Subject sulfur ligands

Most of the first row transition elements, and Cd, exhibit intermediate bonding preferences, sometimes occurring in chelation matrices containing both oxygen and nitrogen or sulfur ligands. Because Cd has been the subject of considerable toxicological study in marine systems, Cd++ will be used as an example of a borderline metal ion. 

Taken together, the above data suggest a stepwise mechanism of Cu(I) transfer from Atxl to Ccc2a as illustrated in Fig. 3 (Brown et al., 1991 Pufahl et al., 1997 Huffman and O Halloran, 2000). When the Cu(I) center can adopt a two-coordinate ligand geometry as in Atxl, the Cu(I) ion is subject to attack by the sulfur ligands of the MXCXXC motif... 

Although the subject of stability of complexes will be discussed in greater detail in Chapter 19 it is appropriate to note here some of the general characteristics of the metal-ligand bond. One of the most relevant principles in this consideration is the hard-soft interaction principle. Metal-ligand bonds are acid-base interactions in the Lewis sense, so the principles discussed in Sections 9.6 and 9.8 apply to these interactions. Soft electron donors in which the donor atom is sulfur or phosphorus form more stable complexes with soft metal ions such as Pt2+ or Ag+, or with metal atoms. Hard electron donors such as H20, NH3( or F generally form stable complexes with hard metal ions like Cr3+ or Co3+. 

Fig, 1 provides a listing of the various sulfur donor ligands whose complexes have been the subject of considerable research. The list of ligands in Fig. 1 is not exhaustive since only potentially bidentate ligands are given. The electronic properties of complexes with bidentate sulfur donor ligands are usually similar although their physical properties, e.g., solubility, can vary widely. This review deals primarily with dithio- and diselenophosphate complexes however, related complexes are discussed wherever they are pertinent to the present discussion. 

A wide range of multidentate amine ligands coordinate to platinum. The conformational analysis of chelate ring systems by NMR has been reviewed by Hawkins, and platinum complexes are included in this work.959 Amine ligands with sulfur groups can also act as chelates, and this subject has also been reviewed.960... 

Square-planar bis(dithiolene) complexes have also been the subject of theoretical investigations (43-46). For example, density functional theory (DFT) calculations indicated that the highest occupied molecular orbital (HOMO) for Ni(S2C2H2)2 is primarily a ligand-based orbital comprising of four 3pz orbitals of sulfur, perpendicular to the molecular xy plane, and four 2p-orbitals of carbon with opposite phases. The lowest unoccupied molecular orbital (LUMO) is a mix of ligand-metal orbitals, but still mostly of the ligand... 

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