An exploration of the solid-state architectures formed by 1,8-naphthyridine-2,7-dicarbonyl derivatives
Building on previous studies of tape formation by dicarbonyl substituted pyridine derivatives in the solid state, it was proposed that expansion of the hydrogen bonding array from three donor-acceptor pairs to four should increase the strength of the hydrogen-bonded array. Accordingly an investigation into the 1,8-naphthyridine-2,7-dicarbonyl derivatives has now been undertaken. Following the synthesis of 1,8-naphthyridine-2,7-dicarboxylic acid, during which the solid-state structures of three key intermediates were obtained, thirty-five novel 1,8-naphthyridine-2,7-dicarboxylates and fourteen novel 1,8-naphthyridine-2,7-dicarboxamides have been synthesised. Solid-state structures have been obtained for thirty-two of these derivatives confirming that the hydrogen bonding motifs observed for the dicarbonyl-substituted pyridines are also adopted by their naphthyridine analogues. In the diesters the familiar one-dimensional taping motif was observed, with additional secondary interactions, caused by the substitution on the pendent arm, influencing the packing of these structural units. For the corresponding diamides, intramolecular hydrogen bonding was found to organise the molecules into a cleft arrangement. Additionally an initial investigation into the solid-state motifs observed upon co-ordination to a metal centre has been carried out. A number of novel pyridine-2,6-dicarbonyl derivatives have also been synthesised and their solid-state behaviour has been studied. One of these structures is thought to be only the second known non-tape-forming pyridine-2,6-dicarboxylate. Finally the successful synthesis of 4,4’-linked pyridine-2,6-dicarboxamides has been achieved, the latter offering the potential for forming extended networks through co-ordination around metal centres
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