Photochemistry and Photophysics of Coordination Compounds

Photochemistry and Photophysics of Coordination Compounds: Copper 81
Fig. 10 Kinetic control in the formation of heteroleptic [CuL 1 L 2 ] + complexes (HETPHEN
approach)
Simple and supramolecular Cu(I)-bisphenanthroline complexes exhibit
very interesting and largely tunable photophysical properties that will be illustrated
in the next sections.
2
Cu(I)-Bisphenanthroline Complexes
2.1
Ground State Geometry
Cu(I)-bisphenanthroline complexes generally display distorted tetrahedral
geometries. The distortion from D2d symmetry can be visualized with the aid
of Fig. 11 [54].
θx, θy, andθz define the interligand angles based on the CuN4 core of the
complex. When a molecule possesses a perfect tetrahedral geometry (D2d), θx
= θy = θz = 90 ◦ ,whereasthesquareplanargeometryD2 implies θx = θy = 90 ◦
and θz = 0 ◦ .Practically,θz is the dihedral angle between the ligand planes and
a decrease from 90 ◦ indicates a flattening distortion of the molecule that progressively
lowers its symmetry to D2.Theθx and θy values indicate the degree
of “rocking” and “wagging” distortions [55].
These distortions are due to intra- and intermolecular (in solid state crystals)
π - stacking interactions which also cause considerable displacement
from D2d symmetry. In practice, combinations of various types of distortions
occur in [Cu(NN)2] + complexes and their extent is dictated by the size,
chemical nature, and positions of the phenanthroline substituents. Recently,
the parameter ξCD has been proposed to quantify the degree of distortion as