Chlorometallate-Pyridinium Boronic Acid Salts for Crystal Engineering

Article pubs.acs.org/crystal

Chlorometallate-Pyridinium Boronic Acid Salts for Crystal Engineering: Synthesis of One‑, Two‑, and Three-Dimensional Hydrogen Bond Networks Yasemin Yahsi, Elif Gungor, and Hulya Kara* Department of Physics, Faculty of Science and Art, Balikesir University, 10145 Balikesir, Turkey S Supporting Information *

ABSTRACT: A series of new crystal structures of salts containing 3- and 4-pyridineboronic acid (3- and 4-pba) with chlorometallate have been prepared: [4-pbaH][MnCl2] (1), [4-pbaH][CdCl2], (2), [4-pbaH]2[CuCl4] (3), [4-pbaH]2[PdCl4] (4), [3-pbaH]2[CdCl4] (5), [3-pbaH][CuCl3(OH2)] (6), and [3-pbaH][PdCl2] (7). In these salts five structural forms for the chlorometallate species are observed: mononuclear square planar [M = Pd (4 and 7)], dimeric square-pyramidal [M = Cu (3)], polymeric square-pyramidal [M = Cu (6)], polymeric trans-edge-sharing octahedral [M = Mn (1), Cd (2)], and polymeric cis-edge-sharing octahedral [M = Cd (5)]. The cyclic R2,2(8) boronic acid dimer is formed in the salt of 1−5. NH···Cl2M synthons A have been exploited in 1−4, 6, and 7. Both NH···Cl2M (sythons A) and B(OH)2···Cl2M (sythons B) interactions give rise to a synthon of form I in 6. The uncommon folded conformation of the NH···Cl2M (synthons A) are formed in 7. The NH or OH donors and consequent branching of the NH···Cl hydrogen-bond network leads to one-, two-, and three-dimensional structures. These structures are further stabilized by CH···O and CH···Cl and π···π stacking interactions.

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INTRODUCTION Recently, boronic acids and its derivatives have attracted a great deal of attention due to their properties and applications in the areas of pharmaceuticals, agrochemicals,1−3 and in medicine as antibiotics,4−6 antibody mimics for polysaccharides,7,8 for the development of enzyme inhibitors like protease inhibitors,9−14 boron neutron capture (BNCT) therapy agents,15−19 and for the treatment of tumors.20 In the area of organic chemistry, boronic acid derivatives have also been widely used in cross-coupling reactions,1 carboxylic acid activation,21,22 and as reagents and starting materials in organic synthesis.23 Therefore, this functional group has been recently used as a new building block in crystal engineering and also has been of current interest in supramolecular chemistry with respect to hydrogen-bonded derivatives.24−31 In supramolecular synthesis, boronic acids, with general formula R−B(OH)2, have been well considered to be potential cocrystal formers,29−39 due to the flexibility of the -B(OH)2 functional group which enables the formation of a variety of hydrogen bonded assemblies in one- or multicomponent systems.40−43 It is known from the literature that the presence of two hydroxyl groups of boronic acids leads to form mainly three types of conformations, identified as syn−anti, syn−syn, and anti−anti,44,45 as shown in Scheme 1, which yield different hydrogen-bonding networks. Among these arrangements, while syn−anti conformation is observed in a majority of structures, the syn−syn and anti−anti conformations are relatively uncommon.33,46 However, it is interesting to note that the hydroxyl groups are arranged in a syn−syn conformation in 6. Orpens and co-workers reported a range of charge-assisted hydrogen-bond acceptor tectons such as anionic [PtCl4]2−, with © 2015 American Chemical Society

Scheme 1

cationic, often pyridinium, and bipyridinium and related tectons, based on the exploitation of the MCl2···HN supramolecular synthon A and related synthons.47−55 Their studies show that A and related synthons allow the synthesis of hydrogen-bonded networks with varying degrees of complexity depending upon the hydrogen-bond donor capability of the cations. Previous publications also reported on N-donor boronic acid studies, which are DNA-binding studies of platinum(II)-terpyridine complexes containing N- and S-donor boronic acid,56 a series of 3- and 4-pyridineboronic acids esters,57 and DFT calculations, IR and Raman analysis of 3- and 4-pyridineboronic acids.58 In our previous work, we reported the use of 3- and 4-protonated pyridine boronic acids as new tectons in crystal synthesis. We have examined a series of crystal structures formed Received: December 5, 2014 Revised: April 30, 2015 Published: May 4, 2015 2652

