Closed-shell molecules that ionize more readily than cesium

F. Albert Cotton, Nadine E. Gruhn, Jiande Gu, Penglin Huang, Dennis L. Lichtenberger, Carlos A. Murillo, Laura O. Van Dorn, Chad C. Wilkinson

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123 Scopus citations


We report a class of molecules with extremely low ionization enthalpies, one member of which has been determined to have a gas-phase ionization energy (onset, 3.51 electron volts) lower than that of the cesium atom (which has the lowest gas-phase ionization energy of the elements) or of any other known closed-shell molecule or neutral transient species reported. The molecules are dimetal complexes with the general formula M2(hpp)4 (where M is Cr, Mo, or W, and hpp is the anion of 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine), structurally characterized in the solid state, spectroscopically characterized in the gas phase, and modeled with theoretical computations. The low-energy ionization of each molecule corresponds to the removal of an electron from the delta bonding orbital of the quadruple metal-metal bond, and a strong interaction of this orbital with a filled orbital on the hpp ligands largely accounts for the low ionization energies.

Original languageEnglish (US)
Pages (from-to)1971-1974
Number of pages4
Issue number5600
StatePublished - Dec 6 2002

ASJC Scopus subject areas

  • General


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