Single-source materials for metal-doped titanium oxide: syntheses, structures, and properties of a series of heterometallic transition-metal titanium oxo cages

Titanium dioxide (TiO(2)) doped with transition-metal ions (M) has potentially broad applications in photocatalysis, photovoltaics, and photosensors. One approach to these materials is through controlled hydrolysis of well-defined transition-metal titanium oxo cage compounds. However, to date very few such cages have been unequivocally characterized, a situation which we have sought to address here with the development of a simple synthetic approach which allows the incorporation of a range of metal ions into titanium oxo cage arrangements. The solvothermal reactions of Ti(OEt)(4) with transition-metal dichlorides (M(II)Cl(2), M = Co, Zn, Fe, Cu) give the heterometallic transition-metal titanium oxo cages [Ti(4)O(OEt)(15)(MCl)] [M = Co (2), Zn (3), Fe (4), Cu (5)], having similar MTi(4)(μ(4)-O) structural arrangements involving ion pairing of [Ti(4)O(OEt)(15)](-) anion units with MCl(+) fragments. In the case of the reaction of MnCl(2), however, two Mn(II) ions are incorporated into this framework, giving the hexanuclear Mn(2)Ti(4)(μ(4)-O) cage [Ti(4)O(OEt)(15)(Mn(2)Cl(3))] (6) in which the MCl(+) fragments in 2-5 are replaced by a [ClMn(μ-Cl)MnCl](+) unit. Emphasizing that the nature of the heterometallic cage is dependent on the metal ion (M) present, the reaction of Ti(OEt)(4) with NiCl(2) gives [Ti(2)(OEt)(9)(NiCl)](2) (7), which has a dimeric Ni(μ-Cl)(2)Ni bridged arrangement arising from the association of [Ti(2)(OEt)(9)](-) ions with NiCl(+) units. The syntheses, solid-state structures, spectroscopic and magnetic properties of 2-7 are presented, a first step toward their applications as precursor materials.     

Sn12O8(OH)4(OEt)28(HOEt)4: an additional member in the family of dodecameric oxo clusters

A tin(IV) oxoalkoxo cluster with unprecedented architecture has been prepared and characterized by single-crystal X-ray diffraction. The cluster obeys the formula Sn 12O 8(OH) 4(OEt) 28(HOEt) 4 (1) and is based on an elongated centrosymmetric assembly of 12 six-coordinate tin centers, 28 peripheral ethoxy groups (terminal and bridging), 8 oxo bridges (mu2 and mu3), 4 hydroxy bridges (mu2), and 4 ethanol molecules that are all bound to tin atoms and interact strongly, through hydrogen bonds, with an ethoxy group located on a vicinal tin atom. This compound has also been fully characterized in solution by multinuclear 1D and 2D NMR, with all of its (119)Sn, (1)H, and (13)C NMR resonances assigned with respect to the structure. Altogether, the data allowed unambiguous location of the hydroxy groups. Information on the exchange of the ethoxy groups is also presented.     

Terminal titanium-ligand multiple bonds. Cleavages of C=O and C=S double bonds with Ti imido complexes

Treatment of (t-)BuN=TiCl(2)Py(3) with 2 equiv lithium ketiminate compound, Li[OCMeCHCMeN(Ar)] (where Ar = 2,6-diisopropylphenyl), in toluene at room temperature gave (t-)BuN=Ti[OCMeCHCMeN(Ar)](2) (1) in high yield. The reaction of 1 with phenyl isocyanate at room-temperature resulted in imido ligand exchange producing PhN=Ti[OCMeCHCMeN(Ar)](2) (2). Compound 1 decomposed at 90 degrees C to form a terminal titanium oxo compound O=Ti[OCMeCHCMeN(Ar)](2) (3) and (t-)BuNHCMeCHCMeNAr (4). Also, the compound 3 could be obtained by reacting 1 with CO(2) under mild condition. Similarly, while 1 reacts with an excess of carbon disulfide, a novel terminal titanium sulfido compound S=Ti[OCMeCHCMeN(Ar)](2) (5) was formed via a C=S bond breaking reaction. A novel titanium isocyanate compound Ti[OCMeCHCMeN(Ar)](2)(NCO)(OEt) (6) was formed on heating 1 with 1 equiv of urethane, H(2)NCOOEt. Compounds 1-6 have been characterized by (1)H and (13)C NMR spectroscopies. The molecular structures of 1, 3, 5, and 6 were determined by single-crystal X-ray diffraction. A theoretical calculation predicted that the cleavage of the C-S double bonds for carbon disulfide with the Ti=N bond of compound 1 was estimated at ca. 21.8 kcal.mol(-1) exothermic.     

