Four novel porous frameworks constructed by formate ligand

Microporous and Mesoporous Materials 91 (2006) 215–220 www.elsevier.com/locate/micromeso

Four novel porous frameworks constructed by formate ligand Yanqin Wang, Rong Cao *, Wenhua Bi, Xing Li, Daqiang Yuan, Daofeng Sun State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, The Chinese Academy of Sciences, Graduate School of the Chinese Academy of Sciences, Fuzhou 350002, China Received 17 March 2005; received in revised form 24 November 2005; accepted 28 November 2005 Available online 18 January 2006

Abstract Four novel porous frameworks, [H2N(CH3)2][M(HCO2)3] (M = Ni 1, M = Co 2), and [M(4,4 0 -bpy)(HCO2)2(H2O)] Æ 4H2O (bpy = bipyridine, M = Co 3, Ni 4) constructed by formate ligand, were synthesized and their structures were characterized by IR spectrum, chemical analysis and single crystal X-ray diffraction. Complexes 1 and 2 are allomers and crystallize in the trigonal space group ˚ and dimethylammonium is included in it. Complexes 3 and 4 are R-3c. They exhibit 3-D frameworks with cubic cavities about 4.9 · 4.9 A also allomers and crystallize in monoclinic space group Cc. In these two structures, central metal ions are connected by formate ligand ˚ . Free water molecules are included in it. Thermography analyses and 4,4 0 -bipyridine to be 3-D networks with channels about 7.0 · 9.2 A were tested to reveal the stability of the frameworks. XRPD results confirm that water molecules can be expulsed from the structures without collapse of the frameworks and the two compounds may have potential application in gas storage and adsorption.  2005 Elsevier Inc. All rights reserved. Keywords: Porous framework; Formate; Crystal structure; Channel

1. Introduction Recently, porous frameworks, which could be relevant for storage and exchange of specific guests, catalysis, and guest alignment [1–5], receive much attention. The synthesis of porous coordination materials has been associated with the hydro- or solvothermal technique for historical reasons, following the work on silicate and phosphate zeolites [6–8]. Solution chemistry has also been used to construct porous frameworks in recent years [9–11]. Yaghi and co-workers [12–15] have developed a strategy, based on the concept of secondary building unit (SBU), and have successfully shown that one can enlarge the pore size by extending the bridging ligands. The large SBU nodes prohibit the interpenetration thus resulting in the nanoporosity. However, it is now well understood that predesigning a building block, in situ or ex situ, is not a strict require-

*

Corresponding author. Tel./fax: +86 591 83796710. E-mail address: [email protected] (R. Cao).

1387-1811/$ - see front matter  2005 Elsevier Inc. All rights reserved. doi:10.1016/j.micromeso.2005.11.046

ment. In many cases, the right choice of the metal centers, the ligand, and the counterion or the templating molecule is the most important factor, and serendipity is usually the prevailing state of things rather than the rule. As for the spacer, carboxylate ligands have been extensively studied to construct porous frameworks [16–18]. However, formate anions, HCO 2 , which is the simplest carboxylate, has been used very infrequently as a building block, although simple metal–formate hydrates have long been known [19–22]. Only recently, two porous formate coordination polymers, [Mn3(HCOO)6] and [Co3(HCOO)6] were synthesized by Kobayashi and Kim, and their magnetic properties were studied [23–25]. In the structure of [Mn3(HCOO)6], there are channels running along the b ˚ , and the void space is estimated direction about 4 · 5 A 32% of the total volume. When the metal ion Mn2+ was replaced by Co2+, the void space was estimated 29.6% of the total volume and the replacement resulted in a contraction of the lattice by 9%. Furthermore, Manson synthesized novel 3-D networks constructed by formate anion and Cu ion with the presence of N-containing bridging ligands pyrazine and 4,4 0 -bipyridine [26]. Even now,

