title: Nickel(II) Complexation with Nitrate in Dry [C4mim][Tf2N] Ionic Liquid: A Spectroscopic, Microcalorimetric, and Molecular Dynamics Study.
abstract: The complex formation of nitrate ions with nickel(II) in dry [C4mim][Tf2N] ionic liquid (IL) was investigated by means of UV-visible spectrophotometry, isothermal titration calorimetry (ITC), extended X-ray absorption fine structure spectroscopy (EXAFS), and molecular dynamics (MD) simulations. EXAFS spectroscopy and MD simulations show that the solvated Ni(II) cation is initially coordinated by the oxygens of the [Tf2N](-) anion of IL, which can behave either as mono- or bidentate. Spectroscopic and thermodynamic data show that Ni(II) is able to form up to three stable mononuclear complexes with nitrate in this solvent. The stability constants for Ni(NO3)j complexes (j = 1-3) calculated from spectrophotometry and ITC experiments decrease in the order log K1 > log K2 > log K3. The formation of the first two species is enthalpy-driven, while the third species is entropy-stabilized. The UV-vis spectra of solutions containing different nitrate/Ni(II) ratios show that the metal ion retains the six-coordinate geometry. Furthermore, the EXAFS evidences that nitrate is always bidentate. Molecular dynamics simulations show that the [Tf2N](-) anions bind Ni(II) through the sulfonyl oxygen atoms and can coordinate either as monodentate or chelate. The analysis of the MD data shows that introduction of nitrates in the first coordination sphere of the metal ion results in remarkable structural rearrangement of the ionic liquid.
authors.affiliation: Dipartimento di Chimica, Fisica e Ambiente, Università di Udine , Via Cotonificio 108, I-33100 Udine, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Melchior
authors.affiliation: Institut de Physique Nucléaire de Lyon, Université de Lyon, CNRS-IN2P3 , 69622 Villeurbanne cedex, France.
authors.forename: Clotilde
authors.initials: C
authors.lastname: Gaillard
authors.affiliation: Dipartimento di Chimica, Fisica e Ambiente, Università di Udine , Via Cotonificio 108, I-33100 Udine, Italy.
authors.forename: Sara
authors.initials: S
authors.lastname: Gràcia Lanas
authors.affiliation: Dipartimento di Chimica, Fisica e Ambiente, Università di Udine , Via Cotonificio 108, I-33100 Udine, Italy.
authors.forename: Marilena
authors.initials: M
authors.lastname: Tolazzi
authors.affiliation: Université Grenoble Alpes, LEPMI, CNRS , F-38000 Grenoble, France.|CNRS, LEPMI , F-38000, Grenoble, France.
authors.forename: Isabelle
authors.initials: I
authors.lastname: Billard
authors.affiliation: Université de Strasbourg, IPHC , 23 rue du Lœss 67037 Strasbourg, France.
authors.forename: Sylvia
authors.initials: S
authors.lastname: Georg
authors.affiliation: Institut de Physique Nucléaire de Lyon, Université de Lyon, CNRS-IN2P3 , 69622 Villeurbanne cedex, France.
authors.forename: Lola
authors.initials: L
authors.lastname: Sarrasin
authors.affiliation: Université de Strasbourg, IPHC , 23 rue du Lœss 67037 Strasbourg, France.|CNRS, UMR7178 , 67037 Strasbourg, France.
authors.forename: Maria
authors.initials: M
authors.lastname: Boltoeva