Self-assembly and photocatalytic property of germanoniobate [H6Ge4Nb16O56]10-: encapsulating four {GeO4} tetrahedra within a {Nb16} cage

An unprecedented organic-inorganic hybrid germanoniobate compound Na-4[Cu(en)(2)(H2O)(2)](5)[Na6Ge8Nb32O108H8(OH)(4)]center dot 41H(2)O (1) was synthesized under the hydrothermal condition. In compound 1, the {Nb-16} cage containing four {GeO4} tetrahedra in its internal cavity results in a heteropolyniobate anion [H4Ge4Nb16O54(OH)(2)](10-)({Ge4Nb16}), which is connected by a {Na-6} cluster into the first germanoniobate-based sandwich-type structure. Further, the sandwich germanoniobates are connected by [Na2Cu(en)(2)O6H8] groups into a porous network with one dimensional channels along the a-axis. Photocatalytic study reveals that compound 1 exhibits good photocatalytic activity for the degradation of methylene blue.