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 K(3,3) graph.
Homo- and heteropentanuclear coordination compounds [MZn(4)Cl(4)(L)(6)] (M(II) = Zn, Fe, Co, Ni, or Cu; L = 5,6-dimethyl-1,2,3-benzotriazolate) were prepared containing mu(3)-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 T(d)-symmetrical compounds is characterized by the nonplanar K(3,3) 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: [MZn(4)Cl(4)(Me(2)bta)(6)].2DMF (M(II) = Zn, Fe, Co, and Cu; DMF = N,N'-dimethylformamide) and [MZn(4)Cl(4)(Me(2)bta)(6)].2C(6)H(5)Br (M(II) = Co and Ni; C(6)H(5)Br = bromobenzene). The mu(3)-bridging benzotriazolate ligands span the edges of an imaginary tetrahedron, in the center of which a redox-active octahedrally coordinated M(II) ion is placed. Four Zn(II) 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 M(II) 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.
Biswas
Shyam
S
Institute of Inorganic Chemistry II, Materials and Catalysis, Ulm University, Albert-Einstein-Allee 11, D-89081 Ulm, Germany.
Tonigold
Markus
M
Speldrich
Manfred
M
Kögerler
Paul
P
Weil
Matthias
M
Volkmer
Dirk
D