The Lanthanide Contraction Is a Variable.

Upon examination of the bond distances of the recently reported series of [Ln(SST)3(THF)2] [Ln = lanthanides, SST = tris(trimethylsilyl)siloxide (OSi(SiMe3)3), and THF = tetrahydrofuran] compounds, it was found that over the Ln-series (La through Lu), the Ln-O(THF) bond changed by 0.257 Å, whereas the Ln-O(SST) bond varied by 0.164 Å. Examination of all similarly ligated Ln-O(THF) (Ln = La vs Lu) structures available in the Cambridge Structural Database (CSD) revealed that this previously unreported, increased Ln-contraction is pervasive. Further evaluations showed that this enhanced Ln-contraction also occurs for pyridine (py) in the [Ln(SST)3(py)2] family as well as the average Ln-N(py) (La vs Lu) structure distances recovered from the CSD. Additional ligands, such as halides (Cl and I) were found to display this enhanced Ln-contraction, while other species (i.e., cyclopentadienide, alkoxide, SST, and dimethyl sulfoxide) yielded a "normal" Ln-contraction (La-L vs Lu-L). Gas-phase electronic structure density functional theory calculations were carried out to evaluate the molecular orbital influence on the Ln-contraction between Ln-O(SST) and Ln-O(THF). The calculated [Ln(SST)3(THF)2] structures were found to demonstrate the same capricious Ln-contraction. Based on these studies, one can say that the variability of the Ln-contraction noted in the [Ln(SST)3(THF)2] experimental data is due to the different bonding types, ion-ion for the Ln-SST bond versus ion-dipole for the Ln-THF bond.

Synthesis and Characterization of Solvated Lanthanide Tris(trimethylsilyl)siloxides.

In an effort to develop precursors for the production of lanthanide silicate (LnSiOx) materials, the reactions of [Ln(NR2)3] (R = SiMe3) with three equivalents of tris(trimethylsilyl)silanol (H-OSi(SiMe3)3) or H-SST) in tetrahydrofuran (THF) were undertaken. The products were crystallographically characterized as [Ln(SST)3(THF)2] (where Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu). In general, these compounds are similar to the previously reported [Gd(SST)3(THF)2] complex, where each metal center of the monomeric species is found to adopt a trigonal bipyramidal (TBP; τ = av 0.95) geometry; however, the crystallographic structure solutions for these crystals invoke a much larger unit cell that reveals the complex disorder of the axial THF ligands. Using incompletely washed H-SST, the tetrahedrally (T-4) bound [Ln(SST)3(NEt3)] (Ln-NEt3 = Pr-NEt3, Ho-NEt3; NEt3 = triethylamine) compounds were isolated from the same reaction run in toluene. Rational syntheses of amine derivatives were realized by performing the same reaction with pure H-SST in toluene containing the appropriate amine and [Ln(NR2)3] with the final products identified as [Tm(SST)3(NEt3)] (Tm-NEt3) or [Tm(SST)3(NHPr2i)] (NHPr2i = di-iso-propylamine; Tm-NHPr2i). The products isolated from reactions undertaken in pyridine (py) were identified as [Ln(SST)3(py)2] (Ln-py = Ce-py, Eu-py, and Tm-py). The Ln-py structures exhibit the larger unit cell noted for the THF derivatives with each Ln adopting a TBP (τ = av 0.98) metal center possessing equatorial SST and axial py ligands. The same reaction run in toluene led to the isolation of [(η6-tol)Tm(SST)3] (Tm-tol). Multinuclear NMR (1H and 29Si) data support the retention of the solid-state structures of all of these compounds in solution. Photoluminescent measurements of Tb, Sm, Dy, and Eu were found to display emission and lifetime profiles in the visible range due to f-f transitions, consistent with trivalent lanthanide metal centers.

Pyridinium Salts of Dehydrated Lanthanide Polychlorides.

