Isostructural series

Table 13.11 Electronic configurations of the isostructural series of complexes containing bridging and...

The problem could be stated from another point of view. In an isostructural series the uranium and neptunium compounds tend to be itinerant electron magnets or band magnets (like iron) and their orbital contribution is at least partially quenched. For much heavier actinides we know that the compounds will make local moment magnets with orbital contributions. It is quite possible that in between these two clear cut forms of magnetism that the intermediate case could be dominated by fluctuations, and no recognizable form of magnetism would occur. To state that the... 

Ishikawa etal. proposed an approach for the determination of the ligand-field (LF) parameters of a set of isostructural lanthanide complexes. This method consists of a simultaneous fit of the temperature dependence of magnetic susceptibilities and NMR spectra for the whole isostructural series [18]. In order to avoid over-parametrization a key restriction is imposed each parameter is expressed as a linear function of the number of f electrons, n ... 

Three (or four, see following text) additional coordination bonds are established with two solvent molecules (pyridine, H20) and the anion X- (Cl- or N03-). The good behaviour of this reaction system led to the preparation and crystallographic characterization of a comprehensive quasi-isostructural series of... 

Anomalies in the relative sizes of Ni2+ and Mg2+ in octahedral coordination were found by Longo and Kafalas (1969) in the series of perovs-kites, CsMF3, and by Shannon and Prewitt (1970) in the series of rutiles MF2, where M = Ni, Mg, Co, Fe, and Mn. In both of these isostructural series the unit cell volume of the compound containing Ni was found to be greater than the volume of the compound containing Mg. This is in contradiction to the relative size of Ni2+ and Mg2+ in oxides. 

The compounds Na3AlP309N and Na2Mg2P309N were the first terms prepared of each of these two isostructural series of nitridooxophos-phates (218). Many isotypic compounds and solid solutions have since... 

Remarks on the crystal chemistry of the alloys of the 3rd group metals. A large number of intermediate phases have been identified in the binary alloys formed by the rare earth metals and actinides with several elements. A short illustrative list is shown in Tables 5.19 and 5.20. Compounds of a few selected rare earth metals and actinides have been considered in order to show some frequent stoichiometries and crystal structure types. The existence of a number of analogies among the different metals considered and the formation of some isostructural series of compounds may be noticed. 

With the same anion, unit-cell volumes in isostructural series are proportional (but not necessarily in a hnear fashion) to the cationic volume. Covalence effects on the shortening of metal-oxygen and metal-fluorine distances are not comparable. 

We are now close to being in a position to examine the effects on CO stretching parameter, for the isoelectronic isostructural series of first row carbonyl halides considered, of changes in metal, degree of substitution, coordination site, and halide. Along the sequence Cr(0), Mn(I), Fe(II), both 5 a and 2n populations fall. In other words, a higher oxidation state of the metal renders it at once a better a-acceptor and a poorer jr-donor perhaps a predictable result. Numerically the a -effect is the greater, but both are in the same direction, and parameters... 

The single crystal X-ray structure of hydrated neodymium hypophosphate, NdHP206-4H20, has been determined.239 The Nd ion is eight-coordinated to four H20 and two bidentate hypophosphate anions. The details of interatomic distances and bond angles were compared with other members of this isostructural series, which extends at least from Nd to Er.240... 

A further application of relaxation rate measurements is that similar 1/71 ratios in a series of lanthanide complexes may be taken to indicate an isostructural series. However, this approach has the limitation that if only part of the complex is studied, perhaps an organic ligand, its 71 ratios would be independent of changes, for example changes in the extent of hydration in the remainder of the complex, provided that the conformation of the ligand relative to the lanthanide ion were preserved. An excellent example of the use of 71 data in a quite different way is its use to determine hydration numbers of lanthanide dipicolinate complexes.562... 

Values for the first isostructural series (Sm has been removed because of its faint paramagnetism). °Values for the second isostructural series. 

The capping of both termini of three tridentate chelating units with covalent tripods provides highly rigid macrobicyclic receptors (i.e., cryptands), which are ideally suited for investigating variations of crystal-field parameters within isostructural series. Platas et al. (1999) have iso-... 

L/t,( I.7-2Ii)3]3 (R = Pr, Eu, Tb-Yb) reported by Reilley et al. (1975,1976) suggested linear behaviours compatible with isostructurality (i.e., invariance of G ) and invariances of F and Bq along the complete lanthanide series. Moreover, least-squares fits of the molecular structure based on G calculated for the crystal structures of (cationEl R(E7-2H)3] showed only minor variations between solid-state and solution structures. Similar conclusions have been proposed by Platas-Iglesias et al. (2001) for H NMR data of [F(L7c-2H)3]3 (R = Nd, Eu, Tb-Yb) except that the existence of a single isostructural series is further supported by linear correlations obtained with the crystal-field independent technique (eq. (51), fig. 31a), and minor variations of F, between R = Dy and R = Ho are detected according the one-nucleus techniques (eqs. (48), (49), fig. 31b). 

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