A holmium complex of a macrocyclic ligand (DOTA) and its isostructural europium analogue

The holmium and europium complexes of the tetraanion of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (H4DOTA), namely, sodium aqua(1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetato)-holmium(III) tetrahydrate, Na[Ho(C 16 H 24 N 4 O 8 )(H 2 O)].4H 2 O, and sodium aqua(1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetato)europium(III) tetrahydrate, Na[Eu(C 16 H 24 N 4 O 8 )(H 2 O)].4H 2 O, show nine-coordination around the metal ion, with a square antiprismatic coordination geometry involving four N- and four O-donor atoms of the DOTA ligand, and a coordinated water molecule in a capping position.