1,2,3-Tris chelated structures

The diethylammonium salt of the tris(tetraphenyldisiloxanediolato)zirconate(IV) anion (33) has been obtained in very low yield from the reaction of [Zr(NEt2)4] with diphenylsilanediol in THF. The ligand results, under the basic reaction conditions, from condensation of two Ph2Si(OH)2 molecules. Anion (33) has an octahedral tris-chelate structure with a twist angle (46.9°) that indicates some distortion towards trigonal prismatic geometry.466... 

Stereoselectivity and In addition to the dissymmetry generated by the tris(chelate) structure of octahedral... 

In addition to the dissymmetry generated by the tris(chelate) structure of octahedral complexes, it is possible to have dissymmetry in the ligand as well. For example, the gauche conformation of ethylenediamine is dissymetric (Fig. 12.27) and could be resolved were it nol for the almost complete absence of an energy barrier preventing... 

Figures 2,3,5, and 6 show anionic compounds 5 to 22 and 25 to 30, which have been described in the literature since 1997. In these adducts, as in examples 1 to 4, the P(VI) derivatives have carbon or oxygen atoms in the immediate proximity of the central (pseudo-)octahedral atom. This is probably due to the accessibility of the ligand precursors, the ease of their manipulation and, more importantly, to the sheer strength of the resulting P-C and P-0 bonds. They all present tris(bidendate) structures in which the three chelating rings can be identical (Fig. 2 and most of Fig. 6) or of two different types (Fig. 3). The ligands can be monooxo (Fig. 6) or dioxo (Fig. 2 and Fig. 3). These differences in composition have, of course, consequences for the making of the derivatives.

The [Co(phen)3]3+ complex is photoactive and a powerful oxidant in its excited state. The ion has no H-bonding groups and hence is considerably more hydrophobic1279 than hexaamine relatives. These properties have proven particularly useful. Aryl and alkyl substituted [Co(phen)3]3+ complexes have received a great deal of attention due to their ability to intercalate within the helical structure of DNA through a combination of electrostatic and hydrophobic forces. The chirality of the tris-chelate complex is crucial in determining the degree of association between the complex and... 

An spontaneous assembly of 15 components is reported in the synthesis of [Ag9L6](OTf)9 where L is the hexadentate, tris-chelating 6,6-bis[2-(6-methylpyridine)]-3j3 -bipyrazine. The structure consists of a 3x3 grid of Ag-atoms (average Ag" Ag = 3.72(3)A), sandwiched between two almost perpendicular sets of three parallel L ligands (Figure 10).641... 

Chelating aldehydes such as 2-pyridine carbaldehyde and 2-dimethylamino benzaldehyde improve the stability of the aldehyde complexes via N,0 chelation. NMR studies show that the complexes are present in solution without an excess of aldehyde and can be formed in the presence of donor ligands. The X-ray structures showed longer and weaker Zn—O bonds when more than one chelating ligand was present. IR demonstrates the variation in C=0 bond strengths and how the environment of the zinc ion will influence potential catalytic activity via reaction rates or pathways. Tetrahedral chelate complexes, and octahedral bis- and tris-chelate complexes, were isolated.843... 

Complexes of simple amino adds with chromium(lll) were first prepared by Ley.1148 The isomers possible for tris chelated complexes of this type are illustrated below (248-251). The consequences of such isomerism were first seriously considered by Gillard.1149 Red complexes of the formulae [Cr(gly)3] and [Cr(L-ala)3] were prepared by neutralizing refluxed solutions of hexaaquachromium(Ill) and the amino add in ratios between 1 5 and 1 10. These complexes were shown to be isomorphous with 0-[Co(gly)3] and D- -[Co(L-ala)3] respectively. The crystal structure of red j8-[Cr(gly)3] has also been reported.1150... 

Involvement of two nucleophilic nitrogen atoms is thus typical for the amino heterocycles. The mutual disposition of the pyridine and amine nitrogen atoms allows the formation of chelate structures for the cobalt complexes of purine, 221 and 222. Structures with the N, iV -five-membered metal cycles were proven for the tri- and tetranuclear complexes of silver ) with 8-aminoquinoline (223) (92IC4370), and polymeric copper- and rhodium-acetate clusters (224). Another coordination mode can be found in the complexes of 4-amino-3,5-bis(pyridin-2-yl)-l,2,4-triazole, (225 or... 

Besides the very stable tris chelates, numerous bis chelates with both bipy and phen have been reported.850,851 Most of them have general formulas [NiX2(N—N)2], [Ni(N—N)2-(H20)2]X2 and [NiX(N—N)2(H20)]X (X = halides, pseudohalides, C104, N02 N—N = phen, bipy).850 All of the complexes are six-coordinate with a cis structure. 

Complexes of pyridine-2-carboxylic acid (picolinic acid, picH) and its substituted derivatives commonly exhibit the N—O bidentate nature of this aromatic amino acid. From aqueous solutions chelates are obtained with the coordinated carboxylic group deprotonated, or neutral ligand forms may be isolated from non-aqueous media.26 Bis chelates are common in either case with bivalent metal ions. The tris chelates of trivalent cobalt27 and manganese28 have been structurally characterized recently. The latter is tetragonally distorted in a structure similar to Mnin(oxine)3. 

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