Adduct Formation between Organic Oxoanions and

exhibits the second example of the macrocycle hosting two ammonium groups. For the bis(tacn) macrocycle, the anions were found to ... contribute to th...
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CRYSTAL GROWTH & DESIGN

Adduct Formation between Organic Oxoanions and Hexaazamacrocycles Andrew C.

Warden,†

Mark

Warren,†

Milton T. W.

Hearn,‡

and Leone

Spiccia*,†

School of Chemistry and Centre for Green Chemistry, School of Chemistry, Monash University, Victoria 3800, Australia

2005 VOL. 5, NO. 2 713-720

Received June 12, 2004

ABSTRACT: Five adducts formed by organic acids and two hexaazamacrocycles, 1,4,7,10,13,16-hexaazacylooctadecane (L1) and 1,2-[bis(1,4,7-triazacyclononan-1-yl]ethane (L2), viz., (H6L1)(ox)2(Hox)2 (1), (H6L1)(TFA)6(H2O)2 (2), (H2L1)(pic)2(H2O)5 (3), (H3L1)(BNPP)3(H2O)5 (4) and (H4L2)(C12H8N2O8P2)4(H2O)0.5, or (H4L2)(BNPP)4(H2O)0.5 (5) (ox ) C2O42-, TFA ) CF3CO2-, pic ) C6H4NO2-, and BNPP ) (O2NC6H4O)2PO2-), were crystallized from aqueous solutions containing the azamacrocycles and the organic oxoanions. Crystal structure determinations have allowed an examination of hydrogen bonding and electrostatic interactions contributing to the supramolecular architectures. The flexible L1 ligand is found in degrees of protonation ranging from fully protonated to diprotonated, with anions binding both above and below the cavity to balance the charge on the macrocycle. Of particular interest are compounds 4, which contains the only structurally characterized example of [18]aneN6 in a triprotonated state, and 3, which exhibits the second example of the macrocycle hosting two ammonium groups. For the bis(tacn) macrocycle, the anions were found to bind only on one side of the macrocycle. With the exception of 4, the macrocycles display the ability to chelate a single anionic oxygen atom. All the structures except 1 employ water in assisting the formation of stable lattices, sometimes showing complex and unique formations including a water-phosphate cage in 4. Introduction While the coordination chemistry of cations has been studied for about a century, complementary research on anions has only recently begun to receive significant attention.1 Polyammonium macrocycles,2-9 cyclic amides,10 and cyclic peptides11 have been reported as hosts for a variety of anions, as have metal complexes of polyoxomacrocycles12 and polyazamacrocycles.13-16 Although much attention has been paid to the solution chemistry of inorganic anions and azamacrocycles (see ref 17 for an extensive review), the behavior of these adducts in the solid state has not been so thoroughly examined. We have recently reported on the supramolecular adduct formation between protonated forms of 1,4,7,10,13,16-hexaazacyclooctadecane ([18]aneN6) and various halide counterions,18 oxoanions derived from phosphoric acid19 and sulfuric acid, and dithionate.20 These studies have indicated that many stable supramolecular architectures can be formed through interactions of [18]aneN6 and a wide variety of anionic substrates, giving insight into the coordination modes of these anions and the conformations able to be adopted by the macrocycle itself. We report herein the synthesis, characterization, and crystal structure determination for adducts formed by organic oxoanions and two hexaazamacrocycles, [18]aneN6 (L1) and 1,2-[bis(1,4,7triazacyclononan-1-yl]ethane (L2) (see Figure 1). The different charges and geometries of the anions induce different modes of binding by macrocycles with varying levels of protonation. We also examine the factors that contribute to the often complex hydrogen-bonding networks found in the structures. * To whom correspondence should be addressed. [email protected]. † School of Chemistry. ‡ Centre for Green Chemistry, School of Chemistry.

E-mail:

Figure 1. 1,4,7,10,13,16-hexaazacyclooctdecane ([18]aneN6, L1) and 1,2-[bis(1,4,7-triazacyclononan-1-yl]ethane (L2).

