Ti Distance Research Articles

High-pressure magnetic and structural properties of TiOX (X=Cl, Br)

We report high-pressure diffraction and magnetization measurements to demonstrate that the partial collapse of electronic gap at high-pressure insulator to metal transition reported in TiOCl (C. Kuntscher et al. Phys. Rev. B 74 184402 (2006).) corresponds to a Ti 3+–Ti 3+ dimerization at room temperature within the space group P2 1/ m. The shortest Ti–Ti distance is comparable to that of the Ti metal, but a Peierls-like distortion prevents a metallic behaviour.

Eu(III) Sorption to TiO2 (Anatase and Rutile): Batch, XPS, and EXAFS Studies

The sorption of Eu(III) on anatase and rutile was studied as a function of ionic strength, humic acid (HA, 7.5 mg/L), and electrolyte anions over a large range of pH (2-12). The presence of HA significantly affected Eu(III) sorption to anatase and rutile. The sorption of Eu(III) on anatase and rutile was independent of ionic strength. Results of an X-ray photoelectron spectroscopy (XPS) analysis showed that Eu(III) was chemically present within the near-surface of TiO2 due to the formation of triple bond SOEu and triple bond SOHAEu complexes. An extended X-ray absorption fine structure (EXAFS) technique was applied to characterize the local structural environment of the adsorbed Eu(III), and the results indicated that Eu(III) was bound to about seven or eight O atoms at a distance of about 2.40 A. The functional groups of surface-bound HA were expected to be involved in the sorption process. The measured Eu-Ti distance confirmed the formation of inner-sphere sorption complexes on a TiO2 surface.

Dimetallocene carbonyls: The limits of the 18-electron rule and metal–metal multiple bonding in highly unsaturated molecules of the early transition metals

The structures and energetics of Cp 2M 2(CO) (M = Mn, Cr, and Ti) have been investigated by density functional theory (DFT) for comparison with previously reported studies on Cp 2V 2(CO). For all four metals energetically competitive structures are found with singlet, triplet, quintet, and septet spin multiplicities. However, significant spin contamination was found for the triplet Cp 2Mn 2(CO) and Cp 2Cr 2(CO) structures. The lowest energy structures for Mn and Cr are both septet states, namely Cp 2Mn 2(η 2-μ-CO) with a four-electron donor bridging carbonyl group and an Mn Mn distance of 2.523 Å and Cp 2Cr 2(μ-CO) with a two-electron donor bridging carbonyl group and a Cr Cr distance of 2.436 Å. However, for the Ti analogue the lowest energy structure is singlet Cp 2Ti 2(η 2-μ-CO) with a four-electron donor bridging carbonyl group and a Ti Ti distance of 2.364 Å. The higher energy singlet structures of Cp 2M 2(CO) have the very short metal–metal distances of 1.879 Å (M = Mn) and 1.729 Å (M = Cr) suggesting very high formal bond orders of five and six, respectively.

Synthesis and crystal structures of two (cyclopentadienyl)titanium(III) hydroborate complexes, [Cp ∗TiCl(BH 4)] 2 and Cp 2Ti(B 3H 8)

