This material consists of a pair of tungsten centers linked by the conjugate base of four hexahydropyrimidopyrimidine (hpp) ligands.

The molecule is of research interest because it has the lowest ionization energy (3.51 eV) of all stable chemical elements or chemical compounds as of the year 2005.

[1] This value is even lower than of caesium with 3.89 eV (or 375 kJ/mol) located at the extreme left lower corner of the periodic table (although francium is at a lower position in the periodic table compared to caesium, it has a higher ionization energy and is radioactive) or known metallocene reducing agents such as decamethylcobaltocene with 4.71 eV.

Dichlorobenzene provides the chlorine atoms and is itself reductively coupled to 2,2′-dichlorobiphenyl.

Because of its low ionization energy, W2(hpp)4 is easily oxidized back to the dichloride by dichloromethane.