Reinforcement of polystyrene by covalently bonded oxo-titanium clusters

Oxo-metallic clusters are employed as inorganic nanobuilding blocks in order to obtain new organic–inorganic hybrid materials. Nanobuilding blocks are well-defined preformed entities which allow a better control of the inorganic domains for the elaboration of hybrid compounds. The oxo-alcoxo cluster Ti₁₆O₁₆(OEt)₃₂ presents a shell of labile ethoxy groups which can be selectively exchanged with the preservation of the oxo-core in order to introduce polymerizable ligands at the surface of this nanobrick. Three different new clusters, Ti₁₆O₁₆(OEt)_32−x(OPhCHCH₂)_x, have been synthesised, each cluster bears exactly 4, 8 and 16 styrenic groups. These functional clusters were copolymerized with styrene leading to three dimensional networks where the inorganic nano-fillers are covalently linked to the organic polymer. Thus new hybrid materials can be obtained and these nanobricks are good models to correlate the structure of hybrid materials and their physical properties especially their mechanical and thermal properties. The structure of the materials in function of the organic–inorganic ratio and in function of the cluster functionalities was investigated by SAXS, and the formation of the different levels of aggregation is reported.     

Highly reduced, polyoxo(alkoxo)vanadium(III/IV) clusters

A family of high nuclearity oxo(alkoxo)vanadium clusters in unprecedentedly low oxidation states is reported, synthesised from simple vanadium diketonate precursors in alcohols under solvothermal conditions. Crystal structures of [V18(O)12(OH)2(H2O)4(EtO)22(O2CPh)6(acac)2] (1), [V16Na2(O)18(EtO)16(EtOH)2(O2CPh)6(HO2CPh)2]infinity (2), [V13(O)13(EtO)15(EtOH)(RCO2)3] in which R=adamantyl (3) or Ph3C (4), and [V11(O)12(EtO)13(EtOH)(Ph3CCO2)2(MePO3)] (5) are reported, revealing these to be {VIII 16VIV 2} (1), {VIII 9VIV 3VV} (3 and 4) and {VIII 3VIV 8} (5) clusters, while 2 consists of isolated {VIII 8VIV 8} clusters bridged into polymeric chains by {Na2(OEt)2} fragments. Solvothermal conditions are essential to the formation of these species, and the level of oxidation of the isolated clusters is in part controlled by the crystallisation time, with the lowest mean-oxidation-state species being isolated by direct crystallisation on controlled cooling of the reaction solutions.     

Self-assembly of alkyl-substituted cubic siloxane cages into ordered hybrid materials

Siloxane-organic hybrids with well-ordered mesostructures were synthesized through the self-assembly of novel amphiphilic molecules that consist of cubic siloxane heads and hydrophobic alkyl tails. The monoalkyl precursors functionalized with ethoxy groups (C(n)H(2n+1)Si(8)O(12)(OEt)(7), 1 Cn, n=16, 18, and 20) were hydrolyzed under acidic conditions with the retention of the siloxane cages, leading to the formation of two-dimensional hexagonal phases by evaporation-induced self-assembly processes. Analysis of the solid-state (29)Si MAS NMR spectra of these hybrid mesostructures confirmed that the cubic siloxane units were cross-linked to form siloxane networks. Calcination of these hybrids gave mesoporous silica, the pore diameter of which varied depending on the alkyl-chain length. We also found that the precursors that had two alkyl chains formed lamellar phases, thus confirming that the number of alkyl chains per cage had a strong influence on the mesostructures. These results expand the design possibility of novel nanohybrid and nanoporous materials through the self-assembly of well-defined oligosiloxane-based precursors.     

