Actinoids complexes

For the actinoid complexes the approximation that the ligand field splittings are small compared with the spin-orbit coupling splittings of the free-ion terms is probably not very good. A proper treatment would involve the simultaneous operation by HER, HEF and HIS on the/ configurations. 

However, there does not seem to be sufficient experimental data of sufficient accuracy to have made that elaborate procedure worthwhile. It has proved possible to use the diagrams published for the lanthanoid ion case with some success for treating the magnetic properties of actinoid complexes in at least some cases.49-85... 

There are a number of significant motivations driving the development of molecular mechanics models of lanthanoid and actinoid complexes which, being relatively unstable, are notoriously difficult to crystallize and structurally characterize. At the same time there is strong interest in these structures. For example, lantha-... 

The two most important structines for [M(bidentate)s] are shown in Figure 16, drawn as idealized bicapped square antiprisms. Isomer I is possible at all values of the normalized bite whereas isomer II is expected only for larger chelate rings. A number of lanthanoid and actinoid complexes with four-membered nitrate or carbonate rings, [M (N03)5] and [M (C03)5] , have structure I. The only monomeric molecule in which structure II is observed is [Ba(MeCONHCOMe)5](C104)2 with six-membered chelate rings. 

See the general references in the Introduction, and some more-speciahzed books [4, 6-58], Some articles in journals discuss actinide complexation and thermodynamics at elevated temperatures [59] classifying lanthanoids by multivariate analysis, albeit with results that seem hard to defend [60] designing sequestering agents for Pu and other actinoids [61] lanthanoid compounds with complex inorganic anions, part of a thematic issue on lanthanoid chemistry [62] Pm, discovery and chemistiy [63] recent Sc chemistiy [64] actinoid complexes [65] the transuranium elements [66] actinoid complexes with OH and [67] coordination numbers [68] the aqueous chemistiy and thermodynamics of Eu [69] photooxidation-reduction of Np and Pu [70] review of Pm [71] Rth thermochemistiy [72] unusual oxidation states of Ln and An [73] and Rth chemistiy [74]. 

In 2003, Danopoulos et al. successfully synthesized a CNC pincer ligand and used it to prepare a Pd complex. This ligand was later applied to the synthesis of ETM and actinoid complexes. Substitution of tmeda with the CNC pincer yielded [(NHC)VCl2(THF)] 37 (Equation (6.8)). This route was alternatively applied to the preparation of titanium, chromium, niobium and uranium complexes. ... 

FIGURE 1.38 The seven /-orbitals of a shell (with n = 3) have a very complex appearance. Their detailed form will not be used again in this text. However, their existence is important for understanding the periodic table, the presence of the lanthanoids and actinoids, and the properties of the later d-block elements. A darker color denotes a positive lobe, a lighter color a negative lobe. 

Since 1975, porphyrin complexes of all metals of the periodic table of elements are known, with the exception of some actinoids (20-22). The most fascinating property of all metalloporphyrins is their intense color porphyrlike in the solid state, brick-red, pinkish red, olive-green, or brown in dilute solutions. The absorption spectra vary with the metal, the porphyrin, and the axial ligand many attempts to rationalize the different types of spectra have been undertaken (20-22, 24, 42-48). As the. .periodic table of metalloporphyrins (24) is now nearly complete, a new approach... 

Spahiu, K. Carbonate complex formation in lanthanoid and actinoid systems Ph.D. thesis, Royal Institute of Technology, Stockholm 1983. 

The members of the actinoids have a somewhat greater tendency to form complexes than those of the lanthanoids. They also show a wider variety of complexes due to their more numerous oxidation states. The cations of the actinoids display coordination numbers which are often greater than 6. Although not many data are available, M02+ and M02" " ions attach 5 or 6 HOH molecules giving the central atom a coordination number of 7 or 8, and the and ions attach 9 or 10 HOH molecules. The coordination numbers with ligands other than HOH are often of these magnitudes, but sometimes may be somewhat smaller. 

In fact, even approximate cubic symmetry seems to be rare for lanthanoid or actinoid element complexes.50 In low symmetry the number of crystal field parameters necessary to account for the system can be quite large. On the other hand, the spectra of lanthanoid complexes contain many... 

In the actinoid elements the approximation of cubic symmetry is probably sufficient to deal with the available experimental data, with some exceptions.85 93 In the chemistry of certain of the actinoid ions the linear 0=M=0 unit can play an important role, as exemplified by the unit U02 in complexes of the uranyl type, e.g. U02(0Ac)42-. This unit introduces a very strong axial component into the ligand field which may be even more important than the cubic one.49-85 However, information on the absolute magnitudes of such components seems difficult to obtain. 

There remains the possibility of g-values which depart substantially from 2.00 but are isotropic because of cubic symmetry. In practice such conditions are rare for transition metal complexes, as the Jahn-Teller theorem ensures departure from cubic symmetry in the electronic structure. However, for the lanthanoid and actinoid elements, where the spin—orbit coupling constant is very much larger than kT, the Jahn—Teller theorem may not be relevant and effective cubic symmetry certain. For the lanthanoids, g-values often depart considerably from 2.00, although some anisotropy arising from ligand field splittings is common. For the actinoids, direct observation of ESR is less common but there is evidence of a similar situation. 

Exhaustive compilations of magnetic properties of transition metal complexes are available.166-192-194 The following sections describe very briefly the magnetic behaviour of a selection of complexes or groups of complexes, from the various electronic configurations which arise for the transition metals. They are intended to be illustrative of the points made in the earlier sections no attempt at completeness of coverage is made. More detailed and intensive accounts of magnetic properties of transition metal complexes are available.99 166 169-174-175 186-195-197 No mention is made of results for lanthanoid and actinoid elements, nor of ESR g-values. 

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