Complexation of uranyl ions by polyphenols.: Crystal structures of two linear oligomers and one uranyl ion complex

The crystal structures of two acyclic phenolic oligomers with ortho-methylene linkages, possessing two (1) or three (2) phenolic units, have been determined. Compound 1 crystallizes with DABCO (1,4-diazabicyclo[2.2.2]octane) and water molecules, with which it forms hydrogen bonds, and is not deprotonated by the basic agent; 2, which is analogous to half a p-tert-butylcalix[6]arene, crystallizes as a cyclic dimer, with hydrogen bonds between the terminal phenolic units of both molecules. In the presence of DABCO, 2 is doubly deprotonated and forms a complex with uranyl ions, in which two triphenol molecules encompass the cation, each of them bonded by two consecutive phenolate oxygen atoms only. Two protonated DABCO molecules form hydrogen bonds with the two uranyl oxygen atoms. The bidentate nature of 2 in this complex is discussed in relation with previous results with calixarenes as ligands.