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 [NiII2L(N3)2(H2O)2]·CH3CN (1) and [NiII2L(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 E½ = −977 and −1155 mV.

Graphical abstractSyntheses, molecular and supramolecular structures, electrochemistry and magnetic properties of two diphenoxo-bridged dinickel(II) compounds [NiII2L(N3)2(H2O)2]·CH3CN (1) and [NiII2L(N3)2(H2O)] (2) derived from a tetraimino diphenolate macrocyclic ligand H2L, obtained on [2 + 2] condensation of 4-methyl-2,6-diformylphenol and 2,2′-dimethyl-1,3-diaminopropane, are presented. Compounds 1 and 2 are produced as a function of temperature from the same reaction mixture of the reactants.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Syntheses, structures, and magnetic properties of two diphenoxo-bridged macrocyclic dinickel(II) complexes. ► Formation of two complexes from the same reaction mixture as function of temperature. ► Stabilization of one square pyramidal and one octahedral nickel(II) centers in a symmetrical dinucleating preorganized ligand. ► Weak interaction assisted two-dimensional topologies. ► Antiferromagnetic coupling between metal centers in the title compounds.