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 H2IDA = iminodiacetic acid and DMA = dimethylammonium cation) (1), has been synthesized solvothermally at 90 °C from reaction of ferric(III) chloride hexahydrate with nitrilotriacetic acid (H3NTA) in stoichiometric ratio. The complex was characterized by single crystal X-ray diffraction (SCXRD) along with spectroscopic analyses. During the reaction process, H3NTA is degraded into IDA2- 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···O4 hydrogen bonds to form anionic 2D supramolecular layers which are further connected by weak C-H···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···O2 hydrogen bonding interactions. Hirshfeld surface analysis and corresponding 2D fingerprint plots indicate that O···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.