I understand that Be2 cannot exist, since it has as many electrons in the antibonding as in the bonding orbitals.

But it seems to me that since the next electron would go into the πu orbital, which is a bonding orbital, Be2- would have a bond order of 0.5, and Be22- would have a bond order of 1, since it would have 4 in bonding (2 in σ and 2 in π)and only 2 in the σ*.

Could Be2- or Be22- at least theoretically be produced? In other words, would the energy released by forming a bond be sufficient to counterbalance the energy needed to stabilize the negative charge gained?

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    $\begingroup$ While it is perfectly fine the way you have formatted your question, we also have MathJax available. If you are curious, please have a look here and here. For the matter at hand, I'd say your reasoning is sound; I wouldn't be too sure about whether one electron is already too much. Anyway, you might find this publication interesting: 10.1126/science.1174326 (it is about the neutral dimer though). Judging from 10.1002/qua.20633, it seems to be stable. $\endgroup$ Commented Dec 14, 2018 at 18:01


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