Crystal structure and electrochemical behavior of Rh polypyridyl complexes

[Rh(tpy)(bpy)(Cl)](ClO4)2 and [Rh(tpy)(phen)(Cl)](PF6)2 (tpy; 2,2′;6′,2″-terpyridine, bpy; 2,2′-bipyridine, phen; 1,10-phenanthroline) have been determined structurally. Both complexes were identified and characterized by spectroscopic methods. ortep drawings of each complex show three pyridyl rings of the tpy ligand that are nearly coplanar, as are the two rings of bpy. The two ligands are coordinated to the metal atom through their nitrogen atoms in a mutually perpendicular fashion. The interatomic distance between chloride and rhodium atom is 2.300(12) and 2.323(2) Å, respectively. The bond angle formed by the axially positioned nitrogen atom, the rhodium atom, and the chlorine atom is 174.96(8) and 176.32(19)°. The oxidation of each [Rh(tpy)(bpy)(OH2)]3+ or [Rh(tpy)(phen)(OH2)]3+ with two equivalents of Ce(IV) yielded the corresponding mono-oxo product, [RhV(tpy)(bpy)(O)](ClO4)3 and [RhV(tpy)(phen)(O)](ClO4)3. A cyclic voltammogram of rhodium aqua complex with a scan rate of 5 mV s−1 displays the redox couple at −0.81 V as reversible wave for the first oxidation from Rh(III) to Rh(IV) and the next Rh(IV)/Rh(V) wave at −0.49 V as quasi-reversible. Electrocatalytic oxidation of benzyl alcohol with rhodium aqua complex gave benzaldehyde as a major product with the turnover ratio of 13.