Article pubs.acs.org/crystal
Disorder for the Sake of Order Viktor A. Tafeenko* and Stanislav I. Gurskiy Chemistry Department, Lomonosov Moscow State University, Leninskie Gory, 1, Building 3, GSP-1, 119991, Moscow, Russia S Supporting Information *
ABSTRACT: Crystal structure analysis of two N,N-dimethylanilinium 3-cyano-4dicyanomethylene-5-oxo-4,5-dihydro-1H-pyrrole-2-olate (DMA+_HA−) polymorphs (α, β) allowed us to conclude that a degree of disorder in crystal is a constant characteristic of the polymorph. A change in the degree of disorder in the crystal requires a change in the crystal phase. The disorder effect on solid-state luminescence of α, β polymorphs is presented.
1. INTRODUCTION Molecular disorder is a phenomenon frequently met in crystals of organic compounds.1 Often, just the disorder plays a key role in understanding physical properties of crystal, while analysis of ideal, well-ordered crystal structure is not sufficient to correlate property with structure.2−4 To scientists, disorder may provide an opportunity to create new materials with unique physical properties impossible for well-ordered crystal structures.5 For instance, dynamic disorder, caused by chaotic molecular rotation under exceeding threshold temperature, allows creation of temperature-switchable and temperature-driven optical,6 dielectric,7,8 and charge-transport materials.9 Static disorder, i.e., when a molecule is disordered over several fixed positions with different occupancies in crystal, may produce several different environments of a key molecule responsible for the desired property of the crystal. As some molecular properties, e.g., luminescence,10−19 are environmentally sensitive, several different environments may give rise to several different values of the same property. By changing the population of each environment, it seems possible to tune the average value of the property in the same crystal, by analogy with the mixed-lanthanide metal−organic complex,20 where variation of the Gd:Eu:Tb ratio tunes complex emission within the full-color region. To make it possible to use the disorder factor for search of new materials, it is necessary first of all to understand the nature of disorder in crystal and know how to change the degree of disorder in crystals. Dynamic disorder can be controlled by means of temperature, but how can one influence static disorder when a change of temperature is useless because of the high energy barrier of molecular motion, or leads to destruction of the crystal? Is it possible to change the degree of disorder in a crystal by changing the crystal growth conditions? Is disorder an accidental characteristic of crystal or it is an essential feature? These are the questions one should answer to be able to use the disorder factor effectively for engineering new materials. Up to now, these questions have not been covered in the literature. © XXXX American Chemical Society
Our previous research showed that salts based on new organic anion HA− (Figure 1) are a convenient model to
Figure 1. Molecular structure and atom numeration of anion 3-cyano4-dicyanomethylene-5-oxo-4,5-dihydro-1H-pyrrol-2-olate (HA−).
