Lanthanide structures

A New Series of Anhydrous Double Nitrate Salts of the Lanthanides. Structural and Spectral Characterization, W.T. Camall, S. Siegel, J.R. Ferraro, B. Tani, and E. Gebert, Inorg. Chem. 12, 560-564 (1973). 

Ronson, T.K., Lazarides, T., Adams, H., et al. (2006) Luminescent PtII(bipyridyl)(diacetylide) chromophores with pendant binding sites as energy donors for sensitised near-infrared emission from lanthanides structures and photophysics of PtII/LnIII assembhes. Chemistry - A European Journal, 12, 9299. 

As described throughout this chapter, CPL is becoming increasingly useful as a probe of the existence of chiral lanthanide structures, and as an indicator of changes in chiral stmcture. However, there are currently no reliable correlations relating specific aspects of chiral stmcture to CPL measurements. The development of such spectra-stmcture correlations is key to the advancement of this technique as a useful probe of the stereochemistry of chiral lanthanide systems. 

The Cm203 (white) displays three crystal modifications, namely the A-, B- and C-type lanthanide structures as shown in table 23 (Eller and Pennemann 1986). A small uptake of oxygen can cause the oxide to acquire a tan to light brown appearance. The C-type (bcc) structure is the low-temperature form, which converts to the B-type (monoclinic) structure above 800°C, which in turn changes to the A-type (hexagonal) structure above 1600°C (Baybarz and Haire 1976). It is the C-type structure that is readily oxidized to higher oxides the monoclinic form is very resistent to oxidation and the monoclinic to cubic transformation via temperature treatment is very diflicult ( irreversible transformation). The B to A and the A to B transformations occur more readily with temperature. Self-irradiation (especially noticeable with the more readily available, shorter-lived Cm-244 isotope) converts the C-form of the sesquioxide to the A-form (Wallmann 1964, Noe et al. 1970). 

In contrast to the situation for L -bridged lanthanide co-ordination polymers [65], where the bridging molecules predominantly (ca. 75%) adopt a syn-conformation, by far the majority of the bridging molecules (ca. 75%) in -bridged d-block metal co-ordination polymers adopt the anti-conformation. This difference is attributed to the fact that double-bridges are common in lanthanide structures [30-35,65] but extremely rare in i/-block complexes. Although,... 

The classical ten-coordinate lanthanide structure is that of H[La(EDTA)(H20)4] 3H20 (Lind et al., 1965). Although there are severe restraints placed on the coordination polyhedron by the EDTA ligand, this coordination polyhedron can be considered to approximate the bicapped square antiprism. 

Reference has been made already to the existence of a set of inner transition elements, following lanthanum, in which the quantum level being filled is neither the outer quantum level nor the penultimate level, but the next inner. These elements, together with yttrium (a transition metal), were called the rare earths , since they occurred in uncommon mixtures of what were believed to be earths or oxides. With the recognition of their special structure, the elements from lanthanum to lutetium were re-named the lanthanons or lanthanides. They resemble one another very closely, so much so that their separation presented a major problem, since all their compounds are very much alike. They exhibit oxidation state -i-3 and show in this state predominantly ionic characteristics—the ions. 

Crystal Structure and Ionic Radii. Crystal stmcture data have provided the basis for the ionic radii (coordination number = CN = 6), which are summarized in Table 9 (13,14,17). For both and ions there is an actinide contraction, analogous to the lanthanide contraction, with increasing positive charge on the nucleus. 

The lanthanides (from La to Lu) and yttrium form isomorphous dicarbides with a structure of the CaC2 type (body-centered tetragonal). These lanthanide carbides are known to have conduction electrons (one... 

There is no single best form of the periodic table since the choice depends on the purpose for which the table is used. Some forms emphasize chemical relations and valence, whereas others stress the electronic configuration of the elements or the dependence of the periods on the shells and subshells of the atomic structure. The most convenient form for our purpose is the so-called long form with separate panels for the lanthanide and actinide elements (see inside front cover). There has been a lively debate during the past decade as to the best numbering system to be used for the individual... 

The radius of the 24-coordinate metal site in MBs is too large (215-225 pm) to be comfortably occupied by the later (smaller) lanthanide elements Ho, Er, Tm and Lu, and these form MB4 instead, where the metal site has a radius of 185-200 pm. The structure of MB4 (also formed by Ca, Y, Mo and W) consists of a tetragonal lattice formed by chains of Bs octahedra linked along the c-axis and joined laterally by pairs of B2 atoms in the xy plane so as to form a 3D skeleton with tunnels along the c-axis that are filled by metal atoms (Fig. 6.11). The pairs of boron atoms are thus surrounded by trigonal prisms of... 

Monochalcogenides, LnZ (Z = S, Se, Te), have been prepared for all the lanthanides except Pm, mostly by direct combination.They are almost black and, like the monoxides, have the NaCl structure. However, with the exceptions of SmZ, EuZ, YbZ, TmSe and TmTe, they have metallic conductivity and evidently consist of Ln -t- Z ions with 1 electron from each cation delocalized in a conduction band. EuZ and YbZ, by contrast, are semiconductors or insulators with genuinely divalent cations, but SmZ seem to be intermediate and may involve the equilibrium ... 

Table 30.5 Stoichiometries and structures of reduced halides (X/M < 2) of scandium, yttrium, lanthanum and the lanthanides...

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