Tweaking the affinity of aryl‐substituted diazosalicylato‐ and pyridine ligands towards Zn (II) and its neighbors in the periodic system of the elements, Cu (II) and Cd (II), and their antimicrobial activity

Abstract

A series of six new Zn (II) compounds, viz., [Zn(HLASA)2(Py)2] (1), [Zn(HLMASA)2(Py)2] (2), [Zn(HLMASA)2(4‐MePy)2] (3), [Zn(HLCASA)2(4‐MePy)2] (4), [Zn(HLBASA)2(Py)2] (5), [Zn(HLBASA)2(4‐MePy)2] (6) and representative Cu (II) and Cd (II) complexes, viz., [Cu(HLASA)2(Py)2(H2O)] (7) and [Cd(HLBASA)2(Py)3] (8) [(HLXASA)− = para‐substituted 5‐[(E)‐2‐(aryl)‐1‐diazenyl]‐2‐hydroxybenzoate with X = H (ASA), Me (MASA), Cl (CASA) or Br (BASA); Py = pyridine; 4‐MePy = 4‐methylpyridine] have been synthesized and characterized by spectroscopic techniques and single‐crystal X‐ray diffraction analysis. The structural characterization of the compounds revealed distorted tetrahedral (1–6), square‐pyramidal (7) and pentagonal‐bipyramidal (8) coordination geometries around the metal atom, in which the aryl‐substituted diazosalicylate ligands are coordinated only through the oxygen atoms of carboxylate groups, either in an anisobidentate or isobidentate mode; meanwhile, the 2‐hydroxy groups of the monoanionic ligand (HLXASA)− are involved only in intramolecular O‐H···O hydrogen bonds with the carboxylate function. In the crystal structures of 1–8, the complex molecules are assembled by π‐stacking interactions giving mostly infinite 1D strands. The intermolecular binding in the solid state structures is accomplished by diverse additional non‐covalent contacts including C‐H···O, C‐H···N, C‐H···π, C‐H···Br, O···Br, Br···π and van der Waals contacts. Although the primary and secondary ligands in the Zn (II) complex series 1–6 carry different substituents at the periphery (X = H, Me, Cl, Br for (HLXASA)− and R = H, Me for 4‐Py‐R), five of the crystal structures were isostructural. Additionally, the antimicrobial activity of the pro‐ligands H2LXASA and their Zn (II), Cu (II) and Cd (II) compounds were studied in a comparative manner, showing high sensitivity (IZD ≥ 20) against Bacillus subtilis.

Recent Studies on the Antimicrobial Activity of Transition Metal Complexes of Groups 6–12

“…Free ligands and complexes showed good antibacterial activity against E. Coli, S. Aureus and E. Faecalis with MICs lower than 0.5 mg/L. A series of zinc(II) compounds of aryl-substituted diazosalicylato-and pyridine ligands, was recently described by Basu Baul et al (85, Figure 15) and tested along with copper and cadmium analogs against B. subtilis, S. aureus and K. pneumonia and C. albicans [187]. The zinc(II) complexes showed comparable activity to the standard chloramphenicol and fluconazole antimicrobial drugs.…”