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) and +1(for other metals).

  1. Be(0)

A 2016 paper gives an insight to the existence of a zero valent beryllium complex compound i.e it has been verified through computational method but it is yet to be synthesized.

[...]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.

  1. 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)

  1. Mg(I)

It has been described in @Ian Bush's answer. For more information, refer to these sources(1 and 2). 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).

  1. 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.

  1. Sr(I)

The high-resolution infrared spectrum of gas-phase $\ce{SrF}$ was obtained in emission with a Fourier transform spectrometer.[...] (Source)

  1. Ba(I)

3 isotopes of barium in $\ce{BaF}$ (Source). In [2018] Wu and Lerner (source) reported a barium(I) in a complex graphite intercalation compound.

I did not had to google each and every element to search for lower oxidation state. The wikipedia article of oxidation element 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.

  • $\begingroup$ How does $\ce{MgB2}$ contain magnesium-magnesium bonds? When I look at sketches of the structure it looks like there are boron-boron and boron-magnesium bonds (the latter possibly having ionic character to make up the electron deficiency in the boron) instead. $\endgroup$ – Oscar Lanzi May 14 '19 at 9:37
  • $\begingroup$ See this reference for the ionic bonding. $\endgroup$ – Oscar Lanzi May 14 '19 at 9:51
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    $\begingroup$ Yes, you are right @Oscar. I will edit my answer. $\endgroup$ – Nilay Ghosh May 14 '19 at 14:01
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    $\begingroup$ @Oscar no worries. You always learn something new everyday : ) $\endgroup$ – Nilay Ghosh Apr 25 '20 at 16:52
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    $\begingroup$ @Oscar I used the option hyperlink to embed links into the text. $\endgroup$ – Nilay Ghosh Apr 25 '20 at 16:58

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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