Lanthanides middle

RE(N0 )2 NH NO 4H20 for light lanthanide separation (La, Nd, Pr) 2RE(N02)3 3Mg(N03)2 24H20 for middle lanthanide separation (Sm, Eu, Gd). Bromates and ethylsulfates have been found useful. Fractional crystallization is particularly slow and tedious for the medium and heavy rare earths. 

B-type, also eonsisting of LnOy units but now of three types, two are eapped trigonal prisms and one is a eapped oetahedron favoured by the middle lanthanides. 

C-type, related to the fluorite strueture but with one-quarter of the anions removed in sueh a way as to reduee the metal eoordination number from 8 to 6 (but not oetahedral) favoured by the middle and heavy lanthanides. 

For an indication of the values of the atomic radii of the different elements and of their trend along the Periodic Table, see Figs 4.5 and 4.14. Notice the variations along each period (each horizontal sequence in Fig. 4.14) and the smaller values (and their small changes) for the metals in the middle of the transition block. Notice also in the lanthanide sequence the greater dimensions of the divalent Eu andYb. 

Gadolinium is silvery-white, soft, malleable, and ductile with a metallic luster. It is the second of what is referred to as the dysprosium, subgroup in the middle of the lanthanide series of rare-earths. It tarnishes in air, forming the oxide (Gd O ) on the surface, which flakes off the surface, exposing a fresh metal that in turn oxidi2es. 

Trivalent yttrium and lanthanide metals, except for promethium, have been complexed to octaethylporphyrin by heating at 210 °C in an imidazole melt.17 The complexes obtained as hydroxides, Mm(OEP)(OH), are unstable in acidic media. As the charge radius ratio rule predicts, the early lanthanide metalloporphyrins, MIU(OEP)(OH) (M = La, Ce, PR, Nd), are demetallated during purification, and the middle series (M = Sm, Eu, Gd, Tb, Dy) in 1 % acetic acid in methanol, while the last five (M = Ho, Er, Tm, Yb, Lu) survive in 2% acetic acid in methanol but are dissociated in dilute hydrochloric acid. The Mnl(OEP)(OH) appears to coordinate more than one equivalent of pyridine and piperidine, and dimerizes in noncoordinating solvents such as benzene and dichloromethane at 10 4 M concentration. The dimer is considered to be a di-p-hydroxo-bridged species, different from the p-oxo dimer, Scin(OEP) 20 (Scheme 6). 

Plots of S /(Sz)j vs Cj/(Sz)j (eq. (48)) and S /Cj vs (Sz)j/Cj (eq. (49)) using crystal-field dependent techniques show systematic abrupt breaks near the middle of the lanthanide series (between R = Eu and R = Tb) which imply a concomitant change of the contact Fi and pseudo-contact BqG terms (table 10, fig. 25). Since G is essentially invariant, an abrupt variation of the crystal-field parameter Bq is required to rationalize the NMR data. 

Fig. 94. Macrocycle (top) used to host the lanthanide-containing pseudo-rotaxane threads (middle and bottom)...

Figure 7.14 (Upper) Different space groups and the types of coordination along the lanthanide series. (Middle) Plots of the SHG intensity along the type I and type II series as according to ionic radius and also (bottom) to the number of unpaired f electrons. Complexes with no unpaired f electrons are shown to follow a different trend (La, Y, Lu).

The type-B (monoclinic) structure is related to type-A, but is more complex as it contains three kinds of non-equivalent M atoms, some with octahedral and the remainder with monocapped trigonal prismatic coordination. In the latter type of coordination geometry, the capping O atom is appreciably more distant than those at the vertices of the prism. For example, in Sni203, the seventh atom is at 273 pm (mean) and the others are at 239 pm (mean). This type is favored by the middle lanthanides (Sm, Eu, Gd, Tb, and Dy). 

We place hydrogen as the first element in the first period, along with helium. When helium was discovered, Mendeleev put it in the second period. We put the triads of iron, cobalt, and nickel ruthenium, rhodium and palladium and osmium, iridium, and platinum in group VIIIB, in the middle of the table. Mendeleev put them in group VIII. We also have two long groups, the lanthanides and actinides, that were a headache for Mendeleev. 

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