Solution and solid state studies with the bis-oxalato building block [Cr(pyim)(C₂O₄)₂]⁻ [pyim = 2-(2′-pyridyl)imidazole]

Abstract

The preparation, X-ray structure, and variable temperature magnetic study of the new compound {Ba(H₂O)_3/2[Cr(pyim)(C₂O₄)₂]₂}_n·9/2nH₂O (1) [pyim = 2-(2′-pyridyl)imidazole and C₂O₄²⁻ = dianion of oxalic acid], together with the potentiometric and spectrophotometric studies of the protonation/deprotonation equilibria of the pyim ligand and the ternary complex [Cr(pyim)(C₂O₄)₂]⁻, are reported herein. The crystal structure of 1 consists of neutral chains, with diamond-shaped units sharing barium(II), with the two other corners occupied by chromium(III). The two metal centers are connected through bis(bidentate) oxalate. Very weak antiferromagnetic interactions between the chromium(III) ions occur in 1. The values of the protonation constants of the imidazole and pyridyl fragments of pyim as well as the acidity constant of the coordinated pyim in [Cr(pyim)(C₂O₄)₂]⁻ are determined for the first time by potentiometry and UV–Vis spectroscopy in aqueous solution (25 °C and 0.15 M NaNO₃ as ionic strength).

Keywords:

• Chromium(III)
• Barium(II)
• Crystal structure
• 2-(2′-Pyridyl)imidazole
• Magnetic properties
• Acidity equilibria

Acknowledgments

The authors are grateful for the financial support of this work provided by the Ministerio Español de Ciencia e Innovación (MICINN) through the projects MAT2010-16981, CTQ2010-15364 and CSD2010-00065 and the Generalitat Valenciana through the project ISIC/2012/002 and PROMETEO 2011/008. F.R. Fortea-Pérez, J. Vallejo and M. Déniz acknowledge the MICINN for predoctoral fellowships and J. Pasán thanks the Proyecto Estructurante NANOMAC (ACIISI-Gobierno de Canarias) for postdoctoral contract.