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Synthesis, structure and properties of the first inorganic framework Ba(II) perchlorate polymer with organic template
Journal of Molecular Structure 1030 (2012) 177–183
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Synthesis, structure and properties of the first inorganic framework Ba(II) perchlorate polymer with organic template Yan-Hong Yu a,⇑, Kun Qian b, Yao-Hui Ye b a b
College of Chemistry and Chemical Engineering, Jiangxi Science and Technology Normal University, Nanchang 330013, PR China Academic Administration, Jiangxi University of Traditional Chinese Medicine, Nanchang 330004, PR China
a r t i c l e
i n f o
Article history: Received 23 January 2012 Received in revised form 9 April 2012 Accepted 9 April 2012 Available online 16 April 2012 Keywords: Metal complex Crystal structure Inorganic-framework Fluorescence
a b s t r a c t The first 2D open-architecture Ba(II) perchlorate with organic template, [(H+4-MP)2Ba(ClO4)4]n (1) (4-MP = 4-methylpyridine), has been synthesized and characterized by single-crystal and powder Xray diffraction, elemental analysis, IR, 1H NMR, TGA, DSC and fluorescence properties. The Ba(II) centers of the icosahedral (BaO12) were chelated through l2-perchlorate donors to form a 2D (4, 4) topology with the protonated amine molecules mounted to the main body of the inorganic framework by N–H O Hbonding interactions. To verify the generality of the synthetic methods, 4-MP has been replaced by other different amine templates. The results have shown that the crystallization processes are very sensitive to the induced effect of the organic templates. Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction The divalent and trivalent metal silicates [1], carboxylates [2–4] and phosphates [5,6] constituted the major families of inorganic framework compounds in the past few decades. And in recent studies, the synthesis and properties of some new inorganic open-architecture compounds have been widely investigated (formed by other oxyanions such as selenates [7], sulfates [8] and selenites [9]). Thus, a variety of new layered frameworks of oxyanion with the kagome structure have been prepared and characterized [10–15]. By comparing these reported organic-template compounds with inorganic-framework structure, it can be found that the four O atoms of oxyanions (XO4, X = P, S, Se and Si) coordinate to the metal centers in double bidentate bridging mode resulting in the formation of homologous inorganic-framework structures. Similarly, the ClO4 has the same XO4 style, and the X herein is halogen Cl. However, its inorganic open-framework structures based on divalent and trivalent metal ions have not yet been reported. Therefore, based on the above conclusions, the ClO4 anion was chosen as first building block to crystallize with the metal ions through the induction of amine templates. And then a series of researches have been carried out (Herein, the metal ions are transition metal ions and alkaline earth metal ions, the organic templates are the aromatic amines, respectively.) [16–26]. Fortunately, one 2D
⇑ Corresponding author. Tel./fax: +86 791 7118811. E-mail address: [email protected] (Y.-H. Yu). 0022-2860/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.molstruc.2012.04.022
organic-template Ba(II) perchlorate with inorganic open-framework structure, [(C6H8N)2Ba(ClO4)4]n (1), has been successfully synthesized by employing 4-methylpyridine (4-MP) as the structure-induced agent through two different reaction routes (Scheme 1). Then, its single crystal structure, IR, X-ray powder diffraction (XRPD), thermogravimetric analysis, elemental analysis, 1H NMR, DSC and luminescent properties were investigated. To verify the generality of the synthetic methods, additional reactions have been carried out with different organic templates (summarized in Scheme 2). Interestingly, they failed to get any open-architecture structures similar to compound 1, and only inorganic compounds, organic single molecule compounds or other types of polymers have been obtained. In other words, this synthetic route is not general for other amines, and it may be due to different spatial stacking. Therefore, different templates will adopt different crystalline forms. Several similar organic-templated structures have been reported in the Cambridge database [27–29], but the DABCO-templated K(I) perchlorate is the only compound to possess the same coordination modes of compound 1 by comparing their detailed crystal structures [10]. 2. Experimental section 2.1. Material and instrument Chemicals and solvents in this work were commercially obtained and used without any further purification. Elemental analysis for carbon, hydrogen and nitrogen were performed on a Vario EL III elemental analyzer. The infrared spectra (4000–450 cm1)
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Scheme 1. Synthesis process and the coordination modes of compound 1.
Scheme 2. The products and their coordination modes by adopting different organic templates.
were recorded by using KBr pellet on a Bruker Vector 22 spectrophotometer. X-ray powder diffraction (XPRD) data were collected with a Siemens D5005 diffractometer with Cu Ka radiation (k = 1.5418 Å). Differential scanning calorimetry (DSC) was carried out on a model Pyris1 differential scanning calorimeter. Thermogravimetric analyses were performed on a simultaneous SDT 2960 thermal analyzer under flowing N2 with a heating rate of 20 °C/min from ambient temperature to 700 °C. The fluorescent spectra were recorded on a Shimadzu Instrument FL/FS-920 fluorescent spectrometer.
2.2. Preparation of the compounds Compound 1 was synthesized by employing mild solvothermal methods in the presence of organic amine. BaO (2 mmol, 0.306 g) was added into an EG/MeOH/HAC mixture solution (5.0, 5.0 and 1.5 mL, respectively) under constant stirring (EG = ethylene glycol, HAC = acetic acid). To this solution, 0.372 g (4 mmol) of 4-methylpyridine was slowly added. Finally, 0.95 g (8 mmol) of NH4ClO4 and 0.33 g (3 mmol) of HCl (36%) were added into the mixture, and the mixture was stirred for 5 h to obtain a homogeneous gel.
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The final mixture with the molar composition of BaO/ClO4 /4-MP (1:4:2) was transferred into a 20 mL Teflon-lined acid digestion bomb and heated at 135 °C for 7 days under autogenous pressure. Then the reaction was slowly cooled to room temperature at a rate of 3 °C/h. Colorless block monophasic crystals suitable for X-ray diffraction were obtained in 51% yield (based on BaO). 1H NMR (300 MHz, DMF, TMS, 298 K): d (ppm): 8.92 (d, 2 H, aromatic-H), 8.12 (d, 2H, aromatic-H) and 2.43 (s, 3H, methyl-H). Elemental analysis for 1, C12H16BaCl4N2O16 (723.41): Anal. (%) calcd. C 19.91, H 2.21, N 3.87; found C 19.82, H 2.13, N 3.74. IR spectrum (cm1, KBr): 3458(s), 3087(m), 2997(s), 2865(m), 1604(w), 1573(m), 1467(m), 1369(w), 1342(w), 1257(m), 1203(m), 1079(s), 1058(m), 927(s), 866(w), 778(m), 728(w), 705(m), 668(w), 649(m), 632(w), 619(m)), 594(w), 554(w), 501(w). For the synthesis of other target compounds in Scheme 2: the same experimental routes were adopted, only the 4-MP was replaced by other templates.
