Cl2âCu Synthon? - American Chemical Society

How Robust Is the N-H‚‚‚Cl2-Cu Synthon? Crystal Structures of Some Perchlorocuprates D. Krishna Kumar, Amar Ballabh, D. Amilan Jose, Parthasarathi Dastidar,* and Amitava Das*

CRYSTAL GROWTH & DESIGN 2005 VOL. 5, NO. 2 651-660

Analytical Science Discipline, Central Salt & Marine Chemicals Research Institute, G. B. Marg, Bhavnagar - 364 002, Gujarat, India Received August 20, 2004;

Revised Manuscript Received September 23, 2004

ABSTRACT: A series of perchlorocuprate salts, namely, [4,4′-H2diazastilbene][CuCl4] 1, [H2-N-(4-pyridyl)isonicotinamide][CuCl4] 2, [H2-N-(3-pyridyl)isonicotinamide][CuCl4] 3, [H2-N-(4-pyridyl)nicotinamide][CuCl4] 4, [H2N,N′-bis(4-pyridyl)urea][CuCl4] 5, [H-isonicotinic acid]2[CuCl4]2H2O 6, [2-aminopyridinium]2[CuCl4] 7, and [3-aminopyridinium]2[CuCl4] 8 have been synthesized and analyzed by single-crystal X-ray diffraction. The results indicate that N-H‚‚‚Cl-Cu hydrogen-bonding interaction is important in supramolecular syntheses of these solids. However, occurrence of bifurcated hydrogen bonding of the type N-H‚‚‚Cl2Cu (synthon A) appears to be dependent on the topology of the cations, geometry of the anions, and other weak interactions such as C-H‚‚‚Cl-Cu. Salts of isomeric cations such as 2, 3 and 4, and 7 and 8 are crystallographically isostructural in their respective groups despite having different hydrogen-bonding site topologies. The hydrogen-bonding-capable backbones (amide and urea moieties) in 2, 3, 4, and 5 do not display the typical hydrogen-bonding network involving these moieties. Introduction Building solid-state materials to order is the main challenge in crystal engineering1 and supramolecular syntheses.2 The main impediments in crystal engineering are (i) the multiplicity of possible orientations of the molecules in crystals, (ii) the inaccuracies in estimating energies, and (iii) the entanglement of thermodynamic and kinetic contributions to crystal growth.3 Sorting out all these problems and predicting the supramolecular assembly (crystal structure) even for a small molecule with modest structural complexity is a daunting task. Out of many approaches to gain control over the arrangement of molecules in space, incorporation of a small number of functional groups that can interact intermolecularly through noncovalent interactions (supramolecular synthon) and therefore limit the possible arrangement of the molecules in the solid state with respect to one another has been considered one of the most rational approaches. Many of the efforts toward this goal have been concentrated on organic crystal engineering and it has been recognized that hydrogenbonding4 interactions, being reasonably strong and highly directional, can be used as structure-directing tools in generating many molecular solids with novel properties.5 Although the majority of these materials are based on nonionic hydrogen-bonding interactions, use of both directional hydrogen bonds and strong but less directional ionic interactions are also investigated.6 On the other hand, in inorganic crystal engineering, metal-ligand coordination remains the main strategy in generating various functional materials.7 However, only recently, deliberate syntheses of hydrogen-bondbased organic-inorganic hybrid materials have gained widespread interests.8 Rheingold, Crabtree and co-workers,9 and van Koten and co-workers10 have shown, in some isolated ex* To whom correspondence should be addressed. E-mail: parthod123@ rediffmail.com; [email protected].

amples, that metal bound chlorine can act as a hydrogenbond acceptor. Recently, in a seminal paper,11 Orpen and Brammer have concluded, based on Cambridge Structural Database analyses, that “metal-bound chlorine often accepts hydrogen bonds” and provided further support to the hydrogen-bond acceptor capability of metal-bound halide species noted anecdotally by Rheingold, Crabtree and van Koten. Since then, deliberate efforts have been made to construct intriguing supramolecular assemblies using metal-bound halide based hydrogen bonds. In these studies, protonated ring nitrogen N+-H (either aromatic or alicyclic) and perhalometalate (MX4; M ) transition metals, X ) halogen, mainly, Cl) have been used as hydrogen-bond donor and acceptor respectively.12

