Five metals

In resolving complex metal-ion mixtures, more than one masking or demasking process may be utilized with various aliquots of the sample solution, or applied simultaneously or stepwise with a single aliquot. In favorable cases, even four or five metals can be determined in a mixture by the application of direct and indirect masking processes. Of course, not all components of the mixture need be determined by chelometric titrations. For example, redox titrimetry may be applied to the determination of one or more of the metals present. 

In the CeSI (115) and NdSBr (334) type of structure, bromine and iodine are coordinated to five metal ions (four of the same layer, and one of the opposite layer) and four halogen ions of the double layer. In the SmSI type (335), iodine is coordinated to three metal ions of a [LS] layer and three other iodine ions of the double layer. In the FeOCl type of compound, such as ErSCl (355) and LuSBr (85), the halogen is surrounded by a polyhedron formed by six sulfur and four halogenide ions. 

Note that the dissociation proceeds with a much lower barrier on the stepped surface. As the structure diagrams show, at all stages in the dissociation the species are more strongly bound on the stepped surface, for reasons discussed in connection with Eq. (87). However, the transition state is most affected, because two N atoms are bound to four metal atoms in the transition state on a perfect surface, whereas that on the stepped surface consists of five metal atoms. As noted above, geometries in which atoms bind to different metal atoms are always more stable than when the two adsorbate atoms share one metal atom. Hence, dissociation is favored over step sites, and if a surface contains such defects they may easily dominate the kinetics. 

By comparing the level of the binding isotherms (figure 3) for both metals and pectins, it became possible to set up an affinity order of pectins, whatever their origin, for the five metal ions Cu2+ Pb + Zn2+ Ni2+ > Ca2+. This scale, already found by pH-measurements, confirmed that Cu2+ and Pb2+ were more strongly bound than the other thi cations with no difference between pectins. 

In tier (1) of the diagram (for the electronic structure of iron(III)), only the total energy of the five metal valence electrons in the potential of the nucleus is considered. Electron-electron repulsion in tier (2) yields the free-ion terms (Russel-Saunders terms) that are usually labeled by term ° symbols (The numbers given in brackets at the energy states indicate the spin- and orbital-multiplicities of these states.)... 

Hartwell, S.I., J.H. Jin, D.S. Cherry, and J. Cairns, Jr. 1989. Toxicity versus avoidance response of golden shiner, Notemigonus crysoleucas, to five metals. Jour. Fish Biol. 35 447-456. 

What is the nature of the multiple metal-metal bonds Let us consider the specific example of HW WH, whose NBO Lewis structure exhibits five metal-metal bonds. Figure 4.24 displays the strongly trans-bent geometry of HW=WH and contour diagrams of the five metal-metal bond NBOs, each drawn in a chosen contour plane (specified in the lower-left-hand corner of the panel) to emphasize its distinguishing characteristics. 

For five-metal clusters, two "parent polyhedra may be considered, viz., the trigonal bipyramid and square-based pyramid. 

It is important to note that in none of the geometric forms are the five metal atoms equivalent. It follows that M-M distances will vary within a given cluster and may reflect geometric or symmetry constraints as well as simple electronic effects. 

Five-metal-atom clusters have been obtained only with osmium. The binary carbonyl Os5(CO)i8 was initially formed in low yield (—10%) by the thermolysis of Os3(CO)12 (201). The yield of the compound may be... 

The structure of [Rh(CO)2Cl]2 in the solid state83) shows association between the dimer molecules, so that for any one dimeric unit there will be a share in five metal-metal bonds [one / (Rh-Rh) = 312 pm four r(Rh-Rh) = 331 pm]. The chlorine atoms bridge the short (intradimer) metal-metal bond. The b.e.cs to the heat of disruption can be written,... 

Sodium and potassium are in the first column, so they, and any other metal in this column, should form a cation with a +1 charge. Magnesium and calcium are in the second column, thus they, and any other metal in the same column, should form a cation with a +2 charge. Aluminum is in the third column (skipping the transition metals), so that aluminum, and any other metal in the same column, should form a cation with a +3 charge. Thus, the cations of these five metals are Na+, K+, Mg2+, Ca2+, and Al3+. 

CODHs catalyse the oxidation of carbon monoxide in a reversible, two-electron process. They are homodimeric enzymes with five metal clusters, two C-clusters that catalyse the oxidation of CO to C02 and three typical [Fe4S4] cubane clusters (Figure 15.4). 

In this lab, a voltage probe is used to measure the flow of electrons through voltaic cells made of different metals. The metal attached to the positive lead of the voltage probe is the cathode and has a higher reduction potential. The metal attached to the negative lead is the anode and has a lower reduction potential. The reduction potentials of five metals will be compared, resulting in a chart for understanding the potentials of metals. 

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