Uranyl(VI) binding by bis(2-hydroxyaryl)diimine and bis(2-hydroxyaryl)diamine ligand derivatives. Synthetic, X-ray, DFT and solvent extraction studies Harold B. Tanh Jeazet a , Kerstin Gloe a , Thomas Doert a , Jens Mizera a , Olga N. Kataeva b , Satoru Tsushima c , Gert Bernhard c , Jan J. Weigand a,⇑ , Leonard F. Lindoy d,⇑ , Karsten Gloe a,⇑ a Department of Chemistry and Food Chemistry, Technical University Dresden, 01062 Dresden, Germany b A.E. Arbuzov Institute of Organic and Physical Chemistry, 420088 Kazan, Russia c Institute of Resource Ecology, Helmholtz Centre Dresden-Rossendorf, 01314 Dresden, Germany d School of Chemistry, The University of Sydney, NSW 2006, Australia article info Article history: Received 4 December 2014 Accepted 7 January 2015 Available online xxxx Dedicated to Catherine Housecroft on the occasion of her 60th birthday. Keywords: Uranyl(VI) Schiff base Europium(III) Solvent extraction Density functional theory abstract The interaction of uranyl(VI) nitrate with a series of bis(2-hydroxyaryl)imine (H 2 L 1 –H 2 L 5 ) and bis(2- hydroxyaryl)amine (H 2 L 8 ,H 2 L 9 ) derivatives incorporating 1,3-dimethylenebenzene or 1,3-dimethylene- cyclohexane bridges between nitrogen sites is reported. Crystalline complexes of type [UO 2 (H 2 L)(NO 3 ) 2 ] (where H 2 L is H 2 L 1 –H 2 L 4 ) were isolated from methanol. X-ray structures of the complexes of H 2 L 1 ,H 2 L 2 and H 2 L 4 show that each of these neutral ligands bind to their respective UO 2 2þ centres in a bidentate fashion in which coordination only occurs via each ligand’s hydroxy functions. Two bidentate nitrate anions complete the metal’s coordination sphere in each complex to yield hexagonal bipyramidal coor- dination geometries. A density functional theory (DFT) investigation of [UO 2 (H 2 L 1 )(NO 3 ) 2 ] in a simulated methanol environment is in accord with this complex maintaining its solid state conformation in solu- tion. Solvent extraction experiments (water/chloroform) employing H 2 L 1 –H 2 L 7 in the organic phase and uranyl(VI) nitrate in the aqueous phase showed that both amine derivatives, H 2 L 8 and H 2 L 9 , yielded enhanced extraction of UO 2 2þ over the corresponding imine derivatives, H 2 L 1 and H 2 L 2 . These results were further compared with those obtained for the corresponding Schiff bases incorporating 1,2-pheny- lene and 1,2-cyclohexane bridged ligands, H 2 L 6 and H 2 L 7 ; these more rigid systems also yielded enhanced extraction of UO 2 2þ relative to the more flexible Schiff bases H 2 L 1 –H 2 L 5 . A very significant synergistic enhancement of the extraction of UO 2 2þ by H 2 L 1 –H 2 L 4 and H 2 L 7 was observed in the presence of a 10-fold excess of n-octanoic acid; the influence of pH on extraction efficiency was also investigated. A parallel set of experiments employing H 2 L 1 –H 2 L 9 as extractants for europium(III) nitrate indicated a clear uptake preference for UO 2 2þ over Eu 3+ in all cases; separation of the uranyl ion from the rare earths is an important objective in mineral processing. Ó 2015 Elsevier Ltd. All rights reserved. 1. Introduction The coordination chemistry of uranyl(VI) has received increas- ing attention over recent years [1,2]. Many such studies [3–6] were motivated by the awareness that an enhanced understanding of the complexation behaviour of this ion has implications for the winning, processing and use of uranium as well as for the appropriate control, processing and storage of nuclear wastes [7–16]. As a consequence, a number of studies have focused on ligand design for selective uranium uptake [17–20], with particu- lar studies focused on the separation of actinides from the lanthanides [21–25] – metals which occur together in nature and nuclear wastes. However, in general, such separations are inherently challenging due to the generally similar chemistry of these ions. In the above context it is noted that a number of Schiff base ligands have been employed for uranyl extraction [23,26,27]. For example, H 2 L 6 (salophen), has been shown to form robust neutral 1:1 uranyl chelate complexes of composition [UO 2 (L 6 )S], each incorporating a solvent molecule (S = DMF, DMSO, H 2 O) [28,29]. Ligand species of this type incorporating a short spacer group http://dx.doi.org/10.1016/j.poly.2015.01.005 0277-5387/Ó 2015 Elsevier Ltd. All rights reserved. ⇑ Corresponding authors. Tel.: +61 (0)2 9351 4400 (L.F. Lindoy). Tel.: +49 (0)351 463 34357 (K. Gloe). E-mail addresses: Len.lindoy@sydney.edu.au (L.F. Lindoy), karsten.gloe@chemie. tu-dresden.de (K. Gloe). Polyhedron xxx (2015) xxx–xxx Contents lists available at ScienceDirect Polyhedron journal homepage: www.elsevier.com/locate/poly Please cite this article in press as: H.B.T. Jeazet et al., Polyhedron (2015), http://dx.doi.org/10.1016/j.poly.2015.01.005