The solid-state crystal structure of Na[Y (dota) (H20)]*4H20 (H,dota = 1.4.7.1 O-tetraazacyclododecane-N,N'.N'',N"-tetraacetic acid) at 11 5 K has been obtained together with the solution structure of the neutral zirconium complex. The yttrium complex shows a mono-capped ( H 2 0 ) square-antiprismatic structure while the solution 'H N M R spectra of [Zr(dota) (H20)] suggest that a structure of lower symmetry is adopted and a minor isomer is observed. The crystal structure of the yttrium complex of N,N"-bis(benzylcarbarnoylmethyl)diethylenetriamine-N,N',N''-triacetic acid has revealed amide carbonyl ligation in a distorted mono-capped square-antiprismatic structure, with one metal-bound water molecule.The complexation chemistry of yttrium has been the subject of renewed interest in recent years because of the need to find yttrium complexes which are sufficiently stable in uiuo for radioimmunotherapy with "Y-labelled antibody conjugates. Following the work of Desreux and co-workers4 on stable lanthanide complexes of H,dota (1,4,7,1 O-tetraazacyclododecane-N,N',N",N"'-tetraacetic acid, H,L'), it was soon apparent that dota was a suitable ligand both for gadolinium

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The synthesis and stability of anionic, neutral and cationic gadolinium complexes based on tetraazaphosphinic acid ligands is compared: lipophilic anionic complexes show biliary rather than renal clearance.