The reaction of lanthanide (Ln) chloride hydrates ([Ln(H2O)n(Cl)3]) with pyridine (py) yielded a set of dehydrated pyridinium (py-H) Ln-polychloride salts. These species were crystallographically characterized as [[py-H-py][py-H]2[LnCl6]] (Ln-6; Ln = La, Ce, Pr, Nd, Sm, Eu, Gd) or [[py-H]2[LnCl5(py)]] ((Ln-5; Ln = Tb, Dy, Ho, Er, Tm, Yb, Lu). The Ln-6 metal centers adopt an octahedral (OC-6) geometry, binding six Cl ligands. The -3 charge is off-set by two py-H moieties and a di-pyridinium (py-H-py) ion. For the Ln-5 species, an OC-6 anion is formed by the Ln cation binding a single py and five Cl ligands. The remaining -2 charge is offset by two py-H+ cations that H-bond to the anion. Significant H-bonding occurs between the various cation/anion moieties inducing the molecular stability. The change in structure from the Ln-6 to Ln-5 is believed to be due to the Ln-contraction producing a smaller unit cell, which prevents formation of the py-H-py+ cation, leading to the loss of the H-bonding-induced stability. Based on this, it was determined that the Ln-5 structures only exist when the lattice energy is small. While dehydrated polychloride salts can be produced by simply mixing in pyridine, the final structures adopted result from a delicate balance of cation size, Coulombic charge, and stabilizing H-bonding.

Organophosphorus-Modified Lanthanide Nitrates as Potential Actinide Oxide Aerosol Surrogates.

In search of suitable simulants for aerosol uranium waste products from Plutonium Uranium Redox Extraction (PUREX) process burns, a series of lanthanide nitrate hydrates ([Ln(κ2-NO3)3·nH2O]) were dissolved in the presence of tributylphosphate (O═P(O(CH2)3CH3)3) referred to as TBP) in kerosene or triphenylphosphate (O═P(O(C6H5) referred to as TPhP) in acetone. The crystal structure of the TPhP derivatives of the lanthanide nitrate series and uranium nitrate were solved as [Ln(κ2-NO3)3(TPhP)3] (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) and [U(O)2(κ2-NO3)2(TPhP)2] (U), respectively. The lanthanide-TBP, Ln, and U were further characterized using FTIR spectroscopy, 31P NMR spectroscopy, thermogravimetric analysis, and X-ray fluorescence spectroscopy. Further, thermal treatment of the lanthanide-TBP, Ln, and U using a box furnace to mimic pyrolysis conditions was found by PXRD analyses to generate a phosphate phase [LnP3O9 or UP2O7) for all systems. The resultant nuclear waste fire contaminant particulates will impact both aerosol transport and toxicity assessments.

Trapped Intermediate of a Meerwein-Pondorf-Verley Reduction of Hydroxy Benzaldehyde to a Dialkoxide by Titanium Alkoxides.

A series of titanium alkoxides ([Ti(OR)4] (OR = OCH(CH3)2 (OPri), OC(CH3)3 (OBut), and OCH2C(CH3)3 (ONep)) were modified with a set of substituted hydroxyl-benzaldehydes [HO-BzA-Lx: x = 1, 2-hydroxybenzaldehyde (L = H), 2-hydroxy-3-methoxybenzaldehyde (OMe-3), 5-bromo-2-hydroxybenzaldehyde (Br-5), 2-hydroxy-5-nitrobenzaldehyde (NO2-5); x = 2, 3,5-di-tert-butyl-2-hydroxybenzaldehyde (But-3,5), 2-hydroxy-3,5-diiodobenzaldehyde (I-3,5)] in pyridine (py). Instead of the expected simple substitution, each of the HO-BzA-Lx modifiers were reduced to their respective diol [(py)(OR)2Ti(κ2(O,µ-O')(OC6H4-x(CH2O)-2)(L)x] (OR = OPri, x = 1, L = H (1a), OMe-3 (2a), Br-5 (3a·py), NO2-5 (4a·4py); x = 2, But-3,5 (5a), I-3,5 (6a), ONep; x = 1, L = H (1b), OMe-3 (2b), Br-5 (3b·py), NO2-5 (4b); x = 2, But-3,5 (5b), I-3,5 (6b·py)), as identified by single crystal X-ray studies. The 1H NMR spectral data were complex at room temperature but simplified at high temperatures (70 °C). Diffusion ordered spectroscopy (DOSY) NMR experiments indicated that 2a maintained the dinuclear structure in a solution independent of the temperature, whereas 2b appears to be monomeric over the same temperature range. On the basis of additional NMR studies, the mechanism of the reduction of the HO-BzA-Lx to the dioxide ligand was thought to occur by a Meerwein-Pondorf-Verley (MPV) mechanism. The structures of 1a-6b appear to be the intermediate dioxide products of the MPV reduction, which became "trapped" by the Lewis basic solvate.

