Synthesis, structures and magnetochemistry of binuclear cobalt(II), nickel(II) and copper(II) complexes of 2,6-diformyl-4-methylphenol dioxime
Abstract
Reaction of 2,6-diformyl- and 2,6-diacetyl-4-methylphenol with a large excess of both NH2OH·HCl and CH3CO2K in EtOH affords high yields of 2,6-diformyl-4-methylphenol dioxime (2-hydroxy-5-methylbenzenedicarbaldehyde dioxime) (H3L1) and 2,6-diacetyl-4-methylphenol dioxime (H3L2), respectively. The crystal structure of (H3L2) shows intramolecular hydrogen bonding with long-range intermolecular π-stacking interactions and an extended intermolecular hydrogen-bonding network. The binuclear complexes of CoII, NiII and CuII—[Co2(H2L1)2(MeOH)2(H2O)2]Cl2·2MeOH, [Ni2(H2L1)2(H2O)4][ClO4]2·2H2O and [Cu2(H2L1)2(ClO4)2], respectively—derived from the dioxime ligand (H3L1) have been synthesized and characterised and their single-crystal structures determined. The structure of [Co2(H2L1)2(MeOH)2(H2O)2]2+ shows each high-spin CoII to be six-co-ordinate and bound to an N2O4-donor array presented by two dioxime ligands and axially co-ordinated H2O and MeOH molecules, the dioxime ligands co-ordinating via the imino N- and phenoxy O-donors. The structure of [Ni2(H2L1)2(H2O)4]2+ shows two octahedrally co-ordinated NiII each with an N2O4 donor set similar to that in [Co2(H2L1)2(MeOH)2(H2O)2]2+ except that the co-ordination sphere of each NiII is completed by axial ligation to two H2O molecules. The structure of [Cu2(H2L1)2(ClO4)2] confirms N2O4 donation at CuII with two bidentate ClO4– anions, Cu
· · ·O 2.51(2), 2.76(2) Å, interacting with the metal centres on either side of the planar oxime–phenolate array. In all three complexes the two dioxime ligands are monodeprotonated at the phenolic oxygen, and the oximes are linked by hydrogen bonds, which results in a pseudo-macrocyclic framework. Magnetic susceptibility measurements on the complexes over the range 2.5–340 K confirm that the complexes are antiferromagnetically coupled with values for the magnetic exchange constant J of –6.9 ± 0.1, –16.0 ± 0.6, and –452 ± 4 cm–1 for [Co2(H2L1)2(MeOH)2(H2O)2]Cl2, [Ni2(H2L1)2(H2O)4][ClO4]2 and [Cu2(H2L1)2(ClO4)2], respectively.
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