Two Tetranuclear Copper(II) Complexes with Open Cubane‐Like Cu₄O₄ Core Framework and Ferromagnetic Exchange Interactions between Copper(II) Ions: Structure, Magnetic Properties, and Density Functional Study

Abstract

Two alkoxo‐bridged copper(II) tridentate Schiff base complexes [{Cu(H2L1)}4] (1) [H2L1 = N‐(2‐hydroxyethyl)‐3,5‐di‐tert‐butylsalicylaldimine] and {Cu(H2L2)}4 (2) [H2L2 = N‐(2‐hydroxyethyl)‐4‐methoxysalicylaldimine] have been synthesized and structurally and magnetically characterized. X‐ray diffraction studies show that 1 and 2 are tetranuclear alkoxo‐bridged copper(II) complexes that contain a rather distorted Cu4O4 cubane core of 4+2 type (four short and two long Cu···Cu distances). The coordination of each copper ion can be described as a distorted square pyramid with one nitrogen and four oxygen atoms from three ligands. Variable‐temperature magnetic susceptibility measurements on the two tetranuclear complexes 1 and 2 in the range 2–300 K indicate ferromagnetic exchange coupling between copper(II) centers. The magnetic susceptibility data were analyzed by using a simple two‐J model with J′ and J″ representing the magnetic exchange couplings through the short and long Cu···Cu exchange pathways, respectively. The J values were as follows: J′ = +28.7 cm–1 and J″ = +7.8 cm–1 for 1, and J′ = +39.8 cm–1 and J″ = +10.2 cm–1 for 2. The sign and magnitude of the exchange coupling constants were justified on the basis of the structural geometric factors of the bridging Cu(O)2Cu fragments, the overlap of the magnetic orbitals, and DFT calculations.

Designing a heterotrinuclear CuII—NiII—CuIIcomplex from a mononuclear CuIISchiff base precursor with dicyanamide as a coligand: synthesis, crystal structure, thermal and photoluminescence properties

“…The molecular structure and packing diagrams for complex (1) are displayed in Figs. The Cu-N and Cu-O bond lengths are similar to those in the literature (Cristovao et al, 2012;Zhao et al, 2015;Gungor et al, 2014). Both Cu II ions in the trinuclear unit present a distorted square-pyramidal geometry, with = 0.145 for Cu1 and = 0.189 for Cu2 [ = | À |/60 , where and are the two largest angles around the central atom; = 0 and 1 for perfect square-pyramidal and trigonal pyramidal geometries, respectively], where the basal plane is formed by imine atoms N1 and N2, and phenolate atoms O1 and O2 of the Schiff base ligand (Figs.…”

Catecholase and phenoxazinone synthase activities of a ferromagnetically coupled tetranuclear Cu(ii) complex

“…2. 17(3) Â 10 À4 cm 3 per Cu mol, C ¼ 0.435(7) cm 3 K per Cu mol, and q ¼ 16.6 K. From C, the effective moment m eff can be estimated using the For small c 0 , this will lead to 1/ c being linear.…”

Structural and Magnetic Characterization of Two Tetranuclear Cu(II) Complexes with Closed‐Cubane‐Like Core Framework

“…Depending on the distribution of Cu−O bond distances in the cube, Mergehenn and Haase classified cubane of type I and type II . Cu 4 O 4 cubane complexes having four long Cu−O distances between two dinuclear subunits are designated as type I, whereas if the long Cu−O distances are within each dinuclear subunit, cubanes are classified as type II . On the other hand, taking into account the Cu⋅⋅⋅Cu distances within the Cu 4 O 4 cubane unit, Alvarez et al .…”