Treatment of Cp ∗TiCl 3 and Cp 2TiCl 2 with NaB 3H 8 affords the titanium(III) hydroborate compounds [Cp ∗TiCl(BH 4)] 2 and Cp 2Ti(B 3H 8), respectively. The former compound arises by means of a new reaction, the metal-induced fragmentation of the B 3H 8 anion, and can also be made by treating Cp ∗TiCl 3 with LiBH 4. The latter compound has been previously described, but not characterized crystallographically. Both compounds have been studied by single crystal X-ray diffraction. Dimeric [Cp ∗TiCl(BH 4)] 2 has bridging chloride ligands and terminal Cp ∗ and BH 4 ligands. The Ti–Ti distance is 3.452(1) Å, which indicates that there is no metal–metal bonding interaction. The Ti–Cl distances are 2.440(2) Å and the Ti–Cl–Ti and Cl–Ti–Cl angles of 89.97(8) and 90.03(8)° so that the Ti 2Cl 2 unit is nearly a perfect square. The BH 4 groups are each tridentate, with a Ti–B distance of 2.220(9) Å and an average Ti–H distance of 1.98(5) Å. In Cp 2Ti(B 3H 8), the B 3H 8 ligand is bidentate, as is usually seen, and the Ti–B and Ti–H distances are 2.600(3) and 1.96(2) Å. The dihedral angle between the Ti–B(1)–B(2) plane and the B(1)–B(2)–B(3) plane is 123.4°. The Ti–B distances are 0.04 Å longer than those in niobium analog, Cp 2Nb(B 3H 8), despite the fact that the single bond metallic radius of Ti is 0.02 Å smaller than that of Nb. This lengthening of the bond is probably a consequence of the presence of one fewer skeletal bonding electron in Cp 2Ti(B 3H 8).

“Unusual Ln3+ substitutional defects”: The local chemical environment of Pr3+ and Nd3+ in nanocrystalline TiO2 by Ln–K edge EXAFS

The local chemical environment of the trivalent lanthanide cations in anatase TiO2 nanopowders doped with 1 mol% of Pr or Nd, prepared via a sol–gel technique, has been studied by means of EXAFS at the Pr and Nd–K edge. Titanium dioxide can be considered an “unusual” host for doping with Ln3+ ions due to the large mismatch of both charge and ionic radii between the dopant and the host constituent cations. However, it can be demonstrated that the lanthanide ions enter the anatase structure as substitutional defects with respect to Ti, but that the amount of disorder around the substitutional defects is very large. For both Pr3+ and Nd3+ ions, the Ln–O and Ln–Ti distances have been found to increase by about 0.45 Å, with respect to what is found for the Ti–O and Ti–Ti distances in pure anatase. Valence-bond calculations have been used to validate the Ln–O distances obtained by the EXAFS fitting. Finally, no evidences for oxygen vacancies clustering around the substitutional defects have been found. Luminescence spectroscopy has shown that the lanthanide ions do not segregate in oxide or pyrochlore impurities phases.

High-pressure polymorphic transformation of rutile to α-PbO 2-type TiO 2 at {0 1 1} R twin boundaries

The presence of nano-scale lamellae of the α-PbO 2-type polymorph of TiO 2 sandwiched between twinned rutile inclusions in jadeite has been confirmed by electron diffraction and high-resolution transmission electron microscopy, backed up by image simulation techniques, from ultrahigh-pressure jadeite quartzite at Shuanghe in the Dabie Mountains, China. The crystal structure is orthorhombic with lattice parameters a = 4.58 Å, b = 5.42 Å, c = 5.02 Å and space group Pbcn. A three-dimensional structural model has been constructed for the rutile to α-PbO 2-type TiO 2 phase transformation based on high-resolution electron microscopic images. Computer image simulation and structural model analysis reveal that rutile {0 1 1} R twin interface is a basic structural unit of α-PbO 2-type TiO 2. Nucleation of α-PbO 2-type TiO 2 lamellae 1–2 nm thick is caused by the displacement of one half of the titanium cations within the {0 1 1} R twin slab. This displacement reduces the Ti–O–Ti distance and is favored by high pressure.

