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.