Coordination Chemistry of the Calixarenes. II. Europium(III) and p-t-Butyl Calix[6]arene

Abstract

The possible nature of p-t-butyl-calix [6] arene complexes of lanthanide elements has been explored by determination of the single-crystal X-ray structure of a complex with a 1:2 europium/ ligand ratio, obtained from dimethylformamide (dmf ≡ Me₂NCHO) solution. This complex is formulated as [ Eu (LH₄)(Me₂NCHO)₆(OH)].LH₆.~4Me₂NCHO (LH₆ = p-t-butyl-calix [6] arene) on the basis of the structure determination. Crystals are monoclinic, P2₁/n, a 36.11(3), b 23.35(2), c 21.85(2)Ǻ, β 97.46(6)°, Z = 4 formula units; R was 0.11 for 8488 'observed' reflections. The complex is remarkable in that the only interaction of either of the two calixarene ligands (one presumably doubly or triply deprotonated ) with the eight-coordinate europium atom is by way of one behaving as monodentate, the other having no interaction. Eu -O( calix ) is 2.35(1) Ǻ; Eu -O( dmf )₆ range from 2.38(2) to 2.49(2)Ǻ, and Eu -O(H _½?) is 2.49(2)Ǻ.