Polymorphism in Zintl Phases ACd4Pn3: Modulated Structures of NaCd4Pn3 with Pn = P, As.

NaCd4P3 and NaCd4As3 were synthesized via short-way transport using the corresponding elements and CdI2 as mineralizer. At room temperature, the two ß-polymorphs adopt the RbCd4As3 structure type which has been recently reported for alkali metal (A)-d(10) transition metal (T)-pnictides (Pn). The title compounds crystallize rhombohedrally in space group R3̅m at room temperature and show reversible phase transitions to incommensurately modulated α-polymorphs at lower temperatures. The low-temperature phases are monoclinic and can be described in space group Cm(α0γ)s with q vectors of q = (-0.04,0,0.34) for α-NaCd4P3 and q1 = (-0.02,0,0.34) for α-NaCd4As3. Thermal properties, Raman spectroscopy, and electronic structures have been determined. Both compounds are Zintl phases with band gaps of 1.05 eV for ß-NaCd4P3 and ∼0.4 eV for ß-NaCd4As3.

One-Dimensional [P15](-) Tubes in Layered Semiconducting AgP15.

AgP15 was synthesized from the elements via a short-way transport reaction following the mineralizer concept. The needle-shaped crystals were characterized by single-crystal and powder X-ray diffraction. It crystallizes triclinically in space group P1̅ with cell parameters of a = 6.937(1) Å, b = 9.000(1) Å, c = 11.103(2) Å, α = 99.95(1)°, ß = 99.61(1)°, and γ = 105.980(9)°. AgP15 exhibits a tubular phosphorus substructure related but neither isotypic nor isostructural to the alkaline phosphides MP15 (M = Li-Rb). The thermal properties, electronic structure, and experimental band gap of this new semiconductor have been determined. Finally, Raman spectra of AgP15 and selected alkaline-metal polyphosphides MP15 have been measured and interpreted. AgP15 represents the first transition-metal representative of this class of materials.