Mixed-valence complexes containing the Rh25+ core. X-ray crystal structure of the dimer-of-dimers [Rh2(form)2(O2CCF3)3-(AgO2CCF3)2]2 (form=N, N′-di-p-tolylformamidinate anion)

The chemical oxidation of the Rh2 4+ formamidinate derivative Rh2(form)2(O2CCF3)2(H2O)2 (form=N,N′-di- p-tolylformamidinate) with the appropriate silver salt leads to the formation of the paramagnetic complexes [Rh2(form)2(O2CCF3)3(AgO2CCF3)2]2 (1), [Rh2(form)2(O2CCF3)2(H2O)2]ClO4 (2) and [Rh2(form)2(O2CCF3)](NO3)2 (3). The complexes were characterized by EPR spectroscopy and X-ray analysis. The EPR spectra in frozen solution consist of two absorption lines. The low-field one is unresolved while the high-field one is split into a triplet. The pattern is interpreted in terms of hyperfine magnetic interaction between the unpaired electron and two equivalent 103Rh nuclei (I=1/2). Complex 1, which consists of two Rh2(form)2(O2CCF3)3 radicals axially linked by CF3COOAg molecules, crystallizes in the monoclinic space group C2/c, with a=32.981(4), b=16.286(2), c=18.642(3) Å, β=94.32(4)°, V=9984.3(4) Å3, Z=4 and Dcalc=1.92 g cm-3.