Coordination-sphere isomers

Coordination-sphere isomers are isomers that differ in which species in the complex are ligands and which are outside the coordination sphere in the solid lattice. For example, three isomers have the formula CrCl3(H20)5. When the ligands are six H2O and the chloride ions are in the crystal lattice (as counterions), we have the violet compound [Cr(H20)6]Cl3. When the ligands are five H2O and one Cl , with the sixth H2O and the two Cl out in the lattice, we have the green compound [Cr(H20)5Cl]Cl2 H20. The third isomer,... 

Which of the three complexes can have (a) geometric isomers, (b) linkage isomers, (c) optical isomers, (d) coordination-sphere isomers ... 

Distinguishing between the fac- and mer-isomers is theoretically possible with far-IR spectra, as the mer-isomer (C2v symmetry in the coordination sphere) should give rise to three u(Os—X) stretching bands, while the C3v... 

FIGURE 16.19 Hydrate isomers. In part (a), the water molecule is simply part of the surrounding solvent in part (b), the water molecule is present in the coordination sphere and a ligand (green sphere) is now present in the solution. 

Although they are built from the same numbers and kinds of atoms, structural isomers have different chemical formulas, because the formulas show how the atoms are grouped in or outside the coordination sphere. Stereoisomers, on the other hand, have the same formulas, because their atoms have the same partners in the coordination spheres only the spatial arrangement of the ligands differs. There are two types of stereoisomerism, geometrical and optical. 

The hydrosilylation of alkynes has also been studied using as catalysts Pt, Rh, Ir and Ni complexes. The improvement of the regioselectivity of the catalyst and the understanding of stereoelectronic factors that control it have been major incentives for the ongoing research. From numerous studies involving non-NHC catalysts, it has been established that there is a complex dependence of the product ratio on the type of metal, the aUcyne, the metal coordination sphere, the charge (cationic versus neutral) of the catalytic complex and the reaction conditions. In the Speier s and Karstedt s systems, mixtures of the thermodynamically more stable a- and -E-isomers are observed. Bulky phosphine ligands have been used on many occasions in order to obtain selectively P-f -isomers. 

In addition to the variation in electronic configuration, the geometric details of the coordination sphere and the properties of iron-ligand bonds (different a- or 71-donor strength) also influence the isomer shift as observed for a series of compounds ... 

Compounds (L)AuC=CR can appear as ligands in the coordination sphere of transition metals. The interaction may be fluxional with metal-metal contacts M-Au and the alkyne coordinated side-on (if, dihapto) to the gold atom. Typical examples are (cp)(CO)(NO)W[Ph3PAuC=C Bu 90 and l, c3(CO)9[R3PAuC=CtBu], with R = Ph, Pr, for which several isomers have been observed in solution.91... 

Assume that the complex MLX2Y2 has a square-base pyramid structure with all ligands able to bond in all positions in the coordination sphere. How many isomers are possible ... 

Isomers are substances that have the same number and kinds of atoms, but arranged differently. Constitutional (structural) isomers, as applied to coordination compounds, are isomers whose differences involve having more than a single coordination sphere or different donor atoms on the same ligand. 

They contain different atom-to-atom bonding sequences. Stereoisomers, on the other hand, are isomers that differ only in the way that atoms are oriented in space, and therefore involve only one coordination sphere and the same ligands and donor atoms. 

An ionization isomer results from the exchange of ions inside and outside the coordination sphere. 

In the following section, we describe the case of adsorption of a Sn complex onto a palladium oxide suspension. In an alkaline medium (a basic PdO hydrosol), chlorides in the SnCL complex are substituted in the coordination sphere of tin(IV) by hydroxo anions, which are in excess, yielding the stannate Sn(OH)g complex. The Sn Mossbauer spectroscopy spectrum of a bimetallic sol (frozen in liquid nitrogen) is compared with a true stannic solution. At the same tin concentration, it shows the changes in the Sn environment due to adsorption onto the PdO surface (Fig. 13.27). The isomer shift S is found to be close to zero for the stannate solution and increases when contacted with the PdO suspension, indicating a modification of the coordination sphere of tin. The increase in 5 can be correlated to an increase in the core level electronic density of tin. The quadrupole splitting A, is related to a modification of the symmetry of the close environment of tin, due to adsorption of Sn(OH)g complexes onto the PdO colloidal nanoparticles. 

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