Crystalline Host–Guest Complexes of Constitutionally Isomeric Diol

ARTICLE pubs.acs.org/crystal

Crystalline Host
Guest Complexes of Constitutionally Isomeric Diol Hosts. A Structural Case Study Konstantinos Skobridis,† Georgios Paraskevopoulos,† Vassiliki Theodorou,† Wilhelm Seichter,‡ and Edwin Weber*,‡ † ‡

Department of Chemistry, University of Ioannina, GR-451 10 Ioannia, Greece Institut f€ur Organische Chemie, Technische Universit€at Bergakademie Freiberg, Leipziger Strasse 29, D-09596 Freiberg/Sachsen, Germany

bS Supporting Information ABSTRACT: The formation of crystalline host
guest complexes of three constitutionally isomeric host compounds 1
3 featuring two diphenylhydroxymethyl groups attached in different positions to a biphenylylene central moiety is studied. Dependent on the connection mode (2,20 -, 3,30 -, or 4,40 -) with reference to the biphenylylene unit, a distinctly different complex behavior of the host compounds is observed. X-ray crystal structures of the solvent-free hosts are reported including a third polymorph with respect to already known polymorphous structures. The crystal structures of eight host
guest complexes of 1
3, including a pair of complexes differing only in the host/guest stoichiometry, are described and comparatively discussed covering the structures of known complex species of the isomeric hosts. Correlations between the constitutional isomerism of the host molecules and their conformational as well as packing structures in the crystalline state, both in unsolvated and solvent complexed form, are demonstrated providing potential usefulness in the future design of crystalline host
guest complexes.

’ INTRODUCTION Molecules comprising two diphenylhydroxymethyl moieties attached to a rigid central unit follow the construction principle of a well-developed class of crystalline host compounds commonly known as “diol hosts”.1 Because of their bulky structure including the hydroxyl groups, they readily form inclusion compounds with a variety of guest molecules.2,3 Typical examples of this category of host molecules are the “wheel-and-axle” compounds,4,5 being distinguished by the attachment of diphenylhydroxymethyl moieties to both ends of a linear spacer unit consisting of ethynylene or arylene units or combinations of both. Using these hosts make possible selective guest inclusions, involving the differentiation of constitutional and stereo isomers.2,3,6 As to the host molecules containing a biphenylylene central unit, the three isomeric species 1
3 (Scheme 1) can be formulated, differing in the position of the hydroxylic substituents and thus also in the molecular geometry being strongly bent (1), less strongly bent (2), and linear (3) around the central unit. While the behavior of these three compounds to form crystalline host
guest complexes has been studied in detail,7 remarkably X-ray crystal structures of respective complexes are only described for the host molecules 1, including pure acetone8 as well as ethyl acetate and different carboxylic acids as guest species in hydrated forms,9 and 3 with acetone, acetophenone, 1,4-dioxane, and p-xylene.10 The plain host compound 3 is also reported to yield two conformationally polymorphous structures when crystallized from diethyl ether or o-xylene, respectively,7 but compound 2 is new territory with reference to determination of crystal structures. r 2011 American Chemical Society

Except for that and based on a generic angle of sight, a challenge is to learn the effect of the different linkage modes being present in the host molecules 1
3 on both the selectivity of complex formation and the crystal structures of the formed host
guest complexes, in particular if the guests correspond or are comparable species. Hence, we report here on the results of a crystallization study of 1
3 from equimolar two-component solvent mixtures and give an account of an extensive series of new crystal structures involving host
guest complexes of 1
3 (Scheme 1) and also the free host compounds. All this together should enable the intended comparative estimation of the inclusion behavior of 1
3 dependent on the different linkage modes of the host framework, that is, between diphenylhydroxymethyl and biphenylylene units.

’ RESULTS AND DISCUSSION Inclusion Properties of the Host Compounds 1
3. A variety of solvents have previously been used to test the inclusion properties of 1
3, showing some obvious differences for the constitutionally isomeric host compounds both regarding the solvents being included and also the host/guest stoichiometric ratios being realized.7
10 For instance, 1 and 3 were found as rather effective for the inclusion of alcohols, while 2 is inferior in this respect.7 Moreover, the hosts 2 Received: June 14, 2011 Revised: August 30, 2011 Published: September 20, 2011 5275

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Crystal Growth & Design Scheme 1. Chemical Structures of the Compounds Studied

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Table 1. Selective Formation of Host
Guest Complexes from Two-Component Solvent Mixture (Host/Guest-1/ Guest-2 Stoichiometric Ratios)a host compound solvent mixture (1: 1, v/v)

1

2

3

MeOH/THF

2:1:0

1:1:0

2:1:2

MeOH/1,4-dioxane

2:1:0

1:0:1

1:0:2

MeOH/acetonitrile

1:3:0

1:1:0

1:1:0

MeOH/acetone

1:1:0

2:1:0

1:1:0

MeOH/DMSO EtOH/THF

2:1:0 1:1:0

1:0:1 2:1:0

1:0:2 1:1:0

i-PrOH/acetone

2:1:0

1:0:1

1:1:0

i-PrOH/2-cyclopenten-1-one

2:1:0

1:0:1

1:0:2

i-PrOH/2-cyclohexen-1-one

b

1:0:1

1:0:1

acetonitrile/acetone

2:1:0

1:0:2

1:2:0

acetonitrile/1,4-dioxane

2:0:1

1:0:1

1:0:1

1,4-dioxane/THF

2:1:0

1:1:0

1:2:0

a

See experimental for the preparation of the crystalline host
guest complexes. b Difficult to crystallize.

and 3 seem to prefer a 1:2 host/guest stoichiometric ratio in the inclusion compounds, as contrasted with 1 mostly demonstrating a 1:1 or even less solvent containing a 2:1 stoichiometric ratio which has been ascribed the formation of an intramolecular hydrogen bond causing paralyzation of one of the hydroxy groups of 1 for guest binding.8,9 The host compound 1 is further described to specifically form hydrated complexes with low molecular weight carboxylic acids and corresponding esters,9 aside from other distinctive marks between 1
3 specified in the literature.7
10 However, all these previous results of inclusion behavior have been obtained via crystallization from pure solvents, whereas inclusion selectivity studies of 1
3 based on crystallization from two component solvent mixtures have not been carried out yet, although being of higher significance for the problem. This has now been investigated with the results obtained from 12 different solvent mixtures as summarized in Table 1. The data show remarkable features. A characteristic of the host 1 is that from all solvent mixtures containing an alcohol as one of the components always the alcohol is included, indicating the preferred inclusion of proton donor solvents. In the category of dipolar aprotic solvent mixtures, acetonitrile is generally preferred to acetone but dioxane to acetonitrile and also to THF. A special case is shown with 3 when crystallized from MeOH/ acetonitrile in that a stoichiometric ratio of 2:1:2 is analyzed, suggesting either the potential formation of a mixed solvent inclusion or a respective mixture of two separate solvent inclusions. With reference to the host/guest stoichiometric ratios of the isolated complexes, a distinction between 1 and 2, 3, similar to the pure solvent crystallization experiments, is perceptible since the complexes of 1 prefer a 2:1 stoichiometric ratio, while 2 favors 1:1 stoichiometry and 3 is balanced between 1:1 and 1:2 stoichiometric ratios, pointing to a causal relation as mentioned before. However, in some cases the stoichiometric ratios found for the respective complexes obtained from pure solvent and mixed solvent experiments differ. This is not an unusual result considering different solvent polarities and the second solvent species serving function as a crystallization additive giving rise to the formation of complexes that do not differ in the kind of components but in the ratio they are contained (sometimes termed pseudopolymorphic11 or solvatomorphic12 structures being under dispute).13,14

