Page 323 - Academic Press Encyclopedia of Physical Science and Technology 3rd InOrganic Chemistry

P1: GPA Final Pages
Encyclopedia of Physical Science and Technology EN010b-481 July 14, 2001 18:45

Noble Metals (Chemistry) 477

usually prepared by substitution of osmium(III) or by re- was the first metal ion found to complex dinitrogen (as
ducing an osmium(IV) derivative. [Ru(NH 3 ) 5 N 2 ] ), as was discussed for osmium. Ruthe-
2+
4
Osmium(IV), d , halides are the most important os- nium(II) forms many cationic, neutral, and anionic species
mium salts, with K 2 [OsCl 6 ] as the most prominent exam- with nitrosyl ligands that serve as models for under-
ple. The most common complexes of osmium(IV) involve standing the role of the nitrosyl function in coordination
oxygen donor ligands. chemistry. Ruthenium(II) species are usually derived from
2
Osmium(VI), d , is present in OsF 6 , OsOF 4 , and ruthenium(III) salts or other ruthenium(II) complexes.
5
OsOCl 4 . OsF 6 is the most stable of the PGM hexafluo- Ruthenium(III), d , is ruthenium’s most stable oxida-
rides. OsO 3 has been detected only in the vapor phase. tion state and resembles rhodium(III) and iridium(III)
Other complexes prepared by reduction of OsO 4 , include more than osmium(III). The salts include the halides,
4−
6−
[OsO 2 (OH) 4 ] , [OsO 2 Cl 4 ] , [OsO 5 ] , [OsO 6 ] , and hydroxides, and oxides; RuCl 3 · 3H 2 O is most impor-
2−
2−
2−
[OsO 2 (NO 3 ) 2 (NO 2 ) 2 ] . tant because it is a good starting material for other
For osmium(−II), the complexes [Os(CO) 4 ] 2− and compounds and reacts readily with olefins and phos-
7
[Os(PF 3 ) 4 ] 2− are known. Osmium(I), d , is found in poly- phines. Complexes of this oxidation state are known
nuclear complexes like [Os(CO) 4 Cl] 2 and Os(C 5 H 5 )(CO), with water, cyanide, oxygenated organics, such as β-
and in a series of carbonyl hydrides [e.g., H 4 Os 4 (CO) 12 ]. diketones and carboxylates, pyridines, carbonyls, cy-
6
Osmium(II), d , occurs in Osl 2 and in a number of clopentadienyls, phosphine, and arsine ligands. A notable
π-acceptor ligand complexes (e.g., cyanide, nitrosyl, differencebetweenruthenium(II)andruthenium(III)isthe
phosphine, arsine, stibine, and carbonyl). The most absence of ruthenium(III) nitrosyl complexes.
4
interesting species are the dinitrogen complexes Ruthenium(IV), d , forms a more limited number of
2+
2+
[Os(NH 3 ) 5 N 2 ] , [Os(NH 3 ) 4 N 2 ] , and OsCl 2 (PEt 3 ) 2 N 2 , complexes involving mainly the halides (except the io-
which are prototypes for nitrogen fixation models. dide), oxalate, and sulfate, together with π-acceptor ni-
Osmium(II) complexes are prepared by reducing os- trogen donor ligands. RuO 2 is used as a catalyst and as an
3
mium(III) or osmium(IV) compounds. Osmium(V), d , electrode material.
7
species are limited to OsF 5 and [OsF 6 ] . The ruthenium(I), d , chloride, bromide, and iodide
−
1
Osmium(VII), d , is found in OsF 7 and OsOF 5 obtained salts have been characterized in solution but not as
from the metal or from OsO 2 . solids. The complexes involve π-acceptor ligands [e.g.,
0
Osmium(VIII), d , compounds are foremost repre- [Ru(CO)Br] n and [(C 5 H 5 )Ru(CO) 2 ] 2 ]. The compounds
3
sented by the strong oxidizing agent OsO 4 and the os- are derived from ruthenium(III) salts. Ruthenium(V), d ,
miamates [OsO 3 N] and OsO 3 = N(iBu). The tetroxide compounds are limited to RuF 5 , [RuF 6 ] , and the oxide
−
−
2
is volatile and toxic so proper care must be taken with its Ru 2 O 5 . Ruthenium(VI), d , is known in RuF 6 , RuOF 4 ,
2−
use. It has a simple tetrahedral structure, but is soluble in [RuO 4 ] , and H 2 [RuO 2 Cl 4 ]; the first three are prepared
1
water to form hydrates. Usage is generally limited due to from the metal. The ruthenium(VII), d , state is present
0
the high toxicity of most compounds with osmium in high in K[RuO 4 ] and the ruthenium(VIII), d , state in RuO 4 .
oxidation states. RuO 4 is a stronger oxidizing agent than OsO 4 , and is
less stable. It can decompose explosively at temperatures
greater than 180 C to yield RuO 2 and oxygen.
◦
8. Ruthenium
Ruthenium is known in oxidation states (−II)–(VIII), the
F. Analytical Procedures
(II), (III), and (IV) states, with six-coordination being the
most common. Figure 6 outlines some typical ruthenium Analysis of the precious metals is very important when the
chemistry.Themetalis inert tomineral acids,but willreact economics of metal recovery from ore or scrap is consid-
with fluorine, bromine, BrF 3 , or oxygen at 1000 C. It will ered. The purity of refined metal is also critical because
◦
also react with KOH and KNO 3 to yield K[RuO 4 ], which trace impurities can be responsible for a product’s lack
is a good starting material for other compounds. Ruthe- of performance. For these reasons, it is important to have
nium(0) carbonyl complexes and clusters are obtained by dependable analytical methods.
the reduction of a ruthenium(III) halide [e.g., Ru(CO) 5 , The method of sample preparation and analysis will de-
Ru 2 Os(CO) 12 , and Ru 6 C(CO) 17 ]. pend on the form of the metal (ore, complex, metal, etc.),
6
Ruthenium(II), d , is known as the binary bromide its concentration, and the presence of potentially interfer-
and as [RuCl 4 ] . The richer complex chemistry involves ing species. If noble metals are mixed with base metals, the
2−
stable compounds with cyanide, amines, halides, water, latter must be removed first, followed by noble metal sep-
nitrosyl, carbonyl, hydride, phosphine, arsine, stibine, aration. The chemistry of noble metal separation is simi-
arene, and cyclopentadienyl ligands. [RuCl 2 (PPh 3 ) 2 ]is lar to that used in the refining of the metals, but it can be
used as a catalyst. Ruthenium(II) is a good π-donor and greatly simplified by knowning what elements are present.