Synergistic Bimetallic Ni/Ag and Ni/Cu Catalysis for Regioselective γ,δ-Diarylation of Alkenyl Ketimines: Addressing ß-H Elimination by in Situ Generation of Cationic Ni(II) Catalysts.

We disclose unprecedented synergistic bimetallic Ni/Ag and Ni/Cu catalysts for regioselective γ,δ-diarylation of unactivated alkenes in simple ketimines with aryl halides and arylzinc reagents. The bimetallic synergy, which generates cationic Ni(II) species during reaction, promotes migratory insertion and transmetalation steps and suppresses ß-H elimination and cross-coupling, the major side reactions that cause serious problems during alkene difunctionalization. This diarylation reaction proceeds at remote locations to imines to afford, after simple H+ workup, diversely substituted γ,δ-diaryl ketones that are otherwise difficult to access readily with existing methods.

Synthesis and Characterization of Tris(trimethylsilyl)siloxide Derivatives of Early Transition Metal Alkoxides That Thermally Convert to Varied Ceramic-Silica Architecture Materials.

In an effort to generate single-source precursors for the production of metal-siloxide (MSiO x) materials, the tris(trimethylsilyl)silanol (H-SST or H-OSi(SiMe3)3 (1) ligand was reacted with a series of group 4 and 5 metal alkoxides. The group 4 products were crystallographically characterized as [Ti(SST)2(OR)2] (OR = OPr i (2), OBu t (3), ONep (4)); [Ti(SST)3(OBu n)] (5); [Zr(SST)2(OBu t)2(py)] (6); [Zr(SST)3(OR)] (OR = OBu t (7), ONep, (8)); [Hf(SST)2(OBu t)2] (9); and [Hf(SST)2(ONep)2(py) n] ( n = 1 (10), n = 2 (10a)) where OPr i = OCH(CH3)2, OBu t = OC(CH3)3, OBu n = O(CH2)3CH3, ONep = OCH2C(CH3)3, py = pyridine. The crystal structures revealed varied SST substitutions for: monomeric Ti species that adopted a tetrahedral ( T-4) geometry; monomeric Zr compounds with coordination that varied from T-4 to trigonal bipyramidal ( TBPY-5); and monomeric Hf complexes isolated in a TBPY-5 geometry. For the group 5 species, the following derivatives were structurally identified as [V(SST)3(py)2] (11), [Nb(SST)3(OEt)2] (12), [Nb(O)(SST)3(py)] (13), 2[H][(Nb(µ-O)2(SST))6(µ6-O)] (14), [Nb8O10(OEt)18(SST)2·1/5Na2O] (15), [Ta(SST)(µ-OEt)(OEt)3]2 (16), and [Ta(SST)3(OEt)2] (17) where OEt = OCH2CH3. The group 5 monomeric complexes were solved in a TBPY-5 arrangement, whereas the Ta of the dinculear 16 was solved in an octahedral coordination environment. Thermal analyses of these precursors revealed a stepwise loss of ligand, which indicated their potential utility for generating the MSiO x materials. The complexes were thermally processed (350-1100 °C, 4 h, ambient atmosphere), but instead of the desired MSiO x, transmission electron microscopy analyses revealed that fractions of the group 4 and group 5 precursors had formed unusual metal oxide silica architectures.

Synthesis and Characterization of Structurally Diverse Alkaline-Earth Salen Compounds for Subterranean Fluid Flow Tracking.