Nevertheless, it is generally to be supposed that the inclusion abilities of the host compounds 1
3 are intimately related to the constitutional isomerism of their framework structures, that is, having the bulky diphenylhydroxymethyl groups attached in 2,20 -, 3,30 -, or 4,40 -positions to the biphenyl core, respectively, challenging the study of selected crystal structures. X-ray Single-Crystal Structures. In order to enable a reasonable response to the raised question, crystalline host
guest complexes formed of different hosts but with the same guest, if possible, are preferential subjects of the intended comparative study. Along these lines, including the crystal structures already known from the literature [1 3 acetone (2:1),8 1 3 HCOOH 3 H2O (1:1/2:1),9 1 3 CH3COOH 3 H2O (1:1/2:2/3),9 1 3 C2H5COOH 3 H2O (1:ca. 1/2:2/3),9 1 3 C3H7COOH 3 H2O (1:1/3:1),9 1 3 CH3COOC2H5 3 H2O (1:1/3:1/2),9 3 3 acetone (1:2),10 3 3 acetophenone (1:2),10 3 3 1,4-dioxane (1:2),10 3 3 p-xylene (4:7)10], crystal structures of the following complexes have been studied by X-ray diffraction technique: 1 3 EtOH (1:1) (1a), 2 3 acetone (1:1) (2a), 2 3 acetone (1:2) (2b), 2 3 2-cyclopenten-1-one (1:1) (2c), 2 3 CH3COOH (1:1) (2d), 3 3 EtOH (1:2) (3a), 3 3 i-PrOH (1:2) (3b), and 3 3 CH3COOH (1:2) (3c). Thus, the complexes of 1
3 with acetic acid, of 1 and 3 with ethanol, and of 2 and 3 with acetone comply with the above set criterion of a direct structural comparison while others serve as discussion support. Another interesting point refers to a comparison of the unsolvated host structures between each other and similarly between a respective host and corresponding host
guest complexes. These unsolvated structures of 1
3 have also been solved, with that of 3 adding a third new polymorph to the two already existing polymorphs of 3.7 ORTEP drawings of the molecular structures and the packing diagrams are shown in Figures 1
8. Crystallographic data, including packing density [KPI-index15 (%)] and potential solvent accessible area (Å3/%), selected conformational parameters and information regarding hydrogen bond interactions, are listed in Tables 2
4. The conformation of the host molecules can be described by a set of dihedral angles between the aromatic rings, which are designated as A
F in the figures showing the molecular illustrations. 5276

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Crystal Growth & Design

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Figure 1. Molecular structures of 1 (a), 2 (b), and 3 (c). Thermal ellipsoids are drawn at 40% probability level. C
H 3 3 3 O and O
H 3 3 3 O type hydrogen bonds are displayed as broken, O
H 3 3 3 π contacts as broken double lines.

Crystal Structure Description. Guest Free Host Compounds 1
3. Crystallization of 1 from chlorocyclohexane yields

a solvent-free crystal structure of the space group P1 with two independent molecules in the asymmetric part of the unit cell 5277

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Figure 2. Packing excerpts of the crystal structures of 1 (a), 2 (b), and 3 (c) including specification of coordinating atoms. C
H 3 3 3 O and O
H 3 3 3 O type hydrogen bonds are displayed as broken, O
H 3 3 3 π and C
H 3 3 3 π contacts as broken double lines. Oxygen atoms are marked as dotted circles. 5278

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Crystal Growth & Design

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Figure 3. Structure of the hexameric aggregate of host (gray) and guest (black, bold) molecules in 1a with labeling of relevant atoms. The arene hydrogens are omitted for clarity. Oxygens are displayed as dotted circles. Broken lines represent hydrogen bond interactions.

Figure 4. Chain structure of the complexes 2a (a) and 2b (b) with labeling of relevant atoms. The arene hydrogens are omitted for clarity. Oxygens are displayed as dotted circles. Broken lines represent hydrogen bond interactions.

[Figure 1a]. The geometric features of the molecules are similar, which is reflected by twist angles of 84.6(1) and 84.9 (1)°

between the rings of the central biphenyl part and interplanar angles of 72.6(1)
78.7(1)° formed by the pairs of terminal 5279

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Crystal Growth & Design

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Figure 5. Chain structure of the complex 2c with labeling of relevant atoms. The arene hydrogens are omitted for clarity. Oxygens are displayed as dotted circles. Broken lines represent hydrogen bond interactions.

Figure 6. Chain structure of the complex 2d with labeling of relevant atoms. The arene hydrogens are omitted for clarity. Oxygens are displayed as dotted circles. Broken lines represent hydrogen bond interactions.

Figure 7. Chain structure of the complexes 3a (a) and 3b (b) with labeling of relevant atoms. The arene hydrogens are omitted for clarity. Oxygens are displayed as dotted circles. Broken lines represent hydrogen bond interactions.

aromatic rings. The conformation of the molecules is fixed by an intramolecular hydrogen bond between the hydroxy groups [O(1)
H(1) 3 3 3 O(2) 1.93 Å, 163°, O(1A)
H(1A) 3 3 3 O(2A) 1.95 Å, 164°] and a relatively strong C
H 3 3 3 O interaction13 [C(12)
H(12) 3 3 3 O(1) 2.32 Å, 101°, C(12A)
H(12A) 3 3 3 O(1A) 2.33 Å, 101°], which are also observed in reported

complex structures of 1.8,9 The distances of the hydroxy hydrogens H(2) and H(2A) to the centers of neighboring aromatic rings indicate the presence of O
H 3 3 3 π interactions [O(2)
H(2) 3 3 3 centroid(C) 2.72 Å, 140°, O(2A)
H(2A) 3 3 3 centroid(C0 ) 2.63 Å, 150°). Thus, all strong donors and acceptors are used for intramolecular hydrogen bonding. The packing structure of 5280

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Crystal Growth & Design

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Figure 8. Chain structure of the complex 3c with labeling of relevant atoms. The arene hydrogens are omitted for clarity. Oxygens are displayed as dotted circles. Broken lines represent hydrogen bond interactions.

