Susanta Kumar Kar

Rhodamine-based molecular clips for highly selective recognition of Al3+ ions: synthesis, crystal structure and spectroscopic properties

A novel fluorescent chemosensor based on a rhodamine derivative (L) was designed, synthesized, and used as a selective Al+3 ion sensor. Upon addition of Al3+ to an aqueous-acetonitrile solution of L, the development of a strong fluorescence signal by a chelation-enhanced fluorescence (CHEF) process was observed with an attractive glowing orange emission. This sensor shows high selectivity towards Al3+ ions in the presence of other competing metal ions. The fluorescence quantum yield of L–Al3+ (Φf = 0.30) was found to be very high compared to the bare ligand. The limit of detection (LOD) of Al3+ ions was calculated to be 2 × 10−8 M by fluorescence titration. The 1 : 1 binding stoichiometry of the metal complex was established by combined UV-vis, fluorescence and TOF-MS spectroscopy.

An orthogonal ferromagnetically coupled tetracopper(II) 2 × 2 homoleptic grid supported by µ-O4 bridges and its DFT study

A pyrazole based ditopic ligand (PzOAP), prepared by the reaction between 5-methylpyrazole-3-carbohydrazide and methyl ester of imino picolinic acid, reacts with Cu(NO3)2·6H2O to form a self-assembled, ferromagnetically coupled, alkoxide bridged tetranuclear homoleptic Cu(II) square grid-complex [Cu4(PzOAP)4(NO3)2] (NO3)2·4H2O (1) with a central Cu4[µ-O4] core, involving four ligand molecules. In the Cu4[µ-O4] core, out of four copper centers, two copper centers are penta-coordinated and the remaining two are hexa-coordinated. In each case of hexa-coordination, the sixth position is occupied by the nitrate ion. The complex 1 has been characterized structurally and magnetically. Although Cu–O–Cu bridge angles are too large (138–141°) and Cu–Cu distances are short (4.043–4.131 A), suitable for propagation of expected antiferromagnetic exchange interactions within the grid, yet intramolecular ferromagnetic exchange (J = 5.38 cm−1) is present with S = 4/2 magnetic ground state. This ferromagnetic interaction is quite obvious from the bridging connections (dx2−y2) lying almost orthogonally between the metal centers. The exchange pathways parameters have been evaluated from density functional calculations.

Syntheses, characterization, and X-ray crystal structures of two cis-dioxovanadium(V) complexes of pyrazole-derived, Schiff-base ligands

Two mononuclear cis-dioxovanadium(V) complexes of pyrazole-derived, Schiff-base ligands have been synthesized and characterized. Single crystal X-ray analyses were performed with N ′-[(3-methyl-1H-pyrazole-5-yl)carbonyl]pyridine-2-carbohadrazonamido cis-dioxovanadium(V), {[VO2(PzOAP)] · H2O} (1), and 5-methyl-N-[(1E)-1-(pyridin-2-yl)ethylidene]-1H-pyrazole-3-carbohydrazonate cis-dioxovanadium(V), {[VO2(PzCAP)]} (2). Both complexes crystallize in monoclinic crystal systems with different space groups. Complex 1 crystallizes in the space group P21/c, 2 in space group C2/C. In each complex, the vanadium sits within a distorted square pyramidal geometry with an N2O3 chromophore. The τ parameters of the complexes (0.33 for 1, 0.22 for 2) support their square pyramidal geometry. The interesting finding in the work is that the alkoxide oxygen, imino nitrogen, and pyridine nitrogen take part in the coordination process leaving the pyrazole rings inactive in coordination.

Synthesis and spectroscopic characterization of nickel(II) complexes with5-methyl-3-formylpyrazole-N(4)-methylthiosemicarbazone (HL4Me): X-ray crystallographic studies of[Ni(HL4Me)2](NO3)·22H2O

Abstract The coordination mode of the title ligand, HL4Me (synthesized and characterized by mass, IR and 1H NMR spectral parameters) is reported by solid-state isolation and physicochemical identification of a few bis complexes of nickel(II) with different counterions. Magnetic and electronic spectral features classify the reported species, [Ni(HL4Me)2]X2 · 2H2O, as six-coordinate, pseudo-octahedral with appreciable tetragonal distortion. Vibrational spectral data have indicated a neutral tridentate (NNS) function of HL4Methrough the pyrazolyl (tertiary) ring nitrogen, azomethine nitrogen and thiocarbonyl sulphur. X-ray crystallographic studies of [Ni(HL4Me)2](NO3)2 · 2H2O (triclinic, P1) has unambiguously proved the distorted octahedral environment of the nickel(II) ion; the ligand molecules are trans coordinated to the central nickel(II) ion.

