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Supramolecular Chemistry

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Supramolecular assemblies through host–guestinteractions of 18-crown-6 with ammoniumsalts: geometric effects of amine groups on thehydrogen-bonding architectures

Shi Wang, Xue-Hua Ding, Yong-Hua Li & Wei Huang

To cite this article: Shi Wang, Xue-Hua Ding, Yong-Hua Li & Wei Huang (2015) Supramolecularassemblies through host–guest interactions of 18-crown-6 with ammonium salts: geometriceffects of amine groups on the hydrogen-bonding architectures, Supramolecular Chemistry,27:4, 213-223, DOI: 10.1080/10610278.2014.964238

To link to this article: http://dx.doi.org/10.1080/10610278.2014.964238

Published online: 01 Oct 2014.

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Supramolecular assemblies through host–guest interactions of 18-crown-6 with ammoniumsalts: geometric effects of amine groups on the hydrogen-bonding architectures

Shi Wanga*, Xue-Hua Dinga, Yong-Hua Lia* and Wei Huanga,b

aKey Laboratory for Organic Electronics & Information Displays (KLOEID), Institute of Advanced Materials (IAM), Nanjing Universityof Posts & Telecommunications, Nanjing 210023, P.R. China; bJiangsu-Singapore Joint Research Center for Organic/Bio-Electronics &

Information Displays, Institute of Advanced Materials, Nanjing University of Technology, Nanjing 211816, P.R. China

(Received 7 August 2014; accepted 8 September 2014)

A series of ammonium salts were introduced into the self-assembly with the same host 18-crown-6, yielding five

supramolecular salts, that is [(C4H6N3)·(18-crown-6)2]þ·(I23 ) (1), [(C6H14N)·(18-crown-6)]

þ·(I23 ) (2), [(C6H14N)·(18-

crown-6)]þ·(FeCl24 ) (3), [(C6H10N2)·(18-crown-6)]2þ·(ClO2

4 )2 (4) and [(C6H8NO2)·(18-crown-6)]þ·[(C7H3N2O6)

2]2 (5).

Structural analysis indicates that different kinds of guest amines, ranging from chain-like aliphatic amine, annular aliphatic

amine to aromatic amine, have a great impact on host–guest interactions and supramolecular architectures. The major

driving force in host–guest systems is found to be the strong NZH· · ·O or/and weak CZH· · ·O hydrogen-bonding

interactions, with various ring motifs and interesting substructures such as the butterfly-like trimer in 1 and the rotator–stator

assembly in 2–5. By analysing and summing up, we can come to the conclusion that the NHþ3 group in 4 exhibits an

optimum value of around 0.755 A from the O-plane and the 18-crown-6 macrocycle displays the minimum distortion. On the

whole, ammonium cations show control over supramolecular assemblies, but counter anions that easily form hydrogen

bonds will affect crystal structures, for instance, ClO24 anion in 4 facilitates the formation of the 3D hydrogen-bonding

network and helical hydrogen-bonding sheets while deprotonated 3,5-dinitrobenzoic acid assists the formation of discrete

subunits.

Keywords: hydrogen bonding; host–guest interactions; 18-crown-6; ammonium salts

Introduction

Inspired by the interesting structural feature with specific

chelate sites, crown ethers have been successfully

introduced into artificial systems by chemists working in

the realms of supramolecular chemistry and crystal

engineering (1–7). They have proven their ability to

construct supramolecular compounds, behaving as macro-

cyclic hosts for metal ions and complementary guest

molecules such as organic salts and hydrogenate cations

(8–14). Generally, crown ethers interact with guest

molecules by non-covalent interactions, for example

hydrogen bonding, p· · ·p stacking, charge transfer and

hydrophobic interactions (15–17). Host–guest interaction

enables the potential applications of crown ethers in the

fields of molecular recognition (18–22), ion transport (5,

23–27) and activated catalysis (28–31), as the complexa-

tion process can enhance salt solubility and accelerate

anion reactivity in non-aqueous solvents (32). The

important secondary interaction is used to not only

mimic natural systems but also synthesise new functional

materials (33–36).

