An NMR investigation of the structure and dynamics of 1,4-disubstituted benzene derivatives in thiourea inclusion compounds
The structure and dynamics of 1,4-disubstituted benzene derivatives (CH 3)3X(C6H4)X(CH3)3 and (CH3)3C(C6H4)X(CH3) 3, where X = Si, Ge and Sn) and their thiourea inclusion compounds, are investigated by solid state NMR techniques, including 2H-NMR techniques, 13C CP/MAS NMR, 29Si CP NMR and 119Sn CP NMR techniques. The results show that the phenyl ring group exhibits different dynamic properties from the -X(CH3)3 group (where X= Si, Ge and Sn). The -X(CH3)3 group undergoes fast C3' methyl rotation and fast C3' trimethyl rotation in both pure guest and their thiourea inclusion compounds. On the other hand, the phenyl ring group is essentially static in pure guests whereas it undergoes fast rotation about the molecular long axis in their thiourea inclusion compounds. The results also show that 1,4-bis(trimethylgermyl) benzene and 1,4-bis(trimethylstannyl) benzene do not form inclusion compounds with thiourea. This is likely due to the size of the trimethylgermyl and trimethylstannyl groups. In addition, quantum chemical calculations of the 13C, 29Si and 119Sn chemical shift tensor components have been carried out. The results show that all the calculated values and the experimental values follow the same trends, and the calculated values can be used to predict the nuclear chemical shift tensors.