Induced helices, tetrahedrons and spirals in yellow InCl

The structure of yellow InCl is explained. The cubic cell contains 20 trigo nally and 12 digonally distorted InCl6-octahedra, due to the (5s)(2)-outer electron configuration of In+. To a good approximation the structure can be seen as distorted rocksalt, due to three equally strong lattice modes. The distortions of the local octahedra, of various symmetry-type, can be calcu lated from the structure, derived from available XRD-data. It is possible f rom these to deduce bilinear forms, which express chirality, tetrahedron fo rming and spiral forming. Chirality is especially interesting, since there is an optical analogue and one of the expressions for chirality resembles t he rotational strength as described by Condon for optical rotation. The oth er form of chirality goes beyond the Condon approximation and arises since the size of these octahedra is about 1/3 of the wave length of the helices. The three lattice modes induce a number of anti-ferrodistortive distributi ons of helices, tetrahedrons and spirals. In addition, there is also one fe rrodistortive component for chirality and one for tetrahedron forming. (C) 1998 Elsevier Science S.A. All rights reserved.