A

Platinum

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MELTING POINT: 1,739°C
BOILING POINT: 4,170°C
DENSITY: 21.45 g/cm³
MOST COMMON IONS: Pt²⁺, Pt(Cl)₆²⁻, Pt(CN)₄²⁻, Pt(CN)₆²⁻

The first reports of the discovery of platinum were the papers of Antonio de Ulloa, who found an unworkable metal, platina (Spanish for "little silver"), in the gold mines of Colombia in 1736. Charles Wood provided the first samples in 1741. Platinum has a concentration of approximately 10⁻⁶ percent in Earth's crust. Platinum crystallizes in the face-centered cubic structure. The pure metal is malleable and ductile, and lustrous and silvery in appearance. It is capable of absorbing gaseous hydrogen. Platinum is found in nature in alluvial deposits and in association with copper, iron, and nickel sulfide ores. The metal is soluble in aqua regia, isolated as (NH₄)₂PtCl₆ from aqua regia, and obtained as a sponge or powder by ignition of (NH₄)₂PtCl₆.

Platinum is used as a catalyst in a wide variety of chemical reactions. Some of the more common catalytic uses are the oxidation of organic vapors in automobile exhaust, the oxidation of ammonia in the production of nitric acid, and the rearrangement of atoms in petroleum reforming. Most of the halides are formed by direct combination of the halogen elements with platinum, resulting in PtF₆, [PtF₅]₄, PtX₄ (where X = F, Cl, Br, or I), and PtX₃ and PtX₂ (where X = Cl, Br, or I). The two oxides, PtO and PtO_2, are unstable and decompose upon heating. In the +2 and +3 oxidation states, platinum forms coordination complexes bonded to carbon, nitrogen, phosphorous, oxygen, and sulfur donor atoms. Perhaps the most well known coordination complex is cis-platin, Pt(NH₃)₂Cl₂, used in chemotherapy treatments of cancer.

D. Paul Rillema

Bibliography

Cotton, F. Albert, and Wilkinson, Geoffrey (1988). Advanced Inorganic Chemistry, 5th edition. New York: Wiley.

Greenwood, Norman N., and Earnshaw, A. (1984). Chemistry of the Elements. New York: Pergamon Press.