X‐ray structural analysis and theoretical studies of new phosphite‐derived ylides

The reaction between dialkyl acetylenedicarboxylates and NH heterocyclic compounds in the presence of triethyl phosphite leads to stable phosphorus ylide derivatives in good yields. The X‐ray crystallographic data and theoretical study show that there is a resonance between two bonds of C₁₉P₁ and C₁₉₁O₁₉₁ in phosphorus ylide 4d . This compound crystallizes in the orthorhombic system, space group (Pca2₁), with unit cell parameters a = 17.3699(3) Å, b = 13.5500(2) Å, c = 18.4627(3) Å, α = 90°, β = 90°, γ = 90°, Z = 8, and V = 4345.4(12) ų. © 2011 Wiley Periodicals, Inc. Heteroatom Chem 22:715–722, 2011; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.20739     

NMR and X‐ray structural studies on 3‐benzyl‐8‐bromoadenine

8‐Bromoadenine was benzylated in the presence of base to give a mixture of two regioisomers. One was easily recognized as 9‐benzyl‐8‐bromoadenine, but the other structure could not be determined with absolute certainty by NMR. Therefore, X‐ray crystallography was used to prove that the benzyl group was attached to N‐3. Furthermore, it is shown that the 3‐benzyl adenine derivative exists as the amine tautomer both in the crystalline state as well as in solution (DMSO‐d₆), with restricted rotation around the N⁶? C6 bond. J. Heterocyclic Chem., (2011).     

Crystal‐Field and Covalency Effects in Uranates: An X‐ray Spectroscopic Study

The electronic structure of U^V‐ and U^VI‐containing uranates NaUO₃ and Pb₃UO₆ was studied by using an advanced technique, namely X‐ray absorption spectroscopy (XAS) in high‐energy‐resolution fluorescence‐detection (HERFD) mode. Due to a significant reduction in core–hole lifetime broadening, the crystal‐field splittings of the 5f shell were probed directly in HERFD‐XAS spectra collected at the U 3d edge, which is not possible by using conventional XAS. In addition, the charge‐transfer satellites that result from U 5f–O 2p hybridization were clearly resolved. The crystal‐field parameters, 5f occupancy, and degree of covalency of the chemical bonding in these uranates were estimated by using the Anderson impurity model by calculating the U 3d HERFD‐XAS, conventional XAS, core‐to‐core (U 4f–3d transitions) resonant inelastic X‐ray scattering (RIXS), and U 4f X‐ray photoelectron spectra. The crystal field was found to be strong in these systems and the 5f occupancy was determined to be 1.32 and 0.84 electrons in the ground state for NaUO₃ and Pb₃UO₆, respectively, which indicates a significant covalent character for these compounds.     

Spectroscopic and X‐ray structural characterization of new polymeric organotin(IV) carboxylates and their in vitro antifungal activities: Part II

The reactions of R₃SnCl (R = Me, Bu or Ph) with sodium 4‐phenylbutyrate, Na(OPh^b), in EtOH yielded three polymeric triorganotin carboxylates, namely [R₃Sn(OPh^b)]_n (R = Me ( 1 ), Bu ( 2 ) or Ph ( 3 )). All complexes were spectroscopically characterized using Fourier transform infrared, ¹¹⁹Sn Mössbauer, ¹H NMR, ¹³C{¹H} NMR and ¹¹⁹Sn{¹H} NMR spectral techniques. In addition, the crystal structures of 1 and 3 were determined using single‐crystal X‐ray diffraction. Their polymeric structures are sustained by bridging carboxylates which connect two five‐coordinate Sn(IV) centres. Each metallic cation displays a distorted trigonal bipyramidal coordination geometry (Addison's parameters ranging from 0.84 in 1 to 0.77–0.91 in 3 ), with the oxygen atoms occupying the apical positions and the organic groups at the equatorial corners. The one‐dimensional zigzag chains of 1 propagate along the b ‐axis, whereas 3 displays wave‐like double polymeric chains along the b ‐axis. For both 1 and 3 , parallel one‐dimensional polymeric chains are interconnected by C─H⋅⋅⋅π interactions. The antifungal activity of 1 – 3 was screened against Candida albicans (ATCC 18804), C. tropicalis (ATCC 750), C. glabrata (ATCC 90030), C. parapsilosis (ATCC 22019), C. lusitaniae (CBS 6936) and C. dubliniensis (clinical isolate 28). The antifungal activity of 3 was noteworthy since it was not only more active than 1 and 2 , but also more active than the control drugs (nystatin and fluconazole nitrate) in some cases.     

