pH-Dependent Assembly of Supramolecular Architectures from 0D to 2D Networks Shu-Ting Wu,† La-Sheng Long,*,†,‡ Rong-Bin Huang,† and Lan-Sun Zheng†
CRYSTAL GROWTH & DESIGN 2007 VOL. 7, NO. 9 1746-1752
State Key Laboratory of Physical Chemistry of Solid Surface and Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen UniVersity, Xiamen 361005, China, and Wuhan Institute of Physics and Mathematics of the Chinese Academy of Sciences ReceiVed December 8, 2006; ReVised Manuscript ReceiVed June 27, 2007
ABSTRACT: Five Cu(II)/benzoate/4,4′-bipy complexes, namely, [Cu(H2O)(benzoate)2(4,4′-bipy)2](benzoic acid)2‚(4,4′-bipy) (1), [Cu2(H2O)2(benzoate)4(4,4′-bipy)3]‚(H2O)9 (2), [Cu2(benzoate)4(4,4′-bipy)3] (3), [Cu3(H2O)4(benzoate)6(4,4′-bipy)4.5]‚(4,4′-bipy)‚ (H2O)5 (4), and [Cu3(OH)2(H2O)2(benzoate)4(4,4′-bipy)2] (5) (4,4′-bipy ) 4,4′-bipyridine), have been synthesized through hydrothermal reaction of copper(II) nitrate, benzoic acid, and 4,4′-bipyridine under different pH conditions. The diverse product structures show the marked sensitivity of the structural chemistry of the aromatic carboxylate ligand to synthesis conditions. Complex 1, which exhibits a zero-dimensional (0D) structure of mononuclear copper(II), is formed at pH ) 5.5. At pH ) 6.0, dimeric copper(II) complexes of 2 and 3 are formed. Reaction at pH ) 7 leads to a one-dimensional (1D) structure of 4. A further increase of the pH to 8.0 results in a two-dimensional (2D) structure of 5. Crystal data are monoclinic, space group P2/n, a ) 13.992(4) Å, b ) 5.7153(14) Å, c ) 31.126(8) Å, β ) 100.513(5)°, Z ) 2 for 1, monoclinic, space group C2/c, a ) 30.283(5) Å, b ) 15.139(2) Å, c ) 14.457(2) Å, β ) 112.776(3)°, Z ) 4 for 2, monoclinic, space group P21/c, a ) 5.8317(12) Å, b ) 21.157(4) Å, c ) 20.679(4) Å, β ) 94.343(3)°, Z ) 2 for 3, triclinic, space group P1h, a ) 14.016(3) Å, b ) 18.492(4) Å, c ) 19.353(4) Å, R ) 66.220(3)°, β ) 79.948(4)°, γ ) 88.390(3)°, Z ) 2 for 4, and monoclinic, space group P21/c, a ) 5.6880(16) Å, b ) 17.917(5) Å, c ) 20.904(6) Å, β ) 92.959(5)°, Z ) 2 for 5. Introduction Constructions of metal-involved supramolecular architectures based on crystal engineering are currently of interest in the field of supramolecular chemistry and material science.1,2 In the effort to design and assemble such kinds of supramolecular architectures, not only a great many supramolecular architectures with intriguing topology have successfully been synthesized,3-5 but also several synthetic strategies, such as the symmetry interaction,6 directional bonding,7 and weak-link synthetic approaches,8 have been developed. Owing to the fact that the assembly of supramolecular architectures is easily affected by external physical or chemical stimuli, however, the reaction pathways frequently change case by case, resulting in poor selectivity. The pH value of the reaction, as one of the external stimuli, is especially important in the assembly of supramolecular architectures.9 It not only affects the ligand coordination ability but also its charge, the metal-to-ligand ratio, and consequently, the resulting structures.10 In this work, we chose the widely used organic ligand, 4,4′-bipyridine (4,4′-bipy), and carboxylate ligands as an example to show the role of the pH value of the reaction in controlling the structure of the supramolecular architecture and report here syntheses and crystal structures of [Cu(H2O)(benzoate)2(4,4′-bipy)2](benzoic acid)2‚(4,4′-bipy)(1), [Cu2(H2O)2(benzoate)4(4,4′-bipy)3]‚(H2O)9 (2), [Cu2(benzoate)4(4,4′-bipy)3] (3), [Cu3(H2O)4(benzoate)6(4,4′-bipy)4.5]‚(4,4′bipy)‚(H2O)5 (4), and [Cu3(OH)2(H2O)2(benzoate)4(4,4′-bipy)2] (5). Their structures range from a zero-dimensional (0D) * Author to whom correspondence should be addressed. E-mail:
[email protected]. Fax: 86-592-2183047. † Xiamen University. ‡ Chinese Academy of Sciences.
