Cooperative Anion Recognition in Copper(II) and Zinc(II) Complexes with a Ditopic Tripodal Ligand Containing a Urea Group

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• 作者：Israel Carreira-Barral ; Teresa Rodr铆guez-Blas ; Carlos Platas-Iglesias ; Andr茅s de Blas ; David Esteban-G贸mez
• 刊名：Inorganic Chemistry
• 出版年：2014
• 出版时间：March 3, 2014
• 年：2014
• 卷：53
• 期：5
• 页码：2554-2568
• 全文大小：607K
• 年卷期：v.53,no.5(March 3, 2014)
• ISSN：1520-510X

文摘

The ability of Cu^II and Zn^II complexes of the ditopic receptor H₂L [1-(2-((bis(pyridin-2-ylmethyl)amino)methyl)phenyl)-3-(3-nitrophenyl)urea] for anion recognition is reported. In the presence of weakly coordinating anions such as ClO₄^{鈥?/sup>, the urea group binds to the metal ion (CuII or ZnII) through one of its nitrogen atoms. The study of the interaction of the metal complexes with a variety of anions in DMSO shows that SO₄2鈥?/sup> and Cl鈥?/sup> bind to the complexes through a cooperative binding involving simultaneous coordination to the metal ion and different hydrogen-bonding interactions with the urea moiety, depending on the shape and size of the anion. On the contrary, single crystal X-ray diffraction studies show that anions such as NO₃鈥?/sup> and PhCO₂鈥?/sup> form 1:2 complexes (metal/anion) where one of the anions coordinates to the metal center and the second one is involved in hydrogen-bonding interaction with the urea group, which is projected away from the metal ion. Spectrophotometric titrations performed for the CuII complex indicate that this system is able to bind a wide range of anions with an affinity sequence: MeCO₂鈥?/sup> Cl鈥?/sup> (log K₁₁ > 7) > NO₂鈥?/sup> > H₂PO₄鈥?/sup> Br鈥?/sup> > HSO₄鈥?/sup> > NO₃鈥?/sup> (log K₁₁ < 2). In contrast to this, the free ligand gives much weaker interactions with these anions. In the presence of basic anions such as MeCO₂鈥?/sup> or F鈥?/sup>, competitive processes associated with the deprotonation of the coordinated N鈥揌 group of the urea moiety take place. Thus, N-coordination of the urea unit to the metal ion increases the acidity of one of its N鈥揌 groups. DFT calculations performed in DMSO solution are in agreement with both an anion-hydrogen bonding interaction and an anion鈥搈etal ion coordination collaborating in the stabilization of the metal salt complexes with tetrahedral anions.}