category: Chemistry

Introduction

Platinum - one of the most precious of precious metals, it has several important properties, whereby not only used in the jewelry industry, but in many industries. The use of platinum in many chemical processes makes it relevant to a deeper study of its physical and chemical properties.
?????Platinum - one of the most important elements of the total number of platinum because of the maximum among them chemical inertness, and because of the most valuable properties of platinum as a major catalyst for many chemical processes.
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Basic properties
Platinum - gray-gray metal is relatively soft, very malleable, ductile, refractory. The special conditions form a spongy platinum (with a strongly developed surface), platinum black (fine powder) and colloidal platinum. Noble metal - is the last (most electropositive) place in the electrochemical series of stresses. Easily fused with platinum metals (except for ruthenium and osmium), as well as Fe, Co, Ni, Cu, Au, and others, hardly fused with Sb, Bi, Sn, Pb, Ag. Chemically very passive - does not react with water, acids (except for "regia"), alkalis, hydrate of ammonia, carbon monoxide. Converted into an aqueous solution of hydrochloric acid, saturated with Cl2. When heated, oxidized by oxygen, halogens, sulfur, at room temperature - Xenon tetrafluoride. Spongy platinum and platinum black actively absorb significant amount of H2, He, O2. It grows wild in its native form (in alloys with Ru, Rh, Pd, Os, Ir).
?????Platinum Pt is characterized by the following constants:
Atomic mass ............................................... 195,09
The valence electrons .................................... 5d96s1
The metallic radius of the atom, they ................ 0,138
Conventional ionic radius, nm:
?????E2 +................................................. ........ 0,090
?????E4 +................................................. ....... 0,064
The ionization energy E0 ==> E + eV ................. 8,9
Content in the earth's crust,% (mol percentage) ... 5 * 10-8
?????For platinum, the most characteristic oxidation state +4. Also known compounds Pt (VI). For platinum, the most stable coordination numbers 4 (tetrahedron or a square) and 6 (octahedron). Oxidation states of elements and their corresponding spatial configurations of the complexes are given in Table. 1.
??????Table 1. Oxidation and structural units of platinum
Oxidation Coordination number of structural units Examples of compounds
0 4 tetrahedron Pt (O2) [P (C6H5) 3] 2
+2 4 tetrahedron
+2 4 square [Pt (NH3) 4] 2, [Pt (CN) 4] 2 -, [PtCl4] 2 -, [Pt (NH3) 2 Cl2] ?, PtO
+2 6 octahedron
+4 6 octahedron Pt (NH3) 6] 4 +, [PtCl6] 2 -, [Pt (NH3) 2Sl4] ?
+6 6 octahedron PtF6
?????Platinum is one of the rare elements found in the copper-nickel ores, as well as in the native state in alloys with low content of other metals (Ir, Pd, Rh, Fe, sometimes Ni, Cu, etc.). Important source of platinum metals are polymetallic sulphide copper-nickel ores.