A family of magnesium and calcium salen-derivatives was synthesized and characterized for use as subterranean fluid flow monitors. For the Mg complexes, di- n-butyl magnesium ([Mg(Bu n)2]) was reacted with N, N'-ethylene bis(salicylideneimine) (H2-salen), N, N'-bis(salicylidene)-1,2-phenylenediamine (H2-saloPh), N, N'-bis(3,5-di- t-butylsalicylidene)-ethylenediamine (H2-salo-Bu t), or N, N'-bis(3,5-di- t-butylsalicylidene)-1,2-phenylenediamine (H2-saloPh-Bu t), and the products were identified by single-crystal X-ray diffraction as [(κ3-(O,N,N'),µ-(O')saloPh)(µ-(O),(κ2-(N,N'),µ-(O')saloPh)2(µ-(O),κ3-(N,N',O')saloPh')Mg4]·2tol (1·2tol; saloPh' = an alkyl-modified saloPh derivative generated in situ), [(κ4-(O,N,N',O')saloPh)Mg(py)2]·py (2·py), [(κ4-(O,N,N',O')salo-Bu t)Mg(py)2] (3), [(κ4-(O,N,N',O')saloPh-Bu t)Mg(py)2]·tol (4·tol), and [(κ3-(O,N,N'),µ-(O')saloPh-Bu t)Mg]2 (5), where tol = toluene; py = pyridine. For the Ca species, a calcium amide was independently reacted with H2-salo-Bu t and H2-saloPh-Bu t to generate the crystallographcially characterized compounds: [(κ4-(O,N,N',O')salo-Bu t)Ca(py)3] (6), [(κ4-(O,N,N',O')saloPh-Bu t)Ca(py)3]·py (7·py). The bulk powders of these compounds were further characterized by a number of analytical tools, where 2-7 were found to be distinguishable by Fourier transform infrared and resonance Raman spectroscopies. Structural properties obtained from quantum calculations of gas-phase analogues are in good agreement with the single-crystal results. The potential utility of these compounds as taggants for monitoring subterranean fluid flows was demonstrated through a series of experiments to evaluate their stability to high temperature and pressure, interaction with mineral surfaces, and elution behavior from a loaded proppant pack.

Synthesis, Characterization, and Nanomaterials Generated from 6,6'-(((2-Hydroxyethyl)azanediyl)bis(methylene))bis(2,4-di- tert-butylphenol) Modified Group 4 Metal Alkoxides.

The impact on the morphology nanoceramic materials generated from group 4 metal alkoxides ([M(OR)4]) and the same precursors modified by 6,6'-(((2-hydroxyethyl)azanediyl)bis(methylene))bis(2,4-di- tert-butylphenol) (referred to as H3-AM-DBP2 (1)) was explored. The products isolated from the 1:1 stoichiometric reaction of a series of [M(OR)4] where M = Ti, Zr, or Hf; OR = OCH(CH3)2(OPr i); OC(CH3)3(OBu t); OCH2C(CH3)3(ONep) with H3-AM-DBP2 proved, by single crystal X-ray diffraction, to be [(ONep)Ti( k4( O,O',O'',N)-AM-DBP2)] (2), [(OR)M(µ( O)- k3( O',O'',N)-AM-DBP2)]2 [M = Zr: OR = OPr i, 3·tol; OBu t, 4·tol; ONep, 5·tol; M = Hf: OR = OBu t, 6·tol; ONep, 7·tol]. The product from each system led to a tetradentate AM-DBP2 ligand and retention of a parent alkoxide ligand. For the monomeric Ti derivative (2), the metal was solved in a trigonal bipyramidal geometry, whereas for the Zr (3-5) and Hf (6, 7) derivatives a symmetric dinuclear complex was formed where the ethoxide moiety of the AM-DBP2 ligand bridges to the other metal center, generating an octahedral geometry. High quality density functional theory level gas-phase electronic structure calculations on compounds 2-7 using Gaussian 09 were used for meaningful time dependent density functional theory calculations in the interpretation of the UV-vis absorbance spectral data on 2-7. Nanoparticles generated from the solvothermal treatment of the ONep/AM-DBP2 modified compounds (2, 5, 7) in comparison to their parent [M(ONep)4] were larger and had improved regularity and dispersion of the final ceramic nanomaterials.

End-On Bridging Dinitrogen Complex of Scandium.

