Chiral dinuclear Ln(iii) complexes derived from S- and R-2-(6-methoxy-2-naphthyl)propionate. Optical and magnetic properties.

The reaction of LnCl3·6H2O with (S)-(+)-2-(6-methoxy-2-naphthyl)propionic acid (S-HL), best known as naproxen, and 1,10-phenanthroline (phen) in EtOH allows the isolation of dinuclear chiral compounds S-1-4 of the formula [Ln2(S-L)6(phen)2]·3DMF·H2O [Ln(iii) = Eu (1), Gd (2), Tb (3) and Dy (4)]. The use of the R-enantiomeric species of the HL ligand led to complexes R-1-4 with the formula [Ln2(R-L)6(phen)2]·3DMF·H2O. Compounds R- andS-1, 3 and 4 show strong sensitized metal-centred luminescence in the visible region. Moreover, Dy(iii) complexes R- andS-4 display field-induced single-molecule magnet (SMM) behaviour. For chiral and emissive compounds circularly polarized luminescence (CPL) measurements have also been performed.

Circularly polarized luminescence on dinuclear Tb(iii) and Eu(iii) complexes with (S-) and (R-) 2-phenylpropionate.

The reaction of Ln(NO3)2·6H2O (Ln = Tb and Eu) with (S)-(+)-2-phenylpropionic acid (S-HL) and 1,10-phenanthroline (phen) in EtOH/H2O allows the isolation of the dinuclear chiral compounds of the formula [Ln2(S-L)6(phen)2]·2.5·S-HL in which Ln = Tb (S-1), Ln = Eu (S-2). The same synthesis by using (R)-(-)-2-phenylpropionic acid (R-HL) instead of (S)-(+)-2-phenylpropionic acid allows the isolation of the enantiomeric compounds with the formula [Ln2(R-L)6(phen)2]·2.5·R-HL where Ln = Tb (R-1), Ln = Eu (R-2). All compounds show sensitized luminescence. The luminescence study, including the circularly polarized luminescence spectra of the four compounds, is reported. The magnetic behavior of S-1 and S-2 is also reported.

EPR interpretation, magnetism and biological study of a Cu(II) dinuclear complex assisted by a schiff base precursor.

A new Cu(II) dinuclear complex, Cu2L2 (1) was afforded employing the potentially pentatentate Schiff base precursor H2L, a refluxed product of o-vanillin and diethylenetriamine in methanol. Complex 1 was systematically characterized by FTIR, UV-Vis, emission and EPR spectrometry. The single crystal X-ray diffraction analysis of 1 reveals that the copper atom exhibits a distorted square planar geometry, comprising two pairs of phenolato-O and imine-N donors from two different H2L ligands. The temperature dependent magnetic interpretation agrees with the existence of weak antiferromagnetic interactions between the bridging dinuclear Cu(II) ions. A considerable body of experimental evidence has been accumulated to elucidate the magneto-structural relationship in this dinuclear Cu(II) complex by DFT computation. Both the ligand and complex 1 exhibit anti-mycobacterial activity and considerable efficacy on M. tuberculosis H37Ra (ATCC 25177) and M. tuberculosis H37Rv (ATCC 25618) strains. The practical applicability of the ligand and complex 1 has been examined in living cells (African Monkey Vero Cells). The MTT assay proves the non-toxicity of the probe up to 100 mg mL-1. A new homometallic dinuclear Cu(II) complex is afforded with a tetradentate Schiff base precursor. EPR interpretation and temperature dependent magnetic studies show that complex 1 has weak antiferromagnetic coupling and DFT computation is governed to explain the magneto-structural correlation.

Self assembled tetranuclear Cu4(II), Ni4(II) [2 × 2] square grids and a dicopper(II) complex of heterocycle based polytopic ligands - Magnetic studies.