Crystal chemistry of layered carbide, Ti 3(Si 0.43Ge 0.57)C 2

The crystal structure of a layered ternary carbide, Ti 3(Si 0.43Ge 0.57)C 2, was studied with single-crystal X-ray diffraction. The compound has a hexagonal symmetry with space group P6 3/mmc and unit-cell parameters a=3.0823(1) Å, c=17.7702(6) Å, and V=146.21(1) Å 3. The Si and Ge atoms in the structure occupy the same crystallographic site surrounded by six Ti atoms at an average distance of 2.7219 Å, and the C atoms are octahedrally coordinated by two types of symmetrically distinct Ti atoms, with an average C–Ti distance of 2.1429 Å. The atomic displacement parameters for C and Ti are relatively isotropic, whereas those for A (=0.43Si+0.57Ge) are appreciably anisotropic, with U 11 (= U 22) being about three times greater than U 33. Compared to Ti 3SiC 2, the substitution of Ge for Si results in an increase in both A–Ti and C–Ti bond distances. An electron density analysis based on the refined structure shows that each A atom is bonded to 6Ti atoms as well as to its 6 nearest neighbor A site atoms, whether the site is occupied by Si or Ge, suggesting that these bond paths may be significantly involved with electron transport properties.

EXAFS investigation of the thermally induced structuring of titanium-doped amorphous carbon films

Amorphous carbon layers doped with 8.5 at.% titanium (a-C:Ti) were produced by dual-source magnetron sputter deposition. To investigate the local atomic environment of Ti, EXAFS analysis was performed for as-deposited layers and after annealing to 700, 1100 and 1300 K, as well as for Ti and TiC bulk samples. After deposition of the a-C:Ti films, most Ti atoms are homogeneously distributed in an amorphous carbon matrix. Annealing to 700 K slightly increases the order in the Ti environment, but TiC-like crystallization is hardly existent. After annealing to 1100 K, clear correspondence to the TiC standard is observed. Annealing to 1300 K further increases the order and TiC crystallite size. Fitting of EXAFS data to a theoretical model was used to derive quantitative parameters for a-C:Ti layers, e.g., Ti–C and Ti–Ti distances and ordering parameters.

Titanium and Zirconium Complexes of a Phosphorus-Containingp-tert-Butylcalix[5]arene Ligand: Importance of Metal and Conformation on Ligand/Metal Binding

Binding of a calix[5]arene containing a single phosphorus ligand and three hydroxyl groups, calix[5]PNMe2(OH)3, 1, toward titanium and zirconium is investigated to yield insight into the factors that determine the strength of the phosphorus/metal interaction within the constraint of the calix[5]arene. Treatment of 1 with tetrakis(dimethylamino)titanium yields three complexes, 4a, 4b, and 4c, each of which shows the loss of 3 mol of dimethylamine in the reaction with the titanium bound to three oxygens. Treatment of 1 with tetrakis(diethylamino)zirconium proceeds similarly, although only two products, 5a and 5b, were isolated. X-ray structures of the products were obtained. Complexes 4a and 5a show similar geometries, with the calix[5]arene in an approximate cone conformation and the phosphorus lone pair directed toward the metal. The P...M distances are, however, markedly different: 3.69 A in 4a and 3.18 A in 5a, the former indicative of no interaction and the latter a weak one. Complexes 4b and 5b each are dimers, featuring a planar four-membered M-O-M-O ring; however, the titanium is five-coordinate in 4b with no phosphorus/metal bond, while the zirconium in 5b is six-coordinate with a P-Zr distance of 2.95 A. Complex 4c is monomeric with the calix[5]arene in an approximate 1,2-alternate conformation with a P...Ti distance of 2.90 A. The two most significant aspects controlling the phosphorus/metal contact are the metal, with the larger zirconium showing stronger interaction, and the calix[5]arene conformation, with the cone conformation showing the weaker interaction.

