BIMETALLIC REACTIVITY - INVESTIGATION OF METAL-METAL INTERACTION IN COMPLEXES OF A CHIRAL MACROCYCLIC BINUCLEATING LIGAND BEARING 6-COORDINATE AND 4-COORDINATE SITES

The cooperative physical properties of a chiral macrocyclic binucleating ligand, S,S-cypim, containing 6-coordinate (closed-site) and four coordinate (open-site) compartments bridged by phenolic oxygen atoms have been examined. The chiral (1S,2S)-trans-1,2-bis(aminomethyl) cyclopentane moiety of the S,S-cypim ligand forces the monometallic and symmetrical bimetallic complexes to adopt one diastereomer. Solution magnetic moments of the bimetallic complexes containing two paramagnetic metals indicate spin-spin coupling at 20 degrees C. Ail of the metals in these: complexes, except for Co(III), are spin-free. EPR spectra were recorded for a series of Cu(II) complexes, [Cu(S,S-cypim)(H+)(2)](2+), [Cu(S,S-cypim)ZnCl](+), [Cu(S,S-cypim)Zn](2+), [Cu(S,S-cypim)Cu](2+), [Zn(S,S-cypim)Cu](2+) [Ni(S,S-cypim)Cu](2+),and [Co(S,S-cypim)Cu](3+) At 77 K in acetonitrile/toluene glasses the EPR spectra indicate that [Cu(S,S-cypim)Cu](2+) may exist as a spin-paired singlet, whereas the spectrum of [Ni(S,S-cypim)Cu](2+) exhibits the spin-interacting doubler state. The EPR spectra were used to monitor both inter- and intramolecular metal site scrambling of these complexes. No scrambling was detected. The electronic absorption spectra for [Co-III(S,S-cypim)M(II)] complexes indicate distorted trigonal bipyramidal open-site metal geometries, whereas the Cu(II) ions in the [M(S,S-cypim)Cu](2+) complexes generally have more planar but distorted four- or five-coordinate structures. Cyclic voltammetry of a series of Cu(II) complexes of the type [M(S,S-cypim)Cu](2+) and of Co(III) complexes of the types [Co(S,S-cypim)MCl](2+) and [Co(S,S-cypim)M](3+) show that the potentials of the invariant metals are dependent on the nature of the neighboring metal. Whereas some of these variations could be due to structural differences in the bimetallic series, metal-metal interaction may also influence the redox properties of the invariant Cu(II) and Co(III) ions in these complexes.