Oligomer coordination

Their Gdm complexes were found to show significantly increased relaxivity upon interaction with Zn11, Ca11, and Mg11 ions. The relaxivity increase was related to an increase of the rotational correlation time, and the mechanism was ascribed to the formation of coordination oligomers or polymers that are typical for bisphosphonate complexes. 

Several related materials, such as metal coordination oligomers and polymers (Ye et al., 2005), interpenetrating two-dimensional cationic coordination frameworks (Wang et al., 2008), organic metals, among others, are currently under intensive research, and their electrochemistry will probably be attracting attention in the next few years. 

Ye, S.H., Wang, X.-S.. Zhao, H., and Xiong, R.-G. 2005. High stable olefin-Cu(I) coordination oligomers and polymers. Chemical Society Reviews 34, 208-225. 

Fleischer, E.B. Shachter. A.M. Coordination oligomers and a coordination polymer of zinc tetraarilporphyrins. Inorg. Chem. 1991,50, 3763. 

Another type of bridged systems contains the central metal atom in the oxidation state + 3. Appropriate bridging ligands are negatively charged molecules as e.g. cyanide, thiocyanate or azide. The displacement of the axial anion X" by bidentate CN , SCN or NJ (L ) in a coordinatively unsaturated compound PcMX (X = Cl, OAc, CCI3COO) provides a direct path to coordination oligomers [PcML] . This route has been utilized for the synthesis of cyano complexes [PcM(CN)] (M = Fe [116], Mn [117]), thiocyanato complexes [PcM(SCN)] (M = Fe [66], Mn [118]), Co [119], and azido complexes [PcM(N3)] (M = Cr [118], Mn [118]). 

With few exceptions no heterosiloxanes of definite composition could be obtained from the group II elements Mg, Ca, Sr, and Ba. Trimethylsiloxy derivatives of all alkali metals, however, are now known and an examination of their physical and spectroscopic properties has shown, that they are coordination oligomers with multiple-coordinating oxygen and alkali atoms, the degree of association depending on the nature of the alkali metal and the solvent. 

Zinc tetrakis(aryloxy)phthalocyanines such as 42 were shown to self-assemble into coordinating oligomers as demonstrated by UV-vis spectroscopy and mass spectrometry (MALDI-TOF) (Figure 29)P The compound was deposited onto carbon-coated grids and observed by TEM, which showed the formation of 50 nm diameter nanowires. As may be anticipated, similarly substituted free base and Ni(ll) phthalocyanines do not form aggregates. 

Figure 9. Prq>aration of coordination oligomers and polymers with fnX2 6 "-terpyridine) ligands...

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