Metal chelates, structure

The synthesis on a metal matrix is mainly applied to prepare chelate complexes. The majority of template synthesis reactions were known long ago, allowing their use for the isolation of hundreds of metal-chelate structures. However, the interest in... 

In reflection of the fact that the purine N-7 is the most favorable metal-binding site in nucleic acids, a number of different metal chelate structures involving this atom can be formed with purine nucleoside 5 -phosphates. This... 

The metal ion not only stabilizes the chelate rings and prevents the formation of undesirable products but also acts as a template. Several reactions have been described in which Schiff base chelates are formed via a metal template or a metal chelate template mechanism. In the presence of nickel(II), /3-mercaptoethylamine and a-diketones give a Schiff base chelate, whereas in the absence of metal ions, thiazolidines are obtained (198, 199). The planar metal chelate (structure CII) has the co-... 

Whereas vicinal hydroxy, mercapto, and hydroselenoaldimines of azoles strongly prefer the aminomethylene tautomeric form (Section II,E,2), their metal chelates 380 are characterized by.pronounced equalization of bond lengths within the chelate ring, which makes their structures similar to those expected for the aldimine tautomeric type. 

T. G. Takhirov X-Ray Structural Investigation of Stereochemi-cally Nonrigid Tetracoordinated Metal-Chelates of Zn(II), Cd(II), Hg(II) and Ni(II) on the Base of Derivatives of 4-... 

On refluxing a toluene solution of benzoisotellurazole and Fe3(CO)L2, cleavage of the Te—N bond occurs, resulting in formation of the metal chelate complex 11 whose structure was determined by X-ray (97MI1). 

Structural Formula Orgotein is a complex protein with a molecular weight of about 33,000. It Is a divalent metal (Mg, Cu, Zn) chelated structure. 

The literature of polyimines is extensive [164-173]. A number of researchers have tried to synthesize high molecular weight polymers but failed due to poor solubility in organic solvents. Polyimines are of great interest because of their high thermal stability [174-176], ability to form metal chelates [174-177], and their semiconducting properties [178-181]. Due to insolubility and infusibility, which impeded characterization of the molecular structure, the application of these polymers is very limited and of little commercial importance. 

Finally, there is active interest in developing catalyst systems, both ballistic and polymerization, that would promote combustion stability at high pressures (especially in metal-free systems for smokeless applications) and allow processing lattitude for relatively large motors. The ferric-based systems currently being used fall short of these performance measures. Compounds that form complex structures with the metal chelate to reduce its activity to acceptable levels seem to be most promising. Interestingly, the use of an antibiotic has been cited in this context [19],... 

Reaction of the diphosphines Ph2P(CH2) PPh2 (n = 1-3) with MCl2(PhCN)2 affords 1 1 m-complexes (Figure 3.46) [102]. (Note the use of the labile PhCN adducts if the MCl salts are used, Magnus type compounds M(P-P)2+MCl4- are formed.) Similar complexes are formed with other halides for the thiocyanates see section 3.8.6. The structures of the palladium complexes have been determined (Table 3.10) with square coordination only achieved for n = 3 with the formation of a six-membered metal-chelate ring. 

A bis(chelate) structure was found for the closely related germylene [MeC(NPr )2]2Ge, which was also made from GeCl2(dioxane) and 2 equivalents of the lithium amidinate (colorless crystals, 81%). The same synthetic approach was used to make bis(amidinato) metal dichlorides of silicon and germanium in high yields (83-95%). Rapid oxidative addition of chalcogen atom sources (styrene sulfide and elemental Se) to the germylene derivatives resulted in a series... 

Fig.1. Structures of porphyrin 1, chlorophyll 2, and phthalocyanine 3. In the presence of metal salts M"+X (M=metal, X=counter anion, n=oxidation state or number of counter anions), porphyrins produce chelate complexes. Some metal chelates of the porphyrins, such as ZnPor, form further coordination bonds with other ligands such as pyridines...

In contrast to the early theoretical work of Rank and coworkers , C-NMR investigations had revealed that the metallated carbon atom in the a-sulphinyl carbanion is nearly planar . A four-centre chelate structure 315 has been proposed for a-lithiosulphoxides, and it is believed to be responsible for the planar configuration of the anionic carbon atom and for the greater stability of o(-sulphinyl carbanions in comparison with a-sulphenyl carbanions This chelation favours one of the two diastereoisomeric carbanions and for this reason a-sulphinyl carbanions react with electrophiles in a highly stereoselective manner (see below). 

Pintacuda, G., Moshref, A., Leonchiks, A., Sharipo, A., Otting, G. Site-specific labeling with a metal chelator for protein-structure refinement. /. Biomol. NMR 2004, 29, 351-361. 

Dijkwel, P.A. and Wenink, P.W. (1986). Structural integrity of the nuclear matrix differential effects of thiol agents and metal chelators. J. Cell Sci. 84, 53-67. 

K. Nomoto, Y. Mino, T. Ishida, H. Yoshioka, N. Ota. M. Inoue, S. Tagaki, and T. Takemoto, X-ray crystal structure of the copper(ll)complex of mugineic acid, a naturally occuring metal chelator of graminaceous plants. J. Client. Soc. Client. Contmun. 338 (1981). 

The given structure shows two molecules of TTA to have reacted with a cobalt ion to form the cobalt-TTA complex, in which the cobalt atom forms a valence bond solid lines) with one, and a coordinate bond (broken lines) with the other, oxygen atom of each TTA molecule. Thus, in the cobalt-TTA complex there is a six-membered ring formed by each TTA molecule with the cobalt atom. Metal chelate complexes of this type have good stability, they are nonpolar and soluble in the organic phase. The usefulness of the chelating extractants in solvent extraction is therefore obvious. 

---