Synthesis, crystal structure, Hirshfeld surface analyses, antimicrobial activity, and thermal behavior of some novel nanostructure hexa-coordinated Cd(II) complexes: Precursors for CdO nanostructure

A new tetradentate Schiff base ligand entitled as (L = (N2E, N2′E)-N1, N1′-(ethane-1,2-diyl)bis(N2-((E)-3-(2-nitrophenyl)allylidene)ethane-1,2-diamine) and its six cadmium(II) complexes formulated as CdLX2 in which X is Cl, Br, I, NO3, NCS, or N3 were synthesized under ultrasound irradiation and characterized by various physical and spectral techniques. Moreover, some complexes were also prepared in nanostructured dimensions confirmed by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDXA), and X-ray powder diffraction (XRPD) techniques and then were used as precursor for preparation of CdO nanoparticles via direct calcination at 600°C. As typical, the crystal structure of cadmium(II) nitrate complex was determined using single crystal X-ray diffraction. Accordingly, it was found that [Cd(L)(NO3)2] complex crystallizes in the monoclinic space group P21/n with two independent molecules in the asymmetric unit with two coordination modes of nitrate anions. This complex has zero-dimensional (0D) coordination supramolecular structure. Hirshfeld surface analyses suggested that H … O (49.5%), H … H (30.3%), and H … C (11.8%) intermolecular interactions are most considerable in the crystal packing. Computational studies of ligand structure leading to electrostatic potentials of the solid state geometry and some occupied molecular orbitals (HOMO, HOMO-1, HOMO-2, and HOMO-5) prevailing the contribution of nitrogen lone pairs are also reported. Thermal behavior studies of the compounds under nitrogen atmosphere from room temperature to 900°C revealed that the ligand is completely decomposed without any residual whereas the complexes are decomposed via two to four thermal steps with trace amount of metallic cadmium as residue. Moreover, antibacterial and antifungal screening well showed that the complexes inhibit from the growth of the various bacteria and fungi more efficient than free ligand especially against Gram-positive bacteria. DNA cleavage potentials of the compounds may be one of the reasons for their antimicrobial activity.