Role of alkyl substituents in the structure and luminescence properties of discrete terbium(III)-lithium(I) Β-Diketonates

Article abstract of DOI:10.1016/j.molstruc.2020.129331

Functionalized perfluoroalkyl lithium β-diketonates LiL react with terbium (III) salts in methanol to give heterobimetallic complexes of general formula [(TbL₃)(LiL)(MeOH)]. The length of both fluoroalkyl and hydrocarbon substituents in ligand was found to affect the crystal packing of metal complexes. Photoluminescence of heterobimetallic β-diketonates in the solid state is reported.

Full text of DOI:10.1016/j.molstruc.2020.129331

Journal of Molecular Structure 1226 (2021) 129331
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstr
Role of alkyl substituents in the structure and luminescence
properties of discrete terbium(III)-lithium(I) B-Diketonates
Yulia S. Kudyakovaa, Pavel A. Slepukhina,b, Marina S. Valovaa, Yanina V. Burgarta,b
Victor I. Saloutina,b, Denis N. Bazhina,b,∗
,
a Postovsky Institute of Organic Synthesis, the Ural Branch of the Russian Academy of Sciences, 22 S. Kovalevskoy Str., 620108 Yekaterinburg, Russia
b Department of Organic and Biomolecular Chemistry, Chemical Technology Institute, Ural Federal University, 19 Mira str., 620002 Yekaterinburg, Russia
a r t i c l e i n f o
a b s t r a c t
Article history:
Functionalized perfluoroalkyl lithium β-diketonates LiL react with terbium (III) salts in methanol to give
heterobimetallic complexes of general formula [(TbL3)(LiL)(MeOH)]. The length of both fluoroalkyl and
hydrocarbon substituents in ligand was found to affect the crystal packing of metal complexes. Photolu-
minescence of heterobimetallic β-diketonates in the solid state is reported.
Received 29 June 2020
Revised 21 September 2020
Accepted 23 September 2020
Available online 25 September 2020
© 2020 Elsevier B.V. All rights reserved.
Keywords:
Terbium
Lithium
Functionalized β-diketonates
Crystal packing
Luminescence
1. Introduction
properties of luminescent materials [12]. The elongation of fluo-
rocarbon chain in the series of Eu (III) β-diketonates was shown
Metal complexes based on trivalent lanthanide (Ln) ions are re-
garded as highly luminescent materials combining the characteris-
tic spectral range, narrow-band emission and long lifetimes [1-10].
However, to optimize the luminescent properties of Ln (III) com-
plexes it is often necessary to fine-tuning the molecular structure
of organic ligands. Therefore, the use of ligands, which can be read-
ily modified, is a platform for identifying more specific character-
istics affecting the properties of molecular complexes of rare earth
metals. In this context, 1,3-diketones are among the most versa-
tile and extensively used structural units in coordination chemistry.
The variation of substituents in 1,3-dicarbonyl fragment as well as
the co-ligands participating in the formation of metal complexes
allows the “structure-property” relationships to be controlled effi-
ciently [11,12].
to be an efficient approach to increase the fluorescence lifetimes
[19]. Moreover, fluorine atoms or polyfluoroalkyl groups often par-
ticipate in intra- and intermolecular interactions thereby providing
the special organization of crystal structure in metal complexes.
Short F…X contacts (where X = H, F, π-system, etc.) can modify
not only the geometry of a molecule, but the crystal packing as
well [20].
Previously we have reported on the synthesis of heterobimetal-
lic complexes with general formulas [LnL3·LiL·(sol)] (Ln
=
Eu
(III), Tb (III), Dy (III), sol = MeOH, H2O) and [LiLnL4·(CH3CN)]
(Ln = Eu (III), Tb(III)) based on the original functionalized lithium
CF3-β-diketonate (LiL) (Fig. 1) [21,22]. These coordination com-
pounds were the first examples of Ln-Li heterobimetallic β-
diketonates for which the crystal structure were identified by
XRD analysis. Interestingly, the structure of [LnL3·LiL·(sol)] differed
from the well-known Ln(III) tris- and tetrakis-β-diketonates. More-
over, a number of [LnL3·LiL·(MeOH)] complexes exhibited bright
(mechano)luminescence [21]. In this work, we have studied the ef-
fect of the substituents in the dicarbonyl moiety on the structure
and luminescent properties of bimetallic Tb(III)-Li β-diketonates.
