Heterometallic Mn^III₄Ln₂ (Ln = Dy, Gd, Tb) Cross-Shaped Clusters and Their Homometallic Mn^III₄Mn^II₂ Analogues

The employment of di-2-pyridyl ketone, (py)₂CO, in heterometallic Mn/4f and homometallic Mn cluster chemistry has yielded six Mn^III₄Ln₂ and two Mn^III₄Mn^II₂ structurally related clusters, namely, [Mn₄Ln₂O₂{(py)₂CO₂}₄(NO₃)₂­(RCO₂)₂(H₂O)₆]­(NO₃)₂ (Ln = Gd, <b>1</b>, <b>5</b>; Dy, <b>2</b>; Tb, <b>3</b>; R = Et, <b>1</b>–<b>3</b>; Me, <b>5</b>), [Mn₄Dy₂O₂{(py)₂CO₂}₄(NO₃)₄­(EtCO₂)₂(H₂O)₃(MeOH)]·0.7MeOH·0.8H₂O (<b>4</b>·0.7MeOH·0.8H₂O), [Mn₄Gd₂O₂{(py)₂CO₂}₄(NO₃)₄­(C₆H₄ClCO₂)₂(MeOH)₂(py)₂]·2MeOH (<b>6</b>·2MeOH), [Mn₆O₂{(py)₂CO₂}₄­(py)₄(H₂O)₄]­(ClO₄)₄·4H₂O (<b>7</b>·4H₂O), and [Mn₆O₂{(py)₂CO₂}₄­(NO₃)₄(py)₄] (<b>8</b>), where (py)₂CO₂^2– is the dianion of the <i>gem</i>-diol derivative of (py)₂CO. The compounds possess a new type of cross-shaped structural core, which in the case of <b>1</b>–<b>6</b> is essentially planar, whereas in <b>7</b> and <b>8</b> it deviates from planarity. Clusters <b>1</b>–<b>6</b> are rare examples of Mn/4f species bearing (py)₂CO or its derivatives, despite the fact that this ligand has been well-studied and proven a rich source of more than 200 metal compounds so far. Variable-temperature, solid-state direct-current and alternating-current magnetization studies were performed on complexes <b>1</b>–<b>5</b>, <b>7</b>, and <b>8</b> revealing that the dominant exchange interactions between the metal ions are antiferromagnetic and indicating ground-state spin values of <i>S</i> = 5 (for <b>1</b>), 6 (for <b>5</b>), and 2 (for <b>7</b> and <b>8</b>)