Iodine molecule crystal structure

The compound 4(Ph3SbI)2OI2 is obtained by the addition of I2 in acetonitrile/water to a solution of triphenyl-antimony. The crystal structure contains a one-dimensional chain 53 and (Ph3SbI)20 molecules which are not coordinated to I2. In the ID chain, the distance between the iodine of the (Ph3SbI)20 molecule and the diiodine... 

Figure 7.19. A packing drawing of iodine molecules in its crystal structure.

Structural studies of amylose have, in turn, revealed a wide range of crystalline polymorphy, both in chain conformation and in crystalline packing. An example is the group of V-amyloses that exist as complexes with small organic molecules, water, or iodine. The latter complex is particularly interesting because it displays an intense blue color. The V-amyloses can be prepared by precipitation or drying from solution, and they crystallize readily. Consequently, their crystal structures are of interest in connection with any regenerated form of starch material. 

Naturally, the number of molecules with carbon-iodine bonds is smallest among the halogen compounds and this also applies to gas-phase and crystal structures for such derivatives. Furthermore, gas-phase studies of iodine compounds are hampered by their low volatility and require elevated temperatures in most cases. 

An x-ray crystallographic analysis of bcnzo[J,2,3- / 4,5,6-cV ]bis(thieno)[2,3-c]thiophene (61) demonstrated that the molecule is planar and symmetrical but has strained bond angles. The crystal structure comprises herring-bone type column stacking with intercolumnar heteroatom interactions. Compound (61) showed the same oxidation potential as perilene and, like perilene, formed an iodine complex with the relatively high electroconductivity of 0.11 S cm-1 <93BCJ2033>. 

Since the Braggs first determination, thousands of structures, most of them far more complicated than that of sodium chloride, have been determined by x-ray diffraction. For covalently bonded low molecular weight species (such as benzene, iodine, or stannic chloride), it is often of interest to see just how the discrete molecules are packed together in the crystalline state, but the crystal structures affect the chemistry of such substances only to a minor degree. However, for most predominantly ionic compounds, for metals, and for a large number of substances in which atoms are covalently bound into chains, sheets, or three dimensional networks, their chemistry is very largely determined by the structure of the solid. 

With the aim of increasing the dimensionality through I S interaction, Imakubo et al. (99) used the IEDT-TTF donor molecule (IEDT-TTF = CxH5S6l, iodoethylenedithiotetrathiafulvalene) (see Scheme 11) derived from EDT-TTF by substituting an iodine for one hydrogen atom on the TTF moiety. Indeed, the crystal structure of (IEDT-TTF)[Pd(dmit)2] reveals T S distances of 3.308(4) A, shorter than the sum of the van der Waals radii (4.0 A), indicating strong I S interactions. Due to these I - S interactions, the donor and the Pd(dmit)2 units are almost parallel, which is not the case in the parent (EDT-TTF)2[Pd(dmit)2]2 compound (97, 98). The complex (IEDT-TTF)[Pd(dmit)2] behaves like a metal down to 4.2 K, whereas (EDT-TTF)2[Pd(dmit)2]2 remains metallic at lower temperatures (500 mK) (97). 

A limited number of organic substances with two lattices is also known all columnar misfit structures. The crystal structure of hepta(tetrathiofulvalene)-pentaiodide, (TTF)7l5, determined by Johnson and Watson is one of the best described. [The substructures of the two components (TTF and iodine) were also determined - but in projection only - by Daly and Sanz ] In it, columns of TTF molecules form a matrix, the channels within which are filled by rows of iodine atoms. The 7 5 ratio of subcell multiplicities is only approximate within about 1% of the true ceD value. Similar structures have been determined for (TTF)Br , with a variable ratio of component subcells... 

Fia. 28.—Crystal structure of the a-dextrin-iodine complex formed in the absence of iodide. The outlines of the Schardinger dextrin molecules have been chosen on the basis of possible packing arrangements the iodine atoms have been located by x-ray crystal structure analysis. In this tan-brown complex, there is little or no interaction between the iodine molecules such as occurs in the highly-colored blue or black canal compounds. 

---