FIGURE 2 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
Structural parameters of the optimized mesogenic Eu(III) complexes
(Table 1) are similar to those for model Eu(III) complexes with similar
ligands without substituents.[49-51] Average Eu–O
bond lengths in the ground state vary through a small range 2.38 - 2.51
Å, whereas according to experimental data for model compounds they are
~2.35 Å. Ground-state Eu–N bond lengths are in the
range 2.49 - 2.73 Å, which correlates with values of 2.58 - 2.64 Å for
model complexes. The average calculated angles correspond to the
experimental ones within 4 degrees. Therefore, Eu–N bond lengths in
mesogenic complexes are 0.1 Å longer than in model compounds7-9 (Table 1), while NEuN angles are 2-3° larger. The
replacement of CPDK3-5 by CPDK5-Th and
CPDK3-Ph βdiketones leads to a decrease in the Eu–N
bond length of complexes 4 and 5 by 0.20-0.13 Å
compared to complex 2 . The average Eu–O bond length of
complexes 1 and 2 with CPDK3-5, and6 with DK12-14 is 0.1 Å longer in contrast to
complexes 3-5 with other βdiketones. This can be attributed to
steric hindrances caused by the more branched geometry of
CPDK3-5 and DK12-14 with long alkyl
substituents, which prevents closer coordination of ligands.
TABLE 1 Average structural parameters (bond lengths in Å,
angles in degrees) of Eu(III) complexes in the ground
(S0) and triplet excited (Т1) states