CHROMATE AND CHROMATE-DICHROMATE COMPLEXES OF LANTHANIDE-CONTAINING MACROCYCLES

Anion metathesis between aqueous K2CrO4 and the [ML(CH3COO)(2)]Cl complexes, where M is a lanthanide(III) ion and L is the six-nitrogen-donor macrocyclic ligand C22H26N6, 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(CrO4)(1.5). 5H(2)O, containing only ionic chromate. The Ce-III analogue was oxidized to CeL(CrO4)(2) . 6H(2)O, 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 [(CrO4)LM(mu CrO4)ML(CrO4)]. nH(2)O (M = Sm-Ho, n = 10 or 11), containing chelating as well as bridging chromate, and the photochromic (golden --> red-brown) [ML(CrO4)(H2O)](2)(Cr2O7). 2H(2)O (M = Sm-Gd), containing chelating chromate and ionic dichromate. In both series the L macrocycle functions as a hexadentate ligand and the lanthanide(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.