Delving into the complex picture of Ti(IV)–citrate speciation in aqueous media: Synthetic, structural, and electrochemical considerations in mononuclear Ti(IV) complexes containing variably dep

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• 作者：Panagiotis Panagiotidis ; Evangelos T. Kefalas ; Catherine P. Raptopoulou ; Aris Terzis ; Thomas Mavromoustakos ; Athanasios Salifoglou
• 关键词：Ti(IV)– ; citrate speciation ; Mononuclear species ; Aqueous complex synthesis ; ; //www.sciencedirect.com/scidirimg/entities/204e.gif"" alt=""greek small letter alpha"" title=""greek small letter alpha"" border=""0"">-Hydroxycarboxylate ligands ; C
• 刊名：Inorganica Chimica Acta
• 出版年：2008
• 出版时间：2 June 2008
• 年：2008
• 卷：361
• 期：8
• 页码：2210-2224
• 全文大小：1082 K

文摘

The aqueous reaction of TiCl₄ with citric acid at pH 4 (KOH), led to the surprising isolation of a species assembly K₃[Ti(C₆H₆O₇)₂(C₆H₅O₇)] · K₄[Ti(C₆H₅O₇)₂(C₆H₆O₇)] · 10H₂O (1). The same system at pH 3 (neocuproine), led to the crystalline material (C₁₄H₁₃N₂)₂[Ti(C₆H₆O₇)₃] · 5H₂O (2), while at pH 5.0 (NaOH), afforded Na₃[Ti(C₆H₆O₇)₂(C₆H₅O₇)] · 9H₂O (3). Analytical, spectroscopic and structural characterization of 1, 2 and 3 revealed their distinct nature exemplified by mononuclear complexes bearing variably deprotonated citrates bound to Ti(IV). Solid-state ¹³C MAS NMR spectroscopy in concert with solution ¹³C and ¹H NMR on 3 provided ample evidence for the existence of bound citrates of distinct coordination mode to the metal ion. Cyclic voltammetry defined the electrochemical signature of complex 2, thereby projecting the physicochemical profile of the species formulated by the aforementioned properties. Comparison of cyclic voltammetric data on available discrete Ti(IV)–citrate species depicts the electrochemical profile and an E_1/2 value trend of the species in that binary system’s aqueous speciation, further substantiating the redox behavior of mononuclear Ti(IV)–citrate species in a pH-sensitive fashion. Collectively, the well-defined discrete species in 1–3 reflect and corroborate a synthetically challenging yet complex pH-specific picture of the aqueous Ti(IV) chemistry with the physiological citric acid, and shed light on the pH-dependent speciation in the binary Ti(IV)–citrate system.