Synthesis and Structural Elucidation of Co(II) and Mn(II) Coordination Polymers Derived from Isonicotinic Acid

The solvothermal reaction of isonicotinic acid (INA) with Co(II) and Mn(II) afforded isostructural coordination polymers of formula [M₂(INA)₄] (M = Co, Mn). The compounds were characterised by FT-IR spectroscopy, elemental (CHN) analysis, solubility studies, magnetic measurements, powder X-ray diffraction and single-crystal X-ray diffraction unit cell determination for the cobalt(II) complex. Infrared spectroscopic data confirmed deprotonation of the isonicotinic acid ligand and coordination through both carboxylate oxygen and pyridyl nitrogen donor atoms. The free ligand, showed absorption bands at 1695 cm⁻¹ and 1289 cm⁻¹ assigned to C = O and C–O stretching vibrations. Upon coordination, the C = N band shifted from 1580 cm⁻¹ in the free ligand to 1560 cm⁻¹ in the Co(II) complex and to 1559 cm⁻¹ in the Mn(II) analogue, with new absorptions near 500 cm⁻¹ and 400 cm⁻¹ corresponding to M–N and M–O vibrations.The coordination polymers exhibit low solubility in common solvents, consistent with their extended polymeric structures. Magnetic susceptibility measurements revealed effective magnetic moments of 5.81 BM for the manganese(II) polymer and 4.53 BM for the cobalt(II) polymer, indicative of high-spin octahedral metal centres. PXRD analysis showed the disappearance of characteristic ligand reflections and the appearance of new peaks associated with the coordination polymers, confirming the formation of new crystalline phases. Unit cell determination for the cobalt(II) compound indicated a monoclinic system with space group P2 ₁ , (a = 9.818 Å, b = 12.804 Å, c = 10.801 Å) consistent with a reported structure (CCDC 886304).