TmSe compounds

In the case of thulium compounds TmSe and TmTe and YI3AI3, distinct multiplet structures due to divalent and trivalent thulium are seen in the 4f region [38]. The multiplet structure in TmTe is more distinct than in the case of TmSe in agreement with magnetic susceptibility data, (i.e.) magnetic moment of TmTe is smaller than that of TmSe. 

It has also been found that the 3-OH group is the least reactive of the hydroxyl groups in lactose under many reaction conditions (Scheme 3.33). Accordingly, direct benzoylation of lactose yielded the 3-OH derivative in 24% crystalline yield [7], tin activated benzoylation of TMSE (3-lactoside gave 85% of the 3-OH lactoside [57] and phase-transfer benzylation of benzyl lactoside produced 26% of the corresponding 3-OH compound [39]. 

Performance of different nebulization and chromatographic systems for the speciation of Se investigated. For selenite- and SeMet-based supplements, the analytical results confirmed the information given by the manufacturer (extraction efficiency 80-95%). For the Se-yeast supplements (extraction efficiency 10-25%), more than 20 selenium compounds were detected, among them SeMet, TMSe and SeEt... 

Pretreatment procedures did not affect native species distribution in urine. For large urine volumes (preconcentration factor 100), at least 10 selenium compounds were separated. The elution behavior of some species was slightly changed in the presence of a urine matrix, as observed in spiking experiments. Only two species were identified in the analyzed samples SeGal -primary species and SeGlu - about 2% of SeGal TMSe, SeMet, SeMM, SeCM and Se cystamine were not detected... 

In Fig. 15 we present both XPS and UPS data for TmSe. In UPS, emission from the Tm(5conduction band and the Se(4p) valence band dominate that from the Tm(4/) shell. A Fermi cutoff is detected, analogous to that of TmS, confirming the metallic nature of TmSe. The spectrum of the Se (4p) emission can be related to that expected for the valence band of NaCl structure compounds (52) and will be discussed in a forthcoming publication (53). At XPS energies these contributions are overwhelmed by the much more intense emission from the Tm(4/12 and 4/13) levels (35), whose final states multiplets have been identified using the calculations of Cox (7). As pointed out by Jorgensen (5), the signal from Tm2+ represents the first observation of a well-resolved 4/13 - 4/12 spectrum. Similar results have since been obtained in preliminary... 

Compound 158 was transformed into aldehyde 159 by performing a sequence of reactions and then it was converted into compoimd 161. Compound 161 on bromination followed by key transformations gave core skeleton 163, which after TMSE deprotection and decarboxylation gave natural product chartelline C (145) (Scheme 13) [74], Synthetic studies as well as synthesis of precursors of chartellines have also been reported in literature [75-80],... 

To reconcile the diverging Raman and neutron scattering results the following point of view has been taken by Giintherodt et al. (1985b) similarly to the valence fluctuations between two integral valence states (4f"< 4f" -l- e ) in IV rare-earth compounds the systems CeAlj, TmSe and Smo Yp jjS show... 

A detailed experimental review on this subject can be found in Lawrence et al. (1981). One of the most frequently used methods to determine a mixed-valent compound and its valency is a lattice constant measurement. This technique assumes the validity of Vegard s law, i.e., the linearity between lattice constant and valence, as well as knowledge of the lattice constants aQ( ) and ao(n - 1) of compounds where the rare earth is in the configurations 41 and 4f , respectively. In this way the intermediate valency of Ce compounds (a-Ce, CeBcij, CePd), of Sm compounds (SmS, SmBg), of Tm compounds (TmSe) and of Yb compounds (YbAlj) was determined [see Lawrence et al. (1981) and Penney (1984)]. 

TmTe and TmSe have been investigated with respect to valence fluctuations. The lattice constants of the R-tellurides and R-selenides were reported by landelli (1961) and from these data it appears that TmTe is divalent and TmSe has an intermediate valence at room temperature. All of these compounds crystallize in the rock salt structure. 

Tm may have a CF singlet ground state. A large number of neutron investigations has been performed on TmSe and will be discussed here in detail. As far as other Tm compounds are concerned, we are only aware of neutron data on the Kondo-lattice TmS (Lassailly et al. 1983, Holtzberg et al. 1985) and on pressure dependent neutron scattering experiments on TmTe (Walter et al. 1992). 

Thermal conductivity of systems with an intermediate valence One could expect nonstandard behaviour of L(T /Lq in these systems too. Unfortunately, this case has not been discussed theoretically and it is not possible to draw any conclusions from the analysis of experimental data on thermal conductivity. In the classical compounds with an intermediate valence of the lanthanide atoms (SmBg, TmSe) kl > (especially in the low-temperature region). The contribution of to K,ot has not been taken into account during investigations of metals from this class of materials [e.g., CePdj (Schneider and Wohllcben 1981)]. 

When MLH had overcome the mentioned difficulties and some smaller ones, he synthesized the western building block 30 via p-ketothioester 34 as summarized in Scheme 8. The route toward diester 33 of L-A-methylglutamic acid, then not a known compound, started from commercially available Cbz-protected L-glutamic acid (73). Esterification with excess 2-(trimethylsilyl) ethan-l-ol ( TMSE-OH ), DCC, and DMAP furnished the diester 74 in 82% yield." It was methylated with Mel/Ag20 (—>93% 75 of 97-98% ee) adhering to a general procedure" and conscious of a specific application to a diester of... 

Fig. 12. The lattice constants of the sulfides, selenides and tellurides of the lanthanides (Campagna et aL 1976). For the trivalent compounds these lattice constants show a regular behaviour, and from the deviations the divalent ones and the mixed valent ones (TmSe and collapsed SmS) are easily discernible.

A similar situation is encountered in TmSe. This compound is, however, thought to be mixed valent whereas TmTe is divalent and TmS is trivalent. An XPS photoemission spectrum of TmSe is shown in fig. 15. Here one sees both the final states of the f f and of the f ->f excitations (Campagna et al. 1974, 1976, Oh et al. 1984). 

These materials have been of interest for many years because of their unusual properties. In the last decade reasonably large crystals have become available by using the mineralization technique (Spirlet and Vogt 1984), so that many different neutron inelastic experiments have been performed. Although TmSe orders with a moment of about 2(Ub (Bjerrum-Moller et al. 1977), we shall discuss the Tm compounds with the NaCl-type structure in sect. 5 in coimcction with effects of intermediate valence (IV). 

---