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example of formate coordination polymers with porous structure is still scarce. In this paper, we report four novel porous frameworks, [H2N(CH3)2][M(HCO2)3] (M = Ni 1, M = Co 2), and [M(4,4 0 -bpy)(HCO2)2(H2O)] Æ 4H2O (bpy = bipyridine, M = Co 3, Ni 4) constructed by formate ligand. 2. Experimental All chemicals were used as received without further purification. 3,3 0 ,4,4 0 -Benzophenonetetracarboxylic dianhydride (bptc) was purchased from Acros chemical company. IR spectra were recorded on a Magna 750 FT-IR spectrophotometer as KBr pellets. Elementary analyses were carried out in the elementary analysis group of this institute. Thermography analyses (TGA) were performed from 30 to 1000 C in N2 using a Netzsch STA449C analyzer at a heating rate of 15 C/min. Powder X-ray diffraction (XRPD) data were obtained using a DMAX2500 ˚ ). diffractometer with Cu Ka1 radiation (k = 1.54056 A The XRPD examples of the dehydrated 3 and 4 were produced from 3 and 4 by heating at 109 and 140 C, respectively, for 2 h. 2.1. Syntheses 2.1.1. [H2N(CH3)2][M(HCOO)3] (M = Ni 1, Co 2) These two complexes were prepared by two different methods. Method I: A mixture of M(NO3)2 Æ 6H2O (0.2 mmol), 3,3 0 ,4,4 0 -benzophenonetetracarboxylic dianhydride (0.2 mmol), DMF 10 ml and H2O 10 ml was sealed in a 25 ml Teflon bomb and heated to 140 C for 2 days, and then cooled to 30 C in 24 h. The resulted green clear solution was kept still and allowed to evaporate at room temperature. A few days later, green block crystals of 1 and red block crystals of 2 were collected and washed with water. Yield: 17 mg (36%) for 1 and 14 mg (28%) for 2. Method II: A mixture of M(NO3)2 Æ 6H2O (0.5 mmol), formic acid (1.7 mmol), dimethylamine (0.6 mmol) in 20 ml distilled water was refluxed for 2 h, and then the resulted solution was kept still and allowed to evaporate at room temperature. A few days later, crystals of 1 and 2 were obtained and washed with water. Yield: 89 mg (74%) for 1 and 82 mg (68%) for 2. The two complexes were observed to be stable in air for months and indiscerptible in water. C5H11NNiO6 (1: 239.86): calc. C 25.04, H 4.62, N 5.84; found C 24.96, H 4.75, N 5.97. IR (KBr, cm1): 3448, 3022, 2943, 2796, 1587, 1475, 1460, 1443, 1367, 1346, 1028, 812 cm1. C5H11NCoO6 (2: 240.08): calc. C 25.01, H 4.62, N 5.83; found C 24.92, H 4.81, N 6.03. IR (KBr, cm1): 3024, 2945, 2796, 2499, 1589, 1473, 1458, 1443, 1367, 1348, 1028, 806 cm1. 2.1.2. [M(4,4 0 -bpy)(HCO2)2(H2O)] Æ 4H2O (bpy = bipyridine, M = Co 3, Ni 4) These two complexes were also produced by two different methods. Method I was similar to the procedure of 1

