Lanthanide complexes complex halides

Although the bonding in actinide cyclopentadienyls is more covalent than in the corresponding lanthanide complexes, the halide ligand is labile and can be substituted by a large variety of anionic ligands. The synthetic routes most commonly involve metathetical halide substitution (eq. 8), or protolysis of the U-Cp bond (eq. 9). The properties of most of these derivatives have been summarized by... 

AH of reaction (17) is an estimate since PuCl4(s) has not been synthesized AfH° [PuCl4(s)] = — 964 kJ is an estimate (Fuger et al. 1983). The dramatic difference in these enthalpies [Pu(IV) is more stable than Pu(III) in this complex chloride by -95-( —4) = - 91 kJ or almost 1.0 V, in comparison with the binary chloride] shows how acid-base effects influence oxidation-reduction properties. As noted above, there are few known lanthanide (IV) complex halides and no thermodynamic data on even these few halides, so no quantitative comparison can be made. Nevertheless it does show how complexation effects by basic complexants make high f-element oxidation states attainable. Perhaps the most dramatic evidence of the enhancement of high oxidation state by a basic fluoride is the existence of the Nd(IV) and Dy (IV) compounds such as Cs2(Cs, Rb, K) (Nd, Dy)Cl2 these AjRF, double fluorides are the only known Nd (IV) and Dy(IV) compounds. 

The study of coordination compounds of the lanthanides dates in any practical sense from around 1950, the period when ion-exchange methods were successfully applied to the problem of the separation of the individual lanthanides,131-133 a problem which had existed since 1794 when J. Gadolin prepared mixed rare earths from gadolinite, a lanthanide iron beryllium silicate. Until 1950, separation of the pure lanthanides had depended on tedious and inefficient multiple crystallizations or precipitations, which effectively prevented research on the chemical properties of the individual elements through lack of availability. However, well before 1950, many principal features of lanthanide chemistry were clearly recognized, such as the predominant trivalent state with some examples of divalency and tetravalency, ready formation of hydrated ions and their oxy salts, formation of complex halides,134 and the line-like nature of lanthanide spectra.135... 

The lanthanide phthalocyanine complexes, obtained by conventional methods starting from metal salts at 170-290°C and phthalonitrile (Example 26), contain one or two macrocycles for each metal atom [5,6,8,63,82,84-98]. Thus, according to Refs. 6,63, and 85, the complexes having compositions LnPc2H, XLnPc (X- is halide anion), and Ln2Pc3 (a super-complex ) were prepared from phthalonitrile as a precursor the ratio of the reaction products depends on the synthesis conditions and the metal nature. The ionic structure Nd(Pc)+Nd(Pc)2 was suggested [85] and refuted [63] for the neodymium super-complex Nd2Pc3 the covalent character of the donor-acceptor bonds in this compound and other lanthanide triple-decker phthalocyanines was proved by the study of dissociation conditions of these compounds [63]. 

The Absorption Spectra and Excited State Relaxation Properties of Lanthanide and Actinide Halide Vapor Complexes. I. ErCl3(AlCl3L, W.T. Camall, J.P. Hessler, H.R. Hoekstra, and C.W. Williams, J. Chem. Phys. 68, 4304-4309 (1978). 

Lanthanide halide complexes free of coordinated Lewis bases, such as alcohols, phosphates, amines, dimethylsulfoxide, or THF, suffer from low solubilities in non-coordinating solvents. Therefore, catalytic systems based on LnCl3 generally require preformation or aging in order to reach maximum activities. In contrast, lanthanide tetrahalogenoaluminate complexes are soluble in aromatic solvents. Such simple Ln/Al heterobimetallic halide... 

Lanthanide complexes with inorganic ligands such as Cl, Br, I, SCN, N03 and sulphate can be either inner sphere LnX2+ or outer sphere or solvent separated complexes, Ln(H20)2+X In the case of halides the complexes are thought to be outer sphere Ln(H20) X2+, although there is evidence for the existence of anionic complexes like LnCl. Similarly EuSCN2+ is supposed to have both inner sphere and outer sphere character [23]. 

Unusually, chloride is foimd in the first coordination sphere of lanthanum as well as nitrate in the serendipitously discovered mixed anion complexes [EaCl2(N03)(12-crown-4)]2 and [LaCl2(N03)(18-crown-6)]. A few complexes have been reported with other halides, such as [Sml3(dibenzo-18-crown-6)] (tricapped trigonal prismatic) and [LaBr3(12-crown-4)(acetone)] (distorted square antiprismatic). Lanthanide thiocyanate complexes of crown ethers are now starting to be studied. Several thiocyanate complexes of the... 

Lanthanide alkoxide complexes can be prepared using a number of methods. The key difference lies in the nature of lanthanide starting materials. These include elemental metals, halides, alkoxides, amides, carboxylates, hydrides, and organometallic species [1, 11], The organic ligands come from aliphatic alcohols, phenols, or their metal salts. 

Wang, R., Selby, H.D., Liu, H., Carducci, M.D., Jin, T., Zheng, Z. etal. (2002) Halide-templated assembly of polynuclear lanthanide-hydroxo complexes. Inorganic Chemistry, 41, 278-286. 

The metathesis reaction of anhydrous lanthanide halide with alkali metal alkoxo-functionalized NHC complex has recently proven to be another efficient and straightforward route to lanthanide NHC complexes (Equation 8.18) [69]. 

The lanthanide halides are usually bi(cyclopentadienyl) and related lanthanide complexes M is an alkali metal or silver, and A is an anionic transition metal carbonyl compound or tetraphenyl borate. The formation of the insoluble salt MX is a driving force for this reaction. 

Divalent lanthanide chemistry has been dominated by the most readily accessible divalent lanthanide metals samarium(II), europium(II), and ytterbium(II) (classical ) for decades, and a large number of divalent lanthanide compounds have been prepared [92], There are three routes to generate divalent organolanthanide complexes oxidative reaction of lanthanide metal, metathesis reaction of a divalent lanthanide halide, and reductive reaction of a trivalent lanthanide complex. 

Isomorphism among compounds of the actinides is common and only a few examples need be given. The dioxides, MO2, of thorium, uranium, neptunium, plutonium and americium all have a fluorite lattice. The trihalides of the transuranic elements are isomorphous not only with the corresponding trihalides of actinium and uranium but also with those of the lanthanides. Isomorphism is also exhibited in many complex halides thus thorium, ura-... 

Anhydrous lanthanide trihalides, particularly the trichlorides, are important reactants for the formation of a variety of lanthanide complexes, including organometallics. Routes for the syntheses of anhydrous lanthanide trihalides generally involve high temperature procedures or dehydration of the hydrated halides.The former are inconvenient and complex for small scale laboratory syntheses, while dehydration methods may also be complex and have limitations, for example, use of thionyl chloride. - Moreover, the products from these routes may require purification by vacuum sublimation at elevated temperatures. Redox transmetalation between lanthanide metals and mercury(II) halides was initially carried out at high temperatures. However, this reaction can be carried out in tetrahydrofuran (THF, solvent) to give complexes of lanthanide trihalides with the solvent. These products are equally as suitable as reactants for synthetic purposes as the uncomplexed... 

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