Insight on the presence of dimethylammonium cation within anionic metal-organic supramolecular host: structural, Hirshfeld surface, optical and theoretical analysis

A new supramolecular metal-organic complex, [(DMA)(+){Fe(IDA)(2)}(-)] (where H(2)IDA = iminodiacetic acid and DMA = dimethylammonium cation) (1), has been synthesized solvothermally at 90 degrees C from reaction of ferric(III) chloride hexahydrate with nitrilotriacetic acid (H(3)NTA) in stoichiometric ratio. The complex was characterized by single crystal X-ray diffraction (SCXRD) along with spectroscopic analyses. During the reaction process, H(3)NTA is degraded into IDA(2-) ligand. Structural analysis reveals that 1 is mononuclear and crystallizes in the monoclinic space group C2/c. Within the [Fe(IDA)(2)](-) unit, Fe3+ shows six-coordinate distorted octahedral geometry. The [Fe(IDA)(2)](-) units are connected by strong N1-H1 center dot center dot center dot O4 hydrogen bonds to form anionic 2D supramolecular layers which are further connected by weak C-H center dot center dot center dot O hydrogen bonds to form a 3D metal-organic supramolecular host (MOSH) structure having 1D supramolecular channels along the crystallographic c-axis. DMA cations are present within the supramolecular channels through N2-H2 center dot center dot center dot O2 hydrogen bonding interactions. Hirshfeld surface analysis and corresponding 2D fingerprint plots indicate that O center dot center dot center dot H interactions are the major supramolecular interactions present between MOSH and guest DMA cation. DFT calculations reveal that the HOMO and LUMO of the [Fe(IDA)(2)](-) unit are composed of mixed metal-ligand orbitals. Both the absorption and emission spectra of the complex were studied in aqueous phase and the result was correlated with the TDDFT study.