DOI: 10.1021/cg501769b Cryst. Growth Des. 2015, 15, 2652−2660

Article

C10H14B2Cl4N2O4Pd triclinic P1̅ 6.9260(14) 7.9568(16) 8.2970(17) 70.25(3) 79.53(3) 83.22(3) 422.38(15) 100(2) 1 1.747 4760 1924 0.0256 C10H14B2CdCl4N2O4 triclinic P1̅ 6.9892(15) 9.0375(18) 14.408(3) 95.14(2) 103.63(2) 107.873(13) 828.8(3) 100(2) 2 1.978 9029 3746 0.0250 C10H14B2Cl4N2O4Pd monoclinic Cc 20.949(4) 7.4938(15) 14.998(3) 90 133.85(3) 90 1697.9(6) 100(2) 4 1.738 9369 3876 0.0220

C5H9BCl3CuNO3 monoclinic Cc 13.863(3) 3.7921(8) 20.094(4) 90 97.46(3) 90 1047.4(4) 100(2) 4 2.826 5436 2390 0.0301

Figure 1. (a) Ribbon motif E involving synthon A in 1. The NH···Cl and OH···O hydrogen bonds are indicated. (b) 3-D packing of the hydrogen-bonded ribbons in 1 viewed parallel to the layer. (c) 3D packing of the hydrogen-bonded network with {MCl2−}n chains and the boronic acid dimers. (d) Space filling representation of 1 as in panel c.

C10H14B2CdCl4N2O4 triclinic P1̅ 3.8030(8) 7.8592(16) 14.179(3) 84.77(3) 82.38(3) 81.11(3) 413.92(15) 100(2) 1 1.981 4644 1879 0.0225

between 3- and 4-pyridineboronic acids and [M(dithiooxalate)2]2− as well as [M(oxalate)2]2− (M = Ni, Cu, Pt, and Pd), showing that the participating building blocks are linked mainly by B(OH)··· O(H)B, B(OH)2···carboxylate, B(OH)2···thiocarboxylate, and + N−H···carboxylate interactions.59 Recently, Campos-Gaxiola and co-workers have reported a related study in which they studied the structures formed between 3- and 4-pyridineboronic acids with K2PtCl4 and H2PtCl6 showing that the primary hydrogen bonding interactions of the resulting one-, two-, and three-dimensional (1D, 2D, and 3D) networks contain at least one of the following synthons: X−H···Cl2Pt− (X = C, N+), B(OH)2···Cl2Pt−, and B(OH)2 ···(HO)2B.60 In order to probe the robustness of the NH···Cl2M sythons A and B(OH)2···Cl2M synthon B and their utility in diversifying the crystal structures, we report on the preparation and structural characterization of a series of new crystal structures of salts containing 3- and 4-pyridineboronic acid (3- and 4-pba) with chlorometallate: [4-pbaH][MnCl2] (1), [4-pbaH][CdCl2], (2), [4-pbaH]2[CuCl4] (3), [4-pbaH]2[PdCl4] (4), [3-pbaH]2[CdCl4] (5), [3-pbaH][CuCl3(OH2)] (6), [3-pbaH][PdCl2] (7).

chemical formula crystal system space group a/Å b/Å c/Å α/° β/° γ/° V/Å3 T/K Z μ/mm−1 reflections collected independent reflections final R1 [I > 2σ(I)]

C10H14B2Cl4MnN2O4 triclinic P1̅ 3.7276(7) 7.8853(16) 14.104(3) 84.92(3) 82.68(3) 81.80(3) 405.94(14) 100(2) 1 1.487 3688 1811 0.0583

C10H14B2Cl4CuN2O4 triclinic P1̅ 9.0727(18) 9.5234(19) 10.835(2) 79.53(3) 65.87(3) 71.62(3) 809.3(3) 100(2) 2 2.026 8899 3679 0.0527

5 2 1

Table 1. Crystallographic Data for Compounds 1−7

3

4

6

7

Crystal Growth & Design

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EXPERIMENTAL SECTION

The metal chloride salts and both pyridine boronic acids were purchased from Aldrich. Syntheses and recrystallizations were carried out in air in standard glassware without special precautions. “Dilute HCl” is taken to mean 0.5 mL of concentrated hydrochloric acid in 10 mL of water. Elemental analyses for C, H, and N were performed on a PerkinElmer analyzer. 2653


