Few compounds of

californium Californium is a radioactive chemical element with the symbol Cf and atomic number 98. The element was first synthesized in 1950 at Lawrence Berkeley National Laboratory (then the University of California Radiation Laboratory), by bombarding ...

have been made and studied. The only californium ion that is stable in

aqueous solution An aqueous solution is a solution in which the solvent is water. It is mostly shown in chemical equations by appending (aq) to the relevant chemical formula. For example, a solution of table salt, or sodium chloride (NaCl), in water would ...

s is the californium(III)

cation An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...

. The other two

oxidation state In chemistry, the oxidation state, or oxidation number, is the hypothetical charge of an atom if all of its bonds to different atoms were fully ionic. It describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. ...

s are IV (strong

oxidizing agent An oxidizing agent (also known as an oxidant, oxidizer, electron recipient, or electron acceptor) is a substance in a redox chemical reaction that gains or " accepts"/"receives" an electron from a (called the , , or ). In other words, an oxid ...

s) and II (strong

reducing agent In chemistry, a reducing agent (also known as a reductant, reducer, or electron donor) is a chemical species that "donates" an electron to an (called the , , , or ). Examples of substances that are commonly reducing agents include the Earth m ...

s). The element forms a water-soluble

chloride The chloride ion is the anion (negatively charged ion) Cl−. It is formed when the element chlorine (a halogen) gains an electron or when a compound such as hydrogen chloride is dissolved in water or other polar solvents. Chloride s ...

nitrate Nitrate is a polyatomic ion with the chemical formula . Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are soluble in water. An example of an insoluble ...

perchlorate A perchlorate is a chemical compound containing the perchlorate ion, . The majority of perchlorates are commercially produced salts. They are mainly used as oxidizers for pyrotechnic devices and to control static electricity in food packaging. ...

, and

sulfate The sulfate or sulphate ion is a polyatomic ion, polyatomic anion with the empirical formula . Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Sulfates occur widely in everyday life. Sulfates are salt (chemistry), ...

and is precipitated as a

fluoride Fluoride (). According to this source, is a possible pronunciation in British English. is an inorganic, monatomic anion of fluorine, with the chemical formula (also written ), whose salts are typically white or colorless. Fluoride salts ...

oxalate Oxalate (IUPAC: ethanedioate) is an anion with the formula C2O42−. This dianion is colorless. It occurs naturally, including in some foods. It forms a variety of salts, for example sodium oxalate (Na2C2O4), and several esters such as dimethyl ...

hydroxide Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and hydrogen atom held together by a single covalent bond, and carries a negative electric charge. It is an important but usually minor constituent of water ...

. If problems of availability of the element could be overcome, then CfBr₂ and CfI₂ would likely be stable. Cf-251

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). Other +3 oxidation states include the sulfide and metallocene. 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).

Compounds

Californium(IV) oxide (CfO₂) is a black-brown solid that has a cubic crystal structure with a lattice parameter, the distance between

unit cell In geometry, biology, mineralogy and solid state physics, a unit cell is a repeating unit formed by the vectors spanning the points of a lattice. Despite its suggestive name, the unit cell (unlike a unit vector, for example) does not necessari ...

s in the crystal, of 531.0 ± 0.2 pm. Crystals of californium(III) oxide normally have a body-centered cubic symmetry. They convert to a

monoclinic In crystallography, the monoclinic crystal system is one of the seven crystal systems. A crystal system is described by three vectors. In the monoclinic system, the crystal is described by vectors of unequal lengths, as in the orthorhombic ...

form upon heating to about 1400 °C and melt at 1750 °C. Californium(III) chloride (CfCl₃) is an emerald green compound with a hexagonal structure that can be prepared by reacting Cf₂O₃ with

hydrochloric acid Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid. It is a component of the gastric acid in the dig ...

at 500 °C. 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. Californium(III) fluoride (CfF₃) is a yellow-green solid with a crystal symmetry that gradually changes from

orthorhombic In crystallography, the orthorhombic crystal system is one of the 7 crystal systems. Orthorhombic lattices result from stretching a cubic lattice along two of its orthogonal pairs by two different factors, resulting in a rectangular prism with ...

trigonal In crystallography, the hexagonal crystal family is one of the six crystal families, which includes two crystal systems (hexagonal and trigonal) and two lattice systems (hexagonal and rhombohedral). While commonly confused, the trigonal crystal ...

when heated above room temperature. Californium(IV) fluoride (CfF₄) is a bright green solid with a monoclinic crystal structure. 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 Sublimation is the transition of a substance directly from the solid to the gas state, without passing through the liquid state. Sublimation is an endothermic process that occurs at temperatures and pressures below a substance's triple point i ...

at ~800 °C.

Californium(III) oxyfluoride Californium(III) oxyfluoride is a radioactive inorganic compound with a chemical formula CfOF, synthesized in the 1960s. This salt crystallizes with the cubic fluorite structure, with the oxide and fluoride anions randomly distributed in anion ...

(CfOF) is prepared by

hydrolysis Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile. Biological hydrolysis ...

of californium(III) fluoride (CfF₃) at high temperature.

Californium(III) oxychloride Californium oxychloride ( Cf OCl) is a radioactive salt first discovered in measurable quantities in 1960. It is composed of a single californium cation and oxychloride consisting of one chloride and one oxide An oxide () is a chemical compo ...

(CfOCl) is prepared by hydrolysis of the hydrate of californium(III) chloride at 280–320 °C. Heating the sulfate in air at about 1200 °C and then reducing with hydrogen at 500 °C produces the sesquioxide (Cf₂O₃). The

Cf(OH)₃ and the trifluoride CfF₃ are slightly

soluble In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution. The extent of the solub ...

(CfOCl) was the first californium compound to be discovered.

Californium(III) polyborate Californium polyborate is a covalent compound with formula Cf 6O8(OH)5 In this compound the californium is in a +3 oxidation state. This compound is the highest atomic number borate with a visible solid phase. Heavier elements than californium dec ...

is unusual in that californium is covalently bound to the borate. Tris(cyclopentadienyl)californium(III) (Cp₃Cf) presents itself as ruby red crystals. This

cyclopentadienyl complex A cyclopentadienyl complex is a coordination complex of a metal and cyclopentadienyl groups (, abbreviated as Cp−). Cyclopentadienyl ligands almost invariably bind to metals as a pentahapto (''η''5-) bonding mode. The metal–cyclopentadien ...

has been prepared by the reaction between Cp₂Be and CfCl₃ on a microgram scale and characterized by X-ray crystallography. Californium is the second-heaviest element for which an organometallic compound is known. A bent californium metallocene has also been isolated and characterized.

References

Bibliography

* * * * * * {{Chemical compounds by element C

Compounds

See also

References

Bibliography