and 2 in method I except that 4,4 0 -bipyridine (0.2 mmol) was used. Red block crystals of 3 and green block crystals of 4 were collected and washed with water. Yield: 19 mg (24%) for 3 and 25 mg (32%) for 4. Method II: A mixture of M(NO3)2 Æ 6H2O (0.5 mmol), formic acid (1.1 mmol), 4,4 0 -bipyridine (0.5 mmol) in 20 ml distilled water was refluxed for 2 h, and then the resulted solution was kept still and allowed to evaporate at room temperature. A few days later, crystals of 3 and 4 were obtained and washed with water. Yield: 126 mg (64%) for 3 and 140 mg (71%) for 4. The crystals of 3 and 4 were observed to be lacklustre after exposure in air for a week and indiscerptible in water. C12H20CoN2O9 (3: 395.23): calc. C 36.47, H 5.10, N 7.09; found C 36.62, H 4.79, N 7.21. IR (KBr, cm1): 3405, 3268, 2861, 2768, 1608, 1537, 1491, 1390, 1348, 1223, 1070, 1008, 831, 781, 634, 528 cm1. C12H20N2NiO9 (4: 395.01): calc. C 36.49, H 5.10, N 7.09; found C 36.46, H 4.65, N 7.32. IR (KBr, cm1): 3412, 3261, 2887, 2841, 1589, 1539, 1493, 1416, 1392, 1365, 1340, 1225, 1072, 1009, 827, 781, 733, 636, 476 cm1. 2.2. X-ray crystallographic determination The intensity data of the four complexes were collected on a SIEMENS SMART CCD diffractometer with graph˚ ) radiation at ite-monochromatized Mo Ka (k = 0.71073 A room temperature. All absorption corrections were performed using the SADABS program [27]. The structures were solved by direct methods [28] and refined on F2 by full-matrix least-squares using the SHELXTL-97 program package [28]. All non-hydrogen atoms were refined anisotropically. The organic hydrogen atoms were generated ˚ ). However, in compounds 1 and geometrically (C–H 0.96 A 2, nitrogen atom of dimethylammonium was disordered over three positions with occupancy of 1/3. The crystallographic data for the complexes are listed in Table 1. CCDC-265463 for 1, CCDC-266305 for 2, CCDC-265464 for 3 and CCDC-265465 for 4 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge at www.ccdc.cam.ac.uk/conts/ retrieving.html (or from the Cambridge Crystallographic Data Center, 12, Union Road, Cambridge CB2 1EZ, UK; fax: (Internet) +44 1223/336 033; E-mail: deposit@ ccdc.cam.ac.uk). 3. Results and discussion 3.1. Synthetic chemistry All of the four complexes were prepared with hydrothermal method and solution method. We have attempted to synthesize new porous frameworks with 3,3 0 ,4,4 0 -benzophenonetetracarboxylic ligand, which has similar size to H2hfipbb [H2hfipbb = 4,4 0 -(hexafluoroisopropylidene)bis(benzoic acid)] in Pan’s work [5]. However, we unexpectedly got six formate coordination polymers from the

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Table 1 Crystallographic data for the four complexes

Formula Fw Crystal size (mm) Crystal system Space group ˚ a/A ˚ b/A ˚ c/A a/ b/ c/ ˚3 V/A

1

2

3

4

C5H11NNiO6 239.86 0.32 · 0.28 · 0.22 Trigonal R-3c 8.1368(19) 8.1368(19) 22.071(7) 90.00 90.00 120.00 1265.5(6) 6 1.888 2.299 293(2) 0.71073 920 253 0.0464 35 1.009 0.0371 0.1091 0.0476 0.1210 0.429 and 0.365

C5H11NCoO6 240.08 0.47 · 0.32 · 0.28 Trigonal R-3c 8.2062(9) 8.2062(9) 22.296(4) 90.00 90.00 120.00 1300.3(3) 6 1.840 1.979 293(2) 0.71073 951 262 0.0480 26 1.140 0.0465 0.1109 0.0538 0.1161 0.397 and 0.604

C12H20CoN2O9 395.23 0.42 · 0.35 · 0.23 Monoclinic Cc 10.5245(11) 20.292(2) 8.1405(8) 90.00 102.250(2) 90.00 1698.9(3) 4 1.545 1.058 293(2) 0.71073 2510 1596 0.0188 234 1.055 0.0367 0.1033 0.0389 0.1068 0.348 and 0.536

C12H20N2NiO9 395.01 0.36 · 0.32 · 0.20 Monoclinic Cc 10.5032(18) 20.087(3) 8.1405(14) 90.00 102.656(3) 90.00 1675.8(5) 4 1.566 1.206 293(2) 0.71073 2554 1730 0.0346 273 1.093 0.0593 0.1540 0.0662 0.1628 0.665 and 0.812