Increasing the length of the fluoroalkyl group or hydrocarbon chain
provokes a change in both the geometry of molecules and in-
termolecular interactions – two main factors responsible for the
“structure-property” relationships.
Incorporation of polyfluoroalkyl groups in 1,3-dicarbonyl moiety
significantly changes the properties of both the ligands and coor-
dination compounds based on them [13]. Replacing a hydrocarbon
substituent by fluorocarbon one is reported to result in better crys-
tallization of metal complexes from the organic solvents [14-18].
–
As compared to C H bonds, C-F bonds decrease the vibrational re-
laxation processes, which dramatically influence the photophysical
∗
Corresponding author.
E-mail address: dnbazhin@gmail.com (D.N. Bazhin).
https://doi.org/10.1016/j.molstruc.2020.129331
0022-2860/© 2020 Elsevier B.V. All rights reserved.

Y.S. Kudyakova, P.A. Slepukhin, M.S. Valova et al.
Journal of Molecular Structure 1226 (2021) 129331
were recorded with a Perkin-Elmer Spectrum One FTIR instrument
in the range 400–4000 cm−1 at a resolution of 4 cm−1 (32 scan
collected). Elemental analysis was performed using a Perkin Elmer
PE 2400 Series II analyzer.
The UV-Visible transmittance spectrum was performed with
UV-2600 Shimadzu spectrometer from 200 to 800 nm. Photolumi-
nescence properties were analyzed by a Varian Cary Eclipse flu-
orescence spectrophotometer with mutually perpendicular beams.
Phosphorescence was measured in the solid state, quartz glass
with the crystals of complex was turned 50° away from the
detector window to avoid reflections. The spectrophotometer
was equipped with a 15 W xenon pulse lamp, Czerny-Turner
monochromators, photomultiplier tube. The photomultiplier detec-
tor voltage was 600 V and the instrument excitation and emis-
sion slits were set at 5 and 5 nm, respectively. The lifetime were
measured on a Varian Cary Eclipse fluorescence spectrophotometer
with a microsecond flash lamp (pulse length: 2 μs).
X-ray diffraction studies of the single crystals of 3 and 4 were
carried out on an Xcalibur 3 diffractometer (Oxford Diffraction, UK)
with CCD detector according to standard procedure [monochrom-
atized Mo Kα radiation; ω-scanning with a step 1° at 295(2) K].
A correction for absorption was applied empirically. The structures
were solved by the direct statistical method and refined by full-
matrix least-squares method (with F2) in an anisotropic approxi-
mation for all non-hydrogen atoms except those for the disordered
fragments. Hydrogen atoms were added in calculated positions and
refined in an isotropic approximation in the “riding” model. All
calculations were performed using Olex shell [23] and SHELX pro-
gram package [24]. The main crystallographic data and experimen-
tal details are collected in Table 1.
Fig. 1. Diketonate-anions used for the synthesis of Tb(III) complexes.
2. Experimental
2.1. Materials
All procedures associated with the synthesis of new lig-
ands and complexes were carried out in air using commer-
cial reagents (TbCl3·6H2O (99.99%), lithium hydride (97%) and
1,2-dimethoxyethane (99%) (Alfa Aesar); Tb(OAc)3·xH2O (99.99%),
methanol (99.9%) (Sigma Aldrich); ethyl trifluoroacetate CF3CO2Et
(99%) and ethyl pentafluoropropionate C2F5CO2Et (98% min) (P&M
Invest)).
2.2. Physicochemical measurements
2.3. Synthesis of the ligands and the complexes
1H, 19 F and 13C NMR spectra were recorded on AVANCE-500
spectrometer in DMSO–d6 using Me4Si and C6F6 as internal stan-
dards. In 1H NMR spectra the solvent residual signals observed at
δ 2.52 (DMSO) and 3.43 (water) ppm. IR diffuse-reflectance spectra
3,3-Dialkoxybutane-2-ones
were
prepared
from
2,3-
butanedione (97%, Alfa Aesar) and the corresponding trialkyl
orthoformate. Lithium β-diketonates 1, 2 were synthesized by
following the reported literature procedures [25,26].
