Molecular and Electronic Structures, Spectra, Electrochemistry and Anti‐bacterial Efficacy of Novel Heterocyclic Hydrazones of Phenanthrenequinone and Their Nickel(II) Complexes

Abstract

A pair of tridentate ligands incorporating heterocyclic hydrazones of 9,10‐phenanthrenequinone viz,. pyridyl‐hydrazino‐phenathrenequinone HLPy 1a and benzothiazolyl‐hydrazino‐phenathrenequinone HLBenz 1b have been synthesized and both behave as monoanionic towards nickel(II), forming meridional octahedral complexes of type [Ni(LPy)2] 2a and [Ni(LBenz)2] 2b as evident from single crystal X‐ray diffraction studies. The complexes are electro‐active in solution and nature of redox orbitals has been analysed by theoretical means. They display two oxidative and two reductive responses that have been ascribed to the redox processes of coordinated ligands. The electronic absorption spectral patterns of two complexes are analogous barring the fact that lower energy transition for 2b is marginally bathochromically shifted relative to that of 2a and it has been clarified by TD‐DFT studies. Anti‐bacterial efficacy of the ligands HLPy 1a, HLBenz 1b and complexes [Ni(LPy)2] 2a, [Ni(LBenz)2] 2b against four Gram‐positive and four Gram‐negative strains has been explored. [Ni(LPy)2] 2a exhibits more pronounced efficacy than [Ni(LBenz)2] 2b and these are greater than those of the corresponding ligands. The mode of action of 2a is essential via DNA damage while protein leakage and membrane lipid damage were observed upon treatment with 2b.

Halogen Bonding in Stereoselective Metal Chloride (M–Cl) Bond Activation and Transformation to Metal Triiodide (M–I3)

“…The ligand 2-pyridylhydrazinophenanthrenequinone HL PyHPQ 1 reported in this work has been synthesized starting from 9,10-phenanthrenequinone and 2-hydrazinopyridine by the reported method. 50 Upon refluxing 1 with [Ru II H(CO)Cl(PPh 3 ) 3 ] (in toluene) in molar ratio of 1:1 for 4 h, with subsequent chromatographic separation leads to isolation of three complexes viz., trans-[Ru II bright green precipitate when [Rh I Cl(PPh 3 ) 3 ] was refluxed in toluene with 1 (1:1 molar ratio) for 1 h via an oxidative coordination reaction, 47,49,61−64 during the course of which the metal center becomes hexacoordinated. In fact, the driving force for this electron transfer is possibly due to the formation of the stable t 2 6 system.…”

“…The ligand 2-pyridylhydrazinophenanthrenequinone HL PyHPQ 1 reported in this work has been synthesized starting from 9,10-phenanthrenequinone and 2-hydrazinopyridine by the reported method . Upon refluxing 1 with [Ru II H­(CO)­Cl­(PPh 3 ) 3 ] (in toluene) in molar ratio of 1:1 for 4 h, with subsequent chromatographic separation leads to isolation of three complexes viz ., trans- [Ru II L PyHPQ (CO)­(PPh 3 )­Cl] 2 (light green), cis- [Ru II L PyHPQ (CO)­(PPh 3 )­Cl] 3 (deep green) (Cl and PPh 3 are trans in 2 and they are cis in 3 ) and [Ru II L PyHPQ (CO)­(PPh 3 ) 2 Cl] 4 (violet).…”

“…The ligand HL PyPHQ 1 was synthesized by a reported method. 50 Syntheses of the Complexes. [Ru II L PyHPQ (CO)(PPh 3 )Cl] ( 2) & ( 3) and [Ru II L PyHPQ (CO)(PPh 3 ) 2 Cl] (4).…”

“…Our group has been striving to comprehend the role of ancillary ligands in influencing the stereoselectivity of C–H bond activation by using platinum group metal complexes. − In this article we have presented how judicious choice of coligands can induce selectivity in M–Cl (M = Ru II , Rh III ) bond activation via the formation of halogen bond (XB). The ligand, 2-pyridylhydrazinophenanthrenequinone, HL PyHPQ 1 was used to synthesize two isomeric complexes trans- and cis- [Ru II L PyHPQ (CO)­(PPh 3 )­Cl] 2 and 3 respectively and in both cases the ligand exhibits tridentate behavior. Additionally, another complex of composition [Ru II L PyHPQ (CO)­(PPh 3 ) 2 Cl] 4 , is formed where the ligand is bidentate, thereby revealing its flexidentate character.…”

Six-coordinated nickel(ii) complexes with benzothiadiazole Schiff-base ligands: synthesis, crystal structure, magnetic and HFEPR study

“…Most of the mononuclear complexes are characterized by a distorted octahedron, due to the geometry restrictions of the two tridentate ligands. A majority of the reports provided only crystallographic information, 12 some offer insights into bioactivity, 13,14 catalysis 15,16 or spectroscopic characteristics. 17 Notably, only a limited number of publications include magnetic measurements.…”