Synthesis and structure of a Cu4O4 cubane core complex from a carboxylate ligand containing a strong π⋯π stacking supramolecular synthon

The reaction of the bifunctional ligand (1,8-naphthalimido)butanoate (LC3−) with Cu2(O2CCH3)4(H2O)2 in the presence of 1,2-bis(4-pyridyl)ethylene (BPE) leads to the formation of a novel tetranuclear complex, [Cu4(OMe)4(MeOH)(LC3)4(BPE)], containing a Cu4O4 cubane type core. The copper(II) centers are triply bridged by four methoxide (CH3O−) anions and the carboxylato oxygen atoms of two LC3− ligands. The BPE ligands covalently link the tetranuclear units forming a coordination polymer. The strong π⋯π stacking 1,8-naphthalimide groups organize these polymeric chains into a three-dimensional supramolecular structure. The flexibility imparted by the LC3− ligand allows the formation of a unique architecture, where each polymeric chain is connected to three other chains by the π⋯π stacking interactions of the naphthalimide rings. The structure is a novel example of a supramolecular metal–organic framework (SMOF) solid and demonstrates the viability of the π-association of the naphthalimide rings as an organizing synthon for crystal engineering.

Graphical abstractA bitopic ligand containing the carboxylate donor and π-stacking naphthalimide groups forms a tetrameric copper(II) cubane complex with these units linked into a coordination polymer by 1,2-bis(4-pyridyl)ethylene. The polymer is organized into a supramolecular metal–organic framework structure by π⋯π stacking interactions on both sides of the naphthalimide rings.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Bifunctional carboxylate ligand forms a novel tetranuclear copper(II) complex. ► 1,2-Bis(4-pyridyl)ethylene links tetranuclear units forming a coordination polymer. ► Strong π⋯π stacking of 1,8-naphthalimide groups organizes supramolecular structure. ► Structure is a novel example of a supramolecular metal–organic framework (SMOF) solid.