Unusual oxidation numbers for alkaline earth metals?

Are there compound of alkaline earth elements showing unusual oxidation numbers? For the sake of the question, every oxidation number different from +2 counts as unusual, most exciting would be oxidation numbers greater than +2.




This answer is an extension to @Ian Bush answer. Not only magnesium, but every group 2 element has a lower oxidation state of +0(beryllium, magnesium) and +1(for all AE metals lighter than radium).


1. Be(0)


[A 2016 paper](https://www.chemistryviews.org/details/news/9426001/Beryllium0_Complex_Found.html) gives an insight to the existence of a zero valent beryllium complex compound. Previously the stability of Be(0) compounds had been computationally predicted; the referenced paper reports the first actual synthesis.



> 
> [...]The team added a single ligand i.e CAAC = cyclic
> (alkyl)(amino)carbene to $\ce{BeCl2}$ in benzene solution to give
> $\ce{(CAAC)BeCl2}$, and obtained the final product,
> $\ce{[Be(CAAC)2]}$, by reducing the beryllium with KC8 in the presence
> of a second equivalent of CAAC ligand.
> 
> 
> 


2. Be(I)



> 
> High resolution infrared emission spectra of beryllium monohydride and
> monodeuteride have been recorded. The molecules were generated in a
> furnace-discharge source, at 1500 °C and 333 mA discharge current,
> with beryllium metal and a mixture of helium and hydrogen or deuterium
> gases.([source](https://aip.scitation.org/doi/10.1063/1.1528606))
> 
> 
> 


3. Mg(I)


It has been described in @Ian Bush's answer. For more information, refer to these sources([1](https://en.wikipedia.org/wiki/Low_valent_magnesium_compounds) and [2](https://science.sciencemag.org/content/318/5857/1754)). Some examples are $\ce{Mg2RuH4, Mg3RuH3, and Mg4IrH5}$ having the $\ce{Mg-Mg}$ bond and magnesium diboride containing the metastable $\ce{Mg2^{2+}}$ ion(Credit @Oscar Lanzi).


4. Mg(0)


This more recent (2021) addition has been obtained as an organic complex containing the $\ce{Na2Mg2^{2+}}$ cluster by [Rösch et al](https://doi.org/10.1038/s41586-021-03401-w). The authors also report a compound containing the mixed $\ce{Mg(0)}$-$\ce{Mg(I)}$ species $\ce{Mg3^{2+}}$.


5. Ca(I)


A Ca(I) Sandwich Complex $\ce{[(thf)3Ca(μ-C6H3-1,3,5-Ph3)Ca(thf)3]}$ is being described in this [2010 paper](https://pubs.acs.org/doi/10.1021/ja105534w).


6. Sr(I)



> 
> The high-resolution infrared spectrum of gas-phase $\ce{SrF}$ was
> obtained in emission with a Fourier transform spectrometer.[...]
> ([Source](https://www.sciencedirect.com/science/article/abs/pii/S0022285296900193?via%3Dihub))
> 
> 
> 


7. Ba(I)


3 isotopes of barium in $\ce{BaF}$ ([Source](https://web.archive.org/web/20050310180822/http://bernath.uwaterloo.ca/media/126.pdf)). In [2018] Wu and Lerner ([source](https://doi.org/10.1021/acs.chemmater.8b03421)) reported a barium(I) in a complex graphite intercalation compound.


8. Ba(III, IV, V)?


Various studies have suggested that elements can assume oxidation states outside their usual range under GPa-level pressures. [Luo et al. (2018)](https://pubs.acs.org/doi/abs/10.1021/acs.jpcc.8b03459) have performed such calculations with barium fluorides and predict the possibility of $\ce{BaF3,BaF4,BaF5}$. These proposed compounds await experimental verification.




---


I did not had to google each and every element to search for lower oxidation state. The [wikipedia article of oxidation element](https://en.wikipedia.org/wiki/Oxidation_state) gave a list of all posible O.S of element. Information regarding unusual O.S of any element can be found in the footnote and thus only clicked the relevant elements for the answer.


 6

Magnesium(I) compounds are known, but they are of the form $\ce{[Mg-Mg]^{2+}}$ rather than a bare $\ce{Mg+}$ - so more like Mercury than Sodium. See <https://pubs.rsc.org/en/content/articlelanding/2011/dt/c0dt01831g#!divAbstract>, and in a way this furthers the similarity between Mg and Zn. Similar compounds are also possible for the heavier metals.


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