2-Amino-3-nitro­pyridinium hydrogen oxalate

In the non-centrosymetric title compound, C5H6N3O2 +·C2HO4 −, the hydrogen oxalate anions form corrugated chains parallel to the c axis, linked by O—H⋯O hydrogen bonds. The 2-amino-3-nitro­pyridinium cations are anchored between theses chains by N—H⋯O and C—H⋯O hydrogen bonds and van der Waals and electrostatic inter­actions, creating a three-dimensional network

Bis(2-amino-3-nitro­pyridinium) dihydrogen­diphosphate

The structure of the title compound, 2C5H6N3O2 +·H2P2O7 2−, contains infinite (H2P2O7 2−)n layers stacked perpendicular to the a axis. The 2-amino-3-nitro­pyridinium cations are arranged in pairs and are anchored between these layers, linking them by N—H⋯O and C—H⋯O hydrogen-bonding and electrostatic inter­actions between anionic and cationic species to form a three-dimensional network

2-Amino-3-nitro­pyridinium perchlorate

The title compound, C5H6N3O2 +·ClO4 −, is comprised of discrete perchlorate anions and 2-amino-3-nitro­pyridinium cations. The anion has a typical tetra­hedral geometry while the cation presents a nearly planar [maximum deviation = 0.007 (8) Å] pyridinium ring. Undulating [C5H6N3O2 +]n chains extending along the c-axis direction are linked via N—H⋯O hydrogen bonds. The cations are further connected to the anions by N—H⋯O hydrogen bonds and weak C—H⋯O inter­actions, leading to the formation of a three-dimensional network

2-Amino-3-nitro­pyridinium perrhenate

In the title mol­ecular salt, (C5H6N3O2)[ReO4], the cations and tetrahedral anions are linked by trifurcated N—H⋯(O,O,O) and bifurcated N—H⋯(O,O) hydrogen bonds, as well as weak C—H⋯O inter­actions. This results in alternating corrugated inorganic and organic layers in the crystal

Bis(2-amino-3-nitro­pyridinium) dichromate(VI)

The title compound, (C5H6N3O2)2[Cr2O7], consists of 2-amino-3-nitro­pyridinium cations and discrete dichromate anions linked together by N—H⋯O and C—H⋯O hydrogen bonds, forming thick layers parallel to (101). Layer cohesion is ensured by N—H⋯O hydrogen bonding in addition to electrostatic and van der Waals inter­actions, forming a three-dimensional framework. The dichromate anion is located on a twofold axis that passes through its bridging O atom

Nombres de Betti des surfaces elliptiques réelles

Minor changesInternational audienceWe prove a new bound for the number of connected components of a real regular elliptic surface with a real section and we show the sharpness of this bound. Furthermore, all possible values for the Betti numbers of such a surface are realized

2-Amino-3-nitro­pyridinium hydrogen selenate

The asymmetric unit of the title compound, C5H6N3O2 +·HSeO4 −, contains two monoprotonated 2-amino-3-nitro­pyridinium cations and two hydrogen selenate anions which are connected through N—H⋯O and O—H⋯O hydrogen bonds, building chains parallel to the a direction. These chains are further connected to each other by weaker C—H⋯O hydrogen-bonding inter­actions, leading to the formation of a three-dimensional network

Bis(2-methyl­anilinium) diaqua­bis[dihydrogendiphosphato(2−)]cobaltate(II)

In the title cobalt(II) complex with 2-methyl­anilinium and diphosphate, (C7H10N)2[Co(H2P2O7)2(H2O)2], a three-dimensional network is built up from anionic layers of [Co(H2P2O7)2(H2O)2]2− units and 2-methyl­anilinium cations located between these layers. The dihydrogendiphosphate groups present a bent eclipsed conformation, while the Co2+ ions lie on inversion centers. An intricate network of O—H⋯O and N—H⋯O hydrogen bonds is established between the different components, assuring the cohesion of the network with other inter­actions, being of electrostatic and van der Waals nature