Chemical oxidation of binuclear rhodium(I) complexes with silver salts. Synthesis, x-ray crystal structure, and electrochemical properties of the rhodium [Rh24+] mixed-ligand complex Rh2(Form)2(O2CCF3)2(H2O)2.0.5C6H6 (Form = N,N'-di-p-tolylformamidinate anion)