Phosphoramides: Synthesis,Spectroscopy, and X‐ray Crystallography

A series of new phosphoramides with general formula RP(O)X₂, where R = amino/p‐methylphenoxy and X = amine, were synthesized and characterized by ¹H, ¹³C, ³¹P nuclear magnetic resonance (NMR), and infrared (IR) spectroscopy and elemental analysis. The ³¹P{¹H} NMR spectra show that among compounds 7–9 containing 2‐, 3‐, and 4‐aminopyridinyl moieties, respectively, the shielding order of the P atom decreases as 7 > 9 > 8 . Also, the structure of compound 7 was determined by X‐ray crystallography. In this structure, repeated noncentrosymmetric dimers are formed by two strong intermolecular N(1)‐H(1N)…N(2) and N(3)‐H(3N)…O(1) hydrogen bonds. Taking into account weak intermolecular C(17)‐H(17C)…N(4), C(17)‐H(17E)…N(4), C(2)‐H(2A)…O(2), and also weak aromatic C—H…C interactions, a three‐dimensional polymeric chain is created in the crystalline network. The density functional theory calculations at B3LYP, B3PW91, and M06 levels using the 6–31+G** basis set were in good agreement with the X‐ray crystallography data.     

X‐ray photoelectron spectroscopy studies of chromium compounds

Photoelectron spectra of a number of chromium oxides and other compounds were studied under high spectral resolution conditions chosen to reduce the possibility of differential charging. Some of the suite of Cr(III) compounds chosen for study produced Cr 2p spectra containing fine structure that could be identified with multiplet splitting. The splitting patterns produced were similar for all trivalent binary and ternary oxides and sulphides whose patterns closely reproduced the splitting predicted for the Cr(III) free ion by Gupta and Sen. The fine structure observed for compounds such as chromium (III) chloride had a distinctly different pattern. A number of other chromium (III) compounds were studied that did not exhibit the fine structure described above; nonetheless, well‐defined line shapes and reproducible peak centroids were obtained by fitting protocols. The use of such information to determine surface chemistry on chromated steels is described, based on the spectral knowledge of chromium (III) oxides and hydroxides and the chromium (VI) oxide systems. Copyright © 2004 John Wiley & Sons, Ltd.     

Computational, 1H NMR,and X‐ray structural studies on 1‐arylurazole tetrazane dimers

Nitrogen‐centered urazole radicals exist in equilibrium with tetrazane dimers in solution. The equilibrium established typically favors the free‐radical form. However, 1‐arylurazole radicals bearing substituents at the ortho position favor the dimeric form. We were able to determine the structure of one of the dimers (substituted at both ortho positions with methyl groups), namely 1,2‐(2,4‐dimethylphenyl)‐2‐[2‐(2,4‐dimethylphenyl)‐4‐methyl‐3,5‐dioxo‐1,2,4‐triazolidin‐1‐yl]‐4‐methyl‐1,2,4‐triazolidine‐3,5‐dione, C₂₄H₂₈N₆O₄, via X‐ray crystallography. The experimentally determined structure agreed well with the computationally obtained geometry at the B3LYP/6‐311G(d,p) level of theory. The preferred syn conformation of these 1‐arylurazole dimers results in the two aromatic rings being proximate and nearly parallel, which leads to some interesting shielding effects of certain signals in the ¹H NMR spectrum. Armed with this information, we were able to decipher the more complicated ¹H NMR spectrum obtained from a dimer that was monosubstituted at the ortho position with a methyl group.     