Gas phase synthesis of Au clusters deposited on titanium oxide clusters and their reactivity with CO molecules

Titanium oxide clusters were formed in the gas phase by the laser ablation of a Ti rod in the presence of oxygen in a He gas. Not only stoichiometric but also nonstoichiometric titanium oxide clusters, Ti(n)O(2n+x)(+) (n = 1-22 and x = -1-3), were formed. The content of oxygen atoms depends strongly on a partial pressure of oxygen. Gold clusters, Au(m) (m = 1-4), were generated by the laser ablation, which were then deposited on Ti(n)O(2n+x) clusters. The formation of Au(m)Ti(n)O(2n+x)(+) follows electron transfer from Au(m) to Ti(n)O(2n+x)(+). The reactivity of Au(m)Ti(n)O(2n+x)(+) cluster ions with CO was examined for different m, n, and x by the mass spectrometry. It was found that Au(m) on Ti(n)O(2n-1)(+) are less reactive than those on the other Ti(n)O(2n+x)(+) (x = 0 and 1). In addition, the reactivity is highest when Au(m) (m = 1 and 3) is on the stoichiometric titanium oxide (x = 0), whereas the reactivity is also high when Au(2) is on the oxygen-rich titanium oxide (x = 1). The reactivity was found to relate to geometrical structures of Au(m)Ti(n)O(2n+x)(+), which were studied by density functional calculations.     

Extending the family of titanium heterometallic-oxo-alkoxy cages

Here we investigate the synthesis of high-nuclearity heterometallic titanium oxo-alkoxy cages using the reactions of metal chlorides with [Ti(OEt)(4)] or the pre-formed homometallic titanium-oxo-alkoxy cage [Ti(7)O(4)(OEt)(20)] (A). The octanuclear Ti(7)Co(II) cage [Ti(7)CoO(5)(OEt)(19)Cl] (1) (whose low-yielding synthesis we reported earlier) can be made in better yield, reproducibly by the reaction of a mixture of heptanuclear [Ti(7)O(4)(OEt)(20)] (A) and [KOEt] with [Co(II)Cl(2)] in toluene. A alone reacts with [Co(II)Cl(2)] and [Fe(II)Cl(2)] to form [Ti(7)Co(II)O(5)(OEt)(18)Cl(2)] (2) and [Ti(7)Fe(II)O(5)(OEt)(18)Cl(2)] (3), respectively. Like 1, compounds 2 and 3 retain the original Ti(7) fragment of A and the II-oxidation state of the transition metal ions (Tm). In contrast, from the reaction of [Ti(OEt)(4)] with [Cr(II)Cl(2)] it is possible to isolate [Ti(3)Cr(V)O(OEt)(14)Cl] (4) in low yield, containing a Ti(3)Cr(V) core in which oxidation of Cr from the II to V oxidation state has occurred. Reaction of [Mo(V)Cl(5)] with [Ti(OEt)](4) in [EtOH] gives the Ti(8)Mo(V)(4) cage [{Ti(4)Mo(2)O(8)(OEt)(10)}(2)] (5). The single-crystal X-ray structures of the new cages 2, 3, 4, and 5 are reported. The results show that the size of the heterometallic cage formed can be influenced by the nuclearity of the precursor. In the case of 5, the presence of homometallic Mo-Mo bonding also appears to be a significant factor in the final structure.     

Vanadate complexes bearing an imidazolidine-bridged bis(aryloxido) ligand: synthesis and solid state and solution structure

A new imidazolidine-bridged bis(aryloxido) ligand precursor (H(2)L) [H(2)L = 2,2'-(imidazolidine-1,3-diylbis(methylene))bis(4-(1,1,3,3-tetramethylbutyl-2-yl)phenol)] was prepared in a relatively high yield (～60%) via a single-step Mannich condensation of 4-(1,1,3,3-tetramethylbutyl)phenol, ethylenediamine and paraformaldehyde at 2:1:3 molar ratio and characterized by chemical and physical techniques including X-ray crystallography. Reactions of H(2)L with [VO(OEt)(3)] at 1:1 and 1:2 molar ratios in toluene afforded [V(L-κ(3)O,N,N,O)(O)(OEt)] (1) and [V(2)(μ-L-κ(4)O,N,N,O)(μ-OEt)(2)(O)(2)(OEt)(2)] (2), respectively. Alcoholysis of 1 with EtOH enables elimination of one molecule of H(2)L and the formation of 2. Compounds 1 and 2 were characterized by IR and NMR spectroscopy as well as ES-MS experiments. The definitive molecular structure of 2 was provided by a single-crystal analysis and revealed its dinuclear nature, featuring two octahedral vanadium centres bridged by both OEt groups and the L ligand. The (51)V, (1)H and (13)C NMR spectra as well as ES-MS showed that 2 does not stay intact in solution and undergoes dissociation to give 1 and [VO(OEt)(3)].     