investigate and develop new approaches toward engineering certain crystal structures with desired properties.21−29 Mainly our research was dedicated to influence such factors as π−π interactions, hydrogen bonds, and coordination bonds on solidstate luminescence of HA−-based salts. In this article we present insight into the nature of the disorder factor and its influence on luminescent properties of organic salt built from N,Ndimethylanilinium cation (DMA+) and 3-cyano-4-dicyanomethylene-5-oxo-4,5-dihydro-1H-pyrrole-2-olate anion (HA−). For the first time, packing of DMA+_HA− in a crystal was presented on the Acta Crystallogr., Sect. C journal cover (vol 60, part 1). However, this figure does not reflect the true crystal structure of the DMA+_HA− salt.22 In fact, as pointed out in the article, DMA+ cations are statically disordered over two interpenetrating sites near the anion, with occupancies of Received: October 21, 2015 Revised: January 6, 2016
A
DOI: 10.1021/acs.cgd.5b01496 Cryst. Growth Des. XXXX, XXX, XXX−XXX
Crystal Growth & Design
Article
Table 1. Results of X-ray Diffraction Study of DMA+_HA− Salt Crystals (α, β), Grown under Various Experimental Conditions no
crystal growth conditions (solvent, temperature)a
diffractometerb /radiationc
1
1
SVP/Cu
2
2
CAD/Cu
3
2
SVP/Cu
4
3
SVP/Cu
5
3
SVP/Cu
6
3
CAD/Cu
7
3
CAD/Cu
8
4
CAD/Cu
9
4
CAD/Cu
10
5
SVP/Cu
11
6
SVP/Cu
12
7
SVP/Cu
13
8
CAD/Cu
14
8
SVP/Cu
15
9
SVP/Cu
16
10
SVP/Mo
17
10
CAD/Cu
18
10
CAD/Cu
19
10
SVP/Cu
20
11
CAD/Cu
21
11
SVP/Mo
22
11
SVP/Cu
SOFd α crystal phase 0.841/0.159 (7) 0.831/0.169 (6) 0.837/0.163 (6) 0.831/0.169 (6) 0.843/0.157 (6) 0.829/0.171 (7) 0.837/0.163 (5) 0.830/0.170 (4) 0.833/0.167 (5) 0.844/0.156 (5) 0.857/0.143 (6) 0.843/0.157 (7) 0.862/0.138 (5) 0.838/0.162 (5) 0.849/0.151 (6) β crystal phase 0.523/0.477 (5) 0.524/0.476 (4) 0.507/0.493 (5) 0.529/0.471 (4) 0.513/0.487 (3) 0.520/0.480 (3) 0.527/0.473 (4)
Re [F2 > 2σ(F2)]
GOOFf on F2
number of reflections (I > 2σ(I))
Δρmax,ming (e· Å−3)
0.050
0.956
581
0.20/-0.25
0.046
1.058
786
0.27/-0.21
0.051
0.905
1291
0.17/-0.02
0.047
0.994
1128
0.18/-0.18
0.037
0.917
934
0.21/-0.15
0.039
1.061
733
0.19/-0.17
0.038
1.119
880
0.20/-0.15
0.034
1.050
711
0.23/-0.15
0.032
1.064
736
0.17/-0.16
0.029
0.903
773
0.11/-0.11
0.086
1.426
856
0.43/-0.34
0.066
1.088
865
0.21/-0.35
0.033
1.051
650
0.09/-0.14
0.044
0.964
1184
0.18/-0.33
0.042
1.085
810
0.28/-0.23
0.051
0.572
600
0.10/-0.08
0.040
1.030
1565
0.13/-0.13
0.041
1.054
1486
0.13/-0.15
0.061
1.055
1568
0.31/-0.24
0.035
1.045
1495
0.13/-0.11
0.025
0.896
1041
0.08/-0.12
0.074
0.945
1937
0.25/-0.32
a
1: water−1,4-dioxane−acetonitrile (1:1:1), 298 K. 2: water−ethanol (1:1), 277 K. 3: ethanol, 277 K. 4: water−acetonitrile (1:1), 277 K. 5: acetonitrile, 277 K. 6: water, 298 K. 7: 1,4-dioxane−acetonitrile (1:1), 298 K; the crystal was grown in 2003 and repeatedly studied in 2015. 8: 1,4dioxane−acetonitrile (1:1), 298 K. 9: ethanol, 277 K; the crystal was annealed at 393 K for 4 h. 10: water−acetonitrile (1:1), 363 K. 11: wateracetonitrile (1:1), 298 K; rapid crystallization from wide glass surface. bSVP: StadiVary Pilatus-100 K diffractometer manufactured by STOE. CAD: CAD-4 Enraf-Nonius diffractometer. cCu: CuKα (λ = 1.54184 Å). Mo: MoKα (λ = 0.71073 Å) radiations. dSite Occupancy Factor. eR = ∑|Fo − Fc|/ ∑|Fo|. fGOOF = S = goodness of fit = [∑[w(Fo2 − Fc2)2]/(n − p)]1/2; n = number of reflections, p = number of parameters refined. gElectron density synthesis with coefficient Fo − Fc, the highest peak/the deepest hole.
comparative description of α, β crystal structures, answers to the questions stated above, as well as the effect of the disorder factor on HA− luminescence are presented below.