Table 1
Crystal structure data for terbium(III) complexes.
3
4
[TbL13·LiL1·(MeOH)]
[TbL23·LiL2·(MeOH)]
[TbL3·LiL·(MeOH)]∗
Chemical formula
Formula wt. (g/mol)
Crystal size (mm)
Crystal system
C
37H44F20LiO17Tb
C41H60F12LiO17Tb
1218.75
C33H44F12LiO17Tb
1106.54
1306.58
0.41 × 0.33 × 0.24
Triclinic
0.47 × 0.38 × 0.26
Orthorombic
P212121
0.25 × 0.20 × 0.15
Monoclinic
Pn
¯
Space group
P1
˚
a (A)
11.1998(5)
11.5161(5)
22.8908(8)
75.995(3)
77.089(3)
70.763(4)
2671.22(19)
2
13.7132(7)
15.4941(12)
26.5653(16)
90
12.1678(6)
12.1989(3)
15.8643(5)
90
˚
b (A)
˚
c (A)
α (°)
β (°)
γ (°)
90
94.541(4)
90
90
3
˚
Volume (A )
5644.4(6)
4
2347.41(15)
2
Z
d (calc., g/cm3)
Abs. coeff. (mm−1
1.624
1.434
1.566
)
1.455
1.352
1.443
Theta range (deg.)
Reflections collected
Data/restraints/param.
R(int) [indep. refl.]
R1, wR2 [(I > 2σ(I)]
R1, wR2 (all data)
Goodness of fit
3.63 to 25.56
26,295
3.77 to 26.70
24,986
1102
13,147
14,280/396/1032
0.054
13,658/184/773
0.0464
6641/134/707
0.030
0.0626, 0.1309
0.1179, 0.1763
1.019
0.0490, 0.1041
0.0810, 0.1385
1.005
0.0344, 0.0792
0.0453, 0.0871
1.002
Largest diff. peak/hole
1.042/−1.271
1.177/−1.295
1.09/−0.693
−3
˚
(eA
)
CCDC deposition no.
∗From ref. [21].
2,011,088
2,011,089
1,855,392
2

Y.S. Kudyakova, P.A. Slepukhin, M.S. Valova et al.
Journal of Molecular Structure 1226 (2021) 129331
The reaction of lithium RF-β-diketonates 1,
2 with ter-
2.3.1. General synthesis of lithium β-diketonates 1, 2
To a solution of F(CF2)nCO2Et (0.1 mol) and the correspond-
ing 3,3-dialkoxybutane-2-one (0.1 mol) in 1,2-dimethoxyethane
(70 mL) LiH powder (0.1 mol) was added. The resulting suspen-
sion was stirred for 4 h under reflux. After 4 h, the reaction mix-
ture was concentrated, the residue was filtered, washed with cold
diethyl ether (2 × 30 mL) and air-dried to afford colorless solid.
bium(III) salts {TbCl3·6H2O or Tb(OAc)3·xH2O} in methanol re-
sulted in heterobimetallic complexes [TbL13·LiL1·(MeOH)] 3 and
[TbL23·LiL2·(MeOH)] 4 (Eq. (1)).
ꢀ
ꢁ
MeOH
4LiL + TbX3 · xH2O −−−→ TbL (LiL)(MeOH) + 3LiX + xH2O
(
)
3
1,2
X=CI,OAc
3,4
Lithium
1,1,1,2,2-pentafluoro-6,6-dimethoxy-5-oxohept-3-en-3-
(1)
olate LiL1 (1). Yield 23.87 g (84%), m.p. 201–203°С (sublimation).
Calc. for C9H10F5LiO4: С, 38.05; Н, 3.55. Found: С, 37.88; Н, 3.41.
