3,5‐Dichloro‐4‐cyano­benzoic acid: two polymorphs and the 0.25‐hydrate,exhibiting two‐dimensional ribbons and nets involving hydrogen‐bonding and inter­molecular Cl⋯N inter­actions

Two polymorphs of 3,5‐dichloro‐4‐cyano­benzoic acid, C₈H₃Cl₂NO₂, viz. triclinic and monoclinic, and its 0.25‐hydrate, C₈H₃Cl₂NO₂·0.25H₂O, form crystals in which hydrogen bonding and Cl⋯N inter­actions appear to be equally important to the structures. In all three structures, there are hydrogen‐bonded (COOH) dimers of the well known cyclic type, but in the hydrate there are also dimers in which the two opposing COOH groups are separated by a water mol­ecule. In the monoclinic polymorph and in the hydrate, the inter­molecular inter­actions form two‐dimensional nets inter­woven three at a time. For both the triclinic and monoclinic polymorphs, Z′= 2.     

Crystal structure, thermal behaviour, protonation and mass spectroscopic studies of racemic 4-[1-(2,3-dimethylphenyl)ethyl]-1H-imidazole hydrochlorides

The crystal structure, thermal behaviour, mass spectrum and protonation of 4-[1-(2,3-dimethylphenyl)ethyl]-1H-imidazole (medetomidine) hydrochloride have been investigated. The title compound crystallizes in both hydrated and anhydrous forms, and their structures have been determined by three-dimensional X-ray structure analysis. The crystals of the anhydrous form are monoclinic and those of the hydrated form (containing one hydrate water molecule) are triclinic with unit-cell dimensions: a = 23.861(9), b = 7.721(4), c = 22.037(9) A, beta = 140.20(4) degrees, Z = 8, and space group C2/c, and a = 7.841(4), b = 8.380(3), c = 12.743(6) A, alpha = 93.66(3), beta = 102.90(3), gamma = 116.85(3) degrees, Z = 2, and space group P1, respectively. Thermal decomposition of the title compound has been interpreted from the TG, DTG and DSC curves with the help of mass spectrometry. Medetomidine hydrochloride monohydrate decomposes in four stages. The first is dehydration at 45-100 degrees C, the second is evaporation of HCl and medetomidine base at 200-320 degrees C, and the third and fourth are decomposition at 340-570 degrees C. The protonation constant is 7.04 in aqueous 0.1 M NaClO4 (25 degrees C).     

Complexation of lanthanum(III) nitrate by N,N′,N,N′-tetraethylmalonamide: Crystal structure of three polymorphic forms

A monoclinic form of the complex between lanthanum(III) nitrate and tetraethylmalonamide (TEMA), La(NO₃)₃(TEMA)₂, 1, differing from the triclinic form 2 previously reported, is described. 1 undergoes an evolution with time which leads to the form 2, which in its turn undergoes a temperature-driven phase transition previously unreported, leading to the formation of 3.     

Two polymorphic modifications of 1-(N-morpholiniomethyl)spirobi- (3-oxo-2,5-dioxa-1-silacyclopentan)- ate hydrate

The compound 1-(N-morpholiniomethyl)spirobi(3-oxo-2,5-dioxa-1-silacyclopentan)ate crystallizes from aqueous solution of γ-butyrolactone in the form of two crystal hydrate modifications: monoclinic (with D = 1.53 g/cm³, space group P 2₁/n) and triclinic (D = 1.45 g/cm³, space group P1^-). For the monoclinic form, an X-ray structural study at -100°C has been performed. For both structures the coordination polyhedron of the silicon atom is a trigonal bipyramid. In the crystal structures there are strong intermolecular hydrogen bonds of NH···O and OH···O types.     

Acceleration of methane hydrate nucleation by crystals of hydrated sodium dodecyl sulfate

It was shown that hydrated crystals of sodium dodecyl sulfate (SDS), which precipitate from dilute SDS solutions sharply accelerate nucleation of methane gas hydrate. This finding adds significant details to the available information on the mechanisms of hydrate formation from SDS solutions and can form the basis for the development of a new class of kinetic promoters of hydrate formation.     

