Article pubs.acs.org/crystal
Crystal Engineering of Molecular Networks: Tailoring HydrogenBonding Self-Assembly of Tin-Tetrapyridylporphyrins with Multidentate Carboxylic Acids As Axial Ligands Ranjan Patra, Hatem M. Titi, and Israel Goldberg* School of Chemistry, Sackler Faculty of Exact Sciences, Tel Aviv University, 69978 Ramat Aviv, Tel Aviv, Israel S Supporting Information *
ABSTRACT: This study reveals the self-assembly patterns of six-coordinate complexes of the tetra(4-pyridyl)- and tetra(3-pyriyl)-tin-porphyrin moieties (SnT4PyP and SnT3PyP, respectively) with multidentate carboxylic acids as axial ligands. Detailed structural characterization of the supramolecular organization in the resulting ordered solids by X-ray diffraction is reported. Crystals of the five new Sn(acid)2-TPyP complexes consist of multiporphyrin polymeric chains and networks that are sustained by extensive hydrogen bonding, involving the functional substituents on the axial ligands as proton donors and the peripheral N-sites of the porphyrin as proton acceptors. The use of different ligands leads to different connectivity features of the supramolecular assemblies that form. Structures with the 5-hydroxyisophthalic acid and trimesic acid ligands (1 and 2) reveal the formation of one-dimensional hydrogen-bonded chains only, as solvation effects prevent interporphyrin interaction in other directions. Reaction of the tin-porphyrin with 5-amino-isophthalic acid yielded a two-dimensional hydrogen-bonding network (3), while the reaction products with cis1,3,5-cyclohexane-tricarboxylic acid (4) and 5-bromo-isophthalic acid (5) are characterized by three-dimensionally interlinked assemblies. The above examples highlight the pronounced effect of the axial ligands (A) on the hydrogen-bonding-driven supramolecular aggregation of the Sn(A)2-TPyP building blocks in crystals.
■
INTRODUCTION This work is part of a continuing evaluation of the self-assembly modes of functionalized tetraarylporphyrins and their metalated derivatives in a comprehensive effort to design new ordered solids with attractive architectures.1,2 Wide interest in such materials has led in recent years to the discovery by others and us of a large number of two-dimensional and single-framework three-dimensional supramolecular porphyrin based-networks sustained by direct interporphyrin hydrogen-bonding and coordination, or tessellated by external metal ion or organic ligand bridging auxiliaries.1−6 In the above context, we focus here on the crystal-engineering of new hydrogen-bondingdriven assemblies with the meso-5,10,15,20-tetra-(4-pyridyl)porphyrin (T4PyP) and meso-5,10,15,20-tetra-(3-pyridyl)porphyrin (T3PyP) scaffolds. T4PyP and T3PyP bear diverging pyridyl functions on the periphery of their molecular framework, which may act as excellent proton acceptors in supramolecular hydrogen bonding with suitable partners of complementary nature. Correspondingly, our earlier reports described the formation of heteromolecular grids by reacting the TPyPs with benzene tri- and tetra-carboxylic acids, utilizing the well-known heteromeric COOH···N(pyridyl) interaction synthon (aromatic-N is one of the better organic acceptors in hydrogen bonds).7 In a different study, a series of threedimensional hydrogen bonding assembly modes of TPyP and aqua nitrates of lanthanoid ions have been described. In the © 2013 American Chemical Society
latter, the hybrid assemblies between the organic and inorganic components are sustained by hydrogen bonding interactions in three dimensions between the pyridyl groups of the porphyrin and the nitrate and water ligands in the coordination sphere of the lanthanoid ion.2d Partial protonation of the TPyP entity can lead also to homomolecular porphyrin arrays. When two of the four pyridyl groups are protonated, this porphyrin building block becomes self-complementary for direct hydrogen bonding, yielding a two-dimensional porphyrin array where every porphyrin unit connects to its porphyrin neighbors via four (N−H)+···N hydrogen bonds.2d The grid-type connectivity scheme with the (H2TPyP)2+ units is similar to that observed in molecular networks stabilized by cooperative selfhydrogen bonding of the (COOH)2 type obtained with various tetra(carboxyphenyl)porphyrin systems.8 In this report, we demonstrate yet another methodology for assembling TPyP-based networks by self-complementary hydrogen bonding, which involves utilizing six-coordinate TPyP complexes with axial ligands that incorporate protondonor-type molecular recognition functionalities. To this end, we have chosen to insert the strongly oxophilic Sn(IV) ion into the porphyrin core and introduce multidentate carboxylic acid entities (A) that may readily coordinate to the central tin ion as Received: January 2, 2013 Published: February 4, 2013 1342
dx.doi.org/10.1021/cg400007y | Cryst. Growth Des. 2013, 13, 1342−1349
Crystal Growth & Design
Article
Scheme 1. Schematic Illustration of the [SnT4PyP(A−)2] Complexes Involved in This Studya
a In 5, the analogous T3PyP (instead of T4PyP) scaffold has been used. The six-membered ring in the axial ligand is an aromatic phenyl moiety in 1− 3 and 5 and a saturated cyclohexyl residue in 4.