Simple matter
?????In the form of simple substances platinum - a brilliant white metal with a silvery tint, crystallizes in a face-centered cubic lattice.
Critical constants Pt are presented below:
Pl., G/cm3 ... ... ... ... ... ... ... ... ... ... ... ... ... 21,46
Mp., OC ... ... ... ... ... ... ... ... ... ... ... ... ... 1772
Bp., OC ... ... ... ... ... ... ... ... ... ... ... ... ... ~ 3900
?????Electrical conductivity (Hg = 1) ... ... 10
?????? Hovozg, 298 kJ / mol ... ... ... ... ... ... ... ... .. 556
?????So298, J / (K * mol) ... ... ... ... ... ... ... ... ... 41,5
?????? about 298 E2 + + 2e = E, V ... ... ... ... ... ... ... ... .. +1,19
?????In comparison with other platinum metals, platinum is slightly more reactive. However, it reacts only at high temperature (often at red heat) and the finely divided state. Obtained in this connection is usually malostoyki and with further heating decompose.
?????For platinum, the most characteristic absorption of oxygen. Great importance is platinum as a catalyst for oxidation of ammonia (in arbitrary HNO3), hydrogen (for purification of O2 admixture H2) and other processes of catalytic oxidation.
?????In the electrochemical electrochemical series platinum is located after hydrogen and dissolved by heating only in aqua regia:
?0 +4
3Pt + 4HNO3 + 18NSl = K2 [RtCl6] + 4NO + 8H2O
?????When fused with alkali, cyanides, and sulfides of alkali metals in presence of oxidants (even O2) platinum passes to the corresponding derivatives of anionic complexes.
?????Platinum is used for the manufacture of corrosion-resistant laboratory glassware, apparatus and instruments for chemical production, for resistance thermometers and thermocouples, as well as electrical contacts. Platinum produce insoluble anodes, for example, for the electrochemical production nadsernoy acid and perborate. Platinum used in jewelry.
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The compounds Pt (0)
?????Like other d-elements, zero (and negative) degree of oxidation of platinum appears in compounds with ligands?-Donor and?-Acceptor type: CO, PF3, CN-. At the same time with the electronic configuration of the central atom d10 structure of complexes with strong field ligands often responsible structure of the tetrahedron.
?????For platinum, as an element of group VIII (with the electronic configuration of d8 - d10) complexes are known in which the role of ligands plays an O2 molecule, for instance Pt (O2) [P (C6H5) 3] 2.
?????Molecule O2 - ligand?-Type (like CN-, CO, N2, NO). His accession to the complexing agent is realized through the donor-acceptor and dative interactions M-O2 participation? -, "- And? *- Orbitals of the molecule O2.
?????Such compounds, by analogy with nitrogenilnymi and carbonyl compounds can be called oksigenilnymi. Oksigenilnye connection - good transmitters of oxygen and catalysts, due to activation of O2 are good oxidizing already under normal conditions. For example, Pt [P (C6H5) 3] 4 absorbs oxygen:
Pt [P (C6H5) 3] 4 + O2 = Pt (O2) [P (C6H5) 3] 2 + 2P (C6H5) 3
and the resulting Pt (O2) [P (C6H5) 3] 2 is an oxidant, for example:
?0 +2
Pt (O2) [P (C6H5) 3] 2 + 2NO2 = Pt (NO3) 2 [P (C6H5) 3] 2
the hydrolysis yields hydrogen peroxide.
?????Activation of molecular oxygen by chelation imeetbolshoe biochemical importance. A classic example is the addition of oxygen to hemoglobin.
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The compounds Pt (II)
?????For Pt (II) are typical of diamagnetic planar complexes, because of significant size parameter splitting?, As with any d-element 5 th and 6 th periods.
?????For large values? an octahedral complex of two electrons are on strongly antibonding molecular? * d-orbitals. Therefore becomes energetically favorable loss of these electrons and the transition Pt (II) in the oxidation state +4, or degeneration of the octahedral complex in planar. Distribution of eight electrons in the orbitals of the planar complex is energetically more favorable than the molecular orbitals of the octahedral complex. The concentration of eight electrons in four molecular orbitals determines the diamagnetic complexes of planar structure.
?????The compounds Pt (II) intensely colored. Structural unit of the compounds of Pt (II) is a square. Thus, in crystals PtO (Fig. 1) Pt atoms surrounded by four oxygen atoms in the vertices of the quadrilateral. These squares are connected by the parties in the chain, which intersect at an angle of 90 ?. Similarly crystals are built PtS.
Fig. 1. The structure of PtO and PtS
?????Dichloride of platinum has a completely different structure. Red-black crystals PtCl2 consist of octahedral cluster groups Pt6Cl12.
?????Chlorides of platinum can be obtained by direct synthesis:
Pt + Cl2 = PtCl2 (t = 500 0C)
Pt + 2Cl2 = PtCl4 (t = 250 0C)
?????Dichloride PtCl2 available and dissociation PtCl4, as well as heating platinohloristovodorodnoy acid:
(H3O) 2RtCl6 * nH2O = PtCl2 + HC1 + (n + 2) H2O + Cl2 (t> 300 0C)
The genetic relationship of anhydrous chlorides of platinum passes the following scheme:
?370? C 475? C 581? C 583? C
PtCl4 ==> RtC13 ==> PtCl2 ==> PtCl ==> Pt
Note the very small magnitude of the temperature range that separates the region of existence of platinum chlorides of different composition. This is one of the specific properties of the compounds of Pt, with basically vysokokovalentnuyu kinetically inert chemical bond.
?????Oxides and hydroxides of Pt (II) in black, do not dissolve in water; PtO also resistant to acids. PtS not soluble in acids.
?????Of the cationic complexes of Pt (II) are very stable and easily formed amminokompleksy [Pt (NH3) 4] 2 +
PtCl2 + 4NH3 = [Pt (NH3) 4] Cl2
Known as a large number of derivatives of cationic complexes of Pt (II) with organic ligands. Even more resistant tetratsianidoplatinat (II) [Pt (CN) 4] 2 - iony (for the latter? 4 = 1 * 1041). Known as H2 [Pt (CN) 4] * 3H2O; in aqueous solutions is a strong dibasic acid (called platinosinerodistoy).
?????Platinaty (II) are very diverse and stable. For example, integrated galogenydy Pt (II) characterized by the following stability constants:
?Ion ............. [PtCl4] 2 - [PtBr4] 2 - [PtI4] 2 -
lg ?.............. 16,0 20,5 -30

