Nh. Hu et al., STRUCTURE OF AN ERBIUM COMPLEX WITH L-PROLINE, Acta crystallographica. Section C, Crystal structure communications, 49, 1993, pp. 2086-2089
In the structure of -(L-proline-O)erbium(III)}-bis-mu-(L-proline-O:O')
hexaperchlorate], each Er3+ ion is coordinated by five carboxyl O ato
ms from the L-proline molecules and three water molecules. Four of the
SiX L-proline molecules act as bidentate bridging ligands to link the
Er3+ ions through the carboxyl groups, thus producing a one-dimension
al chain structure. The other two ligands coordinate unidentately to t
he rare-earth ions. Hydrogen bonds formed between the coordinated wate
r molecules and between the water and unidentate proline ligand stabil
ize the polymeric chain.