Crystal-Engineered Three-Dimensional Hydrogen-Bonding Networks

Aug 6, 2005 - In compound 2, the BTP molecules align in hydrogen-bonded staircase chains along the b axis in which the molecules are bonded together b...
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Crystal-Engineered Three-Dimensional Hydrogen-Bonding Networks Built with 1,3,5-Benzenetri(phosphonic acid) and Bipyridine Synthons

CRYSTAL GROWTH & DESIGN 2005 VOL. 5, NO. 5 1767-1773

Deyuan Kong and Abraham Clearfield* Department of Chemistry, Texas A&M University, College Station, Texas 77842

Jerzy Zon´ Faculty of Chemistry, Department of Organic Chemistry, Wrocław University of Technology, 50-370 Wrocław, Poland Received January 28, 2005

ABSTRACT: The phosphonic acid 1,3,5-benzenetri(phosphonic acid) (BTP; 1,3,5-[(OH)2PO]3-C6H3) can act as both a hydrogen bond donor and acceptor. BTP was reacted with two organic bases, 2,2′-bipyridine and 4,4′-bipyridine, in a 1:1 molar ratio. The bis-deprotonation and tris-deprotonation trigger the formation of self-complementary 3D hydrogen bonding architectures. Layers of the 2,2′-bipyridine compound are formed through hydrogen bonding of the phosphonic acid groups existing in the dianionic motif {1,3-[(OH)PO2]2-5-[PO(OH)2]-C6H3}2-. The ratio of BTP to 2,2′-bipyridine is 1:1.5, with two of the phosphonic acid protons being transferred to the nitrogen atoms, leaving a negatively charged oxygen and a proton on each of the phosphonic acid groups. Discrete dimers are formed by three very short PO-H‚‚‚O-P type hydrogen bonds (2.45-2.48 Å) and one short PO-H‚‚‚OdP hydrogen bond at 2.56 Å interconnecting all dimers into extended layers in the bc plane. The protonated bipyridyls penetrated into the layers by formation of two NH+‚‚‚O-P hydrogen bonds (2.72, 3.14 Å) to complete the 3D network. The compound with 4,4′-bipyridine is triclinic P1 h , in which the ratio of BTP to bipyridine is 1:1. Each amino nitrogen atom is protonated, leaving each phosphonic acid group negatively charged. One additional positive charge is provided by a hydronium ion. The BTP molecules align in hydrogen-bonded staircase chains along the b axis, in which the molecules are bonded together by double hydrogen bonds: P-O-‚‚‚HO-P. The staircases are then interwoven into each other by the NH+‚‚‚O-P hydrogen bonds between the pyridyl and the phosphonic acid groups. Introduction In crystal engineering the combination of the synthesis and analysis should provide systematic patterns of known crystal structures as a guide to be exploited, in order to create specific engineered molecular materials possessing desired crystallographic architecture and specific chemical/physical properties. Considerable effort has been expended to identify reliable and robust intermolecular interactions to this end.1 Particular emphasis has been placed on the use of hydrogen bonds. Strong O-H‚‚‚N bonds, for example, have been used for the creation of cocrystal structures of carboxylic acid and organic bases. By appropriate choice and location of functional groups, tapes, sheets, and three-dimensional network supramolecular motifs can be formed. In the context of designing specific arrays, highly symmetric molecules are of particular interest. C6H3(COOH)3, benzene-1,3,5-tricarboxylic acid, with different organic bases has been extensively reported because of the trigonal symmetry and complementary in-plane directional forces to form two-dimensional hexagonal networks.2 Also recently, our group has successfully used NTP, nitrilotris(methylphosphonic acid), with nonplanar molecular building blocks to construct three-dimensional hexagonal hydrogen-bonding systems.3b Studies on aminophosphonic acids clearly demonstrate that the deprotonation of the organo-phosphonic acids by the amino groups results in very strong and predictable structural aggregates through symmetrical O‚‚‚H‚‚‚O hydrogen bonds or hydrogen-bonded dimers. Actually,