5-硝基-2H-四唑的合成、反应性及产物晶体结构的研究

5-氨基四唑(1)经过重氮化反应得到5-硝基四唑(5),5与甲醛反应得到2-羟甲基-5-硝基四唑(6),6与HCl或HBr反应分别得到5-5氯代四唑(7)和5-溴代四唑(8),采用MS,IR,1H NMR,13C NMR等技术对这些化合物进行了表征.用X射线单晶衍射法测定了化合物5-硝基四唑钠(4),5和6的晶体结构.化合物4属于三斜晶系,P-1空间群;化合物5和6均属于单斜晶系,P21空间群,化合物6的晶胞参数a=0.66131(18)nm,b=0.54905(15)nm,c=0.7566(2)nm,Z=2,V=0.27470(13)nm3,Dc=1.754g/cm3,F(000)=128,μ=0.160mm-1.     

Synthesis and Crystal Structure of a Hydrogen-bonded Supramolecular Compound [(C_6H_5N_2O)_3·Cu_1._5]·6H_2O

1 INTRODUCTION The binding of metal ions by proteins and pep- tides is of fundamental interest due to the impor- tance of metal ions in biological systems. Metals may be part of the active sites of enzymes, stabilize the macromolecular structure of proteins and affect enzymes or membranes to control cell metabolism[1]. Therefore, for many years there has been a great in- terest in the study of complexes able to mimic these active sites of metalloproteins. In this case, metal complexes of…     

Synthesis and Crystal Structure of a Hydrogen-bonded Supramolecular Compound [(C6H5N2O)3·Cu1.5]·6H2O

A hydrogen-bonded supermolecular compound [(C6H5N2O)3·Cu1.5](6H2O was syn- thesized from picolinamide and Cu(NO3)2·6H2O at the presence of sodium pyrophosphate deca- hydrate. It crystallizes in triclinic, space group P with a = 1.05947(8), b = 1.09130(8), c = 1.11456(8) nm, α = 67.8460(10), β = 84.497(1), γ = 74.6210(10)°, C18H27Cu1.5N6O9, Mr = 566.77, V = 1.15077(15) nm3, Z = 2, Dc = 1.636 g/cm3, F(000) = 585, μ = 1.461 mm-1, R1 = 0.0278 and wR2 = 0.0749. In the complex, the Cu(II) ion reveals a distorted tetradentate plane-tetragonal geometry. The structure consists of neutral two-dimensional layers via hydrogen bonds O-H…O and N-H…O between the molecules, and the layers are connected by weak interactions of the Cu-Cu, Cu-N, π-π and hydrogen bonds to form a three-dimensional network structure.     

Crystal Structures of Hydrochlorides of 2,3-Pentamethylene-3, 4-dihydroquinazolin-4-one

The crystal structures of hydrate (1) and anhydrate (2) forms of 2,3-pentamethylene-3,4-dihydroquinazolin-4-one hydrochloride have been determined by X-ray structure analysis. Crystal data of 1 are 2(C₁₃H₁₄N₂O)*3(HCl)*4.5 (H₂O), triclinic P?1, Z=2, a=8.004(5), b=13.129(7), c=15.725(7) Å, α=106.45(4), β=92.61(4), γ=97.98(5), R=0.0652 and 2 are C₁₃H₁₄N₂O*HCl, monoclinic C2/c, Z=8, a=21.360(4), b=5.954(1), c=21.263(4), β=117.89(3), R=0.0556. The crystal of the hydrate form 1is unstable. This form collapses easily with evaporation of H₂O and part of HCl molecules from crystals. By recrystallizing destroyed form has been obtained stable crystal form 2.     

A twinned triclinic polymorph of dibromidotetra­kis(tetra­hydro­furan‐κO)magnesium(II)

The title compound, [MgBr₂(C₄H₈O)₄], forms crystals which appear to be monoclinic but are actually twinned triclinic. The current form is a new triclinic polymorph, with Z′= 2, in addition to the already known tetra­gonal polymorph. Although the geometric parameters of the two polymorphs agree well, their packing patterns are completely different.     

