FIGURE 1 Optimized structures of the mesogenic Eu(III)
complexes in the ground state:
(а) Eu(CPDK35)3Bpy17-17,
(b) Eu(CPDK3-5)3Phen,
(c) Eu(CPDK5-Th)3Bpy17-17,
(d) Eu(CPDK5Th)3Phen,
(e) Eu(DK1214)3Bpy1717,
(f) Eu(CPDK3-Ph)3Phen
From Figure 1 one can see that all of the studied complexes have the
coordination number 8. Their coordination polyhedra includes the Eu(III)
ion and 8 atoms from its first coordination sphere - six O centers of
the β-diketones and two N centers of the Lewis bases. Initial geometries
of the polyhedra were taken from the X-ray diffraction data for similar
Eu(III) complexes without long terminal
substituents[49-51] from the Cambridge Structural
Database.[52]
For the start of the optimization process the geometries of model
Eu(III) complexes[49-51] from the Cambridge
Structural Database were modified by replacement of initial ligands by
various substituted βdiketones and Lewis bases (Figure 1).
The presence of a heavy Eu(III) ion and a large number of atoms results
in a high computational costs especially when optimizing the geometry of
excited states. The geometry optimization of eight isomers for each of
the studied Eu(III) complexes with different arrangement of β-diketones
relative to the plane formed by the Eu(III) ion and the Lewis
base[8,9,11,27] was made. According to the
calculations, the isomers with the crosswise arrangement of βdiketones
have the lowest energy. In this energetically most advantageous
arrangement of βdiketones the long alkyl substitutes do not sterically
hinder each other. Therefore, only one stereoisomer for each of the
coordination polyhedra of the studied Eu(III) complexes was considered.
Exemplarily, eight optimized geometries of
Eu(CPDk35)3Phen isomers are presented
in the Supporting Information (Table S1).
The resulting optimized structures and geometry parameters of the
studied mesogenic Eu(III) complexes are shown in Figure 2. Steric
hindrances caused by long alkyl substituents in the ligands led to
insignificant distortions of the Eu(III) coordination polyhedra during
optimization. Structural parameters of the optimized Eu(III) complexes,
the average Eu–O, C–O, and Eu–N bond lengths, as well as some
characteristic angles are presented in Table 1. Coordination polyhedra
of almost all studied Eu(III) complexes, as well as model compounds,
were defined by the SHAPE program as a slightly distorted square
antiprism. Eu(CPDK35)3Phen, in contrast
to Eu(CPDK35)3Bpy1717,
has a triangular dodecahedron, as well as
Eu(DK1214)3Bpy17-17with long substituents in three β-diketones DK1214.
They are all chiral and correspond to the C1 point group
that often occurs in Ln(III) complexes with a coordination number of
8.[53-55] Therefore, it can be assumed that Lewis
base determines the type of coordination polyhedron in the some of the
mesogenic Eu(III) complexes.