pH-dependent isolations and spectroscopic, structural, and thermal studies of titanium citrate complexes

Titanium(IV) citrate complexes (NH(4))(2)[Ti(H(2)cit)(3)].3H(2)O (1), (NH(4))(5)[Fe(H(2)O)(6)][Ti(H(2)cit)(3)(Hcit)(3)Ti].3H(2)O (2), Ba(2)[Ti(H(2)cit)(Hcit)(2)].8H(2)O (3), and Ba(3)(NH(4))(7)[Ti(cit)(3)H(3)(cit)(3)Ti].15H(2)O (4) (H(4)cit = citric acid) were isolated in pure form from the solutions of titanium(IV) citrate with various countercations. The isolated complexes were characterized by elemental analyses, IR spectra, and (1)H NMR and (13)C NMR spectra. The formation of titanium(IV) citrate complexes depends mainly on the pH of the solutions, that is, pH 1.0-2.8 for the formation of ammonium titanium(IV) citrate 1, pH 2.5-3.5 for ammonium iron titanium(IV) citrate 2, pH 2.8-4.0 for dibarium titanium(IV) citrate 3, and pH 5.0-6.0 for ammonium barium titanium(IV) citrate 4. X-ray structural analyses revealed that complexes 2-4 featured three different protonated forms of bidentate citrate anions that chelate to the titanium(IV) atom through their negatively charged alpha-alkoxyl and alpha-carboxyl oxygen atoms. This is consistent with the large downfield shifts of the (13)C NMR spectra for the carbon atoms bearing the alpha-alkoxyl and alpha-carboxyl groups. The typical coordination modes of the barium atoms in complexes 3 and 4 are six-coordinated, with three alpha-alkoxyl groups and three beta-carboxyl groups of citrate ions. The strong hydrogen bonding between the beta-carboxylic acid and the beta-carboxyl groups [2.634(8) A for complex 2, 2.464(7) A for complex 3, and 2.467(7) A for complex 4] may be the key factor for the stabilization of the citrate complexes. The decomposition of complex 3 results in the formation of a pure dibarium titanate phase and 4 for the mixed phases of dibarium titanate and barium titanate at 1000 degrees C.     

Synthesis, structure and physical properties of the manganese(ii) selenide/selenolate cluster complexes [Mn(32)Se(14)(SePh)(36)(PnPr(3))(4)] and [Na(benzene-15-crown-5)(C(4)H(8)O)(2)](2)[Mn(8)Se(SePh)(16)

The synthesis, molecular structures, and magnetic and optical properties of [Mn(32)Se(14)(SePh)(36)(PnPr(3))(4)] and [Na(benzene-15-crown-5)(C(4)H(8)O)(2)](2)[Mn(8)Se(SePh)(16)] have been investigated which are the first examples of manganese chalcogenide cluster complexes, despite known manganese oxo compounds, which comprise more than four manganese atoms.     

Phosphato, chromato, and perrhenato complexes of titanium(IV) and zirconium(IV) containing Kläui's tripodal ligand

