In the structure of the phenolate salt of the sulfa drug sulfamethazine with 3,5-dinitro-salicylic acid, C12H15N4O2S(+)·C7H3N2O7 (-), the dihedral angle between the pyrimidine and benzene rings of the cation is 59.70 (17)°. In the crystal, cation-anion hydrogen-bonding inter-actions involving pyrim-idine-carb-oxy N(+)-H⋯O and amine-carb-oxy N-H⋯O pairs give a cyclic R 2 (2)(8) motif while secon...

In the title hydrate, C12H12O4·1.5H2O, one of the water mol-ecules in the asymmetric unit is located on a twofold rotation axis. The mol-ecule of the benzo-furan derivative is essentially planar (r.m.s. deviation for the non-H atoms = 0.021 Å), with the ester group adopting a fully extended conformation. In the crystal, O-H⋯O hydrogen bonds between the water mol-ecules and the hy-droxy groups g...

The asymmetric unit of the title salt, {(C(12)H(20)N(4))[Ag(2)Br(4)]}(n), contains one-half of a substituted imidazolium cation, one Ag(+) and two Br(-) ions. The cation is completed by crystallographic inversion symmetry. The crystal structure is made up from polymeric sheets of {[AgBr(2)](-)}(n) anions extending parallel to (100). The basic building unit of the anion is a slightly distorted A...

A general procedure is presented for computing axisymmetric swirling vortices which are steady with respect to an inviscid flow that is either uniform at infinity or includes shear. We consider cases both with and without a spherical obstacle. Choices of numerical parameters are given which yield vortex rings with swirl, attached vortices with swirl analogous to spherical vortices found by Moff...

The Hg(II) ion in the title complex, [HgCl(2)(C(13)H(12)N(2))], adopts a distorted tetra-hedral geometry being coordinated by two Cl anions and by two N atoms of the benz-yl(2-pyridyl-methyl-ene)amine ligand. The Cl-Hg-Cl plane is twisted at 70.1 (1)° from the mean plane of the chelate ring. In the crystal structure, inter-molecular π-π inter-actions [centroid-centroid distance = 3.793 (3) Å] b...

Recently representations over non–commutative rings were used by Cochran, Harvey, Friedl–Kim and Turaev to define Alexander polynomials whose degrees give lower bounds on the Thurston norm. We first show how Reidemeister torsion relates to these invariants. We give lower bounds on the Thurston norm in terms of the Reidemeister torsion which contain all the above lower bounds and give an elegant...

The itle compound, [Ca(C(6)H(3)ClNO(2))(2)(H(2)O)(2)](n), contains polymeric chains extending along [100] that are generated by inversion centres. The Ca(2+) ions are bridged by 2-chloronicotinate groups and exhibit an eight-coordination by six carboxylate O atoms of four different 2-chloronicotinate ligands and two O atoms of water molecules. In the crystal structure, inter-molecular O-H⋯O, O-...

In the title hydrated molecular salt, C22H18BrN4S(+)·Br(-)·H2O, the aromatic rings make dihedral angles of 14.20 (12), 34.29 (10) and 68.75 (11)° with the thia-zole ring. In the crystal, mol-ecules are linked into chains running parallel to the a axis by association of the bromide ions and the water mol-ecules of crystallization with the cations via N-H⋯O, O-H⋯Br, C-H⋯N and C-H⋯Br hydrogen-bond...

In the crystal structure of the title compound, C(14)H(10)FN(3)O, the plane of the isoxazole ring makes dihedral angles of 35.72 (9) and 30.00 (9)°, respectively, with those of the 4-fluoro-phenyl and pyridine rings. The plane of the 4-fluoro-phenyl ring makes a dihedral angle of 45.85 (8)° with that of the pyridine ring. The crystal structure is stabilized by inter-molecular N-H⋯N hydrogen bon...

In the crystal structure of the title compound, C(8)H(14)N(3) (+)·Br(-)·2H(2)O, inter-molecular O-H⋯O and O-H⋯Br hydrogen bonding occurs. The water mol-ecules are connected into chains extending in the a-axis direction. The bromide anions are connected to the water mol-ecules, forming 10-membered rings. The cations are connected to the anions via weak C-H⋯Br inter-actions. Two carbon atoms of t...