Helicates tetranuclear

Bridged binuclear, trinuclear and tetranuclear chelated octahedral structures were examined by Schaffer,17 who used the skew line helical definition for the chirality symbols A and A. The configurational isomers for a tetrakisbidentate, edge-fused-bis-octahedral structure are AA, AA, AA, and AA. 

Argent, S. P., Adams, H., Riis-Johannessen, T., etal, Coordination chemistry of tetradentate N-donor ligands containing two pyrazolyl-pyridine units separated by a 1,8-naphthyl spacer Dodecanuclear and tetranuclear coordination cages and cyclic helicates. Inorg. Chem. 2006, 45, 3905-3919. 

Contrary to this, mechanical coupling is observed if the ligand exhibits structural rigidity. This is illustrated in the coordinative series of mononuclear fr/ s-calecholate 2, helical dinuclear fr/ s-catecholale 4 and the tetranuclear tris-catecholate assembly 6 (Fig. 8). 

The self-assembly of a new category of tetranuclear complexes of both copper(I) and silver(I) has been reported. Interaction of these metal ions with the (bis)bipyri-dine-based macrocycle 34 (Figure 6.17), incorporating phenanthroline pendant arms, results in the assembly of 4 2 (metal ligand) complexes incorporating four helical domains. An X-ray diffraction study of the species of type showed... 

FIGURE 51 Formation of (A) trinuclear and (B) tetranuclear triple-stranded helicates with neutral heterotopic C2v-symmetrical ligands. The structures of the complexes correspond to the crystal structures of [Euj(L28)3] and [Eu4(L29)3] (redrawn after Floquet et al., 2003 Zeckert et al., 2005). 

TABLE 9 Cumulative log( ) stability constants reported for the formation of heterotopic tri- and tetranuclear helicates = 28, 29) in acetonitrile... 

FIGURE 68 Self-assembly of the tetranuclear homo- and heterobimetallic triple-stranded helicates [LaxLu4 (L29)3] showing the possible micro- and macrospecies (Dalla Favera et al., 2007). 

The parallel global fit of binuclear (Lll, L13), trinuclear (L28), and tetranuclear (L29) symmetrical helicates demonstrates that /n1o3 ... 

The considerable stability of trinuclear [1 3(L28)3] and tetranuclear [1 4(L29)3] helicates, which indeed correspond to more than 90% of the ligand speciation at millimolar concentration, can be assigned to the nontrivial parent minute repulsive intramolecular intermetallic interaction AEj 2 10 kj mol operating between two held at a distance... 

The second example is a tetranuclear double-stranded helicate [Cu2Gd2(L50)2(NO3)6(H2O)2] (Figures 130B and 132B) featuring quite... 

More recently Ward and coworkers reported the self-assembly of a tetranuclear circular helicate [BF4CCu4(19)4][BF4]3 (5.22) in 1 1 metal to ligand ratio, from Cu(I)... 

Formation of a tetranuclear circular helicate 5.22 (reprinted with permission from reference, copyright 2006, American Chemical Society). 

An unusual double-stranded trinuclear structure incorporates one two-coordinate bent Ag and two four-coordinate tetrahedral Ag ions. A double-stranded tetranuclear helicate, [Au4L2]", employs two-coordinate Au. The inner phosphorus atoms of this tetraphosphadecane ligand are chiral, but only three of the four possible stereoisomers were isolated. In each of these structures the two phosphorus atoms binding the same Au ion have the same chirality. Aurophilic interactions are ascribed to the outer Au-Au pairs in each structure. 

A large-anion (S04 ) template drives the formation of a hexagonal assembly while the smaller cavity of the pentagonal assembly is favored with a small anion (Cl ). With the insertion of an ether linkage to the tris-bipyridyl ligands, analogous tetranuclear circular helicate squares were... 

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