Holmium -complexes

Holmium, tris(2,2,6,6-tetramethyl-3,5-heptanedione)-photosubstitution, 1,408 Holmium complexes 1,3-diketones, 2,387 phenanthroline, 3,1069 Homoazaporphyrins synthesis, 2, 817 Homolytic cleavage catalysis... 

Hexaniobates, 1028 Hexatamalates, 1029 Hexatungstates, 1034 Hexavanadates, 1027 Holmium complexes phenanthroline, 1069 Homopolymolybdates, 1377 Hydrates, 4 amides, 6 ammines, 4 solvates,4... 

The position of yttrium in rare earth chemistry has always been interesting and this is also the case with respect to complex formation. The electrostatic model suggests placement of yttrium between holmium and thulium. It has been shown that it is not the case [14]. When one considers the stability constant data of group 1 ligands, yttrium is similar to the heavy rare earths. When the second group of ligands is considered, yttrium exhibits a behaviour similar to the lighter rare earth elements. 

The complex Ho(PhCOCHOPh)3 involves distortion of the holmium coordination polyhedron from a capped octahedral arrangement. This complex is similar to Eu(DPM)3 quinuclidine. 

The only complexes of lanthanum or cerium to be described are [La(terpy)3][C104]3 175) and Ce(terpy)Cl3 H20 411). The lanthanum compound is a 1 3 electrolyte in MeCN or MeN02, and is almost certainly a nine-coordinate mononuclear species the structure of the cerium compound is not known with any certainty. A number of workers have reported hydrated 1 1 complexes of terpy with praseodymium chloride 376,411,438), and the complex PrCl3(terpy)-8H20 has been structurally characterized 376). The metal is in nine-coordinate monocapped square-antiprismatic [Pr(terpy)Cl(H20)5] cations (Fig. 24). Complexes with a 1 1 stoichiometry have also been described for neodymium 33, 409, 411, 413, 417), samarium 33, 411, 412), europium 33, 316, 411, 414, 417), gadolinium 33, 411), terbium 316, 410, 414), dysprosium 33, 410, 412), holmium 33, 410), erbium 33, 410, 417), thulium 410, 412), and ytterbium 410). The 1 2 stoichiometry has only been observed with the later lanthanides, europium 33, 411, 414), gadolinium, dysprosium, and erbium 33). 

Notice that Moseley had made a minor mistake in the atomic number determinations of both holmium and dysprosium. The atomic number of holmium is namely 67, and dysprosium has an atomic number of 66. It also appears that Moseley attached some credence to the investigation of Auer von Welsbach who had demonstrated the complexity of thulium in 1911 by splitting it into three components. Moseley had incorporated two of these components (Tml and Tmll) in his atomic number sequence. Moseley therefore ascribed Urbain s neo-ytterbium and lutetium too high an atomic number (in reality the atomic numbers of ytterbium and... 

Lanthanide elements (referred to as Ln) have atomic numbers that range from 57 to 71. They are lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). With the inclusion of scandium (Sc) and yttrium (Y), which are in the same subgroup, this total of 17 elements are referred to as the rare earth elements (RE). They are similar in some aspects but very different in many others. Based on the electronic configuration of the rare earth elements, in this chapter we will discuss the lanthanide contraction phenomenon and the consequential effects on the chemical and physical properties of these elements. The coordination chemistry of lanthanide complexes containing small inorganic ligands is also briefly introduced here [1-5]. 

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