Titanium-oxo clusters functionalized with catecholate-type ligands: modulating the optical properties through charge-transfer transitions

Abstract

Four phenylphosphonate-stabilized titanium-oxo clusters with varying functional ligands, namely, [Ti8(μ3-O)2(μ2-O)2(μ2-OiPr)4(OiPr)8(O3PC6H5)4(cat)2] (cat = catecholate), [Ti8(μ3-O)2(μ2-O)2(μ2-OiPr)4(OiPr)8(O3PC6H5)4(O2C10H6)2] (O2C10H6 = naphthalene-2,3-diolate), [Ti6(μ3-O)2(μ2-O)2(μ2-OiPr)4(OiPr)6(O3PC6H5)2(4-DMAB)2] (4-DMAB = 4-dimethylaminobenzoate), and [Ti6(μ3-O)2(μ2-O)2(μ2-OiPr)4(OiPr)6(O3PC6H5)2(4-CBA)2] (4-CBA = 4-cyanobenzoate) were synthesized and structurally characterized. The introduction of catecholate ligands effectively extended the visible absorption region up to 670 nm and reduced the band gap to 2.1 eV. DFT calculations revealed that the ligand-based energy levels could effectively modify the band structure of titanium-oxo clusters. The ligand-to-core charge transfer (LCCT) transition from the functional ligands to the cluster core is responsible for the low-energy charge transfer states. Photoelectrochemical and photocatalytic experiments show that functional ligands have significant influence on the physicochemical properties of titanium-oxo clusters.

Titanium phosphonate oxo-alkoxide “clusters”: solution stability and facile hydrolytic transformation into nano titania

“…5,43 We wanted to continue our investigation on phosphonate-containing titanium alkoxide complexes, which have recently been reported as hydrolytically stable and tested in aquatic media for UV-driven water-splitting. 29,30,32 Titanium alkoxides are oen modied to contain chelating (and bridging) ligands to stabilize the colloid oxide phase. 45 This modication, however, does not necessarily result in hydrolytic stability of the complexes in solutions with high water content or in pure aqueous solvent, which also has been pointed out by others.…”

“…Because of the high reactivity of modi-ed titanium alkoxo-complexes, 28 these compounds readily hydrolyze into titania 5,28 in the presence of moisture or even traces of water in solvents. The photocatalytic activity of titanium (oxo-) complexes and titanium phosphonate complexes has been reported in several recent papers, [29][30][31][32] in which liquid aqueous medium was applied. However, the authors never investigated the fate of the titanium oxo-complexes in water, using any suitable characterization techniques for analysis of possible transformations such as atomic force microscopy or electron microscopy.…”

Synthesis, structural and physicochemical characterization of a new type Ti6-oxo cluster protected by a cyclic imide dioxime ligand

“…Crystalline polyoxo-titanium clusters (PTCs) have attracted considerable attention the last years [1][2][3][4][5][6][7][8][9][10][11][12] due to their potential applications in catalysis, medicine, electro-optics, and nanotechnology. [13][14][15][16][17][18][19] In particular, the precise structural information of PTCs can help the understanding of the binding modes of sensitizers to Ti-O 20 surfaces and potential applications in photoelectronic [21][22][23][24] and photocatalytic chemistry.…”

“…Ball-and-stick representations of the structure of the anion of 1, along with the polyhedral/ball-andstick view of the metallic core are shown in The bond distances of Ti-μ2-O 2− [1.795(1) Å] and Ti-μ3-O 2− [1.931(2) Å] are in the expected range. 3,7,[9][10][11]22,25, The d(Ti-Ohydroxylamine) = 2.002(6) Å is shorter than the d(Ti-Ooxime) = 2.088(5) Å reflecting the better donor properties of Ohydroxylamine in comparison with the Ooxime atoms (Scheme 2). The d(Ti-Ooxime) in 1 is larger than the Ti-Ooxime distances of other Ti IV -oximates reported in the literature, which is due to the different coordination mode, end-on in 1vs.…”

Metal–Organic Frameworks Based on Group 3 and 4 Metals

“…Ti–oxo clusters are widely considered as a TiO 2 nanomaterial at a molecular level, and receive considerable attention due to their structural diversity as well as potential applications in catalysis, biomedicine and environments. [ 48 ] The number of Ti atoms in Ti–oxo clusters ranges from 3 to 32, including Ti 3 , [ 49–52 ] Ti 4 , [ 50,52–57 ] Ti 5 , [ 57 ] Ti 6 , [ 51,52,54,55,57–64 ] Ti 7 , [ 57 ] Ti 8 , [ 54,64,65 ] Ti 9 , [ 51,55,63 ] Ti 10 , [ 66 ] Ti 11 , [ 54–56,63 ] Ti 12 , [ 57,62,66,67 ] Ti 14 , [ 50,56 ] Ti 16 , [ 54,55,61,66 ] Ti 18 , [ 51,57 ] Ti 19 , [ 63 ] Ti 20 , [ 66,68 ] and Ti 32 clusters. [ 69 ] In general, during the assembly of Ti–oxo clusters, it is vital to control the competition between acids and coordinating ligands.…”