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Synthesis of [4-pbaH]2[CuCl4] (3). A total of 42.6 mg (0.25 mmol) of CuCl2·H2O and 61 mg (0.5 mmol) of pyridine-4-boronic acid were dissolved in dilute HCl to give a green solution. After partial evaporation of the solvent, green crystals of 3 were obtained. Elemental analysis calcd (%) for 3 (C10H14B2Cl4CuN2O4): C 26.5, H 3.11, N 6.18; found: C 27.01, H 3.28, N 6.01. Synthesis of [4-pbaH]2[PdCl4] (4). A total of 80 mg (0.25 mmol) of K2PdCl4 and 61.4 mg (0.5 mmol) of pyridine-4-boronic acid were dissolved in dilute HCl to give an orange solution. After partial evaporation of the solvent, orange crystals of 4 were obtained. Elemental analysis calcd (%) for 4 (C10H14B2Cl4N2O4Pd): C 24.21, H 2.84, N 5.65; found: C 24.01, H 3.03, N 5.26. Synthesis of [3-pbaH]2[CdCl4] (5). A total of 45.8 mg (0.25 mmol) of CdCl2 and 61.4 mg (0.5 mmol) of pyridine-3-boronic acid were dissolved in dilute HCl to give a colorless solution. After partial evaporation of the solvent, colorless crystals of 5 were obtained. Elemental analysis calcd (%) for 5 (C10H14B2CdCl4N2O4): C 23.92, H 2.81, N 5.58; found: C 24.01, H 2.86, N 5.13. Synthesis of [3-pbaH][CuCl3(OH2)] (6). A total of 42.6 mg (0.25 mmol) of CuCl2.·H2O and 61 mg (0.5 mmol) of pyridine-3-boronic acid were dissolved in dilute HCl to give a green solution. After partial evaporation of the solvent, green crystals of 6 were obtained. Elemental analysis calcd (%) for 6 (C5H9BCl3CuNO3): C 19.26, H 2.91, N 4.49; found: C 20.01, H 3.06, N 4.83. Synthesis of [3-pbaH][PdCl2] (7). A total of 80 mg (0.25 mmol) of K2PdCl4 and 61.4 mg (0.5 mmol) of pyridine-3-boronic acid were dissolved in dilute HCl to give an orange solution. After partial evaporation of the solvent, orange crystals of 7 were obtained. Elemental analysis calcd (%) for 7 (C10H14B2Cl4N2O4Pd): C 24.21, H 2.84, N 5.65; found: C 25.01, H 2.77, N 5.59. Single-Crystal X-ray Studies. Diffraction measurements were made on three-circle CCD diffractometers using graphite monochromated Mo−Kα radiation (λ = 0.71073 Å) at 100 K for 1−7. The intensity data were integrated using the SAINT61 program. Absorption, Lorentz and polarization corrections were applied. The structures were solved by direct methods and refined using full-matrix least-squares against F2 using SHELXTL.61 All non-hydrogen atoms were assigned anisotropic displacement parameters and refined without positional constraints. Hydrogen atoms were included in idealized positions with isotropic displacement parameters constrained to 1.5 times the Uequiv of their attached carbon atoms for methyl hydrogens, and 1.2 times the Uequiv of their attached carbon atoms for all others. Figures were created with MERCURY.62 Hydrogen bonding interactions in the crystal lattice were calculated with the PLATON program package.63 Crystal data of 1−7 are listed in Table 1.

Figure 2. (a) Ribbon motif E involving synthon A in 3. The NH···Cl and OH···O hydrogen bonds are indicated. (b) 2D packing of the hydrogenbonded ribbons in 3 viewed parallel to the layer. (c) 3D packing of the hydrogen-bonded ribbons in 3. (d) Space filling representation of 3 as in panel c.