Two isomorphous complexes: di­chloro­[phthalocyaninato(2–)]­tin(IV) and di­chloro­[phthalocyaninato(2–)]­germanium(IV)

Isomorphous triclinic forms of di­chloro­[phthalocyaninato(2−)]­tin(IV), [Sn(C₃₂H₁₆N₈)Cl₂], and di­chloro­[phthalocyaninato(2−)]­ger­manium(IV), [Sn(C₃₂H₁₆N₈)Cl₂], and a monoclinic form of the latter have been obtained from the reaction of pure tin and germanium powder, respectively, with phthalo­nitrile under a stream of ICl vapour. All three crystal structures consist of centrosymmetric [SnPcCl₂] and [GePcCl₂] [Pc is phthalocyaninate(2−)] mol­ecules, which are separated but interacting. In the triclinic forms (Sn and Ge), the Pc macrocycles are not staggered but slipped, and in the monoclinic form (Ge), the mol­ecules are additionally inclined. In both cases, the central Sn or Ge atom is six‐coordinated by the four iso­indole N atoms of the Pc macrocyclic ligand and by two Cl atoms (located trans) into a tetragonal–bipyramidal structure. The arrangement of [SnPcCl₂] and [GePcCl₂] mol­ecules in the crystal structure is determined mainly by intermolecular C—H⃛Cl, π–π and van der Waals interactions.     

Tautomeric equilibrium, stability, and hydrogen bonding in 2'-deoxyguanosine monophosphate complexed with Mg2+

The tautomeric equilibrium and hydrogen bonding in nucleotide 2'-deoxyguanosine monophosphate that interacts with hydrated Mg2+ cation (4H2O.Mg[dGMP]) were studied at the MP2/cc-pVDZ//B3LYP/cc-pVDZ and B3LYP/aug-cc-pVTZ//B3LYP/cc-pVDZ levels of theory. The Mg2+ ion forms two inner-shell contacts with the nucleotide, similar to small phosphorylated molecules under physiological conditions. The presence of the phosphate group and the hydrated magnesium cation leads to a change in guanine tautomeric equilibrium of 4H2O.Mg[dGMP] in comparison to free guanine. The influence of the phosphate group and the magnesium cation on tautomeric equilibrium is larger in the anti conformation where the P=O-->Mg and Mg<--N7 coordinate bonds are formed. The canonical oxo form of guanine is more stable (by 6-8 kcal/mol) than the O6-hydroxo form in anti conformation. Thus, the interaction with Mg2+ ion is capable of further suppressing the likelihood of a spontaneous transient formation of the rare tautomer. In the syn conformation of 4H2O.Mg[dGMP], the interaction of the guanine nucleobase with the phosphate group and the magnesium cation is not as strong as in the anti conformation, and the relative stability of guanine tautomers is close to those in free guanine.     

Structure of the calcium pyrophosphate monohydrate phase (Ca2P2O7·H2O): towards understanding the dehydration process in calcium pyrophosphate hydrates

Calcium pyrophosphate hydrate (CPP, Ca₂P₂O₇·nH₂O) and calcium orthophosphate compounds (including apatite, octacalcium phosphate etc.) are among the most prevalent pathological calcifications in joints. Even though only two dihydrated forms of CPP (CPPD) have been detected in vivo (monoclinic and triclinic CPPD), investigations of other hydrated forms such as tetrahydrated or amorphous CPP are relevant to a further understanding of the physicochemistry of those phases of biological interest. The synthesis of single crystals of calcium pyrophosphate monohydrate (CPPM; Ca₂P₂O₇·H₂O) by diffusion in silica gel at ambient temperature and the structural analysis of this phase are reported in this paper. Complementarily, data from synchrotron X‐ray diffraction on a CPPM powder sample have been fitted to the crystal parameters. Finally, the relationship between the resolved structure for the CPPM phase and the structure of the tetrahydrated calcium pyrophosphate β phase (CPPT‐β) is discussed.     