1 (Figure 2a) (see also Figure S1, Supporting Information) features C
H 3 3 3 O bonded supramolecular strands with the oxygens O(1) and O(1A) acting as acceptors [d(H 3 3 3 O) 2.52, 2.36 Å]. Interstrand association is accomplished by weaker C
H 3 3 3 O contacts16 involving the hydroxy oxygens O(2) and O(2A) [d(H 3 3 3 O) 2.54, 2.45 Å]. Crystallization of 2 from propionic acid yields solvent-free crystals of the monoclinic space group P21/n with the unit cell containing one-half of the molecule. A perspective view of the molecular structure is displayed in Figure 1b. According to inversion symmetry, the biphenyl unit of the molecule is perfectly planar, while the phenyl rings A and B are inclined at angles of 73.8 and 78.9° with respect to the biphenyl plane. The steric requirements of the bulky molecular fragments prevent molecular association by conventional hydrogen bonding, so that the crystal structure is primarily stabilized by weak O
H 3 3 3 π interactions16 [O(1)
H(1) 3 3 3 centroid(C), 2.71 Å, 157°] and C
H 3 3 3 π contacts17 [C(3)
H(3) 3 3 3 C(16) 2.89 Å, 155°; C(16)
H(16) 3 3 3 C(5), 2.94 Å, 174°]. An excerpt of the crystal structure showing the mode of noncovalent bonding is presented in Figure 2b (see also Figure S2, Supporting Information). Crystal structures of 3 in the unsolvated state have already been described in two polymorphic forms,7 that is, the α1- and the α2-form obtained by evaporation solutions of 3 in Et2O and o-xylene, respectively, of which Et2O is a proton acceptor and o-xylene is a nonpolar solvent. In the course of our investigations, we found a third polymorph of unsolvated 3 denoted as the α3form. The colorless crystals obtained from propionic acid, being a strong proton donor and acceptor molecule, have the monoclinic space group P21/c with one molecule in the asymmetric part of the unit cell (Figure 1c). The conformation and the packing structure of the α3-polymorph significantly differ from those of the α1- and α2-form of 3, which crystallize in the space group C2/c and P1, respectively. In the present structure, the aromatic rings of the biphenyl unit adopt a twist angle of 39.4(1)°, whereas the dihedral angles formed by the pairs of aromatic rings A/B and E/F are 76.3 and 76.6°. Furthermore, the molecule is slightly bent along the biphenyl axis. The torsion angles given by the atomic sequences C(14)
C(13)
O(1)
H(1) and C(23)
C(26)
O(2)
H(2) are 173.5(1) and
178.0(1)°; that is, the two hydroxy groups adopt a trans orientation, similar to but not identical to the conformation of 3 in α1. Thus, α3 represents a third conformational polymorph of 3. A superposition of the molecular geometries of 3 regarding the polymorphic structures

α1, α2, and α3, illustrating the conformational differences, is depicted in Scheme 2. The packing structure of 3 lacks strong hydrogen bonds. Instead, the hydroxy hydrogens are engaged in intermolecular O
H 3 3 3 π interactions [Figure 2c, see also Figure S3, Supporting Information]. Moreover, a relatively strong hydrogen bond exists between oxygen O(2) and an aryl hydrogen of an adjacent molecule [C(36)
H(36) 3 3 3 O(2) 2.45 Å, 153°]. Ethanol Complex 1a [1 3 EtOH (1:1)]. In the crystal structure of 1a, which has the space group R3 (Z = 18), the host molecule has been found to assemble into similar hexamer units as in related complexes of 1 containing various carboxylic acids,9 ethyl acetate,9 and acetone8 as guest species. Because of the given space group, the representative structure element of 1a features trigonal symmetry (point group C3i) and is composed of six host and six ethanol molecules (Figure 3) held together by O
H 3 3 3 O hydrogen bonds [d(O 3 3 3 O) 2.591(2)
2.889(2) Å] and C
H 3 3 3 π(arene) contacts.17 Within this structural entity, a cyclic array of solvent molecules resides in a cavity left by the hexameric assembly of host molecules. Although the data collection was carried out at low temperature [93(2) K], the hydrocarbon part of the disordered alcoholic guest (sof: 0.63, 0.37) proved to be difficult to model indicating a high degree of conformational freedom. In the crystal structure, the hexamer host
guest aggregates are packed along the c-axis in a columnar fashion (Figure S4, Supporting Information). Host
Guest Complexes 2a
2d. Crystal growing of 2 from two solvent mixtures each containing acetone as solvent component resulted in the discovery of two complexes, 2a and 2b, which have the monoclinic space group C2/c (Z = 4) but differ in their host/guest stoichiometric ratios. The polymorph 2a, which was obtained from a i-PrOH/acetone solvent mixture, has been found to crystallize as a 1:1 host
guest complex. In the crystal structure, the acetone molecules reside on the 2-fold symmetry axis, while the host molecules occupy symmetry centers. Thus, the biphenyl part of the host adopts planarity. The polymorph 2b, which was obtained from an acetonitrile/acetone mixture, represents a 1:2 host
guest complex. In the crystal structure, the host molecule has C2-symmetry while the acetone molecule is located in a general position. In this complex, the rings of the biphenyl unit are twisted at an angle of 45.6(1)°. The cell parameters of the polymorphs 2a and 2b suggest differences regarding the packing patterns and the modes of molecular association. A common structural feature of the crystal structures can be seen 5281

dx.doi.org/10.1021/cg200750q |Cryst. Growth Des. 2011, 11, 5275–5288

16.2209(8)

19.8491(10) 113.806(2)

97.206(3)

90.329(2)

2809.2(2)

4

1096

1.226

b (Å)

c (Å) α (°)

β (°)

γ (°)

V (Å3)

Z

F(000)

Dc (Mg m
3)

5282

14821

35.4017(7)

6484


15/15


38/45,
45/44,

1.2
26.9

37344

93(2)

0.077

1.250

5400

18

13500.4(8)

120.0

90.0

12.4385(6) 90.0

35.4017(7)

0.900

0.29/
0.29

66.8

S (= goodness of fit on F2)

final ΔFmax/ΔFmin (e Å
3)

KPI-index15 (%)

per unit cell (Å3/%)c

potential solvent accessible area

area per unit cell (Å3/%)b

potential solvent accessible

0.0586 0.1670

R(= Σ|ΔF|/Σ|Fo |) wR on F2

final R-Indices

[I > 2σ(I)]

725

9350

no. of F values used

+ 0.3630P)]


1

[σ2(Fo2) + (0.0681P)2

no. of refined parameters

weighting expression wa

1312.3/9.7

103.0/0.7

68.9

0.52/
0.51

1.048

0.0517 0.1590

4834

395

+ 16.6858P)]


1

[σ2(Fo2) + (0.0875P)2

0.0791 0.0442 Rint refinement calculations: full-matrix least- squares on all F2 values

no. of unique reflections


13/11,
22/22,


27/27

1.4
29.0

within the θ-limit (°)

no. of collected reflections

index ranges ( h, ( k, ( l

153(2)

68337

temperature (K)

0.074

9.6308(4)

a (Å)

μ (mm
1) data collection

P21/n

R3

P1

space group

68.6

0.25/
0.27

0.950

0.0618 0.1800

1291

182

+ 0.9881P)]


1

[σ2(Fo2) + (0.0799P)2

0.0772

2403


29/29


22/22,
11/10,

2.4
25.1

9217

153(2)

0.076

1.261

548

2

1366.4(2)

90.0

97.748(5)

15.5210(14) 90.0

9.9550(9)

8.9247(7)

monoclinic

trigonal

triclinic

C38H30O2 3 C2H6O

crystal system

564.69

C38H30O2

518.62

2

C38H30O2

1a

formula weight

1

empirical formula

compound

Table 2. Crystallographic and Structure Refinement Data of the Compounds Studied

479.0/15.4

68.4

0.35/
0.20

1.033

0.0460 0.1278

3210

202

+ 1.9021P)]


1

[σ2(Fo2) + (0.0639P)2

0.0327

4164


29/29


22/22,
11/10,

2.4
29.2

21085

123(2)

0.076

1.234

1224

4

3104.2(4)

90.0

93.114(2)

