The Fe -Co-Ni Group

The three elements to be treated in this chapter (Fe, Co, Ni) are the sixth, seventh, and eighth members of the first transition series. The first five members (Sc, Ti, V, Cr, Mn) have been treated in previous chapters (Chapters 12, 13, and 14).The ten elements of this first transition series (Sc through Zn) are characterized by electron activity in the 4s-3d levels. All elements in the 3d transition series are metals, and many of their compounds tend to be colored as a result of unpaired electrons. Most of the elements have a strong tendency to form complex ions due to participation of the d electrons in bonding. Unlike the previous three elements (V, Cr, Mn), these three do not show a variety of oxidation states. The higher oxidation states are almost absent in compounds, Fe showing principally the II and III, Co the II and III, and Ni only the II. The III states are less stable than the II states unless they are stabilized by complex formation. The resemblance of these three elements is notable, they being more like each other than they are to the elements below them. 

Name Formula State Color AG° Solubility (kJ/mole)  

The ores are blended with Na2C03 and KNO3, then roasted. Part of the S and As are removed as volatile compounds, leaving Co, Ni, and Cu oxides, with some sulfates, and arsenates. The sulfates and arsenates are leached with HOH, then the oxides are dissolved in hot H2SO4. The solution is treated with the oxidant NaClO, and the hydroxides are selectively precipitated by careful 

The element Co is a hard lustrous bluish-white metal which acquires a somewhat inert coat of C03O4 in air or aerated HOH. It is not further reactive with HOH, air, or bases, but dissolves slowly in non-oxidizing acids and rapidly in dilute oxidizing acids to give pink Co+. When finely powdered, Co heated in air gives black C03O4. 

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CO (in a heterolytic sense) generates Ni(CO)3, 21.28, which is predicted to have one empty frontier orbital and is therefore isolobal to CHs. Now, we have a problem—is Ni(CO)3 isolobal to CH2or CH3+ In fact it is isolobal to both. If we use Ni(CO)3 to reconstruct a trigonal bipyramid, then it is isolobal to CH2 however, if it is used to form a tetrahedral complex then it is isolobal to CH3. Suppose we remove an equatorial CO ligand from Fe(CO)s 21.24. That creates a C2V Fe(CO)4 ligand with one empty hybrid orbital, and the Fe(CO)4 group is isolobal to CHa. Ethylene-Fe(CO)4, 21.29, is then equivalent to protonated cyclopropane, 21.30. But, we had said that ethylene-Fe(CO)4, drawn in the metallacyclopropane form in... 

Meta/ Oxides. The metal oxides aie defined as oxides of the metals occurring in Groups 3—12 (IIIB to IIB) of the Periodic Table. These oxides, characterized by high electron mobiUty and the positive oxidation state of the metal, ate generally less active as catalysts than are the supported nobel metals, but the oxides are somewhat more resistant to poisoning. The most active single-metal oxide catalysts for complete oxidation of a variety of oxidation reactions are usually found to be the oxides of the first-tow transition metals, V, Cr, Mn, Fe, Co, Ni, and Cu. 

Compounds that belong to the two-dimensional category undergo polarization reversal due to atomic displacement in a plane that contains a polar axis. The displacement can be imagined as the rotation of atomic groups around an axis that is perpendicular to a reflection plane. Typical examples of two-dimensional compounds include BaMF4 type compounds, where M = Mg, Mn, Fe, Co, Ni, Zn. 

Both PH3 and S i 114 react similarly with bare transition metal ions except that no simple addition ions [MSiELJ have so far been observed. The Cu+ ion reacts by dehydrogenation and the most unreactive ion, Mn+, does not react in its ground state. The excited-state ion forms [MnH]+. The reactions of several first-row transition metal ions with silane (117-119) have been studied by the GIB method. The major product was [MSiH2]+ for the ground-state ions Ti+, V+, Cr+, Fe+, Co+, Ni+, Cu+, and Zn+. The group 3 (IIIB) ions Sc+, Y+, La+, and Lu+ (49) all reacted with silane in a similar manner to the first-row transition metal ions. 

Hydrogen atoms and part of He are believed to have been created during the Big Bang by proton-electron combinations. Most nuclides lighter than iron were created by nuclear fusion reactions in stellar interiors (cf table 11.1). Nuclides heavier than the Fe-group elements (V, Cr, Mn, Fe, Co, Ni) were formed by neutron capture on Fe-group seed nuclei. Two types of neutron capture are possible slow (s-process) and rapid (r-process). 

The diameter of the SWNTs is typically 1.8-2.1 nm, thicker than the SWNTs produced from the iron-group metals (Fe, Co, Ni). On the other hand, a typical length of the tubes obtained from rare-earth catalysts is shorter (30 to 100 nm) than those obtained from the iron-group metals ( 1 (jliti). 

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