Synthesis, characterization, DFT calculations and antimicrobial activity of pentagonal-bipyramidal Zn(II) and Cd(II) complexes with 2,6-diacetylpyridine-bis(trimethylammoniumacetohydrazone)

Abstract

Isothiocyanate complexes of Zn(II) and Cd(II) with the condensation product of 2,6diacetylpyridine and trimethylammoniumacetohydrazide (Girard's T reagent) were synthesized, characterized, and their antimicrobial activities were evaluated. The structures of the complexes were determined by elemental analysis, IR and NMR spectroscopy. The crystal structure of the Zn(II) complex was also determined. Quantum-chemical calculations of the geometry and total energy of isomers of 2,6-diacetylpyridine-bis(trimethylammoniumacetohydrazone) were performed in vacuum and methanol solution, with the aim to explain conformational behavior and E/Z isomerism of this compound. DFT calculations of the molecular structures and the relative stabilities of linkage isomers of the Cd(II) complex showed that the isomer with N-Cd-N coordination of SCNis the most stable. Complexes of Zn(II) and Cd(II) exhibited low-tomoderate activity against the tested microbial strains.

Molecular Structures and Spin‐States of Pseudohalide Metal Complexes with Hydrazones of Girard's T Reagent

“…Ambidentate thiocyanate could be coordinated through nitrogen or sulfur donor atoms, so DFT calculations of the molecular structures and the relative stabilities of linkage isomers of the PBPY‐7 Cd II complex cation were performed. The results showed the isomer with N–Cd–N coordination of SCN – to be the most stable . Complexes 14 and 15 are not stable in solution.…”

“…Isothiocyanato complexes of Mn II {[Mn( H 2 L 4 )(NCS) 2 ](SCN) 2 · CH 3 OH} ( 10 ), Co II {[Co( H 2 L 4 )(NCS) 2 ](SCN) 2 · 2 H 2 O ( 11 ) and [Co( H 2 L 4 )(NCS) 2 ][Co(NCS) 4 ] · 2 H 2 O ( 12 )}, Ni II {[Ni( H 2 L 4 )(NCS) 2 ](SCN) 2 · 2 H 2 O ( 13 )}, Zn II {[Zn( H 2 L 4 )(NCS) 2 ][Zn(NCS) 4 ] · 2 H 2 O ( 14 )}, and Cd II {[Cd( H 2 L 4 )(NCS) 2 ][Cd(NCS) 4 ] · 2 H 2 O ( 15 )} with the condensation product of 2,6‐diacetylpyridine and the Girard T reagent ( H 2 L 4 Cl 2 , Scheme ) were obtained from the dihydrazone ligand, NH 4 SCN, and the corresponding metal(II) salts [chloride in the cases of Mn II ( 10 ), Ni II ( 13 ), Co II ( 11 and 12 ), and Zn II ( 14 ) complexes or nitrate in the case of Cd II complex ( 15 )]. X‐ray analysis of the Mn II , Ni II , and Zn II complexes 10 , 13 , and 14 , respectively, and of the two Co II complexes 11 and 12 showed pentagonal‐bipyramidal (PBPY‐7) coordination in the surroundings of the metal(II), consisting of dihydrazone ligand symmetrically coordinated through N 3 O 2 donor atoms in the equatorial plane and two N‐coordinated NCS – monodentate ligands in axial positions . In contrast with complexes 10 , 11 , and 13 , in complexes 12 , 14 , and 15 the counterion of the PBPY‐7 complex cation is anionic tetrahedral [M(NCS) 4 ] 2– instead of two SCN – ligands …”

“…X‐ray analysis of the Mn II , Ni II , and Zn II complexes 10 , 13 , and 14 , respectively, and of the two Co II complexes 11 and 12 showed pentagonal‐bipyramidal (PBPY‐7) coordination in the surroundings of the metal(II), consisting of dihydrazone ligand symmetrically coordinated through N 3 O 2 donor atoms in the equatorial plane and two N‐coordinated NCS – monodentate ligands in axial positions . In contrast with complexes 10 , 11 , and 13 , in complexes 12 , 14 , and 15 the counterion of the PBPY‐7 complex cation is anionic tetrahedral [M(NCS) 4 ] 2– instead of two SCN – ligands …”

“…Complexes 14 and 15 are not stable in solution. Two series of signals (ratio 3.4:1 in the spectrum of complex 14 and 4.5:1 in that of complex 15 ) appearing in their 1 H NMR spectra in [D 6 ]DMSO indicate substitution of thiocyanate ligands with solvent …”

“…That review also covers some pseudohalide metal complexes with Girard T reagent hydrazones reported up until 2012 , . In recent years our two research groups (K. Anđelković and co‐workers and I. Turel and co‐workers) have made significant contributions in research into coordination chemistry of pseudohalide metal complexes with Girard T reagent hydrazones . A summary of pseudohalide metal complexes with Girard T reagent hydrazones reported until now is given in Table .…”