Synthesis, Crystal Structures, and Magnetic Properties of Dinuclear and Hexanuclear Copper(II) Complexes with Cyclam-Based Macrocyclic Ligands Having Four Schiff-Base Pendant Arms

Abstract

Reaction of a series of dodecadentate ligands (H4L), 1,4,8,11-tetrakis(salicylideneaminoethyl)-1,4,8,11-tetraazacyclotetradecane and its substituted derivatives, with copper(II) salts afforded dinuclear copper(II) complexes, [Cu2L], which were characterized by IR and UV–vis–NIR spectroscopy, and temperature dependence of magnetic susceptibilities (4.5–300 K). Single-crystal X-ray crystallography of these complexes revealed that each copper(II) ion is bound by the chelating of the two Schiff-base pendant arms outside the central tetraazacyclotetradecane ring forming a distorted square plane with an intramolecular Cu–Cu distance of 8.692(2)–8.949(2) Å. In accordance with the crystal structures, the magnetic interaction between the two copper(II) atoms is very weak. In the case of 1,4,8,11-tetrakis(3-methoxysalicylideneaminoethyl)-1,4,8,11-tetraazacyclotetradecane (H4tmsaec), a hexanuclear complex with a crystallographic inversion center, [Cu6(O2CCH3)8(tmsaec)], was isolated. In the asymmetric unit, one copper atom is bonded to one pendant arm and two copper atoms are bound to another pendant arm with the methoxy group of the Schiff-base moiety with the Cu–Cu distance of 3.096(1) Å, giving a novel system containing monodentate, bidentate, and bridging acetate ions in the same molecule. Magnetic susceptibility data shows that a weak antiferromagnetic interaction is operating between the closest two copper atoms.

Dinuclear Nickel(II) Pivalate with Μ-Aqua and Di-Μ-Pivalato Bridges Showing a Ferromagnetic Interaction

“…The  values of ν as (CO 2 ) -ν s (CO 2 ), 1607 -1362 = 245 cm -1 and 1482 -1407 = 75 cm -1 , are in the ranges of monodentate and syn-syn bridging pivalato, respectively [7,13,14] (Figure 2). The shoulder bands at 3350 and 3140 cm -1 in 1 may be attributed to ν(OH) stretching bands of pivalic acid and water molecules [13].…”

Tetranuclear Nickel(II) Complex with an Unsymmetrical Pentadentate Schiff-base Ligand Having a Defective Double-Cubane Core

“…[1][2][3][4][5][6] In the case of dinucleating Schiff-base ligands having a bridging group, such as alkoxido-oxygen, many dinuclear metal complexes were prepared and their magnetic properties were investigated. [3][4][5][6] Most of these dinucleating ligands are symmetrical concerning the bridging group, and afford dinuclear metal complexes with the same geometry for the two metal centers. On the other hand, metal complexes with unsymmetrical Schiff base-ligands are relatively few.…”

Synthesis, Crystal Structure, and Properties of Copper(II) Complexes with 1,4,7-Tris(2-Aminoethyl)-1,4,7-Triazacyclononane

“…In the crystal, the protonated amino nitrogen atom N4 is surrounded by four perchlorate-oxygen atoms by hydrogen bonds [N4···O3 (x, y, 1 + z) 2.965 Å, N4···O7 (x, y, 1 +z) 3.065 Å] (Figure 4). The magnetic moment of 1 is 1.96 μ B at 300 K. This value is larger than the spin-only value of copper(II) (1.73 μ B , S = 1/2), being typical for the octahedral copper(II) complexes due to spin-orbital coupling with the excited T state [18]. The moment decreases slightly with the lowering of temperature, reaching a value of 1.86 μ B at 4.5 K. In Figure 5, magnetic susceptibilities and inverses of magnetic susceptibilities of 1 were plotted versus temperature.…”

“…The taec ligand forms unique dinuclear metal complexes, where the two metal ions are bound by the four pendant groups outside the cyclam ring. Substitution of the 2-aminoethyl pendant groups by other groups such as salicylideneaminoethyl groups also afforded similar dinuclear metal complexes [17][18][19][20]. Concerning these cyclam-based ligands with four pendant groups, the corresponding tacn-based hexadentate ligands with three pendant groups are of interest [21][22][23].…”