A well-resolved cyclic water tetramer in a dinuclear CuII coordination complex based on 1,2-bis(pyridin-3-yloxy)ethane and capped by pyridine-2,6-dicarboxylic acid.

μ-1,2-Bis(pyridin-3-yloxy)ethane-κ(2)N:N'-bis[aqua(pyridine-2,6-dicarboxylato-κ(3)O(2),N,O(6))copper(II)] tetrahydrate, [Cu2(C7H3NO4)2(C12H12N2O2)(H2O)2]·4H2O, (I), is a C-shaped molecule based on 1,2-bis(pyridin-3-yloxy)ethane (L) and Cu(II) in the presence of pyridine-2,6-dicarboxylic acid (H2pydc). The two five-coordinated Cu(II) centres are chelated by terminal pydc(2-) ligands and bridged by an L spacer. The molecules are arranged in a two-dimensional sheet via 15 O-H...O hydrogen bonds, and C-H...O interactions further bridge neighbouring sheets into a three-dimensional supermolecular architecture. The structure includes a well-resolved cyclic water tetramer, which acts as a subunit to form a larger aggregate. A thermogravimetric analysis of complex (I) was also carried out.