21.3334(15) 90.0

8.6883(5)

16.7727(12)

C2/c

monoclinic

576.70

C38H30O2 3 C3H6O

2a

849.7/24.6

37.3/1.0

68.5

0.41/
0.28

1.111

0.0424 0.1408

4726

220

+ 1.9829P)]


1

[σ2(Fo2) + (0.0792P)2

0.0217

5551


25/25


42/42,
11/11,

1.7
31.1

32220

90(2)

0.077

1.220

1352

4

3455.63(10)

90.0

125.718(1)

17.7056(3) 90.0

8.1932(1)

29.3400(5)

C2/c

monoclinic

634.78

C38H30O2 3 2C3H6O

2b

124.6/16.1

70.9

0.37/
0.24

0.964

0.0372 0.0999

3516

418

+ 0.9902P)]


1

[σ2(Fo2) + (0.0846P)2

0.0303

3891


14/14


11/11,
12/12,

2.0
28.4

15706

123(2)

0.079

1.290

318

1

773.44(2)

109.719(1)

102.808(1)

10.7663(2) 98.617(1)

9.1849(2)

8.7878(1)

P1

triclinic

600.72

C38H30O2 3 C5H6O

2c

168.5/11.6

71.8

0.39/
0.38

1.055

0.0747 0.2317

5400

401

+ 6.0710P)]
1

[σ2(Fo2) + (0.0650P)2

0.0354

6414


18/20


12/12,
13/13,

1.4
27.1

26043

100(2)

0.084

1.320

612

2

1455.97(8)

68.249(2)

72.930(2)

15.8759(5) 71.768(2)

10.6279(4)

9.9861(3)

P1

triclinic

578.67

C38H30O2 3 C2H4O2

2d

Crystal Growth & Design ARTICLE

dx.doi.org/10.1021/cg200750q |Cryst. Growth Des. 2011, 11, 5275–5288

a

95.884(2) 90.0

β (°) γ (°)

0.076

Dc (Mg m
3)

μ (mm
1)


14/13,
19/16,

5283

0.0662

Rint

3037

no. of F values used [I > 2σ(I)]

0.17/
0.20

S (= goodness of fit on F2)

final ΔFmax/ΔFmin (e Å
3)

161.2/19.6

68.9

0.30/
0.22

1.026

0.1261

0.0431

3714

262.6/28.6

65.0 35.1/3.8

0.35/
0.18

1.015

0.1258

0.0438

3546

[σ2(Fo2) + (0.0632P)2 + 0.2633P)]
1 221

0.0217

0.0219 [σ2(Fo2) + (0.0659P)2 + 0.2711P)]
1 211

4508


17/17


11/11,
12/12,

2.4
28.3

133(2) 18191

0.072

1.154

342

1

919.09(4)

70.914(1) 69.720(1)

72.312(1)

13.0499(3)

9.2419(2)

4377


15/15

P = (Fo2 + 2Fc2)/3. b Calculated in the presence of the solvent. c Calculated in the absence of the solvent.

area per unit cell (Å3/%)c

potential solvent accessible

area per unit cell (Å3/%)b

68.5

0.991

wR on F2

KPI-index15 (%) potential solvent accessible

0.0470

0.1070

R(=Σ|ΔF|/Σ|Fo |)

final R-indices

[σ2(Fo2) + (0.0405P)2 + 0.3048P)]
1 363

weighting expression wa no. of refined parameters

refinement calculations: full-matrix least- squares on all F2 values

5228

no. of unique reflections


17/17

2.6
29.1

1.8
25.7

within the θ-limit (°)

index ranges ( h, ( k, ( l


12/12,
12/12,

153(2) 27389

0.078

1.233

326

1

822.48(2)

68.335(1) 62.037(1)

86.037(1)

11.5263(3)

9.4354(2)

153(2) 20517

temperature (K) no. of collected reflections

data collection

1096

1.255

F(000)

2744.98(18)

90.0

α (°)

4

14.6698(6)

c (Å)

Z

16.3027(6)

b (Å)

V (Å3)

11.5385(4)

a (Å) 8.8025(2)

triclinic P1

triclinic P1

monoclinic 9.2880(2)

3b C38H30O2 3 2C3H8O 638.81

P21/c

C38H30O2 3 2C2H6O 610.76

3a

space group

3

crystal system

C38H30O2 518.62

empirical formula formula weight

compound

173.6/20.7

68.1

0.24/
0.22

0.998

0.1441

0.0474

4186

[σ2(Fo2) + (0.0869P)2 + 0.2353P)]
1 220

0.0197

4950


16/16


11/13,
13/13,

2.5
30.2

153(2) 20515

0.084

1.264

338

1

839.34(2)

74.738(1) 62.938(1)

74.907(1)

11.3996(2)

9.4081(1)

9.2341(1)

P1

triclinic

C38H30O2 3 2C3H6O 638.72

3c

Crystal Growth & Design ARTICLE

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Table 3. Relevant Conformational Parameters of the Host Molecules in the Compounds Studied compound

1

1a

2

2a

2b

2c

2d

3

3a

3b

3c

A/B

73.3(1)

85.3(1)

89.0(1)

64.7(1)

89.6(1)

83.7(1)

79.1(1)

76.3(1)

83.7(1)

79.8(1)

79.8(1)

A/C

76.4(1)

67.6(1)

88.9(1)

73.8(1)

74.9(1)

70.8(1)

66.0(1)

85.7(1)

64.9(1)

75.8(1)

73.7(1)

B/C

89.4(1)

85.6(1)

69.8(1)

78.9(1)

73.3(1)

82.2(1)

90.0(1)

84.1(1)

82.8(1)

83.1(1)

77.1(1)

C/D

84.6(1)

83.6(1)

5.5(1)

46.0(1)

39.4(1)

D/E

86.5(1)

70.7(1)

88.1(1)

85.8(1)

84.7(1)

D/F

86.4(1)

81.5(1)

73.9(1)

64.3(1)

71.8(1)

E/F A0 /B0

72.6(1) 78.7(1)

82.9(1)

82.8(1)

77.1(1)

76.6(1)

A0 /C0

76.5(1)

B0 /C0

89.3(1)

C0 /D0

84.9(1)

D0 /E0

89.7(1)

D0 /F0

83.0(1)

E0 /F0

74.8(1)

dihedral angles (deg)a

a

Aromatic rings: Ring A: C(1) 3 3 3 C(6); ring B: C(7) 3 3 3 C(12); ring C: C(14) 3 3 3 C(19); ring D: C(20) 3 3 3 C(25); ring E: C(27) 3 3 3 C(32); ring F: C(33) 3 3 3 C(38); Ring A0 : C(1A) 3 3 3 C(6A); ring B0 : C(7A) 3 3 3 C(12A); ring C0 : C(14A) 3 3 3 C(19A); ring D0 : C(20A) 3 3 3 C(25A); ring E0 : C(27A) 3 3 3 C(32A); ring F0 : C(33A) 3 3 3 C(38A).