Dynamic Titanium Phosphinoamides as Unique Bidentate Phosphorus Ligands for Platinum

Treatment of lithium phosphinoamides, Ph2PN(Li)R [R = tBu, iPr], with TiCl4 results in formation of titanium phosphinoamides, (Ph2PNR)2TiCl2 [R = tBu (1a), iPr (1b)]. Crystallographic studies show that there are covalent bonds between the titanium and two nitrogen atoms, whereas two phosphorus atoms are coordinated to the metal center intramolecularly. Variable-temperature NMR studies suggest reversible dissociation of the phosphorus moieties from the titanium in solution. The dissociated phosphorus moieties are effectively captured by Pt(II) species; reactions of 1a with either (η4-COD)PtCl2, (η4-COD)Pt(R)(Cl) (R = Me, p-Tol), or [Me2Pt(μ-SMe2)]2 afford the corresponding Ti−Pt heterobimetallic complexes. The molecular structures of these complexes reveal that they have a six-membered dimetallacycle, in which a titanium and a platinum are connected by two bridging phosphinoamide ligands; the Pt−Ti distances indicate the existence of a Pt→Ti dative bond. The conformation of the dimetallacycle is a boat form, with two metals at the bow and the stern in the crystal; however, dynamic conformational change involving cleavage and re-formation of the Pt→Ti dative bond is indicated from variable-temperature NMR studies.

Crystal structure of oxotitanium(IV) 2,2,6,6-tetramethyl-3,5-heptanedionate

The structure of titanyl dipivalylmethanate TiO(dpm)2 has been studied by X-ray diffraction analysis. The compound has a molecular structure formed by isolated centrosymmetrical dimers [TiO(dpm)2]2; the unit cell contains two structurally related, crystallographically unique binuclear molecules. The Ti...Ti distance in the dimer is 2.73 A. Crystal data for Ti2C36H76O10: a = 32.477(6) A, b = 14.409(3) A, c = 25.630(5) A; β = 107.82(3)°, space group C2/c, Z = 8, d calc = 1.002 g/cm3.

The structure of supported and unsupported vanadium oxide under calcination, reduction and oxidation determined with XAS

A vanadium oxide powder catalyst supported on titanium oxide (VO x /TiO 2(anatase)) was investigated with in situ X-ray absorption spectroscopy (XAS). This system is applied in industry for partial oxidation processes. The structural changes of the supported vanadium oxide due to different treatments were determined: during a reduction–oxidation cycle at 623 K after calcination in air and after heating in inert atmosphere. Unsupported crystalline V 2O 5 powder was used as a reference system. After calcination in air of the VO x /TiO 2(anatase) a V 2O 5 bulk crystal structure appears, while an octahedral co-ordination with a V O vanadyl bond is present after heating in inert atmosphere. The redox cycle performed on fully oxidized supported vanadium oxide induces similar structural changes as for unsupported V 2O 5: a reduction to V 4+ with a slightly distorted V O octahedron and a re-oxidation to the initial V 2O 5 structure. However, when the supported vanadium oxide is reduced after heating in inert, a valence lower than V 4+ is obtained and a different structure is found: a symmetrical V O octahedron is present with V O and V V distances identical to the Ti O and Ti Ti distances in TiO 2(anatase or rutile). After re-oxidation the V 2O 5 bulk structure is again obtained for the supported vanadium oxide.

Synthesis, crystal structures and spectroscopic characterization of [Ti 8O 8(OOCR) 16] (where R = Bu t, CH 2Bu t, C(CH 3) 2Et)

Multinuclear titanium(IV) oxo carboxylates of the general formula [Ti 8O 8(OOCR) 16] (where R = Bu t ( 1), CH 2Bu t ( 2), C(CH 3) 2Et ( 3)) have been synthesized in a reaction of titanium isopropoxide with the appropriate organic acids in a molar ratio of 1:2. The composition and structure of these compounds were identified by elemental analysis, IR, NMR and X-ray single-crystal diffraction. The crystal structure of 1 was solved in the orthorhombic space group Pbca. Titanium atoms form oligomeric [Ti 8(μ 2-O) 8] rings, where each Ti cation is surrounded by six oxygen atoms (two μ 2-oxo and four μ-carboxylato bridges). Within the ring the Ti–Ti distances between neighboring titanium ions range from 3.333(1) to 3.366(1) Å and the mean value of the Ti–Ti–Ti angle is 134.2(1.3)°. Results of IR, NMR and MS studies proved that in the structures of 2 and 3, multinuclear [Ti 8(μ 2-O) 8] clusters stabilized by carboxylate bridges are also formed. TGA/DTG, MS and variable temperature IR + (VT-IR) studies have been carried out in order to determine the thermal stability and thermal decomposition mechanism of the Ti(IV) carboxylates mentioned above.

