Spin-frustration with two quasi-degenerated spin states of a copper() heptanuclear complex obtained from an amino acid ligand

The Cu( ii ) heptanuclear complex ( Cu 7 atac ) was synthesised using the hydrated amino acid ligand 2-(5-amino-1 H -1,2,4-triazol-3-yl)acetic acid (Hatac·H 2 O). Single crystal X-ray diffraction analysis revealed a μ 3 -hydroxo bridged Cu( ii ) heptanuclear complex, consisting of two triangular subunits and one Cu( ii ) ion as a bridge with the formula [Cu 7 (atac) 6 (μ 3 -OH) 2 (NO 3 ) 2 (H 2 O) 10 ](NO 3 ) 4 . The magnetic behaviour of this discrete 0D complex shows strong antiferromagnetic couplings between Cu( ii ) mediated by N,N bonding and an anti - anti modes of the carboxylate anion of the ligand atac − . The magnetic data were fitted considering a 3 J model. To support the model used to fit the magnetic data of the Cu 7 atac complex, theoretical calculation methods (complete active space self-consistent field, CASSCF, density functional theory (DFT) using the UKS TPSS/Def2-TZVP//Def2-SVP level and periodic boundary conditions (PBC) using PBE/DZVP-MOLOPT-GTH) were performed to obtain the spin states, spin density map and J couplings. The theoretical results suggest that Cu 7 atac is a spin-frustrated complex in the ground state, in which the doublet spin state co-exists with the quartet spin state. A Cu( ii ) heptanuclear complex, Cu 7 atac , synthesized from an amino acid ligand showed to be an antiferromagnetic spin-frustrated bis-triangular system. Cu 7 atac might be a promising qubit candidate for quantum information storage.