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The first in situ organosulfonate-templated 3-fold interpenetrating frameworkbuilt from rare tetrahedral [Cu4(m4-SO4)] SBUs†

Zhao-Peng Deng, Zhi-Biao Zhu, Xian-Fa Zhang, Li-Hua Huo,* Hui Zhao and Shan Gao*

Received 14th January 2011, Accepted 17th March 2011

DOI: 10.1039/c1ce05059a

An interpenetrating framework, [Cu4(SO4)(4,4-bipy)4]n$2n(C6H5SO4) [4,40-bipyridine ¼ 4,40-bipy], has

been successfully synthesized via hydrothermal reaction, in which the in situ generated p-

hydroxybenzenesulfonate as guests are encapsulated within the channels. The tetrahedral [Cu4(m4-SO4)]

SBUs, reported for the first time in 3D architectures, are linked by parallel double 4,40-bipys to generate

a diamondoid network formed of large adamantanoid cages which causes the 3-fold interpenetration of

the networks by self-clathration. Furthermore, the existence of strong p/p interactions between

adjacent 4,40-bipys stabilizes the interpenetrating framework. The binding energies of the Cu 2p3/2 level

in the XPS spectrum are typical for a Cu(I) oxidation state. For the O1s, the XPS spectrum could be

deconvoluted into three peaks corresponding to the three kinds of O atoms with different chemical

environments. This work provides a method for constructing in situ organosulfonate-templated

interpenetrating metal–organic frameworks.

Introduction

Metal–organic frameworks (MOFs) have attracted considerable

interest because of their potential applications and intriguing

variety of topologies and entanglement motifs.1 Interpenetration,

as the most investigated type of entanglement, has provided

a long-standing fascination.2–4 From a structural point of view,

although mutual interpenetration of the networks usually fills up

potential cavities and reduces porosity, excellent gas adsorption

capacity has been proven possible for interpenetrated coordi-

nation networks.5 Materials with interpenetrating lattices can

have free volumes that exceed 80% of the total volume,6 and

some researchers proved interpenetration could be utilized to

strengthen the interaction between the gaseous molecule and the

framework by an entrapment mechanism.7 Thus, inter-

penetrating networks, with their diverse topologies and struc-

tural features, represent one of the most amazing subjects in

crystal engineering of MOFs.

The interpenetrating diamondoid network is the most

common form of interpenetration,3 in which the encapsulated

guests contain solvent molecules (e.g. H2O, MeOH, toluene,

CH2Cl2), inorganic anions (e.g. Cl�, NO3�, ClO4

�, BF4�, PF6

�,

Key Laboratory of Functional Inorganic Material Chemistry, Ministry ofEducation, Heilongjiang University, Harbin 150080, P. R. China.E-mail: lhhuo68@yahoo.com; shangao67@yahoo.com; Fax: (+86) 0451-86608040; Tel: (+86) 0451-86609148

† Electronic supplementary information (ESI) available: Additionalfigures, IR spectra, TG curve, as well as PXRD patterns for complex 1.CCDC reference number 802842. For ESI and crystallographic data inCIF or other electronic format see DOI: 10.1039/c1ce05059a

This journal is ª The Royal Society of Chemistry 2011

SbF6�, AsF6

�), as well as organic amine cations (e.g. triethyl-

amine, triethylenetetramine, 3-dimethylaminopropylamine).

Recently, Wang and co-workers have presented a polyrotaxane

framework formed by molecular squares threading on a 2-fold

interpenetrated diamondoid skeleton, which encapsulated pol-

yoxometalates (POMs) as guests.8 Zhang et al. reported the

only 2-fold interpenetrated diamondoid net templated by the

organic enantiopure D-Hcam (D-camphoric acid) monoanions.9

By contrast, the interpenetrating diamondoid frameworks

encapsulated in situ generated organic anion as template have

not been reported to date. In this sense, 5-sulfosalicylate, with

three functional groups, provides a huge potential ability for in

situ ligand synthesis.10 It has been demonstrated that the 5-

sulfosalicylate can be decarboxylated in the Cd(II) complex in

the presence of chelating neutral ligand.11 In general, chemical

decarboxylation reactions often require extensive heating in

high boiling solvents and copper salts are often added as

catalysts.12 Based on this conception, we present herein the

hydrothermal synthesis and single-crystal X-ray structure of the

first in situ organosulfonate-templated 3-fold interpenetrating

diamondoid framework with rare tetrahedral [Cu4(m4-SO4)]

SBU, namely, {[Cu4(4,40-bipy)4(SO4)]n$2n(C6H5SO4)} (4,40-bipy

¼ 4,40-bipyridine), (1), in which the organosulfonate is in situ

generated from the decarboxylation of the 5-sulfosalicylic acid.