Particularly attractive are that crown ethers often act as

ideal candidates for molecular stators in the field of

molecular machine design. Guest ammonium cations

R–NHþ3 (R ¼ H, alkyl or aryl) are easily anchored in their

cavity, where the R groups usually serve as molecular

rotors or pendulum unit (17, 37). Besides an attempt to

mimic the intelligent function of biological molecular

motors, molecular rotation offers the possibility for the

design of phase change materials and ferroelectric

molecular materials (38–41). Although the systems of

protonated primary amine (R–NHþ3 ) have been exten-

sively studied, the influence of different kinds of guest

amines on supramolecular assemblies with crown ethers

still remains rarely reported.

To explore geometric effects of ammonium salts on the

host–guest system and supramolecular architectures

through hydrogen-bonding interactions, we introduced

different types of ammonium salts into 18-crown-6, ranging

from chain-like aliphatic secondary amine (iminodiacetoni-

trile), annular aliphatic secondary amine (3-methylpiper-

idine) to aromatic primary amine (3-(aminomethyl)pyridine

and 2-aminobenzene-1,3-diol), and obtained five supramo-

lecular salts, namely [(C4H6N3)·(18-crown-6)2]þ·(I23 ) (1),

[(C6H14N)·(18-crown-6)]þ·(I23 ) (2), [(C6H14N)·(18-crown-

6)]þ·(FeCl24 ) (3), [(C6H10N2)·(18-crown-6)]2þ·(ClO2

4 )2 (4)

and [(C6H8NO2)·(18-crown-6)]þ·[(C7H3N2O6)

2]2 (5).We found that the variation of ammonium cations have a

q 2014 Taylor & Francis

*Corresponding authors. Email: iamswang@njupt.edu.cn; iamyhli@njupt.edu.cn

Supramolecular Chemistry, 2015

Vol. 27, No. 4, 213–223, http://dx.doi.org/10.1080/10610278.2014.964238

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great effect on host–guest interactions and supramolecular

architectures. It is clear from our present study that the

aromatic primary amine that has free single bond and small

steric effect is apt to form the rotator–stator assembly and

enriched hydrogen-bonding architectures.

Experimental

Syntheses of the compounds 1–5

All chemical reagents were purchased from Sigma-

Aldrich (Shanghai, China) and used without further

purification.

[(C4H6N3)·(18-crown-6)2]þ·(I23 ) (1)

To a methanol solution (10mL) containing iminodiaceto-

nitrile (0.1mmol) and hydriodic acid (1mmol) was added

18-crown-6 (1mmol) with constant stirring for 30min.

The resultant clear solution was allowed to evaporate

under ambient conditions, affording yellow lamellar

crystals after 1 week. The crystals were separated from

the mother liquor by filtration, washed with cool methanol

solution and dried under vacuum.

[(C6H14N)·(18-crown-6)]þ·(I23 ) (2)

3-Methylpiperidine (1mmol), hydriodic acid (1mmol)

and 18-crown-6 (1mmol) in methanol (10mL) were

mixed with stirring according to the similar procedure for

1. Upon slow evaporation of the solvents, good-quality

yellow lamellar crystals of 2 formed after 2 weeks.

[(C6H14N)·(18-crown-6)]þ·(FeCl24 ) (3)

3-Methylpiperidine (1mmol) and 18-crown-6 (1mmol)

were dissolved in methanol solution. After addition of

tervalent ferric chloride (1 mmol) in concentrated

hydrochloric acid medium, the precipitate was filtered

and washed with a small amount of methanol. Yellow

block single crystals suitable for X-ray diffraction analysis

were obtained from slow evaporation of methanol and

DMF solution at room temperature after several days.

