Bulk tungsten oxides exhibit a wide range of oxidation states, whereas the oxidation states available in molecular oxides such as polyoxometalates (POMs) is limited. In this paper, tungsten oxide clusters with diameters of 1.2±0.4 (W60Ox/C), 1.1±0.4 (W28Ox/C), and 0.9±0.3 nm (W12Ox/C) were produced in a size-selective manner on graphitic carbon by using a phenyl-azomethine-type dendrimer as a template and applying hydrogen reduction after fixing the dendrimers on a support. X-ray photoelectron spectroscopy revealed that the W atoms in the clusters exhibited multiple oxidation states, i. e., Wδ+, W4+, W5+, and W6+. Moreover, X-ray absorption fine structure measurements indicated the W−W bond length of 2.84–2.85±0.01 Å in these clusters. Auto-oxidation with adventitious oxygen after hydrogen reduction is proposed as a reasonable mechanism for the formation of these clusters on the carbon surface.
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