The first (N═N)2- complex of a rare-earth metal with an end-on dinitrogen bridge, {K(crypt)}2{[(R2N)3Sc]2[µ-η1:η1-N2]} (crypt = 2.2.2-cryptand, R = SiMe3), has been isolated from the reduction of Sc(NR2)3 under dinitrogen at -35 °C and characterized by X-ray crystallography. The structure differs from the characteristic side-on structures previously observed for over 40 crystallographically characterized rare-earth metal (N═N)2- complexes of formula [A2Ln(THF)x]2[µ-η2:η2-N2] (Ln = Sc, Y, and lanthanides; x = 0, 1; A = anionic ligand such as amide, cyclopentadienide, and aryloxide). The 1.221(3) Å N-N distance and the 1644 cm-1 Raman stretch are consistent with the presence of an (N═N)2- bridge. The observed paramagnetism of the complex by Evans method measurements is consistent with DFT calculations that suggest a triplet (3A2) ground state in D3 symmetry involving two degenerate Sc-N2-Sc bonding orbitals. Upon brief exposure of the orange Sc3+ bridging dinitrogen complex to UV-light, photolysis to form the monomeric Sc2+ complex, [K(crypt)][Sc(NR2)3], was observed. Conversion of the Sc2+ complex to the Sc3+ dinitrogen complex was not observed with this crypt system, but it did occur with the 18-crown-6 (crown) analog which formed {K(crown)}2{[(R2N)3Sc]2[µ-η1:η1-N2]}. This suggests the importance of the alkali metal chelating agent in the reversibility of dinitrogen binding in this scandium system.

Solution Synthesis, Structure, and CO2 Reduction Reactivity of a Scandium(II) Complex, {Sc[N(SiMe3 )2 ]3 }.

The first crystallographically characterizable complex of Sc2+ , [Sc(NR2 )3 ]- (R=SiMe3 ), has been obtained by LnA3 /M reactions (Ln=rare earth metal; A=anionic ligand; M=alkali metal) involving reduction of Sc(NR2 )3 with K in the presence of 2.2.2-cryptand (crypt) and 18-crown-6 (18-c-6) and with Cs in the presence of crypt. Dark maroon [K(crypt)]+ , [K(18-c-6)]+ , and [Cs(crypt)]+ salts of the [Sc(NR2 )3 ]- anion are formed, respectively. The formation of this oxidation state of Sc is also indicated by the eight-line EPR spectra arising from the I=7/2 45 Sc nucleus. The Sc(NR2 )3 reduction differs from Ln(NR2 )3 reactions (Ln=Y and lanthanides) in that it occurs under N2 without formation of isolable reduced dinitrogen species. [K(18-c-6)][Sc(NR2 )3 ] reacts with CO2 to produce an oxalate complex, {K2 (18-c-6)3 }{[(R2 N)3 Sc]2 (µ-C2 O4 -κ1 O:κ1 O'')}, and a CO2- radical anion complex, [(R2 N)3 Sc(µ-OCO-κ1 O:κ1 O')K(18-c-6)]n .

Structural Properties of the Acidification Products of Scandium Hydroxy Chloride Hydrate.

The structural properties of a series of scandium inorganic acid derivatives were determined. The reaction of Sc(0) with concentrated aqueous hydrochloric acid led to the isolation of [(H2O)5Sc(µ-OH)]24Cl·2H2O (1). Compound 1 was modified with a series of inorganic acids (i.e., HNO3, H3PO4, and H2SO4) at room temperature and found to form {[(H2O)4Sc(κ(2)-NO3)(µ-OH)]NO3}2 (2a), [(H2O)4Sc(κ(2)-NO3)2]NO3·H2O (2b) (at reflux temperatures), {6[H][Sc(µ-PO4)(PO4)]6}n (3), and [H][Sc(µ3-SO4)2]·2H2O (4a). Additional organosulfonic acid derivatives were investigated, including tosylic acid (H-OTs) to yield {[(H2O)4Sc(OTs)2]OTs}·2H2O (4b) in H2O and [(DMSO)3Sc(OTs)3] (4c) in dimethyl sulfoxide and triflic acid (H-OTf) to form [Sc(H2O)8]OTf3 (4d). Other organic acid modifications of 1 were also investigated, and the final structures were determined to be {([(H2O)2Sc(µ-OAc)2]Cl)6}n (5) from acetic acid (H-OAc) and [Sc(µ-TFA)3Sc(µ-TFA)3]n (6) from trifluoroacetic acid (H-TFA). In addition to single-crystal X-ray structures, the compounds were identified by solid-state and solution-state (45)Sc nuclear magnetic resonance spectroscopic studies.