strong symmetrical hydrogen bond motifs will have stabilization energies several times greater than those of normally occurring hydrogen bonds.3 Therefore, it was obvious to us that we can synthesize very stable hydrogen-bonded materials by selective deprotonation of phosphonic acid groups. In our previous reports,3 the monodeprotonation of NTP led to the formation of predictable three-dimensional hexagonal networks. Double deprotonation of NTP results in the formation of one-dimensional chain structures, as strong multiple hydrogen bonds control the network structure. To explore the general idea for construction of a threedimensional hydrogen bonding network with tris(phosphonic acid), BTP (benzene-1,3,5-tri(phosphonic acid), 1,3,5-[(OH)2PO]3C6H3) has been chosen as the building block. This tris(phosphonic acid) might function as a robust synthon for the construction of two-/threedimensional networks through the formation of strong hydrogen bonds. There have only been two reports on 1,3,5-[(OH)2PO]3C6H3, beginning in 2002.4 To understand the conditions required to induce self-assembly in the hydrogen-bonding network, BTP has been reacted with different hydrogen bonding acceptors: 2,2′-bipyridine and 4,4′-bipyridine. In the case of 2,2′-bipyridine, the close proximity of two nitrogen atoms allows only one carboxylic acid to hydrogen bond, and it acts as the single hydrogen bond acceptor.5 4,4′-Bipyridine is a frequently used organic base which has been used as a two-hydrogen-bond acceptor in crystal engineering work.6

10.1021/cg050033w CCC: $30.25 © 2005 American Chemical Society Published on Web 08/06/2005

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Crystal Growth & Design, Vol. 5, No. 5, 2005 Scheme 1. Synthetic Route for 1,3,5-[(OH)2PO]3-C6H3

Kong et al. Table 2. Hydrogen Bond Lengths (Å) and Angles (deg) for Compounds 1 and 2 d(D‚‚‚A)

∠(DHA)

O(5)-H(5A)‚‚‚O(7)#2 N(2)-H(2B)‚‚‚O(7) N(3)-H(3B)‚‚‚O(4) O(1)-H(1A)‚‚‚O(6)#3 O(9)-H(9A)‚‚‚O(4)#3 O(8)-H(8A)‚‚‚O(2)#3

Compound 1a 0.85(4) 1.71(4) 0.94(4) 1.94(3) 1.05(3) 2.15(3) 0.89(5) 1.59(5) 0.85(4) 1.64(4) 0.92(5) 1.54(5)

2.562(3) 2.723(3) 3.138(3) 2.476(3) 2.482(3) 2.453(3)

172(4) 139(3) 155(3) 177(5) 170(4) 174(5)

O(9)-H(9A)‚‚‚O(2W) O(1W)--H(1WA)‚‚‚O(8)#1 N(2)-H(2B)‚‚‚O(3) N(2)-H(2B)‚‚‚O(1W)#2 O(2W)-H(2WB)‚‚‚O(8)#1 O(4)-H(4A)‚‚‚O(2)#3 N(1)-H(1B)‚‚‚O(2)#4 O(1W)-H(1WD)‚‚‚O(2)#4 O(2W)-H(2WA)‚‚‚O(3W) O(3W)-H(3WA)‚‚‚O(5) O(3W)-H(3WB)‚‚‚O(6)#5 O(1)-H(1A)‚‚‚O(6)#6

Compound 2b 0.63(5) 1.90(5) 0.90(5) 1.86(5) 0.88(6) 2.62(5) 0.88(6) 1.84(5) 0.91(4) 1.81(5) 0.77(4) 1.90(4) 0.96(4) 1.72(4) 0.85 1.96 1.11(5) 1.61(5) 0.89(5) 1.85(5) 0.99(7) 1.84(7) 1.255(7) 1.198(7)

2.527(4) 2.744(3) 3.059(4) 2.660(4) 2.715(4) 2.635(3) 2.676(4) 2.794(3) 2.681(4) 2.745(4) 2.822(3) 2.448(3)

179(7) 165(5) 112(4) 156(5) 171(4) 159(4) 171(3) 165.2 159(4) 177(4) 170(5) 173(0)

