Solid-state chemistry of organic polyvalent iodine compounds. I. The crystal structures of two polymorphs of 1-(2′-iodobenzoyloxy)-1,2-benziodoxolin-3-one

Abstract

Solid-state reactions involving organic polyvalent iodine compounds frequently result in the formation of preferentially oriented single-crystal product phases (topotaxy). Geometrical comparisons of the mutually oriented reactant and product crystal structures may define the extent of molecular motions, and suggest geometrical mechanisms of transformation. The crystal structures of two monoclinic polymorphs (α and β) of 1-(2′-iodobenzoyloxy)-1,2-benziodoxolin-3-one are reported in this first in a series of papers describing the crystallography of the transformations. The α crystal structure is formed directly in the three-dimensionally ordered topotactic transformation of the isomeric bis-(orthoiodobenzoyl) peroxide crystal structure, and further is hydrolytically transformed to the single crystal phase of 2-iodobenzoic acid. The asymmetric unit of the acicular α form ( a = 4.21, b = 30.86, c = 22.52 Å, β = 93.3°, Cc, Z = 8) consists of two independent molecules which are mutually associated through two strong IO intermolecular coordination bonds across a pseudo inversion center. In both molecules, the monovalent 2′-iodo substituent and the carbonyl oxygen atom of the adjacent carboxyl group are oriented in an unusual transoid relationship as a consequence of the mutual coordination bonds. By contrast, the configuration of these atoms is cisoid in the prismatic β crystal structure ( a = 8.03, b = 12.58, c = 13.74 Å, β = 92.6°, P2 1 c , Z = 4 ), which moreover does not contain the common IO coordination bonds. However, closely analogous coordination bonds are indicated between the monovalent and trivalent iodine atoms in the β form. A sluggish polymorphic transformation (single crystal → polycrystal) of the α structure to the β structure occurs at ∼110°C.