{{Short description|Class of chemical compounds}} {{multiple image |image1 = Uranocene-2D-skeletal.svg |alt1 = Skeletal formula of uranocene |image2 = Uranocene-3D-balls.png |alt2 = Uranocene ball-and-stick model |image3 = Uranocene-3D-vdW.png |alt3 = Uranocene space-filling model |footer_background = #9bff99 |footer_align = center |footer = Uranocene molecular representations showing the U atom sandwiched between 2 COT<sup>2−</sup> ligands |caption1 = Skeletal formula |caption2 = Ball-and-stick |caption3 = Space-filling |caption_align = center |width1 = 120 |width2 = 106 |width3 = 116 }}
'''Actinocenes''' are a family of organoactinide compounds consisting of metallocenes containing elements from the actinide series. They typically have a sandwich structure with two dianionic cyclooctatetraenyl ligands (COT<sup>2−</sup>, which is {{chem|C|8|H|8|2−}}) bound to an actinide-metal center (An) in the oxidation state IV, resulting in the general formula An(C<sub>8</sub>H<sub>8</sub>)<sub>2</sub>.<ref>{{cite journal |last1= Minasian |first1= Stefan G. |first2= Jason M. |last2=Keith |title= New evidence for 5f covalency in actinocenes determined from carbon K-edge XAS and electronic structure theory |year= 2014 |journal= Chem. Sci. |volume= 5 |issue= 1 |pages= 351–359 |doi= 10.1039/C3SC52030G|url= https://zenodo.org/record/1230028}}</ref><ref name=":0">{{Cite book|last1=Greenwood|first1=Norman N.|title=Chemistry of the Elements|last2=Earnshaw|first2=Alan|publisher=Butterworth-Heinemann|year=1997|isbn=978-0-08-037941-8|pages=1278–1280}}</ref>
== Characterised actinocenes == {| class="wikitable" !Name !Formula !An<sup>IV</sup> centre !First synthesis !Crystal colour !An–COT distance (Å) !Space group |- |Thorocene |Th(C<sub>8</sub>H<sub>8</sub>)<sub>2</sub> |Th |1969 | style='background: #FFFF00' |bright yellow |2.004 |''P''2<sub>1</sub>/''n'' |- |Protactinocene |Pa(C<sub>8</sub>H<sub>8</sub>)<sub>2</sub> |Pa |1974 | style='background: #E9D66B'|yellowish |1.933 (calculated)<ref>{{cite journal | last=Kerridge | first=Andrew | title=f-Orbital covalency in the actinocenes (An = Th–Cm): multiconfigurational studies and topological analysis | journal=RSC Adv. | publisher=Royal Society of Chemistry (RSC) | volume=4 | issue=24 | year=2014 | issn=2046-2069 | doi=10.1039/c3ra47088a | pages=12078–12086| doi-access=free }}</ref> |''P''2<sub>1</sub>/''n'' |- |Uranocene |U(C<sub>8</sub>H<sub>8</sub>)<sub>2</sub> |U |1968 | style='background: #00A550'|<span style="color:#FFFFFF">deep green</span> |1.926 |''P''2<sub>1</sub>/''n'' |- |Neptunocene |Np(C<sub>8</sub>H<sub>8</sub>)<sub>2</sub> |Np |1970 | style='background: #B8860B'|<span style="color:#FFFFFF">yellow-brown</span> |1.909 |''P''2<sub>1</sub>/''n'' |- |Plutonocene |Pu(C<sub>8</sub>H<sub>8</sub>)<sub>2</sub> |Pu |1970 | style='background: #C51E3A'|<span style="color:#FFFFFF">dark red</span> |1.898 |''I''2/''m'' |- | Berkelocene{{NoteTag|Berkelocene was prepared with an annulated COT ligand, hexahydrodicyclopenta[8]annulene (hdcCOT); its properties are not strictly comparable to the other COT-ligated actinocenes in this table, but rather those also prepared with hdcCOT.