D-H‚‚‚A

Table 1. Crystal Data and Structure Refinement Details for Complexes 1 and 2 1 {1,3-[(OH)PO2]25-[PO(OH)2]C6H3}2-‚(C10N2H9)+‚ 0.5(C10N2H10)2+ formula wt 552.32 cryst color; habit light yellow, plate dimens, mm 0.38 × 0.25 × 0.20 cryst syst monoclinic a, Å 10.3098(19) b, Å 15.608(3) c, Å 14.243(3) R, deg 90 β, deg 101.618(3) γ, deg 90 V, Å3 2245.07(8) space group P21/n Z 4 1.631 F(calcd), g cm-3 F(000) 1140 θ range, deg 2.24-24.71 completeness to θ, 99.9 % abs coeff, µ, mm-1 0.327 T, K 110(2) λ, Å 0.710 73 no. of rflns measd 20979 no. of data/params 3820/405 (Rint ) 0.0270) final R indices R1 ) 0.0416; (I > 2.0σ(I)) wR2 ) 0.0999 R indices R1 ) 0.0441; (all data) wR2 ) 0.1092 GOF on F2 1.236 peak, hole, e Å-3 0.489, -0.461 mol formula

2 [1,3,5-(OHPO2)3C6H3]3-‚(C10N2H10)2+‚ (H3O)+‚(H2O)2 528.27 colorless, block 0.15 × 0.06 × 0.05 triclinic 7.2494(18) 12.317(3) 12.528(3) 84.392(4) 77.085(4) 85.179(4) 1082.9(5) P1 h 2 1.620 548 2.26-24.71 98.0 0.343 110(2) 0.710 73 9918 3634/382 (Rint ) 0.0387) R1 ) 0.0674; wR2 ) 0.1696 R1 ) 0.0783; wR2 ) 0.1845 1.132 1.475, -0.672

Experimental Section Infrared (IR) spectra were measured as KBr pellets on a Nicolet Nexus 470 FT-IR spectrometer with spectral resolution of 2.00 cm-1. 1H, 31P, and 13C NMR spectra were recorded on Bruker Avance DRX 300 Hz instrument. Chemical shifts are given in ppm. Infrared absorption spectra of BTP were measured on a Perkin-Elmer FT-IR 1600 spectrometer. Synthesis of Benzene-1,3,5-tri(phosphonic acid). Scheme 1 gives the synthetic route for the BTP synthesis. Synthesis was carried out according to the literature procedures with optimized conditions.4a,7 (a) Hexaethyl Benzene-1,3,5-tris(phosphonate) (II). 1,3,5-Tribromobenzene (I; 6.30 g, 20 mmol) and 1,3-diisopropylbenzene (50 mL) were heated to 180 °C for 15 min under nitrogen. After the reaction mixture was cooled to room temperature, under nitrogen, nickel(II) bromide (1.00 g, 4.6 mmol) was added and the reaction mixture was heated again to 180 °C with stirring. Triethyl phosphite (15 mL, 87.5 mmol) was added dropwise at 175-180 °C over 5 h. The mixture was heated at the same temperature and stirred under nitrogen

d(D-H)

d(H‚‚‚A)

a Symmetry transformations used to generate equivalent atoms: (#1) -x + 2, -y - 1, -z + 2; (#2) -x + 3/2, y - 1/2, -z + 3/2; (#3) -x + 2, -y, -z + 2. a Symmetry transformations used to generate equivalent atoms: (#1) -x, -y, -z + 1; (#2) x + 1, y, z 1; (#3) -x, -y + 1, -z; (#4) x, y, z + 1; (#5) -x, -y + 1, -z + 1; (#6) 1 - x, -y + 1, -z.

