Syntheses and Magnetostructural Investigations on Kuratowski-Type Homo- and Heteropentanuclear Coordination Compounds [MZn₄Cl₄(L)₆] (M^II = Zn, Fe, Co, Ni, or Cu; L = 5,6-Dimethyl-1,2,3-benzotriazolate) Represented by the Nonplanar <i>K</i>_3,3 Graph

Homo- and heteropentanuclear coordination compounds [MZn4Cl4(L)6] (MII = Zn, Fe, Co, Ni, or Cu; L = 5,6-dimethyl-1,2,3-benzotriazolate) were prepared containing μ3-bridging N-donor ligands (1,2,3-benzotriazolate), which are structurally related to the fundamental secondary building unit of Metal−organic Framework Ulm University-4 (MFU-4). The unique topology of these Td-symmetrical compounds is characterized by the nonplanar K3,3 graph, introduced into graph theory by the mathematician Casimir Kuratowski in 1930. The following “Kuratowski-type” compounds were investigated by single-crystal X-ray structure analysis: [MZn4Cl4(Me2bta)6]·2DMF (MII = Zn, Fe, Co, and Cu; DMF = N,N′-dimethylformamide) and [MZn4Cl4(Me2bta)6]·2C6H5Br (MII = Co and Ni; C6H5Br = bromobenzene). The μ3-bridging benzotriazolate ligands span the edges of an imaginary tetrahedron, in the center of which a redox-active octahedrally coordinated MII ion is placed. Four ZnII ions are located at the corners of the coordination units. Each Zn center is bound to a monodentate Cl− anion and three N-donor atoms stemming from different benzotriazolate ligands. The fact that open-shell redox-active MII ions can be introduced selectively into the central octahedral coordination sites is unambiguously proven by a combination of magnetic measurements, UV−vis spectroscopy, and energy-dispersive X-ray and inductively coupled plasma atomic emission spectrometry analysis. The phase purity of all compounds was checked by powder X-ray diffractometry, IR spectroscopy, and elemental analysis. The electronic spectra and magnetic properties of the compounds are in complete agreement with their structures determined from single-crystal data. Thermogravimetric analysis shows that all compounds possess a high thermal stability up to 673 K. The pentanuclear compounds retain their structural integrity in solution, as evidenced by time-of-flight mass spectrometry analysis and comparative solution and solid-state diffuse-reflectance spectroscopy. High stability paired with the presence of redox-active metal ions and Lewis-acidic Zn centers renders Kuratowski-type compounds structural and functional models for future MFU-4-type bi- and multifunctional heterogeneous catalysts.