[(C6H10N2)·(18-crown-6)]2þ·(ClO2

4 )2 (4)

A mixture of 3-(aminomethyl)pyridine (1mmol), per-

chloric acid (1mmol) and 18-crown-6 (1mmol) in

methanol (10mL) was stirred in the air. After several

days, colourless needle-shaped crystals were isolated

suitable for X-ray analysis.

[(C6H8NO2)·(18-crown-6)]þ·[(C7H3N2O6)

2]2 (5)

Similarly to 1, colourless rod-like crystals of 5 were

produced from slow evaporation of methanol solution by

mixing the 1:1:1 stoichiometric 2-aminobenzene-1,3-diol,

3,5-dinitrobenzoic acid and 18-crown-6.

Single crystal X-ray diffraction

Crystal data of 1–5 were collected by a Bruker SMART

APEX diffractometer employing graphite-monochro-

mated Mo Ka radiation (l ¼ 0.71073 A) at 293K. The

data integration and reduction were undertaken with

SAINT. The structure was solved by the direct method

using SHELXL-97 and all the non-hydrogen atoms were

refined anisotropically on F 2 by the full-matrix least-

squares technique using SHELXL-97. Non-H atoms were

refined anisotropically using all reflections with I . 2s(I).All H atoms were added geometrically and refined using

‘riding’ model with Uiso ¼ 1.2Ueq (C and N). The packing

views and the asymmetric units were drawn with the

DIAMOND Visual Crystal Structure Information System

Software. Crystallographic data and structure refinement

are listed in Table 1.

Results and discussion

The preparation of supramolecular salts 1–5 was

performed by a slow evaporation technique. They were

all obtained from the methanol solution using 1:1:1

stoichiometric mixtures of 18-crown-6, organic amines

and corresponding acids. During crystallisation, proton

transferred from acid to the nitrogen atom of easily

protonated sites. Hydrogen-bonding geometries are listed

in Table 2.

Structure description of compound 1

A single-crystal diffraction analysis reveals that supramo-

lecular salt 1 crystallises in the non-centrosymmetrical

orthorhombic space group P212121 and its molecular

structure is composed of one monoprotonated iminodiace-

tonitrile cation, one linear I23 anion and two 18-crown-6

molecules (Figure 1(a)). A wide range of hydrogen bonds

arouse our curiosity about possible interesting supramole-

cular architectures. The guest moiety interacts with the host

18-crown-6 through strong NZH· · ·O and weak CZH· · ·O

hydrogen bonds to form hydrogen-bonding organic frame-

works (HOFs), which are occupied by I23 anions (Figure 1

(b)). Viewed along the a-axis, discrete quadrilateral units

appear and linear iodide ions look like their two sides

(Figure 1(c)). When viewed along the b-axis, independent

hydrogen-bonding chains are observed and interweaved

with parallel I23 anions (Figure 1(d)).

The above independent subunits appeal to us, one of

which has been separated for detailed research in the pale

green background. As shown in Figure 1(e), such subunit

is constructed by iodide ions and butterfly-like structures

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that alternate parallel to the ab plane. The butterfly-like

structure is a trimer of two 18-crown-6 molecules and one

iminodiacetonitrile cation, induced by intermolecular

hydrogen-bonding interactions. O17 exhibits bifurcated

hydrogen bonding with C18ZH3 from another 18-crown-

6 and C14ZH49 from iminodiacetonitrile, which offer a

hydrogen-bonding ring R33ð8Þ together with

N2ZH53· · ·O8. For clarity, we divided the trimer into

two parts to find their same hydrogen-bonding motifs, that

is R21ð5Þ, R2

2ð8Þ, R22ð10Þ and R2

2ð11Þ, which may be attributed

to the symmetrical structure of guest iminodiacetonitrile.

Structure description of compounds 2 and 3

I23 and FeCl24 anions were introduced as counterions to the

18-crown-6/3-methylpiperidine system, yielding 1:1:1

supramolecular salts [(C6H14N)·(18-crown-6)]þ·(I23 ) (2)

and [(C6H14N)·(18-crown-6)]þ·(FeCl24 ) (3), respectively.

