Page 14 - Nomenclature of Inorganic Chemistry (IUPAC Recommendations 2005)

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

Example:
1. Me 2 N
1
C
S 1
S NH 3 3
Mo 1'
S
NH 3
3
C S OH 2
Me 2 N 1'

2
0 0
PBPY-7-12-11 1 33-A
IR-9.3.4.11 The skew-lines convention

Tris(bidentate) complexes constitute a g eneral family for which a u seful, unambiguous
convention has been developed based on the orientation of skew lines which define a h elix.
Examples 1 a nd 2 r epresent the delta (D) a nd lambda (L) f orms of a c omplex s uch as
3þ
[Co(NH 2 CH 2 CH 2 NH 2 ) 3 ] . T he rules define the chiralities of two additional families of
structures. These are the cis-bis(bidentate) octahedral structures a nd the conformations
of certain c helate rings. It is possible t o u se the system described below for complexes of
higher polydentate ligands, but additional rules are required. 15

Examples:

1. 2.

delta (D) lambda (L)

Two skew-lines which are not orthogonal p ossess the property o f h aving one, and only
one, normal in common. They define a h elical s ystem, as illustrated in Figures IR-9.1 and
IR-9.2 (below). In Figure IR-9.1, one of the skew-lines, AA, determines the axis of a h elix
upon a c ylinder w hose radius is equal to the length of the common normal, NN, to the two
skew-lines, AA and BB. The o ther of the skew-lines, BB, is a t angent to the helix at N a nd
determines the pitch of the helix. In Figure I R-9.2, t he two skew-lines AA and BB are seen
in projection onto a p lane o rthogonal to their common normal.
Parts (a) of Figures IR-9.1 and IR-9.2 illustrate a r ight-handed helix to be associated with
the Greek letter delta (D referring to configuration, d to conformation). P arts (b) of Figures
IR-9.1 and IR-9.2 illustrate a l eft-handed h elix to be associated with the Greek letter lambda
(L for configuration, l for conformation). In view of the symmetry of the representation
constituted by two skew-lines, the helix which the first line, say BB, determines around t he
second, AA, has the same chirality as that which AA determines around B B. As one of the
lines is rotated about NN with respect to the other, inversion occurs when t he lines are
parallel or perpendicular (Figure IR-9.1).

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