IR (ATR, ν/cm−1): 2997, 2942, 2839 (C–H); 1645 (C = O); 1517
(С=С); 1479 (CH3); 1325–1139 (C–F). 1H NMR: δ/ppm 1.25 (s, 3H,
Me), 3.09 (s, 6H, 2 MeO), 5.93 (s, 1H, CH). 19 F NMR: δ/ppm 41.49
(br s, 2F, CF2), 81.00 (br s, 3F, CF3). 13C NMR: δ/ppm 20.95 (s),
48.82 (s), 89.52 (s), 101.44 (s), 108.78 (tq, J = 262, 35 Hz), 118.79
(qt, J = 286, 37 Hz), 170.86 (q, J = 21 Hz), 192.82 (s).
3.1. 19 F NMR spectroscopic studies
The significant broadening of signals in the 1H NMR spectra
of complexes 3, 4 registered in DMSO–d6 made them uninforma-
tive for identifying the paramagnetic metal species. However, the
behavior of Ln(III) diketonates in solution was properly investi-
gated by 19 F NMR spectroscopy [27-29]. In the 19 F NMR spec-
trum of complex 4 there are three signals corresponding to dif-
ferent types of diketonates existing in equilibrium in the solution
of DMSO–d6. The value of the highest field signal at δF = 87.7 ppm
is comparable to that observed for the initial lithium β-diketonate
2, but in contrast with the ligand, the complex has this singlet
broadened (ꢀδF = 1.2 ppm). Two broadened signals at δF = 111.5
and 117.7 ppm indicate [TbL4]− and [TbL3] metal species, respec-
tively [30]. The same behavior was observed for C2F5-substituted
β-diketonate 3, but its 19 F NMR spectrum contained a doubled
number of fluorine atoms signals. A similar set of signals in the
19 F NMR spectra was registered for tetrakis-β-diketonates M[TbL4]
(M = Na, K, Cs), and the chemical shift of the high field sin-
glet varied depending on the alkali metal ion [30]. Therefore, 19 F
NMR spectroscopy has proved to be a valuable tool in the qual-
itative analysis of Ln(III) RF-β-diketonates and can also be used
in the complexes purity determination, as well as in the identifi-
cation of the metal ions nature. We have found that the change
of substituents from Me to Et in the acetal fragment of function-
alized CF3-β-diketonates and the nature of alkali metals [30] do
not affect the equilibrium of Ln(III) tris- and tetrakis-diketonates in
solution.
Lithium 1,1,1-trifluoro-5,5-diethoxy-4-oxohex-2-en-2-olate LiL2 (2).
Yield 23.07
g (88%), m.p. 262–263°C (sublimation). Calc. for
C10H14 F3LiO4: С, 45.82; Н, 5.38. Found: С, 45.73; Н, 5.29. IR (ATR,
ν/cm−1): 2984, 2940, 2894 (C–H); 1636 (C = O); 1515 (С=С); 1478
3
(CH3); 1309–1131 (C–F). 1H NMR: δ/ppm 1.10 (t, JHH = 7.1 Hz, 6H,
2Me), 1.26 (s, 3H, Me), 3.28–3.47 (m, 4H, 2 CH2), 5.93 (s, 1H, CH).
19 F NMR: δ/ppm 87.75 (s, 3F, CF3). 13C NMR: δ/ppm 15.32 (s), 21.92
(s), 56.51 (s), 88.03 (s), 101.15 (s), 119.10 (q, J = 289.3 Hz), 170.06
(q, J = 29.4 Hz), 193.93 (s).
2.3.2. General synthesis of the complexes [(TbL3)·(LiL)·(MeOH)] 3, 4
To a solution of the corresponding lithium β-diketonate LiL
(4 mmol) in methanol (15 mL) terbium(III) chloride hydrate [or ter-
bium(III) acetate hydrate] (1 mmol) was added and the mixtre was
stirred under reflux until a clear solution was obtained. After cool-
ing to room temperature, the resulting solution was slowly evapo-
rated to afford crystalline colorless complexes 3 and 4.
[TbL13·LiL1·(MeOH)] (3). Yield 0.84 g (64%), m.p. 142–143°C.
