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 MnIII4Ln2 and two MnIII4MnII2 structurally related clusters, namely, [Mn4Ln2O2{(py)2CO2}4(NO3)2­(RCO2)2(H2O)6]­(NO3)2 (Ln = Gd, 1, 5; Dy, 2; Tb, 3; R = Et, 1–3; Me, 5), [Mn4Dy2O2{(py)2CO2}4(NO3)4­(EtCO2)2(H2O)3(MeOH)]·0.7MeOH·0.8H2O (4·0.7MeOH·0.8H2O), [Mn4Gd2O2{(py)2CO2}4(NO3)4­(C6H4ClCO2)2(MeOH)2(py)2]·2MeOH (6·2MeOH), [Mn6O2{(py)2CO2}4­(py)4(H2O)4]­(ClO4)4·4H2O (7·4H2O), and [Mn6O2{(py)2CO2}4­(NO3)4(py)4] (8), where (py)2CO22– is the dianion of the gem-diol derivative of (py)2CO. The compounds possess a new type of cross-shaped structural core, which in the case of 1–6 is essentially planar, whereas in 7 and 8 it deviates from planarity. Clusters 1–6 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 1–5, 7, and 8 revealing that the dominant exchange interactions between the metal ions are antiferromagnetic and indicating ground-state spin values of S = 5 (for 1), 6 (for 5), and 2 (for 7 and 8).