Isomeric Molecular Rectangles Resulting from Self-Assembly of Dicopper Complexes of Macrocyclic Ligands

Dinuclear copper complexes containing hexaazacyclophane macrocyclic ligands react with the disodium salt of terephthalic acid resulting in the self-assembly of rectangular molecules with the general formula [(Cu₂L)₂(p-(O₂CC₆H₄CO₂)₂)]X₄, where X = CF₃SO₃ and ClO₄ (3X₄, L = Me2p and 4X₄, L = Me2m). Tetranuclear complexes 3(CF₃SO₃)₄ (as polymorphs 3a and 3b) and 4(ClO₄)₄ have been characterized by single-crystal X-ray diffraction analysis providing definitive proof of their structure as well as their metrical parameters. 3a contains, in its unit cell, two isomeric cationic units (3asyn and 3aanti) that differ in the relative position of the two O carboxylate atoms which bind to the Cu atoms of the different macrocyclic complexes, leading to boxes with different metrical parameters. ESI-MS analyses of solutions of the tetranuclear complexes 3(CF₃SO₃)₄ and 4(CF₃SO₃)₄ exhibit cluster ions which match the solid state formulation, thus demonstrating that the cages are retained in solution.