Compound 2 crystallises in the monoclinic space group

P21/c while compound 3 crystallises in the orthorhombic

space group Pbca. For salt 1, the protonated 3-

methylpiperidine joins with 18-crown-6 to result in a

rotator–stator assembly via strong NZH· · ·O and weak

CZH· · ·O hydrogen-bonding interactions, which facilitate

the formation of R22ð8Þ and R2

2ð11Þ rings (Figure 2(a)).

Adjacent rotator–stator assemblies sit with each other face

to face packing parallel to the bc plane, where linear I23anions exist on the side of 3-methylpiperidine cations

(Figure 2(b)). When stacking along the c-axis, [(C6H14N)·

(18-crown-6)]þ cations and I23 anions are arranged

alternately as shown in Figure 2(c). 3-Methylpiperidine

cations were embedded in the crown ether and linear

iodide ions intersect each other.

We wonder how supramolecular architecture will

change when the host–guest system remains unchanged

and only the counter anion is altered. From the asymmetric

unit in Figure 3(a), one FeCl24 anion as a substitute for I23is found to counter one [(C6H14N)·(18-crown-6)]

þ cation

in compound 3. When packing parallel to the ac plane,

host–guest cations alternate with FeCl24 anions similarly

to those in compound 2 (Figure 3(b)). The host–guest

cations in pale green are viewed along the c-axis and

shown on the right. Similar rotator–stator assemblies form

where the head catches the tail. Host–guest interactions

afford ring motifs R21ð5Þ and R2

2ð10Þ besides R22ð8Þ and

R22ð11Þ, the same as those in salt 2.

Structure description of compound 4

For compound 4, the asymmetric unit contains one

diprotonated 3-(aminomethyl)pyridine cation, two ClO24

anions and one 18-crown-6 molecule (Figure 4(a)).

Table 1. Crystallographic data for the complex of 1–5.

Compounds 1 2 3 4 5

Formula C28H54I3N3O12 C18H38I3NO6 C18H38Cl4FeNO6 C18H34Cl2N2O14 C32H38N5O20

Formula weight 1005.44 745.19 562.14 573.37 812.67Crystal system Orthorhombic Monoclinic Orthorhombic Monoclinic MonoclinicSpace group P212121 P21/c Pbca P21/n C2/ca (A) 14.088(3) 10.925 (2) 14.166(8) 15.439 (3) 30.760(6)b (A) 15.806(3) 16.637 (3) 15.932(9) 10.316 (2) 8.6651(17)c (A) 18.117(4) 15.185 (3) 24.942(14) 17.350 (4) 14.786(3)a (8) 90.00 90.00 90.00 90.00 90.00b (8) 90.00 90.33(3) 90.00 105.93(3) 110.28(3)g (8) 90.00 90.00 90.00 90.00 90.00V (A3) 4034.2(15) 2760.0(9) 5629(5) 2657.2 (10) 3696.7(13)Dx (Mg m23) 1.656 1.793 1.327 1.433 1.460m (mm21) 2.38 3.43 0.95 0.31 0.12Z 4 4 8 4 4T (K) 293 293 293 293 293F (000) 1992 1440 2360 1208 1700u range for data collection (8) 3.1–27.5 3.1–27.5 2.5–26 3.1–27.5 3.2–26Index ranges 218 # h # 18 214 # h # 14 217 # h # 17 220 # h # 20 237 # h # 37

220 # k # 20 221 # k # 21 219 # k # 19 213 # k # 13 210 # k # 10223 # l # 23 219 # l # 19 230 # l # 30 222 # l # 22 218 # l # 18

