Solvent coligands fine-tuned the structures and magnetic properties of triple-bridged 1D azido-copper(ii) coordination polymers

Abstract

Based on different alkanol solvents, a family of azido–copper coordination polymers has been successfully synthesized. The as-synthesized compounds share the formula [Cu(4-tfmba)(N₃)(solvent)]_n, where 4-tfmba = 4-trifluoromethyl benzoic acid and solvent = CH₃OH (1), C₂H₅OH (2) and C₃H₇OH (3). Single-crystal structure analysis indicates that the Cu(II) centers in 1–3 are interconnected by an alternant triple-bridge of μ-1,1-azido, syn,syn-carboxy and μ2-alkanols, yielding homoplastically well-isolated 1D metal-chain patterns with tiny disparities in the geometric parameters. Noteworthily, the homologous alkanol solvents with growing carbon chain are not only the reaction solvents but are also employed to be the linkers to embed the structural frameworks of the resulting polymers, regulating in an orderly way the interchain structures and thus fine-tuning the magnetic behaviors of the resulting compounds. As a result, the predominant intrachain ferromagnetic exchanges caused by counter-complementarity of the threefold super-exchange channels are revealed in all three cases, finally giving rise to the ascending magnitudes of magnetic coupling effect (J = 56.21 cm⁻¹ for 1, J = 68.94 cm⁻¹ for 2 and J = 77.94 cm⁻¹ for 3) and the well-organized scenarios of magnetic order and slow relaxation that are infrequent in known azido–Cu(II) coordination networks. Among 1–3, the exchange of CH₃OH for C₂H₅OH or C₃H₇OH, all of which coordinate through a single O atom, induces an interesting dynamic magnetic transition from a vitreous state to quasi-superparamagnet. Moreover, DFT calculations have been carried out to provide a qualitative and quantitative theoretic explanation of the magnetic behaviors of 1–3.