Synthesis and structural characterization of group 4 metal carboxylates for nanowire production.

The synthesis and characterization of a series of group 4 carboxylate derivatives ([M(ORc)4] where M = Ti, Zr, Hf) was undertaken for potential utility as precursors to ceramic nanowires. The attempted syntheses of the [M(ORc)4] precursors were undertaken from the reaction of [M(OBu(t))4] with a select set of carboxylic acids (H-ORc where ORc = OPc (O2CCH(CH3)2), OBc (O2CC(CH3)3), ONc (O2CCH2C(CH3)3)). The products were identified by single-crystal X-ray diffraction studies as [Ti(η(2)-OBc)3(OBu(t))] (1), [Zr2(µ3-O)(µ-OPc)4(µ,η(2)-OPc)(η(2)-OPc)]2 (2), [H]2[Zr(η(2)-OBc)2(OBc)2(OBc)2] (3), [Zr(µ-ONc)2(η(2)-ONc)2]2 (4), or [Hf(µ-ORc)2(η(2)-ORc)2]2 [ORc = OPc (5), OBc (6, shown), ONc (7)]. The majority of compounds (4-7) were isolated as dinuclear species with a dodecahedral-like (CN-8) bonding mode around the metals due to chelation and bridging of the ORc ligand. The two monomers (1 and 3) were found to adopt a capped trigonal prismatic and CN-8 geometry, respectively, due to chelating ORc and terminal ORc or OBu(t) ligands. The metals of the oxo-species 2 were isolated in octahedral and CN-8 arrangements. These compounds were then processed by electrospinning methods (applied voltage 10 kV, flow rate 30-60 µL/min, electric field 0.5 kV/cm), and wire-like morphologies were isolated using compounds 4, 6 (shown), and 7.

Low-energy quasi-circular electron correlations with charge order wavelength in Bi2Sr2CaCu2O8+δ.

Most resonant inelastic x-ray scattering (RIXS) studies of dynamic charge order correlations in the cuprates have focused on the high-symmetry directions of the copper oxide plane. However, scattering along other in-plane directions should not be ignored as it may help understand, for example, the origin of charge order correlations or the isotropic scattering resulting in strange metal behavior. Our RIXS experiments reveal dynamic charge correlations over the qx-qy scattering plane in underdoped Bi2Sr2CaCu2O8+δ. Tracking the softening of the RIXS-measured bond-stretching phonon, we show that these dynamic correlations exist at energies below approximately 70 meV and are centered around a quasi-circular manifold in the qx-qy scattering plane with radius equal to the magnitude of the charge order wave vector, qCO. This phonon-tracking procedure also allows us to rule out fluctuations of short-range directional charge order (i.e., centered around [qx = ±qCO, qy = 0] and [qx = 0, qy = ±qCO]) as the origin of the observed correlations.

Cytotoxic activity of the titanium alkoxide (OPy)(2)Ti(4AP)(2) against cancer colony forming cells.

A novel family of titanium alkoxides with two stable pyridinemethoxide moieties bound to a titanium metal center were synthesized and tested for cytotoxic activity on a variety of cancer cell lines using colony formation assays. One compound, (OPy)(2)Ti(4AP)(2), where OPy is NC(5)H(5)CH(2)O(-), and 4AP is 4-aminophenoxide ((-)OC(6)H(5)(NH(2))-4), demonstrated increased cytotoxicity in breast, colon, and pancreatic cancer cell lines at 100 nanomolar levels with only short exposures. Further, (OPy)(2)Ti(4AP)(2) had activity in colon and pancreatic cancer cell lines that are usually resistant to chemotherapy. This demonstrates that these titanium compounds may have a role in anti-cancer therapy, similar to platinum-based compounds, and the (OPy)(2)Ti(4AP)(2) compound specifically deserves further investigation as an anti-cancer agent in chemo-resistant solid tumors.

