Preparation and Crystal Structure of Au1—xSn1+yP14 and other Polyphosphides with HgPbP14‐Type Structure

The crystal structure of the known compound HgSnP₁₄ (HgPbP₁₄‐type, Pnma, Z = 4) was refined from single‐crystal X‐ray diffractometer data to a residual of R = 0.067 for 1470 structure factors and 83 variable parameters. This polyphosphide has a smaller cell volume than the isotypic compound CdSnP₁₄. For that reason it had been suggested earlier that the mercury atoms in HgSnP₁₄ will show a tendency for linear P—Hg—P 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 CdSnP₁₄. 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 HgSnP₁₄ can be rationalized on the basis of the Zintl‐Klemm concept, resulting in the formula Hg⁺²Sn⁺²(P₁₄)^—4. Accordingly, the environment of the tin atoms shows the lone pair effect. Reactions of the elemental components aiming for the isotypic compounds CuSnP₁₄, CuPbP₁₄, AgSnP₁₄, AgPbP₁₄, AuSnP₁₄, and AuPbP₁₄ resulted in microcrystalline samples. The fibrous habit and the energy dispersive X‐ray fluorescence analyses of the products indicate the formation of these polyphosphides. Only for the gold‐tin compound was it possible to isolate a single crystal suitable for a structure refinement, which confirmed its HgPbP₁₄‐type structure: a = 1259.5(3) pm, b = 982.0(2) pm, c = 1056.2(3) pm, R = 0.046 for 1520 F values and 87 variables. The gold position was found with a lower occupancy, thus resulting in the two possible extreme formulas Au_0.852(4)SnP₁₄ and Au_0.64(1)Sn_1.36(1)P₁₄, depending of whether vacancies or a mixed Au/Sn occupancy is assumed for this position. An analysis of interatomic distances suggests the latter formula to be correct with tetravalent tin on the gold sites corresponding to the formula (Au⁺¹)_0.64(1)(Sn⁺⁴)_0.36(1)]^+2.08(3)SnP₁₄]^—2.