process (see below), due to the strong oxophilicity of the tin(IV) ions, thus allowing directional porphyrin−porphyrin interactions only through intermolecular hydrogen bonding. Correspondingly, we describe below the self-assembled architectures of the following complexes (in their solvated forms): [SnT4PyP(A1−)2]·(DMA·H2O) (1) (DMA = dimethyl acetamide), [SnT4PyP(A2−)2]·(DMSO)2 (2), [SnT4PyP(A3−)2]·S (3), [SnT4PyP(A4−)2]·S (4), and [SnT3PyP(A5−)2]·S (5) (S = intralattice solvent; either DMA, water, or a mixture of DMA and water).
axial ligands (six-coordinate charge-balanced complexes of monocarboxylic acids in a deprotonated form A− with various tin(IV)-porphyrins, including with T4PyP, are well documented in the literature).9,10 When the axial ligands bear additional substituents of proton donating capacity (as e.g., OH, COOH, or NH2 groups) at the meta positions (rather than at the para position, which may lead to coordination polymerization with other metalloporphyrins),9a they may engage also effectively in hydrogen bonds with the pyridyl N-sites of neighboring porphyrin units. Common OH···N, COOH···N, or NH2···N hydrogen bonds represent a relatively weak and thermodynamically labile interaction (with enthalpic contribution within 10− 30 kJ/mol per such H-bond),11 but their cooperative expression in the assembly of supramolecular aggregates may carry adequate stabilization energy (equal to or even exceeding that of a C−C covalent bond) to yield structures with long-range order in two or three dimensions. Evidently, the directionality features make these interactions key elements in targeted solidstate synthesis.12 The above approach represents to a large extent a mirror image of that applied successfully in the selfassembly of six-coordinate complexes of zinc(hexamethylenetetramine)2-5,10,15,20-tetra(4-carboxyphenyl)porphyrin [Zn(HTMA)2-T4CPP] into hydrogen-bonding network polymers.13 In the latter example, the porphyrin fragment contributed four proton-donating carboxylic acid sites, while the two axial HTMA ligands provided the complementary proton acceptor N-sites. Crystallographic characterization of the assembly patterns formed by the six-coordinate [Sn(IV)-TPyP)2+(A−)2] complexes throws light on the optimal supramolecular interaction of these bipyramidal metalloporphyrin units and utilization of their hydrogen bonding molecular recognition features. The acid reactants used in this study are A1 = 5-hydroxy isophthalic acid, A2 = benzene 1,3,5-tricarboxylic acid, A3 = 5-aminoisophthalic acid, A4 = cis-1,3,5-cyclohexane tricarboxylic acid, and A5 = 5-bromo isophthalic acid (Scheme 1). The peripheral pyridyl N-sites are essentially inert to potential coordination to the metal centers of another porphyrin species in the reaction
■
EXPERIMENTAL SECTION
In all reactions, commercially available reagents of analytical grade were used without further purification. The FT-IR spectra were recorded from KBr pellets in the 4000−400 cm−1 range on a Nicolet 5DX spectrometer. UV−vis spectra were recorded on a Perkin-Elmer UV−vis spectrometer. The starting porphyrin materials [Sn(T4TPyP)(OH)2] and [Sn(T3TPyP)(OH)2] and compounds 1−5 were prepared as detailed below. Preparation of [Sn(T4PyP)(OH)2] and [Sn(T3PyP)(OH)2]. 5,10,15,20-Tetrakis(4-pyridyl)-porphyrin (0.800 g, 1.30 mmol) was dissolved in pyridine (250 mL), and SnCl2·2H2O (0.586 g, 2.60 mmol) was added. The reaction mixture was heated at reflux until the reaction was complete. After 9 h, the solvent was removed in vacuo. The residue was dissolved in CHCl3 and filtered through a Celite pad. The solvent of the filtrate was evaporated under reduced pressure to give a crude product. The latter and potassium carbonate (1.14 g, 8.89 mmol) were dissolved in tetrahydrofuran (400 mL) and water (100 mL) and heated at reflux for 4 h. The solution was concentrated on a rotary evaporator to remove the tetrahydrofuran, and then allowed to cool in a refrigerator for a day. The produced microcrystalline solid of trans-dihydroxo[5,10,15,20-tetrakis(4-pyridyl)porphyrinato]tin(IV) was filtered, washed with water, and dried under vacuum. Yield: 85%. FT-IR (KBr, cm−1): 3080, 2560, 1706, 1650, 1432, 1247, 1032, 999, 855, 775, 713, 678, 666, 408. UV−vis in a CHCl3/DMF mixture: λmax/nm (log e) 424 (5.89), 555 (4.04), 595 (3.05). For the transdihydroxo[5,10,15,20-tetrakis(3-pyridyl)porphyrinato]tin(IV), yield: 75%. FT-IR (KBr, cm−1): 3085, 2564, 1696, 1642, 1444, 1249, 1042, 979, 845, 765, 703, 668, 508. UV−vis in a CHCl3/DMF mixture: λmax/nm (log e) 421 (5.79), 553 (4.02), 593 (3.04). 1343
