel (all 99,9%), red phosphorus (Hoechst, "ultrapur"), and tin (Merck, "rein"). The T-nickel alloys were prepared by arc melting of cold-pressed pellets with the atomic ratio T : Ni = 1:1 or 1:2. The alloys were then ground to fine powders and react ed with red phosphorus and tin in the ratio (T /N i): P : Sn = 1:25:20 in evacuated sealed silica tubes (tube volume 5 cm3, P content 0.5 g). The tubes were annealed at 450 °C f...

Preparation, Properties, and Structure of the Polyphosphides VNi4P16, NbNi4P16, and WNi4P16. -The title compounds TNi4P16 (T: V, Nb, W) are prepared by reaction of a T-Ni alloy with red phosphorus in a tin melt. As revealed from single crystal XRD, the isotypic compounds crystallize in the monoclinic space group C2/c with Z = 4 of a new structure type. In this structure the transition metal atom is coordinated with eight P atoms, forming a slightly distorted square antiprism, and the Ni atoms are octahedrally coordinated with P. The P atoms form novel P8 units consisting of 6-membered rings with a P2 side chain. A band structure is proposed for the compounds which show metallic conductivity and Pauli paramagnetic properties.-(JEITSCHKO, W.; WALLINDA, J.; DEWALSKY, M. V.; WORTMANN, U.