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