Crystal and molecular structure and magnetic properties of a tetrameric copper(II) complex with 3-hydroxy-4-[4′-(3″,4″-dichlorophenyl)-4′-hydroxy-2′-azabut-1′-en-1′-yl]-5-hydroxymethyl-2-methylpyridine (H2L2), [(CuL2)4]·9CH3OH

Abstract

The crystal and the molecular structure of the title compound has been determined using three-dimensional X-ray diffractometer data involving 7 045 independent reflections. The compound crystallizes in the monoclinic space group I2/c with eight formula units [(CuL²)₄]·9CH₃OH in a unit cell with dimensions a= 27.062(5), b= 25.062(5), c= 26.390(5)Å, and β= 92.39(1)°. The structure has been calculated by direct methods and refined by least-squares methods to a final R value of 0.054. In the cubane structure (C₁ symmetry) each copper atom is bonded to one deprotonated phenolic oxygen, one imine nitrogen, and three deprotonated alkoxo-oxygen atoms giving a distorted square-pyramidal co-ordination. The six copper–copper distances are in the range 3.021(1)–3.492(2)Å(mean 3.254 ± 0.184 Å). Within the Cu₄O₄ core there are eight shorter copper–oxygen distances [1.917(5)–2.057(5)Å, mean 1.983 Å] and four longer ones [2.327(5)–2.690(6)Å, mean 2.496 ± 0.166 Å]. There are 72 methanol molecules per unit cell which are easily lost in air, giving an amorphous powder. The magnetic properties of the complex can be explained using the isotropic Heisenberg–Dirac–van Vleck model. The exchange parameters for the complex with approximate S₄ symmetry obtained (J₁₂=–9.9 ± 3.0 cm^–1, J₁₃= 20.5 ± 3.0 cm^–1, and g= 2.08 ± 0.02) are in good agreement with those of similar substances and show the presence of both ferromagnetic and antiferromagnetic interactions. The amorphous modification shows a predominant ferromagnetic interaction.