Tricopper(II) Complexes with Octadentate Ligands
Date Issued
2009
Date
2009
Author(s)
Chang, Mu-Chieh
Abstract
New derivatives of octadentate ligands (L2H-6/7-(α)-x, L2H-6/7-(β)-x and L2H-6-(γ); see Chart I) have been synthesized. Two synthetic strategies including Protocol 1: Middle to End or Protocol 2: End to End have been employed for symmetrical and unsymmetrical octadentate ligands synthesis, respectively. The reactions of octadentate ligands with Cu(ClO4)2 yield the corresponding trinuclear copper(II) complexes. Such complexes have been characterized by IR, UV-Vis spectroscopies, ESI-MS, SQUID, ESR, conductivity measurement and elemental analyses. The chemical formulae of a deep blue compound is identified as a tricopper(II) complex [(CuII)3(L)¬(-OH)(ClO4)3(H2O)4]. The temperature dependence of MT measurements for the trinuclear copper(II) complexes ([(CuII)3(L-6-()-1)] and [(CuII)3(L-6-()-1)]) show special magnetic properties of complexes. At high temperature region (300 K), the MT values of tricopper(II) complexes are lower than those expected for three uncoupled S = 1/2 spins, and they decrease steadily with decreasing temperature. This behavior in high temperature region clearly indicates that intratrimer antiferromagnetic coupling is operating. At low temperature region, the MT values of tricopper(II) complexes are lower than 0.4 cm3 mol-1 K. This behavior in low temperature region clearly suggests that antisymmetrical exchange coupling is operating at this tricopper(II) system. The fitting results for high temperature region show that g = 2.046 and 2.062, J = -96.2 cm-1 and -103.4 cm-1 and j = -176.4 cm-1 and -202.7 cm-1 for trinuclear copper(II) complexes [(CuII)3(L-6-()-1)] and [(CuII)3(L-6-()-1)], respectively. From the results of ESI-MS and UV-Vis spectra, in acidic condition, the bridge hydroxide ion between two copper(II) centers of trinuclear copper(II) complex can be replaced by another anions easily, and the trinuclear copper(II) complex will be demetallized. After neutralizing the reaction mixture of demetallization test by NaOH, the evidences of ESI-MS and UV-Vis spectra show that this demetallization process is reversible, and the max and absorbance of the reaction mixture is highly pH dependence. The results of some metal exchange tests indicate that the octadentate ligang have better affinity to Cu(II) ions than other metal ions (i.e. CrII(NO3)3, MnCl2, FeCl3, CoII(ClO4)2, CoIII(NH3)6Cl3, NiII(ClO4)2 and ZnCl2) in experimental conditions.ononuclear copper(II) complexes bearing two amino-pyridie bidentate ligands, also have been synthesized for comparison. In solid state, the crystal structure shows that the geometry of copper(II) center is square bipyramid, which is surrounded by two amino-pyridine bidentate ligands and two perchlorate anions. The four equatorial and two axial position of distorted octahedron copper(II) center are occupied by two amino-pyridines and two perchlorate anions, respectively. After comparing the ESI-MS spectra of different monocopper(II) complexes, these purple mononuclear copper(II) complexes show multiequilibrium with mono-, di- and tricopper(II) clusters in solution state. The magnetic property of mononuclear copper(II) complex follows the Curie-Weiss law with a Curie constant of C = 0.42 cm3 mol-1 K, which is in the expected range for an isolated Cu(II) ion, and a Weiss constant of = -0.08 K, which arise from the weak intermolecular antiferromagnetic interaction. Room temperature X-band EPR spectrum of [(CuII)3(L-6-()-1)] and [CuII(L-(a)-1)2] shows a transition centered at g = 2.07 and g = 2.06, respectively.
Subjects
Tricopper(II) Complexes
Octadentate Ligands
Type
thesis
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