Time and temperature induced phase transformation in L‐isoleucine hydrochloride monohydrated crystal

Semi organic crystals have been intensively studied aiming applications in nonlinear optical (NLO). Such applicability requires crystals with both high quality and thermal stability, which make the full characterization of this material a topic issue. In this paper, single crystals of L‐isoleucine hydrochloride monohydrated (L‐Ile.H2O.HCl) was synthesized by slow evaporation technique and characterized by thermal analysis and X‐ray diffraction (XRD) measurements. XRD results at 298 K showed that the sample crystallize with the orthorhombic structure, and the lattice parameters obtained by Rietveld refinement were a = 5.873(3) Å, b = 24.814(4) Å, and c = 6.873(5) Å. Thermal analysis measurements shows four decomposition stages between 328 ‐480 K which were associated with loss of water by desolvation, loss crystallization water and decomposition of L‐Ile.HCl. XRD measurements as a function of temperature up to 428 K show an irreversible phase transformation. This transformation was obtained after 32 hours keeping the L‐Ile.HCl.H2O sample at 413 K. The analysis shows that phase transformation occurs due to water and chlorine losses without destroy the amino acid carbon chain and in the end of transformation only the precursor amino acid remains. L‐Ile.HCl.H2O present low thermal stability and the phase transformation is time and temperature dependent.     

Incorporation of hafnium (IV) into KTP framework from phosphate‐fluoride fluxes

Solid solutions KTi_1‐XHf_XOPO₄ (х = 0.008 – 0.107) possessing the KTiOPO₄ structure, have been synthesized in molten system K₂O‐P₂O₅‐TiO₂‐HfF₄. The crystal growth experiment of Hf‐doped KTP crystal has been reported. The X‐ray powder diffraction data and chemical analysis are also presented. It has been shown that KTiOPO₄ crystal structure slightly changes when Hf incorporates into the framework. Transmission/absorption spectra of KTi_0.974Hf_0.026OPO₄ crystals have been recorded. The incorporation of Hf ions shifts the optical absorption edge in the UV‐visible spectrum towards the long‐wavelength region with absorption near 387 nm.     

Imines in the Titanium Coordination Sphere – Transformation of Imidoyl Chlorides to Nitrilium Ions

In the reaction of TiCl₄ in benzene as solvent with the imidoyl chloride p‐Tolyl(Cl)C=NPh ( 1 ) the abstraction of the chloride substituent is observed, leading to the nitrilium salt [p‐Tolyl–C≡N–Ph]⁺[Ti₂Cl₉]^– ( 2 ) in quantitative yield. The highly electrophilic salt 2 is characterized by IR‐ and NMR spectroscopy. The observed band for the C≡N stretching mode of 2 clearly indicates the formation of a nitrilium ion. Especially a characteristic line broadening of the ¹³C{¹H}‐NMR signals related to carbon atoms next to the nitrogen is observed. By ¹⁵N,¹H‐HMBC NMR experiments it is shown that the nitrogen signal of 2 is significantly shifted to high‐field in relation to nitriles and imines. The molecular structure of 2 was confirmed by single‐crystal X‐ray diffraction. The C≡N bond length and the linearity of the C–C≡N–C unit in 2 confirm the triple bond character of this bond.     

Activation of Molecular Hydrogen by Bis(η5,η1‐pentafulvene)‐titanium Complexes – Efficient Formation of Titanium(III)hydrides

The synthesis and crystal structures of two dinuclear titanocene hydride complexes are reported. Both complexes, namely bis(η⁵‐(di‐para‐tolylmethyl)cyclopentadienyl)titanium hydride dimer, [(η⁵‐C₂₀H₁₉)₂Ti(μ‐H)]₂ ( 2a ), and bis(η⁵‐2‐adamantylcyclopentadienyl)‐titanium hydride dimer, [(η⁵‐C₁₅H₁₉)₂Ti(μ‐H)]₂ ( 2b ), are formed via activation of molecular hydrogen by the corresponding bis(η⁵,η¹‐pentafulvene)titanium complexes 1a and 1b at ambient temperatures and pressures in high yields. The hydride complexes 2a and 2b exhibit planar [Ti₂H₂] cores and, as a result of the heterolytic cleavage of molecular hydrogen, substituted Cp Ligands were formed during the reaction.     

