Eight-coordinate lanthanide complexes

Eight-Coordinated Lanthanide Complexes with -Diketones... 

Ln = La) and [Ln(phen)2(N03)3] (Ln = La-Lu, Y) are obtained in isomorphous and isostructural series. Both series have 10-coordinate lanthanides with all nitrates present as bidentate ligands. A few other cases are known. Thus, a family of isostructural eight-coordinate lanthanide complexes [Ln (TREN-l,2-HOIQO)] (Ln = La-Lu, except Pm), utilizing a hexadentate tripod ligand based on hydroxamic acid donors, has shown them to be isostructural. ... 

A number of chloride complexes include Pr(terpy)Cl3.8H2O X-ray diffraction established the presence of a [Pr(terpy)C1(H20)5] + ion. Lanthanide nitrates react with 1 mole of terpy in MeCN to give [La(terpy)(N03)3(H20) ] (Ln = La, = 2 Ln = Ce-Ho, n = 1 Ln = Er-Lu, n = 0) with coordination numbers decreasing from 11 (La) to 9 (Er-Lu) if these are crystallized from water [Ln(terpy)(N03)2(H20)4] NO3 (Ln = La-Gd) and [Ln(terpy)(N03)2(H20)3]N03.2H20 (Ln = Tb-Lu) are formed these have both biden-tate and ionic nitrate and nine- and eight-coordinate lanthanides, respectively. Thiocyanate complexes Ln(terpy)2(NCS)3(Ln = Pr, Nd) are also nine coordinate. 

Fig. 49. Plots of the lattice parameters a, and c (A) for the eight coordinated MOC1 complexes of the lanthanides vs. their L-values.

Complexes of PyzO with lanthanide perchlorates (2 79) and hexafluorophosphates 180) are eight coordinate. However, La(III) perchlorate gives the complex La(Pyz0)7(C104)3 2 H20 in which both the water molecules are coordinated to La(III). In the case of complexes of PyzO with lanthanide chlorides 180), the number of coordinated ligands increases as the ionic radius of the lanthanide ion decreases. These complexes probably contain bridging ligands. 

Octacoordination is often encountered in lanthanide complexes. The preferred poly-hedra for eight coordination expected on the basis of interligand repulsivities are square antiprism (D ), dodecahedron with triangular faces (Z)2d), bicapped octahedron (D3(i), truncated octahedron (Z)2ft), 4,4-bicapped trigonal prism (C2v), distorted cube (C2v), and cube (0/,). The most commonly observed polyhedra for this coordination number are, however, the square antiprism and the dodecahedron. 

The Eu—0 (diketonate) distances vary from 2.32 to 2.37 A and agree very well with other lanthanide-/S-diketonate complexes and with eight coordinated Eu(DPM)3(Py)2 complex (see later). Eu—0 (sulphoxide) distance is 2.40 A. The sulphoxide ring is puckered by 35° and the S—0 has equitorial conformation. 

Octacoordination is now recognized to be common for many lanthanide and actinide complexes. Among the < -transition metal ions, however octacoordination is less frequent. The d, d, d and d configurations are known to produce eight coordinated complexes (97). In an excellent review Lvppard (92) surveyed the chemistry of the octa coordinated complexes, especially stereochemical and bonding aspects, and included most of the published material upto 1967. 

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