Photophysical properties of Kuratowski-type coordination compounds [MIIZn4Cl4(Me2bta)6] (MII = Zn or Ru) featuring long-lived excited electronic states

Abstract

The syntheses of Kuratowski-type pentanuclear clusters featuring {MZn(4)Cl(4)} cores (M(II) = Ru or Zn) that incorporate triazolate ligands are described. The coordination compounds are characterized by single-crystal X-ray diffraction, X-ray powder diffraction (XRD), FTIR- and UV-vis spectroscopy. [Ru(II)Zn(4)Cl(4)(Me(2)bta)(6)]·2DMF (Me(2)bta(-) = 5,6-dimethyl-1,2,3-benzotriazolate) (1) crystallizes in the cubic system, while [Zn(5)Cl(4)(ta)(6)] (ta(-) = 1,2,3-triazolate) (3) crystallizes in the tetragonal system. Both compounds feature structurally similar cluster topologies in which the central octahedrally coordinated metal ion is coordinated to six triazolate ligands. Each triazolate ligand is coordinated with two zinc ions (μ(3)-bridging mode), leading altogether to a pentanuclear cluster of T(d) point group symmetry. Photophysical investigations reveal that compound [Zn(5)Cl(4)(Me(2)bta)(6)]·2DMF (2) shows a short-lived excited electronic state, which can be populated with high quantum yield. The isostructural compound [Ru(II)Zn(4)Cl(4)(Me(2)bta)(6)]·2DMF (1), on the other hand, shows a long-lived photoexcited state, owing to an internal singlet to triplet conversion of the electronic states, as revealed by time-resolved fluorescence spectroscopy. Insights gained from these studies open up novel design strategies towards photocatalytically active metal-organic frameworks incorporating photoactive Kuratowski-type secondary building units such as MFU-4 (Metal-Organic Framework Ulm University-4).

Dielectric Relaxation Processes, Electronic Structure, and Band Gap Engineering of MFU‐4‐type Metal‐Organic Frameworks: Towards a Rational Design of Semiconducting Microporous Materials

“…First, for the MFU‐4 cluster (Zn 5 Cl 4 (HBBTA) 6 ), all frontier orbitals are mainly participated by the organic ligand (see Supporting Information, Figure S12). This is in agreement with our previous study of the photophysical properties of the MFU‐4 related compound [Zn 5 Cl 4 (Me 2 BTA) 6 ], where a band at 282 nm (4.4 eV) was measured in the UV‐visible absorption spectrum. This relatively intense band was assigned to the ligand centred π→π* transition of Me 2 BTA − , and is also present in the molecular compound Me 2 BTAH.…”

Beyond click chemistry – supramolecular interactions of 1,2,3-triazoles

“…483 Homo-and heterotrinuclear coordination compounds of type 42e as well as clusters, coordination polymers, and metalorganic frameworks (MOFs) thereof assemble with various metal centers and the obtained materials can feature, for instance, interesting magnetic properties and high porosities. [484][485][486][487][488][489]…”

Metal–organic frameworks in Germany: From synthesis to function

“…Kuratowski-type SBUs feature a central metal ion coordinated to six triazolate ligands (L) that span a Cartesian coordinate system. The central metal ion in the octahedral coordination environment can be varied [91] for the opportunity to obtain redox-active SBUs that are also Lewis acidic, with chemical properties which can be fine-tuned by selecting appropriate metal ions [94]. A graph theoretical analysis proves that [M II Zn 4 X 4 (L) 6 ] units contain the nonplanar K 3,3 graph.…”

“…The design of MFU-4-type framework compounds rests on unique pentanuclear structural building units (SBUs), for which the term "Kuratowski-type" SBUs has been suggested by the authors (Figure 9) [91]. The central metal ion in the octahedral coordination environment can be varied [91] for the opportunity to obtain redox-active SBUs that are also Lewis acidic, with chemical properties which can be fine-tuned by selecting appropriate metal ions [94]. A graph theoretical analysis proves that [M II Zn 4 X 4 (L) 6 ] units contain the nonplanar K 3,3 graph.…”