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

Black Titanium-Oxo Clusters with Ultralow Band Gaps and Enhanced Nonlinear Optical Performance

A series of catecholate-functionalized titanium-oxo clusters (TOCs), PTC-271 to PTC-277, with atomically precise structures were synthesized and characterized, including distinctive "boat" and "chair" conformations in PTC-273 and PTC-274, respectively. These cluster compounds are prominent for their ultralow optical band gaps, as is visually evident from the rather unusual black TOCs (B-TOCs), PTC-272 to PTC-277. The cluster structures were found to be ultrastable with respect to air, water, organic solvents, and even acidic or basic aqueous solutions in a wide pH range (pH 0-13), owing to the stabilizing effects of catecholate and its derivatives, as well as the carboxylate ligands. Another prominent feature is the occurrence of third-order nonlinear optical (NLO) performance, which has previously been unreported in the field of homometallic titanium-oxo clusters. Open-aperture Z-scan experiments show significant solid-state optical limiting (OL) applications of these B-TOCs, with high laser irradiation stability and low minimum normalized transmittance (T_min) of PTC-273 as ∼0.17. Meanwhile, theoretical calculations indicate that the smaller band gaps of B-TOCs were beneficial for strengthening the NLO response. This work not only represents a significant milestone in the construction of stable low-band gap black titanium oxide materials but also contributes to the mechanism insights into their optical applications.

Titanium-Oxo Clusters with Bi- and Tridentate Organic Ligands: Gradual Evolution of the Structures from Small to Big

Homometallic titanium oxo clusters are one of the most important groups of metal oxo clusters, with more than 300 examples characterized by X-ray structure analyses. Most of them are uncharged and are obtained by partial hydrolysis and condensation of titanium alkoxo derivatives. The cluster cores, ranging from 3 to >50 titanium atoms, are stabilized by organic ligands. Apart from residual OR groups, carboxylato and phosphonato ligands are most frequent. The article critically reviews and categorizes the known structures and works out basic construction principles by comparing the different cluster types.

Synthetic strategies, diverse structures and tuneable properties of polyoxo-titanium clusters

A review of polyoxo-titanium clusters (PTCs), with an emphasis on synthetic methodologies, diverse structures, tuneable optical properties and potential applications.

Titanium coordination compounds: from discrete metal complexes to metal–organic frameworks

Recent advances in titanium based MOFs and relevant titanium molecular compounds will be discussed in this review. Particular attention will be devoted to their promising photoredox properties.

On the Question of Site-Selective Ligand Exchange in Carboxylate-Substituted Metal Oxo Clusters

Reaction of [Ti₄Zr₄O₆(OBu)₄(OMc)₁₆] (OMc = methacrylate) with acetylacetone (acacH) resulted in dissection of the cluster and formation of [Ti(OBu)₂(acac)₂] and the smaller cluster [Ti₂Zr₄O₄(OMc)₁₆]. In contrast, the same reaction with [Zr₆O₄(OH)₄(OOCR)₁₂]₂·6RCOOH (R = Et, CH₂CH=CH₂) led to site-selective substitution of two carboxylate ligands and formation of isostructural [Zr₆O₄(OH)₄(OOCR)_12–x(acac)_x]₂·6RCOOH (x ≤ 1).

Retention of the Cluster Core Structure during Ligand Exchange Reactions of Carboxylato-Substituted Metal Oxo Clusters

The exchange of the carboxylato ligands of Zr4O2(methacrylato)12 in reactions with carboxylic acids proceeds with retention of the composition and structure of the cluster core. This was concluded from exchange/re-exchange experiments and from comparison of the IR bands of the cluster core of the original and ligand-exchanged clusters. The IR bands were assigned on the basis of DFT calculations. Scrambling reactions between two Zr4O2(OOCR)12 clusters with different carboxylato ligands are a new way to prepare mixed-ligand oxo clusters.