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Homometallic titanium oxo clusters (TOC) are one of the most important groups of metal oxo clusters. In a previous article, TOC structures with carboxylato and phosphonato ligands were reviewed and categorized. This work is now extended to clusters with other ligands. Comparison of the different cluster types shows how the interplay between condensation of the titanium polyhedra by means of bridging oxygen atoms and the coordination characteristics of the ligands influences the cluster structures and allows working out basic construction principles of the cluster core., (© 2024 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

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., (© 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

Reaction of [Ti 4 Zr 4 O 6 (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 [Ti 2 Zr 4 O 4 (OMc) 16 ]. In contrast, the same reaction with [Zr 6 O 4 (OH) 4 (OOCR) 12 ] 2 · 6RCOOH (R = Et, CH 2 CH=CH 2 ) led to site-selective substitution of two carboxylate ligands and formation of isostructural [Zr 6 O 4 (OH) 4 (OOCR) 12- x (acac) x ] 2 · 6RCOOH ( x ≤ 1).

The exchange of the carboxylato ligands of Zr 4 O 2 (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 Zr 4 O 2 (OOCR) 12 clusters with different carboxylato ligands are a new way to prepare mixed-ligand oxo clusters.

Co3 O4 -modified CeO2 (Co/Ce 1:4) was prepared by a combination of sol-gel processing and solvothermal treatment. The distribution of Co was controlled by means of the synthesis protocol to yield three different morphologies, namely, Co3 O4 nanoparticles located on the surface of CeO2 particles, coexistent Co3 O4 and CeO2 nanoparticles, or Co oxide structures homogeneously distributed within CeO2 . The effect of the different morphologies on the properties of Co3 O4 -CeO2 was investigated with regard to the crystallite phase(s), particle size, surface area, and catalytic activity for CO oxidation. The material with Co3 O4 nanoparticles finely dispersed on the surface of CeO2 particles had the highest catalytic activity., (© 2014 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.)

The mixed-metal oxo clusters LnTi 4 O 3 (O i Pr) 2 (OMc) 11 (Ln = La, Ce; OMc = methacrylate), Ln 2 Ti 6 O 6 (OMc) 18 (HO i Pr) (Ln = La, Ce, Nd, Sm) and Ln 2 Ti 4 O 4 (OMc) 14 (HOMc) 2 (Ln = Sm, Eu, Gd, Ho) have been synthesized from titanium isopropoxide, the corresponding lanthanide acetate and methacrylic acid. The type of cluster obtained strongly depends on the size of the lanthanide ion.

The mixed-metal oxo clusters FeTi 5 O 4 (O i Pr) 4 (OMc) 10 (OMc = methacrylate), Zn 2 Ti 4 O 4 (O i Pr) 2 (OMc) 10 , Cd 4 Ti 2 O 2 (OAc) 2 (OMc) 10 (HO i Pr) 2 , [Ca 2 Ti 4 O 4 (OAc) 2 (OMc) 10 ] n , and [Sr 2 Ti 4 O 4 (OMc) 12 (HOMc) 2 ] n were obtained from the reaction of titanium alkoxides with the corresponding metal acetates and methacrylic acid. Their structures are derived from Ti clusters with the composition Ti 6 O 4 (OR) 8 (OOCR') 8 . The Ca and Sr derivatives consist of chains of condensed clusters.

Compound [Ni(AEAPTS)2]3[Fe(CN)6]2 (AEAPTS = N-(2-aminoethyl)-3-aminopropyltrimethoxysilane), in which Ni(2+) and Fe(3+) ions are ferromagnetically coupled through cyano bridges, was prepared. Sol-gel processing of the AEAPTS derivative resulted in incorporation of the cyanometallate in silica. The obtained material is magnetically ordered below 22 K with an effective magnetic moment μeff of 4.46 μB at room temperature, a maximum of 8.60 μB at approximately 15 K and a narrow hysteresis at 2 K, with a saturation remanence of about 300 emu mol(-1) and a coercitivity of 0.03 T., (© 2014 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA. This is an open access article under the terms of Creative Commons Attribution NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.)

New phosphonate/acetate-substituted titanium oxo/alkoxo clusters were prepared from Ti(O i Pr) 4 and bis(trimethylsilyl) phosphonates in the presence of acetic acid, which served to generate water in situ through ester formation. The process led to clusters with a higher degree of condensation than in previously known phosphonate-substituted titanium oxo clusters. The clusters [Ti 6 O 4 (O i Pr) 10 (OAc) 2 (O 3 PR) 2 ] (OAc = acetate) were obtained for a large variety of functional and non-functional groups R under a range of reaction conditions. This cluster type, which is also retained in solution, therefore appears to be very robust. Two other clusters, [Ti 5 O(O i Pr) 11 (OAc)(O 3 PCH 2 CH 2 CH 2 Br) 3 ] and [Ti 5 O 3 (O i Pr) 6 (OAc) 4 (O 3 P-xylyl) 2 ], were only isolated in special cases.

