A Topological Investigation of the Nonlinear Optical Compound: Iodoform Octasulfur

The crystal structure of the nonlinear optical material, iodoform octasulfur (CHI 3 ·(S 8 ) 3 ), in the polar space group R 3 m, has been shown to contain three unique S···I and several S···S close contacts (≤ 4.0 Å), that fall well below the sum of the van der Waals radii of the two atoms concerned. These interactions have all been characterized topologically following the multipole refinement of the crystal structure of iodoform octasulfur. The natures of the possible charge transfer (S···I) and electrostatic (S···S) interactions in this molecule have been investigated based on charge density studies. The properties of the electron density at the bond critical points provide a tool for determining which of the sulfur or iodine atom acts as the donor and which acts as the acceptor in each of the possible S···I charge-transfer interactions present in this molecule. This all leads to a better understanding of the donor/acceptor nature for both types of atoms in charge-transfer complexes of inorganic nonlinear optical materials. The analysis of the structure of iodoform octasulfur has also provided new insight into the relationship between charge density studies and VSEPR theory.