It should be noted that the tetrahedral [Cu4(m4-SO4)] SBU in 1

with each oxygen bonded to only one metal is detected for the

first time in a 3D architecture (excluding the inorganic

networks formed only by metals and sulfate). Such a conclu-

sion is also demonstrated by a CSD13 research, which reveals

that only three 3D frameworks (two with cadmium14 and one

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with lanthanum15) and one 1D copper(II) complex16 involving

m4-SO4 have been reported.

Experimental

Materials and methods

All chemicals and solvents were of A. R. grade and used without

further purification in the syntheses. Elemental analyses were

carried out with a Vario MICRO from Elementar Analy-

sensysteme GmbH, and the infrared spectrum (IR) was recorded

from KBr pellets in the range of 4000–400 cm�1 on a Bruker

Equinox 55 FT–IR spectrometer. Powder X-ray diffraction

(PXRD) patterns were measured at 293 K on a Bruker D8

diffractometer (Cu-Ka, l ¼ 1.54059 �A). The TG analyses were

carried out on a Perkin Elmer TG/DTA 6300 thermal analyzer

under flowing N2 atmosphere, with a heating rate of 10 �Cmin�1.

The X-ray photoelectron spectroscopy (XPS) spectra were

recorded on a KRATOS AXIS ULTRA DLD equipped with

monochromated Al-Ka radiation. For the calculation of the

binding energies, the C 1s peak of the C–(C,H) component at

284.6 eV was used as an internal standard.

Synthesis of [Cu4(SO4)(4,4-bipy)4]n$2n(C6H5SO4) (1)

Amixture of CuSO4$5H2O (0.50 g, 2 mmol), 5-sulfosalicylic acid

(0.44 g, 2 mmol), 4,40-bipy (0.31 g, 2 mmol), H2O (10 mL), and

methanol (5 mL) was heated in a 25 mL stainless steel reactor

with a Teflon liner at 120 �C for 48 h. Brown crystals of 1 suitable

for X-ray diffraction were isolated in 79% yield (based on Cu

atom). Anal. calcd for C52H42N8O12S3Cu4: C 47.27, H 3.20, N

8.48%. Found: C 47.25, H 3.23, N 8.46%. IR(v/cm�1): 3419m,

1602s, 1558m, 1531m, 1482m, 1417s, 1216s, 1166s, 1124s, 1031m,

817m, 800m, 700m, 617m, 568m.

Table 1 Crystal data and structure refinement parameters of complex 1

1

Empirical formula C52H42N8O12S3Cu4Mr/g mol�1 1321.28Crystal system MonoclinicSpace group C2/ca/�A 10.628(2)b/�A 35.255(7)c/�A 15.059(3)a/� 90.00b/� 110.50(3)g/� 90.00V/�A3 5285(2)Z 4Dc/mg m�3 1.658m/mm�1 1.777q range 3.11–27.40Reflections collected 21 877Unique reflections 6004Observed reflections 4783No. of parameter 371F(000) 2672R1, wR2 [I > 2s(I)] 0.0698, 0.1832R1, wR2 [all data] 0.0854, 0.1977GOF 1.043Largest peak and hole/e A�3 0.840 and �0.559

3896 | CrystEngComm, 2011, 13, 3895–3899

X-Ray crystallographic measurements

Table 1 provides a summary of the crystal data, data collection

and refinement parameters for the complex 1. The diffraction

data from crystal of complex 1 were collected at 295 K on

a RIGAKU RAXIS-RAPID diffractometer with graphite

monochromatized Mo-Ka (l ¼ 0.71073 �A) radiation in u scan

mode. Structure was solved by direct method and difference

Fourier syntheses. All non-hydrogen atoms were refined by full-

matrix least-squares techniques on F2 with anisotropic thermal

parameters. The hydrogen atoms attached to carbons were

placed in calculated positions with C–H ¼ 0.93 �A and U (H) ¼1.2Ueq (C) in the riding model approximation. The p-hydroxy-

benzenesulfonates are disordered over two positions with 50%

occupancy. The vibration of the atoms of the two parts are made

isotropic by an ISOR restraint. All calculations were carried out

with the SHELXL97 program. The CCDC reference number is

802842. Selected bond distances and angles for complex 1 are

presented in Table 2.

