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, [Cu-2(1,3-adc)(2)(H2O)(2)] (1), [Cu-2(1,3-ada)(2)(H2O)(2)] (2), [M-2(1,3-ada)(2)(4,4'-bpy)] M = Cu (3), Co (4), [Ni-2(1,3-ada)(2)(4,4'-bpy)(2)] (5), [Mn-2(1,3-ada)(2)(4,4'-bpy)(2)](1,3-adaH(2)) (H2O)(0.5) (6), and [Ni-2(1,3-adc)(2)(4,4'-bpy)] (7) (1,3-adcH(2) = 1,3-adamantanedicarboxylic acid, 1,3-adaH(2) = 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 I and 2 feature a Cu-2(II) 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. (C) 2012 Elsevier Ltd. All rights reserved.