Block metal II oxides

In Chapter 21, we described the chemistry of the first row d-block metal(II) oxides, but said little about their electrical conductivity properties. The oxides TiO, VO, MnO, FeO, CoO and NiO adopt NaCl lattices but are non-stoichio-metric, being metal-deficient as exemplified for TiO and FeO in Section 27.2. In TiO and VO, there is overlap of the metal t2g orbitals giving rise to a partially occupied band (Figure 27.4) and, as a result, TiO and VO are electrically conducting. In contrast, MnO is an insulator at 298 K... 

Many metallic elements in the p and d blocks, have atoms that can lose a variable number of electrons. As we saw in Section 1.19, the inert-pair effect implies that the elements listed in Fig. 1.57 can lose either their valence p-electrons alone or all their valence p- and s-electrons. These elements and the d-block metals can form different compounds, such as tin(II) oxide, SnO, and tin(IV) oxide, Sn02, for tin. The ability of an element to form ions with different charges is called variable valence. 

Cyclam, with its 14-membered ring, has been demonstrated to complex with a very wide range of metal ions (and especially d-block metal ions) and tends to generate metal complexes that are especially kinetically and thermodynamically stable [22], In particular instances it is also known to aid the stabilisation of less common oxidation states such as Ni(III), Cu(III), Ag(II) and Ag(III) [25,26],... 

Latent forms of MMPs can be activated by mechanisms which cause the dissociation of the intramolecular complex between a particular cysteine residue and the required zinc metal ligand (a complex that blocks the active site) [47], This occurs because the cysteine of the latent enzyme is coordinated to the active site in a particular way that blocks the MMP active site. Collectively, the activation of MMPs occurs through a process which has been termed the cysteine-switch . Activators of the MMPs include proteases (e.g. plasmin), conformational perturbants (SDS, NaSCN), heavy metals and organomercurials (e.g. Au(I) compounds, Hg(II)), oxidants (e.g. OC1-), disulfide compounds (e.g. GSSG) and sulfhydryl alkylating agents (e.g. V-ethylmaleimide) [47 and refs, therein]. 

E3J9 As noted in Section 3.17(a) nonstochiometry is common for the solid state compounds of d-, f-, and heavier p-block elements. All of the metals forming oxides are either d-block (Zn and Fe) or f-block (U) metals. However, Zni+xO would be expected to show nonstoichiometry over very small range because the only significant and sufficiently stable oxidation state for Zn is +2. Thus, in this case as x increases, some of Zn(II) should be reduced to Zn(l), a very unlikely process. The next one would be Fci. O because Fe has two adjacent oxidation states Fe(n) and Fe(in). Finally that leaves UO2+X as the oxide with possible wide range of nonstoichiometry, considering that U, apart from U(rV), has a relatively stable U(VI) state. ... 

First row d-block metal ions are found dominantly in the M(II) or M(III) oxidation states. Heavier members of the d block tend to prefer higher oxidation states. 

A large number of inorganic species are able to undergo electrochemical processes. For example, coordination compoxmds containing f-block metal centres may exhibit metal- and/or ligand-centred redox processes. Some electron transfer processes are reversible, e.g. metal-centred, one-electron reduction and oxidation in an iron(III)/(II) complex, the potential for which depends on the ligand ... 

Copper is the only first row r/-block metal to exhibit a stable +1 oxidation state. In aqueous solution, Cu(I) is unstable by a relatively small margin with respect to Cu(II) and the metal (equations 22.97, 22.100 and 22.101). 

Stable oxidation states for the group 11 metals differ in contrast to the importance of Cu(II) and Cu(I), silver has only one stable oxidation state, Ag(I), and for gold, Au(in) and Au(I) are dominant, with Au(III) being the more stable. Relativistic effects (discussed in Box 13.2) are considered to be important in stabilizing Au(III). As we have already noted, discussing oxidation states of the heavy block metals in terms of independently obtained physicochemical data is usually impossible owing to the absence of IE values and the scarcity of simple ionic... 

A transition element is defined as a d-block metal that forms at least one stable cation with an incomplete 3d sub-level. All the elements in Table 13.3 conform to this except zinc which is therefore not a transition element. Copper is regarded as a transition element since it forms the stable copper(ii) ion, which has an incomplete d sub-level. Scandium is also regarded as a transition element since it can form Sc ([Ar]3d 4s ) and Sc ([Ar]3dHs ) in a limited number of compounds. For example the compound CsScCl3 [Cs Sc 3C1 ] has scandium in oxidation state +2. 

Figure 14 The molecular building blocking metal 5,10,15,20-tetrakis(3,5-biscarboxylphenyl)porphyrin (M-HgOCPP) (M = Mn(III)Cl or Ni(II)) (a) used to construct porous MPFs for catalytic oxidation of alkylbenzenes (b) (Reprinted with permission from Ref. 103. Copyright (2012) American Chemical Society.)...

In the case of d-block metal cations, a lack of correlation with the Eq. 15.1 empirical rule is expected as a consequence of the 7r-back donation of d-electrons. It was already mentioned that the presence of a tt -back-donation contribution does reinforce the strength of the carbonyl bond and does cause a downwards shift of the stretching frequency [22, 24, 25], This was confirmed by plotting the pairs of IR spectroscopic and microcalorimetric data for Cu- and Ag-carbonyls formed either within the zeolite nanopores or at the surface of metal oxides. The reinforcement of the carbonyl bond was witnessed by (i) the large heat of adsorption (qo > lOOkJ moP ) measured for both for Cu- and Ag- carbonyls (see Chap. 1, Fig. 1.14) and (ii) the partial irreversibility of the adsorption upon evacuation of pressure (see Chap. 1, Figs. 1.10 and 1.11). 

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