Trinuclear Cu^II Complexes Containing Peripheral Ketonic Oxygen Bridges and a μ₃‐OH Core: Syntheses, Crystal Structures, Spectroscopic and Magnetic Properties

Abstract

Four new trinuclear copper(II) complexes, [(CuL1)3(μ3‐OH)](ClO4)2·H2O (1), [(CuL2)3(μ3‐OH)](ClO4)2 (2), [(CuL3)3(μ3‐OH)](ClO4)2·H2O (3), and [(CuL4)3(μ3‐OH)](ClO4)2·H2O (4), where HL1 = 8‐amino‐4,7,7‐trimethyl‐5‐azaoct‐3‐en‐2‐one, HL2 = 7‐amino‐4‐methyl‐5‐azaoct‐3‐en‐2‐one, HL3 = 7‐(ethylamino)‐4‐methyl‐5‐azahept‐3‐en‐2‐one, and HL4 = 4‐methyl‐7‐(methylamino)‐5‐azahept‐3‐en‐2‐one, have been derived from the four tridentate Schiff bases (HL1, HL2, HL3, and HL4) and structurally characterized by X‐ray crystallography. For all compounds, the cationic part is trinuclear with a Cu3OH core held by three carbonyl oxygen bridges between each pair of copper(II) atoms. The copper atoms are five‐coordinate with a distorted square‐pyramidal geometry; the equatorial plane consists of the bridging oxygen atom of the central OH group together with three atoms (N, N, O) from one ligand whereas an oxygen atom of a second ligand occupies the axial position. Magnetic measurements 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 = –66.7 and g = 2.19 for 1, J =–36.6 and g = 2.20 for 2, J = –24.5 and g = 2.20 for 3, andJ = –14.9 and g = 2.05 for 4. EPR spectra at low temperature show the existence of spin frustration in complexes 3 and 4, but it has not been possible to carry out calculations of the antisymmetric exchange parameter, G, from magnetic data. In frozen methanolic solution, at 4 K, hyperfine splitting in all complexes and spin frustration in complex 4 seem to be confirmed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Half‐Integer Spin Triangles: Old Dogs, New Tricks

“…0.6 )i nt he case of hydroxo bridges.I na nother "family" of spin triangles, usually with flexible ligandsl ike Schiff bases, the hydroxo/alkoxo bridge is significantly above the M 3 plane (at least 0.8 )f orming ad efective cubane core. Copper(II) chemistry offers severale xamples, which can be either ferro- [95,96] or antiferromagnetic, [96][97][98][99][100] depending on the relative orientationso ft he copper(II) magnetic orbitals.…”

In Situ Assembled Polynuclear Zinc Oxo Clusters Using Modified Schiff Bases as Ligands

“…The broad band at around 3483 cm –1 in compound 3 is assigned to the OH stretching vibration of the coordinated water molecules, which are involved in hydrogen bonding. 22 …”

“…Sharp, strong, single peaks are observed at 1058.74 and 1054.61 cm –1 for the perchlorate ion present in complexes 3 and 5 , respectively. The broad band at around 3483 cm –1 in compound 3 is assigned to the OH stretching vibration of the coordinated water molecules, which are involved in hydrogen bonding …”