Isomers of complexes

Using a triazole-/pyrimidine-containing hybrid ligand, terminally coordinated in a thiocyanate-bridged copper(II) dimer, Haasnoot et al. reported250 the structure of the f3 isomer of complex (288), revealing that the Cu-SCN distance is relatively short compared to other Cu-SCN... 

Reactions of PhC=CC=CPh with iron carbonyls [Fe(CO)s, Fe2(CO)9, or Fe3(CO)i2] give isomers of complexes Fe(CO)4 (diyne)2 (265), Fe2(CO)6 (diyne)2 (266), and Fe2(CO)7 (diyne)2 (267), to which structures analogous to those found for similar products obtained from C2Ph2 were ascribed all three isomers of the second complex were formed. The reactions of hexa-2,4-diyne and Fe(CO)s have been described in more detail. UV irradiation of mixtures of the two... 

Alkenes which have no symmetry planes perpendicular to the plane of the double bond such as Pmr-butene-2 or propene can coordinate to platinum in two enantiomorphous ways (77) and (78). If an optically active ligand is also bound to platinum(H), then two diastereoisomers are found which can be separated by fractional crystallization657,658 or by HPLC.659 Both cis and trans isomers of complexes PtCl(N—0)(alkene) have beenprepared, where N—O is an anion derived from an amino add (equations 235a and 235b).660-664 Epimerization cannot occur by simple rotation of the alkene about its bond axis, but only by a mechanism involving cleavage of the platinum(II)-alkene bond. 

Fig. 3. Possible isomers of complexes with linear hexadentate ligands...

The structures of isomers of complex dibromodicarbonyl cyclopentadienyl-rhenium drawn ... 

Chromic Ferrichrome Complexes. The spectra for the model chromic hydroxamate complexes are reproduced in Figure 6. Since the visible and CD spectra of the isomers are wholly dominated by the metal complex chromophore, these data can be used to characterize and to identify coordination isomers of complexes formed by the siderophores. The preparation and characterization of the chromic complexes of des-ferriferrichrome and desferriferrichrysin have been reported (3). Although an examination of molecular models for both complexes shows two coordination isomers are possible (A-cis and A-cis), both chromic complexes consist exclusively of the A-cis isomer. These results agree with x-ray crystallographic investigations which have shown that both ferri-chrysin and ferrichrome A crystallize as only the A-cis isomer (14, 15). Both chromic complexes have identical CD spectra which are the same as the A-cis Cr(men)3 spectrum (Figure 6). 

Figure 2 Molecular structures of symmetrical isomers of complexes (4) (left) and (8)...

Figure 4 Molecular structure of symmetrical isomer of complex (11)...

One of the products of the reaction of Ph3PCHCHO with [Os3(CO)io(NCMe)2], 15, is the result of a C-H oxidative addition reaction. Complex 15 decomposes at room temperature, under daylight, to give a mixture of isomers of complex 16, one of which has been studied by X-ray diffraction. Similarly, the Ru complex analogous to 16 has been prepared by reacting [Ru3(CO)i2] with the same ylide or with Ph3P=CH2. ... 

Figure 9. Phosphorus-31 NMR spectra of solutions of (a) [U(ai-P2Wi70

Z)- and (E)-isomers of complexes containing 2,5-dioxa-3,4-disilatitanacyclopentane five-membered rings (Scheme 595) can be prepared in high yields by reacting Cp2TiCl2 with the appropriate diastereomerically pure diol. The crystal structures have been determined by X-ray diffraction.1543... 

SCHEME 16 Mechanism for ruthenium-complex-promoted, iridium-complex-catalyzed methanol carbonylation. Alternative geometrical isomers of complexes and coordinated solvent molecules are omitted for clarity. Adapted with permission from Scheme 9 in reference [15], copyright 2006, Elsevier. 

Good separations of the ci 4rans isomers of complexes of the type (Coen2Cl2)X (X = CF, NO3, SCN") and of nitro-compormds of Co are possible. The cis-forms always migrate further than the corresponding trans-ionm. 

Pure optical isomers of complexes such as CpFe(C0)(PPh3)(C0Et), which contain a chiral iron atom on account of their four different substituents arranged in a pseudo-tetrahedral fashion, have been obtained. Decarbonylation leads to... 

Buckingham, Marzilli, and Sargeson separated the conformational isomers of complexes of the type trans-[Co tnen)X 2T and reported evidence for the existence of conformational isomers of j8-[Co(trien)(H202)] in solution, but the isomers were not isolated. One of the latter isomers undergoes mutarotation to give the more stable conformation of trien. 

Hans Jonassen, J. C. Bailar, Jr., and Allan Gott, The Stereoisomerism of Complex Inorganic Compounds. XIII. A Partial Resolution of Racemic Tartaric Acid by Means of Different Stabilities of Isomers of Complex Ions, J. Am. Chem. Soc. 74 3131 (1952). 

Fig. 1.7. The interactions of optical isomers of complexes of phenanthroline, [M(phen)3 showing the differences in steric effects upon binding to DNA. From Reference 66.

One g quantity of each of these three dark green, blue-green and violet-coloured isomers of complexes with the molecular formula CrCl36H20, when treated with dehydrating agents, attain a constant weight of 0.865, 0.932 and 1 g, respectively. 

By a judicious application of this principle it has been possible to prepare many different geometric isomers of platinum(II) complexes, including the three possible isomers of complexes containing four different ligands such as nPtNH3pyN02Cl]. 

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