1-D calcium, 2-D zinc and 3-D manganese coordination polymers derived from pyrazine-2,3,5,6-tetracarboxylic acid

Abstract

Three coordination polymers were synthesized from pyrazine-2,3,5,6-tetracarboxylic acid (H4pztc) in combination with calcium, zinc and manganese ions under hydrothermal conditions and their structures were determined by single crystal X-ray diffraction, powdered X-ray diffraction, Fourier transformed infrared spectroscopy, thermogravimetric and elemental analyses. Structure 1, {(Ca(H2pztc)(H2O)3)n, crystallizes as 1-D chains, with the partially deprotonated ligand in –O,N,O– coordination mode and with the Ca atoms in an uncommon nine coordinate environment. Structure 2, {Zn1(pztc)(H2O)2Zn2(H2O)4}n, is an infinite, 2-D coordination network that contains two nonequivalent Zn atoms, each with octahedral geometry, and the fully deprotonated pztc4− in bis-bridging chelating coordination mode. The stacked 2-D layers are stabilized by extensive inter-layer water-carboxylate hydrogen-bonding with an inter-layer distance of 4.9Å. Structure 3, {(Mn2(pztc)(H2O)2)}n, is a covalently bonded 3-D network containing two nonequivalent Mn atoms, each with octahedral geometry, and the fully deprotonated pztc4− units. Structure 3 exhibits paramagnetic behavior at room temperature, and weak antiferromagnetic properties at very low temperature, which is consistent with their nearest Mn…Mn separation distance of 4.9Å.