Thermoelectric Properties of Lanthanum-Doped Europium Titanate

The thermoelectric properties of lanthanum-doped polycrystalline perovskite-type europium titanate were measured from room temperature to 900 K and compared to those of MTiO 3 (M = Ca, Sr, Ba). The differences in the titanates were calculated in terms of the differences of A-site ion and Ti-O distance that determined the covalent bonding strength. The A-site ion appeared to have little influence on the electrical properties. The small Ti-O(Ti) distance results in strong bonding and it causes high thermal conductivity together with high electrical conductivity. Europium titanate showed power factor similar to and thermal conductivity lower than those of the strontium titanate. Eu 0 . 9 La 0 . 1 TiO 3 showed the highest dimensionless figure of merit of 0.25 at 900 K.

Thermoelectric properties of doped BaTiO 3–SrTiO 3 solid solution

La doped BaTiO 3–SrTiO 3 solid solutions were prepared and the thermoelectric properties were measured from room temperature to 873 K. The electrical conductivity and the Seebeck coefficient changed with the lattice parameter and the result indicated that a shorter TiTi distance was desirable as thermoelectric materials. The thermal conductivity increased with increasing Sr concentration. The figure of merit had a peak around 400–600 K in the temperature range and reached 3.0×10 −4 K −1 for Ba 0.3Sr 0.6La 0.1TiO 3.

Lithium-7 nuclear magnetic resonance and Ti K-edge X-ray absorption spectroscopic investigation of electrochemical lithium insertion in Li 4/3+ xTi 5/3O 4

The spinel compound Li 4/3+ x Ti 5/3O 4 is known to undergo reversible lithium intercalation up to x=1 with almost no change in lattice parameters, hence its designation as a “zero strain” intercalation compound. Structural changes that accompany electrochemical Li intercalation into this compound were studied by both 7 Li nuclear magnetic resonance (NMR) and Ti K-edge X-ray absorption fine structure (XAFS). The NMR results demonstrate that Li occupancies do not follow a simple distribution between two possible sites, one tetrahedral and one octahedral. The presence of at least one additional octahedral site is suggested. Line width measurements show that the Li + ions do not return to their original distribution after cycling. XAFS results indicate the presence of modest static disorder in TiO and TiTi distances above x=0.5. Both methods thus reveal subtle structural details previously unobserved by X-ray diffraction (XRD).

Observation of lattice dimerization in spin-singlet low temperature phase of NaTiSi 2O 6

NaTiSi 2O 6 is a spin- 1 2 member of the quasi-one-dimensional magnets; pyroxene family. This compound exhibits the phase transition at 210 K , which is accompanied by the structural change and the spin-singlet formation. The alternation of Ti–Ti distance within the chain made up of edge-shared TiO 6 octahedra in the low temperature phase was observed in X-ray and neutron diffraction. This is the direct evidence for the formation of Ti 3+–Ti 3+ singlet pairs.