2.3. Crystal structure determination The single crystals were prepared as described above. A colorless block-formed crystal with a dimension of 0.35 0.30 0.30 mm was employed for the X-ray diffraction experiment. Diffraction data were collected with a Bruker SMART APEX CCD based on diffractometer operating at room temperature. Intensities were collected with graphite monochromatized Mo Ka radiation (k = 0.71073 Å) operating at 50 kV and 40 mA, using w–x scans technique. The data reduction was made with the Bruker SAINT package [30]. Absorption corrections were performed using the SADABS program [31]. The structures were solved by direct methods and refined on F2 by full-matrix least-squares with anisotropic
Table 1 Crystal data and structure refinement for 1 and 2. Empirical formula
C12H16BaCl4N2O16
BaCl2H4O2
Formula weight Temperature (K) Crystal size (mm) Wavelength (Å) Crystal system Space group a (Å) b (Å) c (Å) b (°) V (Å3) Z Dcalc. (mg m3) l (mm1) F(0 0 0) h range (°) Index ranges
723.41 293 (2) 0.35 0.30 0.30 0.71073 Monoclinic P21/c 12.295 (4) 9.609 (3) 10.034 (3) 101.489 (5) 1161.7 (7) 2 2.068 2.250 708 2.45–27.48 15 h 15, 10 k 10, 13 l 13 7837/2613 [R(int) = 0.0306] 97.9%
244.27 293 (2) 0.35 0.30 0.30 0.71073 Monoclinic P21/c 6.714 (4) 10.888 (5) 9.705 (3) 132.743 (2) 521.06 (3) 4 3.114 8.501 440 3.42–27.47 8 h 8, 11 k 14, 11 l 12 2808/1131 [R(int) = 0.0938] 94.8%
2613/0/161
1131/0/47
1.194
1.146
R1 = 0.0182, wR2 = 0.0484
R1 = 0.0679, wR2 = 0.1803
R1 = 0.0229, wR2 = 0.0676 0.615 and 0.788e. Å3
R1 = 0.0687, wR2 = 0.1820 2.985 and 5.531e. Å3
Reflections collected/unique Completeness to h = 27.45° Data/restraints/ parameters Goodness-of-fit on F2 Final R indices [I > 2sigma(I)]ab R indices (all data) Largest diff. peak and hole a b
Table 2 Selected structural data for 1. Bond lengths (Å) and bond angles (°) Ba(1)–O(5) 2.8402(19) Ba(1)–O(6)#3 2.8474(17) #2 Ba(1)–O(4) 2.8723(17) Ba(1)–O(3) 2.8742(18) #3 Ba(1)–O(2) 2.8961(18) Ba(1)–O(1)#2 2.9186(17) O(5)–Ba(1)–O(5)#3 180.0 O(5)#3–Ba(1)–O(6) 131.37(5) O(5)–Ba(1)–O(6) 48.63(5) #3 #2 O(5) –Ba(1)–O(4) 69.61(4) #3 #2 70.21(5) O(6) –Ba(1)–O(4) O(5)#3–Ba(1)–O(4)#4 100.39(4) O(6)#3–Ba(1)–O(4)#4 109.79(4) O(4)#2–Ba(1)–O(4)#4 180.0 O(5)–Ba(1)–O(3) 106.87(4) O(6)–Ba(1)–O(3) 62.62(5) #4 O(4)–Ba(1)–O(3) 66.64(5) #3 73.13(5) O(5)–Ba(1)–O(3) O(6)–Ba(1)–O(3)#3 117.38(5) O(4)#4–Ba(1)–O(3)#3 113.36(5) O(5)#3–Ba(1)–O(2) 67.66(5) O(6)#3–Ba(1)–O(2) 111.91(5) O(4)#2–Ba(1)–O(2) 67.25(5) O(3)–Ba(1)–O(2) 47.90(4) #3 #3 O(5) –Ba(1)–O(2) 112.34(5) #3 #3 O(6) –Ba(1)–O(2) 68.09(5) O(4)#2–Ba(1)–O(2)#3 112.75(5) O(3)–Ba(1)–O(2)#3 132.10(4) O(2)–Ba(1)–O(2)#3 180.0 O(5)–Ba(1)–O(1)#2 6.68(5) O(6)#3–Ba(1)–O(1)#2 7.06(5) O(4)–Ba(1)–O(1) 32.31(4) #3 O(3) –Ba(1)–O(1) 0.77(5) 2 O(2)# –Ba(1)–O(1) 10.87(5) O(5)#1–Ba(1)–O(1)#1 13.32(5) O(6)–Ba(1)–O(1)#1 12.94(5) O(4)–Ba(1)–O(1)#1 7.69(4) O(3)#3–Ba(1)–O(1)#1 09.23(5) #2 #1 O(2) –Ba(1)–O(1) 69.13(5) Hydrogen bonds (Å) and (°) D–H A d(D–H) N1–H1 O1 0.86
Ba(1)–O(5)#3 Ba(1)–O(6) Ba(1)–O(4)#4 Ba(1)–O(3)#3 Ba(1)–O(2)#2 Ba(1)–O(1)#4 O(5)#3–Ba(1)–O(6)#3 O(5)–Ba(1)–O(6)#3 O(6)#3–Ba(1)–O(6) O(5)–Ba(1)–O(4)#2 O(6)–Ba(1)–O(4)#2 O(5)–Ba(1)–O(4)#4 O(6)–Ba(1)–O(4)#4 O(5)#3–Ba(1)–O(3) O(6)–Ba(1)#3–O(3) O(4)#2–Ba(1)–O(3) O(5)#3–Ba(1)–O(3)#3 O(6)#3–Ba(1)–O(3)#3 O(4)#2–Ba(1)–O(3)#3 O(3)–Ba(1)–O(3)#3 O(5)–Ba(1)–O(2) O(6)–Ba(1)–O(2) O(4)#4–Ba(1)–O(2) O(3)#3–Ba(1)–O(2) O(5)–Ba(1)–O(2)#3 O(6)–Ba(1)–O(2)#3 O(4)#4–Ba(1)–O(2)#3 O(3)#3–Ba(1)–O(2)#3 O(5)#3–Ba(1)–O(1)#2 (6)#3–Ba(1)–O(1)#2 (4)#1–Ba(1)–O(1)#2 (3)#2–Ba(1)–O(1) (2)#3–Ba(1)–O(1) (5)–Ba(1)–O(1)#1 (6)#1–Ba(1)–O(1)#1 (4)#1–Ba(1)–O(1)#1 (3)#2–Ba(1)–O(1)#1 (2)#3–Ba(1)–O(1)#1 O(1)–Ba(1)–O(1)#1 d(H A) 2.24
d(D A) 3.069(3)
2.8402(19) 2.8474(17) 2.8723(17) 2.8742(17) 2.8961(18) 2.9186(17) 48.63(5) 131.37(5) 180.0 100.39(5) 109.79(5) 69.61(4) 70.21(4) 73.13(4) 117.38(5) 113.36(5) 106.87(5) 62.62(5) 66.64(5) 180.0 112.34(5) 68.09(5) 112.75(5) 132.10(4) 67.66(5) 111.91(5) 67.25(5) 47.90(4) 113.32(5) 12.94(5) 7.69(4) 09.23(5) 9.13(5) 6.68(5) 7.06(5) 32.31(4) 0.77(5) 10.87(5) 180.0 <(DHA) 161.6
Symmetry transformations used to generate equivalent atoms: #1 x 1, y 1/2, z + 3/2. #2 x 1, y, z + 1. #3 x 1, y + 1/2, z + 3/2. #4 x, y 1/2, z 1/2.
displacement parameters for all non-hydrogen atoms in the two structures. Non-hydrogen atoms were refined with anisotropic thermal parameters; those bonded to the C and N atoms were placed in calculated positions and refined in riding mode, with N–H = 0.86 Å (N), C–H = 0.93 Å (aromatic) and 0.96 Å (methyl), and Uiso (H) = 1.2 Ueq (aromatic C and N) and 1.5 Ueq (methyl). All computations were carried out using the SHELXTL-97 program package [32]. Details about data collection and refinement of the compounds are summarized in Table 1, and the selected bond distances, angles and H-bonding are listed in Table 2. 3. Results and discussion 3.1. Synthesis
R1 = R||Fo| |Fc|/R|Fo|. wR2 = {R[w(F 2o F 2o )2]/Rw[(F2o)2]}1/2.
