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Cubane-type cluster
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<h2 id="examples">Examples</h2> <p>Heavier <a href="/facts/Adamantogen/PkWCV3Vx">adamantogen</a> cubanes with all vertices identical are all known, and exhibit only about half as much <a href="/facts/Strain_energy/xQhccQG5">strain energy</a> as cubane per molecule. The <a href="/facts/Inert_pair_effect/bqREzIAU">inert pair effect</a> is believed to drive stability in cubanes with heavy <a href="/facts/Main_group/2AG3QxJl">main group</a> elements: the <a href="/facts/Bonding_orbital/1cpledcB">bonding orbitals</a> are almost entirely <a href="/facts/Orbital_hybridization/Fl7sz8Jm">unhybridized</a> <i>p</i> orbitals, and so naturally adopt 90° angles at the vertices.<a class="footnote-ref" id="fnref:1" href="#fn:1"><sup>1</sup></a> </p><p>Simple inorganic cubane-type clusters include <a href="/facts/Selenium_tetrachloride/K9RHwPgB">selenium tetrachloride</a>, <a href="/facts/Tellurium_tetrachloride/UxAbGDjb">tellurium tetrachloride</a>, and <a href="/facts/Sodium_silox/jA9yBzT0">sodium silox</a>. Many <a href="/facts/Alkyllithium/xgYnjhP3">alkyllithium</a> compounds, including <a href="/facts/Methyllithium/Fo5UzmsP">methyl-</a> and <a href="/facts/Tert-Butyllithium/qokAzb3U"><i>tert</i>-butyllithium</a>, exist as <a href="/facts/Tetramer/qeUFnwC4">tetrameric</a> clusters in solution. The four lithium atoms and the carbon from each alkyl group bonded to them occupy alternating vertices of the cube, with the additional atoms of the alkyl groups projecting off their respective corners.<a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a> </p><p>Cubane clusters are common throughout <a href="/facts/Bioinorganic_chemistry/4JJEL3t1">bioinorganic chemistry</a>. <a href="/facts/Ferredoxin/1qJJjQHk">Ferredoxins</a> containing [Fe4S4] <a href="/facts/Iron%25E2%2580%2593sulfur_cluster/QCbnrAF0">iron–sulfur clusters</a> are pervasive in nature.<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a> The four iron atoms and four sulfur atoms form an alternating arrangement at the corners. The whole cluster is typically anchored by coordination of the iron atoms, usually with <a href="/facts/Cysteine/kbqvUm6d">cysteine</a> residues. In this way, each Fe center achieves <a href="/facts/Tetrahedral_coordination_geometry/583AL1sP">tetrahedral coordination geometry</a>. Some [Fe4S4] clusters arise via dimerization of square-shaped [Fe2S2] precursors. Many synthetic analogues are known including heterometallic derivatives.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a> </p> <p><a href="/facts/Octaazacubane/ndTk3yPF">Octaazacubane</a> is a hypothetical <a href="/facts/Allotrope/2WUdHWxg">allotrope</a> of <a href="/facts/Nitrogen/Nf1QpGDz">nitrogen</a> with formula N8; the nitrogen atoms are the corners of the cube. Like the carbon-based cubane compounds, octaazacubane is predicted to be highly unstable due to <a href="/facts/Angle_strain/seIIaK2k">angle strain</a> at the corners, and it also does not enjoy the <a href="/facts/Kinetic_stability/H72SMWof">kinetic stability</a> seen for its organic analogues.<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a> </p> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>Sekiguchi Akira; Nagase Shigeru (1998). "Polyhedral silicon compounds". In Rappoport, Zvi; Apeloig, Yitzhak (eds.). The Chemistry of Organic Silicon Compounds. The Chemistry of Functional Groups. Vol. 2. Chichester, UK: Interscience (Wiley). pp. 120–125, 136–146. doi:10.1002/0470857250. ISBN 0-471-96757-2. <a href="0-471-96757-2" target="_blank">0-471-96757-2</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>Stey, Thomas; Stalke, Dietmar (2009). "Lead structures in lithium organic chemistry". PATAI'S Chemistry of Functional Groups. John Wiley & Sons, Ltd. doi:10.1002/9780470682531.pat0298. ISBN 9780470682531. <a href="9780470682531" target="_blank">9780470682531</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>Perrin, Jr., B.S.; Ichive, T. (2013). "Identifying sequence determinants of reduction potentials of metalloproteins". Biological Inorganic Chemistry. 18 (6): 599–608. doi:10.1007/s00775-013-1004-6. PMC 3723707. PMID 23690205. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3723707" target="_blank">https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3723707</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>Lee, S. C.; Lo, W.; Holm, R. H., "Developments in the Biomimetic Chemistry of Cubane-Type and Higher Nuclearity Iron–Sulfur Clusters", Chem. Rev. 2014, doi:10.1021/cr4004067 <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>Agrawal, Jai Prakash (2010). High Energy Materials: Propellants, Explosives and Pyrotechnics. Wiley-VCH. p. 498. ISBN 978-3-527-62880-3. <a href="978-3-527-62880-3" target="_blank">978-3-527-62880-3</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> </ol>