Europium hydration number

The hydration munber, or the nimiber of bound water molecules in the lanthanide coordination sphere, can be calculated using a method introduced by Horrocks and Sudnick for terbimn and europium complexes (50). The relationship between Tb or Eu excited state lifetimes (t), which are experimentally determined in H2O and D2O, and the hydration number (q) is given in Eq. (1)... 

The hydration number q-. this parameter influences strongly the IS contribution (equations (3) and (4)). If this number increases from 1 to 2, the relaxivity increases by about 30%, but most of the Gd-complexes have a q number equal to one. This number can be measured by fluorescence study of europium or terbium complexes or by NMR measuring the lanthanide induced shift (LIS). 

A study of hydration of the complex [EuL2(H20) ](BF4)3 where L= (C N-CO-CHr OCH(Me)- 2 shows by lifetime studies of a similar sort that in aqueous acetone, x = 0.9 0.4 which gives a coordination number of nine. This complex was prepared from Eu(MeCN) (BF3)3, itself prepared from the action of NOBF4 on europium metal in acetonitrile. 

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). 

A determination of the stability constants of aquo-complexes of Eu " in acetone showed that as the concentration of water in the solution of europium nitrate in acetone was increased, the first co-ordination sphere of europium(iii) became occupied by three water molecules which replaced three acetone molecules, and only then did the replacement of NO3 anions by water occur. An n.m.r. study of the hydration of lutetium(iii) nitrate in aqueous acetone showed the co-ordination number of lutetium to tend to six with increasing water concentration. The coexistence of several aquo(methyl sulphoxide)lutetium(iii) complexes were identified in the study of the complex formation between lutetium and dimethyl sulphoxide in acetone. 

Hydration of lanthanide complexes. X-ray diffraction studies of the solid complexes of KLn(EDTA)(H20),c showed the number of water molecules in the coordination sphere to be three for the lighter lanthanides and two for the heavier ones for total coordination numbers of nine and eight, respectively, since EDTA is hexadentate (Hoard et al. 1967). Ots (1973) measured a maximum at europium for the heat capacity change AC° for the formation of lanthanide-EDTA complexes. This maximum was taken as a strong evidence for hydration equilibrium between the complexed species,... 

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