Synthesis of [4-pbaH][MnCl2] (1). A total of 49.5 mg (0.25 mmol) of MnCl2·4H2O and 61.4 mg (0.5 mmol) of pyridine-4-boronic acid were dissolved in dilute HCl to give a red solution. After partial evaporation of the solvent, red crystals of 1 were obtained. Elemental analysis calcd (%) for 1 (C10H14B2Cl4MnN2O4): C 27.02, H 3.17, N 6.30; found: C 28.01, H 3.28, N 6.40. Synthesis of [4-pbaH][CdCl2] (2). A total of 45.8 mg (0.25 mmol) of CdCl2 and 61.4 mg (0.5 mmol) of pyridine-4-boronic acid were dissolved in dilute HCl to give a colorless solution. After partial evaporation of the solvent, colorless crystals of 2 were obtained. Elemental analysis calcd (%) for 2 (C10H14B2CdCl4N2O4): C 23.92, H 2.81, N 5.58; found: C 23.70, H 3.01, N 5.31.

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RESULTS AND DISCUSSION Salts of Pyridinium-4-boronic Acid. When protonated 4-pyridine boronic acid (C) is used, the salts 1−4 are formed.

Table 2. Some Selected Bond Lengths [Å] and Angles [°] and Intermolecular Contacts in 1−7 1

2

3

M−Cl

2.5149(10) 2.5727(10) 2.5832(12)

2.5739(9) 2.6502(9) 2.6606(11)

2.2357(12) 2.2657(11) 2.3358(14) 2.3469(14) 2.7189(16)

M−Cl···HN

2.62 2.49

128 144

2.64 2.52

128 140

M−Cl···HOB

2.29

147

2.29

146

BOH···OB

1.94

171

1.93

173

2.57 2.50 2.66 2.48 2.38 2.35 1.95 1.96

4

5

2.2912(9) 2.2985(12) 2.3222(9) 2.3062(12)

137 141 125 155 151 152 166 165

M−Cl···HO (water) (water) O−H···OB 2654

2.42 2.57 2.49 2.56 2.33 2.39 1.92 1.89

145 131 144 134 152 153 177 174

2.5628(7) 2.5916(8) 2.6476(7) 2.6644(9) 2.6793(9) 2.6900(7) 2.34 2.51

2.37 2.25 1.94 1.97

6

7

2.2802(8) 2.2812(9) 2.2823(8)

2.3012(7) 2.3054(9)

143 138

2.52 2.66

137 128

2.41 2.81

152 123

159 155 173 175

2.34 2.33

150 163

2.39

158

2.57 2.02

162 147


Article

Crystal Growth & Design Table 3. Distance between Ring Centroids [Å] of Compounds 1−7a 1 2 3

4 5 6 7 a

Cg(I) → Cg(J)

Cg−Cg

Cg(3) → Cg(3)(−1+x,y,z) Cg(3)→Cg(3)(1+x,y,z) Cg(3) → Cg(3)(−1+x,y,z) Cg(3) → Cg(3)(1+x,y,z) Cg(2) → Cg(2)(1−x,−y,1−z) Cg(2) → Cg(3)(1−x,1−y,1−z) Cg(3) → Cg(2)(1−x,1−y,1−z) Cg(3) → Cg(3)(1‑x,1−y,2−z) Cg(1) → Pd1(x,y,z) Cg(2) → Pd1(−1/2+x,1/2+y,z) Cg(3) → Cg(4)(x,y,z) Cg(4) → Cg(3)(x,y,z) Cg(3) → Cg(3)(x,−1+y,z) Cg(3) →Cg(3)(x,1+y,z) Cg(1) → Cg(1)(1−x,1−y,1−z)

3.727 3.728 3.8031 3.8029 3.594 3.821 3.821 3.996

Cg−M

ring centroid Cg(3) = N1−C3−C2−C1−C5−C4 Cg(3) = N1−C3−C2−C1−C5−C4 Cg(2) = N2−C3−C2−C1−C5−C4 Cg(3)= N1−C8−C7−C6−C10−C9

3.730 3.776 3.7130 3.7131 3.792 3.792 3.6848

Cg(1) = N1−C3−C2−C1−C5−C4 Cg(2) = N2−C8−C7−C6−C10−C9 Cg(3) = N1−C4−C3−C2−C1−C5 Cg(4) = N2−C9−C8−C7−C6−C10 Cg(3) = N1−C4−C3−C2−C1−C5 Cg(1) = N1−C4−C3−C2−C1−C5

Cg(I): Plane number I (= ring number in parentheses above), Cg−Cg: Distance between ring Centroids (Å), Cg−M: Ring-Metal Interactions (Å).

