:Actinocene
{{Short description|Class of chemical compounds}}
{{multiple image
|image1 = Uranocene-2D-skeletal.png
|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
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|footer = Uranocene molecular representations showing the U atom sandwiched between 2 COT2− ligands
|caption1 = Skeletal formula
|caption2 = Ball-and-stick
|caption3 = Space-filling
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|width1 = 120
|width2 = 106
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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 (COT2−, 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(C8H8)2.{{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}}{{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}}
Characterised actinocenes
| class="wikitable"
!Name !Formula !AnIV centre !First synthesis !Crystal colour !An–COT distance (Å) !Space group |
| Thorocene
|Th(C8H8)2 |Th |1969 | style='background: #FFFF00' |bright yellow |2.004 |P21/n |
| Protactinocene
|Pa(C8H8)2 |Pa |1974 | style='background: #E9D66B'|yellowish |P21/n |
| Uranocene
|U(C8H8)2 |U |1968 | style='background: #00A550'|deep green |1.926 |P21/n |
| Neptunocene
|Np(C8H8)2 |Np |1970 | style='background: #B8860B'|yellow-brown |1.909 |P21/n |
| Plutonocene
|Pu(C8H8)2 |Pu |1970 | style='background: #C51E3A'|dark red |1.898 |I2/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.{{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 }}}}
|Bk(C14H16)2 |Bk |2025 | style='background: #3F00FF'|indigo |1.88 |P{{overline|1}} |
The most studied actinocene is uranocene, U(C8H8)2, which in 1968 was the first member of this family to be synthesised and is still viewed as the archetypal example.{{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 }} Other actinocenes that have been synthesised are protactinocene{{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}} (Pa(C8H8)2), thorocene{{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}} (Th(C8H8)2), neptunocene{{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}} (Np(C8H8)2), and plutonocene{{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}}{{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}} (Pu(C8H8)2). Especially the latter two, neptunocene and plutonocene, have not been extensively studied experimentally since the 1980s because of the radiation hazard they pose. Berkelocene (with a modified COT ligand) was synthesised in 2025, the first actinocene with a new actinide in over 50 years.{{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 }}
Bonding
The actinide-cyclooctatetraenyl bonding has been of interest for multiple theoretical studies. Computational chemistry methods indicate bonding with a large covalent character resulting mainly from the mixing of actinide 6d orbitals with ligand π-orbitals, with a smaller interaction involving the actinide 5f and ligand π-orbitals.{{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 }} 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 5f7 electron configuration of Bk4+.
Related compounds
Analogous sandwiched M(C8H8)2 compounds also exist for lanthanides M = Nd, Tb, and Yb, but therein the bonding is mostly ionic rather than covalent (see lanthanocenes).
See also
Notes
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