dx.doi.org/10.1021/cg400007y | Cryst. Growth Des. 2013, 13, 1342−1349
Crystal Growth & Design
Article
Table 1. Crystal and Experimental Data for Structures 1−5 formula Fw crystal system space group a [Å] b [Å] c [Å] α [deg] β [deg] γ [deg] V [Å3] Z ρcalcd [Mg m−3] μ [mm−1] F(000) crystal size [mm3] θmax [deg] refl. collected refl. unique R(int) completeness refl. with I > 2σ(I) refined parameters R1 [I > 2σ(I)] wR2 [I > 2σ(I)] R1 [all data] wR2 [all data] ±Δρmax [e Å−3] average C−C bond precision [Å]
1a
2
3a
4a,b
5a
C64H52N10O12Sn 1271.85 triclinic P1̅ 9.7664(6) 10.2018(6) 14.8809(12) 88.890(2) 83.534(2) 90.719(3) 1453.9(2) 1 1.453 0.513 652 0.25 × 0.20 × 0.20 25.05 15523 5115 0.064 99% 4827 400 0.074 0.182 0.078 0.186 +2.25, −0.79 0.010
C66H58N8O16S4Sn 1466.13 triclinic P1̅ 9.7550(2) 11.6924(3) 14.9150(4) 102.883(1) 94.266(1) 91.933(2) 1651.56(7) 1 1.474 0.588 752 0.25 × 0.25 × 0.10 26.02 14935 6375 0.080 99% 4985 434 0.056 0.119 0.079 0.1 +0.89, −0.97 0.006
C56H36N10O8Sn 1095.64 triclinic P1̅ 8.9854(3) 11.4407(3) 14.6941(4) 91.122(1) 93.739(1) 95.604(1) 1499.61(8) 1 1.213 0.482 556 0.25 × 0.15 × 0.10 25.05 13391 5097 0.017 96% 4930 341 0.029 0.076 0.030 0.077 +0.95, −0.62 0.003
C58H48N8O13Sn 1183.75 monoclinic P21 9.4016(2) 30.7877(8) 11.8342(3) 90.0 90.990(2) 90.0 3424.94(14) 2 1.148 0.431 1212 0.30 × 0.15 × 0.10 25.01 16299 10510 0.083 99% 6298 721 0.070 0.148 0.119 0.165 +0.76, −0.54 0.014
C56H32Br2N8O8Sn 1223.41 monoclinic C2/c 25.4870(12) 12.2710(7) 21.9787(18) 90.0 120.463(1) 90.0 5925.0(7) 4 1.371 1.836 2432 0.15 × 0.12 × 0.07 28.32 24459 7367 0.051 100% 4744 341 0.060 0.167 0.097 0.180 +1.03,-1.13 0.008
a Excluding the intralattice noncoordinated and severely disordered DMA/water solvent. The R-factors refer to crystallographic refinements based on the PLATON-squeezed data. The CCDC deposition numbers of these structures are 917776−917780. bTwinned crystals.
Preparation of [Sn(T4PyP)(A)2] [A = 5-Hydroxy Isophthalic Acid]. trans-Dihydroxo[5,10,15,20-tetrakis(4-pyridyl)porphyrinato]tin(IV) (7.7 mg, 0.01 mmol) and 5-hydroxyisophthalic acid (5.4 mg, 0.03 mmol) was placed in a sealed reactor with 4 mL of DMA. The mixture was heated for 48 h at 100 °C, and after slow cooling to room temperature, X-ray quality red crystals of the porphyrin complex were obtained as DMA/water solvate (1). Yield: 92% based on porphyrin. FT-IR (KBr, cm−1): 3080, 2560, 1706, 1650, 1432, 1247, 1032, 999, 855, 775, 713, 678, 666, 408. UV−vis in a CHCl3/DMF mixture: λmax/nm (log e) 426 (5.49), 556 (4.04), 594 (3.12). Preparation of [Sn(T4PyP)(A)2] (A = Trimesic Acid). transDihydroxo[5,10,15,20-tetrakis(4-pyridyl)porphyrinato]tin(IV) (7.7 mg, 0.01 mmol) and trimesic acid (6.3 mg, 0.03 mmol) were placed in a sealed reactor with 4 mL of DMSO. The mixture was heated for 48 h at 100 °C, and after slow cooling to room temperature, X-ray quality red crystals of the porphyrin complex were obtained as DMSO solvate (2). Yield: 90% based on porphyrin. FT-IR (KBr, cm−1): 3384, 3085, 2926, 1867, 1701, 1673, 1591, 1473, 1258, 1211, 1031, 932, 798, 748, 540, 666, 419. UV−vis in a CHCl3/DMF mixture: λmax/nm (log e) 424 (5.49), 558 (4.09), 590 (3.18). Preparation of [Sn(T4PyP)(A)2] (A = 5-Amino Isophthalic Acid). 5-Amino isophthalic acid (5.4 mg, 0.03 mmol) and transdihydroxo-[5,10,15,20-tetrakis(4-pyridyl)-porphyrinato]tin(IV) (7.7 mg, 0.01 mmol) were completely dissolved in 4 mL of DMA. After reflux for 2 h, the solution was filtered and 6 mL of methanol added. X-ray quality small red crystals were obtained (as DMA/water solvate) by slow evaporation on the solvent after 7 days (3). Yield: 86% based on porphyrin. FT-IR (KBr, cm−1): 3469, 3385, 3084, 2351, 1697, 1650, 1444, 1256, 1032, 997, 854, 769, 716, 692, 675, 661, 421. UV− vis in a CHCl3/DMF mixture: λmax/nm (log e) 423 (5.72), 556 (4.05), 598 (3.09).
