Preparation and structural, spectroscopic, thermal, and electrochemical characterizations of iron(III) compounds containing dipicolinate and 2-aminopyrimidine or acridine

Abstract

Two new iron(III) compounds, (Hamp)[Fe(pydc)₂] · 2H₂O (1) and (Hacr)[Fe(pydc)₂] · 2H₂O (2) (pydc²⁻ = pyridine-2,6-dicarboxylic acid, amp = 2-aminopyrimidine, acr = acridine), have been hydrothermally synthesized. Both compounds were characterized by spectroscopic methods (IR, UV/Vis), and their molecular and crystal structures were determined by X-ray crystal structure analysis and their thermal stability by thermogravimetric analysis/differential thermal analysis (TGA/DTA) methods. Compound 1 consists of Hamp⁺ cation and [Fe(pydc)₂]⁻ anion and 2 consists of Hacr⁺ cation and [Fe(pydc)₂]⁻ anion. Crystallographic characterization revealed an octahedron as a coordination polyhedron for the complex anion in 1 and 2 and the same O,N,O′-chelated coordination mode of pyridine-2,6-dicarboxylate. The crystal structures of 1 and 2 are stabilized by a complicated network of hydrogen bonds between the crystallization water molecules, counter ion, and carboxylates of pydc²⁻. Thermogravimetric (TG) analyses of the two compounds were carried out to examine their thermal stabilities. Cyclic voltammetric response of bare glassy carbon electrode surface in 0.10 mol L⁻¹ phosphate buffer containing 1 and 2 at different pH values indicated that they have the same voltammograms at all pH values and the electrochemical behavior of 1 and 2 has not been affected by different ion pairs. The formal potential of the solutions of 1 and 2 at the glassy carbon electrode surface was also pH-dependent with a slope of −57.0 mV/pH unit at 25°C. This shows that the number of electrons and protons involved in the electrode process is equal.

Keywords:

• Crystal structure
• Dipicolinate
• Iron(III) complex
• π–π Interactions
• Voltammetry

Acknowledgments

This research was supported by the Ministry of Science, Education and Sports of the Republic of Croatia (Grant no. 119-1193079-1332), and Islamic Azad University, Yazd Branch.