Two coordination polymers based on conjugated pyrazine aromatic carboxylic acid ligands: Structural and magnetic research

Two new coordination polymers [M(L)(H2O)2]n (M=Co (1) and Mn (2)) (H2L=5-(pyrazin-2-yl) isophthalic acid) were synthesized by hydrothermal method and systematically characterized. The two compounds were analyzed in depth by x-ray single crystal diffraction, elemental analysis, IR spectroscopy, PXRD and thermal analysis. The x-ray single crystal diffraction results indicate that compound 1 is a 3D framework structure. Through the carboxyl oxygen atoms and pyrazine nitrogen atoms on different L2- ligands, two interesting infinitely extended right helix chains are formed along the c-axis, and the two helix chains are combined to form a 3D framework structure of 1. In compound 2, the adjacent Mn2+ is bridged with four carboxyl oxygen groups in the ligand to form a binuclear structure unit {Mn2O4}. Each {Mn2O4} is linked to six organic ligands, and each ligand is linked to three {Mn2O4}, which together form a (3,6) linked 3D coordination polymer material. It is noteworthy that the interconnections between the layers form a lantern-like structure when viewed from the b-axis direction. Additionally, compounds 1 and 2 demonstrated temperature-dependent magnetic susceptibility (dc) and negative values of theta (equal to -10.59 K and -6.38 K), which are indicates the presence of weak antiferromagnetic interactions in both compounds 1 and 2.