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

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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.