SYNTHESIS, STRUCTURE, ELECTRONIC, REDOX, AND MAGNETIC-PROPERTIES OF ANEW MIXED-VALENT MN-OXO CLUSTER - N)(2)](3-BIS(2-PYRIDYLMETHYL)-1,2-DIAMINOETHANE)() (N,NBISPICEN=N,N)

The synthesis and structural characterization of the novel [(Mn2O2)-O- III,IV(N,Nbispicen)(2)](ClO4)(3) . CH3CN complex employing the tetrade ntate ligand N,Nbispicen = N,N-bis(2-pyridylmethyl)-1,2-diaminoethane are reported. Magnetic properties were determined and show that the gr ound state is a spin doublet. This can be quantitatively interpreted b y antiferromagnetic coupling between a Mn(III) high spin and a Mn(IV) (J = -316 cm(-1)). The 16 line solution EPR spectrum exhibits an unusu al splitting in the low field resonances. The following rhombic tensor s were needed to simulate the EPR spectrum: \A(1x)\ = 160 10(-4) cm(-1 ), \A(1y)\ = 144 10(-4) cm(-1), \A(1z)\ = 109 10(-4) cm(-1), \A(2x)\ = 69 10(-4) cm(-1), \A(2y)\ = 72 10(-4) cm(-1) \A(2z)\ = 75 10(-4) cm(- 1), g(x) = 2.001, g(y) = 1.996, g(z) = 1.984. The classical ligand fie ld theory of local [g(III)] and [g(IV)] tensors implemented with the f irst order perturbation theory to describe the properties of the pair does not result in a satisfying description of the [g(1/2)] tensor unl ess a large reduction in the spin-orbit constant is invoked. A simplif ied version of second-order perturbation theory leads to effects in qu alitative agreement with experiment but weak as expected from the larg e \J\ value. The magnitude of these effects depends, however, on the a nisotropy effects on each Mn ion. It is suggested that determination o f the anisotropy of the magnetic properties of the monomeric Mn(III) a nd Mn(IV) moieties would be a valuable goal for a future study of thes e mixed valent di-manganese-di-mu-oxo complexes. The complex exhibits two quasi-reversible waves in the cyclic voltammogram, one at E-1/2 = 0.18 V vs SCE for the III/IV <-> III/III couple and the other at E-1/2 = 0.98 V vs SCE for the III/IV <-> IV/IV couple. The UV-Vis spectra o f the three redox states have been recorded spectroelectrochemically.