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1.
The present work focuses on the topochemical photoconversion process in which alpha-trans-cinnamic acid becomes alpha-truxillic acid. This solid-state [2 + 2] cycloaddition reaction has previously been studied with X-ray diffraction, atomic force microscopy, and vibrational spectroscopy. However structural and kinetic details about the reaction are still debated. We present results from (13)C cross-polarization magic angle spinning solid-state NMR experiments that suggest that the Johnson, Mehl, Avrami, and Kolmogorov model of phase transformation kinetics can be applied to this system. The model elucidates parameters of the reaction, such as the nucleation rate, diffusion rate, and dimensionality of the reaction. From our data, it is concluded that this reaction follows one-dimensional growth with a decreasing nucleation rate.  相似文献   

2.
13C-CPMAS and other solid-state NMR methods have been applied to monitor the solid-state reactions of trans-cinnamic acid derivatives, which are the pioneer and model compounds in the field of topochemistry previously studied by X-ray diffraction, AFM, and vibrational spectroscopy. Single-crystal X-ray analyses of photoirradiated alpha-trans-cinnamic acid where the monomers are arranged in a head-to-tail manner have revealed the formation of a centrosymmetric alpha-truxillic acid photodimer. For a centrosymmetric dimer, however, two cyclobutane carbon signals and one carbonyl carbon signal were expected apart from other aromatic carbon signals. Instead, four cyclobutane and two carbonyl carbon signals were observed suggesting the formation of a non-centrosymmetric photodimer. Removing hydrogen bonds from the system by esterfication of alpha-truxillic acid yield a centrosymmetric photodimer. Careful analysis of the obtained products via solid-state NMR clearly showed that the observed peak splittings in the 13C-CPMAS spectra did not originate from packing effects but rather result from asymmetric hydrogen bonds distorting the local symmetry. Further evidence of this rather dynamic hydrogen-bonding stems from high-temperature X-ray data revealing that only the joint approach of both X-ray analysis and solid-state NMR at similar temperatures allows for the successful characterization of dynamic processes occurring in topochemical reactions, thus, providing detailed insight into the reaction mechanism of organic solid-state transformations.  相似文献   

3.
Photoreactions of the alpha- and beta-polymorphs of trans-cinnamic acid were studied by (13)C CPMAS solid-state nuclear magnetic resonance spectroscopy, and the reactants and products were spectroscopically characterized in detail. Chemical shifts and chemical shift anisotropy tensors calculated using density functional theory (DFT) were found to be in good agreement with the experimental results and helped to identify the polymorphs and the individual assignments of reactant and photoproduct carbon atoms. The beta-polymorph is metastable. Its transformation into the alpha-cinnamic acid polymorph is monitored by temperature-dependent (13)C NMR spectroscopy. The transformation occurs at a very slow rate at room temperature but is highly accelerated at elevated temperatures. Analysis of the kinetics of the photoreaction shows that the beta-polymorph progresses at a slower rate compared to that of alpha-cinnamic acid. Based on chemical shift tensor values of reactants and products as obtained from 2D PASS spectra, the difference in reaction rates is suggested to be due to the higher amount of molecular reorientation of functional groups upon photoreaction and the larger distance between the reacting double bonds.  相似文献   

4.
Aqueous titanium citrate solutions were prepared from the reaction of citric acid with titanium 2-propoxide in a range of molar ratios. Solutions containing two or fewer citrates per titanium resulted in the slow crystallization of an insoluble titanium oxo-citrate complex. Single-crystal X-ray analysis identified the species as Ti(8)O(10)(citrate)(4)(H(2)O)(12).14H(2)O.3HOPr(i)(), crystallized in the tetragonal space group I4(1)/a, with a = 30.775(7) A, c = 14.528(7) A, V = 13 759(8) A(3), and Z = 8. The trianionic citrate ligands supply both carboxylate and alkoxide coordination and stabilize the structure using simultaneous chelating and bridging modes of attachment. The compound is a neutral species, exhibiting titanium in three contrasting environments. Laser Raman microscopy and (13)C CPMAS solid-state NMR data were consistent with those of the X-ray crystal structure. When exposed to air, the crystals rapidly lost water and became a powder. The dehydrated powder was noncrystalline to X-rays and insoluble, but (13)C NMR results demonstrated retention of the carboxylate linkages.  相似文献   

