Monika Mishra

A highly sensitive and selective fluorescent sensor for Al3+ ions based on thiophene-2-carboxylic acid hydrazide Schiff base

An efficient fluorescent receptor (E)-N-[(2-hydroxy-naphthalen-1-yl)methylene]thiophene-2-carbohydrazide (THN) for Al3+ ions was synthesized and characterized by physicochemical and spectroscopic tools along with single crystal X-ray crystallography. This is the first report showing the crystal structure of THN and its sensing property for Al3+ ions. THN selectively and sensitively detects Al3+ ions without any interference among various cations, Na+, K+, Ca2+, Cr3+, Mg2+, Mn2+, Fe3+, Co2+, Ni2+, Cu2+, Zn2+ and Hg2+ by a strong fluorescent change in ethanol–water medium (EtOH–H2O, 1 : 4 v/v). The THN interacts with Al3+ in a tridentate mode to form a [AlCl2(THN)(H2O)]·H2O complex. The binding constant was determined to be 7.06 × 106 M−1 and the limit of detection (LOD) was calculated to be 1.35 × 10−9 M which is the second highest reported till date in the literature. The 1H NMR titration, ESI-MS and DFT studies have also been performed in support of the binding details of the THN–Al3+ complex.

Synthesis, structural investigations and corrosion inhibition studies on Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) complexes with 2-amino-benzoic acid (phenyl-pyridin-2-yl-methylene)-hydrazide

Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) complexes with 2-amino-benzoic acid (phenyl-pyridin-2-yl-methylene)-hydrazide (Habph) have been synthesized. The complexes were characterized by different physico-chemical and spectral studies viz. molar conductance, magnetic susceptibility measurements, electronic, IR and NMR spectra. The molecular structures of the ligand Habph and its Mn(II), Ni(II), Cu(II), Zn(II) complexes were further confirmed by single crystal X-ray diffraction technique. The Habph acts as a monobasic tridentate ligand coordinating through pyridyl-N, azomethine-N and enolate-O atoms with metal ions. Magnetic moments and electronic spectral studies suggest a high spin octahedral geometry for all the complexes. The ligand molecule exhibits a Z molecular conformation about the >CN– bond, whereas the metal complexes show E-configuration in their single crystal structures. The presence of inter- and intra-molecular H-bonding and various C–H⋯π interactions stabilize the molecular structure of the metal complexes. The structure of the Co(II) complex has been satisfactorily modeled by density functional theory (DFT) and time dependent-DFT (TD-DFT) calculations. The results of electrochemical impedance spectroscopy (EIS) and adsorption behavior of the ligand and metal complexes show appreciable corrosion inhibition efficiency for mild steel in a 1 M HCl medium. The metal complexes show a better inhibition effect than the ligand.

8(E)-4-[{2-(2,4-dinitrophenyl)hydrazono}benzene-1,3-diol] as a solvatochromic Schiff base and chromogenic signaling of water content by its deprotonated form in acetonitrile

A simple, cost effective Schiff base (E)-4-[{2-(2,4-dinitrophenyl)hydrazono}benzene-1,3-diol] (DBH) is synthesized and characterized by various physico-chemical and spectroscopic tools along with single crystal X-ray crystallography. This is the first report which describes its solvatochromism in solution and the signaling behavior of deprotonated DBH for the determination of water content in acetonitrile through UV-visible absorption spectra. Addition of acetate ions in acetonitrile solution of DBH results in the formation of deprotonated DBH. The effect of water content on the formation of deprotonated DBH is utilized in signaling. The deprotonated DBH exhibits a pronounced chromogenic signaling behavior that can be detected by the naked eye in response to the changes in water content in acetonitrile. Prominent color changes are observed up to 2% water content in acetonitrile and limit of detection (LOD) of the deprotonated DBH for determination of the water content in acetonitrile is calculated as 0.012%.

Synthesis, spectral and thermal studies of some polymeric mixed ligand uracil–hydrazide complexes with transition metal ions

Polymeric mixed ligand complexes of the type [MCl(ur)(Bh)(H2O)] n and [M(ur)(Inh)(H2O)2] n , where, M = Co(II), Ni(II), Cu(II) and Zn(II), UR = uracil, Bh = benzoic acid hydrazide and Inh = isonicotinic acid hydrazide, have been prepared and characterized by elemental analyses, magnetic susceptibility measurements, thermo grams (TGA) studies, electronic, IR and ESR spectral studies. The magnetic moments and electronic spectral studies indicate high spin 6-coordinate octahedral geometry for all the complexes. ESR spectral studies on copper(II) complexes in solid state show a tetragonal octahedral environment around the metal ion and as the ground state. IR studies suggest that uracil behaves as monobasic bidentate ligand bonding through N(1) and C(4)=O groups to different metal atoms forming a polymeric framework. The ligand Bh bonds to metal through –NH2 and >C=O groups while Inh through –NH2 and a deprotonated C–O− groups. TGA studies of some of the complexes show multi-step decomposition pattern of their organic frameworks.