Treatment of titanyl sulfate in dilute sulfuric acid with 1 equiv of NaL(OEt) (L(OEt)(-) = [(eta(5)-C(5)H(5))Co{P(O)(OEt)(2)](3)](-)) in the presence of Na(3)PO(4) and Na(4)P(2)O(7) led to isolation of [(L(OEt)Ti)(3)(mu-O)(3)(mu(3-)PO(4))] (1) and [(L(OEt)Ti)(2)(mu-O)(mu-P(2)O(7))] (2), respectively. The structure of 1 consists of a Ti(3)O(3) core capped by a mu(3)-phosphato group. In 2, the [P(2)O(7)](4-) ligands binds to the two Ti's in a mu:eta(2),eta(2) fashion. Treatment of titanyl sulfate in dilute sulfuric acid with NaL(OEt) and 1.5 equiv of Na(2)Cr(2)O(7) gave [(L(OEt)Ti)(2)(mu-CrO(4))(3)] (3) that contains two L(OEt)Ti(3+) fragments bridged by three mu-CrO(4)(2-)-O,O' ligands. Complex 3 can act as a 6-electron oxidant and oxidize benzyl alcohol to give ca. 3 equiv of benzaldehyde. Treatment of [L(OEt)Ti(OTf)(3)] (OTf(-) = triflate) with [n-Bu(4)N][ReO(4)] afforded [[L(OEt)Ti(ReO(4))(2)](2)(mu-O)] (4). Treatment of [L(OEt)MF(3)] (M = Ti and Zr) with 3 equiv of [ReO(3)(OSiMe(3))] afforded [L(OEt)Ti(ReO(4))(3)] (5) and [L(OEt)Zr(ReO(4))(3)(H(2)O)] (6), respectively. Treatment of [L(OEt)MF(3)] with 2 equiv of [ReO(3)(OSiMe(3))] afforded [L(OEt)Ti(ReO(4))(2)F] (7) and [[L(OEt)Zr(ReO(4))(2)](2)(mu-F)(2)] (8), respectively, which reacted with Me(3)SiOTf to give [L(OEt)M(ReO(4))(2)(OTf)] (M = Ti (9), Zr (10)). Hydrolysis of [L(OEt)Zr(OTf)(3)] (11) with Na(2)WO(4).xH(2)O and wet CH(2)Cl(2) afforded the hydroxo-bridged complexes [[L(OEt)Zr(H(2)O)](3)(mu-OH)(3)(mu(3)-O)][OTf](4) (12) and [[L(OEt)Zr(H(2)O)(2)](2)(mu-OH)(2)][OTf](4) (13), respectively. The solid-state structures of 1-3, 6, and 11-13 have been established by X-ray crystallography. The L(OEt)Ti(IV) complexes can catalyze oxidation of methyl p-tolyl sulfide with tert-butyl hydroperoxide. The bimetallic Ti/ Re complexes 5 and 9 were found to be more active catalysts for the sulfide oxidation than other Ti(IV) complexes presumably because Re alkylperoxo species are involved as the reactive intermediates.     

Synthesis,characterization, and rheological properties of hybrid titanium star‐shaped poly(n‐butyl acrylate)

The synthesis of hybrid star‐shaped polymers was carried out by atom transfer radical polymerization of n‐butyl acrylate from a well‐defined multifunctional titanium‐oxo‐cluster initiator. Conditions were identified to prevent possible side reactions among monomer, polymer, and the titanium‐oxo‐cluster ligands. Polymerizations provided linear first‐order kinetics and the evolution of the experimental molecular weight is also linear with the conversion. ¹H DOSY NMR and cleavage of the polymeric branches from the multifunctional initiator by hydrolysis were used to (i) prove the star‐shaped structure of the polymer, and (ii) demonstrate that the shoulder observed on size exclusion chromatograms is not due to a noncontrolled polymerization but to ungrafting of polymeric branches during analysis. Rheological properties of the hybrid star‐shaped poly(n‐butyl acrylate) were studied in the linear regime and show that the Ti‐oxo‐cluster not only increases significantly the viscosity of the polymer relative to its ungrafted arm but has a rheological signature which is qualitatively different from that of stars with organic cores suggesting that the Ti cluster reduces significantly the molecular mobility of the star. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Miniemulsion synthesis of metal-oxo cluster containing copolymer nanobeads

Hybrid nanobeads containing either a manganese-oxo or manganese-iron-oxo cluster have been prepared via the miniemulsion polymerization technique. Two new ligand substituted oxo clusters, Mn(12)O(12)(VBA)(16)(H(2)O)(4) and Mn(8)Fe(4)O(12)(VBA)(16)(H(2)O)(4) (where VBA = 4-vinylbenzoate), have been prepared and characterized. Polymerization of the functionalized metal-oxo clusters with styrene under miniemulsion conditions produced monodispersed polymer nanoparticles as small as ~60 nm in diameter. The metal-oxo polymer nanobeads were fully characterized in terms of synthetic parameters, composition, structure, and magnetic properties.     

