Neodymium complexes structure

Although they are not macrocyclic ligands, polyethyleneglycols behave somewhat similarly to the crown ethers regarding lanthanide complexation, as established by a number of crystal structure determinations. Thus a series of neodymium complexes shows consistent 10-coordination, namely [Nd(N03)3(tri-eg)],458 where tri-eg is triethyleneglycol, [Nd(N03)2(penta-eg)]N03,458 and [Nd(N03)2(N03)(tetra-eg)],459 where N03 is monodentate. The larger La3+ ion shows 11-coordination in [La(N03)3(tetra-eg)].460... 

The blue-green neodymium complex 58f was structurally characterized by X-ray diffraction (Fig. 18). Despite the presence of both the large, flat C8Hl ligand and the very bulky diphenyl-bis(JV-trimethylsilylimino)phosphinate anion, the coordination sphere of neodymium leaves enough room to accomodate an additional THF ligand. The central four-membered ring formed by the neodymium atom and the NPN chelate system is nearly planar. 

The neodymium complex of the formula, Nd(N03)3(Ph3P0)2(C2H50H) has been synthesized and the crystal structure shows it to be nine-coordinate [172]. 

Figure 4.5 Structure of Nd(6)CH3CN(CF3S03)2 [7]. (Redrawn fromR Wei, T. Jin and G Xu, Synthesis and crystal structure of neodymium complex of 1-methyl-1,4,7,10-tetraazacyclododecane, Acra Chimica Sinica, 50, 883, 1992.)...

Complexes Ln(bipy)2(N03)3 have been studied in more detail than the other bipy complexes all appear to have 10-coordinate structures with all nitrates present as bidentate ligands. The coordination geometry has been variously described as a bicapped dodecahedron and as a sphenocorona. Unlike the La complex, the Lu complex does not possess disorder about the twofold axis. Li N distances are 2.46-2.67(1) A and Lu—O distances in the range 2.426(9)-2.556(9) A. [Y(bipy)2(N03)3] is, like [Y(phen)2(N03)3], isostructural with its lanthanide analogues. Similarly, the structure of [Nd(bipy)2(N03)3] has been shown to be isostructural with [Ln(bipy)2(N03)3] (Ln = Y, La, Lu). A number of compounds Ln(bipy)3(N03)3 (Ln = Ce, Pr, Nd, Yb) have been reported the neodymium complex was shown to be [Nd(bipy)2(N03)3]. bipy, with the third bipy molecule not associating with the neodymium-containing complex. ... 

Another interesting structural form (Fig. 21) has been revealed by X-ray diffraction studies for tetrameric Ln4(OCH2-r-Bu) 2 (Ln = La or Nd) (249). Both molecules contain a square of lanthanide metal atoms involving eight p2-OR groups four above and four below the Ln4 plane. However, the neodymium complex contains four molecules of toluene per tetramer within its lattice. 

An interesting as well as unusual structure (Fig. 29) was reported for the compex Nd6(0-/-Pr)17Cl (256) in 1978. This structure attested to the complexity possible in lanthanide alkoxide chemistry (28). The structure of the neodymium complex can be regarded as two triangular Nd3(jt3-OR)(ft2-OR)3(OR)6 (where R = O-i -Pr) units connected by sharing the /x3-Cl site (which becomes a /i6-Cl) and three terminal OR ligands (which become /t2-OR groups). 

Cocondensation of La, Ce, Nd, or Er metal atoms with cyclooctatetraene at — 196°C yielded dinuclear complexes of the formula [CgHgR(THF)2][R(CgHg)2] after extraction with tetrahydrofuran (De Kock et al., 1978). The structure of the neodymium complex (fig. 23, table 15) shows two cyclooctatetraene rings in the anion, which are neither equidistant from the neodymium atom, nor p allel. The neodymium atom in the cation is asymmetrically located with respect to the central cyclooctatetraene ring with neodymium-carbon distances between 2.68 and 4.63 A (Ely et al., 1976 De Kock et al., 1978). 

These new silyl complexes are monomeric in benzene solution, but are dimeric in the solid state. The crystal structure of the samarium analogue (Figure 1) shows that dimers form via intermolecular Sm-CH3-Si interactions. The Sm-Si distance, 3.052 (8) A, is to our knowledge the longest metal-silicon distance known. As with other complexes that display Ln-CH3-Si interactions in the solid state, evidence for these interactions in solution is not observed in NMR spectra. The [H NMR chemical shifts for the neodymium... 

Recently similar complexes of neodymium have been prepared by Karraker 48) containing bromide and iodide in place of chloride. While their chemical properties are similar to the dimeric chloride compound their powder patterns suggest they may have different structures. Since they also have increasing amounts of solvent, the bromide containing three THF molecules and the iodide four, these may be complexes in which the halide bridge is broken by addition of another solvent molecule to give a monomer such as [Ln(COT)X 3 THF]. 

One other structure of a tricyclopentadienide has appeared (57) and it provides a further demonstration of the correlation between ionic size and coordination. Neodymium tris(methylcyclopentadienide) crystallizes as a tetramer (Fig. 10). The Nd + ion (which is slightly larger than Sm3+) is pentahapto bound to three cyclopentadienyl rings and monohapto bound to a fourth ring. This fourth ring is in turn j -bonded to another Nd + ion, until the tetramer is generated. The distances between tetramers are those expected for van der Waals contact. The crystal and molecular parameters are compared with the other tris cyclopentadienyl complexes in Table 5. 

The most important result of the structure studies was undoubtedly the establishment of the fact that the crystalline isopropoxides of all rare earths are not the homoleptic Ln(OPr )3 complexes but oxoalkoxides of Ln50(0Pri)13 composition, where Ln = Sc, Y, Er, Yb (see also Fig. 4.9 a). They appear to be desolvation products of the very unstable [Ln(OPri)3( PrOH)]2 solvates (perfectly soluble and rather reactive) the complex of such composition has been isolated and characterized only for neodymium, but the IR spectroscopic evidence for the existence of such solvates was obtained also for Pr and Er. Desolvation of Ln(OBu )3 2L (Ln = Y, La L = BuOH, THF, Py) leads also to the formation of oxocomplexes the ions corresponding to the fragmentation of the homoleptic species are absent in their mass-spectra (except for [Y3(OBu,)9(tBuOH)2], where the Y3(OR)8+ ion was found along with Y30(0R)6+). The same kind transformations have been observed also for... 

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 neodymium atoms are placed in three different environments as depicted in Fig. 37. However, all neodymium atoms are 7-coordinate adopting a distorted mono capped prismatic geometry. Most interesting structural feature are the presence of terminal ethyl and isopropoxide ligands at neodymium. More simple molecular arrangments were found in ligand related complexes Ln[(jt-... 

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