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I found out that diamonds consist entirely of carbons singly bonded to other carbons, and it made me curious as to what other elements could form the same structure. Silicon came to mind, being in the same group as Carbon, but I believe I read about it being too big to form the structure of a diamond.

The next element to come to mind was sulfur because it was the next element that could form solely single bonds, fill its valence shell (by reaching into the d orbital), and have a neutral formal charge.

So can sulfur atoms form 6 single bonds with 6 other sulfur atoms? Can those, in turn, be connected to each other in a three-dimensional shape like a prism? Would having 6 bonds make the molecule stronger than that of a diamond?

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Answering the question posed in the title: yes, and under relatively mild conditions. A hexacoordinated sulfur is present as μ6-sulfido group $(\ce{S^2-})$ linking two $\ce{[Mo3S(S2)3]^4+}$ cores stabilized with three diethyldithiocarbamate $(\ce{dtc^-})$ ligands each into a dimer [1]. The coordination of $\ce{[S7]}$ moiety resembles a heavily distorted trigonal antiprism:

Crystal structure of [Mo3S(S2)3(dtc)3]2S

Figure 1. Crystal structure of $\ce{[Mo3S(S2)3(dtc)3]2S}.$ Color code: $\color{#EEEEEE}{\Large\bullet}~\ce{H}$; $\color{#909090}{\Large\bullet}~\ce{C}$; $\color{#3050F8}{\Large\bullet}~\ce{N}$; $\color{#FFFF30}{\Large\bullet}~\ce{S}$; $\color{#54B5B5}{\Large\bullet}~\ce{Mo}$. CSD ID: LEBXAR.

Reference

  1. Meienberger, M. D.; Hegetschweiler, K.; Rüegger, H.; Gramlich, V. The Reactivity of Complexes Containing the $\ce{[Mo3(Μ3S)(ΜS2)3]^4+}$ Core. Ligand Substitution, Sulfur Elimination and Sulfide Binding. Inorganica Chim. Acta 1993, 213 (1–2), 157–169. https://doi.org/10.1016/S0020-1693(00)83826-8.
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Actually, cyclo-$\ce{S7}$ is an observable molecule with a ring structure. I believe OP was thinking of a octahedral structure for $\ce{S7}$, analogous to the octrahedron of $\ce{SF6}$. Without getting into the debate over d-orbitals$^1$, I would note that this would leave the terminal $\ce{S}$ atoms with seven valence electrons in addition to the steric problems (cf. apparent non-existence of $\ce{SCl6}$).

Update (2023): There is a report, including a crystal structure from X-ray diffraction, of a $\ce{[SCl6]^{-2}}$ species.$^2$

OP also alludes to a 3D polymeric structure ("diamond"), which one could hypothesize like so: a $\ce{S}$ coordinated by six $\ce{S}$ as in the hypothetical octahedron above. Each of the six $\ce{S}$ would participate in two such octahedra each. I think that such a structure may suffer from rather large holes. In addition, the two kinds of $\ce{S}$ atoms are rather different chemically, which I suspect would be energetically worse than the polymeric alternative observed in nature: polymeric 1D chains.


$^1$ which, in my opinion, is settled anyway against their participation.

$^2$ P. Voßnacker, A. Wüst, C. Müller, M. Kleoff, S. Riedel, Angew. Chem. Int. Ed. 2022, 61, e202209684; Angew. Chem. 2022, 134, e202209684. https://doi.org/10.1002/anie.202209684

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Under high pressure [a six-coordinate form of elemental sulfur is known 1. As one might expect, a higher pressure is required to achieve this phase with sulfur than with its heavier and more nearly metallic concentration selenium:

S-IV is shown to transform to primitive rhombohedral β-Po phase [see figure below, from the reference] phase at 153(3) GPa, the same transition is found in Se at pressure of around 80 GPa.

enter image description here

Reference

  1. O. Degtyareva, E. Gregoryanz, H. K. Mao & R. J. Hemley (2005). "Crystal structure of sulfur and selenium at pressures up to 160 GPa", High Pressure Research, 25:1, 17-33, DOI: 10.1080/08957950412331331682
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  • $\begingroup$ Did you have a chance to inspect the crystal structure or do you at least know where it's been deposited? There are several aspects relatively innocent on its own, but when combined would raise a question whether the S-atom coordination can be reliably determined. First, they used Rietveld. Second, the structure of S-IV was incommensurate modulated. Third, "the amplitude of the atomic displacement in S-IV could not be determined due to the lack of the reliable diffraction intensities." $\endgroup$
    – andselisk
    Mar 15, 2023 at 4:57
  • $\begingroup$ I think the answer would benefit from adding an image of the stacked unit cells (Fig. 11 from the paper could be an inspiration) as well as both structure refinement, displacement, modulation and coordination parameters. I guess we are not getting an ORTEP, but at least some visual aid would add clarity. $\endgroup$
    – andselisk
    Mar 15, 2023 at 5:05
  • $\begingroup$ @andselisk the figures seem to be behind the paywall. If you gave tge referenced fugure can you please include it? $\endgroup$ Mar 15, 2023 at 10:46
  • $\begingroup$ As a reference, here is Figure 11 from Degtyareva2005: i.stack.imgur.com/7gXLs.png $\endgroup$
    – andselisk
    Mar 15, 2023 at 16:59
  • $\begingroup$ Thanks. I incorporate this. $\endgroup$ Mar 15, 2023 at 18:25

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