[Zn(INO)2(DMF)]$DMF: A new three-dimensional supramolecular

open framework containing one-dimensional channels

Jun Hong*

Department of Chemistry, Jilin Normal University, Siping, 136000, People’s Republic of China

Received 15 July 2005; revised 3 August 2005; accepted 5 August 2005

Available online 21 September 2005

Abstract

A three-dimensional supramolecular compound, [Zn(INO)2(DMF)]$DMF (1) (INOZisonicotinic acid N-oxide), has been prepared in the

DMF solution at room temperature, and characterized by elemental analysis, TG and single crystal X-ray diffraction. The three-dimensional

supramolecular open framework of 1 contains rectangular channels with the dimensions of 9.02!10.15 A, assembled from one-dimensional

helical chains via hydrogen-bonding and p–p stacking interactions. Furthermore, compound 1 shows blue photoluminescence at room

temperature.

q 2005 Elsevier B.V. All rights reserved.

Keywords: Crystal structure; Helical chain; Supramolecular network; Channel; Luminescence

1. Introduction

The rational design and synthesis of metal-directed

supramolecular frameworks have received much attention in

coordination chemistry because of their interesting molecular

topologies and their tremendous potential applications in

host–guest chemistry, catalysis, molecular selection, non-

linear optics, ion exchange and microelectronics [1,2]. During

the last decade, varieties of attractive networks with

fascinating structural motifs, including honeycomb, brick

wall, bilayer, ladder, herringbone, diamondiod, rectangular

grid, and octahedral geometries, have been deliberately

designed [3–8]. Generally, the construction of these metal-

containing supramolecular frameworks can be achieved via

two kinds of interactions, i.e. coordinate covalent bonds and

weaker intermolecular forces including hydrogen bonding, p–

p stacking and Coulombic interactions. It should be noted that

these weaker intermolecular forces play an important role in

the formation of high-dimensional frameworks [9–17]. One of

the important targets in the formation of supramolecular

assembly is to establish the possible links between units. In

view of this, organic aromatic ligands are good candidates

0022-2860/$ - see front matter q 2005 Elsevier B.V. All rights reserved.

doi:10.1016/j.molstruc.2005.08.013

* Corresponding author. Tel.: C86 434 3292154.

E-mail address: junhong000@hotmail.com

because they can not only act as hydrogen-bonding accepters

or donors but also may provide recognition sites for p–pstacking interactions to form interesting supramolecular

structures when coordinated with metal ions.

On the other hand, polynuclear d10 metal (CuI, AgII, AuI,

ZnII or CdII) complexes have attracted extensive interest in

recent years in that they not only exhibit appealing structures

but also possess photoluminescent properties [18].

On the basis of the aforementioned points, we chose zinc

nitrate and isonicotinic acid N-oxide [19] (INO) as building

blocks and attempted to synthesize new suprmolecular

compounds and study their luminescent property. In this

paper we report a new three-dimensional supramolecular

coordination polymer, [Zn(INO)2(DMF)]$DMF (1). Inter-

estingly, the compound consists of one-dimensional

rectangular channels assembled by helical chains via

hydrogen-bonding and aromatic p–p stacking interactions.

Furthermore, compound 1 shows blue photoluminescence at

room temperature.

2. Experimental section

2.1. Materials and methods

All chemicals purchased were of reagent grade and used

without further purification. Elemental analyses (C, H

Journal of Molecular Structure 783 (2006) 9–12

www.elsevier.com/locate/molstruc

J. Hong / Journal of Molecular Structure 783 (2006) 9–1210

and N) were performed on a Perkin-Elmer 2400 CHN

elemental analyzer. TG analysis was performed on a Perkin-

Elmer TGA7 instrument in flowing N2 with a heating rate of

108C min–1. Excitation and emission spectra were obtained

on a SPEX FL-2T2 spectrofluorometer equipped with a

450 W xenon lamp as the excitation source.

2.2. Synthesis

Zn(NO3)2$6H2O (1 mmol, 0.2975 g) and isonicotinic

acid N-oxide (2 mmol, 0.2800 g) were dissolved in DMF

(10 mL). The solution was allowed to stand undisturbed for

two weeks and colorless crystals grew at the bottom of

beaker (yield 62% based on Zn). Elemental analysis (%)

found: C 44.5, H 4.6, N 11.2. Calcd.: C 44.32, H 4.55, N

11.49.

