Solid-state chemistry of organic polyvalent iodine compounds. VII. The relationships between crystal packing modes, solid-state intermolecular interactions, and infrared spectra of benzoxiodole compounds
The importance of intermolecular interactions in determining crystal structures has been investigated for a series of 3-oxo-3H,2,1-benzoxiodol-1-substituted compounds. These compounds all contain a trivalent iodine atom which is involved in a stereospecific coordination interaction with an electronegative atom (oxygen or halogen) of a neighboring molecule. It has been found that only four basic packing modes occur for these compounds, formally characterized by the nature of the functional group which is coordinated to iodine. Infrared analysis of solution and solid-state samples of these compounds shows that the structurally identifiable intermolecular coordination modes which occur between I (III) and carbonyl groups do in fact involve chemically stabilizing interactions. Shifts of about 10 cm -1 to lower wavenumber are observed for the carbonyl stretching band of an uncoordinated carbonyl group in solid-state samples, as compared to its frequency in solution samples. The carbonyl stretching frequency of a coordinated carbonyl group is lowered from 20-80 cm -1 (these bands occur at 1614-1678 cm -1 in the solid state). Some of the compounds exist in molecular conformations in the solid state in which a possible intramolecular interaction between I (III) and a carbonyl also may be contributing to the observed frequency shifts.