Experimental Section Materials and Methods. All reagents were purchased from Aldrich or BDH and were used without further purification. 1,4,7,10,13,16-Hexaazacyclooctadecane (L1, [18]aneN6) can be prepared by following the classical Richman-Atkins synthesis.21 In this work, the ligand was collected as a byproduct of the 1,4,7-triazacyclonane (tacn) synthesis as reported previously.19 1,2-[Bis(1,4,7-triazacyclononan-1-yl]ethane was prepared by previously reported methods.22-24 Physical Measurements. Infrared spectra were recorded as KBr disks on a Perkin-Elmer 1640 FTIR spectrophotometer at a resolution of 4.0 cm-1. Microanalyses were performed by the Campbell Microanalytical Service, Dunedin, New Zealand. Syntheses. (H6L1)(C2O4)2(HC2O4)2 (1). A solution containing L1 (20 mg, 0.077 mmol) and oxalic acid (24 mg, 0.22 mmol) in water (2 mL) was heated briefly to 70 °C and left to slowly evaporate at room temperature. After several days clear crystals of 1 were obtained (yield 29 mg, 61%). Anal. Found: C, 38.9; H, 6.3; N, 13.4. Calcd for C20H38N6O16: C, 38.8; H, 6.2; N, 13.6. Selected IR bands (KBr disk, cm-1): ν 3393 s, 1623 s, 1222 s, 767 m. (H6L1)(CF3CO2)6(H2O)2 (2). A solution containing L1 (20 mg, 0.077 mmol) and trifluoroacetic acid (53 mg, 0.46 mmol) in water (1 mL) was prepared and left to slowly evaporate, giving clear crystals of 2 after several days (yield 37 mg, 49%). Anal. Found: C, 30.5; H, 4.1; N, 9.1. Calcd for C24H40N6O14F18: C, 29.5; H, 4.1; N, 8.6. Selected IR bands (KBr disk, cm-1): ν 3378 m, 2849 w, 1674 s, 1438 m, 1196 s, 1134 s, 844 m, 796 m, 725 m.

10.1021/cg049811v CCC: $30.25 © 2005 American Chemical Society Published on Web 10/19/2004

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Table 1. Crystal and Refinement Data for 1-5 1 empirical formula fw cryst syst space group a, Å b, Å c, Å R, deg β, deg γ, deg vol, Å3 Z F(calcd), g cm-3 no. of reflns collected no. of independent reflns no. of params GOF on F2 R1, wR2a [I > 2σ(I)] R1, wR2a (all data) a

2

3

C20H38N6O16 618.56 monoclinic P21/c 6.4794(1) 18.6578(2) 11.0166(4)

C24H40N6O14F18 978.62 monoclinic P21/c 9.4382(2) 17.0558(3) 11.9500(3)

C24H50N8O9 591.7 monoclinic Cc 12.8477(4) 13.4255(4) 18.8452(9)

91.2290(10)

99.0630(10)

104.038(3)

1331.51(5) 2 1.543 10179 3282 266 1.046 0.0436, 0.1093 0.0585, 0.1179

1899.65(7) 2 1.711 15096 4614 360 1.019 0.0486, 0.1121 0.0894, 0.1296

3153.5(2) 4 1.253 11915 6239 388 0.917 0.0739, 0.1666 0.1996, 0.2123

R1 ) ∑||Fo| - |Fc||/∑|Fo|; wR2 ) [∑w(Fo2

-

4

5

C48H67N12O29P3 1369.05 triclinic P1 h 8.6654(2) 17.8083(4) 20.5578(5) 76.871(1) 83.727 (1) 84.805(2) 3063.89(12) 2 1.484 30334 14677 1012 0.911 0.0572, 0.1155 0.1533, 0.1457

C62H69N14O32.5P4 1653.18 monoclinic P21/c 14.7621(5) 18.4102(6) 13.9271(3) 108.575(2) 3587.84(19) 2 1.530 33552 8695 511 0.938 0.1044, 0.1281 0.3495, 0.1789

Fc2)2/∑w(Fo2)2]1/2.