Pallada‐ and platinacycle complexes of phosphorus ylides; synthesis,X‐ray characterization,theoretical and electrochemical studies and application of Pd(II) complexes as catalyst in Suzuki‐Miyaura coupling reaction

The new unsymmetrical phosphonium salts [Ph₂PCH₂PPh₂CH₂C(O)C₆H₄R]Br (R= m ‐Br ( S ₁ ) and p ‐CN ( S ₂ )) were synthesized in the reaction of 1,1‐bis(diphenylphosphino)methane (dppm) and BrCH₂C(O)C₆H₄R (R= m ‐Br and p ‐CN) ketones, respectively. Further treatment with NEt₃ gave the α‐keto stabilized phosphorus ylides Ph₂PCH₂PPh₂C(H)C(O)C₆H₄R (R= m ‐Br ( Y ₁ ) and p ‐CN ( Y ₂ )). These ligands were reacted with [MCl₂(cod)] (M= Pd and Pt; cod= 1,5‐cyclooctadiene) to give the pallada‐ and platinacycle complexes [MCl₂(Ph₂PCH₂PPh₂C(H)C(O)C₆H₄R)] (M= Pd, R= m ‐Br ( 3 ); R= p ‐CN ( 4 ) and M= Pt, R= m ‐Br ( 5 ); R= p ‐CN ( 6 )). Cyclic voltammetry, elemental analysis, IR and NMR (¹H, ¹³C and ³¹P) spectroscopic methods were used for characterization of the obtained compounds. Further, the structure of complexes 3 and 4 were characterized crystallographically. Palladacycles 3 and 4 were proved to be excellent catalysts for the Suzuki‐Miyaura coupling reactions of various aryl chlorides and arylboronic acids in mixed DMF/H₂O media. Also, the bonding situations between two interacted fragments [PtCl₂] and Y ₁ and Y ₂ ligands in platinacycles 5 and 6 were investigated based on DFT method by using NBO, EDA and ETS‐NOCV analysis.     

NMR and X‐ray crystallographic studies of linear and cyclic aminomethanephosphinates

We report the preparation of four diastereoisomeric pairs of ethyl {[(3‐hydroxypropyl)‐ amino](aryl)methyl}phenylphosphinates. In two cases, the phosphinates were transformed to 1,4,2‐oxazaphosphepane heterocycles through one‐pot intramolecular esterification. The analogous reaction with formaldehyde gave the six‐membered ethyl (1,3‐oxazinan‐3‐ylmethyl)phenylphosphinate, which could be transformed in a posterior reaction to the corresponding aminomethanephosphinic acid. The new compounds were characterized by IR, ¹H, ¹³C, and ³¹P NMR. © 2006 Wiley Periodicals, Inc. Heteroatom Chem 17:81–87, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20179     

Synthesis,NMR spectroscopic and X‐ray crystallographic studies of functionalized 2‐aminopyrrolin‐4‐ones

An efficient method for the preparation of novel cyano derivatives of 4‐amino‐3‐hydroxybutenoic acids 4–8 and N‐substituted‐2‐aminopyrrolin‐4‐ones 9–18 is described; the structure of compound 13 has been elucidated with X‐ray analysis.     

Thermal and X‐ray powder diffraction studies of aliphatic polyester dendrimers

The syntheses and thermal and X‐ray powder diffraction analyses of three sets of aliphatic polyester dendrimers based on 2,2‐bis(hydroxymethyl)propionic acid as a repeating unit and 2,2‐dimethyl‐1,3‐propanediol, 1,5‐pentanediol, and 1,1,1‐tris(hydroxymethyl)ethane as core molecules are reported. These dendritic polyesters were prepared in high yields with the divergent method. The thermal properties of these biodendrimers were evaluated with thermogravimetric analysis and differential scanning calorimetry. The thermal decomposition of the compounds occurred around 250 °C for the hydroxyl‐ended dendrimers and around 150 °C for the acetonide‐protected dendrimers. In addition, the crystallinity of the lower generation dendrimers was evaluated with X‐ray powder diffraction. The highest crystallinity and the highest melting points were observed for the first‐generation dendritic compounds. The higher generation dendrimers showed weaker melting transitions during the first heating scan. Only the glass‐transition temperatures were observed in subsequent heating scans. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5574–5586, 2004     

Synthesis and X‐ray Crystal Structures of Homotrimetallic Zinc Bisureate Complexes

Alkane elimination reactions of the tethered bis(urea) proligand 1,4‐(tBuNHCONH)₂‐C₄H₈ ( 1 ) with ZnR₂ (R = Me, Et, nPr) yielded trimetallic zinc complexes [RZn‐1,4‐(tBuNHCON)₂‐C₄H₈]₂Zn [R = Me ( 2 ), Et ( 3 ), and nPr ( 4 )]. 2 – 4 were characterized by heteronuclear NMR (¹H, ¹³C) and IR spectroscopy, elemental analysis, and single‐crystal X‐ray diffraction.     