0.833(5) and 0.167(5). On one hand, we were interested in the possibility to change the degree of disorder of DMA+ in the crystal. On the other hand, we wondered if the disorder influences the luminescence of HA− in crystal, since the luminescence of HA− anions is environmentally sensitive.26−29 To answer these questions we have synthesized the DMA+_HA− salt. Then, we attempted to change the degree of disorder in crystals of the salt by growing crystals under various experimental conditions (different solvents, different temperatures). As a result we succeeded in growing single crystals of the previously reported phase (α),22 and single crystals of a new polymorph of DMA+_HA− salt (β). A
2. EXPERIMENTAL SECTION 2.1. General. All reagents and solvents were purchased from commercial sources and used as received. Ba(HA)2 salt was synthesized using literature methods.30 Elemental analyses (C,H,N) were carried out with the CHNOS elemental analyzer vario MICRO. Photoluminescence spectra of crystals were recorded at room temperature on PerkinElmer LS 55 spectrometer; excitation and emission slits were 15.0 and 20.0 nm, respectively. B
DOI: 10.1021/acs.cgd.5b01496 Cryst. Growth Des. XXXX, XXX, XXX−XXX
Crystal Growth & Design
Article
Figure 2. Infinite ribbon in the crystal structure of α (view along a axis), which is formed by hydrogen-bonded HA− anions and DMA+ cations. Strong hydrogen bonds are depicted as thick dashed lines. Weak hydrogen bonds are depicted as thin dashed lines. Hydrogen atoms of methyl groups are omitted, for clarity. [Symmetry codes: (i) x, y, −1+z; (ii) x, −1+y, z.]
Figure 3. Infinite ribbon in the crystal structure of β (view along a axis), which is formed by hydrogen bonded HA− anions and DMA+ cations. Strong hydrogen bonds are depicted as thick dashed lines. Weak hydrogen bonds are depicted as thin dashed lines. Hydrogen atoms of methyl groups are omitted, for clarity. [Symmetry code: (i) 1−x, 2−y, −0.5+z.] 2.2. Synthesis of DMA+_HA− salt. A solution of N,Ndimethylaniline (0.51 mL, 4 mmol) in 40 mL of CH3CN, a solution of Ba(HA)2 (1.021 g, 2 mmol) in 19.9 mL of H2O, and a solution of H2SO4 (2 mmol) in 20.1 mL of H2O were mixed together. A white precipitate of BaSO4 was filtered after 12 h. The resulting solution was evaporated using a rotary evaporator. A dark-orange crystalline mass was thus obtained. This mass was recrystallized twice from 30 mL of ethanol at 259 K. As a result we obtained 0.650 g of a yellow crystalline mass (yield is 53% based on HA− anion). This mass was used for single crystal growth under various experimental conditions (solvent,
temperature): water, 298 K; ethanol, 277 K; acetonitrile, 277 K; water−ethanol (1:1), 277 K; water−acetonitrile (1:1), 277, 298, 363 K; 1,4-dioxane−acetonitrile (1:1), 298 K; water−1,4-dioxane− acetonitrile (1:1:1), 298 K. As a result we obtained crystals of two polymorphs of DMA+_HA− salt: α (yellow plate crystals),22 β (orange prism crystals). Crystals of both α and β polymorphs melt with decomposition at 496 K. Anal. Calcd for C16H13N5O2 (α): C 62.53, H 4.26, N 22.79; found: C 62.64, H 4.22, N 22.73. Anal. Calcd for C16H13N5O2 (β): C 62.53, H 4.26, N 22.79; found: C 62.40, H 4.19, N 22.88. C
DOI: 10.1021/acs.cgd.5b01496 Cryst. Growth Des. XXXX, XXX, XXX−XXX
Crystal Growth & Design
Article
2.3. X-ray Crystallography. Crystallographic data collection for crystals of α and β polymorphs was carried out at 295(2) K on StadiVary Pilatus-100 K (SVP) manufactured by STOE and CAD-4 Enraf-Nonius (CAD) diffractometers using CuKα (λ = 1.54184 Å) and MoKα (λ = 0.71073 Å) radiations. CAD diffractometer was used for the study of crystals with size >0.2 mm. SVP diffractometer with CuKα radiation was used for the study of crystals with size
