Pentanitrato complexes

Although there are reports on the preparation of anhydrous pentanitrato complexes (other than those of scandium) by precipitation (e.g., (NH4)2Gd(N03)5 Babievskaya and Perel man, 1965), the most convenient method is the use of MNO3/R2O3 melts. By this method Camall et al. (1973) have prepared K2[Er(N03)5] its structure has been reported by Gebert Sherry (1978). 

The hydrated pentanitrato complexes all have a dodecacoordinated central ion [R(N03)5(H20)2] . An interesting case is the ammonium complex (NH4)2La(N03)5 /1H2O ( = 3 or 4) (Eriksson et al., 1982). The two hydrates are structurally closely related because the removal of water does not bring about the collapse of the structure and the coordination geometry and crystal symmetry are preserved. The only significant change is the contraction of the unit cell when there is one water molecule less. The ammonium ions are involved in the network of hydrogen bonds with the complex anions and the noncoordinated water molecules. 

Among the complex nitrates, the pentanitrato series, corresponding to the anion [R(N03)5] , the most extensive because several low valent cations may serve as counter-ions leading to a large number of sohd structures. Furthermore, water plays an active role and may enter the inner coordination sphere, especially in the case of the larger R " " ions, and/or may be included in the sohd structures as water of crystallization. In the case of the dodecanitrato series, M R2(N03)j2 24H2O, may be varied, but the number and role of water molecules is fixed... 

The bicycUc polyethers give rise to complex structures. With lanthanum chloride and Bicy(4,2B,2B), the adduct corresponds approximately to a 1 1 stoichiometry, but a crystalline product is obtained only in the presence of water. The crystal structure analysis shows that partial hydrolysis takes place. In this, the behaviour is reminiscent of the 2 1 TEA complexes with 15C5. Indeed, the unit cell contains a pseudo-centrosymmetric dimer [LaCl(Cl,OH)L]2 with an OH Cl hydrogen bond across the centre of symmetry one site is occupied by Cl in one half and by OH in the other half. The ligand in this structure has an approximate twofold axis of symmetry. The O atoms form an end-capped trigonal prism around La(III) and the metal ion lies in the mean plane formed by the O atoms of the aliphatic unsubstituted chain. The other bicyclic polyether, Bicy(4B,2B,2B), forms 3 2 complexes with lanthanum nitrate. The asymmetric unit contains two dinitrato cations [La(N03)2L] and one pentanitrato anion [La(N03)5(Me0H)] . The La(III) ion is 11-coordinate in the anion and one of the cations, in which there is one bidentate and one monodentate nitrate ion. It is 12-coordinate in the other cation. 

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