Figure 1. Molecular structure of {1,3-[(OH)PO2]2-5-[PO(OH)2]C6H3}2-‚(C10N2H9)+‚0.5(C10N2H10)2+ (1): view of the asymmetric unit showing the labeling scheme and thermal ellipsoids drawn at 50% probability. Selected bond lengths (Å): P(1)O(1) ) 1.552(2); P(1)-O(2) ) 1.500(2); P(1)-O(3) ) 1.529(2); P(2)-O(4) ) 1.514(2); P(2)-O(5) ) 1.565(2); P(2)-O(6) ) 1.496(2); P(3)-O(7) ) 1.499(2); P(3)-O(9) ) 1.531(2); P(3)O(8) ) 1.537(2) Å. next 5 h. Then, volatile components, including 1,3-diisopropylbenzene, were distilled off under reduced pressure to obtain a dark viscous residue. Chromatography of the residue was performed on a column of silica gel eluted first with CHCl3, followed by using a mixed solution of CHCl3 and CH3OH (20: 1). II: yield 3.69 g (38%), colorless liquid, Rf ) 0.37 (silica gel plate with fluorescent indicator 254 nm; eluent CHCl3-CH3OH (20:1); visualization with UV lamp). Anal. Found: P, 18.83. Calcd for C18H33O9P3 (486.37): P, 19.10. 1H NMR (300 MHz, CDCl3): δ 8.42-8.28 with center at 8.35 (m, 3H, aromatic), 4.24-4.00 with center at 4.12 (m, 12H, POCH2C), 1.31 (t, 4JPH ) 7 Hz, 18H, POCCH3). 31P{1H} NMR (121 MHz, CDCl3): δ 17.01 (s). (b) Benzene-1,3,5-tri(phosphonic acid) (III). Hexaethyl benzene-1,3,5-tris(phosphonate) (3.14 g, 6.45 mmol), concentrated hydrochloric acid solution (20 mL), and distilled water

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Figure 2. Cell packing and hydrogen bonding in compound 1 (a, top) along the c axis and (b, bottom) along the b axis. Bipyridine molecules are omitted for clarity in (b). (20 mL) were refluxed for 14 h. The acidic solution was evaporated to dryness. Then the residue was dissolved in distilled water (30 mL), the solution was decolorized with charcoal, and the filtrate was evaporated under reduced pressure to give III as a white solid. Yield: 1.85 g (90%). IR (KBr, cm-1): νmax 3354, 3090, 2891, 2327, 1135, 1006, 942, 692, 537, 514, 472. 1H NMR (300 MHz, D2O): δ 8.11 (t, 3JPH ) 13.7 Hz). 31P{1H} NMR (121 MHz, D2O): δ 14.72 (s). 13C NMR (75

MHz, D2O): δ 135.2 (t, 2JPC ) 9.7 Hz), 133.2 (dt, 1JPC ) 181 Hz, 3JPC ) 12.6 Hz). Synthesis of the Acid-Base Compounds. All starting materials with a purity of ca. 98-99% were obtained from Aldrich and used without any further purification. The general procedure for the synthesis of the compounds is as follows: 50 mg (0.15 mmol) of benzene-1,3,5-tri(phosphonic acid) (abbreviated as BTP) was dissolved in 2 mL of water, 24 mg

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Figure 3. Cell packing and hydrogen bonding in compound 1 showing the connection of dimers along the bc plane. Dashed lines represent hydrogen bonds; all 2,2′-bipyridine molecules are omitted for clarity. (0.15 mmol) of organic base (2,2′-bipyridine, 4,4′-bipyridine, (C5H5N)2) was dissolved in 5 mL of ethanol, and then these two solutions were mixed and stirred overnight. The small amount of solids was filtered off, and the filtrates were left to evaporate slowly at room temperature in air, upon which colorless or light yellow crystals were deposited. The yields are around 40%. X-ray Crystallography. Data collection (2.53° < θ < 24.27°) was performed at 110 K on a Bruker Smart CCD-1000 diffractometer with Mo KR (λ ) 0.710 73 Å) radiation using a stream of liquid nitrogen gas as coolant. Data reduction and cell refinement were performed with the SAINT program, and multiscan absorption corrections were applied also.8 Crystal structures were solved by direct methods and refined with fullmatrix least squares (SHELXTL-97) with atomic coordinates and anisotropic thermal parameters for all non-hydrogen atoms.9 The crystallographic data are summarized in Table 1. Hydrogen atoms bonded to O or N were located in difference Fourier maps and refined isotropically with the O-H and N-H distances set to provide the best fit to the X-ray data. Only hydrogen atoms of C(21) in compound 1 and of O(1w) and O(2w) were placed geometrically. Table 2 lists the hydrogen bonds in the two compounds. All the bond distances and bond angles of the two compounds are in the normal ranges, which are given in the Supporting Information. Mercury and Diamond software were used to visualize the structures.

