Skew-line convention

FIGURE 5.6 Definition of the skew-line convention used to define the absolute configuration of tris- or bis(chelate) complexes and conformation of diamine chelates. 

The chiral identity of a molecule is included in the nomenclature of inorganic compounds, and today s comprehensive system is based upon suggestions made in 1990 in IUPAC s Recommendations on Nomenclature of Inorganic Chemistry [84], and ACS s Inorganic Chemical Nomenclature [90]. The basis for the usage of stereochemical descriptors was laid by Brown [91,92], from which three types of chiral descriptor conventions were developed (i) Steering-wheel-convention [93], (ii) Skew-lines convention [94] and (iii) Oriented-skew-lines convention [95]. 

The oriented skew-lines convention describes orthogonal skew lines that are not defined with the classical system. By analogy, the vector descriptors are chosen to be A/yl, respectively... 

Skew-line convention for octahedral complexes. The second is the skew line convention and applies to octahedral complexes. Tris(didentate) complexes constitute a general family of structures for which a useful unambiguous convention has been developed based on the orientation of skew lines which define a helix. Examples I and 2 represent the della and lambda forms of a complex, such as [CofNHjCHjCHjNHj)]. ... 

The R/S convention for tetrahedral centres The R/S convention for trigonal pyramidal centres The C/A convention for other polyhedral centres The C/A convention for trigonal bipyramidal centres The C/A convention for square pyramidal centres The C/A convention for see-saw centres The C/A convention for octahedral centres The C/A convention for trigonal prismatic centres The C/A convention for other bipyramidal centres The skew-lines convention... 

Application of the skew-lines convention to tris(bidentate) octahedral complexes... 

The second is based on the geometry of the molecule and makes use of the skew-lines convention it is usually applied only to octahedral complexes. The two enantiomers are identified by the symbols A and A in this system. The C/A nomenclature is not required for those chelate complexes where the skew-lines convention is completely unambiguous (see Sections IR-9.3.4.11 to 9.3.4.14). 

The principle of the skew-line convention arises from the geometry of a helix, which is by nature chiral, and is generated by simultaneous movements of translation and rotation. The sense of a helix is unequivocally determined by the relative sense of the translation and rotation vectors. We take the translation movement as a nonoriented axis... 

The skew-line convention for the determination of the absolute (A) or (A) configuration of a propeller. 

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