Counteranion-Stabilized Titanium(IV) Isopolyoxocationic Clusters Isolated from Water

Abstract

A novel titanium(IV) oxo cluster comprised solely of Ti, O, and H atoms, [Ti6(Oμ)8(OtH2)20](8+) (Ti6) was synthesized in high yield via controlled hydrolysis and condensation of TiX4 (X = Cl, Br) in the presence of TBAX (TBA = tetrabutylammonium; X = Cl, Br) from water, while reactions of TiI4 and TBAI yielded [Ti8O12(OH2)24](8+) (Ti8). The structures and compositions of the clusters were determined by single-crystal X-ray crystallography, powder X-ray diffraction, inductively coupled plasma atomic emission spectrometry, and energy-dispersive spectrometry. Ti6 is comprised of six-coordinated titanium(IV) atoms bridged with μ2-O atoms, structurally similar to a typical Lindqvist polyoxometalate. On the basis of a structural comparison of Ti6 and Ti8, density functional theory calculations, and spectroscopic analysis, it is evident that both clusters are stabilized by halide counteranions via the formation of hydrogen bonds. This study not only presents the second example of a titanium(IV) isopolyoxocationic cluster isolated from water but also suggests that counteranions are generally important for synthesizing molecular fragments of titanium oxides.

Beyond Charge Balance: Counter‐Cations in Polyoxometalate Chemistry

“…Furthermore, it has recently been proposed that structure formation in titanium polyoxocations can be controlled by virtue of the halide counter‐anion employed. This suggests that some of the principles laid out in this Review may be relevant for more extensive development of metal–oxo polycation chemistry …”

Jenseits von Ladungsausgleich: Gegenkationen in der Polyoxometallat‐Chemie

“…Weiter wurde vorgeschlagen, dass die Strukturbildung von Titanpolyoxokationen durch Einsatz strukturdirigierender Halogenidgegenionen gesteuert werden könnte. Viele der hier besprochenen Prinzipien könnten daher auch für die Weiterentwicklung der Metall‐Oxo‐Polykationchemie relevant sein …”

Aqueous Bismuth Titanium–Oxo Sulfate Cluster Speciation and Crystallization

“…[1] POMs are stabilized by inert, multiply bonded, terminal oxo ligands,afeature unique to these elements.D iscovered more recently, [2] hexavalent uranyl (UO 2 ) 2+ forms hollow capsule POMs with two terminal oxo groups plus bridging peroxide ligands. [12] Recently,W ang and co-workers have brought to light the potential of aqueous Ti-MOCs; [13] the first was structurally characterized in 1987. Finally,Z r/Hf polycations and polyanions have also been isolated.…”

“…Finally,Z r/Hf polycations and polyanions have also been isolated. [13] However,t here is minimal aqueous speciation/solution stability reported, [13c] and there is much to be learned about self-assembly processes in order to fully exploit these exciting "molecular TiO 2 "e ntities. [12] Recently,W ang and co-workers have brought to light the potential of aqueous Ti-MOCs; [13] the first was structurally characterized in 1987.…”

“…Details concerning occupancyr efinements of the disorder model are summarized in the Supporting Information, Figure S11 and crystallography section. [13] Tw o{ Ti 7 }s ubunits sandwich the aforementioned Ther emaining {TiO 6 }i n{ Ti 22 Bi 7 }e xhibit typical TiÀO(1.8-2.0 )and Ti···Ti(3.4-3.7 )distances for Ti-oxo clusters composed exclusively of corner-shared {TiO 6 }o ctahedra.…”