Dimerization of Paramagnetic Trinuclear Complexes byCoordination Geometry Changes Showing Mixed Valency andSignificant Antiferromagnetic Coupling through-Pt•••Pt-Bonds

Paramagnetic trinuclear complexes,trans-[Pt2M-(piam)4(NH3)4](ClO4)x(t-M; piam = pivalamidate, M = Mn,Fe, Co, Ni, and Cu,x= 2 or 3), aligned as Pt-M-Pt weresuccessfully synthesized and characterized. The dihedral anglesbetween the Pt and M coordination planes int-Mareapproximately parallel, showing straight metal-metal bonds withdistances of approximately 2.6 A. Except fort-Fe, the trinuclearcomplexes are dimerized with close contact (approximately 3.9 A)between the end Pt atoms to form Pt-M-PtmiddotmiddotmiddotPt-M-Ptalignments with high-spin M(+2) containingfive (t-Mn), three(t-Co), two (t-Ni), and one (t-Cu) unpaired electrons localized onM atoms. Several physical measurements and calculations revealedthat the dimerized structures were maintained in MeCN, wherecyclic voltammograms fort-Mexhibited two-step oxidation and reduction attributed to Pt-M(+2)-PtmiddotmiddotmiddotPt-M(+2)-Pt <-> Pt-M(+3)-PtmiddotmiddotmiddotPt-M(+2)-Pt <-> Pt-M(+3)-PtmiddotmiddotmiddotPt-M(+3)-Pt via mixed-valent states. Magnetic susceptibility measurements fort-Mshowed antiferromagnetic interaction,t-Mn:J=-0.9 cm-1,t-Co:J=-3.5 cm-1,t-Ni:J=-7.3 cm-1, andt-Cu:J= 0.0 cm-1,between the two M centers with distances of 9.0 A through PtmiddotmiddotmiddotPt bonds.

Automated summary

Paramagnetic trinuclear complexes with straight metal-metal bonds were successfully synthesized and characterized. The dimerized structures were maintained in the solvent, and showed two-step oxidation and reduction in cyclic voltammograms.