Aluminum/Nitrogen Cycles and an Open Cage with Al–H and N–H Functions

The cyclic tert‐butyl‐amino alane dimer [tBu–N(H)AlH₂]₂ ( 1 ) was obtained from reaction between alane with tert‐butylamine and its boranate derivative [tBu–N(H)–Al(BH₄)₂)]₂ ( 2 ) subsequently from 1 by hydride/chloride exchange using PbCl₂ followed by reaction with LiBH₄. Both compounds form four‐membered Al₂N₂ cycles with typical Al–N bond lengths of 1.940(5) Å ( 1 ) and 1.945(5) Å ( 2 ) as found from X‐ray diffraction analysis. The tert‐butyl substituents at the nitrogen atoms may be situated at the same side of the ring (cis) or at opposite sides (trans). For compound 1 both isomers are present in solution, showing particular temperature dependent NMR shifts. In the solid both compounds 1 and 2 adopt the trans arrangement. When 1 is reacted with PbCl₂ in half of the molarity ratio used for 2 , surprisingly the novel compound 3 , a zwitterion, can be obtained: [(tBu–N)(Al–H)₃(tBu–N(H))₃Cl((H)N–tBu)₃(Al–H)₂(Al–Cl)(N–tBu)]⁺[(tBu–N)(tBu–N(H))(AlCl₂)₂]^–. X‐ray structure analysis reveals that the anion is made of a tert‐butyl amino aluminum dichloride dimer (central Al₂N₂ ring) with one of the two nitrogen atoms being deprotonated. The cationic counterpart consists of three entities: (i) There is a first seco‐norcubane like Al₃N₄ basket with tert‐butyl groups at the nitrogen atoms, two hydride and one chloride ligand at the aluminum atoms and three hydrogen atoms on the open side of the basket, all pointing in the same direction; (ii) There is a second similar Al₃N₄ basket with the same substituent pattern except that all aluminum atoms have exclusively hydrogen ligands; (iii) Both baskets coordinate a central chloride through the six protons at the open nitrogen face of the baskets in such a way that the chloride lies in the center of a H₆ trigonal anti‐prism [mean H–Cl–H = 56.1(9)°]. As each of the open cages has a positive charge the overall charge by combination with the chloride adds to +1. The structure of the cationic part of 3 is unprecedented in AlN polycycles.     

In situ ion beam sputter deposition and X‐ray photoelectron spectroscopy (XPS) of multiple thin layers under computer control for combinatorial materials synthesis

Deposition of ultra‐thin layers under computer control is a frequent requirement in studies of novel sensors, materials screening, heterogeneous catalysis, the probing of band offsets near semiconductor junctions and many other applications. Often large‐area samples are produced by magnetron sputtering from multiple targets or by atomic layer deposition (ALD). Samples can then be transferred to an analytical chamber for checking by X‐ray photoelectron spectroscopy (XPS) or other surface‐sensitive spectroscopies. The ‘wafer‐scale’ nature of these tools is often greater than is required in combinatorial studies, where a few square centimetres or even millimetres of sample is sufficient for each composition to be tested. The large size leads to increased capital cost, problems of registration as samples are transferred between deposition and analysis, and often makes the use of precious metals as sputter targets prohibitively expensive. Instead we have modified a commercial sample block designed to perform angle‐resolved XPS in a commercial XPS instrument. This now allows ion‐beam sputter deposition from up to six different targets under complete computer control. Ion beam deposition is an attractive technology for depositing ultra‐thin layers of great purity under ultra‐high vacuum conditions, but is generally a very expensive technology. Our new sample block allows ion beam sputtering using the ion gun normally used for sputter depth‐profiling of samples, greatly reducing the cost and allowing deposition to be done (and checked by XPS) in situ in a single instrument. Precious metals are deposited cheaply and efficiently by ion‐beam sputtering from thin metal foils. Samples can then be removed, studied and exposed to reactants or surface treatments before being returned to the XPS to examine and quantify the effects. Copyright © 2016 The Authors Surface and Interface Analysis Published by John Wiley & Sons Ltd.     