Coordination chemistry of N,N,N',N'-tetrakis(3,5-substituted benzyl-2-oxide)-2,2'-(ethylenedioxy)diethanamine modified Group 4 metal alkoxides.

The coordination behavior of a set of (ethylenedioxy)diethanamine-based tetraphenol ligands with a series of Group 4 metal alkoxides ([M(OR)(4)]) was determined. The ligands were synthesized from a modified Mannich reaction and fully characterized as N,N,N',N'-tetrakis(3,5-tert-butyl-benzyl-2-hydroxy)-2,2'-(ethylenedioxy)diethanamine, termed H(4)-OEA-DBP(4) (1), and N,N,N',N'-tetrakis(3,5-chloro-benzyl-2-hydroxy)-2,2'-(ethylenedioxy)diethanamine, termed H(4)-OEA-DCP(4) (2). The reaction of 1 with a set of [M(OR)(4)] [M = Ti, Zr, or Hf; OR = iso-propoxide (OPr(i)), neo-pentoxide (ONep), or tert-butoxide (OBu(t))] precursors led to the isolation of [(OPr(i))(2)Ti](2)(µ-OEA-DBP(4)) (3), [(ONep)(2)Ti](2)(µ-OEA-DBP(4)) (4), and [(OBu(t))(2)M](2)(µ-OEA-DBP(4)) where M = Ti (5), Zr (6), or Hf (7). In addition, the [(ONep)(2)Ti](2)(µ-OEA-DCP(4)) (4a) derivative was isolated from the reaction of 2 and [Ti(ONep)(4)], demonstrating the similarity of coordination behavior between the two OEA-R(4) ligands. For 3-7, the metal center adopts a slightly distorted octahedral geometry by binding the two O atoms of the phenoxide moiety, as well as one N and one O atom from the OEA moieties, while retaining two of the original OR ligands. Solution NMR demonstrates inequivalent protons for the majority of the bound OEA ligands, which argues for retention of structure in solution. The synthesis and characterization of these compounds are presented in detail.

Synthesis and structural characterization of a family of modified hafnium tert-butoxide for use as precursors to hafnia nanoparticles.

A series of modified, hafnium tert-butoxide ([Hf(OBu(t))4]) compounds (1-26) were crystallographically characterized, and representative species were then used to produce HfO2nanoparticles. This systematically varied family of [Hf(OR)4] compounds was developed from the reaction of [Hf(OBu(t))4] with a series of (i) Lewis basic solvents, tetrahydrofuran, pyridine, or 1-methylimidazole; (ii) simple phenols, HOC6H4(R)-2 or HOC6H3(R)2-2,6 where R = CH3, CH(CH3)2, or C(CH3)3; and (iii) complex polydentate alcohols, tetrahydrofuran methanol (H-OTHF), pyridinecarbinol (H-OPy), and tris(hydroxymethylethane) (THME-H3). The solvent-modified products were crystallographically characterized as [Hf(OBu(t))4(solv)n] (1-3). The phenoxide (OAr)-exchanged [Hf(OBu(t))4] products isolated from toluene were characterized as dimeric [Hf(OAr)n(OBu(t))4-n]2 (4 and 5) or [Hf(µ-OH)(OAr)3(HOBu(t))]2 (6 and 7) for the less sterically demanding OAr ligands and [Hf(OAr)n(OBu(t))4-n(HOBu(t))] (8 and 9) monomers for the larger OAr ligands. When Lewis basic solvents were employed, solvated monomers of varied OAr substitutions were observed as [Hf(OAr)n(OBu(t))4-n(solv)x], where solv = THF (10, 11, and 13-15) and py (16 and 19-21). The nuclearities of the remaining complex polydentate alcohol derivatives ranged from monomers (24, OPy) to dimers (22, OTHF; 23, OPy) to tetramers (25 and 26, THME). On the basis of their nuclearities, select members of this family of [Hf(OR)4] compounds (monomer, [Hf(OBu(t))4], 8; dimer, 19a, 22; tetramer, 25) were used to determine the validity of using [Hf(OR)4] precursors for the production of hafnia (HfO2) nanoparticles under solvothermal (oleylamine/oleic acid) conditions. After a 650 °C thermal treatment, the resulting powder X-ray diffraction pattern for each powder was found to be consistent with HfO2 (PDF 00-040-1173), and after a 1000 °C treatment, larger particles of HfO2 (PDF 00-043-1017) were reported. Transmission electron microscopy images confirmed that nanomaterials had formed. Because identical processing conditions had been employed for each HfO2 nanomaterial, the morphological variations observed in this study may be attributed to the individual precursors ("precursor structure affect").

