Istikhar A. Ansari

Structurally well-characterized new multinuclear Cu(II) and Zn(II) clusters: X-ray crystallography, theoretical studies, and applications in catalysis

Two new trinuclear Cu(II) and dinuclear Zn(II) clusters are crystallized out by reacting the metal salts with the triethanolamine (H3tea) ligand in the presence of benzoic acid (Hba). The complexes are characterized by elemental, thermal, magnetic, spectral (FTIR, UV-Visible, EPR, and photoluminescence) and single crystal X-ray studies. Single crystal X-ray crystallography reveals the composition of the complexes to be [Cu3(H2tea)2(ba)2(NO3)2] (1) and [Zn2(H2tea)(ba)3]H2O (2). FTIR ascertains the binding modes of H2tea−, ba− and NO3−. Triethanolamine binds in both the complexes in the monoanionic (H2tea−) mode. ba− is present as an anchoring auxiliary to generate di- and trinuclear clusters. The Cu(II) ion is present as a distorted octahedral center in the Cu3 cluster (1), while the two Zn(II) ions in 2 have been reported for the first time to possess distorted octahedral as well as tetrahedral geometry in the same molecule. The intriguing features of the non-covalent supramolecular interactions have been investigated and supported theoretically by using Hirshfeld surface analysis and ab initio methods. The solid state photoluminescence (PL) spectra of 1 and 2 disclose the luminescence property of the complexes. Due to the closed or nearly closed shell configuration (d9 or d10), the present complexes are screened for catalytic properties in the hydrocarboxylation of alkanes and cycloalkanes. The catalytic activity data are indicative of the potential catalytic properties of 1 and 2.

Design, structures and study of non-covalent interactions of mono-, di-, and tetranuclear complexes of a bifurcated quadridentate tripod ligand, N-(aminopropyl)-diethanolamine

A series of five new complexes incorporating N-(aminopropyl)-diethanolamine, H2apdea, has been synthesized and characterized by employing elemental, thermal, magnetic, spectroscopic and single crystal X-ray techniques. The reaction of transition metal salts with H2apdea under ambient conditions affords mono-, di- or tetranuclear complexes with the compositions [Ni(H2apdea)(SCN)2]0.5H2O (1), [Co2(Hapdea)(apdea)(SCN)2]NO3·1.5H2O (2), [Co2(Hapdea)(apdea)(H2O)2]3NO3·H2O (3), [Cu2(Hapdea)2(H2O)2]2NO3·2H2O (4) and [Zn4(apdea)2(OCOCH3)2(SCN)2]2MeOH (5). Single crystal X-ray crystallography of 1–5 confirms that the ligand binds to the metal ions in neutral form (H2apdea) in 1, in mono- as well as dianionic form (Hapdea− and apdea2−) in 2 and 3, in monoanionic form (Hapdea−) in 4, and in dianionic form (apdea2−) in 5. Spectral data and crystal structures confirm the distorted octahedral (1–3), square pyramidal (4) and tetrahedral as well as TBP geometries (5) around the metal ions. While 2 and 3 are dinuclear Co(III) systems, the tetranuclear zinc cluster (5) shows interesting structural features with the first example of both two tetrahedral and two TBP Zn(II) centers present in the same molecule. As a result of non-covalent interactions, 1 forms a 2D sheet while 2–5 exist as 3D supramolecular assemblies. A 2D sheet structure is formed due to the presence of S⋯H interactions in 1 (O–H⋯S = 2.518 A, N–H⋯S = 2.727 A). Intermolecular O⋯H and S⋯H contacts (C–H⋯O = 2.595 A, C–H⋯S = 2.894 A, N–H⋯O = 2.123 and 2.403 A) along with other H-bonding interactions in 2 generate a 3D supramolecular assembly. Coexistence of a cyclic octamer of oxygen and nitrogen atoms also helps consolidate the architecture in 2. The O⋯H contacts, i.e., O–H⋯O, C–H⋯O and N–H⋯O interactions, play an important role in the aggregation of molecular entities of 3 and 4 to form a 3D supramolecular network. In the case of 5, interactions between the two tetranuclear (Zn4) clusters i.e., N–H⋯C (2.795 A) and N–H⋯O (2.229 A) and the interactions formed via lattice solvent molecules (C–H⋯O = 2.495 A, O–H⋯O = 2.003 A, O–H⋯C = 2.741 A) generate a robust 3D supramolecular network. The selected supramolecular interactions (like O⋯H and S⋯H) are further explored using Hirshfeld surface analyses, and electrostatic potential (ESP) and deformation density (DD) calculations.