A novel polyoxovanadium borate incorporating an organic amine ligand: synthesis and structure of [V12B16O50(OH)7(en)]7-

A novel 1D chain organic-inorganic hybrid polyoxovanadium borate Na[V(12)B(16)O(50)(OH)(7)(en)](2)(enH(2))(6)(enH)(2)(OH)(H(2)O)(19) (1, en = ethylenediamine), based on a [V(12)B(16)O(50)(OH)(7)(en)](7-) cluster unit, has been hydrothermally synthesized and characterized. Interestingly, organic amine is incorporating into the V(12)B(16) clusters.     

Titanium(IV) and zirconium(IV) sulfato complexes containing the Kläui tripodal ligand: molecular models of sulfated metal oxide surfaces

Treatment of titanyl sulfate in about 60 mM sulfuric acid with NaL(OEt) (L(OEt) (-)=[(eta(5)-C(5)H(5))Co{P(O)(OEt)(2)}(3)](-)) afforded the mu-sulfato complex [(L(OEt)Ti)(2)(mu-O)(2)(mu-SO(4))] (2). In more concentrated sulfuric acid (>1 M), the same reaction yielded the di-mu-sulfato complex [(L(OEt)Ti)(2)(mu-O)(mu-SO(4))(2)] (3). Reaction of 2 with HOTf (OTf=triflate, CF(3)SO(3)) gave the tris(triflato) complex [L(OEt)Ti(OTf)(3)] (4), whereas treatment of 2 with Ag(OTf) in CH(2)Cl(2) afforded the sulfato-capped trinuclear complex [{(L(OEt))(3)Ti(3)(mu-O)(3)}(mu(3)-SO(4)){Ag(OTf)}][OTf] (5), in which the Ag(OTf) moiety binds to a mu-oxo group in the Ti(3)(mu-O)(3) core. Reaction of 2 in H(2)O with Ba(NO(3))(2) afforded the tetranuclear complex (L(OEt))(4)Ti(4)(mu-O)(6) (6). Treatment of 2 with [{Rh(cod)Cl}(2)] (cod=1,5-cyclooctadiene), [Re(CO)(5)Cl], and [Ru(tBu(2)bpy)(PPh(3))(2)Cl(2)] (tBu(2)bpy=4,4'-di-tert-butyl-2,2'-dipyridyl) in the presence of Ag(OTf) afforded the heterometallic complexes [(L(OEt))(2)Ti(2)(O)(2)(SO(4)){Rh(cod)}(2)][OTf](2) (7), [(L(OEt))(2)Ti(O)(2)(SO(4)){Re(CO)(3)}][OTf] (8), and [{(L(OEt))(2)Ti(2)(mu-O)}(mu(3)-SO(4))(mu-O)(2){Ru(PPh(3))(tBu(2)bpy)}][OTf](2) (9), respectively. Complex 9 is paramagnetic with a measured magnetic moment of about 2.4 mu(B). Treatment of zirconyl nitrate with NaL(OEt) in 3.5 M sulfuric acid afforded [(L(OEt))(2)Zr(NO(3))][L(OEt)Zr(SO(4))(NO(3))] (10). Reaction of ZrCl(4) in 1.8 M sulfuric acid with NaL(OEt) in the presence Na(2)SO(4) gave the mu-sulfato-bridged complex [L(OEt)Zr(SO(4))(H(2)O)](2)(mu-SO(4)) (11). Treatment of 11 with triflic acid afforded [(L(OEt))(2)Zr][OTf](2) (12), whereas reaction of 11 with Ag(OTf) afforded a mixture of 12 and trinuclear [{L(OEt)Zr(SO(4))(H(2)O)}(3)(mu(3)-SO(4))][OTf] (13). The Zr(IV) triflato complex [L(OEt)Zr(OTf)(3)] (14) was prepared by reaction of L(OEt)ZrF(3) with Me(3)SiOTf. Complexes 4 and 14 can catalyze the Diels-Alder reaction of 1,3-cyclohexadiene with acrolein in good selectivity. Complexes 2-5, 9-11, and 13 have been characterized by X-ray crystallography.     

