Supriya Dutta

Syntheses, Structures, and Magnetic Properties of Diphenoxo-Bridged CuIILnIII and NiII(Low-Spin)LnIII Compounds Derived from a Compartmental Ligand (Ln = Ce−Yb)

Syntheses, characterization, and magnetic properties of a series of diphenoxo-bridged discrete dinuclear M(II)Ln(III) complexes (M = Cu or Ni, Ln = Ce-Yb) derived from the compartmental Schiff base ligand, H(2)L, obtained on condensation of 3-ethoxysalicylaldehyde with trans-1,2-diaminocyclohexane, are described. Single crystal X-ray structures of eight Cu(II)Ln(III) compounds (Ln = Ce (1), Pr (2), Nd (3), Sm (4), Tb (7), Ho (9), Er (10), and Yb (12)) and three Ni(II)Ln(III) (Ln = Ce (13), Sm (16), and Gd (18)) compounds have been determined. Considering the previously reported structure of the Cu(II)Gd(III) (6) compound (Eur. J. Inorg. Chem. 2005, 1500), a total of twelve structures are discussed/compared in this study. Four types of composition are observed in the Cu(II)Ln(III) complexes: [Cu(II)LLn(III) (NO(3))(3)(H(2)O)] (1-3: Ln = Ce-Nd), [Cu(II)LSm(III)(NO(3))(3)]·CH(3)COCH(3) (4), [Cu(II)(H(2)O)LLn(III)(NO(3))(3)] (5: Ln = Eu; 6: Ln = Gd), and [Cu(II)LLn(III)(NO(3))(3)] (4A: Ln = Sm; 7-12: Ln = Tb-Yb). On the other hand, the Ni(II)Ln(III) complexes are characterized to have two types of composition: [Ni(II)LLn(III)(H(2)O)(NO(3))(3)] (13-15: Ln = Ce-Nd) and [Ni(II)LLn(III)(NO(3))(3)]·0.5CH(3)COCH(3) (16-24: Ln = Sm-Yb). Among twelve X-ray structures, seven belong to three different isomorphous sets (Cu(II)Ce(III) (1), Cu(II)Pr(III) (2), Cu(II)Nd(III) (3), and Ni(II)Ce(III) (13); Cu(II)Tb(III) (7), Cu(II)Ho(III) (9), Cu(II)Er(III) (10), and Cu(II)Yb(III) (12); Ni(II)Sm(III) (16) and Ni(II)Gd(III) (18)), whereas space group/unit cell parameters of two others (Cu(II)Sm(III) (4) and Cu(II)Gd(III) (6)) are of different types. The lanthanide(III) centers in Cu(II)Ce(III) (1), Cu(II)Pr(III) (2), Cu(II)Nd(III) (3), and Ni(II)Ce(III) (13) complexes are eleven-coordinated, while the lanthanide(III) centers in other compounds are ten-coordinated. As evidenced from the dihedral angle (δ) between the CuO(phenoxo)(2) and LnO(phenoxo)(2) planes, variation in the extent of planarity of the bridging moiety in the Cu(II)Ln(III) compounds takes place; the ranges of δ values are 0.8-6.2° in the 4f(1-7) analogues and 17.6-19.1° in the 4f(8-13) analogues. The Cu(II)Gd(III) (6) compound exhibits ferromagnetic interaction (Eur. J. Inorg. Chem. 2005, 1500). The nature of the magnetic exchange interaction in the Cu(II)Ln(III) complexes has been understood by utilizing the empirical approach; the Ni(II)Ln(III) complexes have been used as references. The metal centers in the Eu(III) complex are uncorrelated, while other 4f(1-6) analogues (Ce(III), Pr(III), Nd(III), and Sm(III)) exhibit antiferromagnetic interaction. Among the higher analogues (4f(7-13)), only Yb(III) exhibits antiferromagnetic interaction, while interaction in other analogues (Gd(III), Tb(III), Dy(III), Ho(III), Er(III), and Tm(III)) is ferromagnetic. An important aspect of the present study is the measurement of the magnetic susceptibility of the unblocked samples as well as on blocking the samples with grease to avoid powder reorientation, if any. Comparison of the two sets of data reveals significant difference in some cases.

