Bera Sudip Kumar, Lahiri Goutam Kumar
Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai-400076, India.
Dalton Trans. 2020 Oct 21;49(39):13573-13581. doi: 10.1039/d0dt02741c. Epub 2020 Sep 24.
Unprecedented metal-metal bonded oxido-carboxylato bridged mixed valence tetraruthenium cluster [(acac)Ru(μ-O)(μ-CHCOO)] 1 (S = 1/2) (acac = acetylacetonate) with {Ru(μ-O)} "butterfly" core has been achieved via the reaction of Ru(acac)(CHCN) with excess CHCOONa (Ru : CHCOONa = 1 : 15) in refluxing EtOH-HO (5 : 1). Structural analysis of 1 ascertained a unique Ru-Ru bonded (Ru2-Ru3: 2.5187(6) Å (DFT: 2.560 Å)) {Ru(Ru-Ru)(μ-O)} butterfly core, unlike the reported other Fe or Mn derived "butterfly" core. The connectivity of Ru(μ-O) core in 1 with three Ru(μ-CHCOO) and two each Ru-(acac)/Ru-acac units resulted in interconnected four RuO octahedral entities. The doubly bridged μ-O ions of the nearly planar central metal-metal bonded RuO core (Ru2-Ru3, "body" or "hinge") linked to the remaining two "wing-tip" Ru atoms (Ru1 and Ru4). Complex 1 with a S = 1/2 spin state displayed paramagnetically shifted H NMR over a wide chemical shift range in CDCl (δ, 13 to -30 ppm) and a metal based anisotropic EPR (g = 2.17, g = 2.01, g = 1.86; Δg = g-g = 0.31 and 〈g〉 = [1/3(g + g + g] = 2.01) at 100 K in CHCN-toluene. The metal based one-electron reversible oxidation at 0.49 V and reduction at 0.485 V versus SCE of 1 led to the EPR inactive (even at 4 K) spin-coupled RuRuRuRu (S = 0) and RuRuRuRu (S = 0) electronic configurations for 1 and 1, respectively. Mixed valence 1 and 1 exhibited low-energy near-infrared (NIR) absorption bands at 1350 nm and 1156 nm, respectively, in CHCN. A combined experimental (UV-vis-NIR and EPR spectroelectrochemistry) and theoretical (DFT) analysis indicated a delocalised mixed valence form of 1 ({Ru(Ru-Ru)(μ-O)}).
通过Ru(acac)(CHCN)与过量CHCOONa（Ru : CHCOONa = 1 : 15）在回流的EtOH-HO（5 : 1）中反应，成功制备出了具有前所未有的金属-金属键合的氧化羧基桥联混合价态四钌簇[(acac)Ru(μ-O)(μ-CHCOO)] 1（S = 1/2）（acac = 乙酰丙酮），其具有{Ru(μ-O)}“蝴蝶”核心。对1的结构分析确定了一个独特的Ru-Ru键合（Ru2-Ru3: 2.5187(6) Å（DFT: 2.560 Å））的{Ru(Ru-Ru)(μ-O)}蝴蝶核心，与报道的其他铁或锰衍生的“蝴蝶”核心不同。1中Ru(μ-O)核心与三个Ru(μ-CHCOO)以及两个Ru-(acac)/Ru-acac单元相连，形成了相互连接的四个RuO八面体实体。近乎平面的中心金属-金属键合RuO核心（Ru2-Ru3，“主体”或“铰链”）的双桥联μ-O离子与其余两个“翼尖”Ru原子（Ru1和Ru4）相连。具有S = 1/2自旋态的配合物1在CDCl中（δ，13至 -30 ppm）的宽化学位移范围内显示出顺磁位移的1H NMR，并且在100 K下于CHCN-甲苯中表现出基于金属的各向异性EPR（g = 2.17，g = 2.01，g = 1.86；Δg = g - g = 0.31且〈g〉 = [1/3(g + g + g)] = 2.01）。相对于SCE，1在0.49 V处发生基于金属的单电子可逆氧化，在0.485 V处发生还原，分别导致1和1的EPR无活性（即使在4 K时）的自旋耦合RuRuRuRu（S = 0）和RuRuRuRu（S = 0）电子构型。混合价态的1和1在CHCN中分别在1350 nm和1156 nm处表现出低能量近红外（NIR）吸收带。结合实验（紫外-可见-近红外和EPR光谱电化学）和理论（DFT）分析表明1（{Ru(Ru-Ru)(μ-O)}）具有离域混合价态形式。
