2,4,6-Tris(2-pyridyl)-1,3,5-triazine (tptz)-Derived [RuII(tptz)(acac)(CH3CN)]+ and Mixed-Valent [(acac)2RuIII{(μ-tptz-H+)-}RuII(acac)(CH3CN)]

• Published in: Inorganic chemistry 2006-03, Vol.45 (6), p.2413-2423
• Main Authors: Ghumaan, Sandeep, Kar, Sanjib, Mobin, Shaikh M, Harish, B, Puranik, Vedavati G, Lahiri, Goutam Kumar
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic0514288

Mononuclear [RuII(tptz)(acac)(CH3CN)]ClO4 ([1]ClO4) and mixed-valent dinuclear [(acac)2RuIII{(μ-tptz-Η +)-}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]ClO4, 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]ClO4 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(CH3)−OC2H5]ClO4 ([2]ClO4) > [(acac)(tptz)RuII−NH2−C6H4(CH3)]ClO4 ([3]ClO4) > [(acac)(tptz)RuII−NHC(CH3)−NHC2H5]ClO4 ([4]ClO4)} and dinuclear {[(acac)2RuIII{(μ-tptz-H+)-}RuII(acac)(N⋮C−CH3)]ClO4 ([5]ClO4), [(acac)2RuIII{(μ-tptz-H+(N+−O-)2)-}RuII(acac)(N⋮C−CH3)]ClO4 ([6]ClO4), [(acac)2RuIII{(μ-tptz-H+)-}RuII(acac)(NHC(CH3)−OC2H5)]ClO4 ([7]ClO4), and [(acac)2RuIII{(μ-tptz-Η +)-}RuII(acac)(NC4H4N)]ClO4 ([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 (K c) values of 1.1 × 1012−2 × 109, with substantial contribution from the donor center asymmetry at the two metal sites. Complexes display RuII- and RuIII-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 K c values for [5]ClO4−[8]ClO4, the expected intervalence charge-transfer transitions did not resolve in the typical near-IR reg