Proton-conducting Layered Structures based on Transition metal oxo-clusters supported by Sb(III) tartrate scaffolds

Two transition metal-antimony oxo-cluster based compounds, H5{MCd(H2O)6[M(H2O)3Co3SbVSb6III(μ3-O)8(L-tta)6]}·7H2O (1) (M =Cd0.5 + Co0.5) 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) (H4tta = tartaric acid) were hydrothermally synthesized and characterized. Compound 1 features a [MCo3SbVSbIII6(μ3-O)8(L-tta)6(H2O)3]9- cluster, while compound 2 contains three types of clusters, namely, [Cd(H2O)5Sb6(μ4-O)5(μ3-O)3(L-tta)6(H2O)]4-, [Cd(H2O)5Sb6(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 sandwich-type with {Sb3(μ3-O)(tta)3} scaffolds on the top and bottom. And Cd (and M in 1) ions interconnect the clusters into layered structures in both compounds. To our best 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). Two compounds exhibit proton conductivity with the values of 2.43 x 10-3 and 2.95 x 10-3 S cm-1 at 85 °C under 98% relative humidity, respectively.