Synthesis and structure of trans-bis(4-amino-3-nitrobenzoato-κO)bis(4-amino-3-nitrobenzoic acid-κO)diaquamanganese(II) dihydrate

The reaction of 4-amino 3-nitrobenzoic acid and manganese dichloride tetrahydrate in an ethanol–water mixture yielded the title complex[Mn(C7H5N2O4)2(C7H6N2O4)2(H2O)2]·2H2O. In the crystal, molecules are linked by N—H⋯O, O—H⋯O and C—H⋯O hydrogen bonds.

There are two intramolecular hydrogen bonds in the complex molecule (Table 1).The first bond is of the usual N-H� � �O N type, closing a six-membered ring with an S 1 1 (6) graph-set motif (Etter 1990;Ibragimov et al., 2017;Ruzmetov et al., 2022).The second is a rarely occurring very strong hydrogen bond closing a nine-membered ring where a common proton, H20, is shared by two uncoordinated oxygen atoms O2 and O6 of neighboring carboxylate groups.The atom H20, situated between the two oxygen atoms, is located closer to atom O2 at a distance of 1.270 (2) A ˚ [and 1.198 (2) A from O6].Despite this, it is impossible to indicate which of the four carboxylic groups present are deprotonated.The total negative charge of the carboxylic groups is 2 and it compensates the +2 charge of the Mn 2+ ion.data reports

Figure 2
The crystal packing viewed along [100] showing the O-H� � �O, N-H� � �O and C-H� � �O hydrogen bonds (dashed red lines) in the crystal structure.
There are 17 proton-acceptor oxygen atoms, 4 proton-donor nitrogen atoms and 2 water molecules in the title complex.These atoms are involved in a complex system of intermolecular hydrogen bonds (Table 1).Moreover, three weak C-H� � �O hydrogen bonds are also observed in the structure (Table 1, Fig. 2).Together these hydrogen bonds link the complex molecules into a three-dimensional network (Fig. 2.).

Synthesis and crystallization
All reagents and solvents were purchased from Sigma-Aldrich (Darmstadt, Germany) and they were used as received.MnCl 2 •H 2 O (0.198 g, 1.0 mmol) was dissolved in a small amount of water.4-Amino 3-nitrobenzoic acid (0.364 g, 2 mmol) was dissolved in a mixed solvent of 3 ml of absolute alcohol and 3 ml of distilled water.After dropwise addition of the 4 A3NBA solution to the manganese salt solution, the resultant solution was stirred for 2 h with a magnetic stirrer at 55 � C. The solution was allowed to stand at 30 � C in a beaker with small holes in the cover for evaporation.After about eight days, block-shaped single crystals ofthe title compound appeared.Analysis calculated: C 28 H 30 MnN 8 O 20 : C, 39.40%; H, 3.54; N, 13.13%.Found: C, 39.32%; H, 3.47%; N, 13.08%.

Refinement
Crystal data, data collection and structure refinement details for the structure of the synthesized compound are summarized in Table 2.

Special details
Geometry.All esds (except the esd in the dihedral angle between two l.s.planes) are estimated using the full covariance matrix.The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry.An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s.planes.Refinement.The hydrogen atoms of water molecules and amino groups were located in difference-Fourier maps and refined freely.The H atoms of the benzene ring were calculated geometrically with C-H = 0.93 A° and U iso (H) = 1.2U eq (C).

Table 2
Experimental details.