Metal Ion Complexing Properties of Dipyridoacridine, a Highly Preorganized Tridentate Homologue of 1,10-Phenanthroline

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• 作者：Joanna M. Hamilton ; Jason R. Whitehead ; Neil J. Williams ; Maya El Ojaimi ; Randolph P. Thummel ; Robert D. Hancock
• 刊名：Inorganic Chemistry
• 出版年：2011
• 出版时间：April 18, 2011
• 年：2011
• 卷：50
• 期：8
• 页码：3785-3790
• 全文大小：910K
• 年卷期：v.50,no.8(April 18, 2011)
• ISSN：1520-510X

文摘

DPA (dipyrido[4,3-b;5,6-b]acridine) may be considered as a tridentate homologue of phen (1,10-phenanthroline). In this paper some of the metal ion complexing properties of DPA in aqueous solution are reported. Using UV鈭抳isible spectroscopy to follow the intense 蟺鈭捪€* transitions of DPA as a function of pH gave protonation constants at ionic strength (渭) = 0 and 25 掳C of pK₁ = 4.57(3) and pK₂ = 2.90(3). Titration of 10^鈭? M solutions of DPA with a variety of metal ions gave log K₁ values as follows: Zn(II), 7.9(1); Cd(II), 8.1(1); Pb(II), 8.3(1); La(III), 5.23(7); Gd(III), 5.7(1); Ca(II), 3.68; all at 25 掳C and 渭 = 0. Log K₁ values at 渭 = 0.1 were obtained for Mg(II), 0.7(1); Sr(II), 2.20(1); Ba(II), 1.5(1). The log K₁ values show that the high level of preorganization of DPA leads to complexes 3 log units more stable than the corresponding terpyridyl complexes for large metal ions such as La(III) or Ca(II), but that for small metal ions such as Mg(II) and Zn(II) such stabilization is minimal. Molecular mechanics calculations (MM) are used to show that the best-fit M鈭扤 length for coordination with DPA is 2.60 脜, accounting for the high stability of Ca(II) or La(III) complexes of DPA, which are found to have close to this M鈭扤 bond length in their phen complexes.