Structural analysis of a melaminium polyphosphate from X-ray powder diffraction and solid-state NMR data

The crystal structure of the environmentally friendly flame retardant melaminium polyphosphate (MPoly) (2,4,6-triamino-1,3,5-triazinium x PO(3))(n)was determined by a direct-space global optimization technique from X-ray powder diffraction data. Solid-state NMR was used to corroborate the proposed hydrogen-bonding model and to determine the average degree of polymerization (n > 100). An analysis of the crystal structure of MPoly reveals aspects of molecular geometry and packing that are characteristic for melamine-containing compounds and polyphosphate salts. A comparison of MPoly with the crystal structures of its precursors melaminium orthophosphate (MP) and melaminium dihydrogenpyrophosphate (MPy) provides insight in the mechanism of the endothermic dehydration processes that takes place in the reaction path MP --> MPy --> MPoly. Solid-state NMR characterization of various samples of the same batch showed inhomogeneities in the MPoly composition. Various quantities of orthophosphates were found, which cannot be assigned to be MP.     

Tautomeric polymorphism in salicylideneamine derivatives: an X-ray diffraction and solid-state NMR study

The crystal structure of the N-(3-hydroxysalicylidene)-4-methoxyaniline has been studied by single-crystal X-ray diffraction and solid-state NMR spectroscopy. This is the first example of a Schiff base derived from 3-hydroxysalicylaldehyde which displays in the asymmetric unit, four distinct molecules linked together in the crystal lattice by two types of intermolecular O–HO hydrogen bonds and formed by two independent tetramers. The ¹³C CPMAS NMR study corroborates the above results; the presence of different tautomeric equilibria in the same crystal structure is demonstrated and a qualitative estimation of the equilibrium mixture composition is given.     

Crystal polymorphism of protein GB1 examined by solid-state NMR spectroscopy and X-ray diffraction

The study of micro- or nanocrystalline proteins by magic-angle spinning (MAS) solid-state NMR (SSNMR) gives atomic-resolution insight into structure in cases when single crystals cannot be obtained for diffraction studies. Subtle differences in the local chemical environment around the protein, including the characteristics of the cosolvent and the buffer, determine whether a protein will form single crystals. The impact of these small changes in formulation is also evident in the SSNMR spectra; however, the changes lead only to correspondingly subtle changes in the spectra. Here, we demonstrate that several formulations of GB1 microcrystals yield very high quality SSNMR spectra, although only a subset of conditions enable growth of single crystals. We have characterized these polymorphs by X-ray powder diffraction and assigned the SSNMR spectra. Assignments of the 13C and 15N SSNMR chemical shifts confirm that the backbone structure is conserved, indicative of a common protein fold, but side chain chemical shifts are changed on the surface of the protein, in a manner dependent upon crystal packing and electrostatic interactions with salt in the mother liquor. Our results demonstrate the ability of SSNMR to reveal minor structural differences among crystal polymorphs. This ability has potential practical utility for studying the formulation chemistry of industrial and therapeutic proteins, as well as for deriving fundamental insights into the phenomenon of single-crystal growth.     

Dynamics of chloromethanes in cryptophane-E inclusion complexes: a 2H solid-state NMR and X-ray diffraction study

In this paper, we present a variable temperature (2)H solid-state NMR investigation of cryptophane-E:chloroform and cryptophane-E:dichloromethane inclusion complexes. The (2)H line shapes and nuclear spin relaxation rates were analyzed in terms of the distribution of C-D bond orientations and the time scale of the guest dynamics. It was found that encaged chloroform produces broad (2)H spectra, and that its reorientation is relatively slow with a correlation time of approximately 0.17 mus at 292 K. In contrast, the (2)H line shapes of encaged dichloromethane are narrow and the motion of this guest molecule is fast with a correlation time of approximately 1.4 ps at 283 K. The (2)H NMR data were complemented by an X-ray diffraction study of the cryptophane-E:dichloromethane structure, which was utilized in the analysis of the NMR parameters.     