Z Dc/g cm3 l/mm1 T/K ˚ kðMo KaÞ=A Reflections collected Unique reflections Rint Parameters S on F2 R1 (I > 2r(I))a b wR2 (I > 2r(I)) R1 (all data) b wR2 (all data) ˚ 3] Dqmin and Dqmax [e/A P P a R1 ¼ kF 0 j  jF c k= jF 0 j. hP .P i1=2 b wR2 ¼ wðF 20  F 2c Þ2 . wðF 20 Þ2

hydrolysis of N,N 0 -dimethylformamide (DMF). Two of the polymers, [M(HCOO)2(H2O)2] (M = Co, Ni), were simple metal–formate hydrates and previously published [29,30]. The other four were novel complexes with porous structures. In 3 and 4, we used 4,4 0 -bipyridine in order to generate different porous frameworks from complex 1 and 2. Usually, DMF undergoes hydrolysis with drastic heating in concentrated acidic or basic solution. In recent years, the hydrolysis of DMF with the presence of metal ions has also been observed [31,32]. Although the mechanism of this reaction has not been very clear, chemists speculated that the metal ions in some way catalyzed this reaction. As the contrast to the hydrolysis reaction of DMF, we used formic acid directly to synthesize the four complexes. We obtained the aimed products with much higher yield under mild conditions. All the four complexes have strong absorptions at 1550–1610 cm1 in their IR spectra, corresponding to the stretching of formate anion. In the IR spectra of 1 and 2, the weak absorption bands at 3022–2796 cm1 are corresponding to the stretching of protonated dimethylammonium. The bonds at 1348, 1028 and 812 cm1 are characteristic absorption of C–N groups. In the IR spectra of 3 and 4, several sharp absorption bands from 1493 to 1223 cm1 are corresponding to the stretching of 4,4 0 bipyridine.

3.2. Description of the structures Complexes 1 and 2 are allomers. These two complexes crystallize in the high symmetry trigonal space group R3c. Selected bond lengths and angles of 1 and 2 are listed in Tables 2 and 3. The ORTEP drawing of 1 is shown in Fig. 1. The central Ni atom is coordinated by six formate anions to complete its octahedral coordination sphere. ˚ in 1 and Co–O The average Ni–O distance is 2.082(3) A ˚ distance is 2.117(3) A in 2. The bond angles around M sites are 88.6–91.4 in 1 (88.8–91.2 in 2) for cis O–M–O angles and 180.0 for trans O–M–O angles, characterizing the distortion of the MO6 octahedra. Every formate anion connects two metal atoms by l2-bridging coordination mode. ˚ in 1 and 6.021 A ˚ in 2, The next M–M distance is 5.967 A which is much longer than that in Co3(HCOO)6 in literature [25]. The l2-bridging formate ligands link the metal Table 2 Selected bond lengths and angles of complex 1 Ni(1)–O(1) O(1)–Ni(1)–O(1)#1 O(1)–Ni(1)–O(1)#2 O(1)#1–Ni(1)–O(1)#2

2.082(3) 180.0 91.36(12) 88.64(12)

Symmetry transformations used to generate equivalent atoms: #1 x, y, z + 1; #2 x + y, x, z.

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Table 3 Selected bond lengths and angles of complex 2 Co(1)–O(1) O(1)#1–Co(1)–O(1) O(1)#1–Co(1)–O(1)#2 O(1)–Co(1)–O(1)#2

2.117(3) 180.0 91.17(13) 88.83(13)

Symmetry transformations used to generate equivalent atoms: #1 x, y, z; #2 x  y, x, z.

Fig. 2. The channel in 1 and 2 viewed along [1 0 0] direction: light blue balls, Co(Ni) atoms; red balls, O atoms; gray balls, C atoms. (For interpretation of color in this figure legend, the reader is referred to the web version of this article.)

