A Rare Inorganic–Organic Hybrid Polyoxoboroniobate Based on Pagoda-Shaped {LiB₂Nb₂₉O₈₆} Clusters and {Cd₂(<i>cis</i>-en)₂(<i>trans</i>-en)} Complexes

A new inorganic-organic hybrid polyoxoboroniobate {H₄K₂[Cu(<i>cis</i>-en)₂(H₂O)]₉[Cu(<i>cis</i>-en)₂]₆[Cd₂(<i>cis</i>-en)₂(<i>trans</i>-en)][LiB₂Nb₂₉O₈₆]₂·79H₂O} (<b>1</b>, en = ethylenediamine), is built from pagoda-shaped {LiB₂Nb₂₉O₈₆} clusters, linear {Cd₂(<i>cis</i>-en)₂(<i>trans</i>-en)} bridging units, and copper-amine complexes. The {LiB₂Nb₂₉O₈₆} cluster represents the first example of combining oxoboron clusters with polyoxoniobate clusters (PONbs). It consists of an unusual HPONb fragment {LiNb₁₈O₅₄}, a fused-ring structural boroniobate cluster {B₂Nb₅O₁₃}, and a classical Lindqvist {Nb₆O₁₉} fragment. The {Cd₂(<i>cis</i>-en)₂(<i>trans</i>-en)} and [Cu(<i>cis</i>-en)₂]²⁺ complexes link the pagoda-shaped {LiB₂Nb₂₉O₈₆} clusters into 1D infinite ladder chains. This is the first instance of simultaneous coordination of the <i>cis</i>-en and <i>trans</i>-en ligands with a single metal cation in the inorganic-organic hybrid PONb family. Furthermore, <b>1</b> exhibits good proton conductivity.