Preparation of [Sn(T3PyP)(A)2] (A = 5-Bromo Isophthalic Acid). 5-Bromoisophthalic acid (7.3 mg 0.03 mmol) and transdihydroxo[5,10,15,20-tetrakis(3-pyridyl)-porphyrinato]tin(IV) (7.7 mg, 0.01 mmol) were completely dissolved in 4 mL of DMA. After reflux for 2 h. this solution was filtered and added 6 mL of methanol. X-ray quality small thin plate red crystals of the porphyrin complex were obtained (as DMA/water solvate) by slow evaporation of the solvent after 7 days (4). Yield: 85% based on porphyrin. FT-IR (KBr, cm−1): 3382, 3084, 2896, 1862, 1743, 1662, 1584, 1463, 1268, 1201, 1032, 902, 856, 744, 548, 654, 421. UV−vis in a CHCl3/DMF mixture: λmax/nm (log e) 423 (5.19), 554 (4.11), 595 (3.17). Preparation of [Sn(T4PyP)(A)2] (A = cis-1,3,5-Cyclohexane Tricarboxylic Acid). cis-1,3,5-Cyclohexane tricarboxylic acid (6.5 mg, 0.03 mmol) and trans-dihydroxo[5,10,15,20-tetrakis(4-pyridyl)porphyrinato]tin(IV) (7.7 mg, 0.01 mmol) were completely dissolved in 4 mL of DMA. After reflux for 2 h, this solution was filtered and 6 mL of methanol added. X-ray quality small thin plate red crystals of the product were obtained by slow evaporation of the solvent after 7 days (5). Yield: 84% based on porphyrin. FT-IR (KBr, cm−1): 3663, 3410, 3092, 2929, 2451, 1722, 1710, 1547, 1443, 1287, 1082, 1066, 963, 856, 742, 714, 567, 438. UV−vis in a CHCl3/DMF mixture: λmax/nm (log e) 425 (5.66), 554 (4.12), 591 (3.15). The uniform identity of the formed crystal lattices in a given reaction were confirmed in each case by spectroscopic data as well as by uniform morphology of crystals in the bulk and repeated measurements of the unit-cell dimensions from different randomly chosen single crystallites. Because of the deterioration of several of the crystalline products when taken out from the crystallization solution and/or during the drying process, elemental analysis and powder diffraction experiments could not be carried out reliably in a systematic manner. For their structure determination, crystals pulled out from the 1344
dx.doi.org/10.1021/cg400007y | Cryst. Growth Des. 2013, 13, 1342−1349
Crystal Growth & Design
Article
Figure 1. Self-assembly of the [SnT4PyP(A−)2] units into 1D hydrogen bonded chains (depicted by dotted lines) (a) along the a + b axis in 1 and (b) along the a − b axis in 2 (Table 2). Note that the additional hydrogen bonding sites on the axial ligands (OH in 1 and COOH in 2) are engaged in hydrogen bonds to the DMA and DMSO solvent moieties, respectively.