Results and Discussion The ligand has been synthesized with optimized synthetic conditions according to the literature procedure. Hexadiethyl benzene-1,3,5-tri(phosphonate) (II) was obtained by a catalytic Arbuzov reaction from 1,3,5tribromobenzene and triethyl phosphite in the presence of nickel(II) bromide. After purification by column chromatography of the phosphonate II, a simple hy-

Figure 4. Molecular structure of [1,3,5-(OHPO2)3C6H3]3-‚ (C10N2H10)2+‚(H3O)+‚(H2O)2 (2): view of the asymmetric unit showing the labeling scheme and the thermal ellipsoids drawn at 50% probability. Selected bond lengths (Å): P(1)-O(1) ) 1.530(2); P(1)-O(2) ) 1.521(2); P(1)-O(3) ) 1.522(2); P(2)O(4) ) 1.581(2); P(2)-O(5) ) 1.485(2); P(2)-O(6) ) 1.528(2); P(3)-O(7) ) 1.528(2); P(3)-O(8) ) 1.496(2); P(3)-O(9) ) 1.559(3) Å.

drolysis reaction yielded benzene-1,3,5-tri(phosphonic acid) (III) as a white solid, very soluble in water and methanol. BTP and 2,2′-Bipyridine Salt, 1. The compound 1 was prepared by cocrystallization of a 1:1 mix of the two reactants in a water-ethanol solution. The crystals are monoclinic, in space group P21/n, with Z ) 4 (Table 1). The unit cell consists of four BTP molecules and six 2,2′bipyridyls bonded together through hydrogen bonds. The asymmetric unit of compound 1 is shown in Figure

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Figure 5. (a) Cell packing and hydrogen bonding in compound 2: (a, top) view along the ac plane and (b, bottom) view showing the involvement of the H3O+ and water in hydrogen bonding along the b axis. Legend: C, white (large); N, black; hydrogen, white (small); O, gray; P, purple. Dashed lines represent hydrogen bonds.

1. The bipyridyl groups have two arrangements relative to the BTP groups: cis and trans. The cis groups contain nitrogens N(1) and N(2), as shown in Figure 1. The N(2) is close to a phosphonic acid group and is protonated, whereas N(1) is far from the phosphonic groups and thus is not protonated. The trans-bipyridyl bridges across two BTP phosphonic acid groups, and both N(3) atoms are protonated. There are four cis and two trans bipyridyls per unit cell. The four BTP molecules each transfer two protons from O(4) and O(2). The O(4) atom is involved in hydrogen bonds to N(3) and O(9) atoms with X‚‚‚O (XdN, O) bond lengths of 3.138(2) and 2.482(3) Å, respectively, thus acting as a double hydrogen bond acceptor. The double-bonded O(7) atom has similar connections with the O(5) and N(2) atoms as donors. The remaining oxygen atoms of each BTP ligand

form single hydrogen bonds, resulting in a total number of eight strong PO-H‚‚‚-O-P bonds, as listed in Table 2 and Figure 2. Four of them are related by symmetry, and the O‚‚‚O distances range from 2.453(3) to 2.562(3) Å. The dianion 1,3-[(OH)PO2]2-5-[PO(OH)2]C6H3]2- selfassembles through these hydrogen bonds to give a cagelike motif with two benzene rings parallel to each other at a distance of 3.87 Å (Figure 2b). These robust hydrogen-bonded cages are connected by intermolecular hydrogen bonds, O(5)‚‚‚O(7) ) 2.562(3) Å, to form discrete zigzag aggregates. O(4) is involved in two hydrogen bonds as acceptor, O(9)‚‚‚O(4) ) 2.482(3) Å and N(3)‚‚‚O(4) ) 3.138(2) Å. The trans conformation of 2,2′-bipyridine is connected with those dimers by two hydrogen bonds along the 〈010〉 axis. The threedimensional network of those dimers is illustrated in

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Figure 6. Hydrogen bonding in compound 2 showing the pseudo-hexagonal channel. Dashed lines represent hydrogen bonds.

