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-m ethylbenzothiazole-2(3H)-selone (2) react with molecular diiodine to f orm 1:1 adducts. From solutions having 1 and diiodine in a 1:1 molar r atio, a neutral charge-transfer compound of formula 1.I-2 (C4H7I2NSSe; I) has been obtained, whereas, in the same conditions, 2 yields the p reviously 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 forme d by one diiodine molecule bonded almost linearly [177.49(3)degrees] t o the selenium atom. From solutions having a 1:2 molar ratio between t he selonic compounds and diiodine, N-methyl-1,3-thiazolidine-2(3H)-sel one (1) affords again the same I adduct, whereas 2 yields a crystallin e compound with formula 2 .2I(2) (C8H7I4NSSe; III). The crystals of II I are triclinic [space group <P(1)over bar>, with a = 11.439(4) Angstr om, b = 14.337(4) Angstrom, c = 16.479(6) Angstrom, alpha = 115.47(2)d egrees, 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 asymmet ric unit. In each molecular adduct, one diiodine molecule is almost li nearly bonded to the selenium atom and lies essentially in the plane o f the organic molecule. These units are packed in the crystal on paral lel stacked planes separated by ''graphite-like'' interactions, betwee n the organic molecules. The other weakly interacting diiodine molecul es fall out of the planes and fit into the cavities left in the packin g. 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 I Br molecule is bonded almost linearly [176.90(4)degrees] to the seleni um atom through the iodine atom and about 25% of bromine is substitute d 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 crys tals 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 = 60.6 6(2)degrees, beta = 74.21(2)degrees, gamma = 82.09(2)degrees, Z = 2, a nd 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 sa mples are discussed compared with their structural features and with t he 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 assign ment 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.