Search

In methanol, the reaction of Cu(ClO(4))(2).6H(2)O and a sterically constrained piperazine imine phenol ligand (H(2)L), in the presence of NEt(3), affords a novel tetranuclear copper(II) complex of formula [Cu(II)(4)(mu(3)-L)(2)(mu-OH)(2)(H(2)O)(2)](ClO(4))(2).H(2)O (1). The X-ray structure of this complex shows an elongated Cu(4) quasi-tetrahedron coordinated to two hexadentate chair-(e,a)-mu(3)-piperazine bridging ligands. Variable-temperature magnetic studies show an S(t) = 0 spin ground state resulting from antiferromagnetic interactions between Cu(II) ions within the complex.

Abstract: The N4O3 coordinating heptadentate imidazolidinyl phenolate ligand, H3L (2-(2′-hydroxyphenyl)-1,3-bis[4-(2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine) forms with Cu(II) a rare aqua bridged complex [{Cu2(μ-L)(μ-H2O)}2](ClO4)2 ·4.5H2O (1 ·4.5H2O). Complex 1 ·4.5H2O contains two crystallographically different but chemically equivalent dinuclear [Cu2(μ-L)(μ-H2O)]+ cationic units in the asymmetric unit. The copper atoms of each dinuclear unit are in a distorted square-pyramidal environment and are held together by phenolate, imidazolidinyl and aqua bridges with a Cu···Cu separation of av. 3.34Å. The compound exhibits a very weak antiferromagnetic exchange interaction (J =−0.77cm−1, Ĥ = −2 J Ŝ 1 Ŝ 2) between the two copper(II) (S =1/2) ions. The 1H NMR spectrum of the complex shows a total of 17 hyperfine shifted peaks, as expected from the idealized Cs symmetry of the compound, spread over a very large window of chemical shift, spanning about 250ppm. The complex, having an appropriate intermetallic separation for catechol binding, shows catecholase like activity in MeCN at 25°C, with the aerobic oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) to 3,5-di-tert-butylquinone (3,5-DTBQ). [Copyright &y& Elsevier]

Abstract: Reaction of Cu(ClO4)2 ·6H2O with dimethylglyoxime (H2dmg) and triethylamine (pH∼4–5) at room temperature affords oxime bridged dicopper(II/II) complex of formula [Cu2(μ-Hdmg)2(Hdmg)]ClO4 ·H2O (1) (H2dmg=dimethylglyoxime). The complex has been characterized by single-crystal X-ray diffraction analysis. The structure consists of one dinuclear complex cation, [Cu2(μ-Hdmg)2(Hdmg)], and one anion. Two copper(II) ions at a distance of 3.558 Å are bridged by one oxime and one oximate groups in cis arrangement. The geometry around each copper atom is square planar with an overall open-book type arrangement of these planes. The average copper–oxygen distance is (1.953 Å) and the average copper-nitrogen distance is 2.003 Å. The Cu–O(oxime) distance (1.963 Å) is higher than the Cu–O(oximate) distance (1.942 Å) due to different protonation label. The room temperature value of χ M T for the title complex (χ M being the molar magnetic susceptibility for two copper atoms) is low (ca. 0.42 cm3 K mol−1) (μ eff =1.52 μ B). The UV–Vis spectrum of the complex shows a characteristic broad band at 470 nm. [Copyright &y& Elsevier]