Structure-Property Correlations in Solid Solutions of (CuI)8P12−xAsx, 2.4≤x≤6.6

A series of P/As mixed pnicogen phases of composition (CuI)8P12−xAsx, in which x=2.4, 4.2, 4.8, 5.4, and 6.6, have been synthesized and characterized by X‐ray single crystal and powder diffraction, solid‐state NMR spectroscopy, thermal gravimetric analysis, and impedance spectroscopy. These materials are isostructural to (CuI)8P12 and consist of neutral, tubular P/As mixed pnicogen chains associated with CuI and I− ions. The As is distributed throughout the pnicogen chains; however, the “roof” sites of the [P8] cage show preferred occupation by As relative to the other sites. Accordingly, the change in cell volume is not a linear function of the As incorporation. Solid‐state 31P NMR spectroscopy of the 40 % As incorporated sample are consistent with the X‐ray structural model, with extensive broadening due to 31P–75As coupling and site disorder, and a change in the chemical shifts of the resonances due to the As substitution into the lattice. The degree of copper ion site disorder, probed by single‐crystal X‐ray diffraction, increases with increasing As content. Although very little change is observed in the copper ionic conductivity of polycrystalline samples, which ranges from 1.8–5.1×10−6 S cm−1 for (CuI)8P12−xAsx, x=0, 4.2, 5.4; a single crystal (x=4.8) measured along the needle axis has a conductivity of 1.7×10−3 S cm−1 at 128 °C. This represents an order of magnitude improvement in conductivity over (CuI)8P12 at the same temperature. The solubility limit of arsenic in polymeric phosphorus: A series of (CuI)8P12−xAsx phases is formed by the partial substitution of arsenic into the neutral chains of phosphorus in (CuI)8P12. The As shows clear site preferences, as reflected in the nonlinearity in the Vegard's law plot (see graph), and up to 60 % As can be adopted into the polymer.