Octahedral hexahalide complexes

Representative examples of rare earth complexes with halides and pseudohalides are given in Table 4.12. Some oxyanions such as nitrates are included in a separate listing. The formulas given for halide complexes as hexahalides are misleading since these compounds are extended lattice compounds and are not always octahedral. 

At the present, the M.O. configuration description of polyatomic molecules and ions containing transition group elements has been most elaborated for octahedral complexes, especially hexahalide complexes MXg with X = F--, Cl, Br, and 1 and... 

As a Chatt-Ahrland type A or Pearson hard cation, association of Am with inorganic ligands proceeds initially through electrostatic interactions to form outer-sphere complexes. However, in some cases (e.g. F", SO "), there is evidence that the ligand displaces the water of hydration, at least to some extent, to form inner-sphere complexes. Spectrophotometric results of Marcus and Shiloh [124] also provide evidence for inner-sphere complexation of chloride and nitrate ions to Am in concentrated LiCl and UNO3 solutions, respectively. Preparation of the solid compound [(CeHslsPHjsAmQg, containing the octahedral hexahalide complex AmCl, has been described by Ryan [107]. 

Empirical correlation of intensities of absorption bands with the structure of complexes in solutions have been made for lanthanide complexes. It has been recognized that forced electric-dipole transitions of low intensities, in some cases lower in intensity than those of magnetic-dipole transitions, may indicate that the ligand field has point group symmetry with a center of inversion. This criterion has been used in the determination of the ligand field by symmetry of Eu3+ aquo ion [202], The absorption band intensity ratios have been used to show the octahedral structure [49] of lanthanide hexahalide complexes, LnXg. ... 

A The sub-shell energy difference A between d)e. and (i) 2 (which we give here as a negative value in order to obtain a better concordance with the description of octahedral complexes) would be the number given in column C of Eq. (7) with opposite sign. A plausible interpretation of the number in column B would be the difference of excitation energy of ( r) 2 and a)ti like the difference 12 to 15 kK observed 4, 6) between (ji + o)tin and a - -n) tin in hexahalides. 

Wave-number /iVj, of first electron transfer band of octahedral samarium(lll), europium(III), thulium(III) and ytterbium(III) hexahalide complexes (Ryan and Jorgensen 1966, Ryan 1969). The parameter M of the refined spin-pairing treatment (table 1, last column) is added to liVj, in the corrected values. 

Among the linear combinations of orbitals from the ligands of an octahedral complex, the two sets odd y are unique in allowing a mixture of a and n character. This will be shown later to be of great importance for the absorption spectra of certcdn hexahalide complexes. 

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