共查询到20条相似文献,搜索用时 15 毫秒
1.
Jiliang Zhang Yong-Mook Kang Guangcun Shan Svilen Bobev 《Acta Crystallographica. Section C, Structural Chemistry》2019,75(5):562-567
The crystal structure of the gadolinium iron bismuthide Gd6FeBi2 has been characterized by single‐crystal X‐ray diffraction data and analyzed in detail using first‐principles calculations. The structure is isotypic with the Zr6CoAl2 structure, which is a variant of the ZrNiAl structure and its binary prototype Fe2P (Pearson code hP9, Wyckoff sequence g f d a). As such, the structure is best viewed as an array of tricapped trigonal prisms of Gd atoms centered alternately by Fe and Bi. The magnetic‐ordering temperature of this compound (ca 350 K) is much higher than that of other rare‐earth metal‐rich phases with the same or related structures. It is also higher than the ordering temperature of many other Gd‐rich ternary phases, where the magnetic exchange is typically governed by Ruderman–Kittel–Kasuya–Yosida (RKKY) interactions. First‐principles calculations reveal a larger than expected Gd magnetic moment, with the additional contribution arising from the Gd 5d electrons. The electronic structure analysis suggests strong Gd 5d–Fe 3d hybridization to be the cause of this effect, rather than weak interactions between Gd and Bi. These details are of importance for understanding the magnetic response and explaining the high ordering temperature in this material. 相似文献
2.
《Acta Crystallographica. Section C, Structural Chemistry》2018,74(4):460-464
Single crystals of the vanadate garnet Ca2NaCd2V3O12 (dicalcium sodium dicadmium trivanadate) were synthesized using the floating‐zone method and the crystal structure was investigated using single‐crystal X‐ray diffraction. We considered the effectiveness of substitution of the Y‐site cation with reference to previous structural studies of vanadate garnets. The structures of vanadate garnets are subject to geometric constraints similar to those of silicate garnets. These constraints force the tetrahedral–dodecahedral shared edge length in vanadate garnets to become shorter than the unshared dodecahedral edge length, as in ugrandite (uvarovite, grossular and andradite) garnets. However, the vanadate garnet Ca2NaCd2V3O12 exhibits the normal structural feature, similar to pyralspite (pyrope, almandine and spessartine) garnets, namely that the dodecahedral–dodecahedral shared edge length is shorter than the unshared dodecahedral edge length. With increasing ionic radius of the Y‐site cation, the atomic coordinates x, y and z of oxygen adopt values which satisfy Pauling's third rule. 相似文献
3.
Alice K. Hui Chun‐Hsing Chen Adam M. Terwilliger Richard L. Lord Kenneth G. Caulton 《Acta Crystallographica. Section C, Structural Chemistry》2014,70(3):250-255
Reaction of a bis‐tetrazinyl pyridine pincer ligand, btzp, with a vanadium(III) reagent gives not a simple adduct but dichlorido{3‐methyl‐6‐[6‐(6‐methyl‐1,2,4,5‐tetrazin‐3‐yl‐κN2)pyridin‐2‐yl‐κN]‐1,4‐dihydro‐1,2,4,5‐tetrazin‐1‐yl‐κN1}oxidovanadium(IV) acetonitrile 2.5‐solvate, [V(C11H10N9)Cl2O]·2.5CH3CN, a species which X‐ray diffraction reveals to have one H atom added to one of the two tetrazinyl rings. This H atom was first revealed by a short intermolecular N...Cl contact in the unit cell and subsequently established, from difference maps, to be associated with a hydrogen bond. One chloride ligand has also been replaced by an oxide ligand in this synthetic reaction. This formula for the complex, [V(Hbtzp)Cl2O], leaves open the question of both ligand oxidation state and spin state. A computational study of all isomeric locations of the H atom shows the similarity of their energies, which is subject to perturbation by intermolecular hydrogen bonding found in X‐ray work on the solid state. These density functional calculations reveal that the isomer with the H atom located as found in the solid state contains a neutral radical Hbtzp ligand and tetravalent d1 V center, but that these two unpaired electrons are more stable as an open‐shell singlet and hence antiferromagnetically coupled. 相似文献
4.
To reveal the surface elemental composition and chemical states of the Ce1 ? x Eux CrO3 nano‐powders (x= 0.0, 0.3, 0.5, 0.7, 0.8, 1.0), X‐ray photoelectron spectroscopy was carried out in two conditions of before and after surface cleaning. This surface characterization described the core level binding energies of cerium, europium and chromium with different oxidation states. These results verified the morphology of the particles' surface which can be a confirmation of the spin disorder in these core‐shell structures. The effect of surface Ar sputtering on the oxidation states were studied. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
5.
