Structure of a Discrete Hexadecameric Water Cluster in a Metal−Organic Framework Structure

Pyrazine-2,3,5,6-tetracarboxylic acid (pytcH4) reacts with Cu(NO3)2·6H2O in 1:2 molar ratio in the presence of pyridine (py) vapor to form blue crystals of a coordination polymer with the empirical formula {Cu2.5(pytc)(py)8(NO3-)·10H2O}n (1). Four such polymeric chains gather around a hexadecameric water cluster to form an overall 3D metal−organic framework structure. Once the water molecules are removed, the 3D structure breaks down. It presents a new mode of association of water molecules not predicted theoretically or found experimentally.