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Issue 19, 2013
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A comparative study of the redox and excited state properties of (nBu4N)2[Mo6X14] and (nBu4N)2[Mo6X8(CF3COO)6] (X = Cl, Br, or I)

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Abstract

The excited-state dynamics, luminescence, and redox properties of a series of hexanuclear molybdenum cluster complexes, (nBu4N)2[Mo6X14] and (nBu4N)2[Mo6X8(CF3COO)6] (X = Cl, Br, or I), were investigated. Substitution of the apical halogen ligands for the trifluoroacetate ligands increased the oxidation potentials and induced a blue shift in the absorption and luminescence bands as well as a considerable increase in the luminescence quantum yields for heavy inner ligands. Time-resolved transient absorption measurements showed that the intersystem crossing from the excited singlet states is ultrafast with time constants ranging between <120 fs and 1.68 ps and leads to hot triplet states. The following cooling occurred at a ps time scale and was assigned to electronic redistribution within the emissive triplet state sublevels. The formation of singlet oxygen, O2(1Δg), suggested earlier on the basis of photooxidation experiments for some complexes, was revised by direct measurements of O2(1Δg) phosphorescence. We showed the effects of the attached ligands on key physico-chemical and photophysical parameters of the title complexes. The synthesis and structural characterisation of a new cluster complex, (nBu4N)2[Mo6Br8(CF3COO)6], completed the series. Our results demonstrated that the complexes with heavy inner ligands (Br, I) and apical trifluoroacetate ligands were photochemically and electrochemically stable, highly luminescent, and good sensitisers of O2(1Δg).

Graphical abstract: A comparative study of the redox and excited state properties of (nBu4N)2[Mo6X14] and (nBu4N)2[Mo6X8(CF3COO)6] (X = Cl, Br, or I)

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Supplementary files

Article information


Submitted
29 Nov 2012
Accepted
28 Feb 2013
First published
01 Mar 2013

Dalton Trans., 2013,42, 7224-7232
Article type
Paper

A comparative study of the redox and excited state properties of (nBu4N)2[Mo6X14] and (nBu4N)2[Mo6X8(CF3COO)6] (X = Cl, Br, or I)

K. Kirakci, P. Kubát, J. Langmaier, T. Polívka, M. Fuciman, K. Fejfarová and K. Lang, Dalton Trans., 2013, 42, 7224
DOI: 10.1039/C3DT32863E

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