Calc. for C37H44F20LiO17 Tb: С, 34.01; Н, 3.39. Found: С, 33.83; Н,
3.29. IR (ATR, ν/cm−1): 3428 (br) (O–H); 2997, 2947, 2840 (C–H);
1650, 1632 (C = O); 1519 (С=С); 1468 (CH3); 1331–1124 (C–F). 19 F
NMR: δ/ppm 40.2–42.8 (br s, CF2, LiL), 55.1–57.7 (br s, CF2, [TbL3]),
61.0–64.0 (br s, CF2, [TbL4]−), 79.7–82.3 (br s, CF3, LiL), 97.7–100.5
(br s, CF3, [TbL4]−), 103.1–105.5 (br s, CF3, [TbL3]). The ratio of
[LiL]:[TbL3]:[TbL4]− = 2:1:4.
3.2. X-Ray crystallographic studies
[TbL23·LiL2·(MeOH)] (4). Yield 0.66 g (54%), m.p. 74–75°C. Calc.
for C41H60F12LiO17 Tb: С, 40.41; Н, 4.96. Found: С, 40.23; Н, 4.79.
IR (ATR, ν/cm−1): 3536, 3465 (br) (O–H); 2983, 2940, 2900 (C–
According to XRD analysis, dinuclear heterometallic complexes
3, 4 are neutral β-diketonates, which crystallize in centrosym-
¯
metric space groups of triclinic P1 (3) and orthorhombic P212121
H); 1651, 1634 (C
= O); 1523 (С=С); 1473 (CH3); 1317–1137
(C–F). 19 F NMR: δ/ppm 86.0–88.6 (br s, CF3, LiL), 109.7–112.7
(br s, CF3, [TbL3]), 115.7–120.2 (br s, CF3, [TbL4]−). The ratio of
[LiL]:[TbL3]:[TbL4]− = 1:0.8:2.4.
(4) systems (Fig. 2, 3, Table 1). The structure of 3, 4 consists
of two metal-containing parts: Tb(III) tris-diketonate TbL1(2) and
3
the initial lithium β-diketonate LiL1(2) serving as a coligand. Cen-
tral Tb(III) ion is octa-coordinated by oxygen atoms of diketonate-
anions, which form three six-membered 4f-metal chelate cycles
(coordination mode A) (Fig. 1, 4a,c), as well as methoxy group
3. Results and discussion
Lithium β-diketonates 1, 2 were obtained according to the re-
ported procedure [25,26] by Claisen condensation of the corre-
sponding fluoroalkylated esters and 3,3-dialkoxybutane-2-ones in
the presence of lithium hydride.
and bridging μ2 O atom of LiL1(2), which form five-membered 4f-
–
metal chelate cycle (coordination mode B) (Fig. 1, 4b,d). Lithium
ion is additionally coordinated with one molecule from the tris-
diketonate fragment via mode B. Methanol solvent molecule satu-
rates the penta-coordinated sphere around Li ion (Fig. 4b,d).
Scheme 1
Scheme 1. Synthesis of lithium RF-β-diketonates.
3

Y.S. Kudyakova, P.A. Slepukhin, M.S. Valova et al.
Journal of Molecular Structure 1226 (2021) 129331
Fig. 2. Crystal structure of terbium(III) complex [TbL13·LiL1·(MeOH)] 3. Hydrogen
atoms are omitted.
However, the structure of Tb(III) tris-diketonate fragments is
different in these complexes: all diketonate anions in [TbL13] of 3
are in the cis-form (Fig. 4a), while the isomerization of one diket-
onate anion into the trans-form occurs in the complex 4 (Fig. 4c).
Fig. 3. Crystal structure of terbium(III) complex [TbL23·LiL2·(MeOH)] 4. Hydrogen
˚
atoms are omitted.
The Tb-Li distance in complex 3 is equal to 3.48 A and simi-
lar to that found in [TbL3·LiL·(MeOH)] [25]. But the replacement of
Fig. 4. Terbium(III) tris-diketonate fragments and heterobimetallic core organization in the complexes 3 (a, b) and 4 (c, d). Hydrogen atoms are omitted.
4

Y.S. Kudyakova, P.A. Slepukhin, M.S. Valova et al.
