Crystal and molecular structure and magnetic properties of a tetrameric copper(II) complex with 3-hydroxy-5-hydroxymethyl-4-(4′-hydroxy-3′-methyl-4′-phenyl-2′-azabut-1′-en-1′-yl)-2-methylpyridine (H2L) : [Cu4L4]·8MeOH, a complex with a ferromagnetic ground state

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Abstract
The crystal and molecular structure of the title compound has been determined from single-crystal X-ray diffraction data and refined to a final R value of 0.053 using 2 514 independent reflections. The compound belongs to the space group P42/n of the tetragonal system with two tetrameric molecules in a unit cell of dimensions a= 17.226(4) and c= 14.667(3)Å. The tetrameric unit with a Cu4O4 core is of S4 symmetry. Copper–copper distances are 3.481(1)(two), 3.259(1)Å(four) and Cu–O distances are 1.945(4)(four), 2.734(4)(four), and 1.977(4)Å(four). The co-ordination about the copper atom is distorted square pyramidal with copper bonded to phenolic oxygen O(2), imine nitrogen N(1), and three alkoxo-oxygen atoms O(1). The complex crystallizes with 16 methanol molecules per unit cell. It easily loses in air the methanol molecules of crystallization giving an amorphous powder. The magnetism of the crystallized complex can be explained on the basis of the isotropic Heisenberg–Dirac–van Vleck model. Taking into account intercluster interactions, the fitting procedure yielded the values g= 2.12, J13= 17.1 cm–1, θ=–1.1 K. These parameters indicate a predominance of ferromagnetic interactions with a quintet ground state (S′= 2). The magnetic behaviour of the amorphous powder is quite different and shows weak antiferromagnetic interactions.

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