Synthesis, structure and magnetic properties of cobalt(II) and copper(II) coordination polymers assembled by phthalate and 4-methylimidazole

New coordination polymers [<i>M</i> (Pht)(4-MeIm)₂ (H₂O)]_<i>n</i> (<i>M</i>=Co (<b>1</b>), Cu (<b>2</b>); Pht²⁻=dianion of o-phthalic acid; 4-MeIm=4-methylimidazole) have been synthesized and characterized by IR spectroscopy, X-ray crystallography, thermogravimetric analysis and magnetic measurements. The crystal structures of <b>1</b> and <b>2</b> are isostructural and consist of [<i>M</i> (4-MeIm)₂(H₂O)] building units linked in infinite 1D helical chains by 1,6-bridging phthalate ions which also act as chelating ligands through two O atoms from one carboxylate group in the case of <b>1</b>. In complex <b>1</b>, each Co(II) atom adopts a distorted octahedral N₂O₄ geometry being coordinated by two N atoms from two 4-MeIm, three O atoms of two phthalate residues and one O atom of a water molecule, whereas the square-pyramidal N₂O₃ coordination of the Cu(II) atom in 2 includes two N atoms of N-containing ligands, two O atoms of two carboxylate groups from different Pht, and a water molecule. An additional strong O–HO hydrogen bond between a carboxylate group of the phthalate ligand and a coordinated water molecule join the 1D helical chains to form a 2D network in both compounds. The thermal dependences of the magnetic susceptibilities of the polymeric helical Co(II) chain compound <b>1</b> were simulated within the temperature range 20–300 K as a single ion case, whereas for the Cu(II) compound <b>2</b>, the simulations between 25 and 300 K, were made for a linear chain using the Bonner–Fisher approximation. Modelling the experimental data of compound <b>1</b> with MAGPACK resulted in: <i>g</i>=2.6,

D

=62 cm⁻¹. Calculations using the Bonner–Fisher approximation gave the following result for compound <b>2</b>: <i>g</i>=2.18, <i>J</i>=–0.4 cm⁻¹.