Molecular dynamics of solid benzothiadiazine derivatives (Thiazides). A study by NMR, DTA and DFT methods

The 1H solid state NMR spectra of four sulphonamide derivatives of 1,2,4-benzothiadiazine-1,1-dioxides (thiazides) were recorded at different temperatures in the range 100–400 K and the temperature dependencies of the second moment ðM2Þ of the resonant line and spinlattice relaxation time ðT1Þ were measured. The minimum in the temperature dependence of the T1 revealed an activation process related to the hindered rotation (jumps) of the -NH2 group. The activation energy of this motion estimated on the basis of the fit of the theoretical model to the experimental points was 36.5 kJ/mol for HCTZ, 31.8 kJ/mol for ATZ, 35.2 kJ/mol for TCTZ and 40.6 kJ/mol for CTZ, and was close to that calculated by the DFT (B3LYP/6-311 þ G(2d,p)) method for the model assuming the -NH2 jumps between two equilibrium positions. This type motion is responsible for the reduction in the NMR line second moment by approximately 1Gs2 observed for all the thiazides studied. Thiazides also perform a quasi-isotropic motion tumbling whose activation energy is higher than that of the hindered jumps of the NH2 group. This motion is characterized only by M2 reduction. According to the increasing strength of the NH2 group bonding in the crystalline lattice, the thiazides studied can be ordered as: ATZ , TCTZ , HCTZ , CTZ, which is consistent with their ordering according to increasing melting points. The lowest activation energy for ATZ means that in this compound the NH2 group is bonded the weakest in the crystalline lattice. q 2004 Elsevier B.V. All rights reserved.