Geometric isomers of coordination compounds

Effects of Isomerism Geometrical isomers of coordination compounds can exhibit different values of redox potential, as accounted for, in various cases, by simple djr orbital level splitting diagrams or by MO calculations. The dependence of the relative stability and redox behavior of the geometrical isomers on the electronic configuration of the metal is also... 

Geometric isomerism Occurs when atoms or groups of atoms can be arranged in different ways on two sides of a rigid structure also called cis-trans isomerism. In geometric isomers of coordination compounds, the same ligands are arranged in different orders within the coordination sphere. 

We use the terms cis and trans to distinguish one geometric isomer of a compound from the other (Section 4.4). Cis means that two particular atoms (or groups of atoms) are adjacent to each other, and trans means that the atoms (or groups of atoms) are on opposite sides in the structural formula. The cis and trans isomers of coordination compounds generally have quite different colors, melting points, dipole moments, and chemical reactivities. Figure 15.10 shows the cis and trans isomers of... 

The proposals of Werner (49) about the structure of coordination compounds were amply justified by the chemical reactions exhibited by them, by the identification of geometrical isomers, and by the resolution of certain compounds into their optical antipodes. Modern methods for the determination of structures and for studying the nature of charged or neutral species in solution have demonstrated the fundamental soundness of Werner s views. 

We see that the structure of coordination compounds can give rise to geometric and/or optical isomers. We become acquainted with the use of a polarimeter in studying optical isomers. (22.4)... 

In 1889 J0rgensen had prepared two isomers with the formula CoCl3.2en, where en is ethylenediamine, H2N.CH2.CH2.NH2. J0rgensen believed that these were structural isomers, but Werner maintained that they were two geometric isomers of the octahedral complex ion (Figure 12.9). In fact Werner cited the existence of two compounds with this formula as evidence for the octahedral configuration in complexes with a coordination number of 6. 

To discuss the structures of coordination compounds, we first defined various types of isomers, compounds that have the same number and types of atoms but differ in their chemical properties. Stereoisomers have the same number and types of chemical bonds, whereas structural isomers do not. Stereoisomers can be subdivided into geometric and optical isomers. 

Jorgensen had synthesized [CoCl2(en)2]Cl, which was known to come in two forms named for their colors video (cis) and praseo (trans). Werner cited the existence of these two (and ody two) isomers as proof of an octahedral coordination sphere. Given that the hidentate ethylenediamine can ody span cis positions, how many geometric isomers wodd this compound have if it assumed a trigonal prismatic coordination sphere Of these, how many wodd he chiral ... 

One area of interest concerns the assignment of the metal ligand vibrations in simple complexes through a comparison of the spectra of similar compounds. Often the observed data can be used to predict the geometrical structures of isomers although in the absence of supporting Raman data, the structures must be considered tentative. As an example of the FT-IR spectra of coordination compounds, we will consider the 1 1 addition compounds formed by triphenyltin(IV) bromide and iodide (Ph3SnX, X = Br, I) with dimethyl-propylene-urea (DMPU) [3]. The bromo complex exhibits three characteristic... 

Because sjmtheses of coordination compounds frequently involve ligand substitution reactions, an understanding of the relative lability (or its opposite, kinetic inertness) of metal complexes is important in the design of experimental procedures. Geometric isomers of labile complexes pose a special problem in synthesis because facile routes for interconversion may allow isomerization, favoring formation of the thermodynamically more stable isomer. 

The spin state of the compounds XFe(R2dtc)2 is 3/2 (64). Mossbauer spectra of ClFe(Et2 tc)2 in solution are almost identical with the spectrum of the six-coordinated Fe(Et2magnetic susceptibility and in the isomer shift and quadrupole splitting parameters suggests a geometrical correspondency in solution, which can be attained by the binding of a solvent molecule to the sixth coordination site of the ClFe(Et2[Pg.98]

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 ... 

Geometric isomers occur as cis-trans isomers in compounds with double bonds like in N2F2 and especially when coordination polyhedra have different kinds of ligands. The... 

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