Lead-thiolate complexes, solid-state absorption

However, detailed insights into the electronic transitions of lead-thiolate complexes can be gained from studies on T1(I) [which is isoelectronic with Pb(ll)] and Pb(ll)-doped alkali halides in the solid state (Fig. 5) (37, 50, 54, 113). The details of the electronic transitions in T1(I) doped alkali halides and related compounds have been studied extensively (both theoretically and experimentally) because these compounds have interesting luminescent properties and are useful in phosphors. [We will not discuss the emission spectra of these compounds, as they are not relevant to our discussion of lead-thiolate CT in coordination complexes rather, the reader is directed to several extensive reviews of luminescence in doped alkali halide systems (95, 113, 114).] The characteristic absorption spectra of alkali halides doped with a Tl(l) type ion consist of four bands, known as the A, B, C, and D bands. The A band is at lowest energy, followed by B, C, and D respectively the extinction coefficients of the bands follow the general trend D > C > A > B (Fig. 6) (115, 116). Two weaker bands labeled D and D" are also shown in Fig. 6, which are attributed to the same CT transitions as the main D band (116). In Section II.E, we will... 

Although we can conclude from the optical electronegativities that LMCT transitions play a role in the absorption spectra of lead thiolates, it is not currently known to what extent intraatomic transitions may also contribute to these bands, or what orbitals are involved in the transitions. There have been no detailed theoretical studies of lead-thiolate CT bands, and very little work in general has been reported on the absorption spectroscopy of Pb(II) coordination complexes. Although the absorption spectra have been reported for solid-state Pb(ll) alkaline earth sulfides (69-71), these data have not been analyzed extensively. In addition, much of the data that have been reported (69-71) are ambiguous due to insufficient information on sample preparation and composition (95). 

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