The Trifluoromethyl Anion: Evidence for [K(crypt‐222)]+

[K(crypt‐222)]⁺ ( 1 ) and [K(crypt‐222)]⁺ ( 3 ) are isostructural, displaying nearly identical unit cell parameters. The two structures are similar to the extent that the previously reported [K(crypt‐222)]⁺ model can be refined against the new data for [K(crypt‐222)]⁺ , with extra electron density being observed from the fourth fluorine atom of the . In agreement with experimental observations, theoretical calculations suggest that deprotonated [K(crypt‐222)]⁺ is highly unstable even at as low as 195 K. The previously considered 1:1 CHF ₃ clathrate of deprotonated [K(crypt‐222)]⁺ (crystallographically indistinguishable from 1 ) is ruled out on the basis of all available data.     

Synthesis,Spectral, X‐Ray Diffraction,DFT, and Nematicidal Activity of Mixed Ligand Complexes of Ethyl 2‐(2‐Hydroxybenzylidine)‐Hydrazine Carboxylate and 1,10‐Phenanthroline with Some Transition Metals

In this work, mixed ligand complexes derived from ethyl 2‐(2‐hydroxybenzylidine)‐hydrazine carboxylate (HL) and 1,10‐phenanthroline (Phen) as ligands were synthesized and their structures elucidated by elemental analysis, infrared (IR), electronic,¹H NMR, and mass spectra, X‐ray diffraction (XRD), magnetic susceptibility measurements, and TG/DTG analyses. The analytical and spectral data support the formation of the complexes with the central ion in each complex six‐coordinated and a slightly distorted octahedral geometry. The IR spectra showed that HL and Phen ligands act as neutral bidentates. The XRD patterns of the complexes showed their crystalline nature. The calculated bond length and the force constant F (U═O) in the uranyl complex are 1.738 Å and 685.90 Nm⁻¹, respectively. The molar conductance values of the synthetic complexes in DMF were found to be in the range 5.00–274.06 S cm²/mol at room temperature. The thermodynamic parameters were evaluated by using the Coats–Redfern (CR) and Horowitz–Metzeger (HM) methods. Theoretical molecular structures were investigated by the density functional theory/B3LYP method using the Gaussian 98 W basis set. The nematicidal activity of the ligands and its metal complexes was also studied.     

X‐ray induced degradation of surface bound azido groups during XPS analysis

Mesoporous silica SBA‐15 was synthesized and silanized with azidopropyl triethoxysilane in order to design a clickable material. Fourier transform infrared analysis permitted to prove the attachment of the azidopropylene groups to SBA‐15 resulting in the reactive and functional material N₃‐SBA‐15. X‐ray photoelectron spectroscopy was used to determine the surface composition of SBA‐15. However, we unexpectedly found that the surface bound azido groups undergo X‐ray induced decomposition during the X‐ray photoelectron spectroscopy analysis resulting in the formation of nitrenes. These are very reactive groups able to intercalate C―C and C―H bonds of the propylene chains as judged from the N1s peak shape. Possible mechanisms of intercalation are suggested. C1s and N1s peaks were recorded at different exposure time. N/C, N⁺/N and N⁺/C undergo exponential decay. N⁺/N reaches the value of zero in less than 80 min of exposure to the X‐ray source. The N⁺/C decay plot was fitted with first‐order kinetics, and the decomposition kinetic constant (k_dec) was found to equal to 516.4 s^?1. This is a fast X‐ray induced degradation which must be considered with care when examining clickable materials with surface bound alkyl azido groups. Copyright © 2016 John Wiley & Sons, Ltd.     

Characterization of high‐aspect‐ratio periodic structures by X‐ray photoelectron spectroscopy

X‐ray photoelectron spectroscopy (XPS) is a powerful surface characterization technique often relied on for quantification of surface species and coverages. Investigation of silicon microrods, considered a model for high‐aspect‐ratio structures, at different angles with respect to substrate normal was determined to have a significant impact on the relative sensitivity of surface‐bound species on rods relative to the base substrate. Comparison between planar silicon and microrod arrays demonstrates that the angular dependence is complicated and that careful studies must optimize conditions to differentiate between surfaces. In addition, the use of reverse angle resolved XPS, where the substrate is turned away from the X‐ray source, is shown to assist in simplifying the spectrum by removing underlying signal from the substrate near the base. Copyright © 2016 John Wiley & Sons, Ltd.