Half-Sandwich Titanium(IV) Complexes with Kläui's Tripod Ligand

Treatment of [Ti(O-i-Pr)(2)Cl(2)] with NaL(OEt) (L(OEt)(-) = [CpCo[P(O)(OEt)(2)](3)](-), Cp = eta(5)-C(5)H(5)) afforded [L(OEt)Ti(O-i-Pr)(2)Cl] that reacted with HCl in ether to give [L(OEt)TiCl(3)] (1). The average Ti-O and Ti-Cl distances in 1 are 1.975 and 2.293 A, respectively. Reaction of titanyl sulfate with NaL(OEt) in water followed by addition of HBF(4) afforded [L(OEt)TiF(3)] (2), the Ti-O and Ti-F distances of which are 2.020(2) and 1.792(2) A, respectively. The Zr(IV) analogue [L(OEt)ZrF(3)] (3) was prepared similarly from zirconyl nitrate, NaL(Oet), and HBF(4) in water. The Zr-O and average Zr-F distances in 3 are 2.139(2) and 1.938(2) A, respectively. Treatment of 1 with tetrachlorocatechol (H(2)Cl(4)cat) afforded [L(OEt)Ti(Cl(4)cat)Cl] (4). The average Ti-O(P), Ti-O(C), and Ti-Cl distances in 4 are 1.972, 1.926, and 2.334 A, respectively. Hydrolysis of 4 in the presence of Et(3)N yielded the mu-oxo dimer [(L(OEt))(2)Ti(2)(Cl(4)cat)(2)(mu-O)] (5). The average Ti-O(P), Ti-O(C), and Ti-O(Ti) distances in 5 are 2.027, 1.926, and 1.7977(9) A. Treatment of 1 with 1,1'-binaphthol (BINOLH(2)) in the presence of Et(3)N afforded [(L(OEt))(2)Ti(2)(mu-O)(2)(mu-BINOL)] x 2BINOLH(2) (6.2BINOLH(2)). Complex 1 is capable of catalyzing ring opening of epoxides with Me(3)SiN(3) under solvent-free conditions presumably via a Ti-azide intermediate.

The isolation and structure of titanium bromide compounds containing 2,6-diphenylphenoxide ligation; terminal and bridging ligand effects on Ti–Ti interactions

The titanium aryloxy bromides [Ti(OC6H3Ph2-2,6)2Br2] 1 and [(2,6-Ph2C6H3O)2Ti(μ-Br)2Ti(OC6H3Ph2-2,6)2] 2 have been isolated and structurally characterized. Compound 1 adopts a pseudo-tetrahedral environment about titanium while 2 contains an edge-shared bis(tetrahedral) coordination geometry. The Ti–Ti distance is 3.0308(8) Å in 2. A comparison of these compounds with their chloride counterparts as well as cyclopentadiene analogues has been made. The Ti–Ti distance in the compounds [Cp′2Ti(μ-X)2TiCp′2] (Cp′ = methylcyclopentadienyl) increases as the bridging ligand X is changed from Cl to Br. In contrast this parameter is almost identical in the aryloxide compounds [(ArO)2Ti(μ-X)2Ti(OAr)2] (ArO = 2,6-diphenylphenoxide), due to the presence of a titanium–titanium bonding interaction.

Synthesis, Characterization, and Reduction Chemistry of Mixed-Cyclopentadienyl/Arylsulfide Titanium Dichlorides

A series of titanium derivatives [CpTi(SAr)Cl2] containing both cyclopentadienyl and various substituted arylsulfide ligands (SAr = SC6H4Me-4 (1), SC6H2Me3-2,4,6 (2), SC6H2Pri3-2,4,6 (3), SC6H2Ph3-2,4,6 (4)) has been synthesized from the reaction of [CpTiCl3] with 1 equiv of the lithium salt of the corresponding arylsulfides in benzene. X-ray diffraction studies show that each metal center possesses a pseudo-tetrahedral geometry. The compounds undergo one-electron reduction to produce sulfur-bridged dimers of the type [CpTiCl(μ-SAr)]2 (SAr = SC6H2Me3-2,4,6 (5), SC6H2Pri3-2,4,6 (6)). The solid-state structures of these dimers show that the cyclopentadienyl rings are arranged in a transoid fashion about the [Ti(μ-SAr)2Ti] core. The Ti−Ti distances, 3.242(1) and 3.225(1) Å, respectively, are similar to those found in previously reported Cp/aryloxide dimers with terminal aryloxides and bridging chlorides.