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).

Crown-ether-like structures derived from a Ti(8)O(8) (carboxylate)(16) metallacycle.

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.

Acetic Acid Mediated Synthesis of Phosphonate-Substituted Titanium Oxo Clusters.

New phosphonate/acetate-substituted titanium oxo/alkoxo clusters were prepared from Ti(OiPr)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 [Ti6O4(OiPr)10(OAc)2(O3PR)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, [Ti5O(OiPr)11(OAc)(O3PCH2CH2CH2Br)3] and [Ti5O3(OiPr)6(OAc)4(O3P-xylyl)2], were only isolated in special cases.

Mixed-Metal Oxo Clusters Structurally Derived from Ti6O4(OR)8(OOCR')8.

The mixed-metal oxo clusters FeTi5O4(OiPr)4(OMc)10 (OMc = methacrylate), Zn2Ti4O4(OiPr)2(OMc)10, Cd4Ti2O2(OAc)2(OMc)10(HOiPr)2, [Ca2Ti4O4(OAc)2(OMc)10] n , and [Sr2Ti4O4(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 Ti6O4(OR)8(OOCR')8. The Ca and Sr derivatives consist of chains of condensed clusters.

Ion-Size-Dependent Formation of Mixed Titanium/Lanthanide Oxo Clusters.

The mixed-metal oxo clusters LnTi4O3(OiPr)2(OMc)11 (Ln = La, Ce; OMc = methacrylate), Ln2Ti6O6(OMc)18(HOiPr) (Ln = La, Ce, Nd, Sm) and Ln2Ti4O4(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.

Preparation of Carboxylato-Coordinated Titanium Alkoxides from Carboxylic Anhydrides: Alkoxido Group Transfer from Metal Atom to Carbonyl Group.

Reaction of titanium(IV) isopropoxide, Ti(OiPr)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 Ti2(OiPr)6(µ2-OOC-C6H4-COOiPr)(η1-OOC-C6H4-COOiPr)(iPrOH) is bridging and the other is η1-coordinated. When the reaction is performed in the presence of 1 mol-equiv. of acetic acid, the oxido cluster Ti6(µ3-O)6(OiPr)6(µ2-OOC-C6H4-COOiPr)6 was instead obtained. The µ3-oxygen groups in the latter compound are due to esterification of acetic acid by the cleaved isopropyl alcohol.

Phosphonate-substituted zirconium oxo clusters.

ABSTRACT: The phosphonate-substituted zirconium oxo clusters Zr6O2(OBu)12(O3PPh)4 and Zr7O2(OiPr)12(O3PCH2CH2CH2Br)6, with octahedrally coordinated Zr atoms, were synthesized by reaction of zirconium alkoxides with phosphonic acid bis(trimethylsilyl) esters. The basic structural motif are Zr3O(µ2-OR)3(OR)3 units which are connected in different ways.

Influence of the Ti(OiPr)4: methacrylic acid ratio on the formed oxo/alkoxo clusters.

ABSTRACT: When Ti(OiPr)4 was reacted with increasing proportions of methacrylic acid (McOH), the compounds Ti2(OiPr)6(OMc)2(iPrOH), Ti6O4(OiPr)8(OMc)8, Ti9O8(OiPr)4(OMc)16, and Ti8O8(OMc)16 were obtained in sequence. This allowed conclusions on the relative ratio of substitution and hydrolysis reactions, the latter being due to ester formation between the acid and cleaved alcohol. This ratio is also influenced by the reaction temperature, since Ti4O2(OiPr)6(OMc)6 was formed instead of Ti6O4(OiPr)8(OMc)8 at lower temperature with the same precursor ratio.

Titanium oxo/alkoxo clusters with both phosphonate and methacrylate ligands.

ABSTRACT: The clusters Ti5O(OiPr)11(OMc)(O3PR)3 (OMc = methacrylate; R = Et, CH2CH2CH2Br) and Ti10(OiPr)16(OMc)4(O3PCH2CH=CH2)10 were obtained when Ti(OiPr)4 was reacted with the corresponding bis(trimethylsilyl) phosphonate and methacrylic acid. Oxo clusters of the composition Ti6O4(OiPr)10(OMc)2(O3PR)2, with a variety of groups R (Et, Ph, CH=CH2, CH2Ph, CH2CH=CH2, CH2CH2CH2Br, CH2CH2CN, CH2C(O)Me, CH2CH2OC(O)C(Me)=CH2), were formed instead, when a stoichiometric amount of water was added to the reaction mixture.

A coordination polymer with unusual structural features from imidazolylbutyric acid and titanium isopropoxide.

ABSTRACT: The coordination polymer [Ti(OiPr)3(OOCCH2CH2CH2C3N2H3)] n was prepared from 4-(imidazol-1-yl)butyric acid and titanium isopropoxide. The structure of the compound is remarkable, as the carboxylate group is coordinated in a chelating manner and no dimerization of the Ti(OiPr)3 groups through OR bridges was observed.

Photoluminescence as Complementary Evidence for Short-Range Order in Ionic Silica Nanoparticle Networks.

Recently we published the synthesis of new hybrid materials, ionic silica nanoparticles networks (ISNN), made of silica nanoparticles covalently connected by organic bridging ligands containing imidazolium units owing to a "click-chemistry-like" reaction. Among other techniques small-angle X-ray scattering (SAXS) experiments were carried out to get a better picture of the network extension. It turned out that the short-range order in ISNN materials was strongly influenced by the rigidity of the bridging ligand, while the position of the short-range order peaks confirmed the successful linking of the bridging ligands. The photoluminescence experiments reported in this communication revealed strongly enhanced emission in the hybrid material in comparison with neat imidazolium salts. Moreover the shift of the emission maximum toward longer wavelengths, obtained when varying the aromatic ring content of the bridging ligand, suggested the existence of strong π-π stacking in the hybrid material. Experiments revealed a stronger luminescence in those samples exhibiting the higher extent of short-range order in SAXS.