Synthesis and characterization of two tris-chelate complexes of cobalt(III) with 3,5-dimethyl-1-(N-methyl/ethyl)thiocarbamylpyrazole (HL1, HL2) — biologically important bidentate ligands with one ambidentate donor site

Abstract Cobalt(III) complexes, of two potentially pyrazole-derived bidentate ligands (with one ambidentate donor site), 3,5-dimethyl-1-( N -methyl/ethyl)thiocarbamylpyrazole (HL 1 for N -methyl, HL 2 for N -ethyl) have been synthesized and characterized by elemental analyses, IR, UV–Vis and 1 H NMR spectral studies. The structure of Co(L 2 ) 3 has been determined by single-crystal X-ray diffraction studies. The complex (triclinic, space group P 1) has a distorted octahedral structure with the ambidentate ligands coordinated to the Co(III) ion as uninegative bidentate chelating agents via the pyrazole ring nitrogen (tertiary) and the thiocarbamyl iminyl nitrogen atoms. The distortion from the regular octahedral geometry is ascribed to the stereochemical limitations imposed by the planar bidentate ligands.

Synthesis and characterisation of nickel(II) complexes with tripodal ligand tris[4-(3-(5-methylpyrazolyl)-3-aza-3-butenyl] amine (MPz3tren): X-ray crystal structure of [Ni(MPz3tren)](BF4)2·0.5H2O

Abstract Nickel(II) complexes of the tripodal ligand (MPz3tren) of the general formula [Ni(MPz3tren)]X2·nH2O (X=Cl, Br, NO3, ClO4 and BF4; n=0 for Cl and Br; n=0.5 for NO3, ClO4 and BF4) have been prepared by template methodology and characterised by elemental analyses, magnetic susceptibility and conductivity measurements at RT, IR and electronic spectra. The molar conductivities measured in MeOH for all the complexes show them to be 1:2 electrolytes. The hexadentate character of the ligand in all the complexes is inferred from IR spectral studies. The electronic spectra in solid state and in MeOH solution suggest octahedral geometry for all the complexes. The structure of [Ni(MPz3tren)](BF4)2·0.5H2O has been determined by single-crystal X-ray diffraction studies (monoclinic, c2/c). Nickel(II) is in a trigonal antiprismatic N6 donor environment and the crystal structure is stabilised by a network of strong H-bonding.

Copper (II) and nickel (II) complexes of pyrazole derived ligands: Synthesis, characterization and coordinating properties of two substituted thiocarbamyl pyrazoles, 3,5-dimethyl-1-N-methyl/ethyl thiocarbamyl pyrazole (HL1, HL2), potential ligands for biological interest. X-ray crystallographic studies of Ni (L2)2

Abstract The solid complexes of Cu (II) with different counterions and Ni (II) having no counterions with 3,5-dimethyl-1-N-methyl thiocarbamylpyrazole (HL1) and 3,5-dimethyl-1-N-ethyl thiocarbamylpyrazole (HL2), the ligands having coordination function of the pyrazole ring and the thiocarbamido group, have been prepared and their geometries established on the basis of molar conductance, magnetic susceptibility, IR, UV and visible spectral data. Magnetic and spectral features indicate paramagnetic [Cu (HL1/HL2)X2] (X = Cl, Br), [Cu (HL1/HL2)2] (ClO4)2 as either planar or tetragonally distorted octahedral species with the ligands in the neutral thione form, while Ni (L1/L2)2 as the diamagnetic square planar species with the ligands in the deprotonated thiol form. X-ray crystallographic studies of Ni (L2)2 has unambiguously proved the distorted square planar environment around the central nickel (II) ion; the ligand molecules are cis-coordinated to the nickel (II) ion.