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