On the proton-acceptor properties of [TeMo6O24]6− in Na4(NH4)2[TeMo6O24] · 16H2O

Colourless triclinic single crystals of Na₄(NH₄)₂TeMo₆O₂₄] · 16H₂O were grown in aqueous solution (space group P1 , a = 1 075.3(1), b = 1 074.2(1), c = 1 089.8(1) pm, = 96.259(9), β = 118.556(7), γ = 113.355(8)°, Z = 1, 295 K, 311 parameters, 3 689 reflections, R_g = 0.0197). There are two crystallographically independent Na⁺ cations. Na(1) is coordinated octahedrally by four water molecules and two oxygen atoms of the centrosymmetric TeMo₆O₂₄]^6? anion. Na(2) is bound to five water molecules in a considerably distorted trigonally bipyramidal fashion. These bipyramids are linked with NH₄⁺ by hydrogen bonds to yield centrosymmetric cluster cations consisting of two NH₄⁺ and two Na(H₂O)₅⁺ each. Hydrogen bonds envolving all except one (O(10)) of the oxygen atoms of the TeMo₆O₂₄]^6? anion as almost equivalent proton acceptors regardless of their bonding mode to Te and Mo, respectively, establish further connections to NH₄⁺ and the water of crystallization.