Figure 2. Structure of K2 [PtCl4]
?????Salts of M2 [PtS14] (red) formed by the interaction of compounds of Pt (II) in hydrochloric acid with the corresponding salts of alkali metals. The most important water-soluble K2 [PtCl4] and Na2 [PtCl4] (Fig. 2), which are precursors for the synthesis of different platinum compounds.
?????Also known compounds, in which Pt (II) are both in the composition and the cation and anion, such as [Pt (NH3) 4] [RtSl4]. This compound (green) is precipitated by mixing solutions of [Pt (NH3) 4] Sl2 and
K2 [PtCl4]:
[Pt (NH3) 4] Cl2 + K2 [PtCl4] = [Pt (NH3) 4] [PtCl4] + 2KC1
Along with cationic and anionic complexes are quite diverse neutral complexes Pt (II)-type [Pt (NH3) 2X2] (where X = C1-, Br-, NO2-). For the compounds of this type is characterized by a geometric (cis-trans) isomerism. For example, the composition [Pt (NH3) 4S12] are two compounds which differ in properties, in particular coloration: the cis-isomer - orange-yellow, trans-izoier - light yellow. Cis-and trans-isomers always have a few (and sometimes very) different solubility in water, acids, as well as kinetic and thermodynamic characteristics.
?????In contrast to the trans-isomer, cis-isomer has pronounced anticancer physiological activity. Significantly different and methods for obtaining these isomers. Cis-isomer is formed during the replacement of two chloride ions in the molecules of ammonia tetrahloroplatinat (II)-complex:
K2 [PtCl4] + 2NH3 = [Pt (NH3) 2Cl2] + 2KC1
??????tsic isomer
Tranc-isomer is obtained by substitution of two molecules of ammonia chloride ions in the complex tetraammin-platinum (II):
[Pt (NH3) 4] Cl2 +2 HC1 = [Pt (NH3) 2Cl2] + 2NH4C1
?trans-isomer
To understand the direction of flow of substitution reactions of ligands in the complexes of importance is the principle of trans-influence ( "The behavior of the complexes depends on transzamestiteley"), set II Chernyayev (1926). According to this principle, some ligands facilitate the substitution of ligands being in trans position. Thus, the synthesis of compounds of platinum plays an important role, not only the nature of reagents, but also the order of the mixing time and concentration ratio: Depending on the synthesis conditions can be obtained isomers situation.
??????Transzamestiteli are on the line (coordinate) passing through the central atom, tsiszamestiteli are like the side of the central atom - on the line (coordinate), not passing through the central atom.
?????Experimentally that for compounds of Pt (II) trans-influence of ligands increases in the number of
H2O
?????The principle of the trans-influence played a prominent role in the development of the synthesis of complex compounds.
?????One well-studied complexes of platinum, named after its discoverer, is the salt Tseyze K [PtCl3 (S2H4)]. It is painted in yellow compound was synthesized by the Danish pharmacist Tseyze back in 1827. Salt Tseyze - one of the first synthetically derived organometallic compounds, one of the ligands in the coordination sphere of platinum (II) there is an ethylene (donor properties showing double bond H2C == CH2).

