Ligands connection modes

Fig. 10. Schematic diagrams showing the various connecting modes of a ligand A to the metal atoms.

The MP2 calculated harmonic vibrational frequencies in Table 39 show all the trends discussed above for protonated fiuoroethyne in the C—H, C—C and C—F stretch frequencies. The lowest energy mode (81 cm for Ag", for example) connects between a more bridging to a more asymmetric structure. The low value for this swing motion in the Ag complex shows how relatively easy such a conversion is for this complex. The next line of vibrational frequencies lists essentially the metal-ligand stretch mode. Here, the Au " complex has the largest energy. 

Many compounds containing the dicarboxylate [OOC(CH2)nCOO] dianion have been prepared and characterized. In fact, the conformational flexibility of the aliphatic dicarboxylate-type ligands is reflected in the diversity of their connecting modes that lead to novel frameworks. In general, aliphatic... 

Among the triatomic ligands (incl. neutral molecules such as HjO, SO2, and CO2) the anions N02, N3 , NCO", NCS, NCSe , and NCTe are well-known as ambidentate ligands. These anions have two or three donor atoms and can coordinate with a metal atom at one or the other position. Furthermore, they can serve not only as unidentate ligands but also as bridging ligands, connecting two or more metal atoms in various ways. This chapter focusses on the thiocyanate anion the various coordination modes will be shown. 

Pyrazines and substituted pyrazines have long been known to act as exo-bidentate ligands to linearly bridge metal ions, and then have also been employed for the self-assembly of polymeric materials. With pyrazine (prz) varying the reaction conditions and stoichiometry, ID, 2D, and 3D structures containing silver(I) atoms with several coordination modes have been prepared.606-609 A 3D racemate is present in [Ag2(2,3-Me2prz)3](SbF6)2.610 A sawhorse connection has been achieved in the compound [Ag(N02)(pyz)] .611 With 2,2 -bipyrazine an infinite loop has been obtained.612... 

For instance, some time ago Newkome et al. reported the synthesis of ruthenium based dendrimers [170]. A dendrimer (80) with twelve peripheral terpyridine ligands was built around a central quaternary carbon-based core. In the final step complexation between the terminal ligand of the dendrimer and a terpyridinyl ruthenium chloride building block afforded the dodecaruthenium cascade molecule 80 (Fig. 35). Thus, preconstructed cores and dendritic fragments were linked by Ru2+ as the connecting unit and this mode of connectivity could be denoted by [—(Ru)—]. 

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