Electron Spin Resonance Absorption for Polycrystalline Substances

The role of ligand covalency in the selective activation of metalloenediynes for Bergman cyclization

One of the key concerns with the development of radical-generating reactive therapeutics is the ability to control the activation event within a biological environment. To that end, a series of quinoline-metal-loenediynes of the form M(QuiED)·2Cl (M = Cu(II), Fe(II), Mg(II), or Zn(II)) and their independently synthesized cyclized analogs have been prepared in an effort to elucidate Bergman cyclization (BC) reactivity differences in solution. HRMS(ESI) establishes a solution stoichiometry of 1:1 metal to ligand with coordination of one chloride counter ion to the metal center. EPR spectroscopy of Cu(QuiED)·2Cl and Cu (QuiBD)·2Cl denotes an axially-elongated tetragonal octahedron (g║ > g⊥ > 2.0023) with a dx2-y2 ground state, while the electronic absorption spectrum reveals a pπ Cl→Cu(II) LMCT feature at 19,000 cm -1, indicating a solution structure with three nitrogens and a chloride in the equatorial plane with the remaining quinoline nitrogen and solvent in the axial positions. Investigations into the BC activity reveal formation of the cyclized product from the Cu(II) and Fe(II) complexes after 12 h at 45 °C in solution, while no product is observed for the Mg(II) or Zn(II) complexes under identical conditions. The basis of this reactivity difference has been found to be a steric effect leading to metal-ligand bond elongation and thus, a retardation of solution reactivity. These results demonstrate how careful consideration of ligand and complex structure may allow for a degree of control and selective activation of these reactive agents.

Synthesis, molecular modeling and spectroscopic characterization of nickel(II), copper(II), complexes of new 16-membered mixed-donor macrocyclic schiff base ligand incorporating a pendant alcohol function

Complexes of Cu(II) and Ni(II) of the composition [M(L)X] [where M=Ni(II), Cu(II) and X=Cl-, NO3-, CH3COO-] were synthesized with 1,5-dioxo-9,10-diaza-3,ol-tribenzo-(7,6,10,11,14,15) peptadecane, a N2O2 macrocyclic ligand. The complexes were characterized by elemental analysis, molar conductance measurements, UV-vis, IR, 1H NMR, 13C NMR, EPR and molecular modeling studies. All the complexes are non-electrolyte in nature. On the basis of spectral studies, an octahedral geometry has been assigned for Ni(II) complexes and a tetragonal geometry for Cu(II) complexes.

Nickel(II) and copper(II) complexes with Schiff base ligand 2,6-diacetylpyridine bis(carbohydrazone): synthesis and IR, mass, (1)H NMR, electronic and EPR spectral studies

Nickel(II) and copper(II) complexes with general formula [M(H(3)DAPC)X] and [M(H(2)DAPC)H(2)O], where M=Ni(II) and Cu(II), X=NO(3)(-), Cl(-) and CH(3)COO(-), and DAPC=2,6-diacetylpyridine-bis(carbohydrazone), have been synthesized and structurally characterized by elemental analyses, molar conductance measurements, magnetic susceptibility measurements and spectral techniques like IR, UV and EPR. The nickel(II) and copper(II) complexes are octahedral and tetragonal coordination geometries, respectively. The EPR spectra of copper complexes in powdered form show a broad signal with g values in order g(||)>g( perpendicular)>2.0023. The value of covalency factor beta and orbital reduction factor k accounts for the covalent nature of the complexes.

EPR, mass, electronic, IR spectroscopic and thermal studies of bimetallic copper(II) complexes with tetradentate ligand, 1,4-diformyl piperazine bis(carbohydrazone)

The synthesis of novel bimetallic Cu(II) complexes with general stoichiometry [Cu(2)(H(2)L)X(2)(H(2)O)(2)], [Cu(2)(H(2)L)(CH(3)COO)(2)] and [Cu(2)(H(2)L)SO(4)(H(2)O)(2)] (where H(2)L=dideprotonated ligand and X=NO(3)(-) and Cl(-)) derived from tetradentate ligand obtained by the condensation of 1,4-diformyl piperazine with carbohydrazide has been discussed. The complexes were characterized by elemental analyses, molar conductance measurements, magnetic susceptibility measurements, IR, mass, UV, EPR spectral studies and thermogravimetric analyses. The value of magnetic moments indicates that the complexes are paramagnetic and show the antiferromagnetic interaction between the two metal centres. The complexes possess the square planar coordination environment. The values of covalency measurements, i.e., in-plane sigma-bonding alpha(2), in-plane pi-bonding beta(2) and orbital reduction factor k indicate the covalent nature of complexes.