Journal of Molecular Structure 1226 (2021) 129331
Fig. 5. The view of heterobimetallic β-diketonates forming the crystal packing of terbium(III) complexes 3 (a) and 4 (b) with the shortest intermolecular Tb…Tb distances.
Only hydrogens participating in the intermolecular H···F interactions (blue dashed lines) are shown.
–
the alkyl substituents in the acetal group from Me to Et leads to an
molecules is realized through the intermolecular C H···F interac-
˚
˚
increase in the distance between metal ions up to 3.52 A in com-
tions (2.61–2.79 A) between trifluoromethyl group and alkyl sub-
plex 4, which is closer to that obtained from the tetrakis-diketonate
[LiTbL4·(CH3CN)] [22].
stituents (Fig. 5b). Molecules with the shortest Tb…Tb distance are
arranged in chains to form zigzag layers’ network providing crystal
packing of the complex 4 (Fig. 7).
According to the calculations performed in the SHAPE 2.1 pro-
gram [31,32], the geometry of the octa-coordinated Tb(III) ion can
be best described as a distorted triangular dodecahedron (TDD-8),
and the penta-coordinated Li(I) ion has a distorted square pyrami-
dal (SPY-5) environment.
3.3. Photoluminescence studies
The solid-state luminescence properties were measured at room
temperature. The UV-absorption spectra of complexes 3 and 4
showed maximum excitation at 323 and 327 nm, respectively. The
photoluminescence spectra exhibited the typical Tb3+-centered
emission bands in the 490–650 nm region corresponding to the
The elongation of the carbon chain in acetal or perfluoroalkyl
groups of ligands 1, 2 resulted in the different crystal packing of
complexes 3 and 4. In 3, the molecules are stacked to produce
square packing with the shortest intermolecular Tb…Tb distance
˚
5D4
→
7FJ (J = 2–6) transitions (Table 2). The phosphorescence
equal to 11.200 A (Figs. 5a, and 6). Between molecules in neighbor-
–
ing stacks, short C H···F contacts are observed with H···F distances
lifetimes of 3 and 4 were 569 and 237 μs, respectively. In Table 3
we have summarized the data for a series of heterobimetallic
Tb(III)-M (M is alkali metal) complexes based on the functionalized
RF-β-diketonates. Varying of both alkali metals and ligands (from
L to L1 and L2) dramatically changes the crystal structure of the
˚
of 2.61–2.96 A (Fig. 5a).
As compared to 3, heterobimetallic Tb(III) β-diketonate 4 has
˚
a shorter intermolecular Tb…Tb distance of 10.994 A (Fig. 5b).
The mutual orientation of two diketonate anions of neighboring
5

Y.S. Kudyakova, P.A. Slepukhin, M.S. Valova et al.
Journal of Molecular Structure 1226 (2021) 129331
Fig. 6. Crystal packing of terbium(III) complex [TbL13·LiL1·(MeOH)] 3 along the b axis. Hydrogen atoms are omitted.
Fig. 7. Crystal packing of terbium(III) complex [TbL23·LiL2·(MeOH)] 4 along the a axis. Hydrogen atoms are omitted.
Table 2
Photophysical data for terbium(III) complexes.
[%] of total
emission
Lifetimes
Complex
Transition
λ [nm]
[μs]
3 [TbL13·LiL1·(MeOH)]
5D4
5D4
5D4
5D4
5D4
5D4
5D4
5D4
5D4
5D4
→
→
→
→
→
→
→
→
→
→
7F6
7F5
7F4
7F3
7F2
7F6
7F5
7F4
7F3
7F2
490
548
582
621
650
491
548
582
621
650
23.0
65.7
6.3
569
3.7
1.3
4 [TbL23·LiL2·(MeOH)]
17.2
73.5
5.1
237
3.1
1.1
6

Y.S. Kudyakova, P.A. Slepukhin, M.S. Valova et al.
Journal of Molecular Structure 1226 (2021) 129331
Table 3
A summary of the main structural characteristics and phosphorescence lifetimes for a series of heterometallic dinuclear complexes.
Tb…Tb
Phosphorescence
distance,
∗
˚
[A]
[LnO8]
geometry∗∗
lifetimes of solids,
№
Complex
Discrete structures
[μs]
Ref.