Zintl Anions of Silicon in the Halides La3Cl2Si3 and La6Br3Si7 La3Cl2Si3 and La6Br3Si7 are prepared at temperatures of around 950 °C from LaX3 (X = Cl, Br), La metal and Si as starting materials. La3Cl2Si3 crystallizes in C2/m with a = 1802(3), b = 420.6(4), c = 1058(2) pm, β = 97.9(2)°, and La6Br3Si7 in Pmmn mit a = 1686.9(2), b = 412.93(11), c = 1185.2(1) pm. In both compounds the Si atoms are located in trigonal prisms of La atoms, which are connected through common triangular and rectangular faces to form layers. The bromine atoms connect the metal atom double layers. In La3Cl2Si3 the Si atoms form zig‐zag chains, in La6Br3Si7 chains build up from ‐connected Si12 rings. Both compounds are metallic conductors. 相似文献
6.
Hagen Poddig Kati Finzel Thomas Doert 《Acta Crystallographica. Section C, Structural Chemistry》2020,76(6):530-540
Crystals of the rare earth metal polytelluride LaTe1.82(1), namely, lanthanum telluride (1/1.8), have been grown by molten alkali halide flux reactions and vapour‐assisted crystallization with iodine. The two‐dimensionally incommensurately modulated crystal structure has been investigated by X‐ray diffraction experiments. In contrast to the tetragonal average structure with unit‐cell dimensions of a = 4.4996 (5) and c = 9.179 (1) Å at 296 (1) K, which was solved and refined in the space group P4/nmm (No. 129), the satellite reflections are not compatible with a tetragonal symmetry but enforce a symmetry reduction. Possible space groups have been derived by group–subgroup relationships and by consideration of previous reports on similar rare earth metal polychalcogenide structures. Two structural models in the orthorhombic superspace group, i.e.Pmmn(α,β,)000(?α,β,)000 (No. 59.2.51.39) and Pm21n(α,β,)000(?α,β,)000 (No. 31.2.51.35), with modulation wave vectors q1 = αa* + βb* + c* and q2 = ?αa* + βb* + c* [α = 0.272 (1) and β = 0.314 (1)], have been established and evaluated against each other. The modulation describes the distribution of defects in the planar [Te] layer, coupled to a displacive modulation due to the formation of different Te anions. The bonding situation in the planar [Te] layer and the different Te anion species have been investigated by density functional theory (DFT) methods and an electron localizability indicator (ELI‐D)‐based bonding analysis on three different approximants. The temperature‐dependent electrical resistance revealed a semiconducting behaviour with an estimated band gap of 0.17 eV. 相似文献
7.
Srinivas Venkata Pullela Vinod Acharya Nagarjuna Reddy Jayvant Harlikar Amar Kulkarni Rakesh Chavan Ajay Yadav Shuvendu Manna Angshuman Ghosh 《Acta Crystallographica. Section C, Structural Chemistry》2016,72(1):14-20
Eribulin mesylate, one of the most synthetically challenging drugs to date, possesses 19 stereocentres in its structure and ascertaining the absolute stereochemistry at every stage of the 64‐stage synthesis is crucial. In our quest to synthesize eribulin, we identified two critical building blocks of this molecule, namely 3,4:6,7‐di‐O‐cyclohexylidene‐D‐glycero‐α‐L‐talo‐heptopyranose methanol monosolvate, C19H30O7·CH3OH, and (2R,3R,4R,5S)‐5‐allyl‐2‐[(S)‐2,3‐dihydroxypropyl]‐4‐[(phenylsulfonyl)methyl]tetrahydrofuran‐3‐ol, C17H24O6S, for which two‐dimensional NMR (2D‐NMR) data were not sufficient to prove the absolute configuration. To ensure structural integrity, single‐crystal X‐ray diffraction data were obtained to confirm the structures. This information provides useful insights into the structural framework of the large eribulin mesylate molecule. 相似文献
8.
