Lanthanide ion complexes of the calixarenes. Part 4. Double inclusion by p-t-butylcalix[4]arene (H4L). Crystal structures of [Eu2(HL)2(dmf)4].7dmf (dmf = dimethylformamide) and H4L.dmso (dmso = dimethyl sulphoxide)

Reaction of europium(III) with p-t-butylcalix[4]arene (H4L) under the same conditions as used for reactions with larger calixarenes yields a yellow crystalline complex structurally characterised as [Eu2(HL)2(dmf)4].7dmf, where dmf =N,N-dimethylformamide. The crystals are monoclinic, space group C2/c with a= 35.03(2), b= 16.12(2), c= 23.38(2)Å, β= 98.40(4)°, and Z= 4 dimers; the structure was refined to R= 0.096 for 9 248 ‘observed’ reflections. The complex is binuclear and centrosymmetric with the europium atoms bridged by one phenoxide group from each calixarene ligand and each europium being bound to two unidentate dmf ligands as well as the three other phenolic oxygens of a calixarene ligand. The calixarene ligands adopt a distorted ‘cone’ conformation in which a dmf molecule is included but in such a manner that there is clearly no co-ordinate interaction with europium. The same type of inclusion is found in the dimethyl sulphoxide (dmso) adduct of p-t-butylcalix[4]arene, H4L·dmso, this compound having been used in ligand purification. It forms large tetragonal crystals, space group P4/n, a= 12.811(4), c= 13.082(4)Å; R= 0.11 for 895 ‘observed’ reflections.