Metal-Ion-Complexing Properties of 2-(Pyrid-2鈥?yl)-1,10-phenanthroline, a More Preorganized Analogue of Terpyridyl. A Crystallographic, Fluorescence, and Thermodynamic Study

详细信息    查看全文

• 作者：Ashley N. Carolan ; Amy E. Mroz ; Maya El Ojaimi ; Donald G. VanDerveer ; Randolph P. Thummel ; Robert D. Hancock
• 刊名：Inorganic Chemistry
• 出版年：2012
• 出版时间：March 5, 2012
• 年：2012
• 卷：51
• 期：5
• 页码：3007-3015
• 全文大小：558K
• 年卷期：v.51,no.5(March 5, 2012)
• ISSN：1520-510X

文摘

Some metal-ion-complexing properties of the ligand 2-(pyrid-2鈥?yl)-1,10-phenanthroline (MPP) are reported. MPP is of interest in that it is a more preorganized version of 2,2鈥?6,2鈥?terpyridine (tpy). Protonation constants (pK₁ = 4.60; pK₂ = 3.35) for MPP were determined by monitoring the intense 蟺鈥撓€* transitions of 2 脳 10^鈥? M solutions of the ligand as a function of the pH at an ionic strength of 0 and 25 掳C. Formation constants (log K₁) at an ionic strength of 0 and 25 掳C were obtained by monitoring the 蟺鈥撓€* transitions of MPP titrated with solutions of the metal ion, or 1:1 solutions of MPP and the metal ion were titrated with acid. Large metal ions such as Ca^II or La^III showed increases of log K₁ of about 1.5 log units compared to that of tpy. Small metal ions such as Zn^II and Ni^II showed little increase in log K₁ for MPP compared to the tpy complexes, which is attributed to the presence of five-membered chelate rings in the MPP complexes, which favor large metal ions. The structure of [Cd(MPP)(H₂O)(NO₃)₂] (1) is reported: monoclinic, P2₁/c, a = 7.4940(13) 脜, b = 12.165(2) 脜, c = 20.557(4) 脜, 尾 = 96.271(7)掳, V = 1864.67(9) 脜³, Z = 4, and final R = 0.0786. The Cd in 1 is seven-coordinate, comprising the three donor atoms of MPP, a coordinated water, a monodentate, and a bidentate NO₃^{鈥?/sup>. CdII is a fairly large metal ion, with r+ = 0.96 脜, slightly too small for coordination with MPP. The effect of this size matching in terms of the structure is discussed. Fluorescence spectra of 2 脳 10鈥? M MPP in aqueous solution are reported. The nonprotonated MPP ligand fluoresces only weakly, which is attributed to a photoinduced-electron-transfer effect. The chelation-enhanced-fluorescence (CHEF) effect induced by some metal ions is presented, and the trend of the CHEF effect, which is CaII > ZnII > CdII LaIII > HgII, is discussed in terms of factors that control the CHEF effect, such as the heavy-atom effect.}