Few compounds of californium have been made and studied.^[1] The only californium ion that is stable in aqueous solutions is the californium(III) cation.^[2] The other two oxidation states are IV (strong oxidizing agents) and II (strong reducing agents).^[3] The element forms a water-soluble chloride, nitrate, perchlorate, and sulfate and is precipitated as a fluoride, oxalate or hydroxide.^[4] If problems of availability of the element could be overcome, then CfBr₂ and CfI₂ would likely be stable.^[5]

The +3 oxidation state is represented by californium(III) oxide (yellow-green, Cf₂O₃), californium(III) fluoride (bright green, CfF₃) and californium(III) iodide (lemon yellow, CfI₃).^[3] Other +3 oxidation states include the sulfide and metallocene.^[6] Californium(IV) oxide (black brown, CfO₂), californium(IV) fluoride (green, CfF₄) represent the IV oxidation state. The II state is represented by californium(II) bromide (yellow, CfBr₂) and californium(II) iodide (dark violet, CfI₂).^[3]

Compounds

Californium(IV) oxide (CfO₂) is a black-brown solid that has a cubic crystal structure with a lattice parameter, the distance between unit cells in the crystal, of 531.0 ± 0.2 pm.^[7] Crystals of californium(III) oxide normally have a body-centered cubic symmetry. They convert to a monoclinic form upon heating to about 1400 °C and melt at 1750 °C.^[7]

Californium(III) chloride (CfCl₃) is an emerald green compound with a hexagonal structure that can be prepared by reacting Cf₂O₃ with hydrochloric acid at 500 °C.^[8] CfCl₃ is then used as a feeder stock to form the yellow-orange triiodide CfI₃, which in turn can be reduced to the lavender-violet diiodide CfI₂.^[9]

Californium(III) fluoride (CfF₃) is a yellow-green solid with a crystal symmetry that gradually changes from orthorhombic to trigonal when heated above room temperature.^[10] Californium(IV) fluoride (CfF₄) is a bright green solid with a monoclinic crystal structure.^[11]

Californium(II) iodide (CfI₂) is a deep purple solid with a stable rhombohedral structure at room temperature and an unstable hexagonal structure. Californium(III) iodide (CfI₃) is a lemon-yellow solid that has a rhombohedral structure and sublimes at ~800 °C.^[12]

Californium(III) oxyfluoride (CfOF) is prepared by hydrolysis of californium(III) fluoride (CfF₃) at high temperature.^[13] Californium(III) oxychloride (CfOCl) is prepared by hydrolysis of the hydrate of californium(III) chloride at 280–320 °C.^[14]

Heating the sulfate in air at about 1200 °C and then reducing with hydrogen at 500 °C produces the sesquioxide (Cf₂O₃).^[8] The hydroxide Cf(OH)₃ and the trifluoride CfF₃ are slightly soluble.^[8]

Californium(III) oxychloride (CfOCl) was the first californium compound to be discovered.^[15]

Californium(III) polyborate is unusual in that californium is covalently bound to the borate.^[16]

Tris(cyclopentadienyl)californium(III) (Cp₃Cf) presents itself as ruby red crystals. This cyclopentadienyl complex has been prepared by the reaction between Cp₂Be and CfCl₃ on a microgram scale and characterized by X-ray crystallography.^[17] Californium is the second-heaviest element for which an organometallic compound is known. A bent californium metallocene has also been isolated and characterized.^[18]

See also

• Californium
• Compounds of berkelium
• Einsteinium compounds

References

Bibliography

• Cotton, F. Albert; Wilkinson, Geoffrey; Murillo, Carlos A.; Bochmann, Manfred (1999). Advanced Inorganic Chemistry (6th ed.). New York City: John Wiley & Sons. ISBN 0-471-19957-5.
• CRC contributors (2006). David R. Lide (ed.). Handbook of Chemistry and Physics (87th ed.). Boca Raton, Florida: CRC Press, Taylor & Francis Group. ISBN 0-8493-0487-3. {{cite book}}: |author= has generic name (help)
• Cunningham, B. B. (1968). "Californium". In Clifford A. Hampel (ed.). The Encyclopedia of the Chemical Elements. New York City: Reinhold Book Corporation. LCCN 68-29938.
• Greenwood, N. N.; Earnshaw, A. (1997). Chemistry of the Elements (2nd ed.). Oxford, England: Butterworth-Heinemann. ISBN 0-7506-3365-4.
• Jakubke, Hans-Dieter; Jeschkeit, Hans, eds. (1994). Concise Encyclopedia Chemistry. trans. rev. Eagleson, Mary. Berlin: Walter de Gruyter. ISBN 3-11-011451-8.
• Seaborg, Glenn T. (2004). "Californium". In Geller, Elizabeth (ed.). Concise Encyclopedia of Chemistry. New York City: McGraw-Hill. p. 94. ISBN 0-07-143953-6.