Lanthanide complexes 1.8- naphthyridine

Polyhedra in these high coordination numbers are often necessarily irregular, but when all the ligands are identical, near-icosahedral geometries occur for the 12-coordinate [Pr(l,8-naphthyridine)6] + and [La(N03)6] ions in crystalline salts. It should also be remembered that the geometries discussed here are found in the solid state, but on dissolution in a solvent, where the influence of counter-ions is lessened, matters may be different (see the aqua ions. Sections 4.3.1 and 4.3.2). In principle, isomers are often possible, but because of the lability of lanthanide complexes they are very rarely observed. 

Note The Meissenheimer conversion of 1,8-naphthyridine A-oxides into halo-geno-l,8-naphthyridines has been covered in Section 24.1 complexes of 1,8-naphthyridine 1-oxide with Cr,555 Cu,496 and Sr,462 and the lanthanide compounds429 have been reported and deoxygenation of an A-oxide is exemplified here. 

Another bidentate ligand whose complexes have been studied in some detail is 1,8-naphthyridine (naph) which, like nitrate, has a small bite angle and is similarly capable of affording high coordination numbers two types of perchlorate complexes have been made, M(naph)6(C104)3 (M = La-Pr) and M(naph)5 (0104)3 (M = Nd-Eu). The former complexes have 12-coordinate lanthanides, confirmed by diffraction methods for the praesodymium complex. The change in stoichiometry is doubtless a manifestation of the lanthanide contraction. 

The ligand, 1,8-naphthyridine, forms complexes with what appear to be very high coordination numbers. With perchlorate as the anion the complexes R(napy)s(C104)3 (R = La-Pr) and R(napy)s(C104)3 (R = Nd-Eu) are isolated from ethyl acetate solutions (Foster et al., 1972). The infrared evidence indicates that in all cases the naphthyridine is functioning as a bidentate ligand and that the perchlorate is present in the ionic form. This would require that the larger lanthanide ions be twelve-coordinate and that the heavier lanthanides be... 

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