Cis and trans linkage of spin frustrated copper triangles creating Cu6 clusters

Abstract

Two C3-symmetric guanidine-based copper triangles bridged by acetates in a cis manner and by chloride anions in a trans manner, respectively gave rise to two antiferromagnetically coupled hexanuclear CuII compounds, namely [Cu6L2Cl(μ-OAc)(DMF)3]·DMF (Cu6) and [Cu6L2(μ-Cl)2(DMF)4] (Cu6Cl)(where L stands for fully deprotonated tris (2-hydroxybenzylidene) triaminoguanidinium chloride, H5L). The experimental magnetic data of the two compounds were analyzed theoretically. A relatively good agreement with the experimental data was obtained when using the wavefunction theory (CASSCF) in combination with DFT (B3LYP) calculations for the very strong antiferromagnetic coupling within the Cu3 triangles (Javg = − 300 cm−1 for Cu6 and Javg = − 250 cm−1 for Cu6Cl), leading to spin-frustrated systems. It is worth mentioning that the electronic structure of each CuII center remains very similar in each complex with a Kramers ground state well separated from the first excited state (over 12000 cm−1) and weakly anisotropic (g∥ ≈ 2.40 and g⊥ ≈ 2.10).

A Cu12 Metallacycle Assembled from Four C3-Symmetric Spin Frustrated Triangular Units

“…where the magnetic moments and magnetic coupling constants of each Cu II center were obtained from the WFT and DFT calculations, respectively. It is worth noting that the validity of such a computational strategy has been successfully confirmed on a related trinuclear copper(II) complex [39] and closely related Cu6 and CuCl6 complexes [41].…”

“…Both complexes exhibit strong antiferromagnetic coupling between the copper(II) ions, leading to a spin-frustrated system. Very recently, by fluctuating the synthetic approach while keeping the same metal-ligand combination, we synthesized two new antiferromagnetic hexa-nuclear Cu II complexes, [Cu 6 L 2 Cl(µ-OAc)(DMF) 3 ]•DMF (Cu 6 ) and [Cu 6 L 2 (µ-Cl) 2 (DMF) 4 ] (Cu 6 Cl), in which two planar triangles with strict C 3 -symmetry were deliberately bridged through acetate and chloride anions in cis and trans fashions, respectively [41]. It was assumed that both Cu 6 and Cu 6 Cl would also present the phenomenon of spin frustration based on their similar structural and experimental magnetic properties to the reference compounds, Cu 3 py and Cu 3 bpy.…”