(H2L1)(C6H4NO2)2(H2O)5 (3). A solution containing L1 (20 mg, 0.077 mmol) and picolinic acid (19 mg, 0.15 mmol) in water (1 mL) was prepared and left to slowly evaporate, yielding clear crystals of 3 after several days (yield 30 mg, 66%). Anal. Found: C, 42.6; H, 7.7; N, 16.8. Calcd for C24H50N8O9: C, 48.5; H, 8.5; N, 18.8. Calcd for C24H50N8O9 (3 with five additional water molecules): C, 42.1; H, 8.8; N, 16.4. Selected IR bands (KBr disk, cm-1): ν 3451 s, 2755 m, 1599 s, 1559 s, 1459 s, 1374 s, 1232 w, 1137 m, 1026 w, 998 w, 758 m, 697 m, 623 w. (H3L1)(C12H8N2O8P2)3(H2O)5 (4). A solution containing L1 (20 mg, 0.077 mmol) and bis(4-nitrophenyl) phosphate (78 mg, 0.23 mmol) in water (1 mL) and ethanol (2 mL) was prepared and left to slowly evaporate. After several days clear crystals of 4 were obtained but were difficult to separate from cocrystallizing HBNPP ((O2NC6H4O)2PO2H), as indicated by microanalyses (estimated yield 79 mg, 75%). Anal. Found: C, 43.6; H, 3.8; N, 9.9. Calcd for C84H94N18O53P6 (4 with three additional HBNPP molecules): C, 42.2; H, 4.1; N, 10.6. Selected IR bands (KBr disk, cm-1): ν 3415 m, 2767 m, 1590 m, 1516 s, 1490 m, 1349 s, 1216 m, 1093 m, 930 m, 859 m, 750 m, 689 w. (H4L2)(C12H8N2O8P2)4(H2O)0.5 (5). A solution containing L2‚6HBr (50 mg, 0.063 mmol) and bis(4-nitrophenyl) phosphate (80 mg, 0.23 mmol) in water (1 mL) and ethanol (2 mL) was prepared and left to slowly evaporate, giving a few clear crystals of 5 (estimated yield 13 mg, 12%). As with 4, cocrystallizing HBNPP was difficult to separate from the product, and this is reflected in the microanalysis. Anal. Found: C, 56.0; H, 5.7; N, 5.3. Calcd for C74H91N6O22P5 (5 with one additional HBNPP molecule and two water molecules): C, 56.6; H, 5.8; N, 5.4. Selected IR bands (KBr disk, cm-1): ν 3422 s, 2950 m, 1591 s, 1560 m, 1508 s, 1490 s, 1458 m, 1347 s, 1221 s, 1093 s, 907 s, 859 m, 749 m. X-ray Crystallography. (a) General Procedures. A summary of the crystal data and structure refinement for 1-5 is given in Table 1. Single-crystal X-ray data were collected on a Nonius-Kappa CCD diffractometer with monochromated Mo ΚR radiation (λ ) 0.71073 Å) at 123(2) K using φ and/or ω scans. Data were corrected for Lorentz and polarization effects. The structures were solved by direct methods and refined using the full-matrix least-squares method of the programs SHELXS-9725 and SHELXL-97,26 respectively. The program X-Seed27 was used as an interface to the SHELX programs, and to prepare the figures. In each case all non-hydrogen atoms were refined anisotropically. In the figures, dashed lines represent hydrogen bonds and, where ORTEP representation has been used, ellipsoids have been drawn at the 50% probability level unless otherwise indicated. Where applicable, asterisks indicate symmetry-generated atoms. (b) Specific Comments. (H6L1)(C2O4)2(HC2O4)2 (1). All hydrogen atoms were located on Fourier difference maps and refined isotropically without restraint. The location of the proton on the HC2O4- anion was corroborated by the elonga-

tion of the C-OH bond by approximately 0.05 Å with respect to its counterparts. (H6L1)(CF3CO2)6(H2O)2 (2). All hydrogen atoms were located on Fourier difference maps and refined isotropically without restraint. (H2L1)(C6H4NO2)2(H2O)5 (3). Most of the macrocyclic hydrogen atoms were placed in calculated geometries with the exception of the amine hydrogens, which were located on Fourier difference maps and then restrained to idealized geometries. Not all of the hydrogen atoms on the solvent water molecules were able to be located. Those whose locations were determined from residual electron density were all restrained to idealized geometries. The structure was solved using the Shelxl97 TWIN instruction in the Cc space group after refinements in noncentrosymmetric space groups failed to converge. (H3L1)(C12H8N2O8P2)3(H2O)5 (4). All macrocyclic hydrogen atoms were placed at calculated geometries with the exception of those on the amines, which were located on Fourier difference maps and refined isotropically without restraint. All solvent water hydrogen atoms were located and then restrained to idealized geometries. Two of the oxygen atoms (O(7) and O(8)) on a BNPP ((O2NC6H4O)2PO2-) moiety were disordered over two positions with 80% and 20% occupancy. Both parts were refined anisotropically. (H4L2)(C12H8N2O8P2)4(H2O)0.5 (5). All hydrogen atoms were placed at calculated positions on both the bis(tacn) moiety and the BNPP anions. The water molecule was refined as having 1/4 occupancy per asymmetric unit, and hence, no hydrogen atoms were assigned to it. One of the oxygen atoms (O(5)) on the nitro group of a BNPP anion is very poorly behaved, but attempts to model disorder with nearby residual electron density resulted in instability and higher R values. Instead, it was refined anisotropically as a whole oxygen atom.