Crystals of 1−4 are isostructural, with the same space group P1̅ for [4-pbaH][MCl2] M = Mn (1) and Cd (2), and [4-pbaH]2[CuCl4] (3), which differ in the unit cell dimensions from 1 and 2, and chiral space group Cc for [4-pbaH]2[PdCl4] (4) (see Table 1). The expected cyclic R2,2(8) boronic acid dimer is formed, and the supramolecular dication C1 results. The -B(OH)2 groups adopt the most preferred syn−anti conformation in the salt of 1−4.33 NH···Cl2M (synthon A) interactions are formed at both ends of the 4-pyridine boronic acid dimer in the salt of 1−4. NH···Cl2M hydrogen-bonded planar E-type ribbons are formed, linked by hydrogen bonds involving the exocyclic hydrogens of the cyclic R2,2(8) boronic acid unit in the salt of 1−4 (see F). In the crystalline architecture of 1−3, the E type ribbons are packed in the crystal structure in a parallel fashion (Figures 1a and 2a). While each ribbon is in close contact with two other neighboring ribbons through edge-to-edge interactions with O−H···Cl and C−H···Cl hydrogen bonds,64−67 its face-to-face neighbor makes significant π−π stacking interactions68−71 through the aromatic rings of the cationic part. There are ring−metal interactions in the structure of 4 (Table 3). Crystal Structures of [4-pbaH][MCl2] [M = Mn (1) and Cd (2)]. The compound crystallizes in the P1̅ space group, and the asymmetric unit contains one [4-pbaH]+ cation and an [MCl2]− moiety. An inversion center is located at the metal atom and at the middle of the boronic acid dimer. [MCl2]− units are polymerized to form a chain in which octahedral MCl6 units linked by trans-edge-sharing into chains (G2). Each [4-pbaH]+ cation is associated with {MCl2−}n chains through NH···Cl and OH···Cl hydrogen bonds. One of the features of the crystal structures is the columnar packing along the a-axis; these columns are connected by the hydrogen-bond network with the boronic acid dimers (Figure 1a,b). The planar ribbons (E) extend along bc, while the {MCl2−}n chains (G2) extend along the a axis (see Figure 1a). In the crystalline architecture, NH···Cl and OH···Cl hydrogen bonds give rise to synthon F and interaction H1 which form 3D polymeric structures. This structures further stabilized by CH···O, CH···Cl, and π···π stacking interactions (Tables S1 and 3). The polymeric networks lie in the bc-plane and stack along the a-axis (Figure 1a) and in the ac-plane and stacks along the b-axis (Figure 1b). The M···M distance within the G2 chain is 3.728 Å for 1 and 3.803 Å for 2,

Figure 3. (a) Ribbon motif E involving synthon A in 4. The NH···Cl and OH···O hydrogen bonds are indicated. (b) Angular arrangements of 1D ribbons in 4. (c) 3D packing of ribbons in crystalline 4. (d) Space filling representation of 4 as in panel c.

while along the E-type ribbons is 21.693 Å for 1 and 21.764 Å for 2, respectively. Crystal Structure of [4-pbaH]2[CuCl4] (3). The compound crystallizes in the P1̅ space group, and the asymmetric unit contains two [4-pbaH]+ cations and an [CuCl4]−2 moiety. A stable polymorph of 3 consists of centrosymmetric anion dimers [(CuCl4)2]−4 that are linked by hydrogen bonding to [4-pbaH]+ forming a motif of form E (see Figure 2a). The metal center may be considered as having a slightly distorted square-pyramidal geometry with four chloride ions (Cl1, Cl2, Cl3, and Cl4) forming the base of the square pyramid and chloride ion Cl3i [i = 1−x, 1−y, 1−z] located at the apex (Table 2). In the crystalline architecture of 3, NH···Cl and OH···Cl hydrogen bonds give rise to sython F and interaction H2 which 2655


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Figure 5. (a) 1D Ribbon motif involving synthon A and synthon B in 6. The NH···Cl and OH···Cl hydrogen bonds are indicated. (b) 3D packing of layers in crystalline 6. (c) 3D packing of chains in crystalline 6. (d) Space filling representation of 6 as in panel c.

