Chelating ligands bismuth

The only example of a ketothiolate adopts a dimeric structure [Bi(PhCH S CH2C 0 Ph)3]2[CH2Cl2] in which one of the three S,0 chelate ligands effects a secondary interaction with a neighboring bismuth [Bi---S 3.494(5) and 3.551(5) A] to impose heptacoordination 62... 

The complex PhBi(S2COMe)2 contains two bidentate xanthogenato chelate ligands which lie equatorially in the coordination octahedron of bismuth, while the phenyl group and the stereochemically active lone-pair of electrons occupy the axial positions. ... 

The oxidation state +3 of bismuth is of primary interest for radiotherapy applications. As such, various polyaminocarboxylate ligands have been investigated as chelates for 212Bi and 213Bi. 

Complexes of bismuth chloride with 2 equiv of the AT,AT-substituted dithioxamide ligands of the general formulas [BiCl3 RNHC(S)C(S) NHR 2] (R = Me, Et, Pr, nBu, CH2Ph) likely involve five-membered chelate interactions (123) as demonstrated by the structurally characterized example [BiCl3 EtNHC(S)C(S)NHEt 2] Me2CO, which involves a seven-coordinate pentagonal bipyramidal environment for bismuth (124), with chlorine atoms in axial positions [Bi-Cl 2.635(10) and 2.717(1) A] and one equatorial [Bi-Cl 2.651(12) A] with four sulfur centers [Bi-S 2.818(13)-3.042(12) A],... 

The strong chelating ability of (multi)amino(multi)carboxylate ligands renders complexes of bismuth substantially more hydrolytically stable than those of bifunctional aminocarboxylate ligands (e.g., glycine). Several compounds have been successfully examined as ligands for bismuth, in that complexes are readily isolable as molecular systems with weak intermolecular interactions. The extent and diversity of these complexes is enhanced by substituent derivatization with, for example, cyclohexyl (e.g., cydtpa) and alkoxyethyl (e.g., oedta) groups. 

Newer agents under investigation include tris(tropolonato) Bi(III) and nitratobis(tropolonato)Bi(in) a host of bis (mercaptoethanol)Bi(III) complexes, which are formed with 0,S-bidentate chelation, with and without deprotonation of the hydroxyl oxygen and usually having an axial fifth ligand and sialic acid derivatives of Bi(III). The interactions of Bi(III) and its compounds with metallothionein, serum albumin and transferrin have been studied by a variety of groups, as have a number of enzymes that may be related to the mechanism(s) of action of bismuth in treating ulcers. 

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