Iso-valence Co(II) and mixed-valence Co(II/III) tetranuclear complexes: Synthesis, structure, magnetic properties and DFT study

Abstract

The reaction of Co(ClO4)2·6H2O with symmetrical N4O3 coordinating heptadentate ligand (H3L) in presence of triethylamine yielded cobalt(II) tetranuclear complexes [Co4(L)2](ClO4)2, 1. When the same reaction is carried out with sodium azide instead of triethylamine afforded tetranuclear mixed-valence Co(II/III) species, [Co4(L)2(μ1,3–N3)2](ClO4)2, 2. Here L3− is the deprotonated form of 2,6-bis[{{(1-hydroxy-2-methylpropan-2-yl)(pyridine-2-ylmethyl)}amino}methyl]-4-methylphenol. Complex 1 crystallizes in the cubic system, space group Fd-3c, with unit-cell parameters a=b=c=43.320(5)Å, Z=48, whereas complex 2 crystallizes in the space group I41/a in the tetragonal crystal system with Z=8 and unit-cell parameters a=b=16.3243(15)Å, c=50.093(4)Å. The X-ray structures of 1 and 2 have revealed a CoII4O6 core in 1 and a [CoII2CoIII2O2(μ1,3–N3)2] core in 2. Tetranuclear Co(II) compound shows interesting magnetic property and exhibit antiferromagnetic interaction between the paramagnetic centers. Density functional theory has been used to justify the exchange pathways for 1. Exchange coupling in the mixed valence cobalt complexes studied is insignificant, due to the large distances of separation of the Co(II) centers in tetranuclear units.