The supramolecular synthon observed in these studies is the bifurcated hydrogen-bonded building block (A), which leads to the formation of a ribbon motif B with linear cation such as 4,4′-bipyridinium cation, and so far the studies in this class of hybrid materials have been confined mainly to cations devoid of other potential hydrogen-bond donors or acceptors, with linear topology such as isomeric cations of bipyridines, 1,4-diazabicyclooctane, piperazine, etc. However, the question that remains is how robust is the synthon A and how tolerant is it of other functional groups? What if the synthon occurs as a result of a far more intricate and incomprehensible poise between intermolecular forces? Is this synthon reliable to control the supramolecular network in such organic-inorganic hybrid composites? To address these points, we have chosen a series of

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Crystal Growth & Design, Vol. 5, No. 2, 2005

Krishna Kumar et al.

Table 1. Crystallographic Parameters of 1-4 crystal data

1

2a

2b

3

4

empirical formula FW crystal size (mm) crystal system space group a/Å b/Å c/Å R/° β/° γ/° volume/Å-3 Z Dcalc F(000) µ MoKR (mm-1) temperature (K) observed reflections [I > 2σ(I)] parameters refined goodness of fit final R1 on observed data final wR2 on observed data

C12H12N2CuCl4 389.58 0.21 × 0.18 × 0.15 triclinic P1 h 7.038(2) 7.067(5) 8.246(3) 69.19(4) 73.90(3) 76.30(4) 363.9(3) 1 1.777 195 2.219 293(2) 917 88 1.038 0.0644 0.1490

C11H11N3OCuCl4 406.57 0.21 × 0.16 × 0.11 triclinic P1 h 7.341(2) 7.401(7) 14.620(7) 104.60(5) 98.24(3) 90.69(5) 759.8(8) 2 1.777 406 2.137 293(2) 1628 217 0.991 0.0532 0.1397




Chart 1

Results

dications (Chart 1) with various backbones and topology. Thus, C is a linear cation having unsaturated backbone, whereas D (linear), E, and F (both angular) are isomeric cations having amide backbone. G, on the other hand, is a linear cation with urea backbone. H is a linear supramolecular cation that can result from the supramolecular self-assembly of its molecular counterpart through a well-known supramolecular synthon, namely, a COOH hydrogen-bonded dimer. The cations are called “linear” or “angular” based on the relative position of the cationic centers. In so doing, we have essentially replaced the innocent covalent backbone of bipyridyl analogues by other functionalities, which are also capable of intermolecular interactions, to test the robustness of the synthon A and also to see their effect on overall supramolecular network in the resulted perchlorocuprate salts. Isomeric monocations I and J are also investigated to assess the role of free amino groups in hydrogen-bonding participation in the corresponding perchlorocuprate salts. The anion chosen in this study is [CuCl4]2- which is known to form variable geometry.13 It should be noted that perhalometalate salts have attracted attention as novel materials for various technological purposes, including the possibility of tunable magnetic, optical, and electronic properties.14,15