5.
在N-甲基吡咯烷酮(NMP)促进下,取代肉桂酸(1a^1g)与二氯亚砜(SOCl2)在20℃酰氯化反应0.5 h,再加入甘氨酸乙酯盐酸盐,在40℃下酰胺化反应4 h,n(取代肉桂酸)/n(SOCl2)/n(甘氨酸乙酯盐酸盐)=1.0/1.2/1.4,合成了一系列取代肉桂酰甘氨酸乙酯(2a^2g),其结构经1H NMR、13C NMR、IR和MS(EI)确证。并探讨了NMP促进取代肉桂酰甘氨酸乙酯反应可能的机理。  相似文献   

6.
We have investigated the polymorphic phase transformations above ambient temperature for 3‐chloro‐trans‐cinnamic acid (3‐ClCA, C9H7ClO2) and a solid solution of 3‐ClCA and 3‐bromo‐trans‐cinnamic acid (3‐BrCA, C9H7BrO2). At 413 K, the γ polymorph of 3‐ClCA transforms to the β polymorph. Interestingly, the structure of the β polymorph of 3‐ClCA obtained in this transformation is different from the structure of the β polymorph of 3‐BrCA obtained in the corresponding polymorphic transformation from the γ polymorph of 3‐BrCA, even though the γ polymorphs of 3‐ClCA and 3‐BrCA are isostructural. We also report a high‐temperature phase transformation from a γ‐type structure to a β‐type structure for a solid solution of 3‐ClCA and 3‐BrCA (with a molar ratio close to 1:1). The γ polymorph of the solid solution is isostructural with the γ polymorphs of pure 3‐ClCA and pure 3‐BrCA, while the β‐type structure produced in the phase transformation is structurally similar to the β polymorph of pure 3‐BrCA.  相似文献   

7.
We report the crystal structure of a new polymorph of l-tyrosine (denoted the β polymorph), prepared by crystallization from the gas phase following vacuum sublimation. Structure determination was carried out by combined analysis of three-dimensional electron diffraction (3D-ED) data and powder X-ray diffraction (XRD) data. Specifically, 3D-ED data were required for reliable unit cell determination and space group assignment, with structure solution carried out independently from both 3D-ED data and powder XRD data, using the direct-space strategy for structure solution implemented using a genetic algorithm. Structure refinement was carried out both from powder XRD data, using the Rietveld profile refinement technique, and from 3D-ED data. The final refined structure was validated both by periodic DFT-D calculations, which confirm that the structure corresponds to an energy minimum on the energy landscape, and by the fact that the values of isotropic 13C NMR chemical shifts calculated for the crystal structure using DFT-D methodology are in good agreement with the experimental high-resolution solid-state 13C NMR spectrum. Based on DFT-D calculations using the PBE0-MBD method, the β polymorph is meta-stable with respect to the previously reported crystal structure of l-tyrosine (now denoted the α polymorph). Crystal structure prediction calculations using the AIRSS approach suggest that there are three other plausible crystalline polymorphs of l-tyrosine, with higher energy than the α and β polymorphs.

A new polymorph of l-tyrosine is reported, with the crystal structure determined by combined analysis of 3D-ED data and powder XRD data, augmented by information from periodic DFT-D calculations and solid-state 13C NMR data.  相似文献   

8.
Polymorphs I and II of phenylpyruvic acid are obtained as mixtures of both crystal forms or relatively pure crystals, from different solvents. Polymorph I is more stable than polymorph II at room temperature. Spectral characteristics of these polymorphs are discussed on the basis of IR, Raman and solid state 13C NMR spectra. Also, the assignment of the IR features observed in the 1600–1700 cm−1 region is re-investigated by referring to the spectra of heavy-atom substituted derivatives. It is suggested that the C=O stretching band is split by the crystal field for both polymorphs.  相似文献   

9.
An integrated suite of synthesis and characterisation techniques that includes synchrotron-based single crystal, powder X-ray diffraction, nuclear magnetic resonance and electron diffraction have been employed to uncover two new distinct structures in the Ca(x)Ba(2-x)P(2)O(7) polymorphic phosphate system. These materials have particular relevance for their application as both biomaterials and phosphors. Calcium barium pyrophosphate, CaBaP(2)O(7), was shown by a combination of spectroscopic and diffraction techniques to have two polymorphs distinct in structure from all of the five previously reported polymorphs of Ca, Sr and Ba pyrophosphate. A high temperature polymorph HT-CaBaP(2)O(7) prepared at 1200 °C is orthorhombic, of space group P(212121) with a = 13.0494 ?, b = 8.9677 ?, c = 5.5444 ?. A low temperature polymorph LT-CaBaP(2)O(7), prepared below 1000 °C, is monoclinic with space group P2(1)/c and dimensions a = 12.065 ?, b = 10.582 ?, c = 9.515 ?, β = 94.609°.  相似文献   

