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(<bold>L</bold><bold>1</bold>)4 (<bold>1</bold>) and Cu3(<bold>L</bold><bold>2</bold>)6 (<bold>2</bold>), based on rigid ethynylene-bridged ditopic ligands containing one picolinate subunit (<bold>L</bold><bold>1</bold> = 5-(pyridin-3-ylethynyl)picolinate anion; <bold>L</bold><bold>2</bold> = 5-((4-(methoxycarbonyl)phenyl)ethynyl)picolinate anion). Both <bold>1</bold> and <bold>2</bold> have a chain structure. In <bold>1</bold>, the repeating unit in the chain is a doubly bridged picolinate dicopper(II) complex, whereas <bold>2</bold> 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 <bold>1</bold> and <bold>2</bold> were analyzed in terms of simple dimer (<bold>H</bold> = -2<italic>J</italic><bold>S</bold><bold>Cu</bold><bold>S</bold><bold>Cu</bold>) and linear trimer [<bold>H</bold> = -2<italic>J</italic>(<bold>S</bold><bold>Cu1</bold><bold>S</bold><bold>Cu2</bold>+<bold>S</bold><bold>Cu2</bold><bold>S</bold><bold>Cu1</bold>)] models, respectively, neglecting the intermolecular interactions between the polynuclear units. The values of the exchange coupling parameters were <italic>J</italic> = −0.59 and <italic>J</italic> = -0.30 cm−1 for <bold>1</bold> and <bold>2</bold>, respectively. [ABSTRACT FROM AUTHOR]