mononuclear complex to a two-dimensional (2D) network, revealing the pH effect on the supramolecular architecture. Experimental Section Materials and Methods. All the reagents and solvents employed were commercially available and used as received without further purification. The C, H, and N microanalyses were carried out with a CE instruments EA 1110 elemental analyzer. The FT-IR spectra were recorded in the range of 4000-400 cm-1 with a Nicolet AVATAR FT-IR360 spectrometer. The pH value of the reaction was measured with a Delta 320 meter. Syntheses. (a) [Cu(H2O)(benzoate)2(4,4′-bipy)2](benzoic acid)2‚ (4,4′-bipy) (1). To 10 mL of methanol-water (1:1 (v/v)) solution was added benzoic acid (1.0 mmol, 0.122 g), 4,4′-bipy (0.5 mmol, 0.08 g), and cupric acetate (0.5 mmol, 0.10 g) while stirring at room temperature. When the pH value of the mixture was adjusted to about 5.5 with ammonia solution (∼12%), the cloudy solution was put into a 25 mL Teflon-lined Parr, heated to 60 °C for 50 h, and then cooled to room temperature at a rate of 2 °C‚h-1. The blue column crystals of 1 (weight 5.0 mg) were obtained in 1.92% yield (based on benzoate ligand). The final pH value of the reaction is about 5.5. Anal. Calcd (Found) for C58H48CuN6O9 (%): C, 67.28 (67.09); H, 4.45 (4.54); N, 8.12 (8.26). IR (KBr, cm-1): 3424m, 3069w, 1684w, 1601s, 1566m, 1415m, 1379s, 1318w, 1274m, 1220m, 1069m, 811m, 723s, 636m, 485w. (b) [Cu2(H2O)2(benzoate)4(4,4′-bipy)3]‚(H2O)9 (2) and [Cu2(benzoate)4(4,4′-bipy)3] (3). Complex 2 was synthesized in the similar way as that described for 1, except that the pH value of the reaction was adjusted to 6.0 with ammonia solution (∼12%). The blue long column crystals of 2 (weight 4.9 mg) were obtained in 1.55% yield (based on benzoate ligand). Anal. Calcd (Found) for C58H66Cu2N6O19 (%): C, 54.50 (53.08); H, 5.20 (4.68); N, 6.57 (6.41). (KBr, cm-1): 3423m, 3074w, 1610s, 1561m, 1490w, 1408m, 1375s, 1218w, 1069w, 1030w, 810w, 722m, 684w, 622w, 497w. In the preparation of 2, the blue purple column crystals of 3 (weight 5.1 mg) accompany the appearance of 2 in 1.89% yield (based on benzoate ligand). The final pH value of the reaction is about 6.0. Anal. Calcd (Found) for C58H44-
10.1021/cg0608965 CCC: $37.00 © 2007 American Chemical Society Published on Web 08/15/2007
pH Effect on Supramolecular Architectures
Crystal Growth & Design, Vol. 7, No. 9, 2007 1747
Table 1. Crystal Data as Well as Details of Data Collection and Refinement for the Complexes 1-5 complex
1
2
3
4
5
formula Mr cryst syst space group a/Å b/Å c/Å R/deg β/deg γ/deg V/Å3 Z Dc/g cm-3 µ/mm-1 no. of data/params θ range/deg obs reflns R1 [I > 2σ(I)] wR2 (all data)
C58H48CuN6O9 1036.56 monoclinic P2/n 13.992(4) 5.7153(14) 31.126(8) 90 100.513(5) 90 2447.3(10) 2 1.407 0.514 4775/343 1.33-26.00 4163 0.0698 0.1472
C58H66Cu2N6O19 1278.25 monoclinic C2/c 30.283(5) 15.139(2) 14.457(2) 90 112.776(3) 90 6111.1(16) 4 1.389 0.773 6641/428 1.46-27.00 5743 0.0400 0.1085
C58H44Cu2N6O8 1080.07 monoclinic P21/c 5.8317(12) 21.157(4) 20.679(4) 90 94.343(3) 90.00 2544.0(9) 2 1.410 0.899 4975/334 1.38-26.00 4566 0.0358 0.0913
C97H92Cu3N11O21 1938.44 triclinic P1 14.016(3) 18.492(4) 19.353(4) 66.220(3) 79.948(4) 88.390(3) 4514.7(14) 2 1.426 0.780 15531/1210 1.17-25.00 13125 0.0527 0.1506