Testing the limits of sensitivity in a solid-state structural investigation by combined X-ray powder diffraction, solid-state NMR, and molecular modelling

A solid state structural investigation of ethoxzolamide is performed on microcrystalline powder by using a multi-technique approach that combines X-ray powder diffraction (XRPD) data analysis based on direct space methods with information from (13)C((15)N) solid-state Nuclear Magnetic Resonance (SS-NMR) and molecular modeling. Quantum chemical computations of the crystal were employed for geometry optimization and chemical shift calculations based on the Gauge Including Projector Augmented-Wave (GIPAW) method, whereas a systematic search in the conformational space was performed on the isolated molecule using a molecular mechanics (MM) approach. The applied methodology proved useful for: (i) removing ambiguities in the XRPD crystal structure determination process and further refining the derived structure solutions, and (ii) getting important insights into the relationship between the complex network of non-covalent interactions and the induced supra-molecular architectures/crystal packing patterns. It was found that ethoxzolamide provides an ideal case study for testing the accuracy with which this methodology allows to distinguish between various structural features emerging from the analysis of the powder diffraction data.     

High-resolution solid-state 73Ge NMR spectra of hexacoordinated germanium compounds

High-resolution solid-state magic angle spinning 73Ge NMR spectra of hexavalent germanium compounds, i.e. diiodogermylene (1a) and bis(1-pyrrolyl)(meso-tetraphenylporphyrinato)germanium (3a), were determined. To the best of our knowledge, this is the first example of high-resolution solid-state 73Ge NMR spectra of hexacoordinated germanium nuclei. The symmetry requirement for observation of high-resolution solid-state 73Ge NMR spectra is discussed.     

Combinatorial multinuclear NMR and X-ray diffraction studies of uranium(VI)-nucleotide complexes

The complex formation of uranium(VI) with four nucleotides, adenosine- (AMP), guanosine- (GMP), uridine- (UMP), and cytidine-monophosphate (CMP), has been studied in the alkaline pH range (8.5-12) by (1)H, (31)P, (13)C, and (17)O NMR spectroscopy, providing spectral integral, chemical shift, homo- and heteronuclear coupling, and diffusion coefficient data. We find that two and only two complexes are formed with all ligands in the investigated pH region independently of the total uranium(VI) and ligand concentrations. Although the coordination of the 5'-phosphate group and the 2'- and 3'-hydroxyl groups of the sugar unit to the uranyl ions is similar to that proposed earlier ("Feldman complex"), the number and the structures of the complexes are different. The uranium-to-nucleotide ratio is 6:4 in one of the complexes and 3:3 in the other one, as unambiguously determined by a combinatorial approach using a systematic variation of the ratio of two ligands in ternary uranium(VI)-nucleotide systems. The structure of the 3:3 complex has been determined by single-crystal diffraction as well, and the results confirm the structure proposed by NMR in aqueous solution. The results have important implications on the synthesis of oligonucleotides.     

X-ray diffraction and NMR studies on a series of Binap-based Ru(II) hydroxyphosphine pi-arene complexes

A series of new Ru(II) arene phosphine complexes derived from Binap have been prepared. Specifically, reaction of Ru(OAc)(2)(Binap) with 3,5-(CF(3))(2)C(6)H(3))(4)B (BArF).H(OEt(2))(2), is shown to afford new mono- and dinuclear Ru(II) hydroxyphosphine pi-arene complexes via a series of P-C bond cleavage reactions. The dinuclear Ru(II) pi-arene complexes contain bridging P(O)(OH)(2) ligands. Crystal structures of five new complexes are reported and suggest an eta(4)-arene rather than an eta(6)-arene coordination mode. However, in solution, their (13)C NMR data are more consistent with a strongly distorted eta(6)-coordination mode. PGSE (1)H and (19)F diffusion measurements on the dinuclear complexes suggest hydrogen bonding of the triflate anion and ion-pairing of the BArF(-) anion.     

Packing interactions in hydrated and anhydrous forms of the antibiotic Ciprofloxacin: a solid-state NMR, X-ray diffraction, and computer simulation study

We present an experimental NMR, X-ray diffraction (XRD), and computational study of the supramolecular assemblies of two crystalline forms of Ciprofloxacin: one anhydrate and one hydrate forming water wormholes. The resonance assignment of up to 51 and 54 distinct (13)C and (1)H resonances for the hydrate is reported. The effect of crystal packing, identified by XRD, on the (1)H and (13)C chemical shifts including weak interionic H-bonds, is quantified; (1)H chemical shift changes up to ～-3.5 ppm for CH···π contacts and ～+2 ppm (CH···O((-))); ～+4.7 ppm (((+))NH···O((-))) for H-bonds. Water intake induces chemical shift changes up to 2 and 5 ppm for (1)H and (13)C nuclei, respectively. Such chemical shifts are found to be sensitive detectors of hydration/dehydration in highly insoluble hydrates.     