Hydrated alkaline earth metal salts of 5‐amino‐1H‐tetrazole ( B ) were synthesized by reaction of B with a suitable metal hydroxide in water. All compounds were fully characterized by analytical (elemental analysis and mass spectrometry) and spectroscopic (IR, Raman, 1H and 13C NMR) methods. Additionally, the crystal structures of the magnesium [ 1· 4H2O: triclinic, P$\bar {1}$ , a = 5.940(1) Å, b = 7.326(1) Å,c = 7.383(1) Å, α = 106.10(1)°, β = 106.51(1)°, γ = 111.85(1)°, V = 258.0(1) Å3], calcium [ 2· 6H2O: monoclinic, P21/m, a = 6.904(1) Å,b = 6.828(1) Å, c = 10.952(2) Å, β = 94.50(2)°, V = 514.6(1) Å3], and strontium [ 3· 6H2O: orthorhombic, Cmcm, a = 6.987(1) Å, b = 28.394(2) Å, c = 7.007(1) Å, V = 1390.3(2) Å3] were determined by low temperature X‐ray diffraction. Additionally, the (gas phase) structure of the 5‐amino‐1H‐tetrazole anion ([ B ]–) was also studied by natural bond orbital (NBO) analysis [B3LYP/6‐31+G(d,p)]. Lastly, standard tests were used to determine the sensitivity towards impact, friction, and electrostatic discharge of the compounds and the thermal stability was assessed by differential scanning calorimetry (DSC) analysis. 相似文献
9.
Lívia O. A. Ferreira Ana Karoline S. M. Valdo Jos Antnio Nascimento Neto Leandro Ribeiro Jefferson R. D. da Silva Luiz H. K. Queiroz Caridad N. Perez Felipe T. Martins 《Acta Crystallographica. Section C, Structural Chemistry》2019,75(6):694-701
We report a new polymorph of (1E,4E)‐1,5‐bis(4‐fluorophenyl)penta‐1,4‐dien‐3‐one, C17H12F2O. Contrary to the precedent literature polymorph with Z′ = 3, our polymorph has one half molecule in the asymmetric unit disordered over two 50% occupancy sites. Each site corresponds to one conformation around the single bond vicinal to the carbonyl group (so‐called anti or syn). The other half of the bischalcone is generated by twofold rotation symmetry, giving rise to two half‐occupied and overlapping molecules presenting both anti and syn conformations in their open chain. Such a disorder allows for distinct patterns of intermolecular C—H…O contacts involving the carbonyl and anti‐oriented β‐C—H groups, which is reflected in three 13C NMR chemical shifts for the carbonyl C atom. Here, we have also assessed the cytotoxicity of three symmetric bischalcones through their in vitro antitumour potential against three cancer cell lines. Cytotoxicity assays revealed that this biological property increases as halogen electronegativity increases. 相似文献
10.
Thomas Baumgartner 《应用有机金属化学》2005,19(7):859-863
A high‐yield synthesis toward 5,5′‐bis(silyl)‐functionalized 3,3′‐dibromo‐2,2′‐dithiophenes with very efficient work‐up procedure is presented. The molecular structures of two silyl functionalized dibromo‐dithiophenes in the solid state have been determined to investigate the structural influences of different functional groups on the degree of π‐conjugation within the dithiophene moieties, as well as their packing properties. The planar alignment of the tert‐butyldimethylsilyl‐functionalized dibromo‐dithiophene shows a significantly higher degree of conjugation of the π‐system with a more favorable molecular packing than the skewed arrangement of the triisopropylsilyl‐substituted species. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
11.
Leonard M. Khalilov Ekaterina S. Mescheryakova Kamil Sh. Bikmukhametov Nataliya N. Makhmudiyarova Kamil R. Shangaraev Arthur R. Tulyabaev 《Acta Crystallographica. Section C, Structural Chemistry》2019,75(10):1439-1447
Single crystals of (2S,5R)‐2‐isopropyl‐5‐methyl‐7‐(5‐methylisoxazol‐3‐yl)cyclohexanespiro‐3′‐(1,2,4,5,7‐tetraoxazocane), C16H26N2O5, have been studied via X‐ray diffraction. The tetraoxazocane ring adopts a boat–chair conformation in the crystalline state, which is due to intramolecular interactions. Conformational analysis of the tetraoxazocane fragment performed at the B3LYP/6‐31G(d,2p) level of theory showed that there are three minima on the potential energy surface, one of which corresponds to the conformation realized in the solid state, but not to a global minimum. Analysis of the geometry and the topological parameters of the electron density at the (3,?1) bond critical points (BCPs), and the charge transfer in the tetraoxazocane ring indicated that there are stereoelectronic effects in the O—C—O and N—C—O fragments. There is a two‐cross hyperconjugation in the N—C—O fragment between the lone electron pair of the N atom (lpN) and the antibonding orbital of a C—O bond (σ*C—O) and vice versa between lpO and σ*C—N. The oxazole substituent has a considerable effect on the geometry and the topological parameters of the electron density at the (3,?1) BCPs of the tetraoxazocane ring. The crystal structure is stabilized via intermolecular C—H…N and C—H…O hydrogen bonds, which is unambiguously confirmed with PIXEL calculations, a quantum theory of atoms in molecules (QTAIM) topological analysis of the electron density at the (3,?1) BCPs and a Hirshfeld analysis of the electrostatic potential. The molecules form zigzag chains in the crystal due to intermolecular C—H…N interactions being electrostatic in origin. The molecules are further stacked due to C—H…O hydrogen bonds. The dispersion component in the total stabilization energy of the crystal lattice is 68.09%. 相似文献
12.