For the open-framework polymer 1, some experimental details have been mentioned in Scheme 1. The reaction process and the molar ratios of reactants are crucial to the final product and the yield. The most reasonable molar proportion of BaO/NH4ClO4/4MP is 1:4:2. If the Ba(ClO4)2 and 4-MP were chosen as the initial reactants, then only white powder can be found. This indicates that the direct method is not feasible. To the mixed solvent: the most reasonable volume proportion should be 1/1/0.3 (HAC possess the minimum amount) to get the highest yield. The small amount
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of HAC in the solvent can play the key role, which makes the BaO and 4-MP slowly dissolved in the solution and bonded with the ClO4 , then the templated polymer 1 slowly crystallized [20–26,33]. To expand the scope of the above studies, 4-MP has been replaced by some different amine templates. However, only inorganic salts, organic single molecule compounds or other types of polymers have been obtained, none of them similar to compound 1. Therefore, this synthetic method is not general for other amine templates. Detailed experimental results were summarized in Scheme 2. To pyridine template: the products are a 2D polymer bridged by l2-H2O and l3-ClO4 or single molecule salt, and the structures are consistent with those in the reported literatures [28,29,34]; for the other amines, they were listed as follows: to 1, 10-phenanthroline: single molecule compound [35], or organic salt [36]; to 2, 2-bipyridine: a 1D polymer bridged by l2-ClO4 [37]; to 3-methylpyridine: 2D polymer bridged by l2-H2O and l3-ClO4 [29]; to 2-methylpyridine, amino-pyridine or isonicotinonitrile: inorganic compound 2. 3.2. IR, UV/Vis spectra and XRPD The structures of 1 and 2 were identified by satisfactory elemental analysis, IR and X-ray diffraction. Compound 1: The IR spectra shown a series of strong peaks at 1573, 1467, 1203, 778 and 705 cm1, those peaks are the characteristic of aromatic ring. The bands at 1079, 1058, 927, 649, 619 cm1 are attributed to the ClO4 groups. To compare with the IR spectrum of free ClO4 group (inorganic perchlorates), the absence of a strong peak at 632 cm1 for 1 shows that the free ClO4 groups disappeared, and 1 the new double peaks at 649 cm and 619 cm1 indicate strong coordination of the ClO4 oxygen to the Ba(II) centers through bidentate bridging mode [38], which is consistent with its X-ray single structure. Moreover, the double peaks at 1079 cm1 and 927 cm1 are the characteristics of mas(ClO4 ) and ms(ClO4 ), respec1 tively. The broad band around 3458 cm of N–H vibrations suggests that the nitrogen atoms of the ligands were protonated to balance the ClO4 anions. The 3087 and 2997 cm1 peaks correspond to aromatic H atoms. The characteristic peaks of methyl are presented at 2865, 1369 and 1257 cm1. Compound 2: The IR spectrum shows the very simple peaks at 3452, 3379, 1105, 1078, 778, 705 and 554 cm1. The UV/Vis spectrum of the ligand and complex 1 were measured in the solid state at room temperature. It shows that both the 4-MP and the complex exhibit absorption bands at the range of 200–400 nm. After coordination, the absorption bands underwent a slightly redshift of 2 nm, owing to the N–H O H-bond interactions to increase the stability. The above spectral analyses are in agreement with the determined single-crystal structure. X-ray powder diffraction (XRPD) analysis: The agreement between the experimental and simulated XRPD patterns indicated the phase purity of 1 (Fig. S1). The difference in reflection intensities between the simulated and experimental patterns was mainly due to the different powder size during collection of the experimental XRPD data.
bonding to the metal ions. The Cl–O bond distances are in the range of 1.423(2)–1.457(2) Å and the O–Cl–O bond angle range is 107.15(10)–110.70(10)°. The icosahedral Ba(II) was located in special position with an occupancy of 0.5, and sits in an irregular 12-coordinate (BaO12) environment composed of six chelate perchlorate anions donors (Fig. 1a). The Ba–O bond distances are in the range of 2.840(2)–2.919(2) Å, and O–Ba–O bond angles in the range of 47.69(4)–180.0°. By eliminating the Ba–O bonds and connecting the neighboring oxygen atoms, the oxygen–oxygen non-bonded schematic diagrams showed the framework of the distorted icosahedral [Ba(ClO4)6] cage (Fig. 1b). These cages are held together through corner-sharing O–Cl(1)–O chelate linkages, thereby forming the straight chain. Such chains are covalently bonded to each other by the Clð1ÞO 4 group forming the layer structure in the bc-plane (Fig. 2a). The Clð1ÞO 4 tetrahedra from the adjacent chains connect alternatively via four Ba–O–Cl linkages to form four connected quadrilateral, leading to the formation of an eight membered aperture (Fig. 2a). The compound 1 has the similar framework with the DABCO K(I) perchlorate and THF Ba(II) perchlorate [10,27]. And the structure can be compared to the mineral sulfoborite which is made up of complex sheets of (MgO6) and (SO4) tetrahedra [39]. In the mineral amarantite, octahedral tetramers are polymerized to form octahedral chains parallel to [1 0 0] and linked by (SO4) tetrahedral. To get better insight into the framework structure, its topological analysis was carried out. As discussed above, every Ba(II) center can be seen as one node, each Ba(II) node coordinated with four Clð1ÞO 4 linkers, thus can be defined as four-connecting juncture. And each Clð1ÞO 4 acts as a twoconnecting linker. According to the simplification principle of the TOPOS software [40], the overall network topology was described as a (4, 4)-connected framework (Fig. 2b). The structure of compound 1 is constructed from macroanionic inorganic-framework layers with the protonated amine molecules residing in the interlamellar space, which ensures the stability of the structure through bounding the organic amine to the main body of the inorganic framework by N–H O H-bond interactions (as shown in Fig. 3). The inorganic compound 2 crystallized in the monoclinic space group P21/c. The asymmetric unit contains two chloride anions, two water molecules and one Ba(II) ion. The irregular nine-coordinate (BaCl5O4) environment composed of three l3-Cl1 bridge chloride anions, two l2-Cl2 bridge chloride anions and four l2-O (two O1W and two O2W molecules) donors (Fig. 4). The neighboring metal centers are connected by two ways: (1) The Ba ions are
3.3. Description of the crystal structure Single-crystal X-ray analysis reveals that complex 1 crystallized in the monoclinic space group P21/c. The asymmetric unit contains two perchlorate anions, one template-amine cation and half Ba(II) ion. The inorganic framework shows negative charges. And the organic-template amine was protonated to maintain the charge bal ance. To the ClO4 anions: the Clð1ÞO 4 adopts double bidentate bridging mode by four O atoms connecting to two Ba(II) centers, and can be seen as a linear linker. But the terminal Clð2ÞO 4 has only one bidentate Cl–O–Ba bond, and the other two O atoms are not
Fig. 1a. View of the coordination environment of Ba(II) in complex 1.
Y.-H. Yu et al. / Journal of Molecular Structure 1030 (2012) 177–183
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Fig. 1b. The 12-coordinated Ba(II) center by six ClO4 anions. Left shows the icosahedral Ba(II) ion by the oxygen–oxygen non-bonded connections; right is the same as left but eliminates part of the oxygen and chlorine atoms.
