Synthesis, crystal structures and magnetic properties of picolinate-bridged copper(II) chains

The paper reports the synthesis, crystal structures, and magnetic properties of two copper(II) coordination polymers, Cu₂(L₁)₄ (1) and Cu₃(L₂)₆ (2), based on rigid ethynylene-bridged ditopic ligands containing one picolinate subunit (L₁ = 5-(pyridin-3-ylethynyl)picolinate anion; L₂ = 5-((4-(methoxycarbonyl)phenyl)ethynyl)picolinate anion). Both 1 and 2 have a chain structure. In 1, the repeating unit in the chain is a doubly bridged picolinate dicopper(II) complex, whereas 2 is built upon trimeric units where the Cu²⁺ ions are also connected by double picolinate bridges. Both compounds exhibit antiferromagnetic interactions in the solid state. The magnetic properties of 1 and 2 were analyzed in terms of simple dimer (H = –2JS_CuS_Cu) and linear trimer [H = –2J(S_Cu1S_Cu2+S_Cu2S_Cu1)] models, respectively, neglecting the intermolecular interactions between the polynuclear units. The values of the exchange coupling parameters were J = −0.59 and J = –0.30 cm⁻¹ for 1 and 2, respectively.