Eu(fod) 3 binding on the 1 H-NMR spectra of bis (2 0 -ethylbenzoate)ethylene glycol podands † Cüneyt H. Ünlü,* Gönül Yapar* and Çakıl Erk The complexing and selective binding constants of Eu(fod) 3 with bis(2 0 -ethylbenzoate)ethylene glycol podands having one to four oxyethylene groups was observed on their 1 H-NMR spectra at 250 MHz and 295 K in CDCl 3 . The Eu(fod) 3 interaction displayed the selective binding role of oxygen on H 2 C–O–CH 2 backbones with referring the 1 H chemical shifts. The estimated equilibrium constants, K a , of 1:1 ratio of interactions were in accordance with the Eu(fod) 3 ionic radii to bind the oxygen sites depending on the size and conformation of the esters. Esters having one or two ethyleneoxy groups gave mainly 2:2 complexes using ester sites. The minimum lanthanide-podand ester distance displayed the maximum stability so that ester with four oxyethylene groups was found to bind the Eu(fod) 3 moderately, whereas ester with three oxyethylene groups showed a large induced chemical shift due to the stability of Eu 3+ complexes with larger ethyleneoxy groups. Copyright © 2012 John Wiley & Sons, Ltd. Keywords: carbonyl compounds; lanthanoids; magnetic dipolar shifts; ion binding Introduction The macrocyclic ethers and their contributions to the different fields of chemistry have been developed since the discovery by Pedersen. The interaction of such molecules via the integrated charge of oxygen dipoles in certain molecular geometries results in binding of the strongly electropositive cations. [1,2] Although several analytical tools and methods have been used to display the cationic binding role of macrocyclic ethers, different methods have given different results. [3] We have been working on the synthesis of various types of macrocyclic ethers and on their cation complex formation using different analytical methods such as potentiometry, fluorescence, and NMR spectroscopy. [4–10] We have recently prepared some bis(2 0 -ethylbenzoate)ethylene glycol podands which have one, two, three, or four ethyleneoxy groups to study their cationic recognition with NMR spectroscopy. The present work is reporting the interaction of europium(III)-tris (1,1,1,2,2,3,3-heptafluoro-7,7-dimethyl-4,6-octanedionate), Eu(fod) 3 (compound 1), with some ester podands by monitoring their 250 MHz 1 H-NMR spectra to compare the Eu 3+ recognition in a nonpolar solvent, CDCl 3 . [9] The effects of Eu 3+ tris(b-diketone) compounds on 1 H-NMR spectra of organic molecules are quite well known and have been used for plenty of molecules. [11–16] This application have covered the open chain bis(2 0 -ethylbenzoate)ethylene glycol podands. Lanthanide-induced shifts mainly involves with two mechanisms: (i) contact shifts, which arise from the delocalization of the unpaired electron-spin through bonds to the nuclei affected; and (ii) pseudocontact shifts of the magnetic moment of paramagnetic cation that generated the secondary field, although both effects may involve depending on lanthanides interacting with Lewis bases to bind. [12–17] Although there is no angular dependence, the magnetic role of Eu 3+ is open to discussions. Probably magnetic moment arises through a second-order paramagnetism, which is large for Eu 3+ , and this effect adducts to produce the remarkable down field shift. [11,13] This study aims to determine complexation between podand and Eu(fod) 3 using 1 H-NMR spectroscopy. We restrict the present study and results to the 1:1 complexes observing the secondary field effect, which dominates podand ester/Eu(fod) 3 complexes and the induced shifts is proportional with 1/r 3 of the distance re- garding the role of cationic radii. [18,13] C-NMR spectroscopy was not studied due to extensive line broadening. Experimental Bis(2 0 -ethylbenzoate) ethylene glycol podans carrying one to four ethyleneoxy groups (compounds 2–5) were synthesized in a parallel study with our group and they were always dried before use. 1 H-NMR spectra (250 MHz) were recorded with a Bruker AC-3000 model spectrometer using CDCl 3 (Merck) with TMS as an internal reference at 292 K. The fresh Eu(fod) 3 (compound 1) dissolved in dry CDCl 3 , then it was added into a 5.0-mm NMR capillary stepwise, containing appropriate amount of the podand. The mole fractions, P M and P E , were calculated using chemical shifts of complex/free podand/free metal mixture (d obs ) and estimated molar shift of complex (d ME ). The equilibrium constants, ln K a (0.05), were estimated according to Eqn (9) with linear regression. * Correspondence to: Cüneyt H. Ünlü and Gönül Yapar, Faculty of Science and Letters, Department of Chemistry, Istanbul Technical University, Maslak TR 34469, Istanbul, Turkey. E-mail: unlucu@itu.edu.tr; yaparg@itu.edu.tr † This article is dedicated to our mentor, Professor Çakıl Erk, who passed away August 21, 2005. Faculty of Science and Letters, Department of Chemistry, Istanbul Technical University, MaslakTR 34469, Istanbul, Turkey Magn. Reson. Chem. 2013, 51, 42–45 Copyright © 2012 John Wiley & Sons, Ltd. Research Article Received: 5 July 2012 Revised: 6 November 2012 Accepted: 6 November 2012 Published online in Wiley Online Library: 22 November 2012 (wileyonlinelibrary.com) DOI 10.1002/mrc.3904 42