Figure 4. (a) Part of a layer formed by [{CdCl4}n]2n− chains cross-linked by hydrogen bonding to [3-pbaH]+ in crystalline 5. The NH···Cl and OH···Cl hydrogen bonds are indicated. (b) 3D packing of layers in crystalline 5. (c) 3D packing of chains in crystalline 5. (d) Space filling representation of 5 as in panel c.

the cross-linked ribbons is 10.127 Å, and between the parallel ribbons is 7.494 Å. Salts of Pyridinium-3-boronic Acid. The expected cyclic R2,2(8) boronic acid dimer is formed, and the supramolecular dication D1 results in 5, while it is not formed in 6 and 7. In two monomeric motifs 6 and 7, two hydroxyl groups in boronic acid are involved in intramolecular hydrogen bonds (see Table S1). These bonds should be strong enough to overcome intermolecular hydrogen bond interactions in the crystal field. Breaking of the dimer motif is possible due to intramolecular hydrogen bond formation.37 The -B(OH)2 groups adopt the most preferred syn−anti conformation in the salt of 5 and 7, while they adopt relatively uncommon syn−syn conformation in the salt of 6.33 In the present case of 6, both -B(OH)2 functions have syn−syn orientation, with the consequence that the water molecules act as hydrogen-bonding donors within the molecule. Interactions A are formed in the salt of 6 and 7, while it is not formed in 5. In the crystalline architecture of 5−7, the ribbons are packed in the crystal structure in a parallel fashion. While each ribbon is in close contact with two other neighboring ribbons through edge-to-edge interactions with O−H···Cl and C−H···Cl hydrogen bonds,64−67 its face-to-face neighbor makes significant π−π stacking interactions68−71 through the aromatic rings of the cationic part (Table 3).

form 2D polymeric structures. However, the packing of these hydrogen-bonded ribbons in the crystal structure is found to be 3D further stabilized by several CH···O and CH···Cl and π···π stacking interactions (Table S1, Table 3 and Figure 2b). The Cu···Cu distance within the dimer (G1) is 3.550 Å, while along the E-type ribbons is 21.512 Å. Crystal Structure of [4-pbaH]2[PdCl4] (4). The compound crystallizes in the chiral space group Cc, and the asymmetric unit contains two [4-pbaH]+ cations and an [PdCl4]−2 moiety. The metal center may be considered as having square-planar geometry as might be expected (see Figure 3a and Table 2). Hydrogen bonded interactions of type A are formed at both ends of the boronic acid dimer and on opposite edges of the square planar dianion, and an extended form of hydrogen-bond ribbon motif E is observed in 4 (Figure 3a). E type ribbons are crosslinked by OH···Cl hydrogen bonds and the ribbons inclined at 59° to one another. In the crystalline architecture, NH···Cl and OH···Cl hydrogen bonds give rise to a synthon of form F which form a 3D polymeric structure in which there are two sets of criss-cross E-type ribbons with every second ribbon parallel and coplanar (see Figure 3b,c). This structure is further stabilized by CH···O, CH···Cl interactions (Tables S1 and 3). The Pd···Pd distance along the E-type ribbons is 21.464 Å, between 2656


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Figure 6. (a) 1D Ribbon motif involving synthon A in 7. The NH···Cl and OH···Cl hydrogen bonds are indicated. (b) 3D packing of chains in crystalline 7. (c) Packing of 1D ribbons in crystalline 7. (d) Space filling representation of 7 as in panel c.

Crystal Structure of [3-pbaH]2[CdCl4] (5). The compound crystallizes in the P1̅ space group, and the asymmetric unit contains two [3-pbaH]+ cations and an [CdCl4]−2 moiety. An inversion center is located at the metal atom and at the middle of the boronic acid dimer. [CdCl4]−2 units are polymerized to form a chain in which octahedral CdCl6 units linked by cis edgesharing into chains (G3). The [{CdCl4}n]2n− chains are hydrogen bonded to [3-pbaH]+ forming neutral sheets perpendicular to a. Interactions A and the hydrogen-bonded planar E-type ribbons are not formed in the salt of 5 (see H3 and I). Each [3-pbaH]+ cation is associated with [{CdCl4}n]2n− chains through NH···Cl and OH···Cl hydrogen bonds. One of the features of the crystal structures is the columnar packing along the a-axis; these columns are connected by the hydrogen-bond network with the

