Cluster-Based Networks: 1D and 2D Coordination Polymers Based on {MnFe₂(μ₃-O)}-Type Clusters

A straightforward approach to heterometallic Mn–Fe cluster-based coordination polymers is presented. By employing a mixed-valent μ₃-oxo trinuclear manganese­(II/III) pivalate cluster, isolated as [Mn^IIMn^III₂O­(O₂CCMe₃)₆(hmta)₃]·(solvent) (hmta = hexamethylenetetramine; solvent = <i>n</i>-propanol (<b>1</b>), toluene (<b>2</b>)) in the reaction with a μ₃-oxo trinuclear iron­(III) pivalate cluster compound, [Fe₃O­(O₂CCMe₃)₆(H₂O)₃]­O₂CCMe₃·2Me₃CCO₂H, three new heterometallic {Mn^IIFe^III₂} cluster-based coordination polymers were obtained: the one-dimensional polymer chain compounds {[MnFe₂O­(O₂CCMe₃)₆(hmta)₂]·0.5MeCN}_<i>n</i> (<b>3</b>) and {[MnFe₂O­(O₂CCMe₃)₆(hmta)₂]·Me₃CCO₂H·(<i>n</i>-hexane)}_<i>n</i> (<b>4</b>) and the two-dimensional layer compound {[MnFe₂O­(O₂CCMe₃)₆(hmta)_1.5]·(toluene)}_<i>n</i> (<b>5</b>). Single-crystal X-ray diffraction analysis reveals a μ₃-oxo trinuclear pivalate cluster building block as the main constituent in all polymer compounds. Different M:hmta ratios in <b>1</b>–<b>5</b> are related to the different structural functions of the N-containing ligand. In clusters <b>1</b> and <b>2</b>, three hmta ligands are monodentate, whereas in chains <b>3</b> and <b>4</b> two hmta ligands act as bridging ligands and one is a monodentate ligand; in <b>5</b>, all hmta molecules act as bidentate bridges. Magnetic studies indicate dominant antiferromagnetic interactions between the metal centers in both homometallic {Mn₃}-type clusters <b>1</b> and <b>2</b> and heterometallic {MnFe₂}-type coordination polymers <b>3</b>–<b>5</b>. Modeling of the magnetic susceptibility data to a isotropic model Hamiltonian yields least-squares fits for the following parameters: <i>J</i>₁(Mn^II–Mn^III) = −6.6 cm^–1 and <i>J</i>₂(Mn^III–Mn^III) = −5.4 cm^–1 for <b>1</b>; <i>J</i>₁ = −5.5 cm^–1 and <i>J</i>₂(Mn^III–Mn^III) = −3.9 cm^–1 for <b>2</b>; <i>J</i>₁(Mn^II–Fe^III) = −17.1 cm^–1 and <i>J</i>₂(Fe^III–Fe^III) = −43.7 cm^–1 for <b>3</b>; <i>J</i>₁ = −23.8 cm^–1 and <i>J</i>₂ = −53.4 cm^–1 for <b>4</b>; <i>J</i>₁ = −13.3 cm^–1 and <i>J</i>₂ = −35.4 cm^–1 for <b>5</b>. Intercluster coupling plays a significant role in all compounds <b>1</b>–<b>5