<ref>{{Cite journal |last=Russo |first=Dominic R. |last2=Branson |first2=Jacob A. |last3=Kelly |first3=Sheridon N. |last4=Sen |first4=Asmita |last5=Gunther |first5=S. Olivia |last6=Peterson |first6=Appie |last7=Smith |first7=Patrick W. |last8=Ouellette |first8=Erik T. |last9=Arnold |first9=John |last10=Autschbach |first10=Jochen |last11=Minasian |first11=Stefan G. |date=2025-02-04 |title=Synthesis and characterization of isostructural annulated actinocenes |url=https://pubs.rsc.org/en/content/articlelanding/2025/cc/d4cc06094f |journal=Chemical Communications |language=en |volume=61 |issue=12 |pages=2504–2507 |doi=10.1039/D4CC06094F |issn=1364-548X|url-access=subscription }}</ref>}} |Bk(C<sub>14</sub>H<sub>16</sub>)<sub>2</sub> |Bk |2025 | style='background: #3F00FF'|<span style="color:#FFFFFF">indigo</span> |1.88 |''P''{{overline|1}} |} The most studied actinocene is uranocene, U(C<sub>8</sub>H<sub>8</sub>)<sub>2</sub>, which in 1968 was the first member of this family to be synthesised and is still viewed as the archetypal example.<ref name=":0" /><ref name="Seyferth">{{cite journal |last= Seyferth |first= D. |title= Uranocene. The First Member of a New Class of Organometallic Derivatives of the f Elements |year= 2004 |journal= Organometallics |volume= 23 |issue= 15 |pages= 3562–3583 |doi= 10.1021/om0400705|doi-access= free }}</ref> Other actinocenes that have been synthesised are protactinocene<ref>{{Cite journal|last1=Goffart|first1=J.|last2=Fuger|first2=J.|last3=Brown|first3=D.|last4=Duyckaerts|first4=G.|date=1974-05-01|title=On the cyclooctatetraenyl compounds of actinide elements part II. Bis-(cyclooctatetraenyl) protactinium(IV)|url=https://dx.doi.org/10.1016%2F0020-1650%2874%2980119-4|journal=Inorganic and Nuclear Chemistry Letters|language=en|volume=10|issue=5|pages=413–419|doi=10.1016/0020-1650(74)80119-4|issn=0020-1650|url-access=subscription}}</ref> (Pa(C<sub>8</sub>H<sub>8</sub>)<sub>2</sub>), thorocene<ref>{{Cite journal|last1=Avdeef|first1=Alex|last2=Raymond|first2=Kenneth N.|last3=Hodgson|first3=Keith O.|last4=Zalkin|first4=Allan|date=1972-05-01|title=Two isostructural actinide .pi. complexes. Crystal and molecular structure of bis(cyclooctatetraenyl)uranium(IV), U(C8H8)2, and bis(cyclooctatetraenyl)thorium(IV), Th(C8H8)2|url=https://doi.org/10.1021/ic50111a034|journal=Inorganic Chemistry|volume=11|issue=5|pages=1083–1088|doi=10.1021/ic50111a034|issn=0020-1669|url-access=subscription}}</ref> (Th(C<sub>8</sub>H<sub>8</sub>)<sub>2</sub>), neptunocene<ref>{{Cite journal|last1=De Ridder|first1=D. J. A.|last2=Rebizant|first2=J.|last3=Apostolidis|first3=C.|last4=Kanellakopulos|first4=B.|last5=Dornberger|first5=E.|date=1996-03-15|title=Bis(cyclooctatetraenyl)neptunium(IV)|url=http://scripts.iucr.org/cgi-bin/paper?S0108270195013047|journal=Acta Crystallographica Section C: Crystal Structure Communications|language=en|volume=52|issue=3|pages=597–600|doi=10.1107/S0108270195013047|issn=0108-2701|url-access=subscription}}</ref> (Np(C<sub>8</sub>H<sub>8</sub>)<sub>2</sub>), and plutonocene<ref name=":3">{{Cite journal|last1=Windorff|first1=Cory J.|last2=Sperling|first2=Joseph M.|last3=Albrecht-Schönzart|first3=Thomas E.|last4=Bai|first4=Zhuanling|last5=Evans|first5=William J.|last6=Gaiser|first6=Alyssa N.|last7=Gaunt|first7=Andrew J.|last8=Goodwin|first8=Conrad A. P.|last9=Hobart|first9=David E.|last10=Huffman|first10=Zachary K.|last11=Huh|first11=Daniel N.