Second and third transition series

These elements formed Group IIB of Mendeleef s original periodic table. As we have seen in Chapter 13, zinc does not show very marked transition-metaf characteristics. The other two elements in this group, cadmium and mercury, lie at the ends of the second and third transition series (Y-Cd, La-Hg) and, although they resemble zinc in some respects in showing a predominantly - - 2 oxidation state, they also show rather more transition-metal characteristics. Additionally, mercury has characteristics, some of which relate it quite closely to its immediate predecessors in the third transition series, platinum and gold, and some of which are decidedly peculiar to mercury. 

As a general rule, elements in the second and third transition series have similar chemical properties. In contrast, the properties of the first member of the series are often different. This pattern of behavior is seen in Group 7 (VIIB). The properties of rhenium and technetium differ considerably from those of manganese. 

The electronic spectra of the hexafluoro complexes of the second and third transition series. G. C. Allen and K. D. Warren, Struct. Bonding (Berlin), 1974,19,105-165 (94). 

Allen GC, Warren KD (1974) The Electronic Spectra of the Hexafluoro Complexes of the Second and Third Transition Series. 19 105-165 Alonso JA, Baibas LC (1993) Hardness of Metallic Clusters. 80 229-258 Alonso JA, Baibas LC (1987) Simple Density Functional Theory of the Electronegativity and Other Related Properties of Atoms and Ions. 66 41-78 Andersson LA, Dawson JH (1991) EXAFS Spectroscopy of Heme-Containing Oxygenases and Peroxidases. 74 1-40 Antanaitis BC, see Doi K (1988) 70 1-26... 

Fig. 5. The change in stability constant for different ligands with metals in the second and third transition series...

SS). Data for the metals of group VIII and for rhenium in group VIIA are given in Fig. 1, which is divided into three fields separating the metals of the first, second, and third transition series. The specific activity is defined as the activity per unit surface area of metal. Metal surface areas required for the determination of specific activities are derived from measurements... 

Allen,G.C., Warren,K.D. The Electronic Spectra of the Hexafluoro Complexes of the Second and Third Transition Series. Vol. 19, pp. 105—165. 

The Electronic Spectra of the Hexafluoro Complexes of the Second and Third Transition Series... 

Bond energy variations over the periodic table will be subject to perturbations which reflect the underlying atomic configurations. Compounds derived from main-group elements of Period 4, for example, will show discontinuities in properties from those of Period 3 because of the extra d-electron shell. Conversely, the insertion of an f-electron shell brings together the properties of the second and third transition series, especially in the earlier groups. 

In conclusion, it is noted that, as an empirical rule, first row transition metal elements generally form superoxide-type dioxygen complexes, whereas elements of the second and third transition series form peroxide-type dioxygen complexes. 

A basic hydride ligand should be present. This is usually realized for electropositive early transition metals or late transition metals in low oxidation states supported by electron-donating ligands. The metals are preferably from the second and third transition series to ensure strong covalent bonding. 

For the second and third transition series, the values J(L -M-L ) depend strongly on geometry, as indicated in 74 and 75, with the trans-interactions being normally much larger than those for the corresponding cis-compounds. 

The ions of the first members of the second and third transition series (Me + = Y, La and Me + = Zr, Hf) are so large, as to achieve higher C.N.s than 6 already in some compounds AMe +F4 (page 33) and AgMe +Fj (47, 42) as well as in their binary fluorides (pages 37, 30). To deal with these structures which correspond closely to those of the lanthanide and actinide fluorides, is beyond the scope of this review. As for the stereochemistry of 8-coordination the reader is referred to papers by Clark et al. 68) and Kepert 189). 

Most commonly, metal ions M2+ and M3+ (M = a first transition series metal), Li+, Na+, Mg2+, Al3+, Ga3+, In3+, Tl3+, and Sn2+ form octahedral six-coordinate complexes. Linear two coordination is associated with univalent ions of the coinage metal (Cu, Ag, Au), as in Ag(NH3)2+ or AuCL Three and five coordination are not frequently encountered, since close-packing considerations tell us that tetrahedral or octahedral complex formation will normally be favored over five coordination, while three coordination requires an extraordinarily small radius ratio (Section 4.5). Coordination numbers higher than six are found among the larger transition metal ions [i.e., those at the left of the second and third transition series, as exemplified by TaFy2- and Mo(CN)g4 ] and in the lanthanides and actinides [e.g., Nd(H20)93+ as well as UC Fs3- which contains the linear uranyl unit 0=U=02+ and five fluoride ligands coordinated around the uranium(VI) in an equatorial plane]. For most of the metal complexes discussed in this book a coordination number of six may be assumed. 

The chief use of molybdenum is in steels. The oxides and sulfides have some applications as catalysts. Molybdenum is the only element in the second and third transition series which appears to have a major role as a trace metal in enzymes. Several aspects of molybdenum chemistry have been widely studied in order to gain a better understanding of the biological relevance. Molybdenum is one of the few elements which currently has its own series of international conferences.1... 

In general, the coordination numbers of the elements of the second and third transition series lend to be greater than for the first series because the ionic radii are larger by about 15-20 pm (0.15-0.20 A) for corresponding species.20 Thus tetrahedral coordination is considerably less frequent although observed in species such as [WO/-, [ReOJ-, and OsO<- Square planar coordination is found in dH species such as Rh(I), Pd(II), Pt(II). and Auflll), which are especially stabilized by LFSE. Octahedral species are quite common, and the occurrence of coordination numbers 7. 8, 9, and 10 is fairly common. 

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