Lanthanum atom

The element lanthanum (atomic number 57) has the electronic configuration... 

The diameter of a C60 molecule (Section 14.16) is approximately 700 pm. (a) Could more than one lanthanum atom occupy the center of a C60 molecule (b) Because it is possible for C60 to undergo reduction (six step-by-step reductions to give Q,(/ have been reported), it is also possible for a lanthanum ion, La34, to exist inside the C60 molecule. Could two La3+ ions be placed inside a C60 molecule ... 

The rare earth elements (R) are those from atomic numbers 57-71, emanating as a particular series from the parent element lanthanum (atomic no. 57). The set of 14 elements from cerium (58) through lutetium (71) inclusive are commonly known as the lanthanoid (or lanthanide Ln) series. The rare earths form a bridge at the... 

Figure 10.7 illustrates the prototype hexaboride crystal structure, that of lanthanum hexaboride. It consists of a simple cubic array of boron octahedra surrounding a metal atom at the body center of each cube. The octahedra are linked by B-B bonds connecting their comers. This makes the overall structure relatively hard with approximately the hardness of boron itself since plastic shear must break B-B bonds. The open volumes surrounded by boron octahedra are occupied by the relatively large lanthanum atoms as the figure shows schematically. 

An alternative version of the lanthanum hexaboride crystal structure has the boron octahedra occupying the body centered positions of the cubic array of lanthanum atoms (Figure 10.8). This version makes it clear that in order to plastically shear the structure, the boron octahedra must be sheared. Note that the octahedra are linked together both internally and externally by B-B bonds. 

The 3rd group of the Periodic Table (the 1st column within the block of the transition elements) contains the metals scandium, yttrium, lanthanum, and actinium. Lanthanum (atomic number 57) may be considered the earliest member of the family of metals, called lanthanides (general symbol Ln), forming, inside the principal transition series, an inner transition series (up to atomic number 71). Scandium and yttrium together with the lanthanides are also called rare earth metals (general symbol R). 

Important ongoing developments in HRTEM that are expected to be valuable in catalysis research include the correction of spherical aberrations in electron microscope lenses and monochromatization of the electron beam for improvement of the spatial and spectral resolution. Recently, scanning-TEM (STEM) of atomically dispersed lanthanum atoms on alumina (63) has provided e.x situ aberration-corrected images, but it is noteworthy that there is no technical limitation in applying the correction devices to instruments used for making measurements of samples in reactive environments. 

The fluoride electrode is a typical example of an ion selective electrode. Its sensitive element is a crystal of lanthanum trifluoride that allows fluorine atoms to migrate into the network formed by lanthanum atoms (Fig. 18.3). Other electrodes use a mineral membrane obtained as agglomerates of crystalline powders (for measurement of Cl-, Br-, I , Pb++, Ag+ and CN ). Generally, the internal electrolyte can be eliminated (by dry contact). However, it is preferable to insert a polymer layer with a mixed-type conductivity to ensure the passage of electrons from the ionic conductivity membrane to the electronic conductivity electrode (Fig. 18.3). 

Tucked into the periodic table between lanthanum (atomic number 57) and hafnium (atomic number 72) are the lanthanides. In this series of 14 metallic elements, the seven 4/orbitals are progressively filled, as shown in Figure 5.17 (page 185). Following actinium (atomic number 89) is a second series of 14 elements, the actinides, in which the 5f subshell is progressively filled. The lanthanides and actinides together comprise thef-block elements, or inner transition elements. 

The lanthanide elements begin with lanthanum (atomic number 57) and go to ytterbium (atomic number 70). The actinide elements begin with actinium (atomic number 89) and go to nobelium (atomic number 102). 

Fig 1 Chemical structure of initiators used in ROP of lactones and lactides.n) stannous oc-toate, b) aluminum isopropoxide, c) lanthanide isopropoxide. Lanthanum atoms are represented by gray circles and oxygen atoms by white circles. The black circle represents the bridging oxygen atom connecting all lanthanum atoms. Alkyl groups are omitted for clarity... 

In KLa2(NH2)7, obtained by reaction of K and La with NH3 under pressure and at 350 °C, the lanthanum atom is eight-co-ordinate.25 The co-ordination polyhedron may be described as a deformed trigonal prism which is bicapped on two four-fold faces. 

