1. Inorganic Chemistry B Chapter 23 1Dr. Said El-Kurdi d-Block metal chemistry: the second and third row metals

2. 2 Dr. Said El-Kurdi 23.1 Introduction

3. Dr. Said El-Kurdi3 The abundances of some of the heavier metals are very low, e.g. Os, 1  10  4 ppm and Ir, 6  10  6 ppm; Tc does not occur naturally Yttrium and lanthanum are similar to the lanthanoids and occur with them in nature. Zirconium is the next most abundant d-block metal in the Earth’s crust after Fe, Ti and Mn Zirconium and hafnium occur naturally together and are hard to separate. Hf is rarer than Zr, 5.3 and 190 ppm, respectively, of the Earth’s crust.

4. 4 Dr. Said El-Kurdi Very pure metals can be obtained by zone refining Beginning with a polycrystalline rod, a small zone (which lies perpendicular to the direction of the rod) is melted. The focus-point of the zone is gradually moved along the length of the rod; under carefully controlled conditions, cooling, which takes place behind the melt-zone, produces single crystals while impurities migrate along the rod with the molten material.

5. 5Dr. Said El-Kurdi Niobium (formerly known as columbium) and tantalum occur together in the mineral columbite (Fe,Mn)(Nb,Ta) 2 O 6 molybdenum and tungsten compounds are usually isomorphous, the elements occur separately. Technetium is an artificial element, available as 99 Tc (a  - particle emitter Rhenium is rare and occurs in small amounts in Mo ores. The platinum-group metals (ruthenium Ru, Osmium Os, Rhodium Rh, iridium Ir, Pd and Pt) are rare and expensive, and occur together either native or in sulfide ores of Cu and Ni.

6. 6Dr. Said El-Kurdi Silver and gold occur native, and in sulfide, arsenide and telluride ores, e.g. argentite (Ag 2 S) Cadmium occurs as the rare mineral greenockite (CdS), but the metal is isolated almost entirely from zinc ores, CdS occurring (<0.5%) in ZnS. Cadmium has a relatively low melting point (594 K) and is used as an alloying agent in low-melting alloys. The main use of cadmium is in NiCd batteries

7. 7Dr. Said El-Kurdi The symbol Hg is derived from hydrargyrum (Latin) meaning ‘liquid silver’. The major source of mercury is cinnabar (HgS), from which the metal is extracted by roasting in air 23.3 Physical properties The electronic configurations of the ground state M(g) atoms change rather irregularly with increasing atomic number more so than for the first row metals the nd and (n+1)s atomic orbitals are closer in energy for n = 4 or 5 than for n = 3

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10. 10Dr. Said El-Kurdi with the exception of Hg (group 12), the heavier metals have higher values of  a H o than their first row congeners. This is a consequence of the greater spatial extent of d orbitals with an increase in principal quantum number, and greater orbital overlap. 5d–5d > 4d–4d > 3d–3d.

11. 11Dr. Said El-Kurdi The heavier metals exhibit many more compounds containing M  M bonds. In general, the stability of high oxidation states increases for a given triad in the sequence first row  second row < third row metals.  easier promotion of electrons for the 5d metals compared with 4d or 3d metals;  better orbital overlap for 5d orbitals (or those with 5d character) than for 4d or 3d orbitals.

12. 12Dr. Said El-Kurdi Relativistic effects If Einstein’s theory of relativity is combined with quantum mechanics, in which case they are attributed to relativistic effects. According to the theory of relativity, the mass m of a particle increases from its rest mass m 0 when its velocity v approaches the speed of light, c, and m is then given by the equation:

13. 13Dr. Said El-Kurdi For a one-electron system, the Bohr model of the atom leads to the velocity of the electron being expressed by the equation: where Z = atomic number, e = charge on the electron,  0 = permittivity of a vacuum, h = Planck constant For n = 1 and Z = 1, v/c is only (1/137) but for Z = 80, v/c = 0.58 leading to m = 1.2m 0. Since the radius of the Bohr orbit is given by the equation

14. Dr. Said El-Kurdi14 the increase in m results in an approximately 20% contraction of the radius of the 1s (n = 1) orbital; this is called relativistic contraction. Other s orbitals are affected in a similar way and as a consequence, when Z is high, s orbitals have diminished overlap with orbitals of other atoms. p orbitals (which have a low electron density near to the nucleus) are less affected. d orbitals (which are more effectively screened from the nuclear charge by the contracted s and p orbitals) undergo a relativistic expansion; a similar argument applies to f orbitals.

15. Dr. Said El-Kurdi15 The relativistic contraction of the s orbitals means that for an atom of high atomic number, there is an extra energy of attraction between s electrons and the nucleus.

16. Dr. Said El-Kurdi16 Effects of the lanthanoid contraction pairs of metals in a triad (Zr and Hf, Nb and Ta etc.) are of similar radii. This is due to the lanthanoid contraction: the steady decrease in size along the series of lanthanoid metals Ce–Lu which lie between La and Hf in the third row of the d-block. This observation is due to the presence of a filled 4f level the shielding of one 4f electron by another is less than for one d electron by another, and as the nuclear charge increases from La to Lu, there is a fairly regular decrease in the size of the 4f n sub-shell.

17. Dr. Said El-Kurdi17 Coordination numbers Consistent with the increase in size in going from a first row to later metals in a triad, the heavier metals tend to show higher coordination numbers. 23.4 Group 3: yttrium In the coordination chemistry of Y 3+, coordination numbers of 6 to 9 are usual. The Y 3+ ion is ‘hard’ and in its complexes favors hard N- and O- donors

18. Dr. Said El-Kurdi18 23.5 Group 4: zirconium and hafnium The Lewis acidity of the halides is seen in the formation of complexes such as HfCl 4 2L (L = NMe 3, THF) 23.6 Group 5: niobium and tantalum The properties of Nb and Ta (and of pairs of corresponding compounds) are similar. At high temperatures, both are attacked by O 2 (equation 23.20) and the halogens (equation 23.21) and combine with most non-metals.

19. Dr. Said El-Kurdi19 The halides NbF 5, TaF 5, NbCl 5 and TaCl 5 are useful starting materials in the chemistry of these metals. 23.7 Group 6: molybdenum and tungsten Octahedral geometries are common for complexes of Mo(IV) and W(IV), The salt K 4 [Mo(CN) 8 ]  2H 2 O was the first example (in 1939) of an 8-coordinate (dodecahedral) complex. However, studies on a range of salts of [Mo(CN) 8 ] 4  and [W(CN) 8 ] 4  reveal cation dependence, both dodecahedral and square antiprismatic anions being found

20. Dr. Said El-Kurdi20 23.8 Group 7: technetium and rhenium

21. Dr. Said El-Kurdi21 23.9 Group 8: ruthenium and osmium Like all platinum-group metals, Ru and Os are relatively noble. Osmium powder reacts slowly with O 2 at 298K to give the volatile OsO4

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