A Two-Dimensional Layered Heteropolyoxoniobate Based on Cubic Sn(IV)-Containing {Sn12Nb56O200} Cages with Good Proton Conductivity Property

The first example of a Sn(IV)-containing heteropolyoxoniobate K6H18[Cu(en)2]8{[Sn(OH)2]12 (HNb7O22)8}·2en·88H2O (1) is built from nanoscale high-nuclearity cubic {[Sn(OH)2]12(HNb7O22)8} cluster and [Cu(en)2]2+ complexes. The cubic {[Sn(OH)2]12(HNb7O22)8} cage is composed of eight {Nb7O22} clusters and 12 SnO6 octahedrons. The eight {Nb7O22} fragments are situated at the vertices of the cubic cage, while the 12 SnO6 octahedrons are positioned along the edges of the cubic cage. The [Cu(en)2]2+ complexes link the {[Sn(OH)2]12(HNb7O22)8} clusters into two-dimensional (2D) (4,4) grid-like layers. The N–H···O hydrogen bonds between the [Cu(en)2]2+ complexes and the {[Sn(OH)2]12(HNb7O22)8} clusters link the layers to form a 3D supramolecular structure. Compound 1 exhibits a good proton conductivity of 3.1 × 10–2 S cm–1 at 85 °C and 98% relative humidity.