First crystallographic report on a novel 2D layer of water pentagons: L5(7) water motif enclathrating [Co(cyclam)Cl2]

X-ray crystallographic study on [CoII(cyclam)Cl2]·3H2O (cyclam = 1,4,8,11-tetraazacyclotetradecane) reveals that the three water molecules form water pentamers, four of such adjacent water pentamers are fused together to form boat-shaped dodecamers (H2O)12 which are further H-bonded to form 2D water layers. Between the successive water layers, H-bonded 1D chains of [Co(cyclam)Cl2] monomers are sandwiched and stacked along the crystallographic c-direction. Thermal studies reveal that the coordinated water molecules are strongly bound to the polymeric framework which can be thermally dehydrated and readsorbed, as evidenced by the PXRD studies of the parent, dehydrated and rehydrated forms of the complex.