Measured reflections 42178 28189 48934 26875 16443Independent reflections 9266 6322 5535 6079 3633Reflections with I . 2s(I) 4636 4287 4007 2919 1873Rint 0.103 0.051 0.058 0.108 0.083R1 [I . 2s(I) ] 0.058 0.049 0.065 0.081 0.097wR2 (all data) 0.121 0.108 0.180 0.218 0.327S 1.01 1.01 1.11 1.05 1.04

Supramolecular Chemistry 215

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Structural analysis indicates that it crystallises in

monoclinic space group P21/n. Extensive hydrogen-

bonding interactions have drawn our keen interest, ranging

from strong NZH· · ·O to weak CZH· · ·O hydrogen bonds,

which codetermine the position and orientation of

components and play a crucial role in the formation of

crystal structure. The 3-(aminomethyl)pyridine cation is

anchored in the cavity of 18-crown-6, forming the rotator–

stator structure. Protonated NHþ3 group is located in the

centre of crown ether and divides it into three parts, where

three NZH bonds all exhibit trifurcated hydrogen bonding

with oxygen atoms from 18-crown-6 generating rings

R12ð4Þ and R2

1ð5Þ.

Running parallel to the bc plane, double zigzag chains

are antiparallel and connected to each other byNHþ3 groups,

which constructs the three-dimensional (3D) hydrogen-

bonding network (Figure 4(b)). When stacking along the c-

axis as depicted in Figure 4(c), ambient ClO24 anions

interact with host–guest cations such as flowers. Such

subunits spread over the ab plane into a 3D supramolecular

architecture, where neighbouring chains are anti-aligned.

In order for better observation of the hydrogen-bonding

interactions, themoiety can be taken apart in pale green and

its side view was given on the right. Two Z-shaped

substructures are disconnected to each other. Viewed along

the a-axis, two hydrogen-bonding sheets are observed

Table 2. Hydrogen-bond distances and parameters for the complex of 1 2 5 (A, 8).

Compound DZH· · ·A DZH H· · ·A D· · ·A DZH· · ·A Symmetry code

1 N2ZH53· · ·O8 0.77(4) 2.02(4) 2.784(6) 173(4) x, y, 21 þ zN2ZH54· · ·O15 1.01(5) 1.78(5) 2.766(6) 163(4) x, 1 þ y, zC18ZH3· · ·O17 0.97 2.58 3.483(10) 156 x, 1 þ y, 1 þ zC14ZH49· · ·O17 0.97 2.30 3.249(7) 164 x, 1 þ y, zC14ZH50· · ·O16 0.97 2.51 3.228(9) 131 x, 1 þ y, zC14ZH50· · ·O18 0.97 2.40 3.322(8) 158 x, 1 þ y, zC15ZH51· · ·O9 0.97 2.40 3.116(6) 130 x, y, 21 þ zC15ZH51· · ·O10 0.97 2.38 3.246(6) 148 x, y, 21 þ zC15ZH52· · ·O12 0.97 2.31 3.166(7) 147 x, y, 21 þ z

2 N1ZH32· · ·O1 0.90 2.17 2.944(7) 143N1ZH33· · ·O4 0.90 2.14 3.024(7) 166C16ZH30· · ·O5 0.97 2.58 3.247(8) 126C17ZH35· · ·O2 0.97 2.53 3.113(7) 119

3 N1ZH30· · ·O1 0.90 2.23 3.044(5) 150 1/2 þ x, 1/2 2 y, 1 2 zN1ZH30· · ·O2 0.90 2.50 3.213(5) 136 1/2 þ x, 1/2 2 y, 1 2 zN1ZH31· · ·O4 0.90 2.22 2.975(5) 142 1/2 þ x, 1/2 2 y, 1 2 zC16ZH32· · ·O6 0.97 2.56 3.357(6) 139 1/2 þ x, 1/2 2 y, 1 2 z