Results and Discussion Synthesis and Characterization. Compounds 1-5 were all crystallized from slowly evaporating aqueous solutions containing the macrocyclic ligands and an excess of the appropriate anions as their acids. The IR spectra all exhibited absorptions corresponding to the macrocycles (C-H and N-H stretches) and certain characteristic bands of the anions (carboxylate (14901650 cm-1), phosphate (900-1250 cm-1), and nitro (1300-1500 cm-1) groups). All the compounds except 1 contain water in the crystal lattice; consequently, OH stretches were observed between 3300 and 3500 cm-1. Crystal Structure Determinations. (H6L1)(C2O4)2(HC2O4)2 (1). The crystal structure of 1 consists of a

Adducts between Oxoanions and Hexaazamacrocycles

Figure 2. ORTEP plot showing H-bonding interactions between the macrocycle and oxalate anions in 1. Methylene hydrogen atoms have been omitted for clarity. Symmetrygenerated atoms are indicated by asterisks.

Figure 3. Oxalate-macrocycle interactions in 1. Methyl hydrogen atoms have been omitted for clarity. Symmetrygenerated atoms are indicated by asterisks.

hexaprotonated [18]aneN6 macrocycle with two oxalate and two monohydrogen oxalate anions balancing the 6+ charge (Figure 2). The macrocycle lies around a crystallographic inversion center, as do both of the oxalate anions. All but two of the twelve ammonium hydrogen atoms (one on N(1) and one on N(1)*) are involved in hydrogen bonding to the anions. One of the oxalate anions is sandwiched between two macrocycles, bound to each by three N-H‚‚‚O hydrogen bonds to two of its oxygen atoms (O(8) and O(7); see Figure 3 and

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Figure 4. 1D chains formed by the HC2O4- anions in 1 bordering macrocycles and oxalate anions (viewed down the a axis). C-H hydrogen atoms have been removed for clarity. Only hydrogen bonds between HC2O4- anions are shown.

Table 2). The other oxalate anion bridges four adjacent macrocycles and, as with its counterpart, does not have any interactions with other oxalate moieties. The HC2O4anions interact with each other through a strong O-H‚‚‚O hydrogen bond (O(3)-H(1)‚‚‚O(2), 2.5393(13) Å, 171(2)°) to form a 1-dimensional chain (Figure 4), and also interact with the macrocycles through one N-H‚‚‚O interaction (N(2)-H(3)‚‚‚O(1), 2.7841(17) Å, 145(2)°). While the C2O42- anions are perfectly planar, the HC2O4- anion has a slight twist, highlighted by an O-C-C-O torsion angle of 20°. The two oxalate anions have all of their oxygen atoms participating in hydrogen bonds with macrocyclic ammonium groups and do not interact with the monohydrogen oxalate anion. Most of the N-H‚‚‚O hydrogen bonds are reasonably strong, with D‚‚‚A distances ranging between 2.8 and 3.0 Å. Several weaker interactions exist however, ranging up to 3.3 Å. Hydrogen bonds (using a distance criterion) are considered to exist where the distance between the hydrogen atom and the acceptor is less than the sum of their van der Waals radii28-30 (1.20 Å for H and 1.40 Å for O).31 Hence, H‚‚‚O distances would be expected to be less than 2.60 Å for a D-H‚‚‚O hydrogen bond, although weaker bonds are also considered to exist, particularly when C-H donors are involved. Hydrogen bonds between protonated oxoanions, such as HC2O4-, HSO4-, H2PO4-, and HPO42-, are significantly stronger

Table 2. Hydrogen Bond Distances (Å) and Angles (deg) in 1 with Esd’s Given in Parenthesesa D-H‚‚‚A

d(D-H)

d(H‚‚‚A)

d(D‚‚‚A)

∠(DHA)

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

0.893(18) 0.893(18) 0.941(19) 0.941(19) 0.94(3) 0.94(3) 0.94(3) 0.94(3) 0.95(3) 0.95(3) 0.97(3) 0.97(3) 1.03(3) 1.03(3) 0.96(2)

2.311(18) 2.484(17) 1.778(19) 2.602(18) 1.96(3) 2.53(3) 1.99(3) 2.16(3) 1.96(3) 2.03(3) 2.03(3) 2.31(3) 1.51(3) 2.63(2) 2.39(2)

3.0070(16) 3.1648(16) 2.7074(15) 3.2091(16) 2.7841(17) 3.3066(17) 2.7618(17) 2.9558(18) 2.7293(16) 2.7870(17) 2.8914(18) 3.0573(19) 2.5393(13) 3.2747(13) 3.3301(19)

134.7(14) 133.4(14) 168.7(16) 122.6(13) 145(2) 140(2) 138(2) 141(2) 136(2) 135(2) 148(2) 134(2) 171(2) 120.0(17) 165.7(19)

