Ligand exchange definition

Pentacoordinate organocobalt(III) species have been suspected to exist either as reactive intermediates in ligand-exchange reactions [137-141] or, less commonly, as relatively stable species [140-142], Clear-cut demonstrations of stable 5-coordinate Co(III) complexes are relatively rare [136,143], One report contains two definitive examples of 5-coordinate complexes of the type Co(saloph)R (R = CH3 and /-C3H7) [136], Several interesting features emerge from these structures. First, the Co atom is displaced toward R. Second, the Co—C bond is shorter than in hexacoordinate compounds, but steric strain remains for z -C3H7, even in the pentacoordinate species. 

Gordshtein et al. (18) proposed that the ability of simple tin mercaptides to undergo ligand exchange reactions was caused by dr — pir conjugation in the Sn-S bonds. They proposed also that tin alkoxides form 1 1 complexes with tin chlorides because of the lack of dir — Pit conjugation in the Sn-O bond. No definite conclusions were stated regarding tin carboxylates. Starnes (19) has reported that di-butyltin dimethoxide is not a very efficient PVC stabilizer. 

DMSA is present in the "mTc-succimer (MediPhysics, Inc.) kit as a 90 10 meso d, 1 isomer mixture. The structure and identity of the 99mTc-species produced in this formulation has not been definitively resolved. The complex(es) formed is (are) believed to contain 99mTc in an oxidation state(s) below five and has been referred to as 99mTc(III) DMSA [66,67], Because of the possibility of multiple complexes, it has been impossible to elucidate the mechanism of localization however, it is reasonable to assume that after GFR, some of the agent is reabsorbed by tubular cells and retained by ligand exchange reactions, in which "mTc becomes bound to SH-containing cytoplasmic proteins [67,68]. 

Catalysis by transition metal complexes and metaUoenzymes involves a sequence of ligand exchange reactions. Such a reaction can he viewed as an interchange of an inner sphere and outer sphere ligand. It is argued therefore that the structure of the second coordination sphere is of direct relevance to catalysis. A method of studying second coordination sphere structure based on dipolar NMR shifts in paramagnetic complexes is discussed. Even in weakly bound complexes, there is a definite preferred structure for the complex which may or may not be favorable for a subsequent substitution reaction. 

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