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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)?

Oscar Lanzi
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riemannium
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  • Related: http://chemistry.stackexchange.com/q/31845/15489 –  Jul 29 '15 at 01:34
  • That depends on what you consider a compound. Well, so called "disodium helide" was made, so Li2Ar perhaps isn't out of question, but it neither Na2He isn't molecular, nor would Li2Ar (probably) be. – Mithoron Mar 28 '23 at 19:23

2 Answers2

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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.

DavePhD
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  • But, could be Li-Ar-Li (AX2E3, linear molecule, trigonal bipyramid orbital) possible or not? Theoretically, at least... – riemannium Jun 16 '14 at 15:23
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    Lithium is very electropositive, so it tends not to form covalent bonds. – DavePhD Jun 16 '14 at 15:50
  • 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. – riemannium Jun 16 '14 at 17:45
  • 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: http://journals.aps.org/pr/abstract/10.1103/PhysRev.179.19 – riemannium Jun 16 '14 at 17:51
  • Or http://www.physics.wisc.edu/~tgwalker/002.Spin-Rotation-Noble.pdf – riemannium Jun 16 '14 at 17:59
  • And even if lithium is very electropositive, you also have the dilithium molecule $Li_2$, two lithium atoms COVALENTLY BOUND in a single dimer molecule...So, I have no reason to neglect a Li-Ar-Li compound by electronegativity, at least... – riemannium Jun 16 '14 at 18:42
  • And finally, if you search, you can find this adduct with sodium http://scitation.aip.org/content/aip/journal/apl/100/11/10.1063/1.3695064 I agree the problem is that the compound can be very unstable in normal conditions, but I can not see a good objection if we allow certain extreme conditions... – riemannium Jun 16 '14 at 18:54
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    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. – DavePhD Jun 16 '14 at 19:13
  • I see. Let me explain why I am asking this question. In some acces exam to the university in my country, it was asked the following question: – riemannium Jun 16 '14 at 21:17
  • Argue what kind of "bonding" will POSSIBLY form between =3 and Z=18. Of course, the normal question IS that argon does not bind with lithium since it has a complete valence shell with eight electrons. But, since Argon is in the 3th period, I was wondering if it could be admissible an answer with hybridation sp³d ...I agree with you in the fact that lithium is very electropositive, but seeing other compounds I don't understand yet why Li-Ar-Li is not possible... – riemannium Jun 16 '14 at 21:22
  • In summary, I want to understand what forbids argon to hybridize sp³d and "bond" two electrons with the single electrons of two lithium atoms... – riemannium Jun 16 '14 at 21:25
  • I have found this http://twitpic.com/e99l3k here ab initio Calculations on Alkali Atom - Rare Gas Van Der Wads Clusters Bosoon Lee and Sungyul Lee* College of Environment and Applied Chemistry, Kyunghee Universi~, Kyungki-do 449-701, Korea (Received March 29, 2000)... Of course, I guess that a Van der Waals complex IS NOT a covalent compound itself, but it seems that it can be "understood" as a week aggregate compound due to Van der Waals forces... – riemannium Jul 31 '14 at 21:20
  • @DavePhd about that electronegativity rule you assert ... this listing gives F=3.98 and H=2.2, so no covalent bond forms between H and F. //Hydrogen halides are generally considered covalent molecules unless they are dissociated in a solvent – Oscar Lanzi May 25 '20 at 18:38
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Wikipedia now lists dozens (hundreds?) of known argon compounds, so the concept is nothing new. Most are a bit contrived, but one compound that could have a real existence on Earth -- or rather, in Earth, is a nickel-argon compound:

At 140 GPa and 1500K nickel and argon form an alloy, NiAr.[1] NiAr is stable at room temperature and a pressure as low as 99 GPa. It has a face-centred cubic (fcc) structure. The compound is metallic. Each nickel atom loses 0.2 electrons to an argon atom which is thereby an oxidant. This contrasts with Ni3Xe, in which nickel is the oxidant. The volume of the ArNi compound is 5% less than that of the separate elements at these pressures. If this compound exists in the core of the Earth it could explain why only half the argon-40 that should be produced during the radioactive decay that produces geothermal heating seems to exist on the Earth.[2]

There is an implication in the above passage that argon can assume a partial negative charge, despite ostensibly having full valence subshells, a feature not evident in the more usual noble gas compound choices such as oxides and fluorides.

Cited references:

1. Dalton, Louisa (30 October 2019). "Argon reacts with nickel under pressure-cooker conditions". Chemical & Engineering News. Retrieved 6 November 2019. Electronic link goes to Ref. 2.

2. Adeleke, Adebayo A.; Kunz, Martin; Greenberg, Eran; Prakapenka, Vitali B.; Yao, Yansun; Stavrou, Elissaios (15 October 2019). "A High-Pressure Compound of Argon and Nickel: Noble Gas in the Earth's Core?". ACS Earth and Space Chemistry. 3 (11): 2517–2524. Link

Oscar Lanzi
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