《Acta Crystallographica. Section C, Structural Chemistry》2018,74(9):991-996
The three binary Tb/Er‐rich transition metal compounds Tb3Pd2 (triterbium dipalladium), Er3Pd2 (trierbium dipalladium) and Er6Co5–x (hexaerbium pentacobalt) crystallize in the space groups Pbam (Pearson symbol oP20), P4/mbm (tP10) and P63/m (hP22), respectively. Single crystals of Tb3Pd2 and Er6Co5–x suitable for X‐ray structure analysis were obtained using rare‐earth halides as a flux. Tb3Pd2 adopts its own structure type, which can be described as a superstructural derivative of the U3Si2 type, which is the type adopted by Er3Pd2. Compound Er6Co5–x belongs to the Ce6Co2–xSi3 family. All three compounds feature fused tricapped {TR6} (R = rare‐earth metal and T = transition metal) trigonal prismatic heterometallic clusters. R3Pd2 is reported to crystallize in the U3Si2 type; however, our more detailed structure analysis reveals that deviations occur with heavier R elements. Similarly, Er6Co5–x was assumed to be stoichiometric Er4Co3 = Er6Co4.5. Our studies reveal that it has a single defective transition‐metal site leading to the composition Er6Co4.72(2). LMTO (linear muffin‐tin orbital)‐based electronic structure calculations suggest the strong domination of heteroatomic bonding in all three structures. 相似文献
13.
Mwaffak Rukiah Thaer Assaad 《Acta Crystallographica. Section C, Structural Chemistry》2013,69(8):815-818
The title two‐dimensional coordination polymer, [Na(C2H8NO6P2)]n, was characterized using powder X‐ray diffraction data and its structure refined using the Rietveld method. The asymmetric unit contains one Na+ cation and one (1‐azaniumylethane‐1,1‐diyl)bis(hydrogen phosphonate) anion. The central Na+ cation exhibits distorted octahedral coordination geometry involving two deprotonated O atoms, two hydroxy O atoms and two double‐bonded O atoms of the bisphosphonate anion. Pairs of sodium‐centred octahedra share edges and the pairs are in turn connected to each other by the biphosphonate anion to form a two‐dimensional network parallel to the (001) plane. The polymeric layers are connected by strong O—H...O hydrogen bonding between the hydroxy group and one of the free O atoms of the bisphosphonate anion to generate a three‐dimensional network. Further stabilization of the crystal structure is achived by N—H...O and O—H...O hydrogen bonding.<!?tpb=18.7pt> 相似文献
14.
