Meridional sites

Figure 7-26. The structure of complexes may be dictated by steric constraints within the ligands. 2,2 6, 2"-Terpyridine (7.42) can only occupy the three meridional sites in an octahedral complex, whereas the /ra(pyrazolyl)borate anion (7.43) must occupy three facial sites.

The embedding of a Ru(terpy)(phen)2+ moiety in a ring is certainly not trivial since the terpy fragment occupies three meridional sites of the metal octahedron and the phen chelate is almost opposite to the terpy in the metal coordination sphere. We thought that a convenient way to connect the phen and the terpy fragments was to interlink a lateral position of the phen (3 position) and the para position (4 ) of the central pyridinic nitrogen atom of... 

Although several examples of complexes containing the [Mn202]"" core type have been studied, only one has been found to catalyze O2 evolution in water. The complex [(terpy)(H20)Mn (/u,-0)2Mn (0H2)(terpy)] + contains the tridentate terpyridine ligand that coordinates to three meridional sites on Mn and thus positions the two terminal aquo ligands trans to the /tr-oxo bridges. The oxidation of this complex by or OCl in water was shown to produce... 

Bis(pyrazolylethyl)ether derivatives (106) have been coordinated to zinc providing an N20 donor set. The structural data shows that the ligand coordinates in a meridional rather than facial geometry limiting the application for the modeling of N20 zinc enzyme sites, (derivatives R = i-Pr or Me).161... 

In the open ocean, the major advective water motion is associated with the surfece-water geostrophic currents and meridional overturning circulation. These flow paths are shown in Figures 4.4b and 4.6. Advection is much fester than molecular diffusion and turbulence. This enables water masses to retain their original temperatures and salinities as they are advected away from their sites of formation. Slow turbulent mixing with adjacent water masses eventually alters this temperatme and salinity signal beyond... 

These data suggest that biogeochemical domains undergo a systems switch on time scales required for return of exported nutrients to the sea surfece. In oligotrophic waters, this return requires decades to centuries as the strong density stratification at these sites forces the return to proceed through the meridional overturning circulation. 

The characterization of compounds 48-54 in the solid state or in solution by multinuclear NMR spectroscopy confirmed the coordination mode of the phosphines. In complexes 51-54 the tridentate heterofunctionalized phosphines display a meridional coordination mode, with the remaining coordination sites being occupied by the oxo group and by other bidentate or mono-dentate coligands [56-58]. 

The terms mer (meridional) and fac (facial) are used commonly to distinguish between stereoisomers of complexes of the form [Ma3b3]. In the mer isomer (Example 2) the two groups of three similar donors each lie on a meridian of the coordination octahedron, in planes that also contain the central atom. In the fac isomer (Example 3) the two groups of three similar donors each occupy coordination sites on the comers of a face of the coordination octahedron. 

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