Copper(II) complexes of tetradentate thioether-oxime ligands

Two dinuclear copper(II) thioether-oxime complexes ([Cu(DtdoH)]2(ClO4)2 and [Cu(DtudH)]2(ClO4)2 · 2CH3OH) have been synthesized. [Cu(DtdoH)]2(ClO4)2 reacted with excess BF3 · OEt2 to yield [Cu(Thyclops)]ClO4, a BF2+-macrocyclized di-oxime. [Cu(DtdoH)]2(ClO4)2 and [Cu(DtudH)]2(ClO4)2 · 2CH3OH are the first representatives of copper(II) thioether oximes which exhibit the classical out-of-plane oximate oxygen-metal dimer structure. [Cu(DtdoH)]2(ClO4)2 and [Cu(Thyclops)]ClO4 have been structurally characterized by single-crystal X-ray diffraction. The geometry about each copper(II) in [Cu(DtdoH)]2(ClO4)2 is a distorted square pyramid (τ = 0.14). The average copper–nitrogen(oxime) bond length is 1.984 Å longer (∼0.03 Å) than the average copper–nitrogen(oxime) bonds in copper(II) bis-glyoximates. The geometry of [Cu(Thyclops)]ClO4 reveals an almost perfect square pyramid (τ = 0.03) of N2S2O donors. Solution, cryogenic glass, and powder ESR spectra show a typical axial pattern, except for the powder spectrum of [Cu(DtudH)]2(ClO4)2 · 2CH3OH which displays a small rhombic distortion. Variable-temperature magnetic susceptibility measurements indicate very weak ferromagnetic interactions in [Cu(DtdoH)]2(ClO4)2, where J = +0.52 cm−1 and very weak antiferromagnetic interactions in [Cu(DtudH)]2(ClO4)2 · 2CH3OH, where J = −0.59 cm−1. Electrochemical measurements reveal that the mixed thioether-oxime coordination environment tends to stabilize Cu(II), as all electrochemical reductions were quasi-reversible or irreversible. [Cu(Thyclops)]ClO4 is more oxidizing than [Cu(DtdoH)]2(ClO4)2 by 0.14 V.

Graphical abstractTwo dinuclear copper(II) thioether-oxime complexes were synthesized. Macrocyclization of [Cu(DtdoH)]2(ClO4)2 with BF2+ yielded the monomer [Cu(Thyclops)]ClO4. The complexes were characterized by X-ray crystallography, UV–visible and ESR spectrometry. Electrochemical measurements indicate that this class of ligands stabilizes copper(II). The dinuclear complexes were additionally characterized by VT magnetometry. Very weak ferromagnetic exchange is the dominating interaction in the dinuclear complexes.Figure optionsDownload full-size imageDownload as PowerPoint slide