The compounds Pt (IV)
?????Oxidation state +4 is typical for platinum. For Pt (IV) are known brown (different shades) oxide PtO2, hydroxide, Pt (OH) 4 (correct PtO2 * nH2O), halides PtHal4, sulfide PtS2 and numerous derivatives of cationic, neutral and anionic complexes.
?????Pt oxides are thermally unstable and dissociate when heated.
PtO2 = Pt + O2
?????Under the action of molecular hydrogen oxides are reduced to Pt metal.
?????The coordination number of Pt (IV) is six, which corresponds to the octahedral configuration of complexes. Last diamagnetic, have the following electronic configuration:? 12?? 6d
?????Binary compound Pt (IV) are the direct interaction of simple substances by heating or by the decomposition of the complex compounds. In binary compounds of Pt (IV) acid properties predominate over basic. Dissolution of hydroxide of platinum (IV) PtO2 * nH2O in acids and alkalis formed complexes of anionic type, for example:
Pt (OH) 4 + 2NaOH = Na2 [Pt (OH) 6]
Pt (OH) 4 + 2HC1 = H2 [RtS16] + 4N2O
For tetrahalides PtHaI4 very typical interaction with hydrohalic acids and major halides with the formation of complexes of the type [PtHal6] 2 - (Hal = Cl, Br, I):
2HC1 + PtCl4 = H2 [RtSl6]
?2NaCl + PtCl4 = Na2 [RtS16]
?????Jonah [PtHal6] 2 - (except for [PtF6] 2 -) are very stable. Thus, under the action of AgNO3 solutions geksahloroplatinatov (IV) formed light-brown precipitate Ag2 [PtCl6], rather than AgCl. In contrast, Na2 [PtCl6] geksahloroplatinaty (IV) K +, Pb +, Cs + and NH4 + poorly soluble in water and stand out in the form of yellow rain, which is used to open these ions in analytical practice.
?????From platinum compounds most important for the practice is platinohloristovodorodnaya acid - a common reagent, commonly used for preparing other compounds of platinum. Fixed H2PtCl6 a red-brown crystals. Mortar her painted in yellow. Although the salt of this acid with multiply charged cations are soluble ions K +, Rb +, Cs + and NH4 + form with the anion PtCl62-soluble compounds, so platinohloristovodorodnaya acid is used as a reagent for the heavy alkali elements:
H2PtCl6 + 2KC1 = K2PtCl6 + 2HC1
?????Obtained by evaporation of its solutions interaction products PtCl4 with hydrochloric acid or dissolving platinum in aqua regia.
3Pt + 18HCl + 4HNO3 = 3H2 [PtCl6] + 4NO + 8H2O
?????Based H2 [RtS16] can go to almost any other platinum compounds. Even given the reaction of receipt of H2 [RtS16] substances such as PtCl4, PtCI2, metallic platinum, and other interesting process takes place in boiling solution of H2 [RtS16] with the alkali. It is formed geksagidroksoplatinat alkali metal:
H2 [RtS16] + 8KON = K2 [Pt (OH) 6] + 6KS1 + 2N2O
?????After acidification of the solution K2 [Pt (OH) 6] mineral acid can be obtained white precipitate geksagidroksoplatinovoy acid:
[Pt (OH) e] 2 - + 2H + = H2 [Pt (OH) 6]
In this connection, neighbor protons and hydroxyl ions, but the neutralization reaction does not happen - so binds the Pt (IV) ligands - OH-ions are located in the inner coordination sphere. Here the most important thing is not the thermodynamic and kinetic stability of platinum compounds.
?????Ammonium salt (NH4) 2PtCl6 used to extract platinum from solutions with its processing, as further thermolysis of this salt leads to the production of metallic platinum (in the form of fine black powder with a strongly developed surface - the so-called platinum black):
(NH4) 2PtCl6 = Pt + 2Cl2 + 2NH4Cl
?????In addition to [PtX6] 2 - (X = Cl-, Br-, I-, CN-, NCS-, OH-) are known numerous anionic complexes with diverse ligands, such as number: M2 [Pt (OH) 6], M2 [ Pt (OH) 5S1], M2 [Pt (OH) 4Cl2], M2 [Pt (OH) 3S13], M2 [Pt (OH) 2Cl4], M2 [Pt (OH) Cl5], M2 [RtC16]. Some platinat (IV)-complexes of this series can be obtained by hydrolysis PtCl4:
PtCl4 + 2NON = H2 [Pt (OH) 2Cl4]
or the action of alkalis on chloroplatinate (IV):
Na2 [PtCl6] + 6NaOH = Na2 [Pt (OH) 6] + 6NaCl
?????On the Diversity of the complexes Pt (IV) can also be judged on the following series of derivatives: [Pt (NH3) 6] C14, [Pt (NH3) 5Cl] Cl3, [Pt (NH3) 4Cl2] Cl2, [Pt (NH3) 3S13] C1 , [Pt (NH3) 2S14], K [Pt (NH3) Cl5], K2 [RtS16].
The nature of the coordination of chloride ion in these compounds can be easily installed by chemical means. Thus, the interaction of solutions of [Pt (NH3) 6] Sl4 and AgNO3 precipitated AgCl 4 mole per 1 mole of Pt. From solutions [Pt (NH3) 5S1] C13 and [Pt (NH3) 4S12] C12 allocated respectively 3 and 2 mol AgCl, and a solution of [Pt (NH3) 2S14] silver chloride is precipitated only by a long standing solution when heated. In accordance with the changing nature of the ionization and electrical conductivity of solutions. It is clear that at the same molar concentration maximum electrical conductivity has a solution [Pt (NH3) 6] Cl4, minimum - solution [Pt (NH3) 2Cl4] (Fig. 3).
?????For the compounds of the [Pt (NH3) 4Cl2] Cl2 and [Pt (NH3) 2Cl4] is characterized by geometric isomers: tsuc-[Pt (NH3) 2Cl4] is orange, and trans-[Pt (NH3) 2Cl4] - yellow. Location trans-[Pt (NH3) 2Cl4] in the crystal is shown in Fig. 4.