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

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Figure 5. ORTEP plot highlighting hydrogen-bonding interactions between trifluoroacetate counterions and [H6L1]6+ in 2. C-H hydrogen atoms have been omitted for clarity. Table 3. Hydrogen Bond Distances (Å) and Angles (deg) in 2 with Esd’s Given in Parenthesesa D-H‚‚‚A N(1)-H(1)‚‚‚O(6)#2 N(1)-H(2)‚‚‚O(5) N(2)-H(3)‚‚‚O(1)W N(2)-H(4)‚‚‚O(1) N(3)-H(5)‚‚‚O(2) N(3)-H(6)‚‚‚O(3) O(1)W-H(1)W‚‚‚O(4)#3 O(1)W-H(1)W‚‚‚F(5)#3 O(1)W-H(2)W‚‚‚O(3)#4 C(4)-H(14)‚‚‚F(6)#5

d(D-H) d(H‚‚‚A) d(D‚‚‚A) ∠(DHA) 0.90(2) 0.96(3) 0.92(3) 0.95(3) 0.94(2) 0.95(2) 0.88(4) 0.88(4) 0.77(4) 0.96(2)

1.89(2) 1.75(3) 1.72(3) 1.81(3) 1.89(2) 1.81(2) 1.86(4) 2.41(3) 1.94(4) 2.72(2)

2.787(2) 2.687(2) 2.644(2) 2.753(2) 2.828(2) 2.722(2) 2.714(2) 2.889(2) 2.695(2) 3.224(2)

176(2) 166(2) 176(2) 171(2) 170(2) 161(2) 165(3) 115(2) 167(4) 113(2)

Figure 6. Packing of the crystal lattice in 2 (viewed down the a axis). TFA anions and water molecules are shown in ORTEP representation; macrocycles are shown in stick representation. Only hydrogen bonds between TFA and water molecules are shown for clarity.

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

than similar O-H‚‚‚O hydrogen bonds involving water. Inter-hydrogen sulfate and inter-hydrogen phosphate O-H‚‚‚O interactions with very short H‚‚‚O distances of 1.5-1.9 Å are typical examples. The better defined D‚‚‚A distances are more commonly used to describe the strength of a hydrogen bond, as the D-H-A angle (usually between 110° and 180°) will be a strong determinant of the H‚‚‚A distance. (H6L1)(CF3CO2)6(H2O)2 (2). The macrocycle in 2 is hexaprotonated and lies around a crystallographic inversion center. The charge is balanced by six trifluoroacetate anions. Two water molecules also form hydrogen bonds with the macrocycle via one ammonium group (Figure 5). The remaining 10 of the 12 ammonium protons are involved in hydrogen bonding to the carboxylate oxygen atoms of the trifluoroacetate anions. A list of all hydrogen bonds in 2 is given in Table 3. None of the fluorine atoms are involved in significant interactions with the exception of a short contact with a C-H group (C(4)-H(14)‚‚‚F(6)*, 3.224(2) Å, 113.3(15)°). The TFA anions pack in a manner that forms alternating hydrophobic and hydrophilic channels between rows of macrocycles that run parallel to the c axis (Figure 6). Each trifluoroacetate anion is unique in its mode of interaction, with one forming a bridge between adjacent ammonium groups on one macrocycle (N(2) ‚‚‚O(1)-C(7)-O(2)‚‚‚N(3)), another bridging between adjacent macrocycles (N(1)‚‚‚O(5)-C(11)-O(6)‚‚‚N(1)*), and the third interacting with a macrocycle and a water molecule (N(3)‚‚‚O(3)-C(9)-O(4)‚‚‚O(1)W). O(3) also hydrogen bonds directly to a symmetry-generated water molecule via N(3)‚‚‚O(3)‚‚‚O(1)W* and is the only oxygen atom to accommodate more than one hydrogen bond.

Figure 7. ORTEP plot of the hydrogen-bonding environment around the macrocycle in 3. C-H hydrogens have been omitted for clarity. Water hydrogen atoms are shown in proposed positions implied by distances between heteroatoms but were not included in the refinement. Thermal ellipsoids drawn at the 25% probability level.