Fig. 2b. The 2-D (4,4)-connected topologic structure of 1.
cross-linked with a common Ba(II) atom culmination, thus the inorganic 2D skeleton was formed parallel to the ac-plane. The 2D inorganic-skeleton planes were parallel-linked by the l3-Cl1 atoms resulting in the formation of a 3D inorganic network (Fig. 5). 3.4. Thermogravimetric analysis
Fig. 2a. The 2-D polymeric layer with metal atoms represented as polyhedra parallel to the bc-plane. Hydrogen atoms are excluded for clarity.
bridged by aqua l2-O1W and l3-Cl1 atoms resulting in the formation of a binuclear (BaO1WCl1Ba) unit (A) with a Ba Ba distance of 4.906(1) Å and the large Ba–O1W–Ba angle (117.079(2)°) and small Ba–Cl1–Ba angle (100.662(7)°). (2) The additional didentate-bridged l2-Cl2 and l2-O2W atoms bonded to the another two Ba ions through forming four-member binuclear unit [BaO2WCl2Ba] (B). The dinuclear framework units A and B are
The thermal behaviors of the title compound 1 and 2 were investigated from 50 to 700 °C. The DSC and TGA curves are shown in Fig. 6. For compound 1: The DSC curve contains one intense endothermic peak and one continuously exothermic peak. The first endothermic stage occurs in the range of 198–215 °C with the peak temperature at 203 °C, which proves that organic-template molecules were lost during this process. The exothermic peak begins at 432 °C indicating the decomposition of inorganic framework. For compound 2: The DSC curve contains only one intense endothermic anomaly with the sharp peak value at 167 °C. This endothermic peak occurs between 145 and 185 °C, which corresponds to the lost of coordinated water molecules. After that the curve remains straight and unchanged. It is indicating that the final residual compound was unhydrous BaCl2. In the TG diagram of 1, [(Ba(ClO4)4]2(C6H8N)2]n, the two main steps of weight losses were observed in the temperature range from room temperature to
Fig. 3. The simplified N–H O H-bonds network of 1 viewed along the b-axis.
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Fig. 4. View of the coordination environment of complex 2. Fig. 7. Fluorescent emission spectra of the compound 1 and free 4-MP ligand.
To confirm the residual white powder of compound 1, further analysis was carried out. Firstly, the residues were collected, weighed and dissolved in HCl (2 M/mL) completely. Then dilute H2SO4 was added into the above solution until no new precipitate was formed. Finally, the solid precipitates were collected and weighed. After quantitative analysis, we confirmed that the final residue is BaO. Also the XRD of the residual white powder and standard BaO powder sample was investigated. The XRD measurements further confirmed that the residual white powder of compound 1 is BaO (Fig. S2). The difference between the two curves is due to the different powder size. Fig. 5. The 3-D framework of compound 2 viewed along the a-axis.
3.5. Photoluminescent properties The solid-state fluorescent property of the complex 1 was investigated at room temperature. As illustrated in Fig. 7, upon excitation of the solid sample at k = 320 nm, the intense broad emission bands at 385 nm was observed. Moreover, for excitation wavelength between 280 and 380 nm, the free 4-MP ligand presents a weak photoluminescence emission at 378 nm under the same experimental conditions. The emission of complex 1 is redshifted about 7 nm compared to that of free ligand 4-MP. Obviously, this emission comes from the organic-templated amine molecule. After coordination, the organic amine molecules were protonated and bound to the inorganic skeleton through N–H O H-bond interactions, which promoted the rigidity and the conjugation effect of aromatic pyridine ring. It plays the main role to luminescence intensity and red-shift effect. Thus, the compound 1 and the 4-MP have shown different luminescence properties.
Fig. 6. The DSC and TGA curves for complex 1 and 2.
700 °C. The first step occurs in the range of 187–235 °C, amounting to about 27.7% weight loss and corresponding to the escape of all organic-template molecules (calculated 26.0%). The framework remains undecomposed up to 425 °C where the second weight loss start. The total observed weight loss at 700 °C is 76.9%, and the final presumably residual is BaO. The two decomposition-temperature stages are within the ranges of 150–250 °C and 400–550 °C, respectively. This is the typical features for inorganic open-framework structures containing organic-template molecules. The TG diagram of 2, (BaCl2)2(H2O), shows that the weight loss only occured in the range of 140–191 °C. The total observed weight loss was amounting to about 15.5% (calculated 14.7%). It indicates that all the coordinated water molecules were lossed, and the final residual compound was unhydrous BaCl2. It is consistent with the DSC measurement.
4. Conclusions In summary, one novel inorganic open-framework alkalineearth metal perchlorate polymer with organic template has been successfully synthesized and characterized. Compound 1 was composed of irregular icosahedral (BaO12) units and organic-template amine molecules. The icosahedral centers were chelated through perchlorate anion donors to form a 2D topology with the protonated amine mounted to the main body of the inorganic framework by N–H O hydrogen bond interactions. The synthesis, crystal structure, TGA, DSC, UV, IR and fluorescence properties of the coordination polymer 1 were discussed in details. To verify the generality of the synthetic routes, 4-MP has been replaced by other different amine templates, then a series of reactions have been carried out. But they failed to get any structures similar to compound 1. The results showed that the crystallization processes are very sensitive to the induced effect of the organic templates.
Y.-H. Yu et al. / Journal of Molecular Structure 1030 (2012) 177–183
Acknowledgment This work was financially supported by the National Natural Science Foundation of China and Jiangxi Province NSF. Appendix A. Supplementary material Crystallographic data (excluding structure factors) for the crystal structure of compound 1 have been deposited to the Cambridge Crystallographic Data Centre as supplementary publication no. 837664. Copies of this information may be obtained free of charge from: The Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK. Fax (+44) 1223 336 033 or E-mail: [email protected] or (http://www.ccdc.cam.ac.ck). Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/ 10.1016/j.molstruc.2012.04.022. References [1] A.K. Cheetham, G. Ferey, T. Loiseau, Angew. Chem., Int. Ed. 33 (1999) 3268. [2] C.N.R. Rao, S. Natarajan, A. Choudhury, S. Neeraj, A.A. Ayi, Acc. Chem. Res. 34 (2001) 80. [3] T.M. Reinke, M. Eddaoudi, M. O’Keeffe, O.M. Yaghi, Angew. Chem., Int. Ed. 38 (1999) 2590. [4] R. Vaidhyanathan, S. Natarajan, C.N.R. Rao, Chem. Mater. 13 (2001) 185. [5] D.W. Breck, Zeolite Molecular Sieves, Wiley, New York, 1974. [6] X.Z. Li, M. Li, Z. Li, J.Z. Hou, X.C. Huang, D. Li, Angew. Chem., Int. Ed. 47 (2008) 6371. [7] T. Bataille, D.J. Louer, Mater. Chem. 12 (2002) 3487. [8] A. Choudhury, D. Udayakumar, C.N.R. Rao, Angew. Chem., Int. Ed. 41 (2002) 158. [9] T.M. Klapötke, M. Saein, J. Stierstorfer, Z. Anorg, Allg. Chem. 634 (2008) 1711. [10] Z.M. Jin, Y.J. Pan, X.F. Li, M.L. Hu, L. Shen, J. Mol. Struct. 660 (2003) 67. [11] L. Carlucci, G. Ciani, D.M. Proserpio, Coord. Chem. Rev. 246 (2003) 247. [12] C.D. Wu, A. Hu, L. Zhang, W.B. Lin, J. Am. Chem. Soc. 127 (2005) 8940. [13] J. Yang, Q. Yuo, G.D. Li, J.J. Cao, G.H. Li, J.S. Chen, Inorg. Chem. 45 (2006) 2857.