Table 2. . Hydrogen-Bonding Parameters in Compounds 1−5a O/NH (donor D) 1 OH(37)COOH OH(38)OH 2 OH(36)COOH OH(39)COOH 3 OH(34)COOH NH(37)NH2 4 OH(60)COOH OH(63)COOH OH(75)COOH OH(78)COOH *OH(80)H2O 5 OH(35) COOH
O (acceptor A)
O/N−H (Å)
H···A (Å)
D···A (Å)
D−H···A (deg)
N17(2 − x, 2 − y, −z) *O39(x, y, z − 1)DMA
0.84 0.84
1.81 1.77
2.650(7) 2.599(10)
174 167
N23(x − 1, 1 + y, z) *O46(x + 1, y, z)DMSO
0.97 0.99
1.66 1.63
2.629(4) 2.598(5)
174 164
N16(1 − x,1 − y, −z) N22(x − 1, y, z − 1)
0.84 0.84
1.79 2.33
2.626(3) 3.114(3)
176 157
N28(x − 1, y, z + 1) N34(−x, y − 1/2, −z) N40(x + 1, y, z − 1) N46(1− x, y + 1/2, 1 − z) O66carboxylate
0.85 0.85 0.84 0.85 0.86
1.79 1.66 1.81 1.93 1.88
2.644(8) 2.513(13) 2.642(9) 2.781(10) 2.746(8)
179 179 171 179 170
N15(x, −y, z − 1/2)
0.84
1.82
2.656(6)
175
a
Atoms marked by an asterisk (*) belong to the DMA, DMSO, or H2O molecules of the solvent, which hydrogen bond to the porphyrin entities. All the O−H···N and N−H···N interactions represent hydrogen bonding between the axial ligand of one porphyrin complex and the tetra(pyridyl)porphyrin macrocycle of an adjacent moiety. Crystal Structure Determinations. The X-ray measurements [Nonius-KappaCCD (1, 2, and 4) and Bruker-ApexDuo (3 and 5)
reaction vials were covered immediately by protective oil and cooled down to 110 K on the diffractometer. 1345
dx.doi.org/10.1021/cg400007y | Cryst. Growth Des. 2013, 13, 1342−1349
Crystal Growth & Design
Article
Figure 2. Supramolecular self-assembly in 3 into 2D hydrogen bonding square-grid-type polymers extending parallel to the (1,−1,0) lattice plane. The COOH···Npyridyl interactions along the vertical direction are indicated by blue dotted lines, and the NH2···Npyridyl bonds along the horizontal axis are depicted by red dotted lines (Table 2). diffractometers, MoKα radiation] were carried out at ca. 110(2) K on crystals coated with a thin layer of amorphous oil to minimize crystal deterioration, possible structural disorder, and related thermal motion effects, and to optimize the precision of the structural results. These structures were solved by direct methods and refined by full-matrix least-squares (SIR-97 and SHELXL-97).14,15 All non-hydrogen atoms were refined anisotropically. The hydrogen atoms were located in idealized/calculated positions and were refined using a riding model; some of those involved in hydrogen bonds were located directly in difference-Fourier maps but were not refined. Compounds 1 and 3−5 were found to contain also disordered crystallization solvent (water, DMA, or a mixture of DMA and water) within the intralattice voids, in addition to ordered solvent molecules that were involved in hydrogen bonds (DMA in 1, DMSO in 2, and water in 4). The disordered solvent species could not be reliably modeled by discrete atoms, and their contribution was subtracted from the diffraction pattern by the SQUEEZE procedure and PLATON software.16 In 1−3 and 5, the metalloporphyrin unit is located on crystallographic inversion. Structure 4 has been determined in the noncentrosymmetric space group P21 with relatively low precision (the crystals were twinned, and this space symmetry was indicated by systematic absences and intensity statistics; transformation to the alternative centrosymmetric space group was found not feasible). Despite the solvent disorder, the crystallographic evaluations provided precise models of the porphyrin structure, the intermolecular organization, and the hydrogen bonding schemes. The crystallographic and experimental data for 1−5 are given in Table 1.
adjacent porphyrin species. Every porphyrin unit is thus linked to its two neighbors by a pair of antiparallel COOH···Npyridyl bonds on each side (Table 2). However, in these two structures, competing solvation (solvation effects occur quite frequently in organic crystals) interferes with the supramolecular aggregation of the porphyrin scaffold in other directions. In 1, the −OH substituents of the axial ligands form O− H···N DMA hydrogen bonds to the dimethyl acetamide molecules of the crystallization solvent. Similarly in 2, the third carboxylic acid functionality of the trimesic acid ligand is solvated by molecules of the dimethyl sulphoxide species, which is a strong proton acceptor in COOH···ODMSO hydrogen bonds.8c In the two structures, only two of the pyridyl groups of each porphyrin are involved in hydrogen bonding. The crystal structures of 1 and 2 are triclinic, in which the porphyrin chains described above are aligned parallel to each other. The DMA and DMSO species peripherally attached to these chains (Figure 1) protrude into the interstitial voids between them. In each case, another DMA or DMSO noncoordinated solvent molecule (per asymmetric unit) fills the interstitial voids in the corresponding crystals. The next example involves the A = 5-amino isophthalic acid derivative of the [SnT4PyP(A−)2] building block, The amino group is a weaker proton donor than the hydroxylic substituent in 1 and correspondingly could be less affected by DMA solvation. As a result, the two available functional groups on the axial ligands (COOH and NH2) are both utilized in interporphyrin hydrogen bonding in 3, leading to the formation of two-dimensional hydrogen bonding square grids (Figure 2).
