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

Pyrazine-2,3,5,6-tetracarboxylic acid (pytcH(4)) reacts with Cu(NO(3))(2)x6H(2)O in 1:2 molar ratio in the presence of pyridine (py) vapor to form blue crystals of a coordination polymer with the empirical formula [Cu(2.5)(pytc)(py)(8)(NO(3)(-))x10H(2)O](n). 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.