Figure 3. Large channels with internal dimensions of ca. 6.66 × 13.30 Å2 run along the a axis. These channels are filled by the bipyridine cations in the 〈022〉 plane, which are bonded to the tris(phosphonic acid) framework through hydrogen bonds, as shown in Figure 2a. The monoprotonated cis bipyridine is perpendicular to the trans bipyridine with one pyridine ring at a close distance of 3.45 Å due to a π-π interaction. Also, the trans bypridines have π-π interactions with their neighboring symmetric motifs at a slightly longer distance of 3.99 Å. Interestingly, supramolecular aggregates prepared from nitrilotris(methylphosponic acid) with various amines were recently reported to give three-dimensional hexagonal structures with channel dimensions of 8.5 × 11 Å.3b BTP and 4,4′-Bipyridine Salt, 2. BTP and 4,4′bipyridine cocrystallized in the triclinic space group P1 h with one BTP, one 4,4′-bipyridine, and three water molecules per asymmetric unit, as shown in Figure 4. Each BTP transfers two protons to the bipyridyl group and one proton to a water molecule, leaving a negative charge on each of the three phosphonate groups. The overall charge of BTP is therefore 3- and is defined as {1,3,5-[(OH)PO2]3-C6H3}3-. The hydrogen bonds linking the molecules together are listed in Table 2. The P-O bonds are in the range of 1.485(2)-1.521(2) Å and have been assigned as PdO bonds. Two longer P-O bonds, 1.581(1) and 1.559(3) Å, have been defined as P-OH bonds. The third P-OH bond is shorter than the first two. The H(1A) atom associated with P(1)-O(1) was found in the final Fourier map with a longer O-H bond distance of 1.25(9) Å because of the extremely short distances2.448 Å between the O(1) and neighboring O(6) atom, as shown in Figure 5. This proton is suggested to be shared by the two oxygen atoms forming the hydrogen bonds. In the solid state typical P-OH‚‚ ‚O-P distances in the range of 2.45-2.60 Å were reported for the organic ammonium salts of phosphonic acids. To the best of our knowledge, the lower limit is determined by a distance of 2.413 Å reported for an aggregate of nitrilotris(methylphosphonic acid) with phenanthroline.3b Recently, another very short OH‚‚‚O distance in BTP with 4-(dimethylamino)pyridine amounting to 2.431(2) Å also has been reported.4b In the dimer

structure of benzene-1,3,5-tris(methylphophonic acid), two similar OH‚‚‚O bonds of 2.442 and 2.484 Å were found with negative charge assisted hydrogen bonding,10 as shown in Figure 6. The trianionic moieties {1,3,5[(OH)PO2]3-C6H3}3- assembled with two hydrogen bonds along the b axis to form staircase-type layers as a result of the planar stacking of the benzene rings (Figure 5a). The double-protonated 4,4′-bipyridine motif is sandwiched betweem two BTP ligands with one benzene ring along the a direction aligning up with another at distances of 3.49-3.62 Å, due to the strong π-π interaction. The 4,4′-bipyridyl rings are rotated relative to each other with a dihedral angle of 26.2°, leading the bipyridyl N(1)-H groups to hydrogen bond to the PO oxygens in the ac plane, as shown in Figure 5b. The anionic BTP layers are interconnected by cationic pyridine and water molecules to give a 3-D hydrogenbonded network. These NH bonds are extremely short at N(1)-H‚‚‚O(2) ) 2.676(4)Å. The other protonated N(2) atom has a short contact with O(1wa) of 2.660(4) Å and also a long contact with the O(3) atom at a distance of 3.059(4) Å. In view of this packing, small tunnels, delimited by the 4,4′-bipridine cations, are formed along the a axis, but the size of these channels (6.0 × 7.2 Å) is not sufficient to expect some porosity in this material. All water molecules are hydrogen bonded to the neighboring phosphonic groups to form a complicated 3-D network (Figure 5b). IR Analyses. IR spectra were recorded between 4000 and 400 cm-1 (see the Supporting Information). The region between 4000 and 1400 cm-1 can be selected to study the lattice water and the P-O-H groups. Both compounds have strong vibration bands for NH+ centered at 3011 cm-1. Compound 2 shows an intense and broad band in the O-H stretching vibration region at 3372-3020 cm-1, which is consistent with the presence of lattice water molecules interacting by hydrogen bonding. The corresponding bending H-O-H (δ(HOH)) vibration bands of the lattice water in 2 are located at ca. 1660 cm-1, which are also broadened by hydrogen bonding. The symmetrical and unsymmetrical vibration bands of PO2 from PO3H- groups in compounds 1 and 2 were observed at 1150 and 1054 cm-1, respectively. The peaks that occur at 980 cm-1 were assigned to

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νs(PO3).11 The bands centered at 2330 and 1050 cm-1 are attributed to PO-H and POH vibrations, respectively, due to unprotonated POH groups in two compounds. Asymmetric vibrating stretching bands of POH (ν(P-OH)) groups are situated at 980 cm-1.