2.3. X-ray crystallography

A colorless single crystal with dimensions 0.34!0.26!0.24 mm3 was glued on a glass fiber. Data were collected on

a Rigaku R-axis RAPID IP diffractometer at 293 K using

graphite-monochromated Mo Ka radiation (lZ0.71073 A)

and IP technique in the range 3.078 !q! 27.488. Empirical

absorption correction was applied. The structure was solved

by the direct method and refined by the full-matrix least-

squares method on F2 using the SHELXTL crystallographic

software package [20]. Anisotropic thermal parameters

were used to refine all non-hydrogen atoms. The hydrogen

atoms of water molecule included at idealized positions.

Table 1

Crystal data and structure refinement for 1

Experical formula C18H22N4O8Zn

Formula weight 487.77

Temperature (K) 293(2)

Wavelength (A) 0.71073

Crystal system Monoclinic

Space group P21/c

a (A) 7.0453(14)

b (A) 13.906(3)

c (A) 22.344(5)

b8 91.64(3)

Volume (A3) 2188.2(8)

Z 4

Pcalc (mg m–3) 1.481

Absorption coefficient (mm–1) 1.173

F(000) 1008

Crystal size (mm) 0.34!0.26!0.24

q range (8) 3.07–27.48

Reflections collected 20458

Independent reflections 4899

Refinement method Full-matrix least-squares on

F2

Data/restraints/parameters 4899/0/280

Goodness-of-fit on F2 1.041

Final R indices [IO2s(I)] R1Z0.0479, wR2Z0.1215

R indices (all data) R1Z0.0785, wR2Z0.1336

Largest diff. peak and hole (e A–3) 0.515 and K0.424

Further details of the X-ray structural analysis are given in

Table 1. Selected bond lengths and angles are listed in

Table 2. CCDC number: 277584.

3. Results and discussion

3.1. Structure description

The single-crystal X-ray structural analysis reveals that

compound 1 exhibits an interesting three-dimensional

supramolecular network containing one dimensional rec-

tangular channel. The asymmetric unit contains one zinc

atom, two INO groups, and two DMF molecules. The

crystallographically unique zinc atom is coordinated by four

oxygen atoms (Zn(1)–O(1A)Z2.013(2) A; Zn(1)–O(3)Z2.242(2) A; Zn (1)–O(4)Z2.088(2) A, Zn(1)–O(5)Z1.997(2) A) from three INO ligands, and one oxygen atom

(Zn(1)–O(7)Z2.028(2) A) from one DMF molecule, show-

ing a distorted trigonal bipyramidal coordination geometry

(Fig. 1). In addition, two types of INO ligands exist in 1:

INOA contains one monodentate bridging carboxylate group

and one bridging N-oxide group, whereas INOB contains

only one chelating carboxylate group (see Scheme 1).

The adjacent Zn atoms are linked by INOA ligands to

form a chiral helical chain running along b axis (Fig. 2a).

The helix is generated around the crystallographic 21 axis

with a pitch of 13.906 A, and decorated by INOB ligands

and coordinated DMF molecules bristling out at the two

sides of the helix. The INOB phenyl rings at each side of the

helix are arranged in a parallel fashion with an inter-ring

distance of 20.87(2) A. This orientation plays a critical role

in packing into a higher network through p–p stacking

interactions. The adjacent helical chains with the same

handedness are further connected into a chiral sheet through

very significant C–H/O hydrogen bonds (C1–H1A/O2

3.088(4) A, C7–H7A/O3 3.100(4)–A) between aromatic

carbon atoms (C1 and C7) and carboxyl oxygen atoms (O2

and O3) (see Fig. 2b). These chiral sheets are racemically

packed through strong aromatic p-p stacking interactions

Table 2

Selected bond lengths (A) and angles (8) for 1

Bonds

Zn(1)–O(5) 1.997(2) Zn(1)–O(1A) 2.013(2)

