Pyrazine-2,3,5,6-tetracarboxylic acid (pytcH(4)) reacts with Cu(NO3)(2)(.) 6H(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)(NO3-)(.)10H(2)O}(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.