The O(3)/O(4) TFA anions form 1D chains with the water molecules that run parallel to the c axis. It is noteworthy that, at the present time, this is the largest mononegative anion to have been complexed with the fully protonated [18]aneN6. More commonly, the fully protonated macrocycle is found to crystallize with conjugate bases of polyprotic acids such as phosphate19 and sulfate.20 Other structures elucidated with [H6L1]6+ have the charge balanced by smaller anions such as chloride18 and nitrate.32,33 Once the steric bulk of the singly charged anion increases, such as in the cases of picolinate, BNPP, or even triflate,34 it is evident that the protonation level of the macrocycle decreases to match the charge on the number of anions that are able to pack around it. In this context, 2 may be considered unusual. (H2L1)(C6H4NO2)2(H2O)5 (3). The structure of 3 consists of a diprotonated macrocycle with a picolinate anion bound on either side of the cavity (Figure 7). The charged ammonium groups (N(1) and N(4)) reside on opposite sides of the macrocycle, each employing both

Adducts between Oxoanions and Hexaazamacrocycles

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Table 4. Bond Distances (Å) and Angles (deg) for Hydrogen Bonds Involving the Macrocycle in 3 (Esd’s Given in Parentheses Where Applicable) D-H‚‚‚A

d(D-H)

d(H‚‚‚A)

d(D‚‚‚A)

∠(DHA)

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

0.92 0.92 0.92 0.996(11) 0.92 0.92 0.92 1.002(11) 1.002(11)

2.11 2.32 1.81 2.28(2) 1.82 2.12 2.21 2.53(6) 2.58(6)

2.962(7) 2.951(7) 2.729(6) 3.243(7) 2.733(6) 2.930(7) 2.886(7) 3.337(7) 3.312(7)

154 125 174 163(5) 169 147 130 137(6) 130(6)

Figure 8. ORTEP plot of the water chain found in 3. Hydrogen atoms are shown in proposed positions implied by interatomic O‚‚‚O distances but were not included in the refinement.

hydrogen atoms to bind to picolinate anions through hydrogen-bonding interactions with the carboxylate oxygen atom and the aromatic nitrogen atom. N(6) and N(3) of the macrocycle do not participate in any hydrogen-bonding interactions, and the remaining amines, N(2) and N(5), accept hydrogen bonds from water molecules. Although the hydrogen atom was not able to be located, there is possibly a weak interaction between O(3)W and N(5) judging from the distance between the heteroatoms (3.16 Å). The O(4)W‚‚‚N(2) interaction is significantly shorter (2.863(7) Å) and indicative of a moderate strength interaction. Interestingly, the macrocycle is symmetrical, showing perfect overlap between centroids drawn between opposing nitrogen atoms, despite the difference in hydrogenbonding distances at N(2) and N(5). The data were of insufficient quality to locate all water hydrogen atoms, preventing more precise elucidation of the hydrogen-bonding interactions involving these hydrogens; however, the presence of interactions can be implied from the O‚‚‚O interatomic distances. The water molecules form chains that run parallel to the c axis. The chains consist of repeating units of the five unique waters and can be described as having a backbone of composition (O(1)W-O(4)W-O(2)W-O(5)W)x with a pendant O(3)W hanging from O(1)W at each repeat (Figure 8). Figure 9 shows the packing of the structure, highlighting the water channels that run through the crystal lattice. These water channels are reminiscent of those found in another structure that we have reported previously19 which also contains [18]aneN6. In that case, however, the macrocycle is tetraprotonated and was complexed with HPO42- anions, and the water chain consists of repeating heptamers rather than the pentamers found in this adduct. (H3L1)(C12H8N2O8P2)3(H2O)5 (4). The asymmetric unit in 4 contains a triprotonated macrocycle with three bis(4-nitrophenyl) phosphate (BNPP) anions and five water molecules (Figure 10). The BNPP occurs in just one of 216 crystal structures containing aromatic phosphate esters,35 therein forming part of a copper(II) complex. 4 represents the first crystallographically

Figure 9. Packing of the crystal lattice in 3 viewed down the c axis. All nonsolvent hydrogen atoms have been omitted for clarity. Macrocycles and picolinate anions are drawn in ORTEP representation with water molecules drawn in stick representation. Hydrogen atoms on the water molecules are in implied positions and were not included in the refinement.

Figure 10. ORTEP plot of the hydrogen-bonding environment around the macrocycle in 4. C-H hydrogen atoms and noninteracting BNPP anions have been omitted for clarity.

characterized example of a triprotonated [18]aneN6 (H3L13+), and 4 and 5 (vide infra) are the only two examples of organic adducts formed by BNPP reported to date. Around the macrocyclic ring, the ammonium groups alternate with the neutral amine functions. The macrocycle has a bowl-shaped conformation and utilizes all six ammonium protons in hydrogen-bonding interactions with phosphate oxygen atoms or water molecules (see Table 5). Interestingly, the hydrogen bonds all lie within a fairly narrow range of geometric parameters, with the longest being N(2)-H(8)‚‚‚O(4)W, 2.888(3) Å, 146(3)°, and the shortest being O(1)W-H(1)W‚‚‚O(5), 2.645(3) Å, 172(3)°, with the D-H-A angles all lying between 146° and 173°. None of the amine protons are participating in hydrogen bonds. This is only the second crystallographically characterized example of [18]aneN6 in an asymmetric conformation, the first having been reported recently by our group.20 In contrast to the vast majority of [18]aneN6 structures reported to date, the macrocyclic cavity is dominated by water molecules rather than anions, most likely due to steric effects introduced by the p-nitrophe-