in the formation of supramolecular strands with an alternating order of host and solvent molecules. Within the zigzag-like chain structure of 2a (Figure 4a), the oxygen of the acetone acts as a bifurcated acceptor for hydrogen bonding with two symmetryrelated host molecules [O(1)
H(1) 3 3 3 O(1G), 1.97 Å, 161°]. Moreover, the oxygen O(1) contributes to host
host association by formation of a weak C
H 3 3 3 O hydrogen bond16 [C(19)
H(19) 3 3 3 O(1), 2.56 Å, 153°]. In the crystal structure, the molecular strands are packed in a parallel fashion (Figure S5, Supporting Information) and connected among one another via C
H 3 3 3 O bonding [C(3)
H(3) 3 3 3 O(1) 2.53 Å, 151°]. The structure of the molecular strand of polymorph 2b (Figure 4b) differs markedly from that of 2a. Within a strand, each host molecule is associated with two acetone molecules. In this arrangement, the solvent oxygen O(1G) acts as a bifurcated acceptor by forming a strong hydrogen bond [O(1)
H(1) 3 3 3 O(1G) 2.00 Å, 165°] and a weaker nonconventional hydrogen bond [C(19)
H(19) 3 3 3 O(1G) 2.43 Å, 153°] to the same host molecule. Moreover, one of the methyl hydrogens of the acetone takes part in C
H 3 3 3 O bonding [C(3G)
H(3G2) 3 3 3 O(1) 2.38 Å, 162°]. Interchain association is accomplished by weak hydrogen bonding involving the oxygen O(1) [C(10)
H(10) 3 3 3 O(1) 2.44 Å, 162°] (Figure S6, Supporting Information). Crystal growing of 2 from 2-cyclopenten-1-one yields the 1:1 host
guest complex 2c of the space group P1 with one host and one molecule of solvent occupying the unit cell, that is, the hydroxy groups of the host participate in a different way in molecular association. The asymmetric binding behavior of the host is also reflected by the torsion angles around the hydroxy groups, which are 52.4(1)° (gauche) and 170.8° (anti) for the atomic sequences C(14)
C(13)
O(1)
H(1) and C(24)
C(26)
O(2)
H(2), respectively. The crystal structure of the complex is composed of supramolecular strands, the structure of which, however, deviate from those of the aforementioned acetone complexes. As illustrated in Figure 5, only the host molecules form continuous hydrogen bonded strands [O(2)
H(2) 3 3 3 O(1) 2.10 Å, 169°] with the solvent molecules being attached in lateral positions [O(1)
H(1) 3 3 3 O(1G) 1.98 Å, 166°]. According to non-centrosymmetry

of the crystal structure, the molecular strands show a unique running direction. As illustrated in the packing diagram of 2c (Figure S7, Supporting Information), the solvent molecules appear to be arranged between pairs of phenyl rings belonging to host molecules of neighboring strands. The coplanar arrangement and a mean distance of 3.5 Å between interacting rings indicate the occurrence of π(CdC) 3 3 3 π(aryl) interactions.18 In the crystal structure of the 1:1 complex of 2 with acetic acid 2d (space group: P1), the asymmetric unit cell contains one host and one molecule of solvent. The twist angle between the rings of the central biphenyl part is 46.0(1)°, whereas the pairs of terminal aromatic rings adopt dihedral angles of 79.1(1) and 77.1(1)°. In a similar fashion as in the crystal structure of 2c, the hydroxy groups of the host molecule are different in their binding state. As illustated in Figure 6, the hydroxy hydrogen H(1) is connected to acetic acid [O(1)
H(1) 3 3 3 O(1G) 2.09 Å, 159°], while H(2) is linked to the hydroxy oxygen of a symmetry related host molecule [O(2)
H(2) 3 3 3 O(1) 2.05 Å, 161°], so that 2:2 host
guest aggregates represent the basic supramolecular aggregates, which are further connected via carboxylic acid dimerization [O(2G)
H(2G) 3 3 3 O(1G) 1.84 Å, 176°] to infinite strands. Molecules of neighboring chains are displaced by ca. 5.3 Å thus realizing a close packing structure (Figure S8, Supporting Information). Host
Guest Complexes 3a
3c. Crystallization of 3 from ethanol and i-PrOH in both cases yields a 1:2 host
guest complex, 3a and 3b, respectively, of the space group P1 with one host and two molecules of solvent in the unit cell. Irrespective of some deviations regarding the cell parameters and molecular geometries (see Tables 2 and 3), which can be attributed to steric effects by the respective solvent species, the crystal structures of 3a and 3b are constructed of the same type of supramolecular strands (Figure 7). Within a strand, the hydroxy group of two host molecules and those of two molecules of the alcoholic guest take part in formation of cyclic O
H 3 3 3 O bonded motifs [d(O 3 3 3 O) 2.717(2)
2.766(2) Å], which can be described by the graph set R44(8).19 Although in both cases the molecular chains are packed in a similar fashion, some structural differences 5284

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Crystal Growth & Design

ARTICLE

Table 4. Distances (Å) and Angles (deg) of Hydrogen Bond Type Interactions of the Compounds Studied D
H 3 3 3 A

symmetry operator

D3 3 3A

H3 3 3A

D
H 3 3 3 A

1 O(1)
H(1) 3 3 3 O(2) O(1A)
H(1A) 3 3 3 O(2A)

x, y, z

2.746(2)

1.93

163

x, y, z

2.765(2)

1.95

164

C(10)
H(10) 3 3 3 O(2) C(10A)
H(10A) 3 3 3 O(2A)

1 + x, y, z

3.261(2)

2.54

133


1 + x, y, z

3.191(2)

2.47

133

C(17A)
H(17A) 3 3 3 O(1) C(12A)
H(12A) 3 3 3 O(1) C(12)
H(12) 3 3 3 O(1A) C(17)
H(17) 3 3 3 O(1A)

O(2)
H(2) 3 3 3 centroid(C)a O(2A)
H(2A) 3 3 3 centroid(C0 )a

C(31)
H(31) 3 3 3 centroid(F)a 1a

x, 1 + y, z

3.305(2)

2.36

171

x, y, z

2.681(2)

2.33

101

x, y, z x, y, z

3.305(2) 2.676(2)

2.36 2.32

171 101

x, y, z

3.402(3)

2.72

140

x, y, z

3.382(3)

2.63

150


x, 1
y,
1
z

3.722(3)

2.83

157 172

x, y, z

2.697(2)

1.86

x
y, x, 1
z

2.889(2)

2.06

168

O(1GA)
H(1GA) 3 3 3 O(1) O(2)
H(2) 3 3 3 O(1G)

x
y, x, 1
z x, y, 1 + z

2.743(2) 2.751(2)

1.90 1.91

177 178

O(2)
H(2) 3 3 3 O(1GA) C(3)
H(3) 3 3 3 centroid(A)a

x, y, 1 + z

2.591(2)

1.76

170

x,
x + y, 1
z

3.733(3)

2.86

154

x
y, x, 1
z

3.669(3)

2.84

147

O(1)
H(1) 3 3 3 O(2) O(1G)
H(1G) 3 3 3 O(1)

C(16)
H(16) 3 3 3 C(9)b 2

a

O(1)
H(1) 3 3 3 centroid(C) C(3)
H(3) 3 3 3 C(16) C(16)
H(16) 3 3 3 C(5) 2a O(1)
H(1) 3 3 3 O(1G) C(3)
H(3) 3 3 3 O(1)

C(19)
H(19) 3 3 3 O(1) C(1G)
H(1G3) 3 3 3 centroid(B)a 2b O(1)
H(1) 3 3 3 O(1G) C(1)
H(19) 3 3 3 O(1G) C(10)
H(10) 3 3 3 O(1) C(3G)
H(3G1) 3 3 3 O(1)