Mixed-metal clusters have been obtained from the reaction of titanium alkoxides with either strontium or lead acetate and methacrylic acid. The structures of the clusters are derived from the metallacycle Ti8 O8 (methacrylate)16 . The Sr and Pb atoms in Sr2 Ti8 O8 X2 (OOCMe)2 (methacrylate)16 (X: acetate or OiPr) and Pb2 Ti8 O8 (OBu)2 X2 (methacrylate)16 (BuOH)2 (X: acetate or methacrylate) occupy the central cavity of the Ti8 O8 ring. In addition to the crown-ether-like coordination of the ring oxygen atoms to the Sr or Pb atoms, bridging carboxylate ligands support the coordination of the latter atoms. In the compound Pb2 Ti6 O5 (OiPr)3 X(methacrylate)14 (X: OiPr or methacrylate), the lead atoms are coordinated by a fragment of the Ti8 O8 (methacrylate)16 metallacycle., (© 2013 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.)

Copper oxide nanoparticles within hollow mesoporous silica spheres were prepared by binding/adsorbing Cu 2+ or [Cu(NH 3 ) 4 (H 2 O) 2 ] 2+ ions on the surface of carbon spheres, followed by formation of a mesoporous silica shell by sol-gel processing and calcination in air. The CuO nanoparticles can subsequently be converted into Cu 3 N nanoparticles by nitridation with ammonia. The effect of the different copper precursors, i.e. Cu 2+ and [Cu(NH 3 ) 4 (H 2 O) 2 ] 2+ , on the nanocomposites was studied. CuO nanoparticles on the outer surface of hollow silica spheres were obtained by thermal treatment of hollow CuSiO 3 spheres in air. Nitridation of the CuSiO 3 spheres with ammonia resulted in Cu 3 N@SiO 2 composites, with aggregated Cu 3 N nanoparticles on hollow silica spheres.

The treatment of titanium alkoxides with 1,5-pentanedioxime or 2,5-hexanedioxime resulted in the formation of complexes [{Ti L (OR) 2 } 2 ] in which the dioximate ligands ( L ) bridge a dimeric Ti 2 (μ 2 -OR) 2 unit. The structures of the complexes were determined by single-crystal structure analysis, ESI mass spectrometry, and 1D and 2D solution NMR spectroscopy. In contrast, the treatment of titanium alkoxides with dioximes bearing cyclic linkers, such as cyclohexyl or aryl groups, resulted in insoluble polymeric compounds. The treatment of various bis(salicylaldiminates) with titanium and zirconium alkoxides resulted in compounds with the same composition [{Ti L (OR) 2 } 2 ], in which, however, two monomeric Ti(OR) 2 units are bridged by the ligands L . The two structural possibilities can be distinguished by low-energy collision-induced dissociation owing to their different fragmentation patterns.

Zinc(II) complexes with dangling functional organic groups were synthesized by reaction of zinc acetate with a series of bifunctional p -substituted benzene derivatives (a combination of carboxylate, oximate, amino, β-ketoimine, and salicylaldime groups). Selective coordination to carboxylate groups was observed when the second functional group was an oxime or β-ketoimine group. When the second group was an amine or salicylaldimine moiety, these groups were additionally coordinated. From the reaction with p -aminobenzoic acid, the compound [Zn 2 (OOCCH 3 )(OOC-C 6 H 4 -NH 2 ) 3 ] ∞ was crystallized. It is a three-dimensional coordination polymer with bridging aminobenzoate ligands.

Reaction of titanium(IV) isopropoxide, Ti(O i Pr) 4 , with an equimolar amount of phthalic anhydride resulted in the transfer of an isopropoxido group from the metal atom to one carbonyl group of the anhydride and coordination of the thus formed monoester to the titanium atom. One monoester ligand in Ti 2 (O i Pr) 6 (μ 2 -OOC-C 6 H 4 -COO i Pr)(η 1 -OOC-C 6 H 4 -COO i Pr)( i PrOH) is bridging and the other is η 1 -coordinated. When the reaction is performed in the presence of 1 mol-equiv. of acetic acid, the oxido cluster Ti 6 (μ 3 -O) 6 (O i Pr) 6 (μ 2 -OOC-C 6 H 4 -COO i Pr) 6 was instead obtained. The μ 3 -oxygen groups in the latter compound are due to esterification of acetic acid by the cleaved isopropyl alcohol.