Results and discussion

Crystal structure of complex 1

Single-crystal X-ray analysis reveals that the molecular structure

of complex 1 consists of two Cu(I) ions, two 4,40-bipyridine (4,40-bipy) molecules, half of one crystallographically independent

sulfate anion and one uncoordinated p-hydroxybenzenesulfonate

(Fig. 1). The two Cu(I) ions, which are formed through the

reduction of Cu(II) ions under hydrothermal conditions,17 exhibit

distorted trigonal geometry, being made up of two nitrogen

atoms from two different 4,40-bipy molecules and one oxygen

atom from sulfate anion. The Cu–O and Cu–N bond lengths

around Cu1 ion are somewhat longer than those of Cu2 ion.

Both the angles of the two Cu(I) ions, ranging from 98.23(14) to

153.46(16)�, are obviously deviated from the ideal trigonal

geometry (Table 2). The sulfate anions with the m4-h1:h1:h1:h1

coordination mode bridge adjacent four Cu(I) ions to form a rare

tetrahedral [Cu4(m4-SO4)] SBU, which are further linked by

parallel double 4,40-bipys to generate a diamondoid network

formed of large adamantanoid cages (Fig. 2). Strong p/p

interactions can be detected between the two 4,40-bipys with the

centroid to centroid distance of 3.578 �A. The adamantanoid cage

exhibits maximum dimensions (the longest intracage distances)

of 35.3 � 28.2 � 31.9 �A3 (Fig. 3). Such a large cavity causes the

3-fold interpenetration of the networks by self-clathration as

shown in Fig. 4, which are stabilized by p/p interactions with

centroid to centroid distance of 3.674 �A. According to the clas-

sification defined by Blatov et al.,18 the present interpenetrated

network belongs to Class Ia, where only one interpenetration

Table 2 Selected bond distances (�A) and angles (�) for 1a

Cu(1)–(N(2)i 1.931(3) Cu(2)–(N(3) 1.919(3)Cu(1)–(N(1) 1.942(3) Cu(2)–(N(4)ii 1.931(3)Cu(1)–(O(1) 2.353(3) Cu(2)–(O(2) 2.308(3)N(2)i–Cu(1)–(N(1) 151.52(16) N(3)–(Cu(2)–(N(4)ii 153.46(16)N(2)i–Cu(1)–(O(1) 110.07(15) N(3)–(Cu(2)–(O(2) 106.96(15)N(1)–(Cu(1)–(O(1) 98.23(14) N(4)ii–Cu(2)–(O(2) 99.35(15)

a Symmetry code: i, x � 1/2, �y + 1/2, z + 1/2; ii, x + 1, �y + 1, z + 1/2.

This journal is ª The Royal Society of Chemistry 2011

Fig. 1 Molecular structure of 1, showing the coordination environments

around the copper(I) centers and the bridging mode of the SO42� anion

(hydrogen atoms are omitted for clarity).

Fig. 2 Dia topology (bottom) of 1 with the tetrahedral [Cu4(m4-SO4)]

SBUs and 4,40-bipy spacers (top).

Fig. 3 A single adamantanoid cage with the maximum dimensions

(corresponding to the longest intracage S/S distances) of 35.3 � 28.2 �31.9 �A3.

Fig. 4 A schematic view of the 3-fold interpenetration in 1.

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vector can be found. An analysis by TOPOS19 reveals that one

dia network is related to the other two by a single translational

vector, [100] of 10.63 �A.

