Syntheses, molecular and supramolecular structures, electrochemistry and magnetic properties of two macrocyclic dinickel(II) complexes

The work in this paper reports syntheses, molecular and supramolecular structures, electrochemistry and magnetic properties of two diphenoxo-bridged dinickel(II) compounds Ni^II₂L(N₃)₂(H₂O)₂]·CH₃CN (1) and Ni^II₂L(N₃)₂(H₂O)] (2), where H₂L is the tetraimino diphenolate macrocyclic ligand, obtained on 2 + 2] condensation of 4-methyl-2,6-diformylphenol and 2,2′-dimethyl-1,3-diaminopropane. Brown colored compound 1 and green colored compound 2 are produced from the same reaction mixture as a function of temperature; 1 is formed from the reaction mixture in acetonitrile at low temperature (ca. 5 °C), while 2 is formed on heating the reaction mixture in acetonitrile. Crystals of compounds 1 and 2 are monoclinic (space group P2₁/c) and orthorhombic (space group P2₁2₁2₁), respectively. Analyses of the crystal packing of the crystalline phases reveal that two-dimensional topologies are resulted in both 1 and 2 due to hydrogen bonding interactions. Variable-temperature (2-300 K) magnetic susceptibility measurements of the two compounds reveal that the metal centers in both the complexes are coupled by moderate antiferromagnetic interactions with J values (H = -2JS₁·S₂) −18.8 and −34.2 cm⁻¹ for 1 and 2, respectively. Electrochemical analyses of 2 reveal that this compound exhibits two-step reduction couples at E_½ = −977 and −1155 mV.