Trinuclear Cu(II) complexes containing peripheral ketonic oxygen bridges and a μ3-OH core: Steric influence on their structures and existence

Two tridentate Schiff bases, HL1(6-amino-3-methyl-1-phenyl-4-azahex-2-en-1-one), and HL2 (6-amino-3,6-dimethyl-1-phenyl-4-azahex-2-en-1-one) on reaction with Cu(II) perchlorate in the presence of triethyl amine yielded two new trinuclear copper(II) complexes, [(CuL1)3(μ3-OH)](ClO4)2 (1) and [(CuL2)3(μ3-OH)](ClO4)2 · 0.75H2O (2), whereas another tridentate ligand HL3 (7-amino-3-methyl-1-phenyl-4-azahept-2-en-1-one) underwent hydrolysis under the same reaction conditions to result in the formation of a mononuclear complex, [Cu(bn)(pn)ClO4] (3) [where bn = 1-benzoylacetonate and pn = 1,3-propanediamine]. All three complexes have been characterized by X-ray crystallography. For both 1 and 2 the cationic part is trinuclear with a [Cu3OH] core held by three carbonyl oxygen bridges between each pair of copper(II) atoms. The structure of 3 is a monomer with a chelating 1,3-propanediamine and a benzoyl acetone moiety. Magnetic measurements of 1 and 2 have been performed in the 2–300 K temperature range. The experimental data could be satisfactorily reproduced by using an isotropic exchange model, H = −J(S1S2 + S2S3 + S1S3), yielding as best fit parameters: J = −25.6 cm−1, g = 2.21 for 1 and J = −11.2 cm−1, g = 2.10 for 2. The EPR spectra at low temperature could be indicative of spin frustration in complex 1.

Two trinuclear copper(II) complexes, [(CuL1)3(μ3-fOH)](ClO4)2 (1) and [(CuL2)3(μ3-OH)](ClO4)2 · 0.75H2O (2), where HL1 and HL2 are two tridentate Schiff base ligands derived from mono condensation of 1-benzoylacetone with 1,2-ethanediamine and 1,2-propanediamine, respectively, and a mononuclear complex, [Cu(bn)(pn)]ClO4 (3), where bn = 1-benzoylacetonato and pn = 1,3-propanediamine, have been synthesized and structurally characterized. Variable-temperature magnetic susceptibility measurements reveal antiferromagnetic coupling in complexes 1 and 2.Figure optionsDownload as PowerPoint slide