{Ca(OH2)(3)[Ca(DOTA)].7.7H(2)O}(n)

The octadentate ligand H(4)DOTA (H(4)DOTA = 1,4,7,10-tetraazacyclododecane-N,N',N '',N triple prime-tetraacetic acid) forms the most stable calcium complexes known. The overall solid-state structure of the title complex {poly[triaqua-mu-(1,4,7,10-tetraazacyclododecane- N,N',N '',N triple prime-tetraacetato)-dicalcium 7.7-hydrate], [Ca-2(C16H24N4O8)(H2O)(3)].7.7H(2)O} contains two independent eight-coordinate Ca2+ ions on a twofold crystallographic axis with the Ca2+ ions bound to four of the eight O atoms [mean Ca-O = 2.45 (3) Angstrom] and the four N atoms [mean Ca-N = 2.59 (2) Angstrom] of the DOTA ligand. The coordination geometry of the Ca atom encapsulated by the DOTA ligand is distorted square antiprismatic. Carboxylate bridges link [Ca(DOTA)](2-) anions to [Ca(OH2)(3)](2+) counterions (on general positions related by the twofold symmetry) to form a neutral tetranuclear unit, which in turn bridges to surrounding units through a carboxylate O atom and generates a one-dimensional chain.