The perchlorocuprate salts, namely, 1-8, have been prepared by treating the corresponding organic moiety with either CuCl2‚2H2O or Cu(OAc)2‚H2O in MeOH/HCl at room temperature. Crystallization attempts of 2 result into two crystal forms, namely, 2a (yellow) and 2b (bluish-green) in two different methods (see experimental). Single-crystal structures of 1, 2a, 2b, and 3-8 have been determined and analyzed to assess the role of various backbones and hydrogen-bonding functionalities on the overall supramolecular architecture. The location and supramolecular nature of the cationic nitrogen centers are also investigated to evaluate the robustness of synthon A. The crystallographic parameters are listed in Tables 1 and 2. All the hydrogen atoms (except for -NH2 and -COOH groups, see experimental) were geometrically fixed at their corresponding normalized distances12e,16 (N-H ) 1.01 Å and C-H ) 1.08 Å) and the hydrogen-bonding parameters are given in Table 3. All the N-H‚‚‚Cl-Cu hydrogen-bond distances are found to be of normal dimensions.11 Crystal Structures. [4,4′-H2diazastilbene][CuCl4] (1). Both the organic and inorganic moieties are located on a center of symmetry. N-H...Cl2Cu (synthon A) is found to be responsible for the formation of hydrogenbonded ribbon motif B involving alternating cations and anions (Figure 1a). The square planar anion is slightly off the plane of the alternating cation-anion ribbon, which is reflected in the torsion angle of the atoms of concern (C(6)-N(1)‚‚‚H(1)-Cl(3) ) 18.2°). The ribbons are packed in the crystal structure in a parallel fashion (Figure 1b). While each ribbon is in close contact with two other neighboring ribbons through edge-to-edge interactions (C-H‚‚‚Cl ) 2.64 Å), its face-to-face neighbor makes significant π-π stacking interactions through the aromatic rings of the cationic part (shortest aromatic-aromatic contact 3.377 Å). [H2-N-(4-pyridyl)isonicotinamide][CuCl4] (2). Compound 2 crystallizes into two crystal forms, namely, 2a and 2b. Both the crystals belong to the same space group (P1 h ) with a slight difference in cell parameters (Table 1). The bipyridinium ions and the [CuCl4]2- are located in a general position in both the crystal struc-

How Robust Is the N-H‚‚‚Cl2-Cu Synthon?

Crystal Growth & Design, Vol. 5, No. 2, 2005 653

Table 2. Crystallographic Parameters for 5-8 crystal data

5

6

7

8

empirical formula FW crystal size (mm) crystal system space group a/Å b/Å c/Å R/° β/° γ/° volume/Å-3 Z Dcalc F(000) µ MoKR (mm-1) temperature (K) observed reflections [I > 2 σ(I)] parameters refined goodness of fit final R1 on observed data final wR2 on observed data

C11H12N4OCuCl4 421.59 0.22 × 0.17 × 0.10 monoclinic P21/c 7.734(5) 17.448(5) 11.609(3) 90.00 98.54(3) 90.00 1549.2(12) 4 1.808 844 2.101 293(2) 1673 237 1.017 0.0343 0.0867

C12H12 N2O4CuCl42H2O 489.61 0.23 × 0.19 × 0.15 triclinic P1 h 7.038(4) 8.510(5) 8.868(4) 86.17(5) 74.51(4) 65.69(4) 465.9(4) 1 1.745 247 1.776 293(2) 1094 144 1.087 0.0503 0.1352



tures. The anion displays a distorted tetrahedral geometry in both 2a and 2b with different interatomic angles. Thus, all four ∠Cl-Cu-Cl angles are ∼98.0° for 2a. However, for 2b, two ∠Cl-Cu-Cl angles are ∼98.0° and the other two angles are close to 94.0°. The cations in both the crystal forms are nonplanar and display a different twist of the amide backbone. Thus, the corresponding torsion angles involving the amide backbone in 2a are [C(8)-N(7)-C(4)-C(5) ) 9.2°; O(9)-C(8)C(10)-C(15) ) 36.1°]. The corresponding values for 2b are [C(8)-N(7)-C(4)-C(3) ) 13.3°; O(9)-C(8)-C(10)C(11)) 27.3°]. Therefore, the main differences between these two crystal forms seem to arise from the relative conformation of the cations and anions. Synthon A mediated alternating cation-anion ribbon motif B is also observed in both 2a and 2b. Interestingly, the amide proton is involved in N-H‚‚‚Cl-Cu hydrogen bonding with the neighboring polymeric chains to form thicker ribbon in both the crystal structures (Figure 2a,b). The hydrogen-bonding acceptor (oxygen) of the amide moiety does not appear to have any short contact in 2a, whereas significant C-H‚‚‚O interaction involving the amide oxygen in 2b is observed. The thicker ribbons are further packed in the crystal lattice (Figure 2c,d) through various C-H‚‚‚Cl interactions (Table 3) with the neighboring ribbons in a parallel fashion as also observed in case of 1.

