Coordination Chemistry Reviews 256 (2012) 328–351 Contents lists available at ScienceDirect Coordination Chemistry Reviews journal homepage: www.elsevier.com/locate/ccr Review Thermodynamics of lanthanide(III) complexation in non-aqueous solvents Plinio Di Bernardo a , Andrea Melchior b , Marilena Tolazzi b,∗ , Pier Luigi Zanonato a a Dipartimento di Scienze Chimiche, Università di Padova, Via Marzolo 1, 35131 Padova, Italy b Dipartimento di Scienze e Tecnologie Chimiche, Università di Udine, Via del Cotonificio 108, 33100 Udine, Italy Contents 1. Introduction ......................................................................................................................................... 329 2. Fundamental properties of Ln ions ................................................................................................................. 329 2.1. Relative stabilities of oxidation states ....................................................................................................... 329 2.2. Ionic radii .................................................................................................................................... 330 3. Lanthanide(III) solvation in non-aqueous solvents ................................................................................................. 332 3.1. Ln(III) ions preferential solvation ........................................................................................................... 332 3.2. Structural aspects of Ln(III) solvation ....................................................................................................... 332 4. Thermodynamics of complex formation with charged inorganic ligands .......................................................................... 333 5. Thermodynamics of complex formation with neutral organic ligands ............................................................................ 335 5.1. Coordination of O-donors ................................................................................................................... 335 5.1.1. Crown ethers ....................................................................................................................... 335 5.1.2. Complexation with diazamacrocycles and cryptands ............................................................................. 340 5.1.3. Solvent influence on crown ethers and cryptands complexation ................................................................. 343 5.1.4. Stabilization of lanthanide low oxidation states .................................................................................. 343 5.2. Coordination of N-donors ................................................................................................................... 343 5.2.1. Monodentate amines .............................................................................................................. 343 5.2.2. Polydentate amines ................................................................................................................ 344 5.2.3. Heterocyclic N-donor ligands ...................................................................................................... 346 6. Conclusions .......................................................................................................................................... 350 Acknowledgments .................................................................................................................................. 350 References ........................................................................................................................................... 350 article info Article history: Received 16 May 2011 Received in revised form 1 July 2011 Accepted 20 July 2011 Keywords: Lanthanides(III) Thermodynamics Complexation Solvation Non-aqueous solvents Neutral donors Charged inorganic ligands Coordination number Ionic radius abstract Lanthanide(III) coordination compounds are employed in several fundamental and applied research fields such as organic synthesis, bioinorganic chemistry, optical and magnetic imaging, catalysis, environment and geochemistry. All these applications have been favoured by the recent developments of a detailed knowledge of fundamental properties (electronic, spectroscopic, thermodynamic, magnetic, structural) of elements, ions and their compounds. Ln 3+ are hard acids and present strong affinity for charged ligands or neutral O- and N-donors, as indicated by a wide number of papers concerning formation of their complexes in solution. These studies allowed one to gain information on the complex stabilities, the metal-ion selectivity of a given ligand, the influence of the solvent on the nature and stability of the species in solution. Most of the above studies deal with aqueous solutions, while studies in non-aqueous media are less common. Despite more limited, investigations in aprotic solvents are particularly interesting as they allow one to extend the knowledge on the coordination chemistry of lanthanide(III), disclosing metal–ligand interactions not easily accessible in water due to ligand protonation equilibria, Ln(III) hydrolysis and strong hydration of the cations, which hampers interactions with neutral donors. This review analyzes a wide number of thermodynamic studies concerning formation of lanthanide(III) complexes with selected, simple neutral N-donors (amines, pyridines), O-donors (crown ethers, aza- crown ethers and cryptands) and charged inorganic ligands (halides, thiocyanate, nitrate, perchlorate, ∗ Corresponding author. Tel.: +39 0432 558852; fax: +39 0432 558803. E-mail address: marilena.tolazzi@uniud.it (M. Tolazzi). 0010-8545/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.ccr.2011.07.010