Supporting Information Available: CIF files giving crystallographic data and a figure giving IR spectra. This material is available free of charge via the Internet at http:// pubs.acs.org.

Conclusions

(1) (a) Crystal Engineering: From Molecules and Crystals to Materials; Braga, D., Orpen, A. H., Eds.; NATO ASI Series; Kluwer: Dordecht, The Netherlands, 1999. (b) Weber, E., Ed. Design of Organic Solids; Topics in Current Chemistry; Springer-Verlag: Heidelberg, Germany, 1998; Vol. 198. (c) Bond, A. D.; Jones, W. In Supramolecular Organization and Materials Design; Jones, W., Rao, C. N. R., Eds.; Cambridge University Press: Cambridge, U.K., 2002, and references therein. (2) (a) Herbstein, F. H. In Comprehensive Supramolecular Chemistry; Atwood, J. L., Davies, J. E. D., MacNicol, D. D., Cogtle, D., Lehn, J.-M., Eds.; Pergamon: Oxford, U.K., 1996; Vol. 6, p 61. (b) Jones, W. Organic Molecular Solids: Properties and Applications; CRC Press: New York, 1997; p 149. (c) Yaghi, O. M.; Li, H.; Davis, C.; Richardson, D.; Groy, R. L. Acc. Chem. Res. 1998, 31, 474. (d) Eddaoudi, M.; Moler, D. B.; Li, H.; Chen, B.; Reineke, T. M.; O’Keeffe, M.; Yaghi, O. M. Acc. Chem. Res. 2001, 34, 319. (e) Hagrman, P. J.; Hagraman, D.; Zubieta, J. Angew. Chem., Int. Ed. 1999, 38, 2638 and references therein. (3) (a) Sharma, C. V. K.; Clearfield, A. J. Am. Chem. Soc. 2000, 122, 1558. (b) Sharma, C. V. K.; Clearfield, A. J. Am. Chem. Soc. 2000, 122, 4394. (c) Sharma, C. V. K.; Clearfield, A.; Cabeza, A.; Aranda, M. A. G.; Bruque, S. J. Am. Chem. Soc. 2001, 123, 2885. (d) Sharma, C. V. K.; Hessheimer, A. J.; Clearfield, A. Polyhedron 2001, 20, 2095. (4) (a) Reiter, S. A.; Assmann, B.; Nogai, S. D.; Mitzel, N. W.; Schmidbaur, H. Helv. Chim. Acta 2002, 85, 1140. (b) Mehring, M. Eur. J. Inorg. Chem. 2004, 3240. (5) (a) Shan, N.; Bond, A. D.; Jones, W. Acta Crystallogr., Sect. E 2001, 57, 811. (b) Shi, X.; Zhu, G. S.; Fang, Q. R.; Wu, G.; Tian, G.; Wang, R. W.; Zhang, D. L.; Xue, M.; Qiu, S. L. Eur. J. Inorg. Chem. 2004, 185. (6) (a) Sharma, C. V. K.; Zaworotko, M. Chem. Commun. 1996, 2655. (b) Shan, N.; Bond, A.; Jones, W. New J. Chem. 2003, 7, 365. (c) Shi, Z.; Li, G. H.; Wang, L.; Gao, L.; Chen, X. B.; Hua, J.; Feng, S. H. Cryst. Growth Des. 2004, 4, 25. (7) (a) Henn, M.; Jurkschat, K.; Mansfeld, D.; Mehring, M.; Schu¨rmann, M. J. Mol. Struct. 2004, 697, 213. (b) Schwan, A. L. Chem. Soc. Rev. 2004, 33, 218. (c) Muthukumaran, K.; Loewe, R. S.; Ambroise, A.; Tamaru, S.; Li, G.; Mathur, Q.; Bocian, D. F.; Misra, V.; Lindsey, J. S. J. Org. Chem. 2004, 69, 1444-1452. (8) SMART version 5.0 and SAINT+ version 6.01 area detector instrument control, data acquisition, and area detector data integration software from Bruker AXS, Inc., Madison, WI. (9) Sheldrick, G. M. SHELXTL (SADABS, XS, XL) Crystallographic Software Package, Version 6.10; Bruker AXS, Inc., Madison, WI, 2000. (10) Shlolnikova, L. M.; Polyanchuk, G. V.; Dyatlova, N. M.; Medved, T. Y. Goryunova, I. B.; Kabachnik, M. I. Russ. Chem. Bull. 1985, 1035. (11) (a) Barja, B. C.; Herszage, J.; Santos Alfons, M. Polyhedron 2001, 20, 1821. (b) Cabeza, A.; Aranda, M. A. G.; Bruque, S. J. Mater. Chem. 1999, 9, 571. (c) Gomez-Alcantara, M. M.; Cabeza, A.; Aranda, M. A. G.; Guagliardi, A.; Mao, J. G.; Clearfield, A. Solid State Sci. 2004, 6, 479. (d) Sahni, S. K.; Bebbekom, E. V. Reedijk, J. Polyhedron 1985, 4, 1643. (12) Kong, D. Y.; Clearfield, A. Unpublished work. (13) Martell, A. E.; Motekaitis, R. J. The Determination and Use of Stability Constants, 2nd ed.; VCH: New York, 1992. (14) Mehring, M.; Schu¨rmann, M.; Ludwig, R. Chem. Eur. J. 2003, 9, 837.