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Figure 11. Side (left) and end-on (right, nitrophenyl groups removed) views of the nanosized water-phosphate cage in 4. The macrocycle has been removed for clarity. Table 5. Hydrogen Bond Distances (Å) and Angles (deg) in 4 with Esd’s Given in Parenthesesa D-H‚‚‚A

d(D-H)

d(H‚‚‚A)

d(D‚‚‚A) ∠(DHA)

N(6)-H(2)‚‚‚O(4)W#1 N(6)-H(3)‚‚‚O(1) N(4)-H(5)‚‚‚O(6) N(4)-H(6)‚‚‚O(1)W N(2)-H(8)‚‚‚O(4)W#1 N(2)-H(9)‚‚‚O(2)W O(1)W-H(1)W‚‚‚O(5)#2 O(1)W-H(2)W‚‚‚O(1) O(2)W-H(3)W‚‚‚O(5)W#3 O(2)W-H(4)W‚‚‚O(3)W O(3)W-H(5)W‚‚‚O(2) O(3)W-H(6)W‚‚‚O(9) O(4)W-H(7)W‚‚‚O(6)#2 O(4)W-H(8)W‚‚‚O(2) O(5)W-H(9)W‚‚‚O(10) O(5)W-H(10)W‚‚‚O(1)W#3

0.96(3) 0.85(3) 0.83(3) 0.98(3) 0.93(4) 0.96(3) 1.001(10) 0.995(10) 0.998(10) 1.001(10) 0.994(10) 0.988(10) 0.989(10) 0.985(10) 1.006(10) 1.003(10)

1.85(3) 1.93(3) 2.10(3) 1.82(3) 2.07(4) 1.88(4) 1.651(11) 1.848(12) 1.87(2) 1.761(11) 1.834(13) 1.764(15) 1.738(10) 1.738(11) 1.83(2) 1.90(3)

2.811(3) 2.776(3) 2.845(3) 2.795(3) 2.888(3) 2.824(3) 2.645(3) 2.834(3) 2.785(3) 2.756(3) 2.812(3) 2.719(3) 2.714(3) 2.711(3) 2.804(3) 2.855(3)

173(3) 171(3) 150(3) 173(3) 146(3) 166(3) 172(3) 170(3) 151(3) 172(3) 167(3) 162(3) 168(3) 169(3) 162(5) 158(6)

a Symmetry transformations used to generate equivalent atoms: #1, x + 1, y, z; #2, x - 1, y, z; #3, -x, -y + 1, -z + 1.

Figure 13. Packing of the chains found in 4 (viewed down the a axis). Each chain is shown as a different color. C-H hydrogen atoms have been removed for clarity.

Figure 12. View of the chain comprised of cages sandwiched by two macrocycles in 4 (viewed down the a axis). C-H hydrogen atoms have been removed for clarity.

nyl group on each phosphate ester (BNPP). The anions occupy the circumference of the macrocycle, interacting primarily through hydrogen bonds with water molecules, and with each other through π-stacking. The bulky anions cause a deformation of the macrocycle from

the apparently more stable symmetric conformations seen in other systems, and also force the formation of a rare triprotonated state. An interesting supramolecular feature in this structure is a nanosized water-phosphate “cage” formed by the BNPP anions and water molecules (Figure 11). The cage measures 10 × 9 × 4 Å, with its interior being devoid of the macrocycle. All crystallographically unique anions (3) and water molecules (5) participate in the formation of the cage. Larger scale supramolecular features are revealed upon expansion of the asymmetric unit. The cages are connected through hydrogen bonds to two macrocycles to form chains of cages that run parallel to the a axis (Figure 12). The chains pack solely through van der Waals interactions between nitrophenyl groups that overlap slightly between chains to give the final lattice arrangement (Figure 13). (H4L2)(C12H8N2O8P2)4(H2O)0.5 (5). The asymmetric unit of 5 consists of two bis(4-nitrophenyl) phosphate

