Assembly of trinuclear and tetranuclear building units of Cu²⁺ towards two 1D magnetic systems: synthesis and magneto-structural correlations

Abstract

Two new 1D coordination polymers, [Cu₃(μ₃-OH)(ppk)₃(μ-N(CN)₂)(OAc)]_n (1) and {[Cu₄(pdmH)₂(pdm)₂(μ₂-OH)(H₂O)].ClO₄}_n (2) based on two different blocking ligands phenyl-2-pyridylketoxime (ppk) and pyridine-2,6-dimethanol (pdmH₂) have been synthesized and were characterized by X-ray single crystal structural analysis. In compound 1, the hydroxido-bridged trinuclear core, {Cu₃(µ₃-OH)(ppk)₃(OAc)}, acts as secondary building units and are connected by the N(CN)₂- anions resulting in a one dimensional (1D) coordination polymer. The 1D coordination chains undergo π-π interactions giving rise to a 3D supramolecular framework. In compound 2, tetrameric [Cu₄(pdmH)₂(pdm)₂(H₂O)]²⁺ cores are linked via hydroxido groups forming a zigzag 1D coordination chain where non-coordinated ClO₄^- ions are intercalated between the chains. Variable temperature magnetic susceptibility study of 1 suggests that Cu(II) ions in the trinuclear Cu₃(µ₃-OH) cores are antiferromagnetically coupled with J = -459.7 cm^-1 and g = 2.11 and the trinuclear cores are further weakly coupled antiferromagnetically (zj' = -5.25 cm^-1) through the N(CN)₂^- bridging ligand. Investigation of the magnetic properties of 2 reveals that Cu(II) ions are coupled antiferromagnetically in the tetranuclear core with J = -27.1 cm^-1 and g = 2.17; the Cu^II₄ building units are further coupled antiferromagnetically with zj' = -9.65 cm^-1. The experimental magnetic behaviours of 1 and 2 are correlated by first principle DFT calculations which provide a qualitative understanding of the origin of antiferromagnetic interactions in both cases.