Synthesis, structural characterization and anion-, cation- and solvent-induced tuning of photophysical properties of a bimetallic Ru(II) complex: combined experimental and DFT/TDDFT investigation

A mixed-ligand bimetallic ruthenium(II) complex of composition [(bpy)2Ru(H2PyImPhen)Ru(bpy)2](ClO4)4 (1), where H2PyImPhen = 2,6-di(1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)pyridine and bpy = 2,2′-bipyridine has been synthesized and characterized using standard analytical and spectroscopic techniques. The X-ray crystal structure of its N–H deprotonated form (2) has been determined which showed that the compound crystallized in monoclinic form with the space group P21/c. The optimized geometrical parameters for the complexes computed both in the gas phase and in solution are reported and compared with the available X-ray data. The absorption spectra, redox behavior and luminescence properties of the complexes were thoroughly investigated. Complex 1 displays strong luminescence at room temperature with lifetimes in the range of 160–500 ns (aerated condition), depending upon the nature of the solvent. The complex is found to undergo one reversible oxidation in the positive potential window and three successive quasi-reversible reductions in the negative potential window. Both the anion and cation binding properties of 1 were thoroughly investigated in acetonitrile solution using absorption, steady state and time-resolved emission spectral studies. The anion sensing studies revealed that the receptor acts as a sensor for F−, AcO− and H2PO4−. It is evident that in the presence of excess F− and AcO− ion, deprotonation of the imidazole N–H fragments of 1 occurs. Anion-induced lifetime quenching by F− and AcO− and enhancement by H2PO4−, makes the receptor 1 a suitable lifetime-based sensor for selective anions. Coordination of metal ions such as Mn2+, Co2+, Cu2+ to the secondary coordination sphere of 1 trigger emission quenching, while metal ions having a completely filled d orbital (such as Zn2+, Cd2+ or Hg2+) do not quench; rather some finite enhancement of the fluorescence intensity of the receptor occurs. Density functional theory (DFT) and time-dependent DFT (TD-DFT) study provides insight into the nature of the ground and the excited states involved in absorption and emission transitions. In particular, the changes in the absorption and emission spectral characteristics of 1 on interaction with anions and cations are also reproduced by our calculations.

A mononuclear copper(II) complex immobilized in mesoporous silica: an efficient heterogeneous catalyst for the aerobic oxidation of benzylic alcohols

The diamide ligand 2,6-bis[(N-phenyl)amido]-4-methylphenol (HL) has been used to synthesize a mononuclear copper(II) complex, [CuL2(DMF)2] (1). The X-ray crystal structure of this complex reveals that the copper(II) center is coordinated to the two phenoxides and two amide carbonyl oxygens of the HL ligand and additionally to the amide carbonyl oxygens of two dimethylformamide molecules. This complex was also characterized using UV-Vis and EPR spectroscopy, along with thermal and electrochemical analysis. Complex 1 was then immobilized in a 2-D mesoporous silica matrix. This immobilized complex, 1a, has been characterized using UV-Vis and FT-IR spectroscopy, as well as small angle X-ray diffraction, N2 sorption and TEM. The immobilized complex was found to heterogeneously catalyze the aerobic oxidation of benzylic alcohols to the corresponding aldehydes in the presence of TEMPO, with high turnover numbers and good recyclability for up to four cycles.