C(3G)
H(3G2) 3 3 3 centroid(A)a 2c

2
x, 1
y, 2
z

3.499(3)

2.71

157

2.5
x,
0.5 + y, 1.5
z

3.768(2)

2.89

155

0.5 + x, 1.5
y, 0.5 + z

3.892(2)

2.94

174

x, y, z

2.775(2)

1.97

161

0.5
x,
0.5 + y, 0.5
z

3.389(2)

2.53

151


x, y, 0.5
z

3.433(2)

2.56

153

x, y, z

3.592(3)

2.84

134

x, 1
y,
0.5 + z

2.817(2)

2.00

165

x, 1
y,
0.5 + z x,
1 + y, z

3.307(2) 3.357(2)

2.43 2.44

153 162

0.5
x,
0.5 + y, 0.5
z

3.329(2)

2.38

162

x, y, z

3.616(3)

2.79

142

x, y, z

2.804(2)

1.98

166


1 + x,
1 + y,
1 + z

2.933(2)

2.10

169

O(1)
H(1) 3 3 3 O(1G) O(2)
H(2) 3 3 3 O(1) C(9)
H(9) 3 3 3 O(1G) C(34)
H(34) 3 3 3 O(1) C(6)
H(6) 3 3 3 O(2)

x, 1 + y, z

3.387(2)

2.51

154


1 + x,
1 + y,
1 + z 1 + x, 1 + y, 1 + z

3.607(2) 3.655(2)

2.71 2.74

158 162

C(4G)
H(4G) 3 3 3 O(2) C(19)
H(19) 3 3 3 O(1G)

x, y, 1 + z

3.406(2)

2.60

142

x, y, z

3.183(2)

2.47

132

x, 1 + y, z

3.640(3)

2.74

158


1 + x,
1 + y, z

3.638(3)

2.83

138

1+x, y, z

3.512(3)

2.73

140


1 + x, y, z

3.549(3)

2.74

143

x,
1 + y, z

3.715(3)

2.83

154

C(10)
H(10) 3 3 3 centroid(A)a C(3G)
H(3G2) 3 3 3 C(10)b

C(4)
H(4) 3 3 3 centroid(C)a C(36)
H(36) 3 3 3 centroid(D)a

C(30)
H(30) 3 3 3 centroid(F)a 2d O(1)
H(1) 3 3 3 O(1G) O(2G)
H(2G) 3 3 3 O(1G) O(2)
H(2) 3 3 3 O(1) C(23)
H(23) 3 3 3 C(11)b C(11)
H(11) 3 3 3 C(37)b

x, y, z

2.890(2)

2.09

159

1
x, 1
y,
z

2.677(2)

1.84

176

1
x, 2
y,
z

2.855(2)

2.05

161

2
x, 2
y,
z

3.839(3)

2.91

166

2
x, 2
y,
z

3.723(3)

2.87

150

5285

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Crystal Growth & Design

ARTICLE

Table 4. Continued D
H 3 3 3 A 3 O(1)
H(1) 3 3 O(2)
H(2) 3 3

b

3 C(32) a 3 centroid(A)

C(36)
H(36) 3 3 3 O(2) C(12)
H(12) 3 3 3 centroid(E)a 3a O(1)
H(1) 3 3 3 O(1G) C(15)
H(15) 3 3 3 O(1G) O(1G)
H(1G) 3 3 3 O(1) C(12)
H(12) 3 3 3 C(18)b C(2G)
H(2G3) 3 3 3 centroid(C)a

symmetry operator

D3 3 3A

H3 3 3A

D
H 3 3 3 A

1 + x, 0.5
y, 0.5
z

3.222(3)

2.45

153


1 + x, 0.5
y, 0.5 + z

3.665(3)

2.90

153


x,
0.5 + y, 1.5
z

3.323(3)

2.45

153

1+x, 0.5-y,
0.5+z

3.562(3)

2.71

150

x, y, z

2.719(2)

1.89

169

x, y, z

3.363(2)

2.47

156


x, 1
y, 1
z 1
x, 1
y,
z

2.717(2) 3.694(3)

1.95 2.82

151 154


x, 1
y, 1
z

3.643(3)

2.77

150

3b x, y, z

2.729(2)

1.92

160


x, 1
y,
z

2.766(2)

1.94

170

C(12)
H(12) 3 3 3 C(16)b 3c


x, 1
y, 1
z

3.590(3)

2.70

156

O(1)
H(1) 3 3 3 O(1G) O(2G)-H(2G) 3 3 3 O(1)

x, y, z 2
x,
y,
z

2.717(2) 2.678(2)

1.90 1.84

164 177

1
x,
y, 1
z

3.612(3)

2.89

134

1
x,
y, 1
z

3.579(3)

2.71

152

O(1)
H(1) 3 3 3 O(1G) O(1G)
H(1G) 3 3 3 O(1)

a

C(18)
H(18) 3 3 3 centroid(A)a C(12)
H(12) 3 3 3 C(18)b

Means center of the aromatic ring. Ring A: C(1) 3 3 3 C(6), ring B: C(7) 3 3 3 C(12), ring C: C(14) 3 3 3 C(19), ring D: C(20) 3 3 3 C(25), ring E: C(27) 3 3 3 C(32), ring F: C(33) 3 3 3 C(38); ring A0 : C(1A) 3 3 3 C(6A), ring B0 : (7A) 3 3 3 C(12A), ring C0 : C(14A) 3 3 3 C(19A), ring D0 : C(20A) 3 3 3 C(25A), ring E0 : C(27A) 3 3 3 C(32A), ring F0 : C(33A) 3 3 3 C(38A). b To achieve a reasonable hydrogen bond geometry, an individual carbon atom instead of the ring centroid was chosen as an acceptor for CH/π interaction.

Scheme 2. Superposition of the Molecular Structures of the Polymorphic Forms α1
α3 of 3

exist. In the crystal structure of 3a, the supramolecular chains extend in the direction of the c-axis (Figure S9, Supporting Information), which means that the distance between consecutive host molecules is 11.526 Å. In the structure of the complex 3b, the molecular strands, however, run parallel to the crystallographic 011 plane (Figure S10, Supporting Information) corresponding to a distance of 13.506 Å between consecutive host molecules, which may explain the reduced degree of intermolecular interaction. Crystal growing of 3 from glacial acetic acid yields the 1:1 host
guest complex 3c of the space group P1 with Z = 1. Because of the donor/acceptor character of the inclusion components, the crystal structure is constructed of supramolecular chains (Figure 8) in which the cyclic supramolecular synthon of O
H 3 3 3 O bonds follows the graph set R44(12).19 In this pattern, the host hydrogen H(1) is associated to the carbonyl oxygen of acetic acid [O(1)
H(1) 3 3 3 O(1G) 1.90 Å, 164°], while the carboxylic

