Binuclear Metal Complexes. XLV. Synthesis and Magnetic, Spectral, and Electrochemical Studies of Strati-bis Copper(II) Complexes of Some Schiff Bases Derived from Primary Tetraamines and Salicylaldehydes

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Abstract
New Schiff base ligands, 1,2,3,4-tetrakis(R-salicylideneamino)-2,3-dimethylbutane (abbreviated as H4(R-sata); R (substituent on the ring)=H, 5-Me, 5-But) and 1,2-bis(R-salicylideneamino)-1,2-bis(salicylideneaminomethyl)cyclohexane (H4(R-sacta)), which are capable of forming “strati-bis” type binuclear copper(II) complexes, have been synthesized. Magnetic, spectral and electrochemical properties of the binuclear copper(II) complexes, Cu2(R-sata) and Cu2(R-sacta), were investigated in comparison with those of mononuclear copper(II) complexes Cu(R-salpn) and Cu(R-sacda), where H2(R-salpn) is N,N′-bis(R-salicylidene)-1,2-propanediamine and H2(R-sacda) 1-(R-salicylideneamino)-1-(R-salicylideneaminomethyl)cyclohexane. ESR spectra of Cu2(sata), Cu2(sacta) and Cu2(5-Me-sacta) showed a seven-lined hyperfine structure whose hyperfine coupling constant (A||≈85 G, 1 G=10−4 T) was about one half of that of the corresponding mononuclear copper(II) complex. Each electronic spectrum of these binuclear complexes showed the π-π* transition originated from the azomethine group at a low frequency compared with that of the corresponding mononuclear complex. Cyclic voltammograms of these three complexes involved two redox couples. The first redox couple attributable to the Cu(II, II)/Cu(II,I) process is higher in potential than the Cu(II)/Cu(I) process of the corresponding mononuclear complex. These characteristics were discussed in terms of the electron-delocalization through the π-π interaction between the two [CuN2O2]-chromophores.
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