Adducts between Oxoanions and Hexaazamacrocycles

Figure 14. ORTEP plot of the hydrogen-bonding environment around the bis(tacn) cation in 5. Asterisks indicate symmetrygenerated atoms. Thermal ellipsoids are drawn at the 25% probability level. C-H hydrogen atoms and the water molecule have been removed for clarity. Table 6. Hydrogen Bond Distances (Å) and Angles (deg) in 5 with Esd’s Given in Parentheses Where Applicablea D-H‚‚‚A

d(D-H)

d(H‚‚‚A)

d(D‚‚‚A)

∠(DHA)

N(2)-H(5)‚‚‚O(9) N(2)-H(6)‚‚‚O(1) N(3)-H(12)‚‚‚O(1) N(3)-H(12)‚‚‚O(15)#1 N(3)-H(11)‚‚‚O(2)#2

0.92 0.92 0.92 0.92 0.92

1.77 1.84 2.12 2.60 1.89

2.683(5) 2.733(5) 2.892(5) 3.052(5) 2.794(5)

170 162 140 111 167

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

anions, a water molecule with 1/4 occupancy, and half of a 1,2-[bis(1,4,7-triazacyclononan-1-yl]ethane unit. The 1,2-[bis(1,4,7-triazacyclononan-1-yl]ethane moiety lies around a crystallographic axis of symmetry located directly between the two carbon atoms of the ethylene bridge. The four secondary amines are protonated to ammonium groups and utilize all hydrogen atoms in hydrogen-bonding interactions with terminal oxygen atoms of six BNPP anions. Two BNPP anions (symmetry related) are chelated by two ammonium groups (N(2)‚‚‚O(1)‚‚‚N(3)), and each one lies above a tacn macrocyclic cavity (Figure 14). The two tertiary amines

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host no hydrogen atoms. The BNPP anions participate to different degrees in the overall hydrogen-bonding regime. The two terminal phosphate oxygen atoms on P(1) host a total of three hydrogen bonds (see Table 6): the above-mentioned N-H chelating O(1) and a bridge to a symmetry-related macrocycle through the other oxygen atom (N(3)-H(11)‚‚‚O(2), 2.794(5) Å, 167°). Only one oxygen on P(2) hosts a hydrogen bond (N(2)H(5)‚‚‚O(9), 2.683(5) Å, 170°). The macrocycle-BNPP constructs link up through hydrogen bonds to form 2D sheets that run parallel to the B-0-C plane (Figure 15). The sheets stack on top of each other to form a layered lattice held together by van der Waals interactions (Figure 16). While this is the first reported structure of a 1,2-[bis(1,4,7-triazacyclononan-1-yl]ethane anion adduct, we believe it has the potential to bind a wide variety of anions. This structure and 4 highlight the “bipolar” nature of the anion, having hydrophilic (phosphate) and hydrophobic (nitrophenyl) functionaties, which encourages interactions among water molecules, positively charged groups, and the phosphate group. This leaves the nitrophenyl groups to interact with each other via π-stacking and van der Waals interactions in stabilizing crystal lattices that contain hydrophilic holes which host the macrocycles and phosphate groups, isolated by hydrophobic sections. Conclusion The nature of the azamacrocyclic constructs allows for hydrogen-bonding interactions that facilitate the binding of organic oxoanions. Electrostatic interactions play an important role, and there appears to be a preference for multiple N-H hydrogen bond donors to interact with single oxygen atoms on the anions. [18]aneN6 has a tendency to bind either anions or water on both sides of the macrocycle, whereas 1,2-[bis(1,4,7triazacyclononan-1-yl]ethane, with its more limited cavity size, retains guests on only one side of each macrocyclic face. This study reports only the second example of an adduct incorporating the diprotonated macrocycle [H2L1]2+, the first example of an adduct incorporating [H3L1]3+, the first two examples of macrocycle-bis(4-nitrophenyl)phosphate adducts, and a novel water-phosphate cage formed around [H3L1]3+.

Figure 15. 2D sheets formed by the macrocycles and BNPP anions in 5 viewed down the c axis. C-H hydrogen atoms and water molecules have been removed for clarity.

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Figure 16. Packing of the 2D sheets in 5 viewed down the b axis interacting through interlocking BNPP anions.

Conformational flexibility and the ability to hold between one to six positive charges provide the macrocycle with many options for binding anions. Factors such as the size and charges on the anions, however, also have a strong influence on the nature of the lattices that are formed. Acknowledgment. This work was supported by the Australian Research Council. A.C.W. was the recipient of a Monash University Research and Teaching Fellowship and a Departmental Scholarship. Supporting Information Available: Crystallographic data in CIF format for 1-5. This material is available free of charge via the Internet at http://pubs.acs.org.

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