References Our present studies demonstrate that the deprotonation of the phosphonic acid BTP with 2,2′-bipyridine and 4,4′-bipyridine leads to the formation of 3D supramolecular hydrogen-bonding architectures. The phosphonic acid moieties form robust anionic hydrogen bonding dimers in 1 and staircase-type chains in 2. Both of them exist as layers with the bipyridine molecules acting as pillars interconnecting the layers which extend the structure to three-dimensional systems. This network contains hexagonal channels which are occupied by 4,4′-bipyridinium cations. With the use of bipyridine, three-dimensional supramolecular hydrogen bonding has been successfully achieved. Three protons of the BTP synthon were transferred in both compounds which may be due to the similar basicities of both amine groups (pKa ) 4.33 for 2,2′-bipyridine and 4.82 for 4,4′bipyridine).12 Only one and two protons have been deprotonated in the case of 4-(dimethylamino)pyridine (pKa ) 9.33).4b In our prelimilary potentiometric titration experiment, the log KnH values of the BTP are log K1 ) 8.56, log K2 ) 7.43, log K3 ) 6.71, log K4 ) 2.61, and log K5 ) 1.44 (the last value is lower than 1; log KnH ) [HnL]/[Hn-1L][H]).13 The first three protons are easily deprotonated. There is a gap of 4.1 logarithm units between the third and fourth proton additions. Considering the number of protonation sites and their localization, this decrease in the constant values can be rationalized in terms of minimization of the electrostatic repulsion between positive charges in the protonated species. The ligand itself has C3 symmetry, on which three positive charges could easily be delocalized with minimum electrostatic repulsion. Also, if those negatively charged moieties aggregate by hydrogen bonds, the removal of a proton from the hydrogen bond in the dimer is increased from ca. 43 kJ mol-1 calculated for [t-BuP(O)(OH)2] to ca. 83 kJ mol-1 for {[t-BuP(O)2(OH)]}{[t-BuP(O)(OH)2]}-.14 In the future, strong amines will be used to achieve more proton deprotonation. In a larger sense the use of phosphonic acids provides a vast array of synthons from which more complementarily designed, highly stable hydrogen-bonded structures will be constructed. Acknowledgment. We acknowledge with thanks financial support from the Department of Energy, Basic Sciences Division, through Grant No. DE-FG03-00ER 15806 and the R. A. Welch Foundation under Grant No. A673. J.Z. thanks Prof. Roman Gancarz (Wrocław) for helpful discussions concerning the NMR spectra of BTP. Thanks go to Ms. Jennifer McBee for her assistance in IR measurements. This work was supported in part by a US-Poland NSF grant, No. OISE-0437490, and the Wroclaw University of Technology (J.Z.).

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