First Order Temperature Dependent Phase Transition in a Monoclinic Polymorph Crystal of 1,6-Hexanedioic Acid: An Interpretation Based on the Landau Theory Approach

Crystals of 1,6-hexanedioic acid (I) undergo a temperature-dependent reversible phase transition from monoclinic P21/c at a temperature higher than the critical temperature (Tc) 130 K to another monoclinic P21/c at temperature lower than Tc. The phase transition is of first order, involving a discontinuity and a tripling of the b-axis at Tc whereas the other unit cell parameters vary continuously. The transition is described by the phenomenological Landau theory. The crystal structure analyses for data collected at 297(2) K and 120.0(1) K show that there is half of a molecule of (I) in the asymmetric unit at 297(2) K whereas there are one and a half molecules of (I) in the asymmetric unit at 120.0(1) K. At both temperatures, 297(2) and 120.0(1) K, intermolecular O-H···O hydrogen bonds link the molecules of I into infinite 1D chains along [101] direction. However there are significantly more O-H···O hydrogen bonds presented in the 120.0(1) K polymorph, thereby indicating this phase transition is negotiated via hydrogen bonds. The relationship of the conformational changes and hydrogen bonding for these two polymorphs are explained in detail

Regional valuation of infrastructure improvements. The case of Swedish road freight

Is it possible to identify regional differences among shippers in their valuation of infrastructure improvements? The question is analysed within a random utility approach where parameters are estimated by a logit model. Data consists of a Swedish stated preference study from 1992. The results indicate that regional differences may exist but a considerable heterogeneity in the empirical material prohibit robust results in some cases. However, regional differences seem to exist when industrial mix, shipping distance and goods values are held constant. Independent of the limitations, the results should render implications to any infrastructure benefit analysis where parameters from spatial averages are used. The results are based on short term decisions and one should recognise that parameters may vary under mid- and long- term.Regional preferences; road transportation; freight demand; stated preference analysis; random utility models; logit model

(E)-4-Methoxy-N00-(2,4,5-trimethoxybenzylidene) benzohydrazide hemihydrate

The title compound crystallizes as a hemihydrate, C18H20N2O5�0.5H2O. The molecule exists in an E conformation with respect to the C N imine bond. The 4-methoxyphenyl unit is disordered over two sets of sites with a refined occupancy ratio of 0.54 (2):0.46 (2). The dihedral angles between the benzene rings are 29.20 (9) and 26.59 (9)�, respectively, for the major and minor components of the 4- methoxy-substituted ring. All methoxy substituents lie close to the plane of the attached benzene rings [the Cmethyl—O—C— C torsion angles range from �4.0 (12) to 3.9 (2)�]. In the crystal, the components are linked into chains propagating along [001] via N—H� � �O and O—H� � �O hydrogen bonds and weak C—H� � �O interactions

Crystal structure of tetraaquabis(3,5-diamino- 4H-1,2,4-triazol-1-ium)cobalt(II) bis[bis(pyridine-2,6-dicarboxylato)- cobaltate(II)] dihydrate

The asymmetric unit of the title compound, [Co(C2H6N5)2- (H2O)4][Co(C7H3NO4)2]2�2H2O, features 1.5 CoII ions (one anionic complex and one half cationic complex) and one water molecule. In the cationic complex, the CoII atom is located on an inversion centre and is coordinated by two triazolium cations and four water molecules, adopting an octahedral geometry where the N atoms of the two triazolium cations occupy the axial positions and the O atoms of the four water molecules the equatorial positions. The two triazole ligands are parallel offset (with a distance of 1.38 A ° between their planes). In the anionic complex, the CoII ion is six-coordinated by two N and four O atoms of the two pyridine-2,6- dicarboxylate anions, exhibiting a slightly distorted octahedral coordination geometry in which the mean plane of the two pyridine-2,6-dicarboxylate anions are almost perpendicular to each other, making a dihedral angle of 85.87 (2)�. In the crystal, molecules are linked into a three-dimensional network via C—H� � �O, C—H� � �N, O—H� � �O and N—H� � �O hydrogen bonds

2-Amino-3-ammonio­pyridinium dichloride

The asymmetric unit of the title compound, C5H9N3 2+·2Cl−, contains two diprotonated 2,3-diamino­pyridine cations and four chloride anions. In the crystal structure, the anions and cations are connected by inter­molecular N—H⋯Cl and C—H⋯Cl hydrogen bonds, forming a three-dimensional network. The crystal structure is further stabilized by π–π inter­actions between pyridinium rings [centroid–centroid distance = 3.695 (1) Å]

2-Amino-5-methyl­pyridinium nicotinate

In the title compound, C6H9N2 +·C6H4NO2 −, the 2-amino-5-methyl­pyridinium cation is essentially planar, with a maximum deviation of 0.023 (2) Å. In the crystal, the cations and anions are linked via strong N—H⋯O hydrogen bonds, forming a two dimensional network parallel to (100). In addition, π⋯π inter­actions involving the pyridinium and pyridine rings, with centroid–centroid distances of 3.6383 (8) Å, are observed

2-Amino-5-chloro­pyridinium (Z)-3-carb­oxy­prop-2-enoate 0.25-hydrate

In the title hydrated salt, C5H6ClN2 +·C4H3O4 −·0.25H2O, the water O atom lies on a twofold axis with 0.25 occupancy. The 2-amino-5-chloro­pyridinium cation is almost planar, with a maximum deviation of 0.015 (3) Å. In the hydrogen malate anion, an intra­molecular O—H⋯O hydrogen bond generates an S(7) ring and results in a folded conformation. In the crystal, the protonated N atom and the 2-amino group of the cation are hydrogen bonded to the carboxyl­ate O atoms of the anion via a pair of N—H⋯O hydrogen bonds, forming an R 2 2(8) ring motif. The ion pairs are further connected via O—H⋯O, N—H⋯O and C—H⋯O hydrogen bonds, forming layers parallel to the ab plane which stack down the c axis

3,4-Diaminopyridinium 2-carboxy-4,6-dinitrophenolate

In the title salt, C5H8N3 +·C7H3N2O7 −, the pyridine N atom of the 3,4-diamino­pyridine mol­ecule is protonated. The 3,5-dinitro­salicylate anion shows whole-mol­ecule disorder over two orientations with a refined occupancy ratio of 0.875 (4): 0.125 (4). In the crystal, the cations and anions are connected by inter­molecular N—H⋯O and C—H⋯O hydrogen bonds, forming a three-dimensional network

5,6-Di-2-thienyl-2,3-dihydro­pyrazine

In the title compound, C12H10N2S2, which was synthesized by the reaction of 2,2′-thenil and ethyl­enediamine, the dihedral angle between the two thio­phene rings is 66.33 (9)°. In the crystal structure, inter­molecular C—H⋯N hydrogen bonds link the mol­ecules into infinite chains along the b axis and weak C—H⋯π inter­actions may further stabilize the structure

2-Amino-5-methyl­pyridinium 2-carb­oxy­acetate

In the title mol­ecular salt, C6H9N2 +·C3H3O4 −, the cation is essentially planar, with a maximum deviation of 0.010 (3) Å. In the anion, an intra­molecular O—H⋯O hydrogen bond generates an S(6) ring and results in a folded conformation. In the crystal, the protonated NH group and the 2-amino group of the cation are hydrogen bonded to the carboxyl­ate O atoms of the anion via a pair of N—H⋯O hydrogen bonds, forming an R 2 2(8) ring motif. Weak inter­molecular C—H⋯O inter­actions help to further stabilize the crystal structure