Crystal Structure And Luminescence of 2,2-Difluoro-4-(4'-Phenylphenyl)-6-Methyl- 1,3,2-Dioxaborin (C6H5C6H4COCHCOCH3BF2)

Article abstract of DOI:10.1007/s10947-010-0118-8

The crystal structure of 2,2-difluoro-4-(4'-phenylphenyl)-6-methyl-1,3,2-dioxaborin (C₆H₅C₆H₄COCHCOCH₃BF₂) (1) is determined. The effect of the π-stacking interaction on the luminescent properties of compound 1 at 300 K and 77 K is shown.

Full text of DOI:10.1007/s10947-010-0118-8

Journal of Structural Chemistry. Vol. 51, No. 4, pp. 785-789, 2010
Original Russian Text Copyright © 2010 by B. V. Bukvetskii, E. V. Fedorenko, and A. G. Mirochnik
CRYSTAL STRUCTURE AND LUMINESCENCE OF
2
1
,2-DIFLUORO-4-(4ꢀ-PHENYLPHENYL)-6-METHYL-
,3,2-DIOXABORIN (ꢀ H C H COCHCOCH BF )
6
5
6
4
3
2
B. V. Bukvetskii, E. V. Fedorenko,
and A. G. Mirochnik
UDC 548.736:546.27:535.37
The
crystal
structure
of
2,2-difluoro-4-(4ꢀ-phenylphenyl)-6-methyl-1,3,2-dioxaborin
(
ꢀ H C H COCHCOCH BF ) (1) is determined. The effect of the ꢁ-stacking interaction on the luminescent
6
5
6
4
3
2
properties of compound 1 at 300 K and 77 K is shown.
Keywords: ꢂ-diketonates of boron difluoride, 2,2-difluoro-4-(4ꢀ-phenylphenyl)-6-methyl-1,3,2-dioxaborin,
crystal structure, excimers, luminescence.
ꢂ-Diketonates of boron difluoride exhibit intense luminescence both in solutions and crystals [1]. 2,2-Difluoro-4-(4ꢀ-
phenylphenyl)-6-methyl-1,3,2-dioxaborin (C
6
H
5
C
6
H
4
COCHCOCH
3
BF ) (1) is a representative of the class of benzoylacetonates
2
of boron difluoride with a substituent in the phenyl ring. We have previously studied the effect of ꢃ-substituent on the
spectral and luminescent properties of crystalline benzoylacetonates of boron difluoride [2]. A change in the number of alkyl
substituents, which does not affect the luminescent properties of a single molecule, results in a change in the supramolecular
architecture of the crystal. At the same time, the luminescent properties of the crystals also change significantly [3]. The
luminescence spectrum of crystalline 1 was found to be bathochromically shifted as compared to other studied
benzoylacetonates. Thus, it is of interest to study the causes of the bathochromic shift in the luminescence spectrum.
Supposed causes are: 1) a change in the supramolecular architecture of the crystal; 2) an increase in the ꢁ electron system of
the molecule. The aim of this single crystal X-ray diffraction study of compound 1 is to determine the possible dominant
effect of one of the above reasons.
Experimental. Compound 1 was synthesized using the double acylation method by passing boron trifluoride gas
through the diphenyl solution in acetic anhydride [4]. The crystals of compound 1 were obtained for single crystal X-ray
diffraction analysis by recrystallization from toluene on slow cooling of the solution.
Institute of Chemistry, Far East Division, Russian Academy of Sciences, Vladivostok; gev@ich.dvo.ru,
mirochnik@ich.dvo.ru. Translated from Zhurnal Strukturnoi Khimii, Vol. 51, No. 4, pp. 812-815, July-August, 2010.
Original article submitted July 8, 2009.
0022-4766/10/5104-0785 © 2010 Springer Science+Business Media, Inc.
785