Notably, even with this interpenetration, the framework is still

highly open, containing three-directional channels of approxi-

mately 15.1 � 5.5, 10.6 � 5.6 and 10.6 � 6.4 �A along the [100],

[001] and [101] directions, respectively (ESI, Fig. S1).† Thus, the

overall cationic 3D nets exactly trap the p-hydroxybenzenesul-

fonate as charge-compensating guests in the nanochannels

(Fig. 5). PLATON20 calculation indicated that the resulting

effective free volume, after removal of encapsulated guests, was

35.0% of the crystal volume (1851.9 �A3 out of the 5285.0 �A3 unit

cell volume).

Fig. 5 View of the 3D framework encapsulating in situ organosulfonates

(shown in space-filling modes) as guests in the open channels along the

a-axis.

IR spectroscopy

In the spectrum of complex 1 (ESI, Fig. S2),† no characteristic

vibrations of nas(COO�) and ns(COO�) were found, which

demonstrates that the 5-sulfosalicylate was decarboxylated. The

peaks observed at 1602, 1558, 1531 and 1482 cm�1 can be assigned

This journal is ª The Royal Society of Chemistry 2011

to the vibrations of C–N and C–C of the benzene and pyridine

rings. The characteristic vibrations of nas(SO3�) are at 1216, 1166,

and 1124 cm�1, whereas the ns(SO3�) absorption is at 1031 cm�1.

The vibration of SO42� dianion may superpose with the nas(SO3

�)

at the very strong peak of 1124 cm�1. In addition, the IR spectrum

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of complex 1 exhibits strong absorptions centered at 3419 cm�1,

occurring because of the existence of hydroxyl group of the in situ

generated p-hydroxybenzenesulfonate.

XPS spectra

In order to confirm the existence of an hydroxyl group and

copper only in the Cu(I) state, XPS spectra were recorded. As

shown in Fig. 6, no characteristic satellite peaks of Cu(II) are

detected. The binding energies of the Cu 2p3/2 level in the XPS

spectrum are 932.3 eV and 935.4 eV, which is also typical for

a Cu(I) oxidation state.21 The difference between the two Cu(I)

species is however too small to be assigned to different coordi-

nated Cu(I) ions.22 For the O1s core level, the spectrum could be

deconvoluted into three peaks: 530.8, 531.9, and 534.6 eV, which

correspond to the sulfate anion (SO42�), sulfonate group (–SO3

�)

and hydroxyl group (–OH), respectively (Fig. 7).23 These results

are consistent with the single-crystal X-ray and IR analyses.

Thermal analysis

To determine the thermostability of the nanoporous structure,

we investigated the thermal decomposition processes by TGA

experiments. The TG curve (ESI, Fig. S3)† of complex 1 shows

the weight loss of 6.21% (calcd 6.07%) from 150 to 250 �C

Fig. 6 XPS spectrum of 1 in the range corresponding to the Cu 2p level.

Fig. 7 XPS spectrum of 1 in the range corresponding to the O 1s level.

3898 | CrystEngComm, 2011, 13, 3895–3899

corresponds to the release of –SO3 groups. Then the following

continuous weight losses occur. Under the guidance of the TG

curve, we investigated PXRD experiments for the as-synthesized

sample of complex 1 and the samples heated at 100, 150 and

250 �C, respectively (ESI, Fig. S4).† The sample of complex 1

used was pure single-crystals. From the PXRD patterns for the

products at 100, 150 and 250 �C, the main peaks around the 2q of

8–10, 12, 19 and 25� are easily to be observed, which reveals that

the 3-fold interpenetration frameworks of complex 1 is nearly

intact before 250 �C.

Conclusions

In summary, we have successfully synthesized and characterized

the first in situ organosulfonate-templated 3-fold inter-

penetrating diamondoid framework, in which the tetrahedral

[Cu4(m4-SO4)] SBUs are reported for the fist time in 3D archi-

tectures. The present results demonstrate that the building block

[Cu4(m4-SO4)] and the bulkiness of the organic guests can effec-

tively influence the degree of interpenetration. This work

provides a method for constructing in situ organosulfonate-

templated interpenetrating metal–organic frameworks.

Acknowledgements

This work is financially supported by the Key Project of Natural

Science Foundation of Heilongjiang Province (no. ZD200903),

the Innovation team of Education bureau of Heilongjiang

Province (no. 2010td03) and Program for New Century Excellent

Talents in University (NCET-06-0349). We thank the University

of Heilongjiang (Hdtd2010-04) for supporting this study.

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