Toward an arsenic analogue of Hittorf's phosphorus: mixed pnicogen chains in Cu(2)P(1.8)As(1.2)I(2).

The new compound Cu(2)P(1.8)As(1.2)I(2), with neutral, mixed pnicogen chains, has been synthesized from a stoichiometric combination of CuI, P, and As heated in vacuo at 550 degrees C. Cu(2)P(1.8)As(1.2)I(2) represents substitution of 40% of P in Cu(2)P(3)I(2) by As, with the As predominantly occupying "roof" positions in the tubular chains. The mixed pnicogen modification demonstrates increased stability (T(d) = 330 degrees C) relative to Cu(2)P(3)I(2) (T(d) = 290 degrees C) but a similar optical band gap (E(g) approximately 1.2 eV). Crystallographic data: Cu(2)P(1.8)As(1.2)I(2), monoclinic P2(1)/c, a = 15.477(3) A, b = 13.200(3) A, c = 15.421(3) A, beta = 115.406(4) degrees, Z = 16 (T = 293 K).