TABLE 1. Crystallographic Data, Characteristics of the Diffraction Experiment, and Refinement Parameters
for the Structure of Compound 1
Parameter
Value
Empirical formula
Molecular weight
Radiation wavelength, Å
Space group
C
16
H
286.07
0.71073
P2(1)/ꢀ
13BF
2
O
2
a, b, c, Å
8.233(1), 12.410(2), 13.592(2)
ꢂ, deg
V, Å ; Z
91.347(2)
1388.4(3), 4
1.369
3
3
d
x., g/cm
–
1
ꢄ, mm
F(000)
0.106
592
Crystal dimensions, mm
0.21ꢅ0.12ꢅ0.10
2.22-30.06
–11 ꢇ h ꢇ 8, –15 ꢇ k ꢇ 17, –18 ꢇ l ꢇ 19
10,864
Data collection over ꢆ, deg
Ranges of reflection indices
Measured reflections
Independent reflections
Completeness, %
Refinement method
40,242 [R(int) = 0.0366]
98.9
least squares method against F2
0.944
S
R factors over I > 2ꢈ(I)
R factors over all reflections
Extinction coefficient
Residual electron density (max/min), e/Å–3
R1 = 0.0449, wR2 = 0.1181
R1 = 0.0862, wR2 = 0.1368
0.0019(17)
0.188/–0.172
The luminescence spectra were measured at 300 K and 77 K using an SDL-1 spectrometer (ꢉexcit = 365 nm). The
kinetics of the luminescence decay was measured on a FluoTime 200 (PicoQuant) laser picosecond spectrfluorimeter.
The single crystal X-ray diffraction study was performed on a SMART-1000 Bruker CCD system at 293(2) K. The
experimental data were collected in three groups of 906 frames each at ꢊ = 0ꢋ, 90ꢋ, and 180ꢋ respectively, ꢌ-scanning with a
step of 0.2ꢋ and 20 s exposure for each frame. The data were edited, the unit cell parameters were refined, and the integral
intensities were recalculated into the structural amplitude modules using the programs [5]. The structure was solved by the
direct method with further refinement of positional and thermal parameters in the anisotropic approximation for all non-
hydrogen atoms using the programs [6]. Positions of hydrogen atoms were well revealed in the electron density synthesis,
however, they did not contain any new information, therefore, for the subsequent study we used those calculated and refined
in the riding model. The crystal chemical data have been deposited with the Cambridge Crystallographic Data Center under
No. CCDC 735612, which is available on request at www.ccdc.cam.ac.uk/data_request/cif. The main crystallographic
parameters of the studied sample, characteristics of the single crystal X-ray diffraction experiment, and details of the
structural model refinement by the least squares method are listed in Table 1, while interatomic distances are presented in
Table 2. The structure of the molecule of 1 is shown in Fig. 1.
Results and Discussion. The crystal structure of the studied compound is based on isolated molecules of 1 (Fig. 1).
A crystallographically independent molecule multiplied by the nearest symmetry center and translation in the [100] direction
makes stacks of molecules with parallel orientation that are infinite along the ꢁ crystallographic axis. The stack multiplied by
the ꢀ glide reflection plane is parallel to the initial one, while the molecular planes are oriented at an angle of 67.56 (0.03)ꢋ
against the initial ones. Hence, the molecules of 1 are packed in a tile- stack arrangement. The infinite stacks of molecules are
combined into a three-dimensional framework by the van der Waals interaction. Molecules of the neighboring stacks have
F…H and ꢁ…ꢂ bifurcated bonds that are described for the boron difluoride complexes in the work [7].
7
86

Fig.1. Molecular structure of compound 1.
TABLE 2. Bond Lengths of Compound 1 (l, Å)
Bond
l
Bond
l
Bond
l
Bond
l
B(1)–F(1)
B(1)–F(2)
B(1)–O(2)
B(1)–O(3)
C(1)–O(2)
C(3)–O(3)
1.361(2)
1.364(2)
1.480(2)
1.479(2)
1.297(2)
1.297(2)
C(2)–C(1)
C(2)–C(3)
C(4)–C(3)
C(4)–C(5)
C(4)–C(9)
C(5)–C(6)
1.370(2)
1.379(2)
1.468(2)
1.394(2)
1.391(2)
1.377(2)
C(7)–C(6)
C(7)–C(8)
C(8)–C(9)
C(7)–C(10)
C(10)–C(11)
C(10)–C(15)
1.391(2)
1.395(2)
1.375(2)
1.488(2)
1.385(2)
1.393(2)
C(11)–C(12)
C(13)–C(12)
C(13)–C(14)
C(15)–C(14)
C(1)–C(16)
1.383(2)
1.356(3)
1.372(3)
1.381(2)
1.481(2)
A molecule of 1 consists of two aromatic rings and one quasi-aromatic (chelate) ring. The C–ꢁ and C–ꢀ bonds of
the chelate ring are leveled in pairs; bond lengths correspond to one-and-a-half bonds (Table 2). First and the second phenyl
ring planes are at an angle of 23.85ꢋ, while the second phenyl and chelate ring planes are at 9.09ꢋ. As the CCDC data analysis
shows, in the crystalline state, a diphenyl molecule has an angle between the phenyl rings when one of them participates in
the formation of ꢁ bonds or ꢁ–ꢁ stacking interaction, for instance [8, 9]. In other cases, the diphenyl molecule is planar [10-
1
2]. In compound 1, the ꢀ(3)–ꢀ(4) bond is shorter than ꢀ(7)–ꢀ(10) (Table 2), which indicates a higher conjugation of ꢁ
systems of the second phenyl and chelate rings than that of two phenyl ones. An increase in the C–ꢀ bond length of the
second phenyl ring in comparison to the first one also shows that ꢁ electrons of the first phenyl ring hardly participate in the
ꢁ
system of the molecule. It seems that in order to evaluate the effect of the first phenyl ring as well as the substituent in
benzoylacetonate of boron difluoride, it is necessary to evaluate only its inductive effect. Indeed, an extension of the
molecular ꢁ system should cause a bathochromic shift of the luminescence maximum in single molecules [13], and the
luminescence band maximum of a dilute solution of 1 is 425 nm as is also for benzoylacetonates of boron difluoride with the
alkyl substituent in the para-position of the phenyl ring [3].
The stack arrangement is shown in Fig. 2. The stack has two types of overlapping: in one case, all three rings of
interacting molecules participate in the ꢁ stacking interaction, in the other case, only the chelate ring and the phenyl ring
bonded to it. The maximum ꢁ–ꢁ stacking interaction is observed when the interacting molecules overlap completely: the
second phenyl rings are coplanar and located at a distance of 3.44 Å. The distance between the first phenyl and chelate ring
planes located at 14.76ꢋ to each other is 3.47-4.02 Å. If the plane overlapping is not complete, the phenyl and chelate rings
that participate in the ꢁ stacking interaction are located at 9.39ꢋ, and the distance between them is 3.45-3.62 Å. All types of
the ꢁ stacking interaction facilitate the formation of pre-excimer positions in the crystals of 1 [14].
The effective ꢁ–ꢁ stacking interaction causes a significant bathochromic shift of the luminescence band in
the crystals of 1 in comparison to other studied benzoylacetonates [15]. Various ꢁ–ꢁ stacking interaction types provide the
7
87

