Bridging ligands substitution

Oxo-Centered Triruthenium-Acetate Cluster Complexes Derived from Axial or Bridging Ligand Substitution... 

Triruthenium Complexes from Bridging Ligand Substitution... 

Unfortunately, despite its poor luminescent properties, tpy is a desirable ligand from a structural point of view in the design of supramolecular photochemical devices. Metal bis(tpy) complexes are achiral, which means that they do not give rise to undesirable mixtures of diastereoisomers when more than one metal centre is present, and as a bridging ligand, substituted tpy compounds are easier to make into rigid linear connectors than bpy or phen derivatives. Furthermore, substituted tpy compounds do not exhibit facimer isomerism as do their bidentate counterparts (Figure 11.9). 

Li JR, Zhou HC (2010) Bridging-ligand-substitution strategy for the preparation of metal-organic polyhedra. Nat Chem 2 893-898... 

With a view to determining the equilibrium constant for the isomerisation, the rates of reduction of an equilibrium mixture of cis- and rra/i5-Co(NH3)4(OH2)N3 with Fe have been measured by Haim S . At Fe concentrations above 1.5 X 10 M the reaction with Fe is too rapid for equilibrium to be established between cis and trans isomers, and two rates are observed. For Fe concentrations below 1 X lO M, however, equilibrium between cis and trans forms is maintained and only one rate is observed. Detailed analysis of the rate data yields the individual rate coefficients for the reduction of the trans and cis isomers by Fe (24 l.mole sec and 0.355 l.mole .sec ) as well as the rate coefficient and equilibrium constant for the cw to trans isomerisation (1.42 x 10 sec and 0.22, respectively). All these results apply at perchlorate concentrations of 0.50 M and at 25 °C. Rate coefficients for the reduction of various azidoammine-cobalt(lll) complexes are collected in Table 12. Haim discusses the implications of these results on the basis that all these systems make use of azide bridges. The effect of substitution in Co(III) by a non-bridging ligand is remarkable in terms of reactivity towards Fe . The order of reactivity, trans-Co(NH3)4(OH2)N3 + > rra/is-Co(NH3)4(N3)2" > Co(NH3)sN3 +, is at va-... 

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