Chromate and chromate-dichromate complexes of lanthanide-containing macrocycles

Abstract

Anion metathesis between aqueous K 2CrO 4 and the [ML(CH 3COO) 2]Cl complexes, where M is lanthanide(III) ion and L is the six-nitrogen-donor macrocyclic ligand C 22H 26N 6, produced a series of crystalline chromate-containing species, the stoichiometry and structure of which depended on the size of the metal centre. The larger lanthanides, La IIINd III, gave yellow, water-insoluble complexes of formula ML(CrO 4) 1.5·5H 2O, containing only ionic chromate. The Ce III analogue was oxidized to CeL(CrO 4) 2·6H 2O, also insoluble and containing only ionic chromate. The smaller lanthanides, Er IIILu III, gave extremely soluble yellow products which were not isolated as analytically pure chromate-only species. The intermediate lanthanides gave two series of complexes, the yellow [(CrO 4)LM( μCrO 4)ML(CrO 4)]· νH 2O (M = SmHo, n =10 or 11), containing chelating as well as bridging chromate, and the photochroic (golden → red-brown) [ML(CrO 4) (H 2O)] 2(Cr 2O 7)·2H 2O (M = SmGd), containing chelating chromate and ionic dichromate. In both series the L macrocycle functions as a hexadentate ligand and the lathanide(III) is 9-coordinate. The chromate-dichromate complexes contain mononuclear coordination entities with bidentate chelating chromate; the chromate-only Eu III complex contains dinuclear coordination entities with both chelating and bridging chromate ligands.