Fig. 3. Molar electrical conductivity of the compounds of Pt (IV) depending on their composition and P. 4. The crystal structure of [Pt (NH3) 2Cl4]

The compounds Pt (VI)
?????All the studied platinum oxides are thermally unstable, but it is obvious that the higher oxides shown by platinum in the oxidation state, the more pronounced acid character of the oxide. Thus, the electrolysis of alkaline solutions, using Pt-electrodes on the anode is obtained RtO3 trioxide, which with KOH gives platinat of K2O * ZPtO3, which proves the ability of platinum (VI) show acidic properties.
?????Platinum, like a number of other 5d-elements, forms a hexafluoride PtF6. This is a volatile crystalline substance (mp. 61 ? C, bp. 69 ? C) dark-red color, get it burning in platinum fluoride.
Pt4 + + 4F-= PtF4, PtF4 + F2 = PtF6.
?????Studying the properties of platinum hexafluoride - a volatile substance, which forms reddish-brown pair - has led to important consequences in the development of inorganic chemistry. In 1960 Bartlett, who worked in Vancouver (Canada), was able to show that the rift may PtF6 fluorine with the formation pentafluoride, which then disproportionates:
PtF6 = PtF5 + 0,5 F2, 2PtF5 = PtF6 + PtF4.
A side result of these experiments was the discovery on the walls of the reaction vessel brown plaque caught oksigenilnym derivative of platinum hexafluoride:
PtF6 + O2 = [O2] + [PtF6] -
The formation of this compound show that PtF6 is a strong oxidant that can tear an electron from molecular oxygen. This observation then led Bartlett to the thought of the possibility to oxidize elemental xenon platinum hexafluoride, which initiated the chemistry of fluoride and oxygen compounds of inert gases.
?????It is important to note that PtF6 - strong oxidizer, apparently surpassing the oxidative action of molecular fluorine. The stability decreases in the series hexafluoride WF6> ReF6> OsF6> IrF6> PtF6>. Particularly fragile PtF6 is among the most powerful oxidants (electron affinity 7 eV), is a fluorinating agent. Thus, it is easy fluoridated VgF3 to BrF5, reacts violently with uranium metal to form UF6. This can be explained by the fact that the connection between Pt-F in PtF6 less durable than us F-F in F2. This makes PtFe source of atomic fluorine - probably the strongest of the existing chemical oxidants acting under milder conditions (lower temperatures) than FS and many other ftorokisliteli.
?????Platinum hexafluoride decomposes water with evolution of oxygen reacts with the glass and also oxidizes molecular oxygen to O2 + [PtF6] -. Since the first ionization potential of molecular oxygen, O2 ==> O2 + is equal to 12,08, ie almost like xenon (12,13 B), it was suggested the possible formation of compounds Xe + [PtF6] -:
Xe + PtF6 = Xe + [PtF6] -
?????Soon, this compound was obtained. Xe [PtF6] - orange-colored crystalline solid, stable at 20 ? C, sublimes in vacuum without decomposition. Synthesis of Xe [PtF6] yarilsya beginning of extensive research that led to the preparation of compounds of noble gases.
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Conclusion
?????Chemistry of platinum is very voluminous, complex and interesting. Perhaps the most common property of its compounds is a narrow temperature range of stability associated with high polarizing effect of platinum and developing its compounds when heated additional effect of polarization, leading to the destruction of chemical bonds and restore the metallic state of platinum.
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References

1. NS Akhmetov. General and Inorganic Chemistry, Moscow, 2001.
2. VI Spitsyn, LI Martynenko. Inorganic Chemistry, Moscow State University, 1994.
3. RA Lidin, VA Milk, LL Andreyev. Chemical properties
?inorganic substances, M., 1996.



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