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

Three coordination polymers were synthesized from pyrazine-2,3,5,6-tetracarboxylic acid (H 4 pztc) 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(H 2 pztc)(H 2 O) 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)(H 2 O) 2 Zn2(H 2 O) 4 } n , is an infinite, 2-D coordination network that contains two nonequivalent Zn atoms, each with octahedral geometry, and the fully deprotonated pztc 4− 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 4.9 A. Structure 3, {(Mn 2 (pztc)(H 2 O) 2 )} n , is a covalently bonded 3-D network containing two nonequivalent Mn atoms, each with octahedral geometry, and the fully deprotonated pztc 4− 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 4.9 A.