hydrogen H(2G) is linked to the hydroxy oxygen of the host [O(2G)
H(2G) 3 3 3 O(1) 1.84 Å, 177°]. Intensive nesting of the host molecules of neighboring strands (Figure S11, Supporting Information) allow weak edge-to-face arene interactions.20 Comparative Study of the Crystal Structures. As mentioned at the beginning, the main object of this study is to work out distinctive features between the host behavior of 1
3 being connected with their constitutionally isomeric structures. This involves a detailed comparison including both the presently obtained and already known structures7
10 formed of 1
3. With reference to the structures of the unsolvated host compounds, the following distinctions can be made. While the central biphenyl moieties of the two independent molecules 1 of the asymmetric part of the unit cell are both strongly twisted (≈ 85°), the respective moiety of the molecule 2 is perfectly planar, and the compound 3, depending on the polymorphic form, the biphenyl moieties are staggered with angles ranging from 39 to 45°. Another structural distinction between 1
3 refers to the orientation of the hydroxy groups being in clear synposition in the unsolvated structure of 1, but anti in 2, and in the polymorphs of 3 they are anti (α1),7 syn (α2),7 and anti (α3). Only the syn orientation of the hydroxyl groups in 1 and α2-3 allows the formation of strong O
H 3 3 3 O hydrogen bonding, however, corresponding to the differents attachment of the diphenylhydroxymethyl fragments with different modes of interaction. This is intramolecular in style for 1 and with two intermolecular hydrogen bonds forming a molecular pair in the case of α2-3. The hydrogens of 1 and α2-3 not participating in the conventional hydrogen bonding are involved in the formation of weaker O
H 3 3 3 π contacts,16 again intramolecular in 1 but intermolecular in α2-3. Owing to the shielding effect of the bulky diphenylhydroxymethyl fragment for the formation of an 5286

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Crystal Growth & Design O
H 3 3 3 O hydrogen bond in general, in 2 as well as in the α1 and α3 polymorphs of 3 intermolecular O
H 3 3 3 π interactions are present primarily stabilizing the packing structures. The calculated packing densities [KPI-index15 (%)] of 1, 2, α1-3, α2-3, and α3-3 are 66.8, 68.6, 70.0, 69.0, and 68.5, respectively (Table 2), showing no clearly perceptible correlation with the number and strength of hydrogen bond interactions in the crystals. The host
guest complexes of 1, including the present ethanol complex 1a and all the known complexes of 1 with acetone, formic acid/H2O, acetic acid/H2O, propionic acid/H2O, butyric acid/H2O, ethyl acetate/H2O demonstrate two different kinds of structural conformity.8,9 One, relevant to the molecular conformation, is related to the intramolecular hydrogen bond, also typical of the unsolvated structure of 1. The other, referring to the packing behavior, is the formation of hexameric hydrogen bonded clusters composed of six alternating host and guest molecules, respectively, in a cyclic array of O
H 3 3 3 O interactions. Owing to the nonpolar surface of the hexamer entities, the structures are further stabilized by multiple arene interactions. As a consequence of the constitutional change from 1 to 2, the structures of the complexes formed of 1 and 2 fundamentally differ, in that no longer cyclic hydrogen bonded clusters but hydrogen bonded strands are created, although in a different manner dependent on the nature of the guest molecule. In the complex structure 2a of the acetone inclusion with 1:1 stoichiometry, the acetone molecule acts as a bifurcated hydrogen acceptor in O
H 3 3 3 O hydrogen bonding with two hosts, while in the complex 2b each host molecule is associated with two acetone molecules. Thus, from a balance of hydrogen bonding in the strands, two O
H 3 3 3 O contacts fall to one acetone molecule of 2a, but in 2b it is only one strong O
H 3 3 3 O contact completed by two weaker C
H 3 3 3 O contacts,16 whereas on the part of the host molecules, the same kind of contacts are used in 2a and 2b. This, however, does not coincide with the calculated packing coefficients (2a: 0.69, 2b: 0.68), showing nearly the same densely packed crystal for 2b. In the complex of 2 with 2-cyclopenten-1-one (2c), the host molecules form a continuous O
H 3 3 3 O hydrogen bonded chain with the guest molecules being laterally O
H 3 3 3 O hydrogen bonded to the chain, while in the inclusion complex of 2 with acetic acid (2d) the hydrogen bonded chains consist of alternating pairs of host molecules and carboxylic dimers. A similar construction unit of host dimers has been observed for the packing structure of unsolvated 3 in the α2-form. Thus, dependent on the guest species, host molecules in the inclusion compounds of 2 show a direct interlinkage via hydrogen bonds or use the guest molecules as a connecting link for the formation of supramolecular strands being the decisive feature of the structures. Regarding the known complexes of the host compound 3, supramolecular hydrogen bonded strand formation comprising hosts that alternate with guests is also the predominant building principle of the crystals as long as proton donor
acceptor guest solvents are concerned. This is evidently shown with the structures of 3a and 3b in which the hydroxyl groups of both the host molecule and the guest alcohol form a cyclic tetramer binding motif.21 Similarly, in the acetic acid complex 3c, a typical symmetric, 12-membered hydrogen bonded cycle containing two host hydroxyl and two guest carboxylic groups link the components. By way of contrast, in the previously studied host
guest complexes of 3 with acetone, benzophenone, and 1,4-dioxane,10 being only proton acceptor guest molecules, isolated 1:2 hydrogen bonded host
guest units determine the packing

ARTICLE

structure, and in the known structure of the p-xylene complex of 3,10 the host molecules are hydrogen bonded into tetrameric clusters with the p-xylene molecules accommodating interstitial lattice space. In all the complex structures of 1
3, the hydrogen bonded host
guest aggregates whether being of cyclic, chain, or isolated nature are interlinked, more or less, via weaker apolar contacts. Another interesting aspect of this study is to structurally compare host
guest complexes containing the same guest but constitutionally different hosts. This is met with the acetone complexes [1 3 acetone (2:1), 2 3 acetone (1:1) (2a), 2 3 acetone (1:2) (2b), 3 3 acetone (1:2)] and the acetic acid complexes [1 3 CH3COOH 3 H2O (1:1/2:1), 2 3 CH3COOH (1:1) (2d), 3 3 CH3COOH (1:1) (3c)] of 1
3 as well as the ethanol complexes of 1 and 3 [1 3 EtOH (1:1) (1a), 3 3 EtOH (1:2) (3a)]. Because of the different stoichiometries, it is highly probable that the structures also markedly differ. Actually, in the acetone complex of 1, the acetone molecule by way of its carbonyl oxygen is involved in the formation of the hydrogen bonded hexameric unit typical of the complexes of 1. In the acetone complexes 2a (1:1) and 2b (1:2), the acetone molecules are inserted into hydrogen bonded strands, while in 3 3 acetone (1:2) isolated host
guest units are present. Regarding the host
guest complexes of 1
3 with acetic acid, the facts are similar showing the hexameric unit with additional water molecules engaged in the cluster formation for 1, but strand formation composed of hydrogen bonded host and acetic acid dimers for 2, while in the case of 3, the strands are linked using as a well-known supramolecular synthon the cyclic array of two hydroxyl and two carboxyl groups.22,23 With reference to the ethanol complexes of 1 and 2, the cyclic hexameric cluster formation, being the typical feature of 1, is also observed here and in the case of 3, a tetramer cycle of hydroxyl groups acts as a link in strand formation.

