Rf block metals

Periodic variations in the surface tension of liquid metals, c1 , are shown in Figure 6.5. The much higher surface tension of rf-block metals compared to the s- and p-block metals suggests that the surface tension relates to the strength of interatomic bonding. Similar periodic trends can be found also for the melting temperature and the enthalpy of vaporization, and the surface tension of liquid metals is strongly... 

Compounds with Bonds between Silicon and rf-Block Metal Atoms 529... 

Contain rf-block metal atoms bonded to groups of nonmetals —> Behave like nano-size compass needles in a magnetic field Can be made with shapes such as rings, tubes, or spheres —> Have potential uses in electronic media storage devices such as computer chips... 

Vanadium, tetranuclear rf-block metal complexes, 274-275 van der Waals surfaces cytochrome c, 106 heme peroxidases, 112-113 lignin peroxidase, 103 Van Vleck equation, 265, 268, 272, 287 Vector coupling, 264... 

Examples of coordination complexes include those involving rf-block metal ions (e.g. [Co(NH3)6], 6.12) and species with a central j-block element (e.g. [BF4] , 6.13, and H3B-THF, 6.14) (THF = tetrahydrofuran) although 6.14 is unstable with respect to hydrolysis in aqueous solution. Equations 6.59-6.61 show the formation of these coordination complexes. 

Similar analyses for other metals can be carried out. For example, Cu and Zn are adjacent rf-block metals, and it is interesting to investigate factors that contribute to the difference between E° values for the Cu +/Cu and Zn +/Zn redox couples, and thus reveal how a balance of thermodynamic factors governs the spontaneous reaction that occurs in the Daniell cell (reaction 7.8). Table 7.3 lists relevant thermodynamic data it is apparent that the crucial factor in making E°q i+ significantly more positive than ii°zn2+/zn is the greater enthalpy of atomization of Cu Na (aq)-I-e Na(s)... 

Such alkali metal intercalates are extremely reactive, igniting in air and exploding on contact with water. Potassium can be replaced by a rf-block metal by reaction of KC with metal chloride, but the choice of solvent for the reactions is critical, as is the nature of the rf-block metal salt (e.g. CuCl2-2H20,... 

Phosphonium halides, PH4X, are formed by treating PH3 with HX but only the iodide is stable under ambient conditions. The chloride is unstable above 243 K and the bromide decomposes at 273 K. The [PH4] ion is decomposed by water (equation 14.29). Phosphine acts as a Lewis base and a range of adducts (including those with low oxidation state rf-block metal centres) are known. Examples include H3B-PH3, C13B-PH3, Ni(PH3)4 (decomposes above 243 K) and Ni(CO)2(PH3)2. Combustion of PH3 5delds H3PO4. 

The three rows of J-block metals are shown in the schematic periodic table at the beginning of the chapter. The term transition elements (metals) is also widely used, but rf-block metal and transition element are not interchangeable. A transition element is one for which an atom has an incomplete fi -subshell, or which gives rise to a cation with an incomplete fi -subshell, and thus elements in group 12 (which are within the fi -block) are not transition elements. The elements in the /-block (see Chapter 24) are sometimes called inner transition elements. Throughout our discussions, we shall use the terms fi -block and /-block metals, so being consistent with the use of the terms i-block and />-block elements in earlier chapters. Three further points should be noted ... 

In this section, we give an overview of the coordination numbers and geometries found within rf-block metal compounds. It is impossible to give a comprehensive account, and several points should be borne in mind ... 

An important point is that spin-orbit coupling is generally large for second and third row rf-block metal ions and this leads to large discrepancies between p(spin-only) and observed values of p ff. The complexes cw-[NbBr4(NCMe)2] and cis-... 

Table 25.4 lists activation volumes for reaction 25.21 with selected hrst row rf-block metal ions. The change from negative to positive values of AV indicates a change from associative to dissociative mechanism, and suggests that bond making becomes less (and bond breaking more)... 

One of the driving forces behind organometallic cluster research is to model metal-surface catalysed processes such as the Fischer-Tropsch reaction. The cluster-surface analogy assumes that discrete organometallic clusters containing rf-block metal atoms are realistic models for the bulk metal. In many small clusters, the arrangements of the metal atoms mimic units from close-packed arrays, e.g. 

Fig. 20.2 Trends in standard enthalpies of atomization, A H°(29S K), across the three rows of s- and rf-block metals K to Zn, Rb to Cd, and Cs to Hg.

In Section 20.5, we stated that paramagnetism is a characteristic of some r/-block metal compounds. In Section 21.9 we consider magnetic properties in detail, but for now, let us simply state that magnetic data allow us to determine the number of unpaired electrons. In an isolated first row rf-block metal ion, the 3d orbitals are degenerate and the electrons occupy them according to Hund s rules e.g. diagram 21.1 shows the arrangement of six electrons. 

Table 21.12 Calculated magnetic moments for first row rf-block metal ions in high-spin complexes at ambient temperatures. Compare these values with those observed (Table 21.11).

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