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Just as $\ce{HArF}$ was synthesized...Could something like $\ce{Li-Ar-Li}$ exist with AXE geometry $\ce{AX2E3}$? Any other argon compound proposals out there?

I also know that there are some posible excimers like $\ce{LiAr}$ and $\ce{KrF} (maybe $\ce{KrF2}$). Can they be considered covalent compounds, even if explained via excited dimers/excimers or the OM theory (recall the technical name for lithium-doped argon matrices in the chemical literature)?

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ArBeO and ArBeS are experimentally known.

ArAuF, ArAgF and ArCuF are also experimentally known.

CUOAr$_n$ and related complexes are known.

ArBeNCN and ArBeNBO are predicted by theory.

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  • $\begingroup$ But, could be Li-Ar-Li (AX2E3, linear molecule, trigonal bipyramid orbital) possible or not? Theoretically, at least... $\endgroup$ – riemannium Jun 16 '14 at 15:23
  • $\begingroup$ Lithium is very electropositive, so it tends not to form covalent bonds. $\endgroup$ – DavePhD Jun 16 '14 at 15:50
  • $\begingroup$ Hydrogen is also electropositive...And we have HArF and, as well, excimer-like Li-Ar (but unstable) compounds. IN the Pauling scale, H is 2.3 and lithium 0.9. I mean, couldn't it be possible? I am not asking if it is hard (likely), but even if electronegativity is LOW, I can not see why it could not be possible in certain extreme conditions such a bond... Of course, lithium doped argon excimers are something different to my idea. $\endgroup$ – riemannium Jun 16 '14 at 17:45
  • $\begingroup$ And I understand, even if they have special features, ionic bonds like "very polar" covalent bonds...Theoretically, what would forbid a Li-Ar-Li "molecule"? Example: journals.aps.org/pr/abstract/10.1103/PhysRev.179.19 $\endgroup$ – riemannium Jun 16 '14 at 17:51
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    $\begingroup$ If the 2 elements being considered have an electronegativity difference of >1.7, a covalent bond will not form. The Allen electronegativity of Ar is 3.24 and of Li is 0.91. The references to LiAr you cite are van der vaals molecules not covalent molecules. Li-Li has an electronegativity different of zero. The sodium reference is Na+, not neutral Na, and says the same type of cluster forms for Li+ with Ar. $\endgroup$ – DavePhD Jun 16 '14 at 19:13

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