Water clusters in mixed ionic complexes with metal dipicolinate anions

Formations of three different types of hydrogen-bonded water clusters in the interstices of mixed ionic complexes with metal dipicolinate anions are reported. In the complex [Co(phen)2(H2O)2][Zn(dpa)2]⋅7H2O (1) (where phen = 1,10-phenanthroline, dpa = dipicolinate), both the cation and anion is hydrophilic in nature, exhibits an unusual 2D infinite cyclic water decamers (H2O)10 stabilized by four identical zinc dipicolinato complex anions. Modulating the cationic unit to a hydrophobic environment by replacing the aqua ligand with 2,2′-bipyridine ligand the water cluster can be modified. The complex [Ni(phen)2⋅bpy][Co(dpa)2]⋅8H2O (2) (where bpy = 2,2′-bipyridine) has unprecedented discrete hydrogen bonded hexadecameric (H2O)16 water clusters encapsulated between eight anionic units. A rare wavelike infinite water chain (H2O)n is observed in complex [Co(phen)3][Mn(dpa)2]⋅12H2O (3), in this case the water chain fills the interstitial space created by packing of large hydrophilic anionic units and hydrophobic cationic units. The reported clusters are indefinitely stable in their respective complex at ambient temperature, but the water loss is irreversible when thermally decomposed.

► Change of metal ions in an anionic part and change of cations can cause formation of different types of water clusters.
► Formation of unusual 2D infinite cyclic decameric (H2O)10 is shown.
► A new type of discrete hexadecameric (H2O)16 water cluster is elucidated.
► A wavelike infinite water chain (H2O)n in the interstices of mixed ionic complex with metal dipicolinate anion is also shown.