Magnetostructural Studies on Ferromagnetically Coupled Copper(II) Cubanes of Schiff‐Base Ligands

Abstract

Three cubane copper(II) clusters, namely [Cu(4)(HL')4] (1), [Cu4L2(OH)2] (2), and [Cu4L2(OMe)2] (3), of two pentadentate Schiff-base ligands N,N'-(2-hydroxypropane-1,3-diyl)bis(acetylacetoneimine) (H3L') and N,N'-(2-hydroxypropane-1,3-diyl)bis(salicylaldimine) (H3L), are prepared, structurally characterized by X-ray crystallography, and their variable-temperature magnetic properties studied. Complex 1 has a metal-to-ligand stoichiometry of 1:1 and it crystallizes in the cubic space group P43n with a structure that consists of a tetranuclear core with metal centers linked by a mu(3)-alkoxo oxygen atom to form a cubic arrangement of the metal and oxygen atoms. Each ligand displays a tridentate binding mode which means that a total of eight pendant binding sites remain per cubane molecule. Complexes [Cu4L2(OH)2] (2) and [Cu4L2(OMe)2] (3) crystallize in the orthorhombic space group Pccn and have a cubane structure that is formed by the self-assembly of two {Cu2L}+ units. The variable-temperature magnetic susceptibility data in the range 300-18 K show ferromagnetic exchange interactions in the complexes. Along with the ferromagnetic exchange pathway, there is also a weak antiferromagnetic exchange between the copper centers. The theoretical fitting of the magnetic data gives the following parameters: J1 = 38.5 and J2 = -18 cm(-1) for 1 with a triplet (S = 1) ground state and quintet (S = 2) lowest excited state; J1 = 14.7 and J2 = -18.4 cm(-1) for 2 with a triplet ground state and singlet (S = 0) lowest excited state; and J1 = 33.3 and J2 = -15.6 cm(-1) for 3 with a triplet ground state and quintet lowest excited state, where J1 and J2 are two different exchange pathways in the cubane {Cu4O4} core. The crystal structures of 2 * 6 H2O and 3 * 2 H2O * THF show the presence of channels containing the lattice solvent molecules.

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

“…On the other hand, either negligible or antiferromagnetic values of J 2 have been obtained, in agreement with similar [4+2] cubane compounds previously reported . Nevertheless, this parameter has been often observed to strongly correlate with the J 1 value in the fitting procedure, and thus the J 2 values obtained should be considered with caution.…”

Amphiphilic and Magnetic Properties of a New Class of Cluster‐Bearing [L2Cu4(μ4‐O)(μ2‐carboxylato)4] Soft Materials

“…Both complexes have been exhaustively characterized by spectroscopic and spectrometric techniques and had their structures solved by X-ray crystallography. Since the magnetic properties of multicopper species depends heavily on the cluster geometry, [26] we also investigated the magnetic properties of these complexes both experimentally and by means of molecular calculations. Trying to ascertain the contributions of different magnetic pathways, we present for the first time density functional theory (DFT) calculations on the whole tetracopper core using broken-symmetry approaches.…”

Recent Progress in the Realm of Homonuclear Ln6 Single molecule magnets: Structural Overview and Synthetic Approaches

“…In efforts to craft novel polynuclear lanthanide clusters showing slow relaxation of magnetization, Tang et al achieved an unparalleled hexanuclear dysprosium cluster (11) (Ke et al, 2011) using 1,3-bis(salicylideneamino)-2-propanol (H 3 L) as ligand, which was well-recognized as a versatile chelating and bridging group taking part in the formation of quite a few number of 3d metal clusters (Mukherjee et al 2005;Dhara et al, 2007;Lu et al, 2009). Interestingly, from a structural point of view, complex 11 indicated an unprecedented "edge-to-edge" arrangement of two Dy 3 triangles.…”