Cooperative lone pair-π and coordination interactions in naphthalene diimide coordination networks

Lone pair-pi interaction is an important but less studied binding force. Naphthalene diimides (NDIs) are ideal to form such an interaction because their quadrupole moment is exceptionally positive. Here, we report the combination of NDI ligands bearing two divergently oriented pyridyl units with different metal nitrates in different solvents resulting in six neutral 1-D coordination networks, in which the nitrate anions not only serve as capping ligands to coordinate to metal centers but also provide lone pairs to interconnect with the p-acidic NDI ligands through lone pair-pi interactions. Interestingly, such lone pair-pi interactions are found to have a synergic effect on the coordination interactions of the aforementioned NDI ligands with metal ions. In other words, metal-ion-directed self-assembly of NDI ligands is supposed to be driven by cooperative lone pair-pi and coordination interactions.