Transition element complexes formation constants

Collection of metal complexes of the analytes on suitable adsorbing materials is often employed as an enrichment step in combination with flame methods. In a procedure proposed by Solyak et al. [20], five metals [Co(II), Cu(II), Cr(III), Fe(III), and Pb(II)] were complexed with calmagite 3-hydroxy-4-[(6-hydroxy-m-tolyl)azo]-naphthalenesulfonic acid and subsequently collected on a soluble cellulose nitrate membrane filter. In this way an effective separation from alkaline and alkaline earth metals was achieved, based on the differences in their complex formation constants and those of the transition elements. The experimental parameters were optimized for the quantitative recovery of the elements. After hot dissolution of the filter with HNO3, the analytes were determined by FAAS. Minimum detectable concentrations ranged from 0.06 pg l-1 for Cu to 2.5 pg l-1 for Cr. 

In general, the formation constants of metals with a specific ligand follow the predicted trend and increase in step with increasing metal hardness. Mg, Al, and Mn complexes, however, do not follow this trend. The stability constants of Mg and Al are well established and thus, their anomalous behaviour may indicate the limitation of this simple correlation when comparing A metals (Mg, Al) with d-transition elements (Fe). The data for Mn need to be thoroughly reviewed before any conclusions can be drawn. 

The logarithms of the stability constants fly for the formation of 1 1 complexes of the actinide ions M +, M " ", MOj and MO with various inorganic ligands are plotted in Fig. 21.1. Carbonato complexes of alkaline-earth elements, lanthanides, actinides and other transition elements play an important role in natural waters and may stabilize oxidation states. 

The fluorescence properties of several europium and samarium ) -diketonates have been measured and assignments of the transitions made. Rare-earth element hexafluoroacetylacetonates with amino-acids have also been reported to fluoresce. The luminescence of the heptafluoroheptane-2,4-dione complexes of Sm, Eu, and Tb has been measured in dilute ethanol at pH8 and 610nm mixed-ligand complexes with 1,10-phenanthroline exhibited an enhanced luminescence. Photolysis of the Tb chelate of 2,2,6,6-tetramethylheptane-3,5-dione has been examined at 311 nm in various alcohols, and loss of one -diketone ligand found to be the primary photochemical step. A linear correlation was demonstrated between the quantum yield of dissociation of the complex and the formation constant of the complex-alcohol adduct. 

For example, let iicOi = 500 cm , a typical value. It seems plausible that the polyatom moiety s potential energy in this coordinate should change at least on the order of 0.1 cm i upon formation of a complex. Then ai(r) = (0.0004)1/2 = 0.02. Substitution of these values into Eq. (II.9) gives a matrix element of 7 cm i for Vi =1. Third, the vibrational predissociation rate constant for a one-quantum transition should vary linearly with the quantum number of the initial state. Since the energy lost to the van der Waals coordinate in a one-quantum change is independent of the initial state quantum number, the vibrational predissociation rate should vary with the square of the coupling function in Eq. (II.9). This equation indicates that the vibrational predissociation rate should then be proportional to the initial state vibrational quantum number Vi. 

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