Thermodynamics of the Complexation of N-(Pyridin-2-ylmethylene) Isonicotinohydrazide with Lighter Lanthanides

Abstract

N-(Pyridin-2-ylmethylene)isonicotinohydrazide, pmINH, has been synthesized and characterized on the basis of elemental and spectral data. The protonation constants of pmINH and the stability constants of the base with trivalent La, Pr, Nd, Sm, Eu, and Gd at constant ionic strength (I, mol • dm -3 ) 0.05 M NaClO 4 ) and at different temperatures, T ) (293, 303, and 313) K, were determined potentiometrically in water-dioxane (30 %) medium. The ligand forms only 1:1 complexes with the lanthanides. Both protonation and complexation reactions are found to be exothermic in nature. The trend in the formation constants follows the order: La 3+ < Pr 3+ < Nd 3+ < Gd 3+ < Sm 3+ < Eu 3+ and shows a break at gadolinium. The thermodynamic parameters associated with the complexation reactions were also calculated. The values of ∆G, ∆H, and ∆S are negative for all the systems and suggest that all reactions are enthalpy driven. The thermodynamic parameters of the complexation are correlated with the reciprocal ionic radii of the metal ions. Raw and normalized isothermal calorimetric data for the titrations of Gd 3+ -pmINH solutions at 303 K show that the reaction was exothermic and metal-ligand stoichiometry to be 1:1.

Rationally designed mineralization for selective recovery of the rare earth elements

“…At pH 6.0, Dy 3+ is at least 100 times more stable than Dy hydroxide species ([Dy(OH)] 2+ , [Dy(OH) 2 ] + , Dy(OH) 3 ), and, thus, this cation is the major species. Therefore, it is easily accepted that almost all Lamp first interacts with Dy 3+ , although this reaction is enthalpically unfavourable (Δ H >0); the formation of an electrostatic bond is itself intrinsically enthalpically favourable, which are over compensated by the energy for removing the coordinating water molecules from Dy 3+ (refs 44 , 48 , 52 ). This process is also entropically unfavourable because the conformational freedom of Lamp in aqueous solution is decreased by the interaction with Dy 3+ (– T Δ S conf >0, T : absolute temperature, Δ S conf : entropy change for the peptide conformation).…”

Sonochemical Synthesis of Cadmium(II) Coordination Polymer Nanospheres as Precursor for Cadmium Oxide Nanoparticles

“…HL (pyridine-2-carboxaldehyde isonicotinoyl hydrazone) was prepared according to a literature method [54,55]. A branched tube method [56,57] was used for the synthesis of 1 (Figure S1, in the supplementary materials).…”

“…These procedures include: (a) a branched tube method with a heat gradient that resulted in a single crystalline form of 1 ( Figure S1), and (b) a sonochemical method that led to the formation of nanoparticles of 1. Both methods are based on a reaction of cadmium(II) nitrate with HL in ethanol (Scheme 1), wherein HL was used as a recognized organic building block for the generation of coordination polymers [54][55][56][57].…”

Antitumoral Properties of a Pincer-Type Isonicotinohydrazone-Hg(II) Complex

“…The chemotherapeutic drugs of metal complexes are effectively used clinically despite their widely recognized side effects and increasing reports of resistance to these drugs (1,2). The discovery of new metal complexes is important in overcoming the potential side effects of existing anticancer agents and in developing more effective and targeted cancer drugs (3,13,14).…”