Nonanuclear Coordination Compounds Featuring {M 9 L 12 } 6+ Cores (M = Ni II , Co II , or Zn II ; L = 1,2,3-Benzotriazolate)

Heteropentanuclear {Ru(II)Cu(II)4} Kuratowski Complexes Assembled from a Ruthenium(II) Precursor Complex to Study Competing Exchange Interactions in M(II)(ta)2 Networks [ta(-) = 1,2,3-Triazolate]

We report a directed two-step synthesis toward pentanuclear Kuratowski complexes. First, six 5,6-dimethylbenzo[1,2,3]triazole ligands (Me2btaH) are coordinated to a single Ru(II) ion, providing a topologically ideal template for the addition of further metal ions. The synthesis and crystal structures of [RuCu4X4(Me2bta)6] [X = acetylacetonate (acac) and tris(3,5-dimethyl-1-pyrazolyl)borate (Tp*)] are described. Both represent new members of the family of so-called Kuratowski (K3,3) complexes. The coordination units feature triazolato-bridged metal-centered {MM4} tetrahedra, which are known for frustrated magnetic interactions in both complexes and metal-organic frameworks. The novel Ru(II)-centered complexes were synthesized in order to investigate the influence of the presence or absence of a paramagnetic central metal ion in the Kuratowski complex. Superconducting quantum interference device and electron spin resonance measurements demonstrate that small deviations in bond lengths and valence angles can lead to the formation of pairs of magnetic exchange-coupled Cu(II) ions. Which Cu(II) ions pair up can be predicted in Jahn-Teller active compounds by the overlap of the respective orbitals. These data are compared with those gleaned for M(II)(ta)2 (ta = 1,2,3-triazolate) lattices, in which structurally similar {MM4} tetrahedra constitute the secondary building units.

A Zinc Coordination Complex Mimicking Carbonic Anhydrase for CO2 Hydrolysis and Sequestration

Carbonic anhydrase (CA) mimicking is an effective and environmentally friendly strategy for carbon dioxide sequestration. Herein, we developed a nonanuclear CA-mimetic zinc coordination complex (1) which possesses a coordination environment similar to that of CA's catalytically active zinc sites. Complex 1 exhibited excellent reusability, solvent and thermal stability, and gram-scale synthesis, which are essential for practical applications. It was found that complex 1 exhibited outstanding catalytic performance that is much better in comparison to that of the popular CA-mimetic compound Zn-cyclen and comparable to that of the reported metal-organic frameworks (e.g., CFA-1). Moreover, we found that its catalytic activity can be significantly improved via OAc^-/OH^- exchange and particle size reduction treatment. This study provides important guidance for the design of highly efficient CA-mimetic materials.

Enabling Homochirality and Hydrothermal Stability in Zn4O-Based Porous Crystals

The [Zn₄O]⁶⁺ cluster is well-known to form the archetypal MOF-5 topology with dicarboxylate ligands. Here we report two new materials (CPM-300 and -301) that show dramatic alteration of topological and chemical behaviors of [Zn₄O]⁶⁺ clusters. In CPM-300, [Zn₄O]⁶⁺ untypically forms the MIL-88/MOF-235 type framework with a small pentane-ring-based chiral dicarboxylate. In contrast, in CPM-301, when mediated by [Zn₉(btz)₁₂]⁶⁺ clusters (btz = benzotriazolate), the MOF-5 topology is regenerated with the same chiral ligand, albeit with alternating [Zn₄O]⁶⁺ and [Zn₉(btz)₁₂]⁶⁺ clusters. Importantly, both CPM-300 and CPM-301 are homochiral, hydrothermally stable in boiling water and alcohol, and thermally stable to 440 °C or higher. It is concluded that small methyl groups on the chiral ligand is sufficiently powerful to shield [Zn₄O]⁶⁺ clusters from degradation by water, even at high temperatures. These results reveal a promising platform for the development of a new class of cluster-based homochiral and hydrothermally stable porous materials.

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.