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Synthesis and Molecular Structure of a Water-Soluble, Dimeric Tri-Titanium(IV)-Substituted Wells–Dawson Polyoxometalate Containing Two Bridging (C5Me5)Rh2+ Groups

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posted on 2015-12-07, 00:00 authored by Yusuke Matsuki, Takahiro Hoshino, Shoko Takaku, Satoshi Matsunaga, Kenji Nomiya
A novel trititanium­(IV)-substituted Wells–Dawson polyoxometalate (POM)-based organometallic complex, i.e., a dimeric POM containing two bridging Cp*Rh2+ groups (Cp* = C5Me5) or [{α-P2W15Ti3O60(OH)2}2(Cp*Rh)2]16– (D-1) with Ci symmetry, was synthesized in an analytically pure form by a 1:2 -molar ratio reaction of the organometallic precursor [Cp*RhCl2]2 with the separately prepared, monomeric trititanium­(IV)-substituted Wells–Dawson POM, “[P2W15Ti3O59(OH)3]9–” (M-1). The crystalline sample (NaK-D-1) of the water-soluble, mixed sodium/potassium salt of D-1 was obtained in the 14.7% yield, which has been characterized by complete elemental analysis, TG/DTA, FTIR, single-crystal X-ray structure analysis, and solution (183W, 31P, 1H and 13C­{1H}) NMR spectroscopy. Single-crystal X-ray structure analysis revealed that the two species of the protonated Wells–Dawson subunits, “[P2W15Ti3O60(OH)2]10‑” were bridged by the two Cp*Rh2+ groups, resulting in the an overall Ci symmetry. The Cp*Rh2+ groups were linked to the two terminal oxygen atoms of the titanium­(IV) sites and one edge-sharing oxygen atom of the surface Ti–O–Ti bond. The 183W NMR of D-1 dissolved in D2O showed that its solution structure was represented as a dimeric POM with a formula of [{α-P2W15Ti3O60(OH)3}2{Cp*Rh­(OH)}2]16– (D-2) with Ci (or S2) symmetry. A trititanium­(IV)-substituted Wells–Dawson POM-supported organometallic complex has never been reported so far, and thus D-1 in the solid state and D-2 in solution are the first example of this type of complex.