Ni(II) coordination compounds based on mixed phthalate and aromatic amine ligands: synthesis, crystal structures and magnetic properties

Three new coordination compounds, [Ni(Pht)(Py)₂ (H₂O)₃] (<b>1</b>), [Ni(Pht)(β- Pic)₂(H₂O)₃] • H₂O (<b>2</b>) and [Ni(Pht)(1-MeIm)₂ (H₂O)₃] (<b>3</b>) (where Pht²⁻ = dianion of o-phthalic acid; Py = pyridine, β-Pic = 3-methylpyridine, 1-MeIm = 1-methylimidazole), have been synthesized and characterized by IR spectroscopy and thermogravimetric analysis. Crystallographic studies <b>1–3</b> reveal that each Ni(II) center has a distorted octahedral geometry being coordinated by two nitrogen atoms of aromatic amines, one oxygen atom from a carboxylate group of a phthalate ligand and three water molecules. Pht²⁻ anions act as monodentate ligands, while the remaining uncoordinated carboxylate oxygen atoms participate in the formation of hydrogen bonding. The uncoordinated oxygen atoms form hydrogen bonds with the coordinated water molecules from adjacent complexes creating a centrosymmetric dimer unit. Further, these dimer units are connected by O–HO hydrogen bonds in double-chains. Depending on the nature of aromatic amines, the arrangement of these double-chains differs. The double-chains are held together only by van der Waals interactions in <b>1</b>. In contrast, in <b>2</b> these chains form layers by π–π interactions between antiparallel molecules of β-Pic as well as by π–π interactions between β-Pic and Pht aromatic rings. In complex <b>3</b>, the double-chains are knitted together via C–HO hydrogen bonds between the methyl group of 1-MeIm and the coordinated carboxylate oxygen atom of Pht, as well as π–π contacts involving antiparallel 1-MeIm cycles. The thermal dependence of the magnetic susceptibilities for compounds <b>1</b> and <b>2</b> shows a weak antiferromagnetic interaction between the two Ni²⁺ ions of the hydrogen bonded dimers. For compound <b>3</b>, a ferromagnetic interaction could be observed. Modeling the experimental data with MAGPACK resulted in: <i>g</i> = 2.22,

<i>D</i>

= 4.11 cm⁻¹ and <i>J</i> = −0.29 cm⁻¹ for compound <b>1</b>, <i>g</i> = 2.215,

<i>D</i>

= 3.85 cm⁻¹ and <i>J</i> = −0.1 cm⁻¹ for compound <b>2</b> and <i>g</i> = 2.23,

<i>D</i>

= 4.6 cm⁻¹ and <i>J</i> = 0.22 cm⁻¹ for compound <b>3</b>.