Metal string molecules

Skeletal structure of some mixed Au/Ag clusters (filled circle, Au open circle, Ag) (a) [Au13Ag12] in [(Ph3P)ioAui3Agi2Br8]SbF6, 

The common formula of a series of polypyridylamines is shown below  

Four fully deprotonated polypyridylamines, or ol igo(cy-pyridyl )amido ligands, can coordinate simultaneously to metal atoms from the upper, lower, front, and back directions to form a metal string molecule  

As an oligo(a-pyridyl)amido ligand has an odd number of donor sites, the corresponding metal string molecule has the same number of metal atoms. 

From the reactions of Ni(II) salts with polypyridylamines, a series of metal string molecules, in which the number of nickel atom varies from 3 (i.e., n = 

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Metal string molecules constructed with oligo(a-pyridyl)amido ligand... 

The Ni-Ni and Ni-N distances in a family of related metal string molecules, in which the numbers of Ni atoms are 3, 5, 7, and 9, are shown in Fig. 19.6.6. The Ni-Ni distances increase from the center toward each terminal, and the Ni-N distances are nearly equal except for the outermost ones. These effects... 

The metal string molecule [CrsCtpda Ckl- 2Et20-4CHCl3 contains alternately long and short metal-metal distances, as shown in Fig. 19.6.7. The short Cr-Cr distances are 187.2 and 196.3 pm, which correspond to the quadruple bond Cr=Cr. The long Cr- Cr distances are 259.8 and 260.9 pm, which are indicative of nonbonding interaction. 

The stmctures of two gold metal string molecules are shown in Fig. 19.6.9. The formula of molecule (a) in this figure is ... 

Structures of two mixed-valence metal string molecules (large filled circle, Au large open circle, R group small filled circle, C small open circle, P bond... 

In the field of molecular knots templated by transition metal ions, another remarkable achievement deserves to be mentioned. Hunter and co-workers recently prepared a trefoil knot in a very satisfactory fashion by first wrapping a string-like molecule around a single transition metal ion with an octahedral coordination sphere (Zn2+) so as to obtain an open knotted structure and, subsequently, they could link the two ends of the string to form a real trefoil knot [38]. This nice piece of work again confirms the power of transition metals when it comes to preparing topologically novel species. 

Stoddart and co-workers have developed molecular switch tunnel junctions [172] based on a [2]rotaxane, sandwiched between silicon and metallic electrodes. The rotaxane bears a cyclophane that shuttles along the molecular string toward the electrode and back again driven by an electrochemical translation. They used electrochemical measurements at various temperatures [173] to quantify the switching process of molecules not only in solution, but also in self-assembled monolayers and in a polymer electrolyte gel. Independent of the environment (solution, self-assembled monolayer or solid-state polymer gel), but also of the molecular structure - rotaxane or catenane - a single and generic switching mechanism is observed for all bistable molecules [173]. 

Fig. 2. Example of an HBDC molecular rotor chemically bound to a polyene chain holding a metal cluster. As in Fig. 1, X-X is the rotation axis. This molecule must be prepared in a quasi-classical state to ensure lifting of the cluster load using the polymer chain as a string...

The combination of s-orbitals could also be demonstrated for a linear string of hydrogen atoms. Otherwise, hydrogen does not form a stable metallic solid, neither a one- nor three-dimensional one. The chain separates into individual hydrogen molecules. A similar... 

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