A Two-Dimensional Layered Heteropolyoxoniobate Based\non Cubic Sn(IV)-Containing {Sn<sub>12</sub>Nb<sub>56</sub>O<sub>200</sub>} Cages with Good Proton Conductivity Property

The first example of a Sn(IV)-containing\nheteropolyoxoniobate K<sub>6</sub>H<sub>18</sub>[Cu(en)<sub>2</sub>]<sub>8</sub>{[Sn(OH)<sub>2</sub>]<sub>12</sub> (HNb<sub>7</sub>O<sub>22</sub>)<sub>8</sub>}·2en·88H<sub>2</sub>O (<b>1</b>) is built from nanoscale\nhigh-nuclearity cubic {[Sn(OH)<sub>2</sub>]<sub>12</sub>(HNb<sub>7</sub>O<sub>22</sub>)<sub>8</sub>} cluster and [Cu(en)<sub>2</sub>]<sup>2+</sup> complexes. The cubic {[Sn(OH)<sub>2</sub>]<sub>12</sub>(HNb<sub>7</sub>O<sub>22</sub>)<sub>8</sub>} cage is composed of eight {Nb<sub>7</sub>O<sub>22</sub>} clusters and 12 SnO<sub>6</sub> octahedrons.\nThe eight {Nb<sub>7</sub>O<sub>22</sub>} fragments are situated at\nthe vertices of the cubic cage, while the 12 SnO<sub>6</sub> octahedrons\nare positioned along the edges of the cubic cage. The [Cu(en)<sub>2</sub>]<sup>2+</sup> complexes link the {[Sn(OH)<sub>2</sub>]<sub>12</sub>(HNb<sub>7</sub>O<sub>22</sub>)<sub>8</sub>} clusters into\ntwo-dimensional (2D) (4,4) grid-like layers. The N–H···O\nhydrogen bonds between the [Cu(en)<sub>2</sub>]<sup>2+</sup> complexes\nand the {[Sn(OH)<sub>2</sub>]<sub>12</sub>(HNb<sub>7</sub>O<sub>22</sub>)<sub>8</sub>} clusters link the layers to form a 3D supramolecular\nstructure. Compound <b>1</b> exhibits a good proton conductivity\nof 3.1 × 10<sup>–2</sup> S cm<sup>–1</sup> at 85\n°C and 98% relative humidity.