Metals platinum triads

These six metals located beneath the iron triad on the periodic chart are very much alike. The first three are called the light platinum triad. The heavy platinum triad includes the other two and platinum itself. They are usually found together in nature and are used for similar things. All are shiny and beautiful and they do not tarnish or rust. 

Most of the transition elements do not react with strong acids, such as HCl and H2SO4. Some do have negative standard reduction potentials for the reaction M"+ -I- ne - M, and liberate hydrogen from hydrochloric acid. These include Mn, Cr, and the iron triad. Silver, gold, the palladium triad, and the platinum triad, the so-called noble metals, are especially inert to acids, both to the nonoxidizing species, such as hydrochloric and hydrofluoric acids, and to the oxidizing acids, such as nitric acid. 

The platinum-group metals (PGMs), which consist of six elements in Groups 8— 10 (VIII) of the Periodic Table, are often found collectively in nature. They are mthenium, Ru rhodium, Rh and palladium, Pd, atomic numbers 44 to 46, and osmium. Os indium, Ir and platinum, Pt, atomic numbers 76 to 78. Corresponding members of each triad have similar properties, eg, palladium and platinum are both ductile metals and form active catalysts. Rhodium and iridium are both characterized by resistance to oxidation and chemical attack (see Platinum-GROUP metals, compounds). 

The nine elements, Fe, Ru, Os Co, Rh, Ir Ni, Pd and Pt, together formed Group VIII of Mendeleev s periodic table. They will be treated here, like the other transition elements, in vertical triads, but because of the marked horizontal similarities it is not uncommon for Fe, Co and Ni to be distinguished from the other six elements (known collectively as the platinum metals) and the two sets of elements considered separately. 

The mechanism by which this low oxidation state is stabilized for this triad has been the subject of some debate. That it is not straightforward is clear from the fact that, in contrast to nickel, palladium and platinum require the presence of phosphines for the formation of stable carbonyls. For most transition metals the TT-acceptor properties of the ligand are thought to be of considerable importance and there is... 

Heteronuclear Clusters Containing Platinum and the Metals of the Iron, Cobalt, and Nickel Triads... 

Numerous dmit chelates have been synthesized following that route. Although dmit chelates of common metal ions are known, considerable interest has been focused on those of d8 ions (nickel triad). Nickel chelates are listed in Tables 26 and 27. Table 28 summarizes all other salts of bis-chelates of dmit, including the other two elements of nickel triad, palladium and platinum. 

Oxidative additions are frequently observed with transition metal d8 systems such as iron(0), osmium(O), cobalt(I), rhodium(I), iridium(I), nickel(II), palladium(II) and platinum(II). The reactivity of d8 systems towards oxidative addition increases from right to left in the periodic table and from top to down within a triad. The concerted mechanism is most important and resembles a concerted cycloaddition in organic chemistry (Scheme 1.1). The reactivity of metal complexes is influenced by their... 

In Group VIII, each position instead of being filled by a single element is occupied by a group of three elements. Thus there appear in triads iron, cobalt, and nickel ruthenium, rhodium, and palladium and osmium, iridium, and platinum. In this group there is no subdivision into families, but all the members are heavy metals. 

Platinum (Z = 78) is a whitish, noble metal found in group 10 (or VIIIB) of the periodic table, in the triad with and lying below nickel and palladium (see Periodic Table Trends in the Properties of the Elements). It can be found in elemental form in the mountains of Columbia, where the pre-Columbian natives used it. European chemists discovered and reported it in the mid-1700s. Like gold and silver, it has a positive reduction potential ... 

Comparison of data in Tables II and III for the cobalt triad indicates that aquation proceeds, on average, about the same for Rh(III) as for Co(III) and substantially slower for iridium(III). As has been observed earlier, however, lability of CF3SO3" complexes is actually enhanced relative to other complexes (such as Cl" complexes) for iridium(III), and for second- and third-row metal ions generally. The property of CF3SO3" as a good leaving group is essentially constant, but the rate of displacement is clearly mediated by the metal ion aquation of the iridium(III) complex is over 100 times slower than for cobalt(III) whereas loss from the exceptionally inert platinum(IV) is slower still (84). 

These rather rare elements usually occur together and are called tlie platinum metals. Their ground-state electronic configurations are in doubt, but the tendency to complete the n — l)d level at the expense of the ns level increases across each triad. The almost uniform atomic radii arc naturally accompanied by great physical similarity. Because the radii of Pd + and Pt + are so small, the metals rarely form uncomplexed cations. 

The Iron Triad, Platinum Group, and Coinage Metals... 

The nearly identical atomic radii of the iron triad—iron, cobalt, and nickel —help explain the similar chemistry of these three elements. The similarities among the platinum group elements in Periods 5 and 6 emphasize the fact that there is little difference between the atomic radii of the elements in these periods in which inner d orbitals are being filled. The coinage metals show the expected similarity among elements in the same group. 

By the late 1950s, Chatt and Bernard Shaw had succeeded in preparing several alkyl-, aryl- and hydrido-metal complexes of the nickel triad. Because of our mutual interest in the kinetic trans effect of platinum(ii) complexes, Chatt and I decided to examine the rates of ligand substitution of these new organometallics. Shaw prepared the compounds and Harry Gray did the kinetic studies. Years later Chatt gave the following account of why the research was so rapidly accomplished. 

A second group of triads was also known in which the atomic weights of the constituent elements were closely similar these were the iron and platinum metals. In the accompanying list the modern atomic weights are used as in the previous table... ... 

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