2,4,6-Tris(2-pyridyl)-1,3,5-triazine (tptz)-Derived [Ru^II(tptz)(acac)(CH₃CN)]⁺ and Mixed-Valent [(acac)₂Ru^III{(<i>μ</i>-tptz-H⁺)^-}Ru^II(acac)(CH₃CN)]⁺^†

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 (Kc) 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 Kc values for [5]ClO4−[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)(CΗ3CN)] (1) and [(acac)2RuIII{(μ-tptz-Η+)•2-}RuII(acac)(CH3CN)] (5), however, show a free-radical-type EPR signal near g = 2.0 with partial metal contribution.本研究通过RuII(acac)2(CH3CN)2分别与2,4,6-三(2-吡啶基)-1,3,5-三嗪（2,4,6-tris(2-pyridyl)-1,3,5-triazine, tptz）以1:1和2:1的摩尔比反应，合成了单核配合物单高氯酸[RuII(tptz)(acac)(CH3CN)]ClO4（[1]ClO4）以及混合价双核配合物单高氯酸[(acac)2RuIII{(μ-tptz-H+)-}RuII(acac)(CH3CN)]ClO4（[5]ClO4；其中acac为乙酰丙酮基（acetylacetonate））。在[1]ClO4中，tptz以三齿N,N,N配位模式与RuII离子结合（基元A）；而在[5]ClO4中，tptz以不对称桥联方式与两个金属离子结合：一端通过三齿中性N,N,N模式与RuII中心配位，另一端以环金属化的N,C-模式与RuIII位点配位（基元F）。在乙醇和烷基胺存在下，[1]ClO4和[5]ClO4中配位的腈基发生活化反应，分别生成亚胺酯类衍生物([2]ClO4和[7]ClO4)以及脒类衍生物([4]ClO4)。对[2]ClO4的晶体结构分析表明，其形成了具有椅式构象的八元水簇。该水簇通过氢键与tptz上悬挂的吡啶环氮原子以及高氯酸根离子的氧原子相连，进而与邻近分子形成短程(C−H···O)接触，最终构建出氢键网络。单核系列{[(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)}以及双核系列{[(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)以及[(acac)2RuIII{(μ-tptz-H+)-}RuII(acac)(NC4H4N)]ClO4 ([8]ClO4)}中，对应RuII价态的氧化还原电位会随第六位配位配体的电子性质发生系统性变化。然而，双核配合物中涉及RuIII中心的氧化还原电位基本保持不变。混合价RuIIRuIII物种（[5]ClO4−[8]ClO4）具有1.1 × 1012−2 × 109的高归中平衡常数（Kc），该数值很大程度上源于两个金属位点的给体中心不对称性贡献。这类配合物在可见光区分别出现基于RuII和RuIII的金属到配体、配体到金属电荷转移跃迁，在紫外区则出现配体基跃迁。尽管[5]ClO4−[8]ClO4具有较高的归中平衡常数，但在2000 nm以内的典型近红外区域并未观测到预期的区间电荷转移跃迁。顺磁性RuIIRuIII物种（[5]ClO4−[8]ClO4）在77 K下展现出菱形电子顺磁共振（Electron Paramagnetic Resonance, EPR）光谱（〈g〉 ∼ 2.15和Δg ∼ 0.5），这是扭曲八面体环境中低自旋RuIII离子的典型特征。然而，经单电子还原的tptz配合物[RuII(tptz•-)(acac)(CH3CN)]（1）和[(acac)2RuIII{(μ-tptz-H+)•2-}RuII(acac)(CH3CN)]（5）则在g = 2.0处出现类自由基的EPR信号，且该信号伴随有部分金属轨道贡献。