■
RESULTS AND DISCUSSION The hydrogen bonding associations in compounds 1 and 2 are illustrated in Figure 1. They represent continuous self-assembly in one direction only, utilizing one carboxylic functionality on each of the axial ligands to connect to the N(pyridyl) site of an 1346
dx.doi.org/10.1021/cg400007y | Cryst. Growth Des. 2013, 13, 1342−1349
Crystal Growth & Design
Article
above. The saturated nonplanar nature and added flexibility of the axial cyclohexane tricarboxylic acid ligand in 4 allows extra orientational divergence of its COOH proton donors at positions 3 and 5 of the cyclohexyl ring (Scheme 1). The sixcoordinate porphyrin complex adopts an S-shape, with the two axial ligands binding toward opposite directions. As a result, a more complex intermolecular interaction pattern in space group P21 is expressed in structure 4. Here, each porphyrin unit is hydrogen bonded directly to six (rather than four in 3) neighboring porphyrin moieties (Figure 4), all preserving nearly the same orientation of the porphyrin framework. While it is still connected by a pair of COOH···Npyridyl and Npyridyl···HOOC hydrogen bonds to each of its two neighbors along one direction (a−c of the crystal), single links connect the other carboxylic acid substituents and two of the pyridyl sites of a given porphyrin to four other neighboring species. Correspondingly, the hydrogen-bonding environment around every porphyrin complex (Table 2) is of pseudo-octahedral nature, imparting three-dimensional connectivity features to the supramolecular interporphyrin organization in the crystal. The interstitial voids between the porphyrin units are relatively small and accommodate disordered molecules of the water and DMA solvent. Compound 5 involves building blocks of inherent asymmetry, mainly due to the fact that the T4PyP porphyrin backbone was replaced by T3PyP. The latter is characterized by a chairlike conformation, where two syn-related pyridyl substituents point upward with respect to the macrocyclic ring, while the other two are oriented in the opposite directions.2e,f This has an immediate effect on the spatial alignment of the hydrogen bonds the 3-pyridyl groups are involved in, as well as on the overall crystal symmetry. The interaction pattern in this structure can be best described in a modular way. Figure 5a illustrates the disposition of the COOH···Npyridyl hydrogen bonds in this structure. Every porphyrin unit associates via single H-bonds (through their two COOH functions and two trans-related pyridyl groups) to four different neighboring units (Table 2). This gives rise to a layered hydrogen-bonded arrangement of the porphyrin units (oriented in a herringbone manner) aligned parallel to the (1,1,0) plane of the crystal. Then, the bromo substituents on the axial ligands and the two remaining pyridyl functions are involved in additional halogen-bond-type Br···Npyridyl (or Br···π) interactions. Although the halogen bonds are relatively weak, as it is evident from the relatively long 3.347 Å Br···N distance (the sum of the corresponding van der Waals radii is 3.4 Å), they seem to be well exhibited in the structure of 5 (Figure 5b). In the resulting lattice, every porphyrin unit is associated with eight surrounding moieties by a combination of hydrogen and halogen bonding, representing a three-dimensional self-assembly pattern. The supramolecular self-assembly directed by specific interactions of the bulky and rigid porphyrin frameworks is commonly associated with the appearance of interporphyrin voids in the lattice. These provide the driving force for incorporation of noncoordinated solvent species in the corresponding crystals in all the five structures.
As in the previous examples, along one direction, adjacent porphyrin units interact via a pair of antiparallel COOH···Npyridyl hydrogen bonds. Then, along a nearly perpendicular direction, they interact via a pair of weaker NH2···Npyridyl bonds. Thus, every porphyrin moiety interlinks through eight hydrogen-bonding interactions with four neighboring [SnT4PyP(A−)2] species in the grid, engaging all four pyridyl sites of the porphyrins. Extension of this binding pattern throughout the crystal yields corrugated two-dimensional layers, parallel to the (1,−1,0) lattice plane, with large void space between adjacent units. In the crystal, these layers are offset-stacked one on top of the other along the a + b axis. In the resulting arrangement, wide channel voids of approximately 0.8 × 0.4 nm2 cross-section propagate through the crystal of 3 parallel to the a-axis of the unit-cell (Figure 3), to be filled by severely disordered DMA/water crystallization solvent.
Figure 3. Space-filling illustration of the crystal packing in 3, viewed down the a-axis of the crystal (c is horizontal). Note the channel voids that are accommodated by the DMA/water crystallization solvent (omitted).