10.
Infrared and Raman spectroscopies have been used to monitor the [2 + 2] photodimerisation reactions of alpha-trans-cinnamic acid and of a number of its derivatives. The principal changes observed in the spectra upon dimerisation are decay of a band around 1637 cm(-1), which is assigned to v(C=C) of the ethene bond of the monomer, and growth of bands just above 3000 cm(-1), which result from v(C-H) of saturated carbon atoms of the dimer. The use of microscope attachments has allowed us to follow the reactions of single crystals and we conclude that the reactions are topotactic in nature. We have carried out preliminary kinetic experiments in which spectra of one single crystal are recorded after sequential periods of photolysis. We find that the rates of dimerisation of differently substituted cinnamic acids are similar, with physical effects, such as the thickness of an individual crystal, outweighing any observed electronic effects (inductive or mesomeric).  相似文献   

11.
Seven novel R2Sn(IV)-oxydiacetate (oda) and -iminodiacetate (ida) compounds of the form [R2Sn(oda)(H2O)]2 (R = Me, nBu, and Ph) (1-3), [(R2SnCl)2(oda)(H2O)2]n (R = Et, iBu, and tBu) (4-6), and [Me2Sn(ida)(MeOH)]2 (7) have been synthesized and characterized by IR, 1H, 13C, and 119Sn NMR (solution), solid-state 119Sn CPMAS NMR, and (119m)Sn M?ssbauer spectroscopy. The crystal structure of [Me2Sn(oda)(H2O)]2, 1, shows it to be dinuclear (centrosymmetric), with two seven-coordinated tin atoms, bridged by one arm of the carboxylate group from each oda. By contrast, the crystal structure of [(Et2SnCl)2(oda)(H2O)2]n, 4, comprises a zigzag polymeric assembly containing a pair of different alternating subunits, {Et2SnCl(H2O)} and {Et2SnCl(H2O)(oda)}, which are connected by way of bridging oda carboxylates, thus giving seven-coordinate tin centers in both components. Finally, the structure of [Me2Sn(ida)(MeOH)]2, 7, also centrosymmetric dinuclear, is comprised of a pair of mononuclear units with seven-coordinate tin. The 119Sn solid-state CPMAS NMR and (119m)Sn Mossbauer suggest the presence of seven-coordinate Sn metal atoms in some derivatives and the existence of two different tin sites in the [(R2SnCl)2(oda)(H2O)2]n compounds.  相似文献   

12.
The structure of 1,3-bis(4,6-dimethyl-1H-nicotinonitrile-1-yl)1,3-dioxy propane polymorphs has been characterized by X-ray diffraction, FT-IR, 1H and 13C NMR spectroscopies. The influence of intra and intermolecular weak interactions is thoroughly studied in solid state using single crystal X-ray diffraction and FT-IR. These polymorphs belong to monoclinic space group 'P2(1/n)' and 'P2(1/c)'. These polymorphs have C-H?n (lone pair), hydrogen bonds, C-N?π, C-H?π and π?π intermolecular non-covalent interactions. These polymorphs are the result of weak interactions and solvent used in crystallization. The FT-IR spectra have been recorded in the solid phase and NMR has been recorded in solvent. The optimized geometry has been calculated by B3LYP methods using different basis sets. The FT-IR and NMR spectra of 1st polymorphs has been calculated at B3LYP/6-31G (d) level. The scaled theoretical wave number showed good agreement with the experimental values. These two polymorphs as well as other stereomers are studied by DFT calculations.  相似文献   

13.
A new organically templated gallium oxalatophosphate, (C7H20N2)0.5[Ga3(C2O4)0.5(PO4)3], has been synthesized by using a low-melting-point eutectic mixture of choline chloride and oxalic acid as a solvent and characterized by single-crystal X-ray diffraction, thermogravimetric analysis and solid-state NMR spectroscopy. It is the first example of ionothermal synthesis of organically templated metal oxalatophosphate. The structure contains double 6-ring units of the composition Ga6(PO4)6 which are connected by oxalate ligands and P-O-Ga bonds to form a 3-D framework. The charge-compensating organic ammonium cations which are disordered over two positions are located at the intersections of two types of 8-ring channels. 1H MAS and 13C CPMAS NMR studies confirm the presence of N,N,N',N'-tetramethyl-1,3-propanediammonium cation. The 71Ga and 31P MAS NMR spectra are also consistent with the crystal structure analysis results.  相似文献   

