Ti₈O₈(OOCR)₁₆, a New Family of Titanium–Oxo Clusters: Potential NBUs for Reticular Chemistry

Abstract

The reactions of titanium alkoxides with a large excess of different carboxylic acids under nonhydrolytic conditions leads to the reproducible formation of well‐defined nano‐building units (NBUs) with the formula [Ti8O8(OOCR)16] [R = C6H5, C(CH3)3, CH3]. The structures of these titanium–oxo–carboxylate clusters have been determined by crossingdifferent characterization techniques and methodologies (single‐crystal X‐ray diffraction, 13C and 1H NMR spectroscopy, and FTIR spectroscopy). These NBUs are obtained in high yields and, since all the alkoxo ligands have been removed by using solvothermal‐synthesis conditions, they present better stability upon hydrolysis than the often reported alkoxo–carboxylate–titanium–oxo clusters [TinO2n–x/2–y/2(OR′)x(OOCR)y] (n ≥ 2; x ≥ 1; y ≥ 1). In addition, the solubility and transferability of these clusters in common solvents can be tuned by selecting the nature of the organic ligand. Moreover, we also report for the first time, a robust post‐modification of the carboxylate ligands by transesterification reactions on the titanium–oxo clusters. These reactions keep the integrity of the octameric titanium–oxo core intact, while completely exchanging the organic shell of the cluster. This family of [Ti8O8(OOCR)16] clusters, which present 16 points of extension, a symmetric shape, and the ability to be post‐modified with conservation of the core structure, can therefore be considered as interesting NBUs to form new metal–organic frameworks.

Bulk-to-Surface Proton-Coupled Electron Transfer Reactivity of the Metal–Organic Framework MIL-125

“…Parallel studies using a known, well-defined molecular cluster, Ti 8 O 8 (OOC t Bu) 16 (Ti 8 ), 35 provide additional insight into the nature of the photoreduced state and possible degradation pathways. Cluster Ti 8 serves as a model for the nodes of MIL-125, with a similar ring of eight Ti atoms that are connected via bridging oxo ligands in a relatively flat arrangement (Figure 3).…”

A Flexible Photoactive Titanium Metal–Organic Framework Based on a [TiIV3(μ3‐O)(O)2(COO)6] Cluster

“…[6][7][8][9][10][11][12][13] However,for titanium, very few crystalline three-dimensional frameworks with guestaccessible porosity have been described. [19][20][21] Theprime hurdle in the synthesis of Ti MOFs is the high reactivity of the commonly used Ti precursors,w hich are susceptible to fast olation and oxolation and thus readily form ill-defined oxyhydroxides. [19][20][21] Theprime hurdle in the synthesis of Ti MOFs is the high reactivity of the commonly used Ti precursors,w hich are susceptible to fast olation and oxolation and thus readily form ill-defined oxyhydroxides.…”

[Ti8O10(OOCR)12] [R = CH(CH3)2 and CCl3] Carboxylate Titanium Oxo‐Clusters: Potential SBUs for the Synthesis of Metal‐Organic Frameworks

“…In [Ti 8 O 8 (OOCR) 16 ], we demonstrated the presence of two different resonances for the axial and the equatorial ligands in 1 H, 13 C in liquid or solid state NMR spectroscopy. [20] In the same way, the three structurally different carboxylate ligands in 1 are clearly distinguished in 1 H (Figure 5a) and 13 C (Figure 5b) liquid-state NMR spectroscopy. In 1 H NMR, methine peaks stand at δ = 2.13, 2.32, and 2.55 ppm and methyl at δ = 1.03, 1.17, and 1.28 ppm.…”

“…[14] Up to now, the only pure oxo-cluster reported is the [Ti 8 O 8 (OOCR) 16 ] cluster. [20,22] Interestingly, its building unit is composed of eight octahedral titanium atoms and sixteen carboxylates (Figure 3 and Figure 4) 12 ] are the only examples of titanium oxo-cluster presenting only carboxylate ligands. In both cases, the release of all the alkoxides is possible by the use of an excess of carboxylic acids in solvothermal conditions.…”

“…The heating of a solution of titanium(IV) isopropoxide, Ti(O i Pr) 4 , with an excess of isobutyric acid (1/10) 16 ] cluster [20] (one trichloroacetic molecule for each isobutyrate or pivalate ligand). The solution was heated in solvothermal conditions (120°C) during 3 d. The obtained small yellow crystals were analyzed by single-crystal X-ray diffraction.…”