Synthesis and Crystal Structure of Diethyl-2,6- dimethyl-3,5- diyl- （ 1- （2- chlorob enzoyl）- 1H- pyrazole-3-diethyl-carboxylate）-pyridine

The reaction of hydrazine hydrate with a new α,γ-diketone ester 3, derived from the reaction of 2,6-dimethyl-3,5-diacetyl-pyridine 2 with diethyl oxalate in the presence of sodium ethoxide, afforded the pyrazole derivative 4. Treatment of 4 with 2-chlorobenzoyl chloride gave diethyl 2,6-dimethyl-3,5-diyl-（1-2（chlorobenzoyl）-1H-pyrazole-3-diethyl-carboxylate） pyridine 5. Fine crystal of 5 suitable for XRD analysis was obtained form recrystalization in ethyl acetate. The crystal belongs to the triclinic system, space group P1^-, with a = 1.0342（11）, b = 1.2211（12）, c = 1.5013（15） nm, α = 82.5190（10）,β = 85.7960（10）,γ = 85.3150（10）°, V= 1.8697（3） nm^3, Dc= 1.173 g/cm^3, μ = 0.219 mm^-1, F（000） = 684, Z = 2, the final R = 0.0720 and wR = 0.2211.     

Kristall- und Molekülstruktur von Bis(1,1-diethyl-3-thiobenzoyl-thioureato)nickel(II)

Crystal and Molecular Structure of Bis(1,1-diethyl-3-thiobenzoyl-thioureato)nickel(II). Bis(1, 1-diethyl-3-thiobenzoyl-thioureato)nickel(II) forms two modifications, whose structures have been determined by X-ray structure analysis. The monoclinic modification crystallizes in the space group P2₁/n with a = 13.709, b = 8.571, c = 12.803 Å, β = 68.10° and Z = 2. The triclinic modification crystallizes in the space group I1 with a = 14.406, b = 7.761, c = 11.734 Å, α = 86.10, β = 97.39, γ = 90.18° and Z = 2. The molecular structures of both modifications are nearly identical (packing polymorphism). The coordination is exactly planar, the ligands are arranged in trans position. The average Ni? S bond length is 2.153 Å in the monoclinic form and 2.163 Å in the triclinic form. The chelate rings deviate from planarity.     

A Novel Dimer--Heteropolytungstate with a Vanadium Atom as the Centre--Synthesis and Structural Characterization of (H3O)4[VW12O40Na(H2O)4]2

A novel dimer-tungstovanadate,(H3O)4［VW12O40Na(H2O)4］2,was hydrothermally synthesized and structurally characterized by single crystal X-ray diffraction,IR spectra,TGA-DSC thermal analysis and polarograpy.The yellowish crystal crystallized in the triclinic system,space group ,a=1.464 5(3) nm,b=1.4686(3) nm,c=1.4111(3) nm,α=111.82(2)°,βA novel dimer-tungstovanadate,(H3O)4［VW12O40Na(H2O)4］2,was hydrothermally synthesized and structurally characterized by single crystal X-ray diffraction,IR spectra,TGA-DSC thermal analysis and polarograpy.The yellowish crystal crystallized in the triclinic system,space group ,a=1.464 5(3) nm,b=1.4686(3) nm,c=1.4111(3) nm,α=111.82(2)°,β=93.17(3)°,γ=117.47(3)°,V=2.2106(8) nm3,Z=1,Dc=4.552 g.cm-3,λ(Mo Kα)=0.071073 nm,μ=31.402 mm-1,F(000)=2648,R=0.0780.The title compound consists of two Keggin structure units linked together with two hydrated sodium cations to form a dimer with a porous structure with the pore dimension of 0.766 nm×0.7785 nm.     

