CHARGE-TRANSFER COMPLEXES OF N-METHYLTHIAZOLIDINE-2(3H)-SELONE (1) AND N-METHYLBENZOTHIAZOLE-2 (3H)-SELONE (2) WITH I-2 AND IBR - CRYSTAL-STRUCTURES OF 1-CENTER-DOT-I-2,1-CENTER-DOT-I1.25BR0.75, 2-CENTER-DOT-2I(2), AND 2-CENTER-DOT-2IBR

In CH2Cl2 solution, N-methyl-1,3-thiazolidine-2(3H)-selone (1) and N-methylbenzothiazole-2(3H)-selone (2) react with molecular diiodine to form 1:1 adducts. From solutions having 1 and diiodine in a 1:1 molar ratio, a neutral charge-transfer compound of formula 1.I-2 (C4H7I2NSSe; I) has been obtained, whereas, in the same conditions, 2 yields the previously described ionic compound [(2)(2)I]I-+(3)-, having the 2.I-2 stoichiometry. The crystals of I are monoclinic [space group Cc with a = 16.400(7) Angstrom, b = 5.976(3) Angstrom, c = 12.942(4) Angstrom, beta = 127.66(2)degrees, Z = 4, and R = 0.024] and contain units formed by one diiodine molecule bonded almost linearly [177.49(3)degrees] to the selenium atom. From solutions having a 1:2 molar ratio between the selonic compounds and diiodine, N-methyl-1,3-thiazolidine-2(3H)-selone (1) affords again the same I adduct, whereas 2 yields a crystalline compound with formula 2 .2I(2) (C8H7I4NSSe; III). The crystals of III are triclinic [space group <P(1)over bar>, with a = 11.439(4) Angstrom, b = 14.337(4) Angstrom, c = 16.479(6) Angstrom, alpha = 115.47(2)degrees, beta = 97.02(3)degrees, gamma = 97.85(3)degrees, Z = 6, and R = 0.028]. Unexpectedly, this compound is not ionic as [(2)(2)I]I-+(3)-, and contains three independent 2.2I(2) molecular adducts per asymmetric unit. In each molecular adduct, one diiodine molecule is almost linearly bonded to the selenium atom and lies essentially in the plane of the organic molecule. These units are packed in the crystal on parallel stacked planes separated by ''graphite-like'' interactions, between the organic molecules. The other weakly interacting diiodine molecules fall out of the planes and fit into the cavities left in the packing. In the same solvent and for a 1:1 molar ratio, the reaction between 1 and IBr yields 1. IBr (C4H7IBrNSSe) microcrystals, whereas for a 1:2 molar ratio, violet crystals of formula 1.I1.25Br0.75 (C4H7I1.25Br0.75NSSe; II) isotypic with those of I, have been obtained [space group Cc, with a = 16.233(8) Angstrom, b = 5.900(4) Angstrom, c = 12.793(6) Angstrom, beta = 127.43-(3)degrees, Z = 4, and R = 0.038]; here, the IBr molecule is bonded almost linearly [176.90(4)degrees] to the selenium atom through the iodine atom and about 25% of bromine is substituted by iodine thus obtaining a solid solution formed by 25% of the 1.I-2 adduct and 75% of the 1.IBr adduct. The reaction of 2 with IBr yields both 2.IBr (C8H7-IBrNSSe) microcrystals and 2.2IBr (C8H7I2Br2NSSe; IV) brown crystals using 1:1 and 1:2 molar ratios respectively. The crystals of IV are triclinic [space group <P(1)over bar>, with a = 9.078(5) Angstrom, b = 9.872(5) Angstrom, c = 9.979(3) Angstrom, alpha = 60.66(2)degrees, beta = 74.21(2)degrees, gamma = 82.09(2)degrees, Z = 2, and R = 0.027]. On the basis of the large lengthening of the I-Br bond [3.129(1) Angstrom] in the molecule coordinated to selenium, IV can be almost envisaged as an ionic [2I](+)IBr(2)(-)compound, with the ions strongly interacting with each other. FT-Raman spectra of the solid samples are discussed compared with their structural features and with the spectra of CH2Cl2 solutions containing equimolecular concentrations of 1 (or 2) and I-2 (or IBr). The strong Se-I bonds, obtained-in all the reported compounds, indicate that these CT-complexes are different from those obtained from the sulfur compounds and that for the assignment of the infrared and Raman bands the three-body system Se...I...I(Br) should be better considered. A correlation between v(I-Br) and d(I-Br) is also reported.