Structure 3 represents an optimal realization of the crystalengineering concept put forward at the outset (without effects of competing salvation). The square bipyramidal [SnT4PyP(A−)2] entities are involved through their four proton-donors (the COOH and NH2 groups of the two axial ligands directed in opposite directions) and four proton acceptors (the laterally diverging pyridyl groups of the porphyrin scaffold) in an extended grid of multiply hydrogen bonded species, where every unit connects along the equatorial directions to four other porphyrins via eight hydrogen bonds. The corrugated nature of the layered arrays thus formed allows tight stacking of the layers in the normal direction, with the convex surfaces of one layer (represented by the axial ligands) fitting into the concave areas (formed by the peripheral TPyP framework) of two adjacent layers from above and below. The resulting channeled structure of 3 resembles closely the supramolecular organization observed earlier for the [Zn(HTMA)2-T4CPP] compound bearing proton donating functions on the porphyrin and proton acceptors on the axial ligands.13 The hydrogen bonding scheme expressed in the next two examples deviates from the regular grid pattern described
■
CONCLUDING REMARKS The above results demonstrate new types of porphyrin-based network materials supramolecularly organized into diverse architectures mainly by means of cooperative hydrogen bonding. They show that six-coordinate complexes of 1347
dx.doi.org/10.1021/cg400007y | Cryst. Growth Des. 2013, 13, 1342−1349
Crystal Growth & Design
Article
Figure 4. Hydrogen bonding pattern (dotted lines) around the porphyrin unit in 4. Note that, along the inclined vertical direction, adjacent porphyrins are linked by a pair of antiparallel COOH···Npyridyl hydrogen bonds (along the a−c axis of the crystal). Along the horizontal direction of the drawing (b axis of the crystal), the central porphyrin connects on each side by single carboxylic acid-to-pyridyl hydrogen bonds to two different neighboring units. The ordered water molecule H-bonded to one of the carboxylate groups and the remaining disordered solvent are not shown.
Figure 5. Interporphyrin interactions (dotted lines) in 5. (a) The hydrogen bonding pattern between adjacent units in layers parallel to the bc-plane of the crystal. (b) The Br···Npyridyl/Br···πpyridyl contacts between neighboring units parallel to the (1,0,−1) lattice plane; the hydrogen-bonds associated with the central unit are indicated as well.
These findings add to our earlier observations on effective hydrogen-bonding driven self-assembly of six-coordinate tetra(carboxyphenyl)-metalloporphyrins with axial ligands showing good coordination affinity for metal ions and containing effective proton acceptors.13 They further confirm that a
tetrapyridyl metalloporphyrins with multidentate axial ligands can be used as as building blocks in such an endeavor. The use of carboxylic acid ligands (that can readily coordinate to the tin ion in the porphyrin core) with additional substituents of proton donating capacity is particularly attractive to this end. 1348
dx.doi.org/10.1021/cg400007y | Cryst. Growth Des. 2013, 13, 1342−1349
Crystal Growth & Design
Article
(3) (a) Kosal, M. E.; Chou, J.-H.; Wilson, S. R.; Suslick, K. S. Nat. Chem. 2002, 1, 118. (b) Smithenry, D. W.; Wilson, S. R.; Suslick, K. S. Inorg. Chem. 2003, 42, 7719. (c) Suslick, K. S.; Bhyrappa, P.; Chou, J.H.; Kosal, M. E.; Nakagaki, S.; Smithenry, D. W.; Wilson, S. R. Acc. Chem. Res. 2005, 38, 283. (4) (a) Choi, E.-Y.; Barron, M. B.; Novotny, R. W.; Son, H.-T.; Hu, C.; Choe, W. Inorg. Chem. 2009, 48, 426. (b) Barron, M. B.; Son, H.T.; Hu, C.; Choe, W. Cryst. Growth Des. 2009, 9, 1960. (c) Barron, M. B.; Wray, C. A.; Hu, C.; Guo, Z.; Choe, W. Inorg. Chem. 2010, 49, 10217. (d) Burnet, B. J.; Barron, M. B.; Hu, C.; Choe, W. J. Am. Chem. Soc. 2011, 133, 9984. (e) Burnet, B. J.; Barron, M. B.; Choe, W. CrystEngComm 2012, 14, 3839. (f) DeVries, L. D.; Choe, W. J. Chem. Crystallogr. 2009, 39, 229. (5) Fateeva, A.; Chater, P. A.; Ireland, C. P.; Tahir, A. A.; Khimyak, Y. Z.; Wiper, P. V.; Darwent, J. R.; Rosseinsky, M. J. Angew. Chem., Int. Ed. 2012, 51, 7440. (6) (a) Motoyama, S.; Makiura, R.; Sakata, O.; Kitagawa, H. J. Am. Chem. Soc. 2011, 133, 5640. (b) Xu, G.; Yamada, T.; Otsubo, K.; Sakaida, S.; Kitagawa, H. J. Am. Chem. Soc. 2012, 134, 16524. (7) (a) Koner, R.; Goldberg, I. CrystEngComm 2009, 11, 1217. (b) Koner, R.; Goldberg, I. J. Incl. Phenom. Macrocycl. Chem. 2010, 66, 403. (8) (a) Diskin-Posner, Y.; Goldberg, I. Chem. Commun. 