Poly(hexamethylene terephthalate)—I. Interpretation of its diffraction patterns

X-ray diffraction, electron microscopy and electron diffraction studies of poly(hexamethylene terephthalate) reveal a variety of structures and morphologies. Polymer micro-single crystals, grown from nitrobenzene-hexane or nitrobenzene-decane solutions exist in three crystal structures. Two forms are triclinic, the third is monoclinic. The single chain triclinic unit-cell (form I) has dimensions $\text{a = 5.217, b = 5.284, c = 15.738}\text{A}\text{?}\text{(}\text{fibre axis}\text{) α = 129.4, β = 97.6, γ = 95.6°}$. The double chain triclinic unit-cell, (form II), has all dimensions and angles equal to those of form I but for b which is twice as large. There are six chains in the monoclinic unit-cell (form III) with dimensions $\text{a = 9.100, b = 17.560, c = 15.74}\text{A}\text{?}\text{(}\text{fibre axis}\text{), α = 127.8°}$. All three forms have a common value of the fibre repeat, $\text{c = 15.74}\text{A}\text{?}$, indicating that in all three forms the polyester presents itself in a fully extended conformation. The differences between the various polymorphs arise from different packing modes of the chains. In the fibre, both the monoclinic and the triclinic forms coexist.     

Two polymorphs of aqua[N,N′-ethyl­enebis(salicylideneaminato-N,O)]oxovanadium(V) nitrate

The title compound, aqua­[bis­(salicyl­idene)­ethyl­enediamin­ato-O,N,N′,O′]­oxovanadium(V) nitrate, [VO(C₁₆H₁₄N₂O₂)(H₂O)]NO₃, crystallizes as two polymorphs in the triclinic and monoclinic crystal systems. In both, the V atom has a distorted octahedral coordination geometry with a long V—O_water bond trans to V=O. The coordinated water mol­ecules are hydrogen bonded to the nitrate ions so that pairs of cations are linked to give neutral centrosymmetric dimers. The V=O and V—O_water distances are 1.598 (2) and 2.257 (2) Å, respectively, in the triclinic form, and 1.588 (3) and 2.230 (3) Å, respectively, in the monoclinic form. In the triclinic form, the dimers pack so that the salen [bis(salicyl­idene)ethylenediaminate] ligands are parallel to each other, whereas in the monoclinic form, which is the denser, there is a herring-bone arrangement.     

The Richest Collection of Tautomeric Polymorphs: The Case of 2‐Thiobarbituric Acid

Five new polymorphs and one hydrated form of 2‐thiobarbituric acid have been isolated and characterised by solid‐state methods. In both the crystalline form II and in the hydrate form, the 2‐thiobarbituric molecules are present in the enol form, whereas only the keto isomer is present in crystalline forms I (reported in 1967 by Calas and Martinex), III , V and VI . In form IV , on the other hand, a 50:50 ordered mixture of enol/keto molecules is present. All new forms have been characterised by single‐crystal X‐ray diffraction, 1D and 2D (¹H, ¹³C, and ¹⁵N) solid‐state NMR spectroscopy, Raman spectroscopy and X‐ray powder diffraction at variable temperature. It has been possible to induce keto–enol conversion between the forms by mechanical methods. The role of hydrogen‐bond interactions in determining the relative stability of the polymorphs and as a driving force in the conversions has been ascertained. To the best of the authors’ knowledge, the 2‐thiobarbituric family of crystal forms represents the richest collection of examples of tautomeric polymorphism so far reported in the literature.     

Thermal studies on polymorphic structures of tibolone

Tibolone polymorphic forms I (monoclinic) and II (triclinic) have been prepared by recrystallization from acetone and toluene, respectively, and characterized by different techniques sensitive to changes in solid state, such as polarized light microscopy, X-ray powder diffractometry, thermal analysis (TG/DTG/DSC), and vibrational spectroscopy (FTIR and Raman microscopy). The nonisothermal decomposition kinetics of the obtained polymorphs were studied using thermogravimetry. The activation energies were calculated through the Ozawa’s method for the first step of decomposition, the triclinic form showed a lower E _a (91 kJ mol⁻¹) than the monoclinic one (95 kJ mol⁻¹). Furthermore, Raman microscopy and DSC at low heating rates were used to identify and follow the thermal decomposition of the triclinic form, showing the existence of three thermal events before the first mass loss.