A 3D heteropolyoxoniobate framework based on heart-shaped {Te2Nb19O60} clusters with proton conductivity property

Abstract

A 3D tellurium-substituted heteropolyoxoniobate framework H₅K₃Na[Cu(en)₂]₂[Cu(en)_0.75(H₂O)_2.5]{[(Te₂Nb₁₉O₅₈)(μ₃-OH)₂]}·24H₂O (1, en = ethylenediamine) with a 6-connected pcu topology is built from heart-shaped {Te₂Nb₁₉O₆₀} clusters and copper complexes. The {Te₂Nb₁₉O₆₀} cluster represents the new tellurniobate structure type with a 19-nuclearity Nb cluster. It consists of two new monovacant Lindqvist {Nb₅O₁₉} clusters, one boat-shaped {Nb₉O₃₂} cluster and two TeO₃²⁻ anions. The {Te₂Nb₁₉O₆₀} polyanions are interlinked by [Cu(en)₂]²⁺ complexes into a 2D (4, 4) grid-like layer containing rhombic sheets. The Cu²⁺ supports the adjacent layers through Te–O–Cu–O–Te– bonds to form a three-dimensional heteropolyoxoniobate framework with 1D channels. This compound exhibits good chemical and solvent stability and proton conductivity, with a conductivity of 7.9 × 10⁻³ S cm⁻¹ at 85 °C under 98% RH.