D-group elements

A characteristic feature of d-group elements is their ability to form complexes with Tt-acceptor type ligands such as CO. All group-6 elements Cr, Mo, and W form very volatile and stable hexacarbonyls and constitute the only complete family of carbonyls. However, direct production of carbonyls from the elements and CO is only — if at all — accomplished at high pressures and temperatures. 

There are now hundreds if not thousands of compounds of the d group elements, lanthanides and actinides. All manner of ligands may be present such as CO, PR3, V-QHj, arenes, CN , halides, pyrazolylborates, and so on. Some compounds will be noted under the chemistry of the particular element involved. 

The third section of the periodic table comprises transition metals or the d-group elements, which are involved in many biological defence mechanisms against toxic radicals. As in chemical catalysis the same metals are active in biochemical systems. Surprisingly these redox mediators are involved in both, the generation and the removal of reactive oxygen species. 

The Group 12 atoms are on the edge of the transition metal part of the periodic table, and because these elements don t form any compounds in which the d-orbital shell is not full, they re not considered a transition metal. They do, however, resemble the d-group elements in their ability to form complexes with amines, halide ions, ammonia, and even cyanide. In the case of bonding with cyanide, CN, the possibility for dre bonding between the metals and the ligand is much lower when compared with the rest of the transition metals. 

The redox behaviour of Th, Pa and U is of the kind expected for d-transition elements which is why, prior to the 1940s, these elements were commonly placed respectively in groups 4, 5 and 6 of the periodic table. Behaviour obviously like that of the lanthanides is not evident until the second half of the series. However, even the early actinides resemble the lanthanides in showing close similarities with each other and gradual variations in properties, providing comparisons are restricted to those properties which do not entail a change in oxidation state. The smooth variation with atomic number found for stability constants, for instance, is like that of the lanthanides rather than the d-transition elements, as is the smooth variation in ionic radii noted in Fig. 31.4. This last factor is responsible for the close similarity in the structures of many actinide and lanthanide compounds especially noticeable in the 4-3 oxidation state for which... 

Hellwinkel, D. Penta- and.Hexaorganyl Derivatives of the Main Group Elements. 109, 1-63... 

FIGURE 4. Medium-long form table showing highest and most common oxidation states of the d-block elements. Only two of these 30 ions, Ag+1 and Au+3, (shown in bold-face) show anomalous electronic configurations with respect to other ions in the same groups. 

Figure C.6 shows another pattern in the charges of monatomic cations. For elements in Croups 1 and 2, for instance, the charge of the ion is equal to the group number. Thus, cesium in Group 1 forms Cs+ ions barium in Group 2 forms Ba2+ ions. Figure C.6 also shows that atoms of the d-hlock elements and some of the heavier metals of Groups 13/111 and 14/IV can form cations with different charges. An iron atom, for instance, can lose two electrons to become Fe + or three electrons to become Fe 1. Copper can lose either one electron to form Cu or two electrons to become Cu2+.

D.21 A main-group element E in Period 3 forms the molecular compound EH4 and the ionic compound Na4E. Identify element E and write the names of the compounds described. 

All d-block elements are metals (Fig. 1.63). Their properties are transitional between the s- and the p-block elements, which (with the exception of the members of Group 12) accounts for their alternative name, the transition metals. Because transition metals in the same period differ mainly in the number of /-electrons, and these electrons are in inner shells, their properties are very similar. 

The product of the second reaction is sodium aluminate, which contains the alumi-nate ion, Al(OH)4. Other main-group elements that form amphoteric oxides are shown in Fig. 10.7. The acidic, amphoteric, or basic character of the oxides of the d-block metals depends on their oxidation state (Fig. 10.8 also see Chapter 16). 

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