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

Abstract

A novel trititanium(IV)-substituted Wells-Dawson polyoxometalate (POM)-based organometallic complex, i.e., a dimeric POM containing two bridging Cp*Rh(2+) 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 ((183)W, (31)P, (1)H and (13)C{(1)H}) 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*Rh(2+) groups, resulting in the an overall Ci symmetry. The Cp*Rh(2+) 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 (183)W 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.

Synthesis and Molecular Structure of a Novel Compound Containing a Carbonate-Bridged Hexacalcium Cluster Cation Assembled on a Trimeric Trititanium(IV)-Substituted Wells–Dawson Polyoxometalate

“…The 183 W NMR spectra in D 2 O of both Ti 3 Monomer (Figure b) and Ti 16 Tetramer (Figure c) showed three line peaks with 1:2:2 intensity ratio ( Ti 3 Monomer at −158.11, −193.51, and −233.90 ppm; Ti 16 Tetramer at −145.0, −181.5, and −201.4 ppm). These spectra are consistent with the molecular structures of Ti 3 Monomer with C 3 v symmetry and Ti 16 Tetramer with T d symmetry, respectively.…”

“…However, it was always contaminated with soluble unidentified titanium(IV) compounds, i.e., it has never been obtained in pure form. 27 It should also be noted that Na-Ti 3 Monomer has never been transformed to an organic-solvent-soluble form, such as a Bu 4 N + salt. Moreover, Ti 3 Monomer readily reverts to the tetrameric species under acidic or neutral conditions and is stable only under basic conditions.…”

“…In fact, we recently isolated the sodium/potassium salt of the trititanium(IV)-substituted Wells−Dawson POM-supported organometallic complex [{P 2 W 15 Ti 3 O 60 (OH) 2 } 2 (Cp*Rh) 2 ] 16− in analytically pure form, by the reaction of in situ generated Cp*Rh 2+ species with Ti 3 Monomer contaminated with soluble titanium(IV) species. 27 X-ray crystallography revealed that this complex took an unusual dimeric form, composed of the two trititanium(IV)substituted Wells−Dawson POMs bridged by two Cp*Rh 2+ groups.…”

“…The trititanium­(IV)-substituted Wells–Dawson POM has been reported to exist as two stable tetrapod-shaped tetramers formed by the reaction of the trilacunary Wells–Dawson POM [P 2 W 15 O 56 ] 12– with Ti IV , − though not as the monomeric form “[P 2 W 15 Ti 3 O 62 ] 12– ”. One of the tetramers, [{P 2 W 15 Ti 3 O 57.5 (OH) 3 } 4 Cl] 25– ( Ti 12 Tetramer ), is composed of four Wells–Dawson units linked through intermolecular Ti–O–Ti bonds and one encapsulated Cl – ion .…”

“…In our preliminary experiments, we isolated the “[P 2 W 15 Ti 3 O 59 (OH) 3 ] 9– ” monomer ( Ti 3 Monomer ) in the solid state as a water-soluble sodium salt of the form protonated at the Ti–O–Ti sites ( Na-Ti 3 Monomer ). However, it was always contaminated with soluble unidentified titanium­(IV) compounds, i.e., it has never been obtained in pure form . It should also be noted that Na-Ti 3 Monomer has never been transformed to an organic-solvent-soluble form, such as a Bu 4 N + salt.…”