Meridional isomers

The presence of substituents on the bidentate ligands often degenerate their local C2-symmetry and, as a consequence, further isomerism occurs. This results in trisbidentate derivatives of type P(ab)3 in the presence of facial or meridional isomers, as depicted in Fig. 17 [102]. Usually, the meridional isomer is preferred over the facial and a statistical 3 1 ratio is observed. Compounds 6,9,12 and 30... 

In this isomer, three of the same ligands lie on an equatorial circle about the complex. Such a circle is called a meridian, and this isomer is the meridional isomer, abbreviated mer. 

Preparation of [IrH3(PPh3)3] according to literature procedures (25) gives a mixture of facial and meridional isomers that are separated by recrystallization from benzene-methanol. Irradiation of a degassed benzene solution of the synthetic mixture yields a rapid decrease in intensity of the 1740 cm-1 yIr H of the meridional isomer, a slow decrease of the 2080 cm-1 vIr.H of the facial isomer,... 

Sievers and his coworkers have used the volatility of the metal diketonates in the separation and analysis of heavy metals and have done interesting stereochemical work on a few of them. They have achieved at least partial resolution of the optical isomers of tris(hexafluoroacetyl-acetonato)chromium(III) by passing the vapor through a column of quartz powder at 55 °C, and have separated the facial and meridional isomers of tris(trifluoroacetylacetonato)chromium(III) by gas chromatography at 115 °C.40... 

Ans. Two isomers, one with each Cl trans to NH3 (facial isomer), one with 1 Cl trans to NH3 (meridional isomer)... 

This is a populous class of complex most known tertiary phosphines seem to have been utilized in preparing at least one complex of this type. Meridional isomers are normally the rule, but small tertiary phosphines are also capable of forming facial isomers. 

The facial isomers are obtained only from small tertiary phosphines, usually in poor yield. They are both less soluble and less stable than the meridional isomers. 

FIGURE 9-8 Facial and Meridional Isomers of [CoCNHjlsClj] and [Co(dien)2] ... 

The prefix fac designates facial stereoisomer—in this case an octahedron with three CO groups at the comers of the same triangular face. Meridional isomers (abbreviated mer) correspond to stereoisomers in which three identical groups (e.g., COs) lie in the same plane. 

J mol K in favor of the meridional isomer. The detailed investigation of equilibrium (4) in acetonitrile for L19 , L19, and L19 shows that both experimental enthalpic, entropic,... 

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