boronic acid dimer (Figure 4c). In the crystalline architecture of 5, NH···Cl and OH···Cl hydrogen bonds give rise to a synthon of form I and interaction H3 which form three-dimensional polymeric structures (Figure 4b). This structure is further stabilized by CH···O, CH···Cl, and π···π stacking interactions. The polymeric networks lie in the ac-plane and stacks along the b-axis (Figure 4b). The Cd···Cd distance within the G3 chain is 3.989 and 4.049 Å, while the Cd ···Cd distance along the I-type ribbons is 14.408 Å. The ribbons I extend along c, while the [{CdCl4}n]2n− chains G3 extend along a. Crystal Structure of [3-pbaH][CuCl3(OH2)] (6). The compound crystallizes in the Cc space group, and the asymmetric unit contains one [3-pbaH]+ cation and an [CuCl3(OH2)]− moiety. [CuCl3(OH2)]− units are polymerized to form a chain (G4). 2657


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Crystal Growth & Design Scheme 2. Molecular Cations and Supramolecular Dications Formed in Crystal Synthesis of 1−7

expected (see Figure 6a and Table 2). Hydrogen bonded interactions of type A are formed on opposite edges of the square planar dianion. In the crystalline architecture of 7, NH···Cl and OH···Cl hydrogen bonds give rise to a synthon of form K which form a 1D structure along c axis (Figure 6a). However, the packing of these hydrogen-bonded ribbons in the crystal structure is found be 3D further stabilized by several CH···O, CH···Cl, and π···π stacking interactions (Table S1, Table 3 and Figure 2b). Although it is known, the folded conformation of the NH···Cl2Pd synthon is uncommon (see K). Generally, this synthon is planar or at least almost planar.72,73 The Pd···Pd distance within K-type ribbons is 9.356 Å.

The metal center may be considered as having a slightly distorted square-pyramidal geometry with three chloride ions (Cl1, Cl2, Cl3) and one water molecule forming the base of the square pyramid and a chloride ion Cl1ii [ii = x, −1 + y, z] is located at the apex (Table 2). The expected cyclic R2,2(8) boronic acid dimer is not formed in the salt of 6. Interactions A are formed but the hydrogen-bonded planar E-type ribbons are not formed in the salt of 6. In the crystalline architecture of 6, the [3-pbaH]+ cations and [CuCl3(OH2)]− anions are connected by NH···Cl2Cu (sythons A) and B(OH)2···Cl2Cu (sythons B) interactions give rise to a synthon of form J and interaction H4 which form a threedimensional polymeric structure. This structure is further stabilized by CH···O, CH···Cl, and π···π stacking interactions (Tables S1 and 3). The polymeric networks lie in the ac-plane and stacks along the b-axis (Figure 5b). The Cu···Cu distance within the G4 chain is 3.792 Å, while the Cu···Cu distance along the J-type ribbons is 10.871 Å. The ribbons J extend along c, while the [{CuCl3(OH2)}n]n− chains G4 extend along b (Figure 5b). Crystal Structure of [3-pbaH][PdCl2] (7). The compound crystallizes in the P1̅ space group, and the asymmetric unit contains one [3-pbaH]+ cation and an [PdCl2]− moiety. An inversion center located at the metal atom. The metal center may be considered as having square-planar geometry as might be

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DISCUSSION The structures of 1−7 described here fall into two categories based on their isomeric monocations (3- and 4-pba). The crystal structures of 1−3 and 5 belong to the same space group (P1̅) except for 4 and 6 (Cc). Salts 1 and 2 are isostructural and isomorphous structure in which {MCl2−}n trans-edge-sharing chains are linked by a R2,2(8) boronic acid dimer by NH···Cl2M (sythons A) and BOH···Cl hydrogen bonds into a 3D network. The structure of 3 is isostructural with that of salts 1 and 2 but 2658