Morphology of polyanhydride copolymers: Time‐resolved small‐angle X‐ray scattering studies of crystallization

Synchrotron small‐angle X‐ray scattering (SAXS) was used to study the isothermal crystallization kinetics of a family of polyanhydride copolymers consisting of 1,6‐bis(p‐carboxyphenoxy)hexane and sebacic acid monomers. In situ SAXS experiments permitted the direct observation of the crystallization kinetics. The structural parameters (the long period, lamellar thickness, and degree of crystallinity) were obtained from Lorentz‐corrected intensity profiles, one‐dimensional correlation functions, and interface distribution functions to form a comprehensive picture of the crystal morphology. The combination of these three analyses provided information not only on the lamellar dimensions but also on the polydispersity (nonuniformity) of these dimensions. Where possible, the crystallization kinetics were interpreted with a modified version of the Avrami equation. The results can be used to perform the rational design of controlled‐drug‐release formulations because crystallinity affects drug‐release kinetics. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 463–477, 2005     

Uncertainty quantification in theoretical spectroscopy: The structural sensitivity of X‐ray emission spectra

We present a methodology for analyzing the dependence of molecular spectra calculated with quantum‐chemical methods on the underlying molecular structure. This analysis is applied to investigate the structural sensitivity of calculated valence‐to‐core X‐ray emission (VtC‐XES) spectra for the test case of three iron carbonyl complexes, Fe(CO)₅, [FeCp(CO)₂(THF)]⁺ (Cp = cyclopentadienyl, THF = tetrahydrofuran), and Fe(CO)₃(cod) (cod = cyclooctadienyl). Based on this analysis, we discuss how the VtC‐XES spectra depend on changes of metal–ligand bond distances and bond angles as well as on the structure of the ligands. The benefits of such an analysis of the structural sensitivity are discussed. Our methodology can serve as a first step toward quantifying and accounting for uncertainties due to the underlying model structure in theoretical spectroscopy.     

Molecular relaxation of isotactic polystyrene: Real‐time dielectric spectroscopy and X‐ray scattering studies*

The molecular relaxation processes and structure of isotactic polystyrene (iPS) films were investigated with real‐time dielectric spectroscopy and simultaneous wide‐ and small‐angle X‐ray scattering. The purpose of this work was to explore the restrictions imposed on molecular mobility in the vicinity of the α relaxation (glass transition) for crystallized iPS. Isothermal cold crystallization at temperatures of T_c = 140 or 170 °C resulted in a sigmoidal increase of crystallinity with crystallization time. The glass‐transition temperature (T_g), determined calorimetrically, exhibited almost no increase during the first stage of crystal growth before impingement of spherulites. After impingement, the calorimetric T_g increased, suggesting that confinement effects occur in the latter stages of crystallization. For well‐crystallized samples, the radius of the cooperativity region decreased substantially as compared with the purely amorphous sample but was always smaller than the layer thickness of the mobile amorphous fraction. Dielectric experiments directly probed changes in the amorphous dipole mobility. The real‐time dielectric data were fitted to a Havriliak–Negami model, and the time dependence of the parameters describing the distribution of relaxation times and dielectric strength was obtained. The central dipolar relaxation time showed little variation before spherulite impingement but increased sharply during the second stage of crystal growth as confinement occurred. Vogel–Fulcher–Tammann analysis demonstrated that the dielectric reference temperature, corresponding to the onset of calorimetric T_g, did not vary for well‐crystallized samples. This observation agreed with a model in which constraints affect primarily the modes having longer relaxation times and thus broaden the glass‐transition relaxation process on the higher temperature side. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 777–789, 2004     

Synthesis,X‐ray Analysis,and Biological Activities of Novel Oxazolidinethiones

Oxazolidinethione compounds were synthesized starting from racemic and enantiopure β‐amino alcohols. The molecular structure of oxazolidinethione 6a was elucidated by single‐crystal x‐ray crystallography. Oxazolidinethione compounds screened for antimicrobial activity showed mild minimum inhibitory concentration values.