|date=2020-09-21|title=A Single Small-Scale Plutonium Redox Reaction System Yields Three Crystallographically-Characterizable Organoplutonium Complexes|url=https://pubs.acs.org/doi/10.1021/acs.inorgchem.0c01671|journal=Inorganic Chemistry|language=en|volume=59|issue=18|pages=13301–13314|doi=10.1021/acs.inorgchem.0c01671|pmid=32910649 |osti=1680020 |s2cid=221623763 |issn=0020-1669}}</ref><ref name=":1">{{Cite journal|last1=Apostolidis|first1=Christos|last2=Walter|first2=Olaf|last3=Vogt|first3=Jochen|last4=Liebing|first4=Phil|last5=Maron|first5=Laurent|last6=Edelmann|first6=Frank T.|date=2017-04-24|title=A Structurally Characterized Organometallic Plutonium(IV) Complex|url= |journal=Angewandte Chemie International Edition|language=en|volume=56|issue=18|pages=5066–5070|doi=10.1002/anie.201701858|pmc=5485009|pmid=28371148}}</ref> (Pu(C<sub>8</sub>H<sub>8</sub>)<sub>2</sub>). Especially the latter two, neptunocene and plutonocene, have not been extensively studied experimentally since the 1980s because of the radiation hazard they pose.<ref name=":3" /><ref name=":1" /> Berkelocene (with a modified COT ligand) was synthesised in 2025, the first actinocene with a new actinide in over 50 years.<ref name=":4">{{Cite journal |last=Russo |first=Dominic R. |last2=Gaiser |first2=Alyssa N. |last3=Price |first3=Amy N. |last4=Sergentu |first4=Dumitru-Claudiu |last5=Wacker |first5=Jennifer N. |last6=Katzer |first6=Nicholas |last7=Peterson |first7=Appie A. |last8=Branson |first8=Jacob A. |last9=Yu |first9=Xiaojuan |last10=Kelly |first10=Sheridon N. |last11=Ouellette |first11=Erik T. |last12=Arnold |first12=John |last13=Long |first13=Jeffrey R. |last14=Lukens |first14=Wayne W. |last15=Teat |first15=Simon J. |date=2025-02-28 |title=Berkelium–carbon bonding in a tetravalent berkelocene |url=https://www.science.org/doi/10.1126/science.adr3346 |journal=Science |volume=387 |issue=6737 |pages=974–978 |doi=10.1126/science.adr3346|url-access=subscription }}</ref>
== Bonding == The actinide-cyclooctatetraenyl bonding has been of interest for multiple theoretical studies.<ref name=":1" /><ref name=":2" /> Computational chemistry methods indicate bonding with a large covalent character resulting mainly from the mixing of actinide 6''d'' orbitals with ligand π-orbitals, with a smaller interaction involving the actinide 5''f'' and ligand π-orbitals.<ref name=":2">{{cite journal |last= Kerridge |first= Andrew |title= f-Orbital covalency in the actinocenes (An = Th–Cm): multiconfigurational studies and topological analysis |year= 2014 |journal= RSC Advances |volume= 4 |issue= 24 |pages= 12078–12086 |doi= 10.1039/C3RA47088A|bibcode= 2014RSCAd...412078K |url= http://discovery.ucl.ac.uk/1426903/1/c3ra47088a.pdf |doi-access= free }}</ref> The covalent component is characterised by donation of electron density to the actinide. This donation is notably reduced in berkelocene relative to other characterized actinocenes, due to the stable 5f<sup>7</sup> electron configuration of Bk<sup>4+</sup>.<ref name=":4" />
== Related compounds == Analogous sandwiched M(C<sub>8</sub>H<sub>8</sub>)<sub>2</sub> compounds also exist for lanthanides M = Nd, Tb, and Yb, but therein the bonding is mostly ionic rather than covalent (see lanthanocenes).<ref name="Seyferth" />
==See also== *Organoactinide chemistry *f-block metallocene
==Notes== {{reflist|group=note}}
==References== {{reflist}}
{{thorium compounds}}
Category:Organoactinide compounds Category:Metallocenes