[4-K2(BEt3)]2 is extremely reactive, particularly in solution, and has limited solubility in compatible solvents; as such, it can be characterized by 1 H NMR spectroscopy and X-ray crystallography only. The centro-symmetric structure revealed crystallographically reveals four K + cations encapsulated by a combination of O-atom and aryl p system ligation. Two molecules of triethylborane are also incorporated into the molecular framework, bound to the terminal O-atoms of the [C4O4] .