Proton-conducting layered structures based on transition metal oxo-clusters supported by Sb(iii) tartrate scaffolds

Abstract

Two transition metal–antimony oxo-cluster based compounds, H₅{MCd(H₂O)₆[M(H₂O)₃Co₃Sb^VSb^III₆(μ₃-O)₈(L-tta)₆]}·7H₂O (1) (M = Cd_0.5 + Co_0.5) and H₃K₅(H₂O)₁₁{Cd(H₂O)₄[Cd(H₂O)Fe₄Cd₂Sb₆(μ₄-O)₅(μ₃-O)₃(L-tta)₆][Cd(H₂O)₂Fe₄Cd₂Sb₆(μ₄-O)₄(μ₃-O)₄(L-tta)₆][Cd(H₂O)₂Fe₄Cd₂Sb₆(μ₄-O)₄(μ₃-O)₄(L-tta)₆Cd(H₂O)₅]}·17H₂O (2) (L-H₄tta = L-tartaric acid) were hydrothermally synthesized and characterized. Compound 1 features a [MCo₃Sb^VSb^III₆(μ₃-O)₈(L-tta)₆(H₂O)₃]⁹⁻ cluster, while compound 2 contains three types of clusters, namely, [Cd(H₂O)Fe₄Cd₂Sb₆(μ₄-O)₅(μ₃-O)₃(L-tta)₆]⁴⁻, [Cd(H₂O)₂Fe₄Cd₂Sb₆(μ₄-O)₄(μ₃-O)₄(L-tta)₆]⁴⁻ and [Cd(H₂O)₂Fe₄Cd₂Sb₆(μ₄-O)₄(μ₃-O)₄(L-tta)₆Cd(H₂O)₅]²⁻. All the clusters are of sandwich-type with {Sb₃(μ₃-O)(L-tta)} scaffolds on the top and bottom. The Cd (and M in 1) ions interconnect the clusters into layered structures in both compounds. To the best of our knowledge, this is the first report of transition metal–antimony oxo-clusters that simultaneously contain the first-row and second-raw transition metal ions, and compound 1 represents the first example of such type of clusters that contain Sb(V). The two compounds exhibit proton conductivity with the values of 2.43 × 10⁻³ and 2.95 × 10⁻³ S cm⁻¹ at 85 °C under 98% relative humidity, respectively.