1999, 1961. (b) George, S.; Goldberg, I. Cryst. Growth Des. 2006, 6, 755. (c) George, S.; Lipstman, S.; Muniappan, S.; Goldberg, I. CrystEngComm 2006, 8, 417. (9) (a) Shetti, V. S.; Pareek, Y.; Ravikanth, M. Coord. Chem. Rev. 2012, 256, 2816. (b) Arnold, D. P.; Blok, J. Coord. Chem. Rev. 2004, 248, 299. (c) Kim, H.-J.; Jo, H. J.; Kim, J.; Kim, S.-O.; Kim, D.; Kim, K. CrystEngComm 2005, 7, 417. (10) Allen, F. H. The Cambridge Crystallographic Database. Acta Crystallogr. 2002, B52, 380. (11) Jeffrey, G. A. An Introduction to Hydrogen Bonding; Oxford University Press: Oxford, U.K., 1997. (12) (a) Desiraju, G. R. Angew. Chem., Int. Ed. 1995, 34, 2311. (b) Allen, F.; Raithby, P. R.; Shields, G. P.; Taylor, R. Chem. Commun. 1998, 1043. (13) Vinodu, M.; Goldberg, I. New. J. Chem. 2004, 28, 1250. (14) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, M.; Giacovazzo, C.; Guagliardi, A.; Polidori, G. J. Appl. Crystallogr. 1994, 27, 435. (15) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112. (16) Spek, A. L. Acta Crystallogr. 2009, D65, 148. (17) Muniappan, S.; Lipstman, S.; Goldberg, I. Chem. Commun. 2008, 1777.
concerted utilization of hydrogen-bonding and halogenbonding attractions between large and rigid building blocks (such as e.g., the tetraarylporphyrins) often has adequate driving force during the nucleation stage in solution for the preferred construction of supramolecular frameworks with long-range order.1,8,13,17 Evidently, the choice of building blocks with preorganized molecular recognition functions is essential to this end. A priori, it was anticipated that compounds 1−3 may have the desired functionality for assembling by extensive hydrogen bonding (with eight hydrogen bonds per porphyrin unit) into two-dimensional grids. This turned out to be the case only in 3, but not in 1 and 2. The inability to ensure full utilization of the hydrogenbonding potential solely for tessellation of the tailored porphyrin building presents a major weakness in this type of crystal-engineering investigations. In materials 1 and 2, solvent molecules from the reaction mixture (DMA and DMSO, which are essential to solubilize the reagents during the synthetic procedures) blocked (in an unpredictable manner) some of the hydrogen bonding sites on the axial ligands. However, no competing solvation effects were expressed in the interporphyrin self-assembly in compounds 3−5. It is also noted that, by using building blocks with reduced symmetry and/or added flexibility, as in 4 and 5, it is possible to invoke also the formation of 3D hydrogen-bonding frameworks. Evidently, while it is relatively easy to design multidentate organic linkers with diverging molecular recognition groups for the construction of hydrogen/halogen-bonding network polymers, it seems much more difficult to control the dimensionality of the supramolecular architectures that form. These findings provide, nevertheless, further useful insights to our continuing crystalengineering efforts of porphyrin-based supramolecular materials and framework solids.
■
ASSOCIATED CONTENT
S Supporting Information *
X-ray crystallographic details in CIF format. This material is available free of charge via the Internet at http://pubs.acs.org.
■
AUTHOR INFORMATION
Corresponding Author
*Tel: +972-3-6409965. Fax: +972-3-6409293. E-mail:
[email protected] (I.G.);
[email protected] (R.P.). Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS This research was supported by The Israel Science Foundation (Grants No. 502/08 and 108/12).
■
REFERENCES
(1) (a) Goldberg, I. Chem.Eur. J. 2000, 6, 3863. (b) Goldberg, I. Chem. Commun. 2005, 1243. (c) Goldberg, I. CrystEngComm 2008, 10, 637 and references therein. (2) (a) Lipstman, S.; Muniappan, S.; George, S.; Goldberg, I. Dalton Trans. 2007, 3273. (b) Muniappan, S.; Lipstman, S.; George, S.; Goldberg, I. Inorg. Chem. 2007, 46, 5544. (c) Lipstman, S.; Goldberg, I. Acta Crystallogr. 2009, C65, m371. (d) Lipstman, S.; Goldberg, I. Cryst. Growth Des. 2010, 10, 1823. (e) Lipstman, S.; Goldberg, I. Cryst. Growth Des. 2010, 10, 4596. (f) Lipstman, S.; Goldberg, I. Cryst. Growth Des. 2010, 10, 5001. 1349
dx.doi.org/10.1021/cg400007y | Cryst. Growth Des. 2013, 13, 1342−1349
