SYNTHESIS, STRUCTURE AND METAL REDOX OF A FAMILY OF COPPER-COMPLEXES DERIVED FROM HEXADENTATE LIGANDS INCORPORATING THIOETHER AND TRIAZENE 1-OXIDE FUNCTIONS

Hexadentate ligands of type RN(O)NN(H)C6H4S(CH2)(x)SC6H4(H)NN(O)NR (H( 2)L(1): R = Me, x = 2;H(2)L(2): R = Ph, x = 2;H(2)L(3): R = Me, x = 3; general abbreviation H(2)L) have afforded copper(II) complexes of typ e [CuL]. The X-ray structure of [CuL(2)]. 1/2CH(2)Cl(2) reveals the pr esence of a distorted CuS2N2O2 coordination sphere which is strongly e longated along an OCuS axis. The axial and equatorial bond lengths are : Cu-S, 2.636(5) and 2.473(6) Angstrom; Cu-O, 2.222(10) and 2.039(11) Angstrom, respectively. Both the Cu-N bonds, 1.939(13) and 1.904(12) A ngstrom, lie on the equatorial plane. The structure is compared with t hat of [ZnL(2)]. 1/2CH(2)Cl(2), which does not display the above-noted axial elongation. The findings are rationalized in terms of simple an gular overlap considerations. The EPR spectrum of [CuL(2)]. 1/2CH(2)Cl (2) has g(parallel to) > g(perpendicular to), showing that the hole li es in the d(x2-y2) orbital. The [CuL] complexes are electroactive in d ichloromethane solutions and successive quasireversible responses due to the [Cu(II)L]/[Cu(I)L](-) and [Cu(III)L](+)/[Cu(II)L] couples are o bserved, the E(1/2) values being similar to -0.9 V and similar to 0.8 V vs SCE, respectively. The E(1/2) of the copper(III)-copper(II) coupl e lies close to that of the corresponding nickel(III)-nickel(II) coupl e of [NiL]. A thermodynamic rationale is provided.