Synthesis and structure of trans -bis-(4-amino-3-nitro-benzoato-κ O )bis-(4-amino-3-nitro-benzoic acid-κ O )di-aqua-manganese(II) dihydrate.

The manganese title complex, [Mn(C 7 H 5 N 2 O 4 ) 2 (C 7 H 6 N 2 O 4 ) 2 (H 2 O) 2 ]·2H 2 O, is one of the first 4-amino 3-nitro-benzoic acid (4 A3NBA) monoligand metal complexes to be synthesized. It crystallizes in the centrosymmetric monoclinic space group P 2 1 / n with the complex mol-ecules located on inversion centers. Four 4 A3NBA ligand mol-ecules are monodentately coordinated by the Mn 2+ ion through the carb-oxy-lic oxygen atoms while the other two positions of the inner coordination sphere are occupied by water mol-ecules, giving rise to a distorted octa-hedron, and two water mol-ecules are in the outer coordination sphere. There are two intra-molecular hydrogen bonds in the complex mol-ecule. The first is of the common N-H⋯O=N type, while the second is a rarely occurring very strong hydrogen bond in which a common proton is shared by two uncoordinated oxygen atoms of neighboring carboxyl-ate groups. In the crystal, an intricate system of inter-molecular hydrogen bonds links the complex mol-ecules into a three-dimensional-network.