137495-90-0Relevant academic research and scientific papers
Chemistry of the [Ru(RQ)(tap)2]z family: Authentic catecholates, reduction potentials, and spectra (RQ = quinone/semiquinone/catecholate; tap = 2-(m-tolylazo)pyridine; z = 0, ±, ±2)
Bag, Nilkamal,Pramanik, Amitava,Lahiri, Goutam Kumar,Chakravorty, Animesh
, p. 40 - 45 (2008/10/08)
Diamagnetic complexes of type Ru(RQc)(tap)2 are synthesized by reacting [Ru(OH2)2(tap)2](ClO4) 2·H2O with catechols in the presence of base (RQc = catecholate having R = H, 4-t-Bu, 3,5-(t-Bu)2 or 3,4,5,6-Cl4; tap = 2-(m-tolylazo)pyridine). Oxidation of these by cerium(IV) affords paramagnetic (S = 1/2) [Ru(RQs)(tap)2]ClO4 (RQs = semiquinone). The X-ray structure of [{Ru(RQc)(tap)2}2H2O]·CH 2Cl2 (R = H) is reported: space group P1, Z = 2, a = 12.465 (2) A?, b = 14.983 (3) A?, c = 16.775 (3) A?, α = 90.21 (2)°, β = 100.26 (1)°, γ = 104.86 (2)°, and V = 2976 (1) A?3. The water molecule hydrogen bridges two chelate molecules via RQc oxygen atoms to give a dimer. The average Ru-O and C-O distances are 2.022 (5) and 1.342 (9) A?, respectively. Here the interacting metal dπ and RQ pπ redox orbitals are fully occupied (eight electrons). The EPR spectrum of [RuII(RQs)(tap)2]+ in frozen (77 K) dichloromethane glass shows a small anisotropy corresponding to a minor contribution of the RuIII(RQc) cannonical form. The complexes display four voltammetric responses corresponding to the processes RQn/RQs, RQs/RQc, (tap)2/(tap?-)(tap) and (tap?-)(tap)/(tap?-)2 (RQn = quinone). The E1/2 values in the R = H case are 0.97, 0.20, -0.68 and -1.24 V, respectively. Comparison with the bpy congeners reveals that replacement of the bpy pair by the tap pair raises the reduction potentials of both RQ and the metal by a remarkable ～800 mV. The Ru(RQc)(tap)2 species, unlike the bpy analogues, are perfectly stable in air. The former complexes absorb strongly in the near-IR region (800-1300 nm) due to interligand RQc(pπ) → tap(azo pπ*) excitation. The corresponding absorption in [Ru(RQs)(tap)2]+ occurs near 700 nm. There is also a feature near 1000 nm assignable to the MLCT excitation Ru(dπ) → RQs(pπ). The transition energies are in qualitative agreement with observed reduction potentials.
