Spectroscopic investigations of Eu 3 þ -complexes with ligands containing multiple diglycolamide pendant arms in a room temperature ionic liquid Arijit Sengupta a , Prasanta K. Mohapatra a,n , Mudassir Iqbal b , Jurriaan Huskens b , Willem Verboom b a Radiochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085, India b Laboratory of Molecular Nanofabrication, MESA þ Institute for Nanotechnology, University of Twente, P. O. Box 217, 7500AE Enschede, The Netherlands article info Article history: Received 12 March 2014 Received in revised form 1 May 2014 Accepted 4 May 2014 Available online 21 May 2014 Keywords: Luminescence J–O parameter Diglycolamides Ionic liquid Site symmetry abstract Fluorescence spectroscopy was used to study the complexation of different ligands containing multiple diglycolamide (DGA) pendent arms such as T-DGA (tripodal diglycolamide), C4DGA (upper rim functionalized calix [4] arene with four DGA moieties), and C8DGA (both side functionalized calix [4] arene with eight DGA moieties) with Eu 3þ in ionic liquids such as C 4 mimNTf 2 and C 8 mimNTf 2 (1-alkyl-3-methylimidazolium bis (trifluoromethylsulphonyl)imide). Mainly five sets of emission profiles were observed in all the spectra (1st set at 580 nm assigned as the 5 D 0 - 7 F 0 transition, 2nd set at 593 nm assigned as the 5 D 0 - 7 F 1 transition, 3rd set at 613 nm assigned as the 5 D 0 - 7 F 2 transition, 4th set at 650 nm assigned as the 5 D 0 - 7 F 3 transition, and 5th set at 700 nm assigned as the 5 D 0 - 7 F 4 transition). The difference in the spectral features revealed that the nature of the complexes differs significantly from one another. Judd–Offelt constant Ω 2 , which is a measure of the covalency of the metal–ligand bond, follows the order Eu 3þ –C4DGA (C 8 mimNTf 2 ) 4Eu 3þ –C8DGA (C 8 mimNTf 2 ) 4Eu 3þ –TODGA (C 4 mimNTf 2 ) 4Eu 3þ –T-DGA (C 4 mimNTf 2 ) 4Eu 3þ aq . The high intensity of the 5 D 0 - 7 F 2 transitions in all complexes suggests that Eu 3þ resides in a highly asymmetric environment. From the splitting patterns of the transitions, the local site symmetry around Eu 3þ was found to be C 2V for the Eu 3þ –T-DGA complex in both C 4 mimNTf 2 and a 1:5 acetonitrile–water mixture, C 4V for Eu 3þ –C8DGA and Eu 3þ –TODGA complexes, and either C 1 ,C 2 , or C S for the Eu 3þ –C4DGA complex. A linear relationship between the 5 D 0 – 7 F 1 splitting vs E( 5 D 0 – 7 F 0 ) and E( 5 D 0 – 7 F 0 ) vs E( 5 D 0 – 7 F 1 ) was observed. The crystal field parameters in the different complexes follow the trend Eu 3þ –C4DGA4Eu 3þ – TODGA4Eu 3þ –T-DGA in C 4 mimNTf 2 Eu 3þ –C8DGA4Eu 3þ –T-DGA in 5:1 acetonitrile-water mixture. & 2014 Elsevier B.V. All rights reserved. 1. Introduction Diglycolamide- (DGA) based ligands such as TODGA (N,N,N', N'-tetraoctyl diglycolamide) have been found to be some of the most promising extractants of minor actinide ions such as Am 3 þ and Cm 3 þ from nitric acid feed conditions, which has relevance in radioactive waste management [1]. Recently, we have synthesised DGA- functionalized calix[4]arenes and found them to be significantly more efficient than TODGA [2]. Furthermore, a very significant enhance- ment in the metal ion extraction takes place when using room temperature ionic liquids instead of molecular diluents [3–6]. We have recently reported the excellent extraction / separation behaviour of several DGA-functionalized ligands such as TODGA [7], tripodal- diglycolamide (T-DGA) [8], and diglycolamide-functionalized calix[4] arene ligands for actinide ions using room temperature ionic liquids as the diluent [9–11]. The calix[4]arene-based ligands used in these studies comprised of a set of lower rim functionalized calix[4]arenes containing four DGA pendent arms with varying substituents/spacer lengths, an upper rim functionalized ligand with four DGA moieties (C4DGA), and a both side DGA-functionalized calix[4]arene containing eight DGA functionalities (C8DGA). In view of the many donor atoms in these ligands, it was intriguing to understand the nature of their coordination to the metal ions. In most of these cases, the nature of the extracted complexed species was ascertained by the slope analysis method, which revealed a 1:1 stoichiometry (M:L) in most cases, although incidentally 1:2 complexes were also formed. Our attempts to grow single crystals were unsuccessful. Therefore, we have performed spectroscopic investigations to get a better insight into the complexation behaviour. Time resolved laser induced fluorescence spectroscopy (TRLIFS) is one of the important tools to study the structure of metal ligand complexes [12–17] and was exploited to understand the nature of Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jlumin Journal of Luminescence http://dx.doi.org/10.1016/j.jlumin.2014.05.001 0022-2313/& 2014 Elsevier B.V. All rights reserved. n Corresponding author. Fax: þ91 2225505151. E-mail address: mpatra@barc.gov.in (P.K. Mohapatra). Journal of Luminescence 154 (2014) 392–401