A series of difunctionalized monosubstituted octasilsesquioxanes have been synthesized that bear ester, amino acid, alcohol, haloalkyl, or azido functional groups. These units are suitable nanobuilding blocks for the preparation of new organic-inorganic hybrid materials., (Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

An unprecedented, intramolecular metal-to-metal silyl ligand migration reaction has been discovered in a series of phosphido-bridged iron-platinum complexes and which may be triggered by an external nucleophile. Thus, reaction of solutions of [(OC)3-(R1/3Si)Fe(mu-PR2R3)Pt(1,5-COD) (1a R1 = OMe, R2 = 3 = Ph; 1b R1 = OMe, R2 = R3 = Cy; 1c R1 = Ph, R2 = R3 = Ph; 1d R1 = Ph, R2 = R3 = Cy; 1e R1 = Ph, R1 = H, R3 = Ph) in CH2Cl2 with CO rapidly afforded the corresponding complexes [(OC)4Fe(mu-PR2R3)Pt(SiR1/3)-(CO)] (2a-e) in which the silyl ligand has migrated from Fe to Pt, while two CO ligands have been ligated, one on each metal. When 1a or 1c was slowly treated with two equivalents of tBuNC at low temperature, quantitative displacement of the COD ligand was accompagnied by silyl migration from Fe to Pt and coordination of an isonitrile ligand to Fe and to Pt to give [(OC)3-(tBuNC)Fe(mu-PPh2)Pt[Si(OMe)3](CNtBu)] (3a) and [(OC)3(tBuNC)-Fe(mu-PPh2)Pt[SiPh3](CNtBu)] (3c). Reaction of 2a with one equivalent of tBuNC selectively led to substitution of the Pt-bound CO to give [(OC)4-Fe(mu-PCy2)Pt[Si(OMe)3](CNtBu)] (4b), which reacted with a second equivalent of tBuNC to give [(OC)4Fe(mu-PCy2)-Pt[Si(OMe)3](CNtBu)2] (5b) in which the metal-metal bond has been cleaved. Opening of the Fe-Pt bond was also observed upon reaction of 3a with tBuNC to give [(OC)3(tBuNC)-Fe(mu-PPh2)Pt[Si(OMe)3](CNtBu)2] (6). The silyl ligand migrates from Fe, in which it is trans to mu-PR2R3 in all the metal-metal-bonded complexes, to a position cis to the phosphido bridge on Pt. However, in 5a,b and 6 with no metal-metal bond, the Pt-bound silyl ligand is trans to the phosphido bridge. The intramolecular nature of the silyl migration, which may be formally viewed as a redox reaction, was established by a cross-over experiment consisting of the reaction of 1a and 1d with CO; this yielded exclusively 2a and 2d. The course of the silyl-migration reaction was found to depend a) on the steric properties of the -SiR1/3 ligand, and for a given mu-PR2R3 bridge (R2 = R3 = Ph), the migration rate decreases in the sequence Si(OMe)3> SiMe2Ph> SiMePh2>>SiPh3; b) on the phosphido bridge and for a given silyl ligand (R1 = OMe), the migration rate decreases in the order mu-PPh2 >> mu-PHCy; c) on the external nucleophile since reaction of 1c with two equivalents of P(OMe)3, P(OPh)3 or Ph2PCH2C(O)Ph led solely to displacement of the COD ligand with formation of 11a-c, respectively, whereas reaction with two equivalents of tBuNC gave the product of silyl migration 3c. Reaction of [(OC)3-[(MeO)3Si]Fe(mu-PPh2)Pt(PPh3)2] (7a) with tBuNC (even in slight excess) occurred stereoselectively with replacement of the PPh3 ligand trans to mu-PPh2, whereas reaction with CO led first to [(OC)3((MeO)3Si)Fe(mu-PPh2)Pt(CO)-(PPh3)] (8a), which then isomerized to the migration product [(OC)4Fe(mu-PPh2)Pt[Si(OMe)3](PPh3)] (9a). Most complexes were characterized by elemental analysis, IR and 1H, 31P, 13C, and 29Si NMR spectroscopy, and in five cases by X-ray diffraction.

Air, air, air…︁ and some solid skeleton; this is the basis for an interesting class of materials-the aerogels (shown schematically on the right). Can one therefore speak of "simple" chemistry? The design of such a filigrane network requires the very careful control of chemical parameters. The reward is an assortment of different property profiles owing to the richness of possible variations., (Copyright © 1998 WILEY-VCH Verlag GmbH, Weinheim, Fed. Rep. of Germany.)