Coordination compounds linkage isomers

Figure 16.18 summarizes the types of isomerism found in coordination complexes. The two major classes of isomers are structural isomers, in which the atoms are connected to different partners, and stereoisomers, in which the atoms have the same partners but are arranged differently in space. Structural isomers of coordination compounds are subdivided into ionization, hydrate, linkage, and coordination isomers. 

Two or more coordination compounds in which the donor atom of at least one of the ligands is different. Linkage isomers have different physical and chemical properties. Ligands that can form these isomers are CN-, SCN-, and N02-. 

Structural (constitutional) isomers (Applied to coordination compounds.) Isomers whose differences involve more than a single coordination sphere or else different donor atoms they include ionization isomers, hydrate isomers, coordination isomers, and linkage isomers. 

Shapes and IR spectra patterns for chloro, O-nitrito and IV-nitrito cobalt(III) ammine compounds. The thick lines represent the vibrations associated with the coordinated ammonia molecule, whereas the thin lines represent the vibrations associated with the linkage isomer of nitrite (two and three bands for N- and O-bound isomers respectively). 

Selenium, bis(diethyldithiocarbamato)-stereochemistry, 60 Selenium, bis(dithiofurancarbamato)-stereochemistry, 60 Selenium(II) complexes bis(dithiochelate), 60 Selenocyanate complexes linkage isomers, 186 Selenonium ions, trifluoro-stereochemistry, 37 Self-exchange reactions, 333 electron transfer rate constants, 347-353, 366 rate constants calculation, 348 rate constants, 362 Semicarbazide, 1,4-diphenylthio-ruthenium determination, 546 Semi-glycinecresol red metallochromic indicator, 557 Semi-xylenol orange metallochromic indicator, 557 Seven-coordinate compounds stereochemistry, 69-83 Sidgwick, Nevil Vincent, 16 Silicon, tris(acetylacetone)-configuration, 195... 

Linkage isomers Linkage isomers occur when a ligand species can attach to the metal atom in different orientations. For example, when thiocyanate (SCN ) bonds to a metal, in one isomer the metal can be linked through the nitrogen atom whereas in the other isomer it s linked though the sulfur atom. (The orientation of these links affects the name of the coordination compound, which we describe in the next section.)... 

Werner also described and named the various other types of isomerism observed in coordination compounds. These are ionisation isomerism, displayed by [Co(NH3)5C1]S04 and [Co(NH3)5S04]Cl hydrate isomerism, for example [Cr(H20)5]Cl3 and [Cr(H20)5Cl]Cl2.H20 and coordination isomerism, which occurs when both cation and anion are complexes, for example [Co(NH3)5][Cr(CN)6] and [Cr(NH3)5][Co(CN)6] Werner also explained one case of what is now known as linkage isomerism in [Co(NH3)5N02]Cl2 and [Co(NH3)50NO]Cl2, where the NO2 ligand has two possible sites of attachment to the metal atom. It was many years before other linkage isomers were prepared. 

We can subdivide the broad category of structural isomers into two types coordination isomers and linkage isomers. Coordination isomers occur when a coordinated ligand exchanges places with the uncoordinated counterion. For example, two different compounds have the general formula Co(NH3)5 BrCl. In one of them, the bromine coordinates to the metal and chloride is a counterion, pentaamminebromocobalt(II) chloride, [Co(NH3)5Br]Cl in the other one, the chlorine coordinates to the metal and bromide is the counterion, pentaamminechlorocobalt(II) bromide, [Co(NH3)5Cl]Br. 

An interesting study with BATO compounds concerns the linkage isomerization of coordinated [NCS] in [Tc(NCS)(cdoh)2(cdo)(BMe)] (440). Both a red, N-bond isothiocyanato complex [Tc(NCS)(cdoh)2(cdo)(BMe)] and the brown, S-bond thiocyanato complex [Tc(SCN)(dmg)3(BR)] (441) were isolated from the direct synthesis from [Tc04] . The N-bound (440) was found to be thermodynamically more stable than the S-bound isomer (441) and the conversion was monitored elegantly by spectroscopic methods. The X-ray crystal structure of (440) was determined. The NCS and SCN -substituted analogues exhibited r c N stretch at 2,114-2,124 cm and at 2,055-2,079 cm , respectively. " (Scheme 59). 

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