In La202S, the lanthanum atom is located35 on a three-fold axis with a triangle of sulphide ions above and a triangle of O atoms, and one axial O atom below. 

Europium is a metallic element discovered in 1901 in Paris by the French scientist Eugene-Anatole Demarcay. It belongs to a series of elements called lanthanides, or 4f elements, extending from lanthanum (atomic number 57) to lutetium (atomic number 71). These elements have low abundances Europium occurrence in Earth s crust is only 2.1 ppm (parts per million), that is, 2.1 grams (0.07 ounces) per metric ton, and in seawater, its concentration is as low as 4 X 10 8 ppm. 

According to the hypothetical catalytic cycle (Figure 36), the lanthanum atom is believed to function as a Lewis acid and a lithium binaphthoxide moiety as a Brpnsted base. The nature of the coordination of the aldehyde appears to be of first importance. This coordination provides activation of the aldehyde for reaction with the hypothetical LLB-enolate (II) (which on the basis of pKa values can be present at most in low concentration), and also controls of the orientation of the aldehyde for enantioselective reaction. A H NMR study also supports the existence of the coordination between aldehydes and the lanthanum cation.89... 

Fullerenes can encapsulate various atoms within the cages, and these compounds have been referred to as endohedral fullerenes. For example, the symbolic representations La C6o and La2 Cso indicate that the fullerene cage encapsulates one and two lanthanum atom(s), respectively. The IUPAC description refers to these fullerenes species as incar-fullerenes, and the formulas are written as t LaCeo and tl Cso, (i is derived from incarcerane). Some metal endohedral fullerenes are listed in Table 14.2.1. The endohedral fullerenes are expected to have interesting and potentially very useful bulk properties as well as a fascinating chemistry. Some non-metallic elements, such as N, P, and noble gases, can be incarcerated into fullerenes to form N 0,0, P C6o, N C o, Sc3N C80, Ar Oo, etc. 

It features agostic interactions with two methyl groups if the lanthanum atom were just bound to an -cyclopentadienyl and also formed two an a-bonds to alkyl groups, it would be regarded as five coordinate and thus coordinatively unsaturated and electron-deficient. The agostic interactions relieve this. 

La-S distance is 0.2803 ran. The tin atom is located in an octahedral arrangement of the sulfur atoms. The shortest Sn-S distance is 0.2529 nm. The SI atoms adopt a square coordination sphere of the four lanthanum atoms. The S2 and S3 atoms have five-coordination spheres. 

Structure type LasCuSiSy (Collin and Laruelle, 1971) (Figure 91, Table 41). SGP63, Z = 2, a = 1.0310, c = 0.5794 run. The sulfur atoms form bicapped trigonal prismatic arrangement aroimd the lanthanum atom, and the shortest La-S distance is 0.2869 nm. The copper atom is located on the... 

Structure type La4Ag2ln4Si3 (Gulay et ah, 2008d) (Figure 106, Table 56). SG Pham, Z = A, a = 2.0523, h = 2.5118, c = 0.40241 nm. All four independent lanthanum atoms are located in bicapped trigonal prisms made of sulfur, and the shortest La-S distance is 0.2933 nm. The silver atoms... 

Structure Non-hydrated rare earth fluorides have two different crystal systems, a hexagonal system (lanthanum to terbium) and an orthorhombic system (dysprosium to lutetium, yttrium). In the crystal of LaFs, the central ion is nine coordinated by nine fluoride atoms. Each fluoride atom further connects with two lanthanum atoms through a [13-bridge to form an infinite polymer. 

Mo36Oi08(NO)4(MoO)2La2(H2O)28] possesses of a one-dimensional chain structure, in which the Mo36(NO)4 units are linked to each other by two parallel lanthanum atoms [74]. 

Figure 3. FT-ICR mass spectrum showing the existence of fuUerenes with up to three lanthanum atoms trapped inside.

In a series of XeCl excimer laser photofragmentation and reaction tests with O2 and ammonia reactants, we were able to prove that all these clusters were, in fact, (Lax C,) lanthanum fuUerenes. As levitated positive ions in the FT-ICR apparatus, they are chemically inert, and they fragment only by successive C2 loss. Laser shrink wrapping experiments showed that the smallest cage that can surround two lanthanum atoms is and the minimum cage that can fit around three is Cgg. 

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