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Journal of Molecular Structure journal homepage: www.elsevier.com/locate/molstruc
Synthesis, structure and properties of the first inorganic framework Ba(II) perchlorate polymer with organic template Yan-Hong Yu a,⇑, Kun Qian b, Yao-Hui Ye b a b
College of Chemistry and Chemical Engineering, Jiangxi Science and Technology Normal University, Nanchang 330013, PR China Academic Administration, Jiangxi University of Traditional Chinese Medicine, Nanchang 330004, PR China
a r t i c l e
i n f o
Article history: Received 23 January 2012 Received in revised form 9 April 2012 Accepted 9 April 2012 Available online 16 April 2012 Keywords: Metal complex Crystal structure Inorganic-framework Fluorescence
a b s t r a c t The first 2D open-architecture Ba(II) perchlorate with organic template, [(H+4-MP)2Ba(ClO4)4]n (1) (4-MP = 4-methylpyridine), has been synthesized and characterized by single-crystal and powder Xray diffraction, elemental analysis, IR, 1H NMR, TGA, DSC and fluorescence properties. The Ba(II) centers of the icosahedral (BaO12) were chelated through l2-perchlorate donors to form a 2D (4, 4) topology with the protonated amine molecules mounted to the main body of the inorganic framework by N–H O Hbonding interactions. To verify the generality of the synthetic methods, 4-MP has been replaced by other different amine templates. The results have shown that the crystallization processes are very sensitive to the induced effect of the organic templates. Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction The divalent and trivalent metal silicates [1], carboxylates [2–4] and phosphates [5,6] constituted the major families of inorganic framework compounds in the past few decades. And in recent studies, the synthesis and properties of some new inorganic open-architecture compounds have been widely investigated (formed by other oxyanions such as selenates [7], sulfates [8] and selenites [9]). Thus, a variety of new layered frameworks of oxyanion with the kagome structure have been prepared and characterized [10–15]. By comparing these reported organic-template compounds with inorganic-framework structure, it can be found that the four O atoms of oxyanions (XO4, X = P, S, Se and Si) coordinate to the metal centers in double bidentate bridging mode resulting in the formation of homologous inorganic-framework structures. Similarly, the ClO4 has the same XO4 style, and the X herein is halogen Cl. However, its inorganic open-framework structures based on divalent and trivalent metal ions have not yet been reported. Therefore, based on the above conclusions, the ClO4 anion was chosen as first building block to crystallize with the metal ions through the induction of amine templates. And then a series of researches have been carried out (Herein, the metal ions are transition metal ions and alkaline earth metal ions, the organic templates are the aromatic amines, respectively.) [16–26]. Fortunately, one 2D
⇑ Corresponding author. Tel./fax: +86 791 7118811. E-mail address: [email protected] (Y.-H. Yu). 0022-2860/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.molstruc.2012.04.022
organic-template Ba(II) perchlorate with inorganic open-framework structure, [(C6H8N)2Ba(ClO4)4]n (1), has been successfully synthesized by employing 4-methylpyridine (4-MP) as the structure-induced agent through two different reaction routes (Scheme 1). Then, its single crystal structure, IR, X-ray powder diffraction (XRPD), thermogravimetric analysis, elemental analysis, 1H NMR, DSC and luminescent properties were investigated. To verify the generality of the synthetic methods, additional reactions have been carried out with different organic templates (summarized in Scheme 2). Interestingly, they failed to get any open-architecture structures similar to compound 1, and only inorganic compounds, organic single molecule compounds or other types of polymers have been obtained. In other words, this synthetic route is not general for other amines, and it may be due to different spatial stacking. Therefore, different templates will adopt different crystalline forms. Several similar organic-templated structures have been reported in the Cambridge database [27–29], but the DABCO-templated K(I) perchlorate is the only compound to possess the same coordination modes of compound 1 by comparing their detailed crystal structures [10]. 2. Experimental section 2.1. Material and instrument Chemicals and solvents in this work were commercially obtained and used without any further purification. Elemental analysis for carbon, hydrogen and nitrogen were performed on a Vario EL III elemental analyzer. The infrared spectra (4000–450 cm1)
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Scheme 1. Synthesis process and the coordination modes of compound 1.
Scheme 2. The products and their coordination modes by adopting different organic templates.
were recorded by using KBr pellet on a Bruker Vector 22 spectrophotometer. X-ray powder diffraction (XPRD) data were collected with a Siemens D5005 diffractometer with Cu Ka radiation (k = 1.5418 Å). Differential scanning calorimetry (DSC) was carried out on a model Pyris1 differential scanning calorimeter. Thermogravimetric analyses were performed on a simultaneous SDT 2960 thermal analyzer under flowing N2 with a heating rate of 20 °C/min from ambient temperature to 700 °C. The fluorescent spectra were recorded on a Shimadzu Instrument FL/FS-920 fluorescent spectrometer.
2.2. Preparation of the compounds Compound 1 was synthesized by employing mild solvothermal methods in the presence of organic amine. BaO (2 mmol, 0.306 g) was added into an EG/MeOH/HAC mixture solution (5.0, 5.0 and 1.5 mL, respectively) under constant stirring (EG = ethylene glycol, HAC = acetic acid). To this solution, 0.372 g (4 mmol) of 4-methylpyridine was slowly added. Finally, 0.95 g (8 mmol) of NH4ClO4 and 0.33 g (3 mmol) of HCl (36%) were added into the mixture, and the mixture was stirred for 5 h to obtain a homogeneous gel.
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The final mixture with the molar composition of BaO/ClO4 /4-MP (1:4:2) was transferred into a 20 mL Teflon-lined acid digestion bomb and heated at 135 °C for 7 days under autogenous pressure. Then the reaction was slowly cooled to room temperature at a rate of 3 °C/h. Colorless block monophasic crystals suitable for X-ray diffraction were obtained in 51% yield (based on BaO). 1H NMR (300 MHz, DMF, TMS, 298 K): d (ppm): 8.92 (d, 2 H, aromatic-H), 8.12 (d, 2H, aromatic-H) and 2.43 (s, 3H, methyl-H). Elemental analysis for 1, C12H16BaCl4N2O16 (723.41): Anal. (%) calcd. C 19.91, H 2.21, N 3.87; found C 19.82, H 2.13, N 3.74. IR spectrum (cm1, KBr): 3458(s), 3087(m), 2997(s), 2865(m), 1604(w), 1573(m), 1467(m), 1369(w), 1342(w), 1257(m), 1203(m), 1079(s), 1058(m), 927(s), 866(w), 778(m), 728(w), 705(m), 668(w), 649(m), 632(w), 619(m)), 594(w), 554(w), 501(w). For the synthesis of other target compounds in Scheme 2: the same experimental routes were adopted, only the 4-MP was replaced by other templates.