Jeanette A. Krause Daoli Zhao Sayandev Chatterjee Roland Falcon Kristen Stoltz John C. Warren Sara E. Wiswell William B. Connick Sibrina N. Collins 《Acta Crystallographica. Section C, Structural Chemistry》2014,70(3):260-266
Different salts of the 2‐phenyl‐1,10‐phenanthrolin‐1‐ium cation, (pnpH)+, are obtained by reacting 2‐phenyl‐1,10‐phenanthroline (pnp), C18H12N2, (I), with a variety of anions, such as hexafluoridophosphate, C18H13N2+·PF6−, (II), trifluoromethanesulfonate, C18H13N2+·CF3SO3−, (III), tetrachloridoaurate, (C18H13N2)[AuCl4], (IV), and bromide (as the dihydrate), C18H13N2+·Br−·2H2O, (V). Compound (I) crystallizes with Z′ = 2, with both independent molecules adopting a coplanar conformation. In (II)–(IV), a hydrogen bond exists between the cation and anion, while one of the lattice water molecules serves as a hydrogen‐bonded bridge between the cation and anion in (V). Reaction of (I) with HAuCl4 gives the salt complex (IV); however, reaction with KAuCl4 produces the monodentate complex trichlorido(2‐phenyl‐1,10‐phenanthroline‐κN10)gold(III), [AuCl3(C18H12N2)], (VI). Dichlorido(2‐phenyl‐1,10‐phenanthroline‐κ2N,N′)copper(II), [CuCl2(C18H12N2)], (VII), results from the reaction of CuCl2·2H2O and (I), in which the CuII center adopts a tetrahedrally distorted square‐planar geometry. The pendent phenyl ring twists to a bisecting position relative to the phenanthroline plane. The square‐planar PdII complex, bromido[2‐(phenanthrolin‐2‐yl)phenyl‐κ3C1,N,N′]palladium(II), [PdBr(C18H11N2)], (VIII), is obtained from the reaction of (I) with [PdCl2(cycloocta‐1,5‐diene)], followed by addition of bromine. A coplanar geometry for the pendent ring is adopted as a result of the tridentate bonding motif. 相似文献
15.
Nataliya E. Novikova Timofei A. Sorokin Alexander M. Antipin Nadezhda B. Bolotina Olga A. Alekseeva Nataliya I. Sorokina Valentina I. Voronkova 《Acta Crystallographica. Section C, Structural Chemistry》2019,75(6):740-749
Crystals with the La18W10O57‐type structure (6H and 5H polytypes) were obtained by a self‐flux method from high‐temperature solutions. Some of the crystal samples were studied by single‐crystal X‐ray structure analysis. The diffraction patterns indicated that two phases co‐exist in each sample. The hexagonal lattices have a common period of a ≈ 9.0 Å and are non‐equal in length but have equally oriented superstructure periods 6c (phase I) and 5c (phase II), c ≈ 5.4 Å. The structures of phases I and II were solved in the symmetry groups P2c and P321, respectively, based on the X‐ray data for crystals I and II, with predominant content of the first and second phase. The motif of isolated WO6 prisms with W atoms on the cell edges is common to both phases. WO6 octahedra, both isolated and joined by faces, are distributed along the c axis within the unit cells. Phase I contains extra layers of isolated WO6 octahedra compared to phase II. Tungsten sites in joined octahedra are disordered and partially occupied. Disordering is more expressed in phase II, which in return contains rather more W and O per atom of La. The refined chemical compositions are La18W10O57 for I and La15W8.5O48 for II. 相似文献
16.
Marina A. Zhuravleva Daniel Bilc S. D. Mahanti Mercouri G. Kanatzidis 《无机化学与普通化学杂志》2003,629(2):327-334
The cubic La4.87Ni12Sn24 was synthesized in reactions involving liquid Sn. The compound crystallizes in the cubic syngony, space group Im3¯, Z = 2, cell parameter a = 11.9662(14) Å, and is related to the Gd3Ni8Sn16 structure type previously refined from powder X‐ray data. The crystal structure of La4.87Ni12Sn24 was solved and refined using single crystal X‐ray data to final R1 = 2.67%, wR2 = 6.92%. The refinement showed no mixed occupancy with Sn for the La(1) site, contrary to what was proposed for Gd3Ni8Sn16. Instead, a partial occupancy of 87% was detected for the La(1) at 2a. Electronic structure calculations show that the system is metallic, and the density of states at the Fermi level falls at a peak with the highest contribution coming from La(1) atoms, if the compound with ideal occupancies La5Ni12Sn24 is assumed. The deficiency of the La(1) site could therefore originate in the lowering of the total energy of the system due to the loss of 0.39 electrons per formula unit. Magnetic measurement data indicates nearly temperature independent Pauli paramagnetism. Theoretical estimation of the magnetic susceptibility after including core diamagnetic corrections agrees well with experiment. 相似文献
17.
