Coordination chemistry geometrical isomers

Geometrical isomerism This is an important topic which played a crucial role in the development of coordination chemistry. Werner used the number of isomers... 

Two milestones in chemistry may be addressed to the geometric isomers of diamminedichloroplatinum(II). About 100 years ago Alfred Werner laid down the principles of modem coordination chemistry with the help of isomeric [PtCl2(NH3)2] [1]. About 70 years later Barnett Rosenberg and co-workers discovered that the cis isomer is antitumor active, whereas the trans isomer is not [2,3]. Today m-[PtCl2(NH3)2] (cisplatin) is routinely used as a drug, particularly effective against testicular and ovarian cancer [4],... 

Cations [Cr(NH3)4X2]+ have as and trans geometrical isomers (see Coordination Organometallic Chemistry Principles). The higher syrmnetry of the trans form makes its d d spectrum easier to analyze. We assume NH3 to be a pure a donor (see Ammonia N-donor Ligands). Hence e (NH3) is zero. The axial hgands are n donors (e r > 0). The AOM orbital energies E are given in equations (27-30). 

One of the classical tetradentate Schiff bases is the open-chain N2O2 donor ligand salen (137), which has flexibihty sufficient to permit it to form different geometric isomers on complexation. The ability of the ubiquitous salen and close analogues to bind O2 reversibly as its cobalt complex, as in [(02)Co(salen)(py)], has been central to most investigations of its coordination chemistry. Complexes of the [Co(salen)] family also mediate the electrocatalytic reduction of O2 to H2O2, whereas those incorporating chiral centers on... 

Additional opportunities for optical activity arise in molecules containing chelating ligands (A-A). For example, a compound of general formula M(A-A)2B2 has two geometric isomers, one of which is chiral. The propeller-like tris-chelated M(A-A)3 compounds are always chiral. Werner and his collaborators took advantage of the ready optical activity of such complexes to provide additional proof that the coordination spheres of his many and varied cobalt compounds were octahedral. After 20 years of work, Werner s coordination theory was thoroughly established, and he received the Nobel Prize in chemistry in 1913. In a final positive proof, Werner and co-workers... 

Four-coordinate d8 complexes can display a closely related electronic and geometric equilibrium between paramagnetic tetrahedral and diamagnetic planar isomers. Numerous examples are known in nickel(II) chemistry (80). In this case, as well as with the octahedral complexes described above, there is no change in the coordination number of the metal ion. 

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