Titanium hydride nanoparticles and nanoinks for aerosol jet printed electronics.

Conductive inks commonly rely on oxidation-resistant metallic nanoparticles such as gold, silver, copper, and nickel. The criterion of air stability limits the scope of material properties attainable in printed electronic devices. Here we present an alternative approach based on air-stable nanoscale metal hydrides. Conductive patterns based on titanium hydride (TiH2) nanoinks were successfully printed on polyimide under ambient atmosphere and cured using intense pulsed light processing. Nanoparticles of TiH2 were generated by heating TiH2 powder in octylamine followed by wet ball milling, yielding <100 nm platelets. The addition of a suitable polymer dispersant during ball milling yielded stable colloidal dispersions suitable for liquid-phase processing. Aerosol jet printing of the resultant TiH2 nanoinks was demonstrated on glass and polyimide substrates, with a resolution as fine as 20 µm. Following intense pulsed light curing, samples on polyimide were found to exhibit a sintered, porous morphology with an electrical sheet resistance of ∼150 Ω â–¡-1.

Stabilization of three-dimensional charge order through interplanar orbital hybridization in PrxY1-xBa2Cu3O6+δ.

The shape of 3d-orbitals often governs the electronic and magnetic properties of correlated transition metal oxides. In the superconducting cuprates, the planar confinement of the [Formula: see text] orbital dictates the two-dimensional nature of the unconventional superconductivity and a competing charge order. Achieving orbital-specific control of the electronic structure to allow coupling pathways across adjacent planes would enable direct assessment of the role of dimensionality in the intertwined orders. Using Cu L3 and Pr M5 resonant x-ray scattering and first-principles calculations, we report a highly correlated three-dimensional charge order in Pr-substituted YBa2Cu3O7, where the Pr f-electrons create a direct orbital bridge between CuO2 planes. With this we demonstrate that interplanar orbital engineering can be used to surgically control electronic phases in correlated oxides and other layered materials.

Synthesis, characterization, and electrochemical properties of a series of sterically varied iron(II) alkoxide precursors and their resultant nanoparticles.

A new family of iron(II) aryloxide [Fe(OAr)(2)(py)(x)] precursors was synthesized from the alcoholysis of iron(II) mesityl [Fe(Mes)(2)] in pyridine (py) using a series of sterically varied 2-alkyl phenols (alkyl = methyl (H-oMP), isopropyl (H-oPP), tert-butyl (H-oBP)) and 2,6-dialkyl phenols (alkyl = methyl (H-DMP), isopropyl (H-DIP), tert-butyl (H-DBP), phenyl (H-DPhP)). All of the products were found to be mononuclear and structurally characterized as [Fe(OAr)(2)(py)(x)] (x = 3 OAr = oMP (1), oPP (2), oBP (3), DMP (4), DIP (5); x = 2 OAr = DBP (6), DPhP (7)). The use of tris-tert-butoxysilanol (OSi(OBu(t))(3) = TOBS) led to isolation of [Fe(TOBS)(2)(py)(2)] (8). The new Fe(OAr)(2)(py)(x) (1-6) were found, under solvothermal conditions, to produce nanodots identified by PXRD as the γ-maghemite phase. The model precursor 3 and the nanoparticles 6n were evaluated using electrochemical methods. Cyclic voltammetry for 3 revealed multiple irreversible oxidation peaks, which have been tentatively attributed to the loss of alkoxide ligand coupled with the deposition of a solid Fe-containing coating on the electrode. This coating was stable out to the voltage limits for the acetonitrile solvent.