Organobimetallic Ru-II-Re-I 4-ethynylpyridyl complexes: structures and non-linear optical properties

A series of heterobimetallic complexes, [RuCp(C Cpy-4)(P-P)][Re(CO)(3)(N-N)](+) (P-P = dppf, N-N = bpy 5, Me(2)bpy 6, (t)Bu(2)bpy 7, phen 8, tpy 9; P-P = 2PPh(3), N-N= bpy 10) have been obtained from Lewis addition between the metalloligands [RuCp(C Cpy-4)(P-P)] (P-P = dppf 1; 2PPh(3) 2) and solvent-stabilised fac-[Re(CH3CN)(CO)(3)(N-N)](+). All new complexes 5-10, together with fac-[ReBr(CO)(3)(tpy)] (3) and fac-[Re(CH3CN)(CO)(3)(tpy)][PF6] (4), are characterized by solution spectroscopy; 3 and 5-9 are also characterized by single-crystal X-ray crystallography. The terpyridine ligands in 3 and 9 are in an unusual eta(2)-bidentate coordination mode with a pendant pyridyl. Electrochemical studies showed successive metal-based oxidations and a ligand-centered reduction in 5-10. Significant oxidation changes are observed at the Ru(II) and Re(I) centers in 5-10 when compared with their respective monometallic components. Cubic nonlinearities of 5-10 determined by the Z-scan technique at 750 nm reveal two-photon absorption that increases significantly on progression from Ru(II) monomeric precursors to heterobimetallics, suggesting NLO enhancement upon heterometallic complex formation.