Zn(1)–O(7) 2.028(2) Zn(1)–O(4) 2.088(2)

Zn(1)–O(3) 2.242(2)

Angles

O(5)–Zn(1)–O(1A) 101.36(9) O(5)–Zn(1)–O(7) 97.57(10)

O(1A)–Zn(1)–O(7) 101.15(10) O(5)–Zn(1)–O(4) 108.65(10)

O(1A)–Zn(1)–O(4) 144.28(10) O(7)–Zn(1)–O(4) 93.77(10)

O(5)–Zn(1)–O(3) 93.52(9) O(1A)–Zn(1)–O(3) 99.42(9)

O(7)–Zn(1)–O(3) 154.16(9) O(4)–Zn(1)–O(3) 60.51(8)

C(12)–O(3)–Zn(1) 85.86(18) C(12)–O(4)–Zn(1) 92.65(18)

N(1)–O(5)–Zn(1) 119.00(17) C(13)–O(7)–Zn(1) 122.6(2)

Symmetry transformations used to generate equivalent atoms: A: Kx,yC1/

2,KzC1/2.

Fig. 1. ORTEP representation of the coordination environment around the

zinc center for 1 (50% probability ellipsoids). Symmetry transformations

used to generate equivalent atoms: A: Kx,yC1/2,KzC1/2.Fig. 2. (a) A single-stranded helical chain; (b) a view of the two-

dimensional chiral sheet formed by C–H/O hydrogen bonds (dashed line).

J. Hong / Journal of Molecular Structure 783 (2006) 9–12 11

(face to face distance is 3.242(5) A) from lateral INO

ligands into the resulting three-dimensional supramolecular

network.

The most interesting feature of compound 1 is that the

three-dimensional network consists of one-dimensional

rectangular channels along the [100] direction, and the

dimensions of a cross section are 9.02!10.15 A (Fig. 3).

Guest DMF molecules are located in the channels and form

the acceptor hydrogen bond with the aromatic carbon atom

of coordinated DMF molecules (C14/O8 3.18(4) A).

3.2. Thermal analysis

The TG curve of 1 exhibits two weight loss stages. The

first weight loss of 14.7% occurred over the temperature

range 130–155 8C, corresponding to the removal of one free

DMF molecule (calcd. 14.98%), leaving to a framework of

[Zn(INO)2(DMF)]. This framework is stable up to 220 8C

where the decomposition starts and ends at 360 8C,

Scheme 1. Two types of coordination modes of INO ligand in 1.

consistent with the removal of coordinated INO and DMF

ligands (found: 68.7%, calcd. 68.34%). The remaining

weight of 16.6% corresponds to the percentage (16.68%) of

the Zn and O components, indicating that the final product is

ZnO.

3.3. Photoluminescence properties

The emission spectrum of compound 1 in the solid state

at room temperature is shown in Fig. 4. It can be observed

Fig. 3. Perspective view of the three-dimensional supramolecular frame-

work, highlighting the one-dimensional rectangular channels. Guest DMF

molecules included in the channels.

Fig. 4. Solid-state emission spectrum of 1 at room temperature.

J. Hong / Journal of Molecular Structure 783 (2006) 9–1212

that compound 1 exhibits blue photoluminescence with an

emission maximum at ca. 475 nm upon excitation at

399 nm. In order to understand the nature of the emission

band, we analyzed the photoluminescence of free INO, and

a similar emission band at about the 483 nm has also been

observed for solid INO ligand when excited with the same

excitation wavelength. Therefore, the band at 475 nm for 1

can be assigned to the intraligand fluorescent emission of

coordinated INO ligands [21].

4. Conclusions

In this paper, a novel three-dimensional supramolecular

network containing one-dimensional channels, formed by

hydrogen-bonding and aromatic p-p stacking interactions,

has been synthesized and structurally characterized. Mean-

while, the solid-state photoluminescent property of the

compound is studied. The work demonstrates that weaker

intermolecular interactions contribute to the formation of

higher-dimensional networks. Rational choice of organic

aromatic ligands may provide multiple binding forces,

which may endow enormous potential for assembly

supramolecular architectures.

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