Fig. 1. ORTEP drawing of complex 1.

atoms into a 3-D network. The network defines a 3-D interconnected channel system parallel to h4 2 1i with ˚ in size (shown in rectangular apertures about 6.4 · 4.9 A Fig. 2). The dimethylammonium cations occupy the structural cavities as shown in Fig. 3. The void volume of the cavities lined by the formate ligands is estimated by PLATON [33] to be 30.2% of the total volume in 1 and 33.9% in 2. Additionally, the result of hydrolysis of DMF, formate anion was very easily captured by the metal ions through coordination bond, but dimethylammonium was very rarely captured in crystals [34–36]. XRPD patterns of the two complexes are very similar to the simulated ones, which confirmed the accuracy of the two structures (shown in the supplementary materials S1, S2). Thermography analyses of 1 and 2 were tested to reveal the stability of the frameworks. There is no weight loss in the thermography curves until 222.0 C for 1 and 213.0 C for 2, and then the frameworks began to collapse. This indicates that dimethylammonium is difficult to be expulsed from the frameworks, so the two complexes cannot be used for gas storage in spite of their large void space. Complexes 3 and 4 are also allomers and they crystallize in non-centrosymmetric space group Cc. Selected bond lengths and angles of 3 and 4 are listed in Tables 4 and 5, respectively. Fig. 4 illustrates the coordination environ-

Fig. 3. The cavities filled by ðCH3 Þ2 NHþ 2 in complexes 1 and 2.

ment of center Co atom in 3. In this structure, Co(II) is coordinated by two l2-bridged 4,4 0 -bipyridine, two l2bridged formate anions, one end-coordinated formate anion and one water molecule to finish a distorted octahe˚ and dral geometry. The average Co–O distance is 2.102 A ˚ Co–N distance is 2.152 A in 3 and the relevant distances ˚ . The bond angles around M sites in 4 are 2.091 and 2.126 A are 84.1–96.0 in 3 (84.6–94.9 in 4) for cis O–M–O/N

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Table 4 Selected bond lengths and angles of complex 3 Co(1)–O(5) Co(1)–O(1) Co(1)–O(3) O(5)–Co(1)–O(1) O(5)–Co(1)–O(3) O(1)–Co(1)–O(3) O(5)–Co(1)–O(4)#1 O(1)–Co(1)–O(4)#1 O(3)–Co(1)–O(4)#1 O(5)–Co(1)–N(1) O(1)–Co(1)–N(1)

2.076(6) 2.091(5) 2.112(4) 174.9(2) 92.2(2) 92.56(18) 88.3(2) 87.09(18) 177.53(19) 88.8(2) 88.83(18)

Co(1)–O(4)#1 Co(1)–N(1) Co(1)–N(2)#2 O(3)–Co(1)–N(1) O(4)#1–Co(1)–N(1) O(5)–Co(1)–N(2)#2 O(1)–Co(1)–N(2)#2 O(3)–Co(1)–N(2)#2 O(4)#1–Co(1)–N(2)#2 N(1)–Co(1)–N(2)#2

2.116(4) 2.149(5) 2.154(5) 95.97(18) 86.47(18) 90.3(2) 92.09(19) 84.05(18) 93.53(18) 179.1(3)

Symmetry transformations used to generate equivalent atoms: #1 x + 1/2, y + 1/2, z + 1/2; #2 x + 1/2, y  1/2, z.

Table 5 Selected bond lengths and angles of complex 4 Ni(1)–O(1) Ni(1)–O(2) Ni(1)–N(4) O(1)–Ni(1)–O(2) O(1)–Ni(1)–N(4) O(2)–Ni(1)–N(4) O(1)–Ni(1)–O(6) O(2)–Ni(1)–O(6) N(4)–Ni(1)–O(6) O(1)–Ni(1)–O(3)#1 O(2)–Ni(1)–O(3)#1

2.075(9) 2.084(8) 2.079(9) 89.0(4) 91.1(4) 93.3(3) 174.5(4) 86.5(3) 92.3(3) 92.3(3) 177.6(4)

Ni(1)–O(6) Ni(1)–O(3)#1 Ni(1)–N(1)#2 N(4)–Ni(1)–O(3)#1 O(6)–Ni(1)–O(3)#1 O(1)–Ni(1)–N(1)#2 O(2)–Ni(1)–N(1)#2 N(4)–Ni(1)–N(1)#2 O(6)–Ni(1)–N(1)#2 O(3)#1–Ni(1)–N(1)#2

