Abstract

The arsenic triiodide–sulfur adduct, AsI₃·3S₈ is a new nonlinear optical acceptor–donor intermolecular complex of relatively high second-order susceptibility, χ⁽²⁾ ca. 10^–11 m V^–1. Single crystals formed by addition of AsI₃, and octasulfur, S₈, in the molar ratio 1 : 3 were grown from solution. The space group is R3m, a 24.739(2) Å, c 4.412(3) Å, V 2338(1) ų, Z 3. The arsenic triiodide molecules occupy C_3v symmetry sites with the molecular three-fold symmetry axis parallel to the polar crystal c axis. S₈ retains the crown conformation. Each of the three iodine atoms of the acceptor molecule, AsI₃, is involved in charge-transfer contacts to the chalcogen donor atoms of the partner S₈ molecules. The adduct structure has been analysed in the context of remarkable differences between nonlinear optical properties of AsI₃·3S₈ and the isomorphous complexes, CHI₃·3S₈ and SbI₃·3S₈.