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

The syntheses of Kuratowski-type pentanuclear clusters featuring {MZn4Cl4} 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. [(RuZn4Cl4)-Zn-II(Me(2)bta)(6)]center dot 2DMF (Me(2)bta(-) = 5,6-dimethyl-1,2,3-benzotriazolate) (1) crystallizes in the cubic system, while [Zn5Cl4(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 (mu(3)-bridging mode), leading altogether to a pentanuclear cluster of T-d point group symmetry. Photophysical investigations reveal that compound [Zn5Cl4(Me(2)bta)(6)]center dot 2DMF (2) shows a short-lived excited electronic state, which can be populated with high quantum yield. The isostructural compound [(RuZn4Cl4)-Zn-II(Me(2)bta)(6)]center dot 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).Financial support from the German Research Foundation (DFG Priority Program 1362 "Porous Metal-Organic Frameworks", VO 829/5-1) is gratefully acknowledged. M.T. is grateful to the Landesgraduiertenforderung Baden-Wurttemberg for financial support. GS thanks Ministerio de Ciencia e Innovacion of Spain for funding through project MAT2007-64682. BSC (Barcelona Supercomputing Centre) is thanked for providing computer resources. Helpful discussions with Dr Virginie Lhiaubet are gratefully acknowledged.Liu, Y.; Grzywa, M.; Tonigold, M.; Sastre Navarro, GI.; Schuettrigkeit, T.; Leeson, NS.; Volkmer, D. (2011). Photophysical properties of Kuratowski-type coordination compounds [MIIZn4Cl4(Me2bta)6] (MII=Zn or Ru) featuring long-lived excited electronic states. Dalton Transactions. 40(22):5926-5938. https://doi.org/10.1039/c0dt01750g592659384022Shaw, R., Laye, R. H., Jones, L. F., Low, D. M., Talbot-Eeckelaers, C., Wei, Q., … McInnes, E. J. L. (2007). 1,2,3-Triazolate-Bridged Tetradecametallic Transition Metal Clusters [M14(L)6O6(OMe)18X6] (M = FeIII, CrIIIand VIII/IV) and Related Compounds: Ground-State Spins Ranging fromS= 0 toS= 25 and Spin-Enhanced Magnetocaloric Effect. 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