TRANSITION ELEMENTS AND ACTINIDES

There is a lacuna of serious chemical studies upon the reactions of phosgene with the transition metals, even extending to a shortage of published data concerning the rate of attack of phosgene upon the metals most commonly used in its storage, transfer, reactions and transport. 

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The quasirelativistic (QR) PP of Hay and Wadt [61] use two-component wave functions, but the Hamiltonian includes the Darwin and mass-velocity terms and omits the spin-orbit effects. The latter are then included via the perturbation operator after the wave functions have been obtained. The advantage of die method is the possibility to calculate quite economically rather large systems. The method is implemented in the commercial system Gaussian 98 It has extensively been applied to calculations of transition-element and actinide systems [62],... 

Ab Initio Relativistic Quantum Chemistry of Third-Row Transition Elements and Actinides... 

AB INITIO FULLY RELATIVISTIC DF SCF CALCULATIONS FOR DIATOMICS OF THIRD-ROW TRANSITION ELEMENTS AND ACTINIDES... 

We also conclude from our ab initio DF SCF calculations that the 5d, 6d and 5f DFAOs (and their associated electrons) are definitely involved (due to relativistic effects in the electronic structure and bonding of the diatomics of the heavy third-row transition elements and actinides, and they present the formidable dual challenge to quantum chemists of the accurate calculation of the relativistic and electron correlation effects for such systems. 

A one-component quasirelativistic DFT method, also a part of the ADF package [92], was extensively used in the calculations for transition element and actinide compounds. (Earlier, the quasirelativistic Hartree-Fock-Slater (QR HFS) method was widely used for such calculations [93]). In this method, the Hamiltonian contains relativistic corrections already in the zeroth-order and is therefore called the zeroth-order regular approximation (ZORA) [94, 95]. The spin operator is also included in the ZORA Fock operator [96]. Other popular quasirelativistic 2c-DFT methods are based on the DKH approximation [97, 98] and implemented in many program packages. The following codes should also be mentioned of Rbsch [99, 100], Ziegler [101], and Case and Young [102]. They were, however, not used for the heaviest elements. A review on relativistic DFT methods for solids can be found in [103]. 

Elements in the s and p blocks of the table are referred to as typical elements whilst those in the d block are called transition elements and those in the/block are called actinides and lanthanides (or rare earth elements). 

VIIIB, with the number of (outer) d electrons plus two for the transition elements, and the number of (outer) / electrons plus three for the lanthanides and actinides. 

Herein we have reported the synthesis, characterization, and reactivity of both transition metal and actinide elements supported by tripodal ligand scaffolds. The carbon-anchored ligands TIME normally form polynuclear species while the nitrogen-anchored ligands TIMEN can coordinate to transition metals in a 1 1, fashion, rendering the coordinated metal centers in well-protected pockets. 

Symbol Md atomic number 101 atomic weight (most stable isotope) 257 a man-made radioactive transuranium element an inner-transition element of actinide series electron configuration [Rn]5/i37s2 valence +2, -i-3. Isotopes, half-lives and their decay modes are ... 

Fig. 3. Wigner-Seitz radii of d-transition metals and actinides vs atomic number Z. To the plot, elements displaying empty and full d- and f-shell have been added. In abscissae, the groups of the Periodic Chart of Elements have been indicated (see, e.g. Handbook of Chemistry and Physics). The figure shows the sudden jump in radius between Pu and Am discussed in this chapter, and, more deeply, in Chap. C...

The remaining exceptions concern the lanthanide series, where samarium at room temperature has a particular hexagonal structure and especially the lower actinides uranium, neptunium, and plutonium. Here the departure from simple symmetry is particularly pronounced. Comparing these three elements with other metals having partly filled inner shells (transition elements and lanthanides), U, Pu, Np have the lowest symmetry at room temperature, normal pressure. This particular crystallographic character is the reason why Pearson did not succeed to fit the alpha forms of U, Pu, and Np, as well as gamma-Pu into his comprehensive classification of metallic structures and treated them as idiosyncratic structures . Recent theoretical considerations reveal that the appearance of low symmetries in the actinide series is intimately linked to the behaviour of the 5f electrons. 

The conversion of CO + H2 (syn-gas) to hydrocarbons and oxygenates (Fischer-Tropsch chemistry)119 is of considerable industrial importance and recently the activation and fixation of carbon monoxide in homogeneous systems has been an active area for research.120,121 The early transition elements and the early actinide elements, in particular zirconium124 and thorium,125 126 supported by two pentamethylcyclopentadienyl ligands have provided a rich chemistry in the non-catalytic activation of CO. Reactions of alkyl and hydride ligands attached to the Cp2M centers with CO lead to formation of reactive tf2-acyl or -formyl compounds.125,126 These may be viewed in terms of the resonance forms (1) and (2) shown below. 

Methods to calculate the electronic structures of very heavy element compounds are the same relativistic methods which can be applied to any relativistic systems. They were overviewed in application to transition elements [13], actinides [38], and transactinides [15-17]. They will, therefore, be only shortly described here with the accent put on those which were used for calculations of the transactinide systems. 

The rules above gave maximum and minimum oxidation numbers, but those might not be the only oxidation numbers or even the most important oxidation numbers for an element. Elements of the last six groups of the periodic table, for example, may have several oxidation numbers in their compounds, most of which vary from one another in steps of 2. For example, the major oxidation states of chlorine in its compounds are -1, +1, +3, +5, and +7. The transition metals have oxidation numbers that may vary from one another in steps of 1. The inner transition elements mostly form oxidation states of +3, but the first part of the actinide series acts more as transition elements and the elements have maximum oxidation numbers that increase from +4 for Th to +6 for U. These generalizations are not absolute rules, but allow students to make educated guesses about possible compound formation without exhaustive memorization. These possibilities are illustrated in Fig. 14-1. 

The second series of inner transition elements, the actinides, have atomic numbers ranging from 90 (thorium, Th) to 103 (lawrencium, Lr). All of the actinides are radioactive, and none beyond uranium (92) occur in nature. Like the transition elements, the chemistry of the lanthanides and actinides is unpredictable because of their complex atomic structures. What could be happening at the subatomic level to explain the properties of the inner transition elements In Chapter 7, you ll study an expanded theory of the atom to answer this question. 

Block The table divides naturally into s, p, d and /blocks according to the outer electron structure configurations, 5 andp blocks form the main groups, the d block the transition elements, and the / block the lanthanides and actinides. 

The elements of the transition, lanthanide and actinide series are all metallic, and the great majority of them possess one or more of the three crystal structures characteristic of the true metals. The transition series is of the greatest importance in chemical theory and also includes many elements which find wide application in metallurgical technology. 

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