Styryl dyes. Synthesis and study of the solid-state [2+2] autophotocycloaddition by NMR spectroscopy and X-ray diffraction

New styryl dyes of the pyridine and benzothiazole series were synthesized with the aim of investigating the solid-state [2+2] autophotocycloaddition (PCA) reaction. The ¹H NMR spectroscopy showed that for most of the compounds under study, the visible light irradiation of thin polycrystalline films of the dyes affords cyclobutane derivatives. The rate of the photoreaction depends on the structure of the dye and is higher for compounds, which contain a short N-substituent in the heterocyclic moiety and have strong absorption in the visible region. Dyes bearing electron-releasing substituents in the benzene ring undergo the stereospecific PCA in the syn-head-to-tail dimeric pair to give the only rctt isomer of cyclobutane derivatives. Electron-withdrawing and bulky substituents in the benzene fragment of styryl dyes extend the range of the mutual orientations of the molecules in the dimeric pairs, resulting in the formation of two or even four isomeric cyclobutanes in the PCA reactions. The structures of some dyes were established by X-ray diffraction. In the overwhelming majority of the structures, one of two packing modes, either syn-head-to-tail or syn-head-to-head, with extensive stacking interactions is observed. A rare example of the anti-head-to-head stacking mode was found for the dicationic dye containing the bulky N⁺(Et)Me₂ substituent in the benzene ring. The syn-head-to-tail and anti-head-to-head stacking modes can facilitate the PCA reaction due to the close spatial proximity of the ethylenic bonds and their parallel orientation in the dimeric pairs of the dye molecules. Dedicated to Academician G. A. Abakumov on the occasion of his 70th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1797–1819, September, 2007.     

Solution and solid-state NMR studies of some cadmium-selenone complexes

Cadmium(II) complexes of Imidazolidine-2-selenone (ImSe) and its derivatives have been prepared with the general formula Cd(RImSe)2Cl2 (where R=Me, Et, Pr, etc.). These complexes are characterized by elemental analysis, IR and NMR (1H, 13C, 77Se and 113Cd) spectroscopy. An upfield shift in C=Se resonance of selenones in 13C NMR and in 77Se and high-frequency shifts in N-H resonances in 1H are consistent with the selenium coordination to Cd(II). The 77Se nucleus in Cd(ImSe)2Cl2 is shielded by 38 ppm on coordination, relative to the free ligand. The principal components of the 77Se, 113Cd and 13C shielding tensors for the complexes were determined from solid-state NMR data. Large selenium chemical shift anisotropies were observed for these complexes.     

Activation of molecular hydrogen over a binuclear complex with Rh2S2 core: DFT calculations and NMR mechanistic studies

The dicationic complex [(triphos)Rh(mu-S)(2)Rh(triphos)](2+), 1 (modeled as 1c) [triphos = CH(3)C(CH(2)PPh(2))(3)], is known to activate two dihydrogen molecules and produce the bis(mu-hydrosulfido) product [(triphos)(H)Rh(mu-SH)(2)Rh(H)(triphos)](2+), 2 (modeled as 2b), from which 1 is reversibly obtained. The possible steps of the process have been investigated with DFT calculations. It has been found that each d(6) metal ion in 1c, with local square pyramidal geometry, is able to anchor one H(2) molecule in the side-on coordination. The step is followed by heterolytic splitting of the H-H bond over one adjacent and polarized Rh-S linkage. The process may be completed before the second H(2) molecule is added. Alternatively, both H(2) molecules are trapped by the Rh(2)S(2) core before being split in two distinct steps. Since the ambiguity could not be solved by calculations, (31)P and (1)H NMR experiments, including para-hydrogen techniques, have been performed to identify the actual pathway. In no case is there experimental evidence for any Rh-(eta(2)-H(2)) adduct, probably due to its very short lifetime. Conversely, (1)H NMR analysis of the hydride region indicates only one reaction intermediate which corresponds to the monohydride-mu-hydrosulfide complex [(triphos)Rh(H)(mu-SH)(mu-S)Rh(triphos)](2+) (3) (model 5a). This excludes the second hypothesized pathway. From an energetic viewpoint the computational results support the feasibility of the whole process. In fact, the highest energy for H(2) activation is 8.6 kcal mol(-1), while a larger but still surmountable barrier of 34.6 kcal mol(-1) is in line with the reversibility of the process.     

