Kartik Chandra Mondal

Zn(II) Schiff base complexes are good precursors for preparation of ZnO nanoparticles which find several biomedical applications. Herein, a fluorescent hexanuclear Zn(II) Schiff base complex [Zn(II) 6 (L−Me) 6 (MeOH) 2 ]⋅12MeOH(1) [H 2 L-Me=diprotic Schiff base ligand] has been synthesized and characterized by single crystal X-ray diffraction, NMR spectroscopy and mass spectrometry. Fluorescence properties of this Zn(II) 6 -complex have also been studied in solid state and solution. Lifetime measurement and quantum yield calculation have been performed to further investigate the fluorescence properties. Temperature dependent stability of complex 1 has been studied in air and inert gas atmospheres. Fluorescent ZnO nano-particles were prepared by thermal decomposition of 1 at 400 °C and higher temperatures under aerobic atmosphere.

A series of six hetero-bimetallic complexes having umbrella shape topology and general formula (L)2CuLn(NO3)(Ph3PO) have been synthesized by reacting a methanolic solution of diprotic ligand (H2L) [(E)-2-(((2-hydroxyphenyl)imino)methyl)-6-methoxyphenol] and co-ligand Ph3P=O with CuCl2.2H2O and Ln(NO3)3⋅6H2O (Ln= Gd(1), Tb(2),Dy(3), Ho(4), Er(5) and Y(6)) in the presence of triethylamine base. The iso-structural complexes (1-6) have been characterized by Single crystal XRD measurement. Elemental analysis, EPR, IR and UV/Vis spectra have been recorded to further characterise these complexes. The direct current (dc) and alternating current (ac) magnetic susceptibility measurements has been carried out to study magnetic properties of the complexes. Thermogravimetric analysis (TGA) has also been done to assess thermal stability of the complexes.

The cyclic alkyl(amino) carbene (cAAC) bonded chlorophosphinidene (cAAC)P−Cl (2/2') was isolated from the direct reaction between cAAC and phosphorus trichloride (PCl3). Compound 2/2' has been characterized by NMR spectroscopy and mass spectrometry. 31P NMR investigations [δ≈160 ppm (major) and δ≈130 ppm (minor)] reveal that there are two different P environments of the P−Cl unit. X-ray single-crystal determination suggests a co-crystallization of two conformational isomers of (cAAC)P−Cl (2/2'); the major compound possessing a cAAC−PCl unit with CcAAC−P 1.75 Å. This C−P bond length is very close to that of (NHC)2P2 [NHC=N-heterocyclic carbene]. The residual density can be interpreted as a conformational isomer with a shorter CcAAC−P bond similar to a non-conjugated phosphaalkene [R−P=CR2]. Our study shows an unprecedented example of two conformational isomers with different Ccarbene−element bonds. Additionally, Br (3c/3c'), I (4c/4c'), and H (5c/5c') analogues [(Me2-cAAC)P−X; X=Br (3), I (4), H (5)] of 2c/2c'[(Me2-cAAC)P−Cl] were also synthesized and characterized by NMR spectroscopy suggesting similar equilibrium in solution. The unique property of cAAC and the required electronegativity of the X (X=Cl, Br, I, and H) atom play a crucial role for the existence of the two isomers which were further studied by theoretical calculations.

The existence of a metal-metal bond in organometallic and coordination complexes is a very important aspect. Metal-carbonyl, carbene-metal-carbonyl and metal-carbene complexes were studied for having this feature. Herein, an air stable dark green color dicobalt coordination complex [Co(III)2(hep)3(N3)3] (1) [hepH = 2-(2-ethylhydroxy)pyridine] with three μ-alkoxide bridges has been synthesized and characterized by X-ray single crystal diffraction, NMR and UV/vis spectroscopy. Complex 1 has a short Co⋅⋅⋅Co distance (2.595(6) Å) and thus it has been studied by theoretical calculations. QTAIM (quantum theory of atoms in molecules) as well as EDA-NOCV analysis (energy decomposition analysis - natural orbitals for chemical valence) do not indicate any significant metal-metal interaction. The bonding in 1 can be best represented by the interaction of two alkokxy bridged valence electrons fragment Co(III)(hep)2N3 (3d6) with Co(III)(hep)(N3)2 (3d6) where the donation of the lone pair of electrons from three bridging Ohep-atoms stabilizes the dinuclear Co(III) complex. Additionally, thermolysis of 1 at 550 oC led to the formation sponge like Co3O4 oxide.

This work describes employment of two structurally similar Schiff-base ligands (H2L and H2L-Me) [H2L = C14H13NO3 and H2L-Me = C15H15NO3] for the synthesis of three homo-metallic ZnII and two hetero-bimetallic ZnII–NiII based multinuclear complexes {[ZnII4L4(MeOH)2] (1), [ZnII5(L)5(MeOH)2]·MeOH·CH3CN (2), [(L)2ZnII4Cl2(µ3-OMe)2(MeOH)2]·2MeOH (3), [NiII2ZnII2(L)4(MeOH)2] (4) and [Ni3Zn2(L-Me)5(H2O)2]·MeOH·CH3CN (5)} with different interesting structural core topologies. All of these complexes (1–5) have been characterized by single-crystal X-ray diffraction (XRD), elemental analysis, and UV/Vis and Fourier transform infrared (FTIR) spectroscopy. The fluorescence properties of ZnII-containing complexes have been studied by measuring fluorescence spectra in solid state and solution phase. The luminescence behavior has been further quantified by fluorescence life-time and quantum yield measurements. Using high resolution mass spectrometry (HR-MS), the molecular integrity of complexes in the solution phase has been demonstrated by simulating isotopic distribution of molecules with theoretically calculated molecular isotopic patterns. The magnetic properties of ZnII–NiII containing complexes (4–5) have been studied in the temperature range from 5 K to 300 K. Thermogravimetric analysis (TGA) has been carried out to study the thermal stabilities of these complexes (1–5).

Two novel 3d (Ni)/4 f (Dy and Y) metal ions and polydentate organic ligands (H2L1 and H2L2) based tetranuclear coordination complexes, [(L1)4NiII2DyIII2(DMF)2(NO3)2]⋅DMF (1) and [(L2)4NiII2YIII2(DMF)2(NO3)2]⋅DMF⋅H2O (2), have been synthesized and characterized using IR, elemental analysis and single crystal X-ray diffraction studies. The application of these complexes as C−C bond coupling homogeneous catalysts has been logically shown. The complex 1 acts as an excellent catalyst (with a very low catalyst loading of 0.17 mol%) for the syntheses of a wide range of bis(indolyl)methane derivatives in good yields using various indoles and aromatic/hetero aromatic aldehydes under optimized reaction conditions. A plausible reaction mechanism has been proposed showing the coordinative binding of the aromatic aldehyde at NiII centre along with the associative π-stacking interaction between the ligand (H2L1) and the phenyl ring of the aromatic aldehyde and/or indole leading to the formation of the desired bis(indolyl)methanes under the metal assisted C−C bond forming reaction with subsequent elimination of water molecule in polar protic solvent.