Formation, solution structure and reactivity of alkylperoxo complexes of titanium

A detailed in situ ¹³C and ¹H NMR spectroscopic characterization of the following families of alkylperoxo complexes of titanium is presented: Ti(η²-OOtBu)_n(OiPr)_4−n, where n = 1–4; binuclear complexes [(iPrO)₃Ti(μ-OiPr)₂Ti(OiPr)₂(η²-OOtBu)] and [(η²-OOtBu)(iPrO)₂Ti(μ-OiPr)₂Ti(OiPr)₂(η²-OOtBu)]; complexes with β-diketonato ligands: Ti(LL)₂(OEt)(η²-OOtBu), Ti(LL)₂(OiPr)(η²-OOtBu), Ti(LL)₂(η²-OOtBu)₂, Ti(LL)₂(OtBu)(η¹-OOtBu), where HLL = acetylacetone, dipivaloylmethane. These alkylperoxo complexes could not be isolated due to their instability and were studied in situ at low temperatures. Whereas the side-on (η²) coordination mode of tert-butylperoxo ligand is generally preferable, the end-on (η¹) coordination caused by spatial hindrance from surrounding bulky ligands is found in two cases. The quantitative data on the reactivity of alkylperoxo complexes found towards sulfides and alkenes were obtained. The system TiO(acac)₂/tBuOOH in C₆H₆ was reinvestigated using ¹³C and ¹H NMR spectroscopy. The structure of the complex Ti(acac)₂{CH₃C(O)(OOtBu)COO} actually formed in this system was elucidated. Four types of titanium(IV) alkylperoxo complexes were detected in the Sharpless–Katsuki catalytic system using ¹³C NMR spectroscopy.     

Unprecedented oxo-titanium citrate complex precipitated from aqueous citrate solutions, exhibiting a novel bilayered Ti8O10 structural core

Aqueous titanium citrate solutions were prepared from the reaction of citric acid with titanium 2-propoxide in a range of molar ratios. Solutions containing two or fewer citrates per titanium resulted in the slow crystallization of an insoluble titanium oxo-citrate complex. Single-crystal X-ray analysis identified the species as Ti(8)O(10)(citrate)(4)(H(2)O)(12).14H(2)O.3HOPr(i)(), crystallized in the tetragonal space group I4(1)/a, with a = 30.775(7) A, c = 14.528(7) A, V = 13 759(8) A(3), and Z = 8. The trianionic citrate ligands supply both carboxylate and alkoxide coordination and stabilize the structure using simultaneous chelating and bridging modes of attachment. The compound is a neutral species, exhibiting titanium in three contrasting environments. Laser Raman microscopy and (13)C CPMAS solid-state NMR data were consistent with those of the X-ray crystal structure. When exposed to air, the crystals rapidly lost water and became a powder. The dehydrated powder was noncrystalline to X-rays and insoluble, but (13)C NMR results demonstrated retention of the carboxylate linkages.     

Synthesis,crystal structure,and photocatalytic property of heterometallic calcium‒titanium oxo cluster with high aqueous stability

Transition Metal Chemistry - A new heterometallic calcium?titanium oxo cluster formulated as [Ca2Ti8(μ3-O)8(AcO)2(OiPr)2(BA)16]·4H2O (BA?=?benzoate) was synthesized and...     

A SERIES OF TRINUCLEAR MOLYBDENUM CLUSTERS WITH LOOSE COORDINATION SITES

<正> The cluster compound Mo3S4[S2P(OEt)2]4(H2O) with a comparatively stable cluster core [Mo3(μ3-S)(μ-S)3]4+ and some labile ligands or loosely coordination sites has been already prepared successfully by a self-assembly reaction. Its surprising chemical reactivity in the reactions of substitution, addition, and oxidation has been noted and used widely for the syntheses of a series of new, trinuclear Mo cluster compounds, of which the structures of the 12 selected compounds characterized by X-ray diffraction analysis are exhibited in diagrams. Meanwhile, those compounds with the same cluster core [Mo3(μ3-S)(μ-S)2]4+ show two groups of characteristic IR bands at ~480 cm-1 for the Mo-(μ-S) vibration and -450cm-1. for the Mo- (μ3-S), and their selected bond distances are tabulated as well.In a cluster-catalyzed homogeneous process, it is important that clusters have loose coordination sites or are coordination unsaturated. In our further research on the medium-valence molybdenum clusters[1], we have foun