Preparation and X-ray diffraction studies of curium hydrides

Curium hydrides were prepared by reaction of curium-248 metal with hydrogen and characterized by X-ray powder diffraction. Several of the syntheses resulted in a hexagonal compound with average lattice parameters of a₀ = 0.3769(8) nm and c₀ = 0.6732(12) nm. These products are considered to be CmH_3?δ by analogy with the behavior of lanthanide-hydrogen and lighter actinide-hydrogen systems. Face-centered cubic products with an average lattice parameter of a₀ = 0.5322(4) nm were obtained from other curium hydride preparations. This parameter is slightly smaller than that reported previously for cubic curium dihydride, CmH_2+x (B. M. Bansal and D. Damien, Inorg. Nucl. Chem. Lett., 6, 603, 1970). The present results established a continuation of typical heavy trivalent lanthanide-like behavior of the transuranium actinide-hydrogen systems through curium.     

NMR assignments and single-crystal X-ray diffraction analysis of deoxyloganic acid

7-Deoxyloganic acid (1), citrusin C (2), 3,4-dihydroxyl benzoic acid (3) and (E)-caffeic acid (4) were isolated from the water-soluble fraction of ethanol extracts of Morina nepalensis var. alba Hand.-Mazz. and their structures were determined on the basis of spectroscopic evidence. The total assignments of 1H and 13C NMR spectra of 1 in solvents CD3OD, D2O and CDCl3 were reported, in addition to the single-crystal X-ray diffraction analysis of its tetraacetate 1a. All compounds were obtained from Morina genus for the first time.     

含氧催化剂的17O固体核磁共振谱学研究

含氧催化剂在工业催化等多个领域有重要应用.氧离子半径很大,而且往往出现在材料的关键位点,所以一般认为氧与吸附和催化过程密切相关.17O是氧的唯一有核磁共振响应的稳定同位素,其化学范围极宽(>1000 ppm),能灵敏反映结构信息;由于是四极核(I>1/2),其四极耦合作用也能用于结构研究.因此,17O固体核磁共振谱学应是一种能提供丰富催化剂结构信息的理想表征手段.然而,目前17O固体核磁共振研究催化剂并非常规手段,这主要是因为17O的天然丰度很低,同位素标记较为昂贵和困难,其较低的旋磁比和较大的四极耦合作用导致谱线加宽,难以获得高质量的谱图并加以解析.随着高磁场和高速魔角旋转等技术的发展,17O固体核磁共振谱学可以用于一系列简单氧化物和沸石等催化剂的结构研究.近年来,随着双旋转(DOR)、动态角旋转(DAS)、多量子魔角旋转(MQMAS)以及卫星跃迁魔角旋转(STMAS)等新技术的发展,能够消除二阶四极耦合作用带来的谱线展宽,显著提升谱图分辨率.而诸如交叉极化(CP)和旋转回波双共振(REDOR)技术,已经能用于探索氧与其它原子核空间相关方面的信息,成为研究催化剂相关作用的基础.本文综述了氧化物及相关催化剂17O固体核磁共振谱学研究的新进展.17O核磁共振谱学用于简单氧化物催化剂的结构研究,已经能够区分催化剂结构中不同晶相以及不同结晶学位点的氧物种,而1H→17O双共振实验也能用于选择表面羟基物种.对纳米氧化物结构的近期研究表明,17O核磁共振能将纳米氧化铈材料表面第1、2、3层、表面羟基、与氧空位靠近的氧物种与“体相”氧物种区分开来;此外借助17O-水和纳米氧化物作用,实现表面选择标记,为进一步探索催化剂结构和催化机理提供了新的可能.对于复合氧化物和负载催化剂,17O核磁共振谱学能够有效研究与催化性能最为相关的界面结构.在重要的氧化物催化材料沸石的研究中,17O核磁共振也发挥了巨大作用.借助高分辨率17O核磁共振方法,能够区分沸石中Si-O-Si和Si-O-Al物种,在一部分沸石中还能将不同结晶学位置的T-O-T’物种区分开来,并观测到天然沸石中违反Lowenstein规则,出现Al-O-Al物种的情况.借助双共振实验能够对与催化活性最为相关的B酸位Si-O(H)-Al结构和酸性进行研究,这一方法与探针分子相结合,已经能够对沸石和小分子的相互作用进行研究,提供吸附过程的重要信息.包括杂多酸和层状双氢氧化物在内的重要含氧催化材料也能够借助17O固体核磁共振进行局域结构和相互作用的研究.随着表面选择标记和动态核极化等选择表面研究的17O核磁共振技术的发展,我们能实现更为高效的表面结构的17O核磁共振观测,这一谱学方法将提供更多有关含氧催化剂和外来物种相互作用的信息,为研究氧化物催化剂及其催化应用提供新的策略.     