The ditopic ligand PyPzOAP (N-[(Z)-amino(pyridin-2-yl)methylidene]-5-methyl-1-(pyridin-2-yl)-1H-pyrazole-3-carbohydrazonic acid) and the polytopic ligand 2-PzCAP (N'(3),N'(5)-bis[(1E)-1-(pyridin-2-yl)ethylidene]-1H-pyrazole-3,5-dicarbohydrazide) were synthesized in situ by condensation of methyl imino picolinate with 5-methyl-1-(2-pyridyl) pyrazole-3-carbohydrazide and 2-acetyl pyridine with pyrazole-3,5-dicarbohydrazide respectively. The ligands PyPzOAP and PzOAP (reported earlier, Dalton Trans., 2007, 1229) self-assemble to form homoleptic [2 × 2] tetranuclear M(4) (M = Cu(II) and Ni(II)) square grids structures [Cu(4)(PyPzOAP)(4)](NO(3))(4) (1), [Cu(4)(PzOAP)(4)](ClO(4))(4) (2) and [Ni(4)(PyPzOAP)(4)](NO(3))(4)·8H(2)O·2CH(3)CN (3). While the ligand 2-PzCAP forms a dicopper(II) complex [Cu(2)(2-PzCAP)(OH)(NO(3))(H(2)O)](NO(3))·2H(2)O (4). The complex 1 is a perfect square grid (a = 4.201 Å), whereas, 2 and 3 are almost square grids. All these compounds have been characterized by X-ray structural analyses and variable temperature magnetic susceptibility measurements. EPR studies have also been carried out for complexes 1, 2 and 4. In the Cu(4) grid (1), all the Cu(II) centers are in a distorted octahedral environment with N(4)O(2) chromophore, while, in complex 2, all four Cu(II) centers have a square pyramidal environment with N(3)O(2) chromophore. In complex 3, all four Ni(II) centers have distorted octahedral geometry with N(4)O(2) chromophore. In compound 4, the Cu(II) centers are in square pyramidal environment with N(3)O(2) chromophore. The magnetic properties of compounds 1 and 2 show the presence of intramolecular ferromagnetic exchange interaction (J = 5.88 cm(-1) for 1 and 4.78 cm(-1) for 2). The complex 3 shows weak intramolecular antiferromagnetic interaction (J = -4.02 cm(-1)). While, complex 4, shows strong antiferromagnetic behavior (J = -443 cm(-1)).

Ferro- and anti-ferromagnetically coupled tetracopper(II) 2 x 2 homoleptic rectangular grids supported by both mu-O and mu-(N-N) bridges derived from a new pyrazole based polydentate Schiff base ligand-magneto-structural correlations and DFT calculation.

The pyrazole derived Schiff base polytopic ligand 5-methyl-N'-[1-(pyridin-2-yl)ethylidene]-1H-pyrazole-3-carbohydrazide (PzCAP), prepared by the reaction between 5-methylpyrazole-3-carbohydrazide and 2-acetyl pyridine, has two potentially bridging functional groups [mu-O and mu-(N-N)] and consequently can exhibit different coordination conformations. Two tetranuclear homoleptic copper(II) 2 x 2 rectangular grid-complexes [Cu(4)(PzCAP)(4)(NO(3))(2)] (NO(3))(2).8H(2)O (1) and [Cu(4)(PzCAP)(4)(ClO(4))(2)] (ClO(4))(2) (2) were formed by a strict self-assembly process employing metal and ligand under 1:1 mol proportion. Each pair of the ligand molecules in the two complexes are arranged in roughly parallel fashion but under different conformations. The ligand PzCAP contains terminal pyridine and pyrazole residues bound to a central flexible diazine subunit (N-N). The rectangular Cu(II) 2 x 2 grid complexes having [Cu(4)(mu-N-N)(2)(mu-O)(2)] core involve a mixture of two diazine (Cu-N-N-Cu approximately 160 degrees ) and two alkoxo (Cu-O-Cu approximately 138 degrees ) bridges along the length and breadth respectively. In the [Cu(4)(mu-N-N)(2)(mu-O)(2)] core in , out of the four Cu(II) centers, all are hexa-coordinated but there are two penta-coordinated and two hexa-coordinated Cu(II) centers in the same core of . Each complex having the central [Cu(4)(mu-N-N)(2)(mu-O)(2)] core, exhibits quite different magnetic interactions among the metal centers. The paramagnetic Cu(II) centers bridged through the diazine fragment are involved in anti-ferromagnetic interaction while a dominant ferromagnetic interaction prevails between the alkoxo-bridged Cu(II) centers. The [Cu(4)(mu-N-N)(2)(mu-O)(2)] cluster in shows both ferromagnetic and anti-ferromagnetic interaction (J(1) = -0.80 cm(-1) and J(2) = +3.49 cm(-1)), a very unusual characteristic in this system while the same cluster in exhibits dominant anti-ferromagnetic coupling (J(1) = -89.1 cm(-1) and J(2) = +5.5 cm(-1)) through the trans Cu-(N-N)-Cu bridging arrangement, typical for systems of this sort. Both the complexes and have been characterized structurally, magnetically and spectroscopically. The exchange pathways parameters (J(1) and J(2)) have also been evaluated from density functional theoretical calculations to corroborate the bridging signatures with experimental findings.

