Two new dinuclear complexes with dipicolinate and bridging 2-aminopyrazine ligands: preparation, structural, spectroscopic, and thermal characterizations

Abstract

Treatment of an aqueous solution of dipicolinic acid (dipicH₂) and 2-aminopyrazine (apyz) with Cu(NO₃)₂ · 3H₂O or ZnCl₂ (in molar ratio 1 : 1 : 1) led to formation of dinuclear complexes, [M₂(H₂O)₄(dipic)₂(µ-apyz)] (M = Cu (1) and Zn (2)). Both complexes were characterized by elemental analyses, IR, and UV-Vis spectroscopy. Their molecular and crystal structures were determined by X-ray crystal structure analysis and their thermal stabilities were confirmed by TGA/DTA methods. Complex 1 crystallizes in the triclinic P-1 space group, while 2 crystallizes in the monoclinic P2₁/c space group. The dinuclear complexes are analogous and composed of two metal ions bridged by 2-aminopyrazine. Each M(II) is coordinated by one nitrogen atom and two oxygen atoms of tridentate dipicolinate, one heterocyclic nitrogen of 2-aminopyrazine, and two coordinated water molecules. The resulting geometry for the MN₂O₄ coordination environment can be described as distorted octahedral. Extensive hydrogen-bonding interactions involving all water ligands, dipicolinate oxygen atoms, and amino groups further stabilize the complex units by linking them to form 3-D networks for 1 and 2.

Keywords:

• Dinuclear complex
• Copper complex
• Zinc complex
• Dipicolinic acid
• 2-Aminopyrazine

Acknowledgments

This research was supported by Yazd Branch, Islamic Azad University, Yazd, Iran and by the Ministry of Science, Education and Sports of Croatia (grant no. 098-1191344-2943).