14.
The gallium aryloxide polymer, [[((t)Bu)(2)Ga](2)(mu-OC(6)H(4)O)](n)(1) is synthesized by the addition of Ga((t)()Bu)(3) with hydroquinone in a noncoordinating solvent, and reacts with pyridines to yield the yellow compound [((t)()Bu)(2)Ga(L)](2)(mu-OC(6)H(4)O) [L = py (2), 4-Mepy (3), and 3,5-Me(2)py (4)] via cleavage of the Ga(2)O(2) dimeric core. The analogous formation of Ga((t)()Bu)(2)(OPh)(py) (5) occurs by dissolution of [((t)Bu)(2)Ga(mu-OPh)](2) in pyridine. In solution, 2-4 undergo dissociation of one of the pyridine ligands to yield [((t)()Bu)(2)Ga(L)(mu-OC(6)H(4)O)Ga((t)Bu)(2)](2), for which the DeltaH and DeltaS have been determined. Thermolysis of compounds 2-4 in the solid-state results in the loss of the Lewis base and the formation of 1. The reaction of 1 or [((t)Bu)(2)Ga(mu-OPh)](2) with the vapor of the appropriate ligand results in the solid state formation of 2-4 or 5, respectively. The deltaH and deltaS for both ligand dissociation and association for the solid-vapor reactions have been determined. The interconversion of 1 into 2-4, as well as [((t)Bu)(2)Ga(mu-OPh)](2) into 5, and their reverse reactions, have been followed by (13)C CPMAS NMR spectroscopy, TG/DTA, SEM, EDX, and powder XRD. Insight into this solid-state polycondensation polymerization reaction may be gained from the single-crystal X-ray crystallographic packing diagrams of 2-5. The crystal packing for compounds 2, 3, and 5 involve a head-to-head arrangement that is maintained through repeated ligand dissociation and association cycles. In contrast, when compound 4 is crystallized from solution a head-to-tail packing arrangement is formed, but during reintroduction of 3,5-Me(2)py in the solid state-vapor reaction of compound 1, a head-to-head polymorph is postulated to account for the alteration in the deltaH of subsequent ligand dissociation reactions. Thus, the deltaH for the condensation polymerization reaction is dependent on the crystal packing; however, the subsequent reversibility of the reaction is dependent on the polymorph.  相似文献   

15.
Comprehensive structural analyses were performed for o-, m-, and p-nitrophenyl 2,3,4-tri-O-acetyl-β-d-xylopyranosides. Single-crystal X-ray diffraction data were collected and revealed that meta isomer undergoes temperature-dependent polymorph transition (crystal structures of two polymorphs were obtained). This transition was verified by differential scanning calorimetry. The number of molecules in the independent part of the crystal unit cells of the compounds under investigation was in agreement with the number of resonances in solid-state 13C and 15N NMR spectra. The o- and p-nitrophenyl 2,3,4-tri-O-acetyl-β-d-xylopyranosides exist as single polymorph at room temperature, as confirmed by powder X-ray diffraction measurements.  相似文献   

16.
Three polymorphic modifications A-C of [Fe(II)(DPPA)(NCS)(2)], where DPPA = (3-aminopropyl)bis(2-pyridylmethyl)amine is a new tetradentate ligand, have been synthesized, and their structures, magnetic properties, and M?ssbauer spectra have been investigated. For polymorph A, variable-temperature magnetic susceptibility measurements as well as M?ssbauer spectroscopy have revealed the occurrence of a rather gradual HS if LS transition without hysteresis, centered at about 176 K. The same methods have shown that polymorph B is paramagnetic over the temperature range 4.5-295 K, whereas polymorph C exhibits a very abrupt S = 2 if S = 0 transition with a hysteresis. The hysteresis width is 8 K, the transitions being centered at T(c) downward arrow = 112 K for decreasing and T(c) upward arrow = 120 K for increasing temperatures. The crystal structures of the three polymorphs have been solved by X-ray diffraction at 298 K. Polymorph A is triclinic, space group P&onemacr; with Z = 2, a = 8.710(2) ?, b = 15.645(2) ?, c = 7.985(1) ?, alpha = 101.57(1) degrees, beta = 112.59(2) degrees, and gamma = 82.68(2) degrees. Polymorph B is monoclinic, space group P2(1)/c with Z = 4, a = 8.936(2) ?, b = 16.855(4) ?, c = 13.645(3) ?, and beta = 97.78(2) degrees. Polymorph C is orthorhombic, space group Pbca with Z = 8, a = 8.449(2) ?, b = 14.239(2) ?, and c = 33.463(5) ?. In the three polymorphs, the asymmetric units are almost identical and consist of one chiral complex molecule with the same configuration and conformation. The distorted [FeN(6)] octahedron is formed by four nitrogen atoms belonging to DPPA and two provided by the cis thiocyanate groups. The two pyridine rings of DPPA are in fac positions. The main differences between the structures of the three polymorphs are found in their crystal packing. The stabilization of the high-spin ground state of polymorph B is tentatively explained by the presence of two centers of steric strain in the crystal lattice resulting in the elongation of the Fe-N(aromatic) distance. The observed hysteresis in polymorph C seems to be due to the existence of an array of intermolecular contacts in the crystal lattice making the spin transition more cooperative than in polymorph A.  相似文献   