’ CONCLUSION The present study clearly shows that the construction of host molecules using identical subunits, in this case a biphenylylene moiety and two diphenylhydroxymethyl groups, but applying different connection modes, as with the hosts 1
3, leads to distinctly different complex behavior. For instance, this is noticeably manifested with the preferred complexation of alcohols by the host compound 1 while 2 and 3 are inferior in this respect. And what is more, the complexes of 1 prefer a 2:1 host/guest stoichiometric ratio, while 2 favors 1:1 stoichiometry and 3 shows a balance between 1:1 and 1:2 stoichiometric ratios, pointing to a causal relation to the particular structure of the host molecule. Both in the guest free state of 1 as well as in its host
guest complexes, the host molecule is locked in its conformation by a strong intramolecular hydrogen bond leading to a compact geometry with an inner arrangement of hydroxy substituents. This may explain the tendency of the molecule to form cyclic hexameric host
guest aggregates with a hydrophobic periphery which in the crystal structures adopt a columnar packing. Hence, the presence of the intramolecular hydrogen bond in 1 exclusively governs the structural behavior. Also the crystal of the isomeric host compounds 2 and 3 seem to follow a unique construction principle. The stepwise changing from the cluster type molecular geometry of 1 to increasing linear geometry as in 2 and 3 gives rise to more accessible hydroxyl groups not being partly consumed in intramolecular hydrogen bonding. This favors the 5287

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Crystal Growth & Design formation of molecular strands in the structures with 2 and 3 in general. However, dependent on the nature of the guest solvent, the chain structure is characterized by an alternation of host and guest species or is dominated by coordination of host molecules with a lateral arrangement of solvent molecules. Another reasoning derived from this study refers to the occurrence of the complexes 2a and 2b with acetone (1:1 and 1:2 host/guest stoichiometry, respectively) obtained from crystallization of 2 from different solvent mixtures. The point behind the result is that those species of the solvent mixtures, although not involved in the complex formation, can exercise a fundamental controlling effect on the host/guest stochiometry and thus the pattern of molecular association in host
guest crystals. Similar behavior may be expected for other types of constitutionally isomeric host molecules, giving to the results of this study a potential cue of possible usefulness in the future host design and crystal engineering of particular host
guest complexes.

’ EXPERIMENTAL SECTION Materials. The host compounds 1
3 were prepared as described in the literature.7 The solvents were dried prior to use. The competition experiments, specified in Table 1, were carried out on dissolution a fixed quantity of the respective host compound in an equimolar mixture of the two guest solvents under heating, whereby the total host/guest ratio in the solutions was always >100. The crystals which formed on slow cooling were collected and dried. The host/guest stoichiometric ratios were determined by 1H NMR integration. Single crystals of the host
guest complexes (1a, 2a
2d, 3a
3c) were grown by slow evaporation of solutions of the respective host compound in the corresponding solvent or solvent mixture. X-ray Crystallography. The intensity data were collected on a Kappa APEX II diffractometer (Bruker-AXS) with graphite monochromated MoKα radiation (λ = 0.71073 Å) using j and ω scans. Reflections were corrected for background, Lorentz and polarization effects. Preliminary structure models were derived by application of direct methods24 and were refined by full-matrix least-squares calculation based on F2 values for all unique reflections.24 Empirical absorption correction based on multiscans was applied by using the SADABS program.25 All nonhydrogen atoms were refined anisotropically. All hydrogen atoms were included in the models in calculated positions and were refined as constrained to bonding atoms.

ARTICLE

(3) Toda, F. In Inclusion Compounds; Atwood, J. L., Davies, J. E. D., Mac Nicol, D. D., Eds.; Oxford University Press: Oxford, 1991; Vol. 4, pp 126
187. (4) Toda, F.; Akagi, K. Tetrahedron Lett. 1968, 3695–3698. (5) Weber, E. In Molecular Inclusion and Molecular Recognitation Clathrates I; Topics in Current Chemistry; Weber, E., Ed.; SpringerVerlag: Berlin-Heidelberg, 1987; Vol. 140, pp 3
20. (6) Weber, E. In Comprehensive Supramolecular Chemistry; Mac Nicol, D. D., Toda, F., Bishop, R., Eds.; Elsevier: Oxford, 1996; Vol. 6, pp 535
592. (7) Weber, E.; Skobridis, K.; Wierig, A.; Nassimbeni, L, R.; Johnson, L. J. Chem. Soc., Perkin Trans. 2 1992, 2123–2130. (8) Toda, F.; Akira, K; Toyotaka, R.; Yip, W.-H.; Mak, T. C. W. Chem. Lett. 1989, 1921–1924. (9) Cs€oregh, I.; Hirano, S; Toyota, S.; Bombicz, P.; Toda, F. CrystEngComm 2004, 6, 60–69. (10) Johnson, L.; Nassimbeni, L.; Weber, E.; Skobridis, K. J. Chem. Soc., Perkin Trans. 2 1992, 2131–2136. (11) Ibragimov, B. T. CrystEngComm 2007, 9, 111–118. (12) Wei, W.; Wang, G.; Zhang, Y.; Jiang, F.; Wu, M.; Hong, M. Chem.—Eur. J. 2011, 17, 2189–2198. (13) Desiraju, G. R. Cryst. Growth Des. 2008, 8, 3–5. (14) Bernstein, J. Cryst. Growth Des. 2005, 5, 1661–1662. (15) Kitaigorodskii, A. I. Molecular Crystals and Molecules; Academic Press: New York, 1973. (16) Desiraju, G. R.; Steiner, T. The Weak Hydrogen Bond; Oxford University Press: New York, 1999. (17) Nishio, M.; Umezawa, Y.; Honda, K.; Tsuboyama, S.; Suezawa, H. CrystEngComm 2009, 11, 1757–1788. (18) Dance, I. In Encyclopedia of Supramolecular Chemistry; Atwood, J. L., Steed, J. M., Eds.; Dekker: New York, 2004; pp 1076
1092. (19) Bernstein, J.; Davies, R. E.; Shimoni, L.; Chang, N.-L. Angew. Chem., Int. Ed. 1995, 34, 1555–1573. (20) Ringer, A. L.; Sinnokrot, M. O.; Lively, R. P.; Sherrill, C. D. Chem.—Eur. J. 2006, 12, 3821–3828. (21) Cs€oregh, I.; Gallardo, O.; Weber, E.; D€ orpinghaus, N. J. Chem. Soc., Perkin Trans. 2 1994, 303–308. (22) Burrows, A. D. In Supramolecular Assembly via Hydrogen Bonds I; Structure and Bonding; Mingos, D. M. P., Ed.; Springer-Verlag: BerlinHeidelberg, 2004; Vol. 108, pp 55
96. (23) Weber, E. J. Mol. Graphics 1989, 7, 12–27. (24) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112–122. (25) Sheldrick, G. M. SADABS, Siemens Area Detector Absorption Correction Program; University of G€ ottingen: G€ottingen, Germany, 2004.

’ ASSOCIATED CONTENT

bS

Supporting Information. X-ray crystallographic data in CIF format for the structures reported in this paper along with the packing diagram of compounds 1
3, 1a, 2a
2d, and 3a
3c (Figures S1
S11). This material is available free of charge via the Internet at http://pubs.acs.org.

’ AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected]; fax: (+49) 373139 3170.

’ REFERENCES (1) Bishop, R. Chem. Soc. Rev. 1996, 25, 311–319. (2) Toda, F. In Comprehensive Supramolecular Chemistry; Mac Nicol, D. D., Toda, F., Bishop, R., Eds.; Elsevier: Oxford, 1996; Vol. 6, pp 465
516. 5288

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