4 N1ZH1· · ·O2 0.89 2.55 2.877(6) 103N1ZH1· · ·O3 0.89 1.95 2.810(5) 162N1ZH1· · ·O4 0.89 2.47 2.868(4) 108N1ZH2· · ·O4 0.89 2.51 2.868(4) 104N1ZH2· · ·O5 0.89 2.04 2.928(5) 174N1ZH2· · ·O6 0.89 2.50 2.913(6) 109N1ZH3· · ·O1 0.89 1.98 2.857(4) 169N1ZH3· · ·O2 0.89 2.51 2.877(6) 106N1ZH3· · ·O6 0.89 2.52 2.913(6) 107N2ZH9· · ·O14 0.86 2.29 2.881(5) 126 x, 21 þ y, zN2ZH9· · ·O11 0.86 2.23 2.907(6) 135 1 2 x, 1 2 y, 2 2 zC1ZH5· · ·O8 0.97 2.39 3.301(6) 156 1 2 x, 1 2 y, 1 2 zC4ZH7· · ·O10 0.93 2.39 3.289(7) 162 x, y, 1 þ zC5ZH8· · ·O7 0.93 2.48 3.214(7) 135 x, y, 1 þ zC5ZH8· · ·O12 0.93 2.55 3.271(7) 135 1 2 x, 1 2 y, 2 2 zC7ZH12· · ·O9 0.97 2.59 3.530(8) 164 1/2 2 x, 21/2 þ y, 1/2 2 zC14ZH25· · ·O9 0.97 2.59 3.515(7) 160 1/2 2 x, 1/2 þ y, 1/2 2 z

5 N1ZH3· · ·O3 0.89 2.00 2.886(5) 173N1ZH3· · ·O4 0.89 2.46 2.875(5) 109N1ZH4· · ·O2 0.89 2.54 3.017(5) 114N1ZH4· · ·O3 0.89 2.58 2.886(5) 101 2 2 x, y, 3/2 2 zN1ZH4· · ·O4 0.89 1.99 2.875(5) 169 2 2 x, y, 3/2 2 zN1ZH5· · ·O1 0.89 2.34 2.792(7) 111N1ZH5· · ·O4 0.89 2.57 2.875(5) 101N1ZH5· · ·O2 0.89 2.19 3.017(5) 153 2 2 x, y, 3/2 2 zN1ZH5· · ·O3 0.89 2.44 2.886(5) 111 2 2 x, y, 3/2 2 zO1ZH6· · ·O8 0.82 1.87 2.673(8) 168 1/2 þ x, 1/2 þ y, 1 þ z

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where diprotonated 3-(aminomethyl)pyridine cations are

antiparallel to the nearby one (Figure 4(d)). NHþ3 groups are

arranged outside and hydrogen bonded to their bilateral 18-

crown-6 as molecular stators. The NZH from pyridine

shows bifurcated hydrogen bonding with oxygen atoms

from ClO24 ions, affording the ring motif with graph set

notation R42ð8Þ. Moreover, the participation of CZH· · ·O

hydrogen bonds produce another kind of ring R22ð7Þ.

Interestingly, such hydrogen-bonding sheets are found to be

helical.

Figure 1. (Colour online) (a) The asymmetric unit of 1 together with the numbering scheme; (b) the HOFs parallel to the ab plane; (c)view of molecular structure viewed along the a-axis; (d) independent hydrogen-bonding chains viewed along the b-axis and (e) thebutterfly-like substructures.

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Structure description of compound 5

As illustrated in Figure 5(a), structure determination

revealed that compound 5 crystallises in the monoclinic

space group C2/c with half of monoprotonated 2-

aminobenzene-1,3-diol cation, one 3,5-dinitrobenzoic

acid anions and half of 18-crown-6 molecule in the

asymmetric unit. Different from the above four salts,

compound 5 just exhibits strong hydrogen-bonding

interactions (NZH· · ·N and OZH· · ·O), which direct

the formation of interesting supramolecular arrays

(Figure 5(b)). The layer of [(C6H8NO2)·(18-crown-6)]þ

cations alternates with that of 3,5-dinitrobenzoic acid

anions. The host–guest cations interact with the anions

on their both sides, resulting in the declining discrete

substructures.

