Abstract
In the anion of the title salt hydrate, H5N2+·C7H5N2O4-·2H2O, the carboxyl-ate and nitro groups lie out of the plane of the benzene ring to which they are bound [dihedral angles = 18.80 (10) and 8.04 (9)°, respectively], and as these groups are conrotatory, the dihedral angle between them is 26.73 (15)°. An intra-molecular amino-N-H⋯O(carboxyl-ate) hydrogen bond is noted. The main feature of the crystal packing is the formation of a supra-molecular chain along the b axis, with a zigzag topology, sustained by charge-assisted water-O-H⋯O(carboxyl-ate) hydrogen bonds and comprising alternating twelve-membered {⋯OCO⋯HOH}2 and eight-membered {⋯O⋯HOH}2 synthons. Each ammonium-N-H atom forms a charge-assisted hydrogen bond to a water mol-ecule and, in addition, one of these forms a hydrogen bond with a nitro-O atom. The amine-N-H atoms form hydrogen bonds to carboxyl-ate-O and water-O atoms, and the amine N atom accepts a hydrogen bond from an amino-H atom. The hydrogen bonds lead to a three-dimensional architecture. An analysis of the Hirshfeld surface highlights the major contribution of O⋯H/H⋯O hydrogen bonding to the overall surface, i.e. 46.8%, compared with H⋯H contacts (32.4%).
Highlights
In the anion of the title salt hydrate, H5N2+ÁC7H5N2O4ÀÁ2H2O, the carboxylate and nitro groups lie out of the plane of the benzene ring to which they are bound [dihedral angles = 18.80 (10) and 8.04 (9), respectively], and as these groups are conrotatory, the dihedral angle between them is 26.73 (15)
The main feature of the crystal packing is the formation of a supramolecular chain along the b axis, with a zigzag topology, sustained by charge-assisted water-O—HÁ Á ÁO(carboxylate) hydrogen bonds and comprising alternating twelve-membered {Á Á ÁOCOÁ Á ÁHOH}2 and eight-membered {Á Á ÁOÁ Á ÁHOH}2 synthons
An analysis of the Hirshfeld surface highlights the major contribution of OÁ Á ÁH/ HÁ Á ÁO hydrogen bonding to the overall surface, i.e. 46.8%, compared with HÁ Á ÁH contacts (32.4%)
Summary
The present structure determination of the title salt dihydrate, [NH2NH3][O2C6H4NO2-4]Á2H2O (I), is a continuation of ongoing structural studies of the relatively unexplored chemistry of 2-amino-4-nitrobenzoic acid. This acid carries several groups capable of hydrogen bonding, viz. The anion has been found coordinating in the carboxylate-O, amino-N mode towards PbII in the coordination polymer catena-[bis(2-2-amino-4-nitrobenzoato)lead(II)] (Chen & Huang, 2009), with the remaining literature structures being salts. While there is an intramolecular amino-N—HÁ Á ÁO(carboxylate) hydrogen bond, Table 1, a significant twist of the carboxylate group with respect to the benzene ring to which it is connected is noted, as evidenced in the value of the C2—C1—C7—O1 torsion angle of 18.83 (17). The terminal groups are conrotatory, forming a dihedral angle of 26.73 (15)
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