Abstract: The complexes LnBr_3(18-C-6)·nH_2O (Ln=La, n=1; Ln=Nd, Sm, Gd, Tb, Er, Y, n=3)were prepared and those FT-IR, Raman spectra were measured over the region of 3500—100 cm~(-1).
By means of normal coordinatiou analysis of La(NO_3)_3(18-C-6) and structural determination of some crown ether complexes, the bands charactering Ln—O_6 (crown), Lu—O(H_2) and Ln—Br as well as the coupling mode between vibrations of Ln—O(crown) and Ln—Br can be assigned respectively. The band near 880 cm~(-1) is attribued to the symmetrical vibration of the ring inherent in the fragment LnO_6 (crown) which is important for clarifying whether or not Ln~(3+) in the complex is coordinated to the crown ring. Due to a similar trend existing in the low frequency spectra of Ln=La, Nd, Sm, Gd, Tb, Er complexes except Y, the analogous structures would be expected.
As a consequence, La~(3+) (n=1) is coordinated by six oxygen atoms of crown ether ring, three bromine atoms and one oxgaen atom from the water with CN=10. For complexes of Ln=Nd, Sm, Gd, Tb (n=3), the molecular structures are like La-complex additionally more two lattice water. As the smaller ionic radius of Y~(3+), the Y-complex exists with CN=9. Therefore the structure of YBr_3 (18-C-6)·3H_2O may be similar to [GdCl_2(18-C-6)·EtOH]~+Cl~-, e.g.[YBr_2(18-C-6)·OH_2]~+Br~- with CN=9, that can explain why the low frequency spectrum of Y-complex is different from the others.