A lanthanide-tellurium heterometal encapsulated sandwich-type heteropolyoxoniobate with a 3D pcu-type hydrogen-bonded network.

A rare sandwich-type heteropolyoxoniobate cluster, [Eu(H 2 O) 3 Te 6 Nb 18 O 64 (OH) 4 ] 15- {EuTe 6 Nb 18 }, has been isolated by simultaneously incorporating a lanthanide cation and tellurite anions into polyoxoniobate. The {EuTe 6 Nb 18 } cluster represents the first example of lanthanide-incorporated telluroniobate with unprecedented Eu-Te heterometal cations in the sandwiched sites. The N-H⋯O hydrogen bonds link the copper-amine complexes and {EuTe 6 Nb 18 } polyoxoanions into a 3D supramolecular framework 1 with pcu topology. Furthermore, compound 1 exhibits moderate proton conduction and water vapor adsorption properties.