17.
We report the highly convergent synthesis and solid-state characterization of six crystalline "molecular compasses" consisting of a central phenylene rotor with polar substituents, or compass needle, and two trityl groups axially connected by acetylene linkages to the 1,4-positions. Compounds with fluoro-, cyano-, nitro-, amino-, diamino-, and nitroamino substituents are expected to emulate the parent compound which was shown to form crystals where the central phenylene can rotate about its 1,4-axis with rate constants in the 10(3) -10(6) s(-)(1) dynamic ranges near ambient temperature, depending on crystal morphology. With data from single-crystal X-ray diffraction analysis, solid-state CPMAS (13)C NMR, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA), it is shown that a relatively small structural perturbation by a single polar group (F, CN, NO(2), NH(2)) results in isomorphous structures with analogous properties. In analogy to the parent compound, crystals grown from benzene formed clathrate structures in the space group Ponemacr; with one molecular compass and two benzene molecules per unit cell. Solvent-free crystals with the same space group obtained by a first-order phase transition between 60 and 130 degrees C were shown to be spectroscopically identical to those obtained by slow solvent evaporation from a mixture of CH(2)Cl(2) and hexanes. A qualitative analysis of the positionally disordered phenylene groups in terms of the expected solid-state rotational dynamics suggests a nonsymmetric, 2-fold rotational potential, or a process involving full 360 degrees turns.  相似文献   

18.
Characterization of clarithromycin polymorph was performed by solid-state cross polarization and magic angle spinning (CP/MAS) 13C-NMR spectroscopy. Two polymorphs, form II and form I, of clarithromycins indicated characteristic resonances of C1 carbonyl carbon at 176.2 and 175.2 ppm, respectively. Since each peak of C1 carbon was well separated in the spectrum of the two polymorphs, we performed quantitative analysis of the polymorphic fraction from the peak area of these peaks. The peak area of form I was found to linearly increase with an increase of its content, with a correlation coefficient of above 0.99. Solid-state NMR was found to be a useful technique to determine the characteristics of the polymorphic forms.  相似文献   

19.
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.  相似文献   

20.
Well-ordered cubic mesoporous silicas SBA-1 functionalized with sulfonic acid groups have been synthesized through in situ oxidation of mercaptopropyl groups with H(2)O(2) via co-condensation of tetraethoxysilane (TEOS) and 3-mercaptopropyltrimethoxysilane (MPTMS) templated by cetyltriethylammonium bromide (CTEABr) under strong acidic conditions. Various synthesis parameters such as the amounts of H(2)O(2) and MPTMS on the structural ordering of the resultant materials were systematically investigated. The materials thus obtained were characterized by a variety of techniques including powder X-ray diffraction (XRD), multinuclear solid-state Nuclear Magnetic Resonance (NMR) spectroscopy, (29)Si{(1)H} 2D HETCOR (heteronuclear correlation) NMR spectroscopy, thermogravimetric analysis (TGA), and nitrogen sorption measurements. By using (13)C CPMAS NMR technique, the status of the incorporated thiol groups and their transformation to sulfonic acid groups can be monitored and, as an extension, to define the optimum conditions to be used for the oxidation reaction to be quantitative. In particular, (29)Si{(1)H} 2D HETCOR NMR revealed that the protons in sulfonic acid groups are in close proximity to the silanol Q(3) species, but not close enough to form a hydrogen bond.  相似文献   

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