Page 15 - Nomenclature of Inorganic Chemistry (IUPAC Recommendations 2005)

C O O R D I N A T I O N C O M P O U N D S IR-9.3

A A

B B

N N
N N

B B
A A
(a) ∆ or δ (b) Λ or λ
Figure IR-9.1. Two skew lines AA and BB which are not orthogonal define a h elical system. In the
Figure, AA is taken as the axis of a c ylinder whose radius is determined by the common normal NN of
the two skew-lines. The line BB is a t angent to the above cylinder at its crossing point with NN and
defines a h elix upon this cylinder. Cases (a) and (b) illustrate a r ight- and left-handed helix,
respectively.

B B
A A A A
B B
(a) ∆ or δ (b) Λ or λ
Figure IR-9.2. The figure shows pairs of non-orthogonal skew-lines in projection upon a p lane
parallel to both lines. The full line BB is above the plane of the paper, the dotted line AA is below this
plane. Case (a) corresponds to (a) of Figure IR-9.1 and defines a r ight-handed helix. Case (b)
corresponds to (b) of Figure IR-9.1 and defines a l eft-handed helix.

IR-9.3.4.12 Application of the skew-lines convention to tris(bidentate) octahedral c omplexes
Any two o f t he three chelate rings may be chosen to designate t he configuration of
tris(bidentate) c oordination compounds. The d onor atoms of each chelate ring define a l ine.
Two such lines for a p air of chelate r ings in the same c omplex d efine a h elix, one line being
the axis of the helix and the other a t angent to the helix at the normal common to the skew-
lines. The tangent describes a r ight-handed ( D) o r a l eft-handed (L) h elix with respect to the
axis and thereby defines the chirality of that configuration.

IR-9.3.4.13 Application of the skew-lines convention to bis(bidentate) octahedral complexes

Figure IR-9.3(a) shows a c ommon orientation of an octahedral tris(bidentate) structure
projected onto a p lane orthogonal t o t he three-fold axis of the structure. F igure IR-9.3(b)

192