Closed-shell molecules that ionize more readily than cesium |
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Authors: | Cotton F Albert Gruhn Nadine E Gu Jiande Huang Penglin Lichtenberger Dennis L Murillo Carlos A Van Dorn Laura O Wilkinson Chad C |
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Institution: | Department of Chemistry and Laboratory for Molecular Structure and Bonding, Texas A&M University, Post Office Box 30012, College Station, TX 77842-3012, USA. cotton@tamu.edu |
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Abstract: | 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-pyrimido1,2-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. |
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