Photochemistry and Photophysics of Coordination Compounds

82 N. Armaroli et al.
Fig. 11 Relative orientation of the two ligand planes (xz and yz) and of the reference θx
(rocking), θy (wagging), and θz (flattening) angles. θz is on the plane of the sheet; the
grey circles represent the N phenanthroline atoms; the Cu ion is centered on the origin
of the reference axes; the vector ξ lies on the yz plane, the vector η is perpendicular to it.
In this schematic representation the phenanthroline on the left-hand side is assumed to
be placed on the plane of the sheet (yz) and that on the right-hand side on the xz plane
perpendicular to it
a combination of θx, θy and θz (Eq. 1) [56]:
� �� �� �
90◦ + θx 90◦ + θy 90◦ + θz
ξCD =
1803 where CD stands for “combined distortion”.
Detailed X-ray crystallographic studies have shown that the specific geometry
in the solid state is dictated by packing forces and considerable variation
is found for the same complex as a function of the counteranion. In the case
of [Cu(1)2] (Fig. 12) θz varies from 88◦ in the tetrafluoroborate and tosylate
salts to 73◦ in the picrate [57].
As an example, the θz dihedral angles between the two phenanthroline
planes in [Cu(1)2]PF6, [Cu(2)2]PF6 and [Cu(3)2]PF6 are 79.4◦ [57], 87.5◦ [56,
58] and 79.8◦ [59], respectively, according to X-ray crystal structures; ligands
1, 2 and 3 are depicted in Fig. 12.
(1)