A strategy focusing on framework stability and proton-conducting hydrogen-bonding networks in polyoxoniobates (PONbs) has been implemented, wherein protonated organic amines act as exclusive counter cations, synergistically enhanced by embedded 4p–4f metal-oxo clusters. This approach yields a new family of three-dimensional (3D) supramolecular frameworks, H6(CN3H6)8As4Ln4O12(H2O)4(CO3)4(Nb5O14)2·34H2O (1-Ln, Ln = Sm, Eu, Tb, Dy, Ho, Er, Yb), representing the first reported PONbs featuring a “double-tetrahedral, coaxially nested” 4p–4f metal-oxo cluster (As4Ln4). Impedance measurements show that 1-Eu exhibits a proton conductivity of 1.21 × 10–2 S·cm–1 at 85 °C and 98% RH. Water vapor adsorption reaches saturation at P/P0 = 0.946 with a maximum uptake of 296.6 cm3·g–1. In addition, 1-Eu and 1-Tb display characteristic lanthanide-centered luminescence.
Wen et al. (Tue,) studied this question.