| Summary: | Two types of isostructural iron-cobalt/nickel-antimony-oxo tartrate cluster-based compounds, namely (H<sub>3</sub>O)(Me<sub>2</sub>NH<sub>2</sub>)[<i>M</i>(H<sub>2</sub>O)<sub>6</sub>]<sub>2</sub>[Fe<sup>II</sup><sub>2</sub>Sb<sup>III</sup><sub>12</sub>(<i>μ</i><sub>4</sub>-O)<sub>3</sub>(<i>μ</i><sub>3</sub>-O)<sub>8</sub>(tta)<sub>6</sub>]·6H<sub>2</sub>O (<i>M</i> = Co (<b>1</b>); Ni (<b>3</b>)), H<sub>5/3</sub>[Co<sub>2.5</sub>Fe<sup>II</sup><sub>4/3</sub>Fe<sup>III</sup><sub>3</sub>(H<sub>2</sub>O)<sub>13</sub>Sb<sup>V</sup><sub>1/3</sub>Fe<sup>III</sup><sub>2/3</sub>(<i>μ</i><sub>4</sub>-O)<sub>2</sub>(<i>μ</i><sub>3</sub>-O)<sub>4</sub>Sb<sup>III</sup><sub>6</sub>(<i>μ</i><sub>3</sub>-O)<sub>2</sub>(tta)<sub>6</sub>]·2H<sub>2</sub>O (<b>2</b>) and H<sub>2</sub>[Ni<sub>2.25</sub>Fe<sup>II</sup><sub>1.5</sub>Fe<sup>III</sup><sub>3</sub>(H<sub>2</sub>O)<sub>14</sub>Sb<sup>V</sup><sub>0.25</sub>Fe<sup>III</sup><sub>0.75</sub>(<i>μ</i><sub>4</sub>-O)<sub>2</sub>(<i>μ</i><sub>3</sub>-O)<sub>4</sub>Sb<sup>III</sup><sub>6</sub>(<i>μ</i><sub>3</sub>-O)<sub>2</sub>(tta)<sub>6</sub>]·2H<sub>2</sub>O (<b>4</b>) (H<sub>4</sub>tta = tartaric acid) were synthesized via simple solvothermal reactions. All the clusters in the structures adopt sandwich configurations, that is, bilayer sandwich configuration in <b>1</b> and <b>3</b> and monolayer sandwich configuration in <b>2</b> and <b>4</b>. Interestingly, the monolayer sandwiched compounds <b>2</b> and <b>4</b> represent rare examples of cluster-based compounds containing mixed-valence Sb(III, V), whose center of the intermediate layer is the co-occupied [Fe<i><sub>x</sub></i>Sb<sup>V</sup><sub>1−<i>x</i></sub>]. This is different from that of previously reported sandwich-type antimony-oxo clusters in which the center position is either occupied by a transition metal ion or a Sb(V) alone. Thus, the discovery of title compounds <b>2</b> and <b>4</b> makes the evolution of center metal ion more complete, that is, from <i>M</i>, <i>M<sub>x</sub></i>Sb<sup>V</sup><sub>1−<i>x</i></sub> to Sb<sup>V</sup>. All the title compounds were fully characterized, and the photocatalysis, proton conduction and magnetism of compounds <b>2</b> and <b>4</b> were studied.
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