Such discrete subunits appeal to us, one of which has

been chosen as the further study object in the pale-green

background. The three components all get involved in the

formation of V-shaped structure. Two OH groups from 2-

aminobenzene-1,3-diol are hydrogen bonded to their

bilateral nitryls of 3,5-dinitrobenzoic acid by hydrogen

bonds O1ZH6· · ·O8 and protonated amidogen via

hydrogen bonds N1ZH5· · ·O1 forming intramolecular

S(5) rings. 2-Aminobenzene-1,3-diol as the molecular

rotor connects to 18-crown-6 acting as the molecular stator

through NZH· · ·O hydrogen-bonding interactions

between the NHþ3 group and oxygen atoms of 18-crown-

6. Complicated hydrogen-bonding patterns are caused by

their interactions, which do not be detailed here. This is

largely due to the symmetrical existence of hydrogen

Figure 2. (Colour online) (a) The asymmetric unit of 2 together with the numbering scheme; (b) view of crystal packing parallel to thebc plane and (c) the crystal stacking along the c-axis.

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atoms from the amino cation. From this, we can see that

2-aminobenzene-1,3-diol plays a decisive role in the

crystal packing.

Geometric effects of amine groups on the interactionsof host–guest systems

To explore the influence of ammonium cations on host–

guest systems, we employ the same host 18-crown-6 and a

series of guest amines that have different kinds of amine

groups from chain-like aliphatic amine, annular aliphatic

amine to aromatic amine, resulting in the formation of

salts 1–5. The schematic representations show host-guest

interactions between 18-crown-6 and ammonium cations

in Scheme 1. Hydrogen-bonding interactions induce the

butterfly-like trimer in 1 but the rotator–stator assembly in

2–5, where various ring motifs are observed. Interestingly,

1 and 3 display the same hydrogen-bonding patterns while

Figure 3. (Colour online) (a) The asymmetric unit of 3 together with the numbering scheme and (b) view of crystal packing parallel tothe ac plane.

Supramolecular Chemistry 219

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2 and 4 reveal similar hydrogen-bonding rings, namely to

divide the 18-crown-6 macrocycle into two and three parts,

respectively. However, complicated hydrogen-bonding

motifs are caused in 5 largely due to the symmetrical

existence of hydrogen atoms from the amino cation.

Although compounds 2–5 have similar rotator–stator

substructures, it is probably easier for the NHþ3 group in 4

to rotate in comparison with the ammonium in 2, 3 and 5.

Because the atoms around ammonium cations are

hydrogen bonded to the 18-crown-6, this may impact on

molecular rotations.

We have summarised the distances that the oxygen

atoms deviate from the median O-plane of 18-crown-6 and

the distances of the amino nitrogen atoms from the median

O-plane for complexes 1–5 in Table 3. From the

comparison of the average value of the deviation and the

distances of amino nitrogen atoms from the median O-

plane, we may conclude that the primary amine in 4 shows

closer interaction with the host. At this time, the NHþ3

group from the O-plane exhibits an optimum value of

around 0.755 A and the 18-crown-6 macrocycle displays

the minimum distortion. In contrast, the deviated average

value is much larger and the distance of the N atom from

the O-plane is a little longer in compound 5, although the

aromatic amine, 2-aminobenzene-1,3-diol, has been

utilised as a guest as well. This may be attributed to the

less free anilino group than the benzylamino group in 4

and the constraint of bilateral OH groups on H atoms of the

amine group through hydrogen-bonding interactions,

which causes that the 18-crown-6 macrocycle has to

distort more to form hydrogen bonds with the NHþ3 group.

