Structural evolution and magnetic properties of a series of coordination polymers featuring dinuclear secondary-building units and adamantane- dicarboxylato ligands

A series of coordination polymers, [Cu₂(1,3-adc) ₂(H₂O)₂] (1), [Cu₂(1,3-ada) ₂(H₂O)₂] (2), [M₂(1,3-ada) ₂(4,4′-bpy)] M = Cu (3), Co (4), [Ni₂(1,3-ada) ₂(4,4′-bpy)₂] (5), [Mn₂(1,3-ada) ₂(4,4′-bpy)₂](1,3-adaH₂)(H ₂O)_0.5 (6), and [Ni₂(1,3-adc) ₂(4,4′-bpy)] (7) (1,3-adcH₂ = 1,3- adamantanedicarboxylic acid, 1,3-adaH₂ = 1,3-adamantanediacetic acid, 4,4′-bpy = 4,4′-bipyridine) were synthesized under hydrothermal conditions. Single-crystal X-ray diffraction studies revealed that a majority of these complexes feature a laminated structure based on the cross-linking of dinuclear metal units and organic connectors. Both compounds 1 and 2 feature a Cu^II₂ paddle-wheel secondary-building unit that can be linked by the rigid 1,3-adc or flexible 1,3-ada, forming a linear chain structure in 1 and a rhomboidal net structure in 2. Substituting the apical aqua ligands of 2 for 4,4′-bpy afforded a (4,4) square layer of 3. Replacing Cu^II for Co^II yielded isostructural compound 4. The uses of Ni^II and Mn^II ions in the synthesis of compounds 5 and 6 significantly altered the rhomboidal layer into a different kind of layered structure that features double-helix metal-dicarboxylate chains circumambulating the central 4,4′-bpy pillar. On the other hand, the use of rigid 1,3-adc in replacement of 1,3-ada led to the formation of the 2-fold interpenetrated layer of 7. Magnetic measurements indicated that there exist weak antiferromagnetic interactions in the dinuclear units of compound 5.