C48H42Cu3N4O12 1057.48 monoclinic P21/c 5.6880(16) 17.917(5) 20.904(6) 90 92.959(5) 90 2127.5(10) 2 1.651 1.559 4155/304 1.50-26.00 3422 0.0480 0.1257
Cu2N6O8 (%): C, 64.44 (64.59); H, 4.07 (4.15); N, 7.78 (7.72). (KBr, cm-1): 3438w, 3078w, 1603s, 1569m, 1494w, 1451w, 1407m, 1373s, 1215w, 1066w, 1023w, 847w, 823m, 720s, 687w, 624w, 501w. The separation of 2 and 3 is based on their shape. Compound 2 crystallized in blue long column crystals, whereas 3 crystallized in purple podgylike ones. (c) [Cu3(H2O)4(benzoate)6(4,4′-bipy)4.5]‚(4,4′-bipy)‚(H2O)5 (4). Complex 4 was synthesized in the similar way as that described for 1, except that the pH value of the reaction was adjusted to 7.5 with ammonia solution (∼12%). The blue block crystals of 4 (weight 2.0 mg) were obtained in 0.61% yield (based on benzoate ligand). The final pH value for the reaction is about 7.5. (d) [Cu3(OH)2(H2O)2(benzoate)4(4,4′-bipy)2] (5). Complex 5 was synthesized in the similar way as that described for 1, except that the pH value of the reaction was adjusted to 8.0 with ammonia solution (∼12%). The blue column crystals of 5 (weight 9.9 mg) were obtained in 3.75% yield (based on benzoate ligand). The final pH value for the reaction is about 7.9. Anal. Calcd (Found) for C48H42Cu3N4O12 (%): C, 54.52 (54.91); H, 4.00 (3.91); N, 5.30 (5.29). (KBr, cm-1): 3311m, 3052m, 3015w, 1669w, 1600s, 1563s, 1497w, 1419m, 1386s, 1225m, 1065w, 1026w, 937w, 840w, 810m, 718s, 769m, 644m, 571w, 492m, 419w. In the preparation of 1-5, a large number of green powders always accompanied. The elementary analysis for the green powders produced in each reaction indicates that they consist of very close ratio of C to N to H (C, 58.52%; N, 3.70%; H, 3.49%). From which, the mole ratio of 4,4′-bipy to benzoate is about 1:4 and the formula for the green powder can be deduced as [Cu2(4,4′-bipy)(benzoate)4(H2O)] (Calcd: C, 58.39%; N, 3.59%; H, 3.84%). Consistently, the IR spectrum for the green powder also approved the presence of both 4,4′-bipyridine and benzoate (Supporting Information). X-ray Crystallography. Data collections were performed on a Bruker SMART Apex CCD diffractometer at 123 K for complexes 1,
2, 4, and 5 and at 173 K for complex 3. Absorption corrections were applied by using the multiscan program SADABS.11 The structures were solved by direct methods, and non-hydrogen atoms were refined anisotropically by least-squares on F2 using the SHELXTL program.12 The hydrogen atoms of the organic ligand were generated geometrically (C-H, 0.96 Å). Crystal data as well as details of data collection and refinement for the complexes are summarized in Table 1
Results and Discussion Description of Crystal Structures. The asymmetric unit in complex 1 consists of one copper(II) cation, two benzoates, two benzoic acids, two 4,4′-bipy ligands, and one water molecule. Crystal structural analysis reveals that complex 1 is a discrete mononuclear copper(II) unit with its copper(II) center coordinated by two 4,4′-bipy ligands, two monodentate carboxylates of benzoates, and one water molecule in a distorted squarepyramidal geometry. Benzoic acid is hydrogen-bonded to uncoordinated 4,4′-bipy ligand in the mononuclear copper(II) unit as shown in Figure 1. Connection of adjacent copper(II) complexes through hydrogen-bonding interactions between coordination water and carboxylate group (O1w‚‚‚O12 ) 2.675(3) Å, O1w-H1wa‚‚‚O12 ) 1.94(3) Å,