2.3. Crystal structure determination The single crystals were prepared as described above. A colorless block-formed crystal with a dimension of 0.35 0.30 0.30 mm was employed for the X-ray diffraction experiment. Diffraction data were collected with a Bruker SMART APEX CCD based on diffractometer operating at room temperature. Intensities were collected with graphite monochromatized Mo Ka radiation (k = 0.71073 Å) operating at 50 kV and 40 mA, using w–x scans technique. The data reduction was made with the Bruker SAINT package [30]. Absorption corrections were performed using the SADABS program [31]. The structures were solved by direct methods and refined on F2 by full-matrix least-squares with anisotropic
Table 1 Crystal data and structure refinement for 1 and 2. Empirical formula
C12H16BaCl4N2O16
BaCl2H4O2
Formula weight Temperature (K) Crystal size (mm) Wavelength (Å) Crystal system Space group a (Å) b (Å) c (Å) b (°) V (Å3) Z Dcalc. (mg m3) l (mm1) F(0 0 0) h range (°) Index ranges
723.41 293 (2) 0.35 0.30 0.30 0.71073 Monoclinic P21/c 12.295 (4) 9.609 (3) 10.034 (3) 101.489 (5) 1161.7 (7) 2 2.068 2.250 708 2.45–27.48 15 h 15, 10 k 10, 13 l 13 7837/2613 [R(int) = 0.0306] 97.9%
244.27 293 (2) 0.35 0.30 0.30 0.71073 Monoclinic P21/c 6.714 (4) 10.888 (5) 9.705 (3) 132.743 (2) 521.06 (3) 4 3.114 8.501 440 3.42–27.47 8 h 8, 11 k 14, 11 l 12 2808/1131 [R(int) = 0.0938] 94.8%
2613/0/161
1131/0/47
1.194
1.146
R1 = 0.0182, wR2 = 0.0484
R1 = 0.0679, wR2 = 0.1803
R1 = 0.0229, wR2 = 0.0676 0.615 and 0.788e. Å3
R1 = 0.0687, wR2 = 0.1820 2.985 and 5.531e. Å3
Reflections collected/unique Completeness to h = 27.45° Data/restraints/ parameters Goodness-of-fit on F2 Final R indices [I > 2sigma(I)]ab R indices (all data) Largest diff. peak and hole a b
Table 2 Selected structural data for 1. Bond lengths (Å) and bond angles (°) Ba(1)–O(5) 2.8402(19) Ba(1)–O(6)#3 2.8474(17) #2 Ba(1)–O(4) 2.8723(17) Ba(1)–O(3) 2.8742(18) #3 Ba(1)–O(2) 2.8961(18) Ba(1)–O(1)#2 2.9186(17) O(5)–Ba(1)–O(5)#3 180.0 O(5)#3–Ba(1)–O(6) 131.37(5) O(5)–Ba(1)–O(6) 48.63(5) #3 #2 O(5) –Ba(1)–O(4) 69.61(4) #3 #2 70.21(5) O(6) –Ba(1)–O(4) O(5)#3–Ba(1)–O(4)#4 100.39(4) O(6)#3–Ba(1)–O(4)#4 109.79(4) O(4)#2–Ba(1)–O(4)#4 180.0 O(5)–Ba(1)–O(3) 106.87(4) O(6)–Ba(1)–O(3) 62.62(5) #4 O(4)–Ba(1)–O(3) 66.64(5) #3 73.13(5) O(5)–Ba(1)–O(3) O(6)–Ba(1)–O(3)#3 117.38(5) O(4)#4–Ba(1)–O(3)#3 113.36(5) O(5)#3–Ba(1)–O(2) 67.66(5) O(6)#3–Ba(1)–O(2) 111.91(5) O(4)#2–Ba(1)–O(2) 67.25(5) O(3)–Ba(1)–O(2) 47.90(4) #3 #3 O(5) –Ba(1)–O(2) 112.34(5) #3 #3 O(6) –Ba(1)–O(2) 68.09(5) O(4)#2–Ba(1)–O(2)#3 112.75(5) O(3)–Ba(1)–O(2)#3 132.10(4) O(2)–Ba(1)–O(2)#3 180.0 O(5)–Ba(1)–O(1)#2 6.68(5) O(6)#3–Ba(1)–O(1)#2 7.06(5) O(4)–Ba(1)–O(1) 32.31(4) #3 O(3) –Ba(1)–O(1) 0.77(5) 2 O(2)# –Ba(1)–O(1) 10.87(5) O(5)#1–Ba(1)–O(1)#1 13.32(5) O(6)–Ba(1)–O(1)#1 12.94(5) O(4)–Ba(1)–O(1)#1 7.69(4) O(3)#3–Ba(1)–O(1)#1 09.23(5) #2 #1 O(2) –Ba(1)–O(1) 69.13(5) Hydrogen bonds (Å) and (°) D–H A d(D–H) N1–H1 O1 0.86
Ba(1)–O(5)#3 Ba(1)–O(6) Ba(1)–O(4)#4 Ba(1)–O(3)#3 Ba(1)–O(2)#2 Ba(1)–O(1)#4 O(5)#3–Ba(1)–O(6)#3 O(5)–Ba(1)–O(6)#3 O(6)#3–Ba(1)–O(6) O(5)–Ba(1)–O(4)#2 O(6)–Ba(1)–O(4)#2 O(5)–Ba(1)–O(4)#4 O(6)–Ba(1)–O(4)#4 O(5)#3–Ba(1)–O(3) O(6)–Ba(1)#3–O(3) O(4)#2–Ba(1)–O(3) O(5)#3–Ba(1)–O(3)#3 O(6)#3–Ba(1)–O(3)#3 O(4)#2–Ba(1)–O(3)#3 O(3)–Ba(1)–O(3)#3 O(5)–Ba(1)–O(2) O(6)–Ba(1)–O(2) O(4)#4–Ba(1)–O(2) O(3)#3–Ba(1)–O(2) O(5)–Ba(1)–O(2)#3 O(6)–Ba(1)–O(2)#3 O(4)#4–Ba(1)–O(2)#3 O(3)#3–Ba(1)–O(2)#3 O(5)#3–Ba(1)–O(1)#2 (6)#3–Ba(1)–O(1)#2 (4)#1–Ba(1)–O(1)#2 (3)#2–Ba(1)–O(1) (2)#3–Ba(1)–O(1) (5)–Ba(1)–O(1)#1 (6)#1–Ba(1)–O(1)#1 (4)#1–Ba(1)–O(1)#1 (3)#2–Ba(1)–O(1)#1 (2)#3–Ba(1)–O(1)#1 O(1)–Ba(1)–O(1)#1 d(H A) 2.24
d(D A) 3.069(3)
2.8402(19) 2.8474(17) 2.8723(17) 2.8742(17) 2.8961(18) 2.9186(17) 48.63(5) 131.37(5) 180.0 100.39(5) 109.79(5) 69.61(4) 70.21(4) 73.13(4) 117.38(5) 113.36(5) 106.87(5) 62.62(5) 66.64(5) 180.0 112.34(5) 68.09(5) 112.75(5) 132.10(4) 67.66(5) 111.91(5) 67.25(5) 47.90(4) 113.32(5) 12.94(5) 7.69(4) 09.23(5) 9.13(5) 6.68(5) 7.06(5) 32.31(4) 0.77(5) 10.87(5) 180.0 <(DHA) 161.6
Symmetry transformations used to generate equivalent atoms: #1 x 1, y 1/2, z + 3/2. #2 x 1, y, z + 1. #3 x 1, y + 1/2, z + 3/2. #4 x, y 1/2, z 1/2.
displacement parameters for all non-hydrogen atoms in the two structures. Non-hydrogen atoms were refined with anisotropic thermal parameters; those bonded to the C and N atoms were placed in calculated positions and refined in riding mode, with N–H = 0.86 Å (N), C–H = 0.93 Å (aromatic) and 0.96 Å (methyl), and Uiso (H) = 1.2 Ueq (aromatic C and N) and 1.5 Ueq (methyl). All computations were carried out using the SHELXTL-97 program package [32]. Details about data collection and refinement of the compounds are summarized in Table 1, and the selected bond distances, angles and H-bonding are listed in Table 2. 3. Results and discussion 3.1. Synthesis
R1 = R||Fo| |Fc|/R|Fo|. wR2 = {R[w(F 2o F 2o )2]/Rw[(F2o)2]}1/2.