As for complexes 1–3, steric effect of substituted

amidogen can well account for the much distorted 18-

crown-6 macrocycle and the long distances of amino

nitrogen atoms from the O-plane. Specifically, salts 2 and 3

afford similar average value of the deviation and the

distance of the N atom from the O-plane, which

indicates that the influence of counter anions on the

Figure 4. (Colour online) (a) The asymmetric unit of 4 together with the numbering scheme; (b) the 3D hydrogen-bonding networkparallel to the bc plane; (c) the 3D hydrogen-bonding network parallel to the ab plane and the chain in pale green viewed along the b-axisand (d) hydrogen-bonding sheets viewed along the a-axis and their helical structure.

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same host–guest cations is not obvious. Compared with

the annular aliphatic amine in 2 and 3, the chain-like

secondary amine can be easier to rotate free in salt 1,

leading to the less distorted 18-crown-6 macrocycle but the

longer distance of the nitrogen atom from the O-plane.

Besides free rotation of the chain-like single bond,

symmetrical structure of the secondary amine may be

prone to bring the butterfly-like trimer, where crown ether

macrocycles exhibit the similar distortion and the N atom

shows similar distance from the O-plane.

Figure 5. (Colour online) (a) The asymmetric unit of 5 together with the numbering scheme and (b) view of crystal packing parallel tothe ac plane and the V-shaped substructure.

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Conclusion

A series of supramolecular salts have been obtained by

supramolecular assembly of 18-crown-6 with different

kinds of ammonium salts, ranging from chain-like

aliphatic amine, annular aliphatic amine to aromatic

amine. Interesting substructures are observed between host

crown ether and guest ammonium, such as the butterfly-

like trimer in 1 and the rotator–stator assembly in 2–5.

We find that the NHþ3 group in 4 exhibits a optimum value

of around 0.755 A from the O-plane and the 18-crown-6

macrocycle displays the minimum distortion. Structural

analysis indicates that guest amines greatly influence

host–guest systems and supramolecular architectures

through hydrogen-bonding interactions.

It is clear from our present study that the aromatic

primary amine that has free single bond and small steric

effect is apt to result in the rotator–stator assembly.

Although ammonium cations show control over supramo-

lecular assemblies, counter anions that easily form

hydrogen bonds will affect crystal structures, for instance,

ClO24 anion in 4 facilitates the formation of the 3D

hydrogen-bonding network and helical hydrogen-bonding

sheets while deprotonated 3,5-dinitrobenzoic acid assists

the formation of discrete subunits.

The roles of guest amines have been established in

directing the formation of supramolecular architectures

between crown ether and ammonium salts by host–guest

hydrogen-bonding interactions. The examples here should

expand the understanding of the vital role of ammonium

cations in the design and construction of supramolecular

host–guest materials. These results are significant not only

for the evaluation of the specific case in this work, but also

for other host–guest systems with crown ethers.

Funding

The authors gratefully acknowledge financial support from theNatural Science Foundations of China [grant number 51173082],

Table 3. Summary of the deviations (A) of oxygen atoms from the median O-plane of 18-crown-6 in complexes 1–5 and the distances(A) of N atoms from the median O-plane.

Complex Deviations above Deviations below Average Distances

1 0.544, 0.301 0.331, 0.240, 0.182, 0.092 0.282 2.3020.153, 0.143, 0.393 0.413, 0.211, 0.064 0.230 2.177

2 0.548, 0.566, 0.124, 0.099 0.671, 0.667 0.446 1.6253 0.620, 0.641, 0.001 0.627, 0.635, 0.000 0.421 1.6464 0.278, 0.155, 0.081 0.257, 0.185, 0.072 0.171 0.7555 0.714, 0.714 0.239, 0.239, 0.475, 0.475 0.476 1.133

Scheme 1. (Colour online) Host–guest interactions of 18-crown-6 with ammonium salts in the supramolecular salts 1–5. Irrelevanthydrogen atoms and anions are omitted for clarity.

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from Jiangsu Province [grant number 13KJB150028], [grantnumber BM2012010], [grant number BK20141425], [grantnumber PAPD], and Program for Postgraduates ResearchInnovation in University of Jiangsu Province [grant numberCXZZ12-0456].

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