The title compound, C25H27N4C14I, DYE, is an efficient spectral sensitizer of silver halide photographic systems and is known to form J-aggregates with ease. We have determined the crystal structures of the 2:1 methanol:DYE solvate (DYEM) and the 1:1 acetonitrile: DYE solvate (DYEA) from single-crystal X-ray intensity data collected with an automated diffractometer. DYEM is monoclinic, P21/a, with a=22.547 (9), b= 11-036 (5), c= 13.375 (5).~, fl= 107.48 (1) ° and Z=4; DYEA is triclinic, P1, with a= 10.392 (3), b=8-242 (2), c=9.284 (2) A, ~=93.92 (2), fl= 107.81 (1),),=77.71 (2) ° and Z=I. The structures were solved by the heavy-atom technique and refined by block-diagonal least-squares methods. The final R values are 0.033 for DYEM and 0.040 for DYEA. The distances and angles for the cations in the two structures agree very well with each other and with the usual accepted values. In spite of the extensive conjugation the cations are only approximately planar. In both structures, the cations pack plane to plane, and end to end on edge in sheets parallel to (100) separated by sheets containing the anions and solute molecules. There is a remarkable similarity of the (100) projections of the cation sheets in the two structures to each other and to the arrangement of ions in (111) faces of AgBr.
IntroductionSpectral sensitization, the process by which the photographic or photoconductive sensitivity of a material is extended into spectral regions outside its intrinsic absorption region, was discovered a century ago by Vogel (1873). Since then, the effect, which is indispensable to photographic technology, has been studied intensively 2794 THE CRYSTAL STRUCTURES OF TWO SOLVATES OF CzsHz7N4C14I (West, 1970;West & Gilman, 1969;Brooker, 1966;West & Carroll, 1966). Most spectral sensitizers of silver halides have been organic dyes, and the cyanine dyes, with their strong absorption and tendency to form aggregates with close intermolecular spacings and strong coupling, have been studied and used most extensively. A given cyanine dye may simultaneously form several different kinds of aggregates which exhibit spectral shifts of the order of + 100 nm from the solution monomer spectrum. Red-shifted aggregates with intense sharp absorption maxima were first reported by Jelley (1936) and by Scheibe (Scheibe, Kandler & Ecker, 1937;Scheibe, Mareis & Ecker, 1937) to form well-ordered, multilayer J-aggregates with ease (Zuckerman, 1967 Zuckerman & Ames, 1968; Bird, Norland, Rosenoff & Michaud, 1968;Walworth, Rosenoff, and Bird, 1970;Rosenoff, Walworth & Bird, 1970;Gray, Brewer & Bird, 1970;Bird, 1971) have used the slipped deck model, the thiacarbocyanine crystal structures of Wheatley (1959a, b), and the arrangement of silver ions in the (111) and (100) planes of AgBr to arrive at a model of aggregation and sensitization in silver halide systems.Generally, however, because of a lack of firm experimental structure data, our understanding of the structure and packing of these dyes is deficient. We undertook to determine the crystal ...