Two C 3-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 Cu II compounds, namely [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) (where L stands for fully deprotonated tris (2-hydroxybenzylidene) triaminoguanidinium chloride, H 5 L). 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 Cu 3 triangles (J avg = − 300 cm −1 for Cu 6 and J avg = − 250 cm −1 for Cu 6 Cl), leading to spin-frustrated systems. It is worth mentioning that the electronic structure of each Cu II 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).