EVALUATION OF THERMODYNAMIC PARAMETERS FOR HIGHLY CORRELATED CHEMICAL-SYSTEMS - A SPECTROPHOTOMETRIC STUDY OF THE 1 1 AND 2/1 EQUILIBRIA BETWEEN I-2 AND 1,1'-METHYLENEBIS(3-METHYL-4-IMIDAZOLINE-2-THIONE) (MBIT) AND 1,1'-ETHYLENEBIS(3-METHYL-4-IMIDAZOLINE-2-THIONE) (EBIT) - CRYSTAL AND MOLECULAR-STRUCTURES OF MBIT-CENTER-DOT-2I(2) AND EBIT-CENTER-DOT-2I(2)/

The reactions of I-2 with 1,1'-methylene- and 1,1'-ethylene-bis(3-meth yl-4-imidazoline-2-thione) (mbit and ebit) have been investigated in C HCl3 solution at different temperatures by spectrophotometry. The expe rimental data have been processed using two different procedures of co mputer analysis: SUPERSPEC based on the conventional Gauss-Newton-Marq uardt least-squares method; and POWELSPEC, based on Powell's direct se arch method for the refinement of Delta H degrees and Delta S degrees. The ability of the two methods to identify the involved equilibria co rrectly was compared. Evidence for the stepwise formation of the 1:1 a nd 1:2 adducts has been obtained by the two methods for the mbit case, while POWELSPEC only was able to solve the ebit case satisfactorily. The crystal structures of the adducts mbit . 2I(2) and ebit . 2I(2) ha ve been determined. They show that the thionic sulfur atoms co-ordinat e two diiodine molecules, with S-I 2.683(2) (mbit . 2I(2)) and 2.642(3 ) (ebit . 2I(2)) Angstrom and with I-I 2.897(1) and 2.903(2) Angstrom respectively, the two S-I-I groups being related by a two-fold axis. T he structural features of the S-I-I linear group are in accordance wit h Fourier-transform IR and Raman spectral data and can be taken into a ccount with a three-centre two-electron axial orbitally deficient bond ing scheme.