Evaluation of thermodynamic parameters for highly correlated chemical systems: a spectrophotometric study of the 1 : 1 and 2 : 1 equilibria between I2 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·2I2 and ebit·2I2
Abstract
The reactions of I2 with 1,1′-methylene- and 1,1′-ethylene-bis(3-methyl-4-imidazoline-2-thione)(mbit and ebit) have been investigated in CHCl3 solution at different temperatures by spectrophotometry. The experimental data have been processed using two different procedures of computer analysis: SUPERSPEC based on the conventional Gauss–Newton–Marquardt least-squares method; and POWELSPEC, based on Powell's direct search method for the refinement of ΔH° and ΔS°. The ability of the two methods to identify the involved equilibria correctly was compared. Evidence for the stepwise formation of the 1 : 1 and 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·2I2 and ebit·2I2 have been determined. They show that the thionic sulfur atoms co-ordinate two diiodine molecules, with S–I 2.683(2)(mbit·2I2) and 2.642(3)(ebit·2I2)Å and with I–I 2.897(1) and 2.903(2)Å respectively, the two S–I–I groups beings related by a two-fold axis. The structural features of the S–I–I linear group are in accordance with Fourier-transform IR and Raman spectral data and can be taken into account with a three-centre two-electron axial orbitally deficient bonding scheme.