Methoxo-bridged diiron(III) complex of m-xylylenebis(acetylacetonate) showing remarkable thermal stability for encapsulated dichloromethane

The synthesis, structural characterization, spectroscopic, magnetic, electrochemical and thermal properties of a methoxo-bridged dinuclear iron(III) inclusion compound [Fe2(m-xba)2(μ-OCH3)2]·CH2Cl2 (1) derived from m-xylylenebis(acetylacetone) H2(m-xba) are reported. In 1, the symmetry related two distorted octahedral iron(III) centres are separated by 3.164(8) A and the distance between the centroids of the aromatic ring planes is 11.836 A. In the solid state molecular association takes place through C–H⋯O and C–H⋯Cl types of hydrogen bondings leading to the remarkable thermal stability of 1 whose desolvation takes place between 140 and 220 °C. The enthalpy change due to the loss of dichloromethane, as determined by differential scanning calorimetric measurement, is −103 kJ mol−1. Variable-temperature (4–300 K) magnetic susceptibility measurements indicated antiferromagnetic exchange interaction (H = −2JS1S2) in 1 with J = −13.5 cm−1. The 1H NMR spectrum of 1 in CD2Cl2 is consistent with its symmetric structure and exhibits maximum paramagnetic shift for the methoxy protons (ca. 200 ppm). The cyclic voltammogram of 1 in dichloromethane in the potential range 0 to −1.2 V exhibits a quasi-reversible redox couple due to FeIIIFeIII/FeIIIFeII with E1/2 = −0.85 V. Further reduction to the FeIIFeII state at −1.5 V leads to decomposition of the complex species.

An abiotic receptor and its Cu(II) complex as selective 'turn-off' chemosensor for bisulfate ion.

The ligand 2,6-bis[(N-phenyl)amido]-4-methylphenol (receptor 1) and its copper(II) complex (receptor 2) having amide moiety have been designed and synthesized for selective sensing of anions. The anion recognition behavior of the receptor 1 and its copper complex (receptor 2) has been studied in acetonitrile. Quenching of fluorescence was observed for both receptors in presence of HSO4(-) anion whereas other physiologically and environmentally important anions such as F(-), Cl(-), Br(-), I(-), CN(-), OAc(-), HCO₃(-), H₂PO₄(-), NO₃(-), NO₂(-) and SO₄(2-) show fluorescence enhancement behavior. The sensing protocol has been studied both spectrophotometrically as well as spectrofluorometrically. Fluorescence quenching is suggested to proceed via both dynamic and static processes.

Synthesis and characterization of mononuclear copper(II) complexes of pyridine 2-carboxamide: Their application as catalyst in peroxidative oxidation and antimicrobial agents

AbstractFour water soluble copper(II) complexes, [Cu(HL)2(H2O)2]Cl2 (1), [Cu(HL)2(ClO4)2] (2), [Cu(HL)2(SCN)2] (3) and [CuL2]⋅8H2O (4), where HL is pyridine 2–carboxamide, have been synthesized and characterized by various spectroscopic techniques. Structures have been determined by single crystal X-ray crystallography. The pH induced inter-conversion of Cu(HL)2(H2O)2]Cl2 (1) and [CuL2]⋅8H2O (4) through co-ordination mode switching was investigated thoroughly with the help of absorption spectroscopy. Complexes 1–3 were found to be active catalysts for the oxidation of toluene, ethyl benzene and cyclohexane in the presence of hydrogen peroxide as the oxidant under mild conditions. Toluene was oxidized to benzyl alcohol and benzaldehyde, ethyl benzene was oxidized to 1-phenylethanol and acetophenone and cyclohexane was oxidized to yield cyclohexanol and cyclohexanone Antimicrobial activities have been investigated with these copper(II) complexes against gram + ve bacteria, gram −ve bacterial and fungal species. Graphical AbstractX-ray structural characterization, pH-induced co-ordination mode switching phenomenon, peroxidative oxidation catalysis and antimicrobial activity of water soluble, discrete mononuclear complexes of copper(II) using the simplest pyridine 2–carboxamide ligand (HL) and its deprotonated form have been investigated thoroughly.