X-ray diffraction studies of platinum-alumina catalysts in a high-temperature chamber

X-ray diffraction studies of platinum-alumina catalysts in a high-temperature chamber have revealed that for the catalysts obtained by the reduction of preactivated samples, no complete reduction of platinum takes place.

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Synthesis, solid-state NMR, and X-ray powder diffraction characterization of group 12 coordination polymers, including the first example of a C-mercuriated pyrazole

Cadmium and mercury acetates have been reacted with pyrazole (Hpz) and 3,5-dimethylpyrazole (Hdmpz), affording distinct mixed-ligand species, selectively prepared upon slightly modifying the reaction conditions. Two polymorphs of [{Cd(mu-ac)2(Hpz)2}n], as well as the [{Cd(mu-ac)2(Hdmpz)2}n] species (Hac = acetic acid), were obtained by solution chemistry, while the two-dimensional [{Cd3(mu3-ac)4(mu-pz)2(Hpz)2}n] and [{Cd(mu-ac)(mu-pz)}n] polymers were prepared upon controlled thermal treatment of one of the [{Cd(mu-ac)2(Hpz)2}n] forms. Two mercury derivatives, [{Hg3(mu-ac)3(mu-pz)3}n] and [{Hg(ac)(mu-dmpz)}n], were also prepared, the latter containing one-dimensional chains of Hg(II) ions bridged by C-mercuriated Hdmpz ligands. All their crystal structures (but one) were determined by powder diffraction methods using conventional X-ray laboratory equipment, supported by 13C CPMAS NMR measurements. The latter method helped in assigning a C-metalated nature to an amorphous material of [Hg(ac)(pz)] formula, obtained by employing EtOH as a solvent. A few other Hdmpz-containing cadmium acetates were also prepared, but their polyphasic nature, evidenced by diffraction methods, hampered their complete structural characterization.     

NMR and X-ray diffraction studies of the influence of adsorbed molecule nature on phase transitions in a ZSM-5 silicalite

Pulsed NMR and X-ray diffraction analysis are employed to study the influence of adsorbed toluene, p-xylene, acetone, and di(ethylene glycol) (DEG) molecules on phase transitions in a ZSM-5 silicalite. In the region of phase transitions, times T₁ and T₂ of longitudinal and transverse magnetic relaxation of apolar molecules adsorbed in silicalite micropores increase and decrease in a jumpwise manner, respectively, with a rise in the total content of the liquid. Such changes in T₁ and T₂ occur for hexane, decane, toluene, and p-xylene molecules. Qualitatively different concentration dependences of T₁ and T₂ are observed for polar acetone and DEG molecules, because these liquids do not cause a earrangement in the crystal lattice of silicalite; this is confirmed by the X-ray diffraction data.Translated from Kolloidnyi Zhurnal, Vol. 66, No. 6, 2004, pp. 802–806.Original Russian Text Copyright © 2004 by Pimenov, Skirda, Maksimenko, Morozov, Opanasyuk.