CROWN-ETHER MOLECULAR-COMPLEXES WITH UREA AND THIOUREA

Crystalline complexes of urea and thiourea with crown ethers, have bee n prepared, viz., 18-crown-6 (18C6), benzo-18-crown-6 (B18C6), dibenzo -18-crown-6 (DB18C6), dicyclohexano-18-crown-6 (DC18C6) and dibenzo-24 -crown-8 (DB24C8). While the complexes of the large ring size crown et her, DB24C8, have high ether to (thio)urea ratios, the stoichiometry o f the others lies between one molecule of crown ether and from one to six molecules of(thio)urea. An IR spectral study of the urea and thiou rea complexes showed that the behavior of thiourea in these complexes is clearly different from that of urea, indicating the role of sulphur in the interaction of thiourea with crown ethers. The urea and thiour ea complexes were classified according to their stoichiometries and th eir IR spectral behavior into three classes for which credible structu res were proposed.