Water's Lewis base character makes it a common ligand in transition metal complexes, examples of which include metal aquo complexes such as  to perrhenic acid, which contains two water molecules coordinated to a rhenium center.  In solid hydrates,  water can be either a ligand or simply lodged in the framework, or both.  Thus,  consists of [Fe(HO)] centers and one "lattice water". Water is typically a monodentate ligand, i.e., it forms only one bond with the central atom.