Assembly of titanium embedded polyoxometalates with unprecedented structural features

Abstract

Two titanium embedded polyoxometalates with unprecedented structural features are presented: a monotitanium containing tungstoantimonate Na(13)H(3)[TiO(SbW(9)O(33))(2)]·33 H(2)O featuring a {Ti=O}(2+) moiety (1) and a hexatitanium containing tungstoarsenate K(6)[Ti(4)(H(2)O)(10)(AsTiW(8)O(33))(2)]·30 H(2)O containing a {Ti(4)(H(2)O)(10)}(16+) moiety (2). Both compounds have been fully characterised by single crystal X-ray diffraction, elemental analysis, IR and TGA. 1 is constructed from two α-B-{Sb(III)W(9)O(33)} fragments linked by five sodium cations and an unprecedented square pyramidal Ti(O)O(4) group with a terminal Ti=O bond, and 2 exhibits a Krebs-type structure composed of two {AsTiW(8)O(33)} fragments, where one W(VI) centre has been substituted for a Ti(IV) centre in each, fused together via a belt of four additional Ti(IV) centres. This system represents the tungsten Ti-incorporated polyoxoanion with one of the highest Ti:W ratios so far reported. Additionally, 2 could also be isolated as an n-tetrabutylammonium salt and has been further characterised by electrochemistry and electrospray ionisation (ESI) MS studies. Due to the unique nature of these systems, both have been fully investigated using DFT calculations yielding highly interesting results. Structure 1 has been optimised with five sodium atoms in the belt position, which in addition to reducing the high charge of the cluster influence a stabilisation of the antimony lone pairs. Electrostatic potential calculations highlight the high electronegativity of the terminal oxygen on the titanium centre, enhancing real potentiality as a reactive site for catalysis.

Structure, properties and reactivity of polyoxometalates: a theoretical perspective

“…This system was computationally analysed in the framework of the interest of Ti-derivatives as catalysts for H 2 O 2 -based oxidation processes. 129 Electrostatic potential calculations highlight the high electronegativity of the terminal oxygen on the titanium centre, enhancing real potentiality as a reactive site for catalysis. Another DFT study on a sandwich compound with some special redox properties, built upon four Fe ions coordinated by two lacunary Keggin tungstates, [Fe III 4 (H 2 O) 2 (PW 9 O 34 ) 2 ] 6À (Fig.…”

A novel dicobalt-substituted tungstoantimonate polyoxometalate: Synthesis, characterization, and photocatalytic water oxidation properties

“…There are very few reports on TM-substituted tungstoantimonates that act as WOCs, because Sb 3+ hydrolyzes in aqueous solutions, which to a great extent impedes combination with TM ions into POM clusters. A majority of the addressed TM-substituted tungstoantimonates were prepared through the assembly of the trivacant Keggin polyoxoanion [SbW9O33] 9-with different types of TM ions [27][28][29][30][31][32][33][34]. This is of great interest to us, as it provides an excellent opportunity to further research on tungstoantimonate incorporating TM clusters.…”

Pathways towards true catalysts: computational modelling and structural transformations of Zn-polyoxotungstates

“…Transition metal substituted sandwich-type POMs (TMSPs) are attractive catalyst building blocks, which embed a variety of metal cores between diverse lacunary POM shell types. [28][29][30][31][32][33][34][35] The manifold applications of noble metal-free TMSPs, such as the sandwich-type [Co 4 (H 2 O) 2 (α-PW 9 O 34 ) 2 ], 10,36,37 triggered an intense debate concerning their true active species in various catalytic assays. This in turn has raised further need for the speciation of homogeneous POM catalysts and related systems in order to explore their dynamic transformations for targeted catalyst design.…”