Dicyanamide-interlaced assembly of Zn(II)-schiff-base complexes derived from salicylaldimino type compartmental ligands: Syntheses, crystal structures, FMO, ESP, TD-DFT, fluorescence lifetime, in vitro antibacterial and anti-biofilm properties

• Published in: Inorganica Chimica Acta Vol. 489; pp. 244 - 254
• Main Authors: Majumdar, Dhrubajyoti, Das, Dhiraj, Sreejith, S.S., Das, Sourav, Kumar Biswas, Jayanta, Mondal, Monojit, Ghosh, Debarati, Bankura, Kalipada, Mishra, Dipankar
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01-04-2019; Elsevier Science Ltd
• Subjects: Antibacterial; Biofilms; Carbon 13; Coordination compounds; Crystal structure; Crystals; Damage assessment; Dicyanamide; Fluorescence; Imines; Ligands; Molecular orbitals; NMR; Nuclear magnetic resonance; Property damage; Schiff base; Single crystals; TD-DFT; Tetranuclear Zn(II); X ray powder diffraction; X-ray diffraction; Schiff base; Fluorescence; Dicyanamide; Antibacterial; Tetranuclear Zn(II); TD-DFT
• ISSN: 0020-1693; 1873-3255
• DOI: 10.1016/j.ica.2019.02.022

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•Two new tetranuclear Zn(II) dicyanamide complexes were synthesized.•Complexes are characterized by different spectroscopic techniques.•Crystal structure discloses Zn4 molecular ensembles reflecting µ1,5 & µ1-dicyanamide bridging propensity.•FMO, ESP and TD-DFT methods were employed to substantiate the experimental results.•In vitro antibacterial and anti-biofilm properties were evaluated.
Two new dicyanamide-interlaced tetranuclear Zn(II)-Schiff-base complexes [Zn2(LOMe)(µ-dca-κN1κN5)(µ-dca-κN1)]2(1) and [Zn2(LOEt)(µ-dca-κN1κN5)(µ-dca-κN1)]2(2) were synthesized by using salicylaldimino type Schiff bases (H2LOMe) and (H2LOEt) respectively. Schiff base ligands and the complexes were characterized by elemental analyses, powder X-ray diffraction, FT-IR, FT-Raman, 1H NMR, 13C NMR, UV–Vis, TGA and fluorescence spectroscopy. Dicyanamide modulated complexes were structurally characterized by single crystal X-ray diffraction studies. X-ray crystal structure divulges that the two complexes are isostructural. In both the complexes, the Zn1 metal centers fulfill 5-coordinated distorted square pyramidal geometry having ZnN3O2 chromospheres where Schiff bases are mainly trapped in their complete deprotonated dianionic forms[L]2−, whereas Zn2 metal center attained distorted octahedral geometry. In both complexes two asymmetric units are connected by double μ1,5-dicyanamide ion thus forming Zn4-nuclear metal complex. B3LYP/def2-TZVP level of theory (DFT) successfully applied in both complexes. The complexes (1–2) exhibit intraligand (π → π*) fluorescence in DMSO solvent with lifetimes in the range 0.66–0.82 ns. In vitro antibacterial, membrane damage assay and anti-biofilm properties of both complexes are evaluated against some important Gram-positive and Gram-negative bacterial strains. Finally, the UV–Vis experimental spectral findings are well rationalized with the electronic distribution of HOMO-LUMO through TD-DFT level of calculations.