For the open-framework polymer 1, some experimental details have been mentioned in Scheme 1. The reaction process and the molar ratios of reactants are crucial to the final product and the yield. The most reasonable molar proportion of BaO/NH4ClO4/4MP is 1:4:2. If the Ba(ClO4)2 and 4-MP were chosen as the initial reactants, then only white powder can be found. This indicates that the direct method is not feasible. To the mixed solvent: the most reasonable volume proportion should be 1/1/0.3 (HAC possess the minimum amount) to get the highest yield. The small amount
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of HAC in the solvent can play the key role, which makes the BaO and 4-MP slowly dissolved in the solution and bonded with the ClO4 , then the templated polymer 1 slowly crystallized [20–26,33]. To expand the scope of the above studies, 4-MP has been replaced by some different amine templates. However, only inorganic salts, organic single molecule compounds or other types of polymers have been obtained, none of them similar to compound 1. Therefore, this synthetic method is not general for other amine templates. Detailed experimental results were summarized in Scheme 2. To pyridine template: the products are a 2D polymer bridged by l2-H2O and l3-ClO4 or single molecule salt, and the structures are consistent with those in the reported literatures [28,29,34]; for the other amines, they were listed as follows: to 1, 10-phenanthroline: single molecule compound [35], or organic salt [36]; to 2, 2-bipyridine: a 1D polymer bridged by l2-ClO4 [37]; to 3-methylpyridine: 2D polymer bridged by l2-H2O and l3-ClO4 [29]; to 2-methylpyridine, amino-pyridine or isonicotinonitrile: inorganic compound 2. 3.2. IR, UV/Vis spectra and XRPD The structures of 1 and 2 were identified by satisfactory elemental analysis, IR and X-ray diffraction. Compound 1: The IR spectra shown a series of strong peaks at 1573, 1467, 1203, 778 and 705 cm1, those peaks are the characteristic of aromatic ring. The bands at 1079, 1058, 927, 649, 619 cm1 are attributed to the ClO4 groups. To compare with the IR spectrum of free ClO4 group (inorganic perchlorates), the absence of a strong peak at 632 cm1 for 1 shows that the free ClO4 groups disappeared, and 1 the new double peaks at 649 cm and 619 cm1 indicate strong coordination of the ClO4 oxygen to the Ba(II) centers through bidentate bridging mode [38], which is consistent with its X-ray single structure. Moreover, the double peaks at 1079 cm1 and 927 cm1 are the characteristics of mas(ClO4 ) and ms(ClO4 ), respec1 tively. The broad band around 3458 cm of N–H vibrations suggests that the nitrogen atoms of the ligands were protonated to balance the ClO4 anions. The 3087 and 2997 cm1 peaks correspond to aromatic H atoms. The characteristic peaks of methyl are presented at 2865, 1369 and 1257 cm1. Compound 2: The IR spectrum shows the very simple peaks at 3452, 3379, 1105, 1078, 778, 705 and 554 cm1. The UV/Vis spectrum of the ligand and complex 1 were measured in the solid state at room temperature. It shows that both the 4-MP and the complex exhibit absorption bands at the range of 200–400 nm. After coordination, the absorption bands underwent a slightly redshift of 2 nm, owing to the N–H O H-bond interactions to increase the stability. The above spectral analyses are in agreement with the determined single-crystal structure. X-ray powder diffraction (XRPD) analysis: The agreement between the experimental and simulated XRPD patterns indicated the phase purity of 1 (Fig. S1). The difference in reflection intensities between the simulated and experimental patterns was mainly due to the different powder size during collection of the experimental XRPD data.
bonding to the metal ions. The Cl–O bond distances are in the range of 1.423(2)–1.457(2) Å and the O–Cl–O bond angle range is 107.15(10)–110.70(10)°. The icosahedral Ba(II) was located in special position with an occupancy of 0.5, and sits in an irregular 12-coordinate (BaO12) environment composed of six chelate perchlorate anions donors (Fig. 1a). The Ba–O bond distances are in the range of 2.840(2)–2.919(2) Å, and O–Ba–O bond angles in the range of 47.69(4)–180.0°. By eliminating the Ba–O bonds and connecting the neighboring oxygen atoms, the oxygen–oxygen non-bonded schematic diagrams showed the framework of the distorted icosahedral [Ba(ClO4)6] cage (Fig. 1b). These cages are held together through corner-sharing O–Cl(1)–O chelate linkages, thereby forming the straight chain. Such chains are covalently bonded to each other by the Clð1ÞO 4 group forming the layer structure in the bc-plane (Fig. 2a). The Clð1ÞO 4 tetrahedra from the adjacent chains connect alternatively via four Ba–O–Cl linkages to form four connected quadrilateral, leading to the formation of an eight membered aperture (Fig. 2a). The compound 1 has the similar framework with the DABCO K(I) perchlorate and THF Ba(II) perchlorate [10,27]. And the structure can be compared to the mineral sulfoborite which is made up of complex sheets of (MgO6) and (SO4) tetrahedra [39]. In the mineral amarantite, octahedral tetramers are polymerized to form octahedral chains parallel to [1 0 0] and linked by (SO4) tetrahedral. To get better insight into the framework structure, its topological analysis was carried out. As discussed above, every Ba(II) center can be seen as one node, each Ba(II) node coordinated with four Clð1ÞO 4 linkers, thus can be defined as four-connecting juncture. And each Clð1ÞO 4 acts as a twoconnecting linker. According to the simplification principle of the TOPOS software [40], the overall network topology was described as a (4, 4)-connected framework (Fig. 2b). The structure of compound 1 is constructed from macroanionic inorganic-framework layers with the protonated amine molecules residing in the interlamellar space, which ensures the stability of the structure through bounding the organic amine to the main body of the inorganic framework by N–H O H-bond interactions (as shown in Fig. 3). The inorganic compound 2 crystallized in the monoclinic space group P21/c. The asymmetric unit contains two chloride anions, two water molecules and one Ba(II) ion. The irregular nine-coordinate (BaCl5O4) environment composed of three l3-Cl1 bridge chloride anions, two l2-Cl2 bridge chloride anions and four l2-O (two O1W and two O2W molecules) donors (Fig. 4). The neighboring metal centers are connected by two ways: (1) The Ba ions are
3.3. Description of the crystal structure Single-crystal X-ray analysis reveals that complex 1 crystallized in the monoclinic space group P21/c. The asymmetric unit contains two perchlorate anions, one template-amine cation and half Ba(II) ion. The inorganic framework shows negative charges. And the organic-template amine was protonated to maintain the charge bal ance. To the ClO4 anions: the Clð1ÞO 4 adopts double bidentate bridging mode by four O atoms connecting to two Ba(II) centers, and can be seen as a linear linker. But the terminal Clð2ÞO 4 has only one bidentate Cl–O–Ba bond, and the other two O atoms are not
Fig. 1a. View of the coordination environment of Ba(II) in complex 1.
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Fig. 1b. The 12-coordinated Ba(II) center by six ClO4 anions. Left shows the icosahedral Ba(II) ion by the oxygen–oxygen non-bonded connections; right is the same as left but eliminates part of the oxygen and chlorine atoms.