Isolation of proton transfer complexes containing 4-picolinium as cation and pyridine-2,6-dicarboxylate complex as anion: crystallographic and spectral investigations, antioxidant activities and molecular docking studies

Three novel complexes with stoichiometry [4-pic-H][M(pda)2]·2H2O [M = Cr (1), Fe (2) and Co (3); H2pda = pyridine-2,6-dicarboxylic acid and 4-pic = 4-picoline] have been prepared. The complexes (1–3) are characterized using elemental analysis, TGA, CV, FTIR, ESI mass, 1H & 13C NMR, EPR, UV Visible, fluorescence, magnetic and X-ray studies. Spectral data ascertained the bonding modes and the geometry of the complexes. Single crystal X-ray data of (2) and (3) revealed the formation of proton transfer complexes in which a proton is transferred from the H2pda moiety to the pyridine nitrogen of 4-pic. Thermal and ESI mass data confirmed the proposed stoichiometry of the complexes. Cyclic voltammetric (CV) studies confirm the formation of MII/MIII quasi-reversible redox couples in solution. The antioxidant activity of (3) assessed using DPPH and hydrogen peroxide assays has suggested that the present compounds may be used as potent antioxidants. Molecular docking studies performed for (2) and (3) reveal that the present complexes can efficiently bind with DNA receptor with free energy of binding (FEB) values of −314 (2) and −276.8 kcal mol−1 (3). The molecular docking studies indicated a higher binding ability of (2) to DNA compared to that of (3).

Syntheses, crystal structures, and genotoxic studies of cis-µ-1,2-peroxo dicobalt(III) complexes

Two peroxo-bridged dinuclear Co(III) complexes, {[Co2(ea)2(Phen)2(O2)]·5.5H2O·2Cl} (1) and {[Co2(ea)2(Bipy)2(O2)]·2H2O·2NO3} (2) (Hea = ethanolamine, Phen = 1,10-phenanthroline, Bipy = 2,2′-bipyridine), are prepared by reaction of CoCl2·6H2O or Co(NO3)2·6H2O with Hea in the presence of an α-diimine (Phen or Bipy) under reflux. The complexes have been characterized by IR, NMR, thermal gravimetric analysis, cyclic voltammetric (CV), powder X-ray diffraction, and single-crystal XRD techniques. Single-crystal X-ray crystallographic investigations of 1 and 2 reveal that each Co(III) is coordinated by one deprotonated ethanolamine and an α-diimine chelate. The remaining coordination sites of the metal ions are satisfied by bridging peroxide (O22−) in a cis-μ-1,2 manner. The distances [O–O = 1.487(6) (1) and 1.462(3) Å (2) and Co⋯Co = 2.731(12) (1) and 2.7426(6) Å (2)] support the peroxo bridging in a cis manner in both complexes. The crystal lattice is consolidated via extensive H-bonding and π‒π interactions to form a 3-D supramolecular architecture. Thermal data are consistent with the proposed stoichiometry and presence of lattice water. The CV studies of 1 indicate the presence of a quasi-reversible redox couple (CoIII‒CoIII/CoII‒CoII) in solution. Genotoxic studies are also performed on 1 to investigate the possible applications and side effects of the compounds in medicine. The present work describes syntheses and X-ray studies of two unusual cis-peroxo bridged dinuclear Co(III) complexes. The genotoxic studies performed on the complex reveal that the complex can be exploited for industrial applications at low concentration.

Synthesis, crystal structures and spectral characterization of Cu(II) and Mn(II) complexes of 4-hydroxy-3-methoxybenzaldehyde: antioxidant properties and molecular docking studies

Abstract [Cu(L)2(H2O)2] (1) and [Mn(L)2(H2O)2] (2) (HL = 4-hydroxy-3-methoxybenzaldehyde) were synthesized and characterized using elemental, spectral (FTIR, ESI-MS, UV–visible, fluorescence and EPR), thermal, cyclic voltammetric, powder, and single crystal X-ray crystallographic studies. Spectral and X-ray data ascertained the structural features, binding modes of ligand and distorted octahedral geometry around the metal ions. Cyclic voltammetric studies confirmed the formation of a quasi reversible redox couple in solution. Crystal structure analysis of 1 and 2 reveal the presence of non-covalent interactions, resulting in a 1-D polymeric chain. Antioxidant properties (using DPPH and hydrogen peroxide assay) and molecular docking studies (using 1BNA) are also examined. The binding free energies (calculated from docked models), −270 (1) and −295 kJ mol−1 (2), suggest that the complexes reasonably bind to DNA, and the DNA-binding affinity of 2 is stronger than that of 1.