882072-06-2Relevant academic research and scientific papers
2,4,6-Tris(2-pyridyl)-1,3,5-triazine (tptz)-derived [RuII(tptz) (acac)(CH3CN)]+ and mixed-valent [(acac) 2RuIII{(μ-tptz-H+)-}Ru II(acac)(CH3CN)]+
Ghumaan, Sandeep,Kar, Sanjib,Mobin, Shaikh M.,Harish,Puranik, Vedavati G.,Lahiri, Goutam Kumar
, p. 2413 - 2423 (2006)
Mononuclear [RuII(tptz)(acac)(CH3CN)]ClO4 ([1]ClO4) and mixed-valent dinuclear [(acac)2Ru III{(μ-tptz-H+)-}RuII(acac) (CH3CN)]ClO4 ([5]ClO4; acac = acetylacetonate) complexes have been synthesized via the reactions of RuII(acac) 2(CH3CN)2 and 2,4,6-tris(2-pyridyl)-1,3,5- triazine (tptz), in 1:1 and 2:1 molar ratios, respectively. In [1]ClO 4, tptz binds with the RuII ion in a tridentate N,N,N mode (motif A), whereas in [5]ClO4, tptz bridges the metal ions unsymmetrically via the tridentate neutral N,N,N mode with the RuII center and cyclometalated N,C- state with the RuIII site (motif F). The activation of the coordinated nitrile function in [1]ClO 4 and [5]ClO4 in the presence of ethanol and alkylamine leads to the formation of iminoester ([2]ClO4 and [7]ClO4) and amidine ([4]ClO4) derivatives, respectively. Crystal structure analysis of [2]ClO4 reveals the formation of a beautiful eight-membered water cluster having a chair conformation. The cluster is H-bonded to the pendant pyridyl ring N of tptz and also with the O atom of the perchlorate ion, which, in turn, makes short (C-H- - - - -O) contacts with the neighboring molecule, leading to a H-bonding network. The redox potentials corresponding to the RuII state in both the mononuclear {[(acac)(tptz)RuII-N≡C-CH3]ClO4 ([1]ClO4) ? [(acac)(tptz)RuII-NH=C(CH 3)-OC2H5]ClO4 ([2]ClO4) > [(acac)(tptz)RuII-NH2-C6H 4(CH3)]ClO4 ([3]ClO4) > [(acac)(tptz)RuII-NH=C(CH3)-NHC2H 5]ClO4 ([4]ClO4)} and dinuclear {[(acac) 2RuIII{(μ-tptz-H+)-}Ru II(acac)(N≡C-CH3)]ClO4 ([5]ClO 4), [(acac)2RuIII{(μ-tptz-H +(N+-O-)2)-}Ru II(acac)(N≡C-CH3)]ClO4 ([6]ClO 4), [(acac)2RuIII{(μ-tptz-H +)-}RuII(acac)(NH=C(CH3)-OC 2H5)]ClO4 ([7]ClO4), and [(acac)2RuIII{(μ-tptz-H+) -}RuII(acac)(NC4H4N)]ClO 4 ([8]ClO4)} complexes vary systematically depending on the electronic nature of the coordinated sixth ligands. However, potentials involving the RuIII center in the dinuclear complexes remain more or less invariant. The mixed-valent RuIIRuIII species ([5]ClO4-[8]ClO4) exhibits high comproportionation constant (Kc) values of 1.1 × 1012-2 × 10 9, with substantial contribution from the donor center asymmetry at the two metal sites. Complexes display RuII- and Ru III-based metal-to-ligand and ligand-to-metal charge-transfer transitions, respectively, in the visible region and ligand-based transitions in the UV region. In spite of reasonably high Kc values for [5]ClO 4-[8]ClO4, the expected intervalence charge-transfer transitions did not resolve in the typical near-IR region up to 2000 nm. The paramagnetic RuIIRuIII species ([5]ClO4-[8] ClO4) displays rhombic electron paramagnetic resonance (EPR) spectra at 77 K (〈g〉 ～ 2.15 and Δg ～ 0.5), typical of a low-spin RuIII ion in a distorted octahedral environment. The one-electron-reduced tptz complexes [RuII(tptz?-) (acac)(CH3CN)] (1) and [(acac)2RuIII{(μ- tptz-H+)?2-}RuII(acac)(CH3CN)] (5), however, show a free-radical-type EPR signal near g = 2.0 with partial metal contribution.