Fig. 2b. The 2-D (4,4)-connected topologic structure of 1.
cross-linked with a common Ba(II) atom culmination, thus the inorganic 2D skeleton was formed parallel to the ac-plane. The 2D inorganic-skeleton planes were parallel-linked by the l3-Cl1 atoms resulting in the formation of a 3D inorganic network (Fig. 5). 3.4. Thermogravimetric analysis
Fig. 2a. The 2-D polymeric layer with metal atoms represented as polyhedra parallel to the bc-plane. Hydrogen atoms are excluded for clarity.
bridged by aqua l2-O1W and l3-Cl1 atoms resulting in the formation of a binuclear (BaO1WCl1Ba) unit (A) with a Ba Ba distance of 4.906(1) Å and the large Ba–O1W–Ba angle (117.079(2)°) and small Ba–Cl1–Ba angle (100.662(7)°). (2) The additional didentate-bridged l2-Cl2 and l2-O2W atoms bonded to the another two Ba ions through forming four-member binuclear unit [BaO2WCl2Ba] (B). The dinuclear framework units A and B are
The thermal behaviors of the title compound 1 and 2 were investigated from 50 to 700 °C. The DSC and TGA curves are shown in Fig. 6. For compound 1: The DSC curve contains one intense endothermic peak and one continuously exothermic peak. The first endothermic stage occurs in the range of 198–215 °C with the peak temperature at 203 °C, which proves that organic-template molecules were lost during this process. The exothermic peak begins at 432 °C indicating the decomposition of inorganic framework. For compound 2: The DSC curve contains only one intense endothermic anomaly with the sharp peak value at 167 °C. This endothermic peak occurs between 145 and 185 °C, which corresponds to the lost of coordinated water molecules. After that the curve remains straight and unchanged. It is indicating that the final residual compound was unhydrous BaCl2. In the TG diagram of 1, [(Ba(ClO4)4]2(C6H8N)2]n, the two main steps of weight losses were observed in the temperature range from room temperature to
Fig. 3. The simplified N–H O H-bonds network of 1 viewed along the b-axis.
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Fig. 4. View of the coordination environment of complex 2. Fig. 7. Fluorescent emission spectra of the compound 1 and free 4-MP ligand.
To confirm the residual white powder of compound 1, further analysis was carried out. Firstly, the residues were collected, weighed and dissolved in HCl (2 M/mL) completely. Then dilute H2SO4 was added into the above solution until no new precipitate was formed. Finally, the solid precipitates were collected and weighed. After quantitative analysis, we confirmed that the final residue is BaO. Also the XRD of the residual white powder and standard BaO powder sample was investigated. The XRD measurements further confirmed that the residual white powder of compound 1 is BaO (Fig. S2). The difference between the two curves is due to the different powder size. Fig. 5. The 3-D framework of compound 2 viewed along the a-axis.
3.5. Photoluminescent properties The solid-state fluorescent property of the complex 1 was investigated at room temperature. As illustrated in Fig. 7, upon excitation of the solid sample at k = 320 nm, the intense broad emission bands at 385 nm was observed. Moreover, for excitation wavelength between 280 and 380 nm, the free 4-MP ligand presents a weak photoluminescence emission at 378 nm under the same experimental conditions. The emission of complex 1 is redshifted about 7 nm compared to that of free ligand 4-MP. Obviously, this emission comes from the organic-templated amine molecule. After coordination, the organic amine molecules were protonated and bound to the inorganic skeleton through N–H O H-bond interactions, which promoted the rigidity and the conjugation effect of aromatic pyridine ring. It plays the main role to luminescence intensity and red-shift effect. Thus, the compound 1 and the 4-MP have shown different luminescence properties.
Fig. 6. The DSC and TGA curves for complex 1 and 2.
700 °C. The first step occurs in the range of 187–235 °C, amounting to about 27.7% weight loss and corresponding to the escape of all organic-template molecules (calculated 26.0%). The framework remains undecomposed up to 425 °C where the second weight loss start. The total observed weight loss at 700 °C is 76.9%, and the final presumably residual is BaO. The two decomposition-temperature stages are within the ranges of 150–250 °C and 400–550 °C, respectively. This is the typical features for inorganic open-framework structures containing organic-template molecules. The TG diagram of 2, (BaCl2)2(H2O), shows that the weight loss only occured in the range of 140–191 °C. The total observed weight loss was amounting to about 15.5% (calculated 14.7%). It indicates that all the coordinated water molecules were lossed, and the final residual compound was unhydrous BaCl2. It is consistent with the DSC measurement.
4. Conclusions In summary, one novel inorganic open-framework alkalineearth metal perchlorate polymer with organic template has been successfully synthesized and characterized. Compound 1 was composed of irregular icosahedral (BaO12) units and organic-template amine molecules. The icosahedral centers were chelated through perchlorate anion donors to form a 2D topology with the protonated amine mounted to the main body of the inorganic framework by N–H O hydrogen bond interactions. The synthesis, crystal structure, TGA, DSC, UV, IR and fluorescence properties of the coordination polymer 1 were discussed in details. To verify the generality of the synthetic routes, 4-MP has been replaced by other different amine templates, then a series of reactions have been carried out. But they failed to get any structures similar to compound 1. The results showed that the crystallization processes are very sensitive to the induced effect of the organic templates.
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Acknowledgment This work was financially supported by the National Natural Science Foundation of China and Jiangxi Province NSF. Appendix A. Supplementary material Crystallographic data (excluding structure factors) for the crystal structure of compound 1 have been deposited to the Cambridge Crystallographic Data Centre as supplementary publication no. 837664. Copies of this information may be obtained free of charge from: The Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK. Fax (+44) 1223 336 033 or E-mail: [email protected] or (http://www.ccdc.cam.ac.ck). Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/ 10.1016/j.molstruc.2012.04.022. References [1] A.K. Cheetham, G. Ferey, T. Loiseau, Angew. Chem., Int. Ed. 33 (1999) 3268. [2] C.N.R. Rao, S. Natarajan, A. Choudhury, S. Neeraj, A.A. Ayi, Acc. Chem. Res. 34 (2001) 80. [3] T.M. Reinke, M. Eddaoudi, M. O’Keeffe, O.M. Yaghi, Angew. Chem., Int. Ed. 38 (1999) 2590. [4] R. Vaidhyanathan, S. Natarajan, C.N.R. Rao, Chem. Mater. 13 (2001) 185. [5] D.W. Breck, Zeolite Molecular Sieves, Wiley, New York, 1974. [6] X.Z. Li, M. Li, Z. Li, J.Z. Hou, X.C. Huang, D. Li, Angew. Chem., Int. Ed. 47 (2008) 6371. [7] T. Bataille, D.J. Louer, Mater. Chem. 12 (2002) 3487. [8] A. Choudhury, D. Udayakumar, C.N.R. Rao, Angew. Chem., Int. Ed. 41 (2002) 158. [9] T.M. Klapötke, M. Saein, J. Stierstorfer, Z. Anorg, Allg. Chem. 634 (2008) 1711. [10] Z.M. Jin, Y.J. Pan, X.F. Li, M.L. Hu, L. Shen, J. Mol. Struct. 660 (2003) 67. [11] L. Carlucci, G. Ciani, D.M. Proserpio, Coord. Chem. Rev. 246 (2003) 247. [12] C.D. Wu, A. Hu, L. Zhang, W.B. Lin, J. Am. Chem. Soc. 127 (2005) 8940. [13] J. Yang, Q. Yuo, G.D. Li, J.J. Cao, G.H. Li, J.S. Chen, Inorg. Chem. 45 (2006) 2857.
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