Teshica Chatturgoon Matthew P. Akerman 《Acta Crystallographica. Section C, Structural Chemistry》2016,72(3):234-238
The application of transition metal chelates as chemotherapeutic agents has the advantage that they can be used as a scaffold around which ligands with DNA recognition elements can be anchored. The facile substitution of these components allows for the DNA recognition and binding properties of the metal chelates to be tuned. Copper is a particularly interesting choice for the development of novel metallodrugs as it is an endogenous metal and is therefore less toxic than other transition metals. The title compound, [Cu(C16H11N2O)2], was synthesized by reacting N‐(quinolin‐8‐yl)benzamide and the metal in a 2:1 ratio. Ligand coordination required deprotonation of the amide N—H group and the isolated complex is therefore neutral. The metal ion adopts a flattened tetrahedral coordination geometry with the ligands in a pseudo‐trans configuration. The free rotation afforded by the formal single bond between the amide group and phenyl ring allows the phenyl rings to rotate out‐of‐plane, thus alleviating nonbonded repulsion between the phenyl rings and the quinolyl groups within the complex. Weak C—H…O interactions stabilize a dimer in the solid state. Density functional theory (DFT) simulations at the PBE/6‐311G(dp) level of theory show that the solid‐state structure (C1 symmetry) is 79.33 kJ mol−1 higher in energy than the lowest energy gas‐phase structure (C2 symmetry). Natural bond orbital (NBO) analysis offers an explanation for the formation of the C—H…O interactions in electrostatic terms, but the stabilizing effect is insufficient to support the dimer in the gas phase. 相似文献
18.
π‐Allyl (η3‐C3H5), a four‐electron donor, was used as a ligand model to replace η5‐C5Me4SiMe3 in DFT calculations on the tetranuclear yttrium polyhydrido complex (η5‐C5Me4SiMe3)4Y4H8 containing a Y4H8 tetrahedral core structure, which may separate the four π‐allyl groups and hence suppress the allyl ligand coupling during the computation. In terms of the calculated core geometry, isomerization energy barrier, charge population, and frontier orbital features of the complex, the η3‐C3H5 ligand model is comparable to η5‐C5H5. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 相似文献
19.
Rodolfo Moreno-Fuquen Kevin Arango-Daravia Diana Becerra Juan-Carlos Castillo Alan R. Kennedy Mario A. Macías 《Acta Crystallographica. Section C, Structural Chemistry》2019,75(3):359-371
An efficient approach for the regioselective synthesis of (5‐amino‐3‐methylsulfanyl‐1H‐1,2,4‐triazol‐1‐yl)(2‐fluorophenyl)methanone, C10H9FN4OS, (3), from the N‐acylation of 3‐amino‐5‐methylsulfanyl‐1H‐1,2,4‐triazole, (1), with 2‐fluorobenzoyl chloride has been developed. Heterocyclic amide (3) was used successfully as a strategic intermediate for the preparation of 2‐fluoro‐N‐(3‐methylsulfanyl‐1H‐1,2,4‐triazol‐5‐yl)benzamide, C10H9FN4OS, (4), through a microwave‐assisted Fries rearrangement under catalyst‐ and solvent‐free conditions. Theoretical studies of the prototropy process of (1) and the Fries rearrangement of (3) to provide (4), involving the formation of an intimate ion pair as the key step, were carried out by density functional theory (DFT) calculations. The crystallographic analysis of the intermolecular interactions and the energy frameworks based on the effects of the different molecular conformations of (3) and (4) are described. 相似文献
20.
Shuichao Dong Yaqiu Tao Xiaodong Shen Zhigang Pan 《Acta Crystallographica. Section C, Structural Chemistry》2013,69(8):896-900
A new polymorph of bis(2‐aminopyridinium) fumarate–fumaric acid (1/1), 2C5H7N2+·C4H2O42−·C4H4O4, was obtained and its crystal structure determined by powder X‐ray diffraction. The new polymorph (form II) crystallizes in the triclinic system (space group P), while the previous reported polymorph [form I; Ballabh, Trivedi, Dastidar & Suresh (2002). CrystEngComm, 4 , 135–142; Büyükgüngör, Odabaşoğlu, Albayrak & Lönnecke (2004). Acta Cryst. C 60 , o470–o472] is monoclinic (space group P21/c). In both forms I and II, the asymmetric unit consists of one 2‐aminopyridinium cation, half a fumaric acid molecule and half a fumarate dianion. The fumarate dianion is involved in hydrogen bonding with two neighbouring 2‐aminopyridinium cations to form a hydrogen‐bonded trimer in both forms. In form II, the hydrogen‐bonded trimers are interlinked across centres of inversion via pairs of N—H...O hydrogen bonds, whereas such trimers are joined via single N—H...O hydrogen bonds in form I, leading to different packing modes for forms I and II. The results demonstrate the relevance and application of the powder diffraction method in the study of polymorphism of organic molecular materials. 相似文献