2.100(8) 2.103(8) 2.126(8) 84.6(3) 92.3(3) 88.5(4) 87.2(3) 179.4(5) 88.1(4) 94.9(4)

Symmetry transformations used to generate equivalent atoms: #1 x + 1/2, y + 1/2, z + 1/2; #2 x + 1/2, y + 1/2, z.

angles and 174.9–177.5 in 3 (174.5–179.4 in 4) for trans O–M–O/N angles. The bridged formate anion connects Co atoms into a chain and the 4,4 0 -bipyridine forms another chain. The M–M distance linked by formate anion ˚ in 3 (5.899 A ˚ in 4) and the M–M distance linked is 5.932 A ˚ in 3 (11.334 A ˚ in 4). The Co-forby 4,4 0 -bpy is 11.409 A mate chains are all aligned parallel to [1 0 1], but Co-bipyridine chains align alternately in [1 1 0] or [1 1 0] directions. Fig. 5 shows the sheet formed by Co-formate chains aligned along [1 0 1] and Co-bipyridine chains aligned along

Fig. 5. The sheet parallel to h1 1 1i direction in complexes 3 and 4: light blue balls, Co(Ni) atoms; red balls, O atoms; blue balls, N atoms; gray balls, C atoms. (For interpretation of color in this figure legend, the reader is referred to the web version of this article.)

[1 1 0] containing every other Co atom. Sheets are linked in the third direction by Co-bipyridine chain parallel to [1 1 0] containing the alternate Co atoms. The 3-D structure defines a 1-D channel system parallel to the [0 0 1] direction (see Fig. 6) with rectangular apertures of about ˚ . The free water molecules fill in the channels 7.0 · 9.2 A and form plenty of hydrogen bonds with each other, which enhance the stability of the framework greatly. The void space is estimated 26.5% of the total volume in 3 and 27.3% in 4, which is smaller than those in 1 and 2. Thermography analyses of 3 and 4 were also tested. Complex 3 lost 23.49% of total molecular weight from 61.0 to 109.0 C, corresponding to the loss of five water molecules in the structure (calc. 22.77%). At 270.0 C, the framework began to collapse. Complex 4 lost 23.35% of the total molecule weight from 69.0 to 140.0 C, corresponding to the loss of the water molecules (calc. 22.78%) and the framework collapsed at 219.0 C. XRPD patterns were used to check the phase of both 3 and 4. The XRPD patterns of the two complexes before and after water expulsion are

Fig. 4. ORTEP drawing of complex 3.

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References

Fig. 6. The porous structure of 3 and 4 viewed along [0 0 1] direction (the free water molecules and the end-coordinated formate anions were omitted for clarity): light blue balls, Co(Ni) atoms; red balls, O atoms; blue balls, N atoms; gray balls, C atoms. (For interpretation of color in this figure legend, the reader is referred to the web version of this article.)

almost the same (shown in the supplementary materials S3, S4), indicating that the framework does not collapse after removal of guest water molecules. This makes them possible for the application in gas storage materials. 4. Conclusion We have reported the syntheses and structures of four porous frameworks constructed by formate anion. The complexes were synthesized not only by hydrothermal method but also by solution method. X-ray single crystal diffraction shows that they have 3-D porous networks and there are plenty of cavities in the four structures. The void space is estimated 26.5% and 27.3% of the total volume in 3 and 4 by PLATON, which is close to 29.6% in [Co3(HCOO)6] in literature [25]. TGA shows the frameworks could be stable until 219–270 C. XRPD confirm that water molecules can be expulsed from the structures without collapse of the frameworks, so complexes 3 and 4 may find useful applications in gas storage and catalysis. Acknowledgements We are grateful to the financial support from NNSF of China (90206040, 20325106, and 20333070), NSF of Fujian Province (E0520003), and the ‘‘One Hundred Talent’’ project from CAS. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.micromeso. 2005.11.046.

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