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Crystal Growth & Design with a different pattern in which [(CuCl4)2]−4 dimers are linked R2,2(8) boronic acid dimer by NH···Cl2M (sythons A) and BOH···Cl hydrogen bonds into a 2D network. The structure of 4 is isostructural with that of salts 1, 2 and 3 but with a different space group Cc and different pattern in which [PdCl4]−2 are linked R2,2(8) boronic acid dimer by NH···Cl2M (sythons A) and BOH···Cl hydrogen bonds into a criss-cross type 3D network. The structure of 5 is isomorphous with that of salts 1 and 2 but with a different pattern of NH hydrogen bonding as a result of the different isomer of pyridinium boronic acid being present. The A-type synthon is not formed in 5, wherein [{CdCl4}n]2n− cis edge-sharing chains are linked R2,2(8) boronic acid dimer via more simpler NH···Cl and BOH···Cl hydrogen bonds into a 3D network. The salt 6 has a different structure in which the CuII ions are coordinated with a water molecule. In the crystalline architecture of 6, [CuCl3(OH2)]− chains are linked by [3-pbaH]+ cations by NH···Cl2Cu (sythons A) and B(OH)2··· Cl2Cu (sythons B) and Cu−Cl···HO (water), (water) O−H···OB hydrogen bonds into a 3D network. The structure of 7 is isomorphous with that of salts 4 but with a different pattern of NH hydrogen bonding as a result of the different isomers of pyridinium boronic acid present. In the crystalline architecture of 7, [PdCl2]− is linked by [3-pbaH]+ cations via an uncommon folded conformation of the NH···Cl2Pd synthon and BOH···Cl hydrogen bonds into 1D structures.

can be versatile ditopic building blocks for crystal engineering of higher-dimensional networks when combined with chlorometallate. We have shown that chlorometallate anions are good hydrogen bond acceptors. The NH or OH donors and consequent branching of the NH···Cl hydrogen-bond network lead to 1D, 2D, and 3D structures. This structure is further stabilized by CH···O and CH···Cl types of interactions. π···π stacking interactions through the aromatic rings are observed in the hydrogen bonded assembly of 1−3 and 5−7, while ring−metal interactions are observed in 4.

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ASSOCIATED CONTENT

S Supporting Information *

Additional figure (Figures S1) and X-ray data files (CIF). The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/cg501769b.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors are grateful to the Scientific and Technological Research Council of Turkey (TUBITAK) (Grant Number TBAG-108T431) for the financial support. Dr. Kara would like to thank TUBITAK for NATO-B1 and the Royal Society short visit fellowship for financial support and Prof. A. Guy Orpen (School of Chemistry, University of Bristol, U.K.) for his hospitality. Dr. Kara are also very grateful to Dr. Christopher J. Adams and Dr. Mairi F. Haddow (The School of Chemistry, University of Bristol) for their support.

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CONCLUSIONS In conclusion, the observation of two series of isostructural salts in which the metal varies without changing the form of the crystal structure obtained offers some promise that these materials can be “engineered” so as to modify their properties. In this study, we have used 3- and 4-pyridineboronic acid as “organic” synthons shown in Scheme 2 to attempt formation of supramolecular dications. The expected cyclic R2,2(8) boronic acid dimer is formed in 1−5 (not formed in 6 and 7). The -B(OH)2 groups adopt the most preferred syn-anti conformation in the salt of 1−5 and 7, while they adopt relatively uncommon syn-syn conformation in the salt of 6. We consider progress toward these objectives in the work reported here. (1) Control over composition of the final synthetic product, the crystal structure. Here the objective is to obtain the desired stoichiometry. These have proven very useful (but not 6 in which solvent is incorporated inadvertently). (2) Control over supramolecular synthon formation. Here we seek to form both the hydrogen bonds between the functional groups and the synthon in its entirety. The main tool in the present study has been the 3- and 4-pyridineboronic acid MCl2···HN hydrogen bonds in synthon A. This has proven robust in 1−4, 6, and 7 (but not in 5). NH···Cl2M hydrogenbonded planar E-type ribbons are formed, linked by hydrogen bonds involving the exocyclic hydrogens of the cyclic R2,2(8) boronic acid dimer in 1−4. Synthon of form I is formed in 5 with NH···Cl and OH···Cl hydrogen bonds. Both NH···Cl2M (synthons A) and B(OH)2···MCl2 (synthons B) interactions give rise to a synthon of form J in 6. The uncommon folded conformation of the NH···Cl2Pd synthon K is formed in 7. (3) Control over periodic motif formations. The Desiraju/ Wuest paradigm requires that linking the tectons using the supramolecular synthons will lead to formation of periodic motifs that then form the crystal structure. The excellent reproducibility, for example, of the 1D motif E in the structures of 1−4 is evidence of the merit of this view. 3- and 4-Pyridineboronic acids

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REFERENCES

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Chlorometallate-Pyridinium Boronic Acid Salts for Crystal Engineering

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