Role Reversal of the Carboxylate Group from Coordination to Hydrogen Bonding Only, in Structurally Diverse Metal-2-amino,5-Nitro-benzoates: A First Report

Abstract

The remarkable structural diversities arising from a small ligand, 2-amino,5-nitro-benzoic acid (L1H), equipped with different functional groups, conferring tunable coordination sites as well as H-bonding abilities, have been explored. Six new crystal structures of Cs(I), Na(I), K(I), and Li(I) ions with L1 have been realized. Notably, for the medium-sized alkali metal ions, a role reversal between the coordination and H-bonding nature of −COO– and −NO2 groups, respectively, has been observed for the first time. Since L1 possesses three potential sites for coordination as well as H-bonding interactions, we realized a delicate control of noncovalent interactions on the resulting supramolecular assemblies. Structural diversities observed range from one-dimensional helices and linear threads to two-dimensional brick-wall types or three-dimensional networks. The electrostatic surface potential (ESP) of three representative complexes provided an insight into the electronic-deficient and electron-rich regions. The coordination of Na(I) and K(I) ions through the nitro groups extends the electron-deficient region of the complexes. The electron densities at the bond critical paths of the representative complexes were calculated to understand the supramolecular outcome of the coordination polymers. Unravelling of such critical electronic information is paramount toward the systematic construction of a new generation of complex coordination polymers.