Coordination Behaviour of Novel Macrobicyclic Tricompartmental Ligands: Synthesis, Magnetic, Electrochemical and Kinetic Studies of Unsymmetrical Mono- and Binuclear Copper(II) Complexes

摘要

Several mono- and binuclear copper(II) complexes of general formula [CuL](ClO_4) and [Cu_2L(ClO_4)](ClO_4) have been synthesized from macrobicyclic ligands having different compartments originating from their corresponding precursor compound (PC: 3,4:9,10-dibenzo-1,12[N,N'-bis{(3-formyl-2-hydroxy-5-methyl)benzyl}diaza]-5,8-dioxacyclohexadecane). Electrochemical studies show that one quasi-reversible reduction wave (E_(pc) = -0.75 to -0.83 V) for the mononuclear complexes and two quasi-reversible one-electron transfer reduction waves (E_(pc)~1 = -0.78 to -0.86 V, E_(pc)~2 = -1.01 to -1.28 V) for the binuclear complexes are obtained in the cathodic region. Room temperature magnetic moment studies indicate the presence of antiferromagnetic coupling in the binuclear complexes (μ_(eff) = 1.44-1.56 BM), which is confirmed by the broad ESR spectra with g = 2.10-2.11, whereas the mononuclear complexes show hyperfine splitting in the ESR spectra and have magnetic moment values close to the spin-only value (μ_(eff) = 1.69-1.72 BM). Variable temperature magnetic susceptibility study of the complex finds that the observed -2J values for the binuclear complexes [Cu_2L~1(ClO_4)](ClO_4) and [Cu_2L~4(ClO_4)]-(ClO_4) are 216 cm~(-1) and 236 cm~(-1), respectively. The observed initial rate constant values for catechol oxidation using the complexes as catalysts range from 6.57 * 10~(-3) to 4.93 * 10~(-2) min~(-1) and the values are found to be higher for the binuclear complexes than the corresponding mononuclear complexes. It is proposed that a distortion of the copper ion geometry arises as the macrocyclic ring size increases. This is supported by spectral, electrochemical and catalytic studies.