An orthogonal ferromagnetically coupled tetracopper(II) 2 x 2 homoleptic grid supported by micro-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[micro-O4] core, involving four ligand molecules. In the Cu4[micro-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 degrees) 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 (d(x2-y2)) lying almost orthogonally between the metal centers. The exchange pathways parameters have been evaluated from density functional calculations.

Magnetic Studies on &mgr;-Azido Polynuclear Nickel(II) Compounds with the 222-tet Ligand. Crystal Structure of (&mgr;-N(3))(2)[Ni(222-tet)](2)(BPh(4))(2) (222-tet = Triethylenetetramine) and EXAFS Structural Characterization of the Triangular Compounds (&mgr;-N(3))(3)[Ni(222-tet)](3)(X)(3) (X = PF(6)(-), ClO(4)(-)).

The nickel(II) dinuclear 1,3-azido-bridged compound (&mgr;-N(3))(2)[Ni(222-tet)](2)(BPh(4))(2) (1) and the trinuclear compounds (&mgr;-N(3))(3)[Ni(3)(222-tet)(3)](PF(6))(3) (2) and (&mgr;-N(3))(3)[Ni(3)(222-tet)(3)](ClO(4))(3) (3) were synthesized and characterized. 222-tet is the tetraaminate ligand triethylenetetramine. The crystal structure of 1 was solved by X-ray diffraction. 1 crystallizes in the monoclinic system: space group P2(1)/n, a = 10.639(4) Å, b = 19.770(7) Å, c = 13.609(6) Å, beta = 97.78(3) degrees, Z = 2, formula C(60)H(76)B(2)N(14)Ni(2). In the absence of single crystals of 2 and 3, we carried out an EXAFS study of 1-3 at the nickel K-edge, using compound 1 as a model, in order to obtain structural information for compounds 2 and 3. The analysis of XANES and EXAFS spectra of compounds 1-3 reveals the occurrence of azido-bridged trinuclear nickel(II) compounds for 2 and 3 with Ni-Ni separations of 5.16 and 5.12 Å, respectively. Each nickel(II) atom is placed in an octahedral NiN(6) environment: four nitrogen atoms of the amine and two nitrogen atoms of two azido bridges. The magnetic properties of the three compounds were studied by susceptibility measurements at variable temperatures (300-4 K). From the spin Hamiltonian H = -JS(1)S(2), the calculated J value for 1 is -83.6 cm(-)(1), in good agreement with the expected value. From the spin Hamiltonian H = -J(1,2)(S(1)S(2) + S(1)S(3)) - J(3)(S(2)S(3)), the obtained J values are J(1,2) = -72(3) cm(-)(1), J(3) = -36(3) cm(-)(1) for 2 and J(1,2) = -60.3(3) cm(-)(1), J(3) = -29.4(2) cm(-)(1) for 3.