自從Fujishima和Honda等人發現二氧化鈦在紫外線下具有光催化特性以來，對現有和新型鈦化合物的研究引起了極大的關注；自那時以來，鈦衍生材料在催化 ,儲能和生物醫學等領域得到了廣泛應用。雖然二氧化鈦衍生化合物因低成本、蘊藏豐富、輕量和無毒性而在商業上取得成功，但因其低電子和離子導電性，以及Ti4+/Ti3+氧化還原對的低電位，它們並未在儲能領域得到廣泛應用。
在此，我們合成了兩種新型鈦‒有機化合物，Ti6O6L8(DMF)8 (NCKU-1)和Ti6O9L6(DMF)2(Prop)2 (NCKU-2) (LH4=1,4-dicyano-2,3,5,6-tetrahydroxybenzene，Prop = propionate，DMF = N',N'-dimethylformamide)。以這種類型的配位基分子來說，特別的是它沒有形成配位高分子，而是金屬氧簇。LH4經歷了氧化和脫質子化再與金屬配位，經由測量兩種化合物中L配位基的鍵長顯示出鄰苯醌類結構。具氧化還原活性的苯醌類配位基L通過鍵的電荷轉移促進了電荷離域。這些材料的半導體導電性比二氧化鈦高出三個數量級。作為鋰離子電池的陰極時，兩種材料在0.5 A g−1 的電流密度下，NCKU-1和NCKU-2分別顯示出240 mAh g−1 和260 mAh g−1的初始容量。在高達64 A g −1的電流密度下，NCKU-1和NCKU-2分別穩定地保持60 mAh g−1和90 mAh g−1的電容量，表現優異的氧化還原動力學，歸因於其導電性和易被接觸的氧化還原位點。重要的是，兩種化合物皆顯示出異常高的Ti3+/Ti4+氧化還原電位(NCKU-1和NCKU-2分別為3.2 V和2.7 V相對於Li/Li+)，適合應用於正極材料。

Since the discovery of the photocatalytic property of titanium dioxide (TiO2) under ultraviolet light by Fujishima and Honda et al., much attention has been brought to existing and novel titanium-based compounds, which have shown a wide range of applications in the field of catalysis, energy storage, and biomedical applications. While TiO2-derived compounds remain commercially successful due to their low cost, abundance, lightweight, and non-toxicity, they are not widely utilized in the field of energy storage due to their low electrical and ionic conductivity as well as the low redox potential of the Ti4+/Ti3+ couples.
Herein, we report two new titanium-based organometallic compounds, Ti6O6L8(DMF)8 (NCKU-1) and Ti6O9L6(DMF)2(Prop)2 (NCKU-2) (LH4=1,4-dicyano-2,3,5,6-tetrahydroxybenzene, Prop = propionate, DMF = N',N'-dimethylformamide). Unusually, instead of forming infinite networks, oxygen-bridged titanium clusters coordinated by ligand L are built. The ligand LH4 undergoes subsequent oxidation and deprotonation before coordinating with the metal; bond lengths measured on the coordinated ligand in both compounds reveal an o-quinoid-type structure. The redox-active quinonoid ligand L promotes through-bond charge transfer, leading to strong charge delocalization. The improved electron transfer of these materials leads to semiconducting behaviors, exhibiting electrical conductivity that is approximately 103 greater than that of bulk TiO2. When used as a cathode for lithium-ion batteries at the current density of 0.5 A g−1, both materials show high initial capacities of 240 mAh g−1 and 260 mAh g−1 for NCKU-1 and NCKU-2, respectively. In addition, both compounds can undergo battery cycling at a current density as high as 64 A g−1 with a stable capacity of 60 mAh g−1 for NCKU-1 and 90 mAh g−1 for NCKU-2. These results show the excellent redox kinetics of Ti-cluster materials, which is enabled by their improved electrical conductivity and highly accessible redox sites. Noteworthy, both compounds display unusually high Ti3+/Ti4+ redox potentials (3.2 and 2.7 V vs. Li/Li+ for NCKU-1 and NCKU-2, respectively), suitable to be applied as cathode materials.

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