Fig. 2. Stack fragment in the crystal of 1.
Fig. 3. Luminescence spectra of the
crystals of 1: 300 K (1), 77 K (2).
existence of several luminescent centers in the crystal of 1. Indeed, as the study of the kinetics of the luminescence decay
shows, the kinetics is two exponential with the life time ꢍ
1
= 19.0 ns (23.92%) and ꢍ = 5.5 ns (76.08%). The presence of two
2
luminescent centers is supported by the measurements of the luminescence spectrum at low temperatures (Fig. 3): when the
temperature is lowered, there is a distinct hypsochromic shift of the luminescence spectrum maximum (30 nm), and the
second band appears. As shown previously in [16], these changes in the luminescence spectrum occur if with a temperature
decrease to 77 K the repulsive forces are most important in the stacking interaction, which hinders the occurrence of excimer
fluorescence. In the crystals of 1 with complete overlapping of the neighboring molecules (3.44 Å) the distance between the
second phenyl rings corresponds to the minimum intermolecular distance at which the excimer formation is possible [17].
The temperature decrease to 77 K is likely to cause crystal compression resulting in shortening of this distance, strengthening
of the intermolecular repulsion, and the hypsochromic shift of the luminescence spectrum.
REFERENCES
1
2
3
. V. E. Karasev, A. G. Mirochnik, and E. V. Fedorenko, Photophysics and Photochemistry of ꢂ-Diketonates of Boron
Difluoride [in Russian], Dal’nauka, Vladivostok (2006).
. A. G. Mirochnik, E. V. Gukhman, V. E. Karasev, and P. A. Zhikhareva, Izv. Akad. Nauk, Ser. Khim., No. 6, 1030
(2000).
. A. G. Mirochnik, B. V. Bukvetskii, E. V. Gukhman, and V. E. Karasev, J. Fluor., 13, 157 (2003).
7
88

4
5
. V. A. Reutov and E. V. Gukhman, Zh. Obshch. Khim., 69, No. 10, 1672 (1999).
. Bruker, SMART and SAINT-Plus. Versions 5.0. Data Collektion and Processing Software for the SMART System.
Bruker AXS Inc., Madison, Wisconsin, USA (1998).
6
. G. M. Sheldrick SHELXTL/PC, Versions 5.10, An Integrated System for Solving, Refining and Displaying Crystal
Structures from Diffraction Data, Bruker AXS Inc., Madison, Wisconsin, USA (1998).
. D. Rohde, C.-J. Yan, and L.-J. Wan, Langmuir., 22, 4750 (2006).
. A. Lipka and D. Mootz, Z. Anorg. Allg. Chem., 440, 217 (1978).
. R. E. Morris, R. E. Aird, and P. del Socorro Murdoch , J. Med. Chem., 44, 3616 (2001).
7
8
9
1
1
1
1
1
0. G. P. Charbonneau and Y. Delugeard, Acta Crystallogr. Sec. B, 32, 1420 (1976).
1. J. H. Noordik, J. Schreurs, R. O. Gould, et al., J. Phys. Chem., 82, 1105 (1978).
2. L. Pasimeni, G. Guella, C. Corvaja, et al., Mol. Cryst. Liq. Cryst., 91, 25 (1983).
3. B. M. Krasovitskii and B. M. Bolotin, Organic Luminophores [in Russian], Khimiya, Moscow (1984).
4. É. A. Silin’sh, M. V. Kurik, and V. Chapek, Electronic Processes in Organic Molecular Crystals: Localization and
Polarization Phenomena [in Russian], Zinatne, Riga (1988).
1
5. A. G. Mirochnik, E. V. Gukhman, V. E. Karasev, and P. A. Zhikhareva, Izv. Akad. Nauk, Ser. Khim., No. 6, 1030
(2000).
1
1
6. E. V. Fedorenko, A. G. Mirochnik, V. E. Karasev, and B. V. Bukvetskii, Zh. Fiz. Khim., 80, No. 12, 2192 (2006).
7. M. L. Glowka, D. Martynowski, and K. Kozlowska, J. Mol. Struct., 474, 81 (1999).
7
89