1
2
3
4
5
6
[TbL3·LiL·(MeOH)]
10.552
11.658
11.200
9.923
TDD-8
TDD-8
TDD-8
TDD-8
BTRP-8
TDD-8
648
640
569
520
480
237
[21]
[30]
Na[TbL4](MeOH)(H2O)
[TbL13·LiL1·(MeOH)] (3)
[TbL3·LiL·(H2O)]
[21]
[22]
[LiTbL4·(H2O)](CH3CN)
[TbL23·LiL2·(MeOH)] (4)
9.545
10.994
Polymeric structures
7
8
K[TbL4](H2O)
Cs[TbL4]
10.455
10.995
TDD-8
292
48
[30]
[30]
SAPR-8
∗The shortest intermolecular distance.
∗∗Based on the calculations performed in the SHAPE 2.1 program [31,32] (TDD-8 – triangular dodecahedron (D2d symmetry); BTRP-8
– biaugmented trigonal prism J50 (C2v symmetry); SAPR-8 – square antiprism (D4d symmetry)).
resulting complexes, including the geometry of the Ln(III) environ-
ment, the distances between heterometals in the molecules, and
the crystal packing. Since the emission of Ln(III) ions is primarily
associated with the geometry of the crystal field and the electron
distribution around coordinating atoms of the ligand, these param-
eters were used to identify “structure-property” relationships. The
longest afterglow times are exhibited by heterometallic dinuclear
complexes with TDD-8 geometry of the LnO8 coordination polyhe-
dron. Although the use of ligand L1 does not modify the geometry
of the Ln(III) environment in complex 3, but (perfluoro)alkyl sub-
stituents in diketonate anions affect the π-electron-density distri-
bution in metal cycles. In particular, replacing the CF3-substituent
with C2F5-group decreases the negative inductive effect on the
oxygen atom of the adjacent carbonyl group thereby increasing
the electron density at the coordinating oxygen atom and reduc-
ing the hardness of Lewis acid. However, the changes in the acetal
group of L resulted in a more drastic decrease of the phosphores-
cence lifetimes of complexes. The reorientation of one ligand in the
Tb(III) tris-diketonate fragment due to ethoxy group incorporation
(Fig. 4c) provokes the significant redistribution of electron density
in the LnO8 coordination polyhedron.
Declaration of Competing Interest
The authors declare that they have no known competing finan-
cial interests or personal relationships that could have appeared to
influence the work reported in this paper.
CRediT authorship contribution statement
Yulia S. Kudyakova: Conceptualization, Investigation, Funding
acquisition, Writing - original draft. Pavel A. Slepukhin: Investiga-
tion. Marina S. Valova: Investigation. Yanina V. Burgart: Writing
- review & editing. Victor I. Saloutin: Writing - review & editing.
Denis N. Bazhin: Methodology, Investigation, Supervision, Writing
- original draft.
Acknowledgements
This work was financially supported by the Russian Science
Foundation (project no. 19–73–00242). XRD experiments and
physicochemical studies were carried out using the equipmentof
the Center for Joint Use “Spectroscopy and Analysis of Organic
Compounds” at the Postovsky Institute of Organic Synthesis UB
RAS.
In addition, the elongation of (perfluoro)alkyl groups in ligands
influences the crystal packing of the corresponding complexes 3, 4.
Despite the discrete structure, they have more close-packed crys-
tals and, therefore, do not exhibit the mechanoluminescence typi-
cal for the heterobinuclear complexes based on the ligand L.
Supplementary materials
Supplementary material associated with this article can be
found, in the online version, at doi:10.1016/j.molstruc.2020.129331.
4. Conclusion
References
We have demonstrated herein how the elongation of (perflu-
oro)alkyl substituents in the initial functionalized RF-β-diketonate
ligand L affects the organization of the crystal packing in the re-
sulting complexes. A bulkier ethoxy-substited acetal group modi-
fies the Tb(III) tris-diketonate structure due to the isomerization of
one diketonate anion into trans-form. The long-lived emission in
the discrete Tb(III) β-diketonates is realized through both reducing
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