Liberation of Pnicogen Chains from Cu₂P_1.8As_1.2I₂:  Synthesis and Characterization of a New Allotrope of P−As

Abstract

Removal of CuI from Cu(2)P(1.8)As(1.2)I(2) results in a novel P--As allotrope. Although the product is X-ray amorphous, lattice fringes are observed in the transmission electron micrographs with spacings reflecting the diameter of the linear pnicogen polymer in Cu(2)P(1.8)As(1.2)I(2), suggesting the pnicogen chains remain intact upon loss of CuI. The straight needles present in Cu(2)P(1.8)As(1.2)I(2) appear to be kinked in the P--As phase due to lattice mismatch between the liberated polymers, ultrasonic treatment, or a combination of these effects. This new P--As modification is semiconducting with a band gap of 1.05 eV.

Icosahedral and Ring‐Shaped Allotropes of Arsenic

“…[26] Allotropes of arsenic, similar to the various forms of red phosphorus, have not yet been studied extensively. So far, only mixed P-As chains ]X4(4)[X8] with up to 55 % As [12][13][14] together with violet phosphorus incorporating 5 % arsenic [15] have been prepared experimentally. Thus it might be reasonable to first focus on the synthesis of ring-shaped allotropes of phosphorus.…”

“…After that, the techniques could be applied for As and mixed P-As rings. The copper halide matrix techniques used in several successful syntheses of phosphorus [9] and P-As chains [12][13][14] could be a starting point for the synthesis of the rings.…”

“…[12,13] Isolating the mixed chains from the matrix results in semiconducting PAs polymers. [14] In the case of the violet phosphorus, 5 % of arsenic can be introduced into the crystal structure. [15] Mixtures of phosphorus and arsenic vapors have been found to contain tetra-atomic As 3 P, As 2 P 2 , and AsP 3 molecules.…”

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

“…Recently, it has been shown that the pnicogen chains in both (CuI) 8 P 12 and (CuI) 8 P 7.2 As 4.8 can effectively be liberated from the CuI host by treatment with aqueous potassium cyanide, producing novel allotropes of phosphorus and binary P-As, respectively. [13,14] Although each pnicogen position in (CuI) 8 P 7.2 As 4.8 has shared occupancy of both P and As, the "roof" positions in the [Pn8] cages (indicated by * in Figure 1) appear to be As rich, suggesting that these are not true solid solutions, but that there are preferred sites for As within the structure. Furthermore, the Cu I lattice in the 40 % As phase shows increased disorder relative to the parent compound, suggesting that As substitution may lead to augmented copper ion conductivity.…”

Ag Ion-Exchange Reactions of Cu2P3I2 and Cu2P1.8As1.2I2

“…Recently, a mixed pnictogen analog, Cu 2 P 1.8 As 1.2 I 2 , with an unprecedented 40 % As substitution into the neutral chain, has been synthesized [4]. This new phase has a larger number of partially occupied copper sites relative to the parent compound, and some of the sites are located outside of a normal bonding distance to P/As.…”