Figure 1. (a) Ribbon motif B involving synthon A in 1; (b) parallel packing of the 1-D hydrogen-bonded ribbons in 1.

[H2-N-(3-pyridyl)isonicotinamide][CuCl4] (3). Nonplanar cation [C(2)-C(3)-N(7)-C(8) ) 11.34°; O(9)C(8)-C(10)-C(11) ) 34.94°] and distorted tetrahedral anion (∠Cl-Cu-Cl ) ∼98.0°) are present in the asymmetric unit in 3. While the hydrogen attached to ring nitrogen of isonicotinic acid moiety of the organic part displays bifurcated N-H‚‚‚Cl2Cu (synthon A), the other ring nitrogen proton (namely, 3-aminopyridine moiety) is involved in much simpler non-bifurcated hydrogenbonding interactions N-H‚‚‚Cl-Cu with the anion moieties resulting into a cyclic network of the ions. The amide hydrogen is also found to be involved in N-H‚‚‚Cl-Cu type hydrogen bonding with the adjacent anion moiety. These interactions result into a 1-D hydrogen-bonded ribbon network (Figure 3a). The ribbons are further packed in the crystal lattice in a parallel fashion (Figure 3b) and appear to have stabilized via several C-H‚‚‚Cl contacts (Table 3). [H2-N-(4-pyridyl)nicotinamide][CuCl4] (4). The anion CuCl42- displays a distorted tetrahedral geometry (∠Cl-Cu-Cl ) ∼96-98.0°). A significant twist around the amide backbone [C3-C4-N7-C8 ) 18.14°; N7C8-C10-C15 ) 33.98°] makes the cation nonplanar. Both the protons associated with nicotinic acid moiety

Figure 2. (a, b) Ribbon motif B displaying synthon A in 2a and 2b, respectively; (c, d) corresponding packing of the ribbons in 2a and 2b, respectively.

654



Table 3. Hydrogen-Bonding Parameters for 1-8 D-H‚‚‚A

D-H/Å

H‚‚‚A/Å

D‚‚‚A/Å

D-H‚‚‚A/°

symmetry operation for A

N(1)-H(1)‚‚‚Cl(1) N(1)-H(1)‚‚‚Cl(3) C(2)-H(2)‚‚‚Cl(1) C(3)-H(3)‚‚‚Cl(3)

1.01 1.01 1.08 1.08

2.35 2.38 2.64 2.64

1 3.190(5) 3.178(5) 3.644(6) 3.611(6)

139 135 154 149

x, 1+y, z x, 1+y, z -x, 2-y, -z x, 1+y, -1+z

N(1)-H(1)‚‚‚Cl(1) N(1)-H(1)‚‚‚Cl(3) N(7)-H(7)‚‚‚Cl(1) N(13)-H(13)‚‚‚Cl(2) N(13)-H(13)‚‚‚Cl(4) C(2)-H(2)‚‚‚Cl(1) C(2)-H(2)‚‚‚Cl(4) C(3)-H(3)‚‚‚Cl(1) C(6)-H(6)‚‚‚Cl(3) C(14)-H(14)‚‚‚Cl(4) C(15)-H(15)‚‚‚Cl(2)

1.01 1.01 1.01 1.01 1.01 1.08 1.08 1.08 1.08 1.08 1.08

3.11 2.66 2.32 2.28 2.67 2.82 2.53 2.75 2.24 2.73 2.67

2a 3.593(8) 3.473(8) 3.307(6) 3.185(7) 3.358(7) 3.553(7) 3.546(7) 3.627(7) 3.153(6) 3.392(8) 3.446(7)

111 138 165 148 126 125 156 139 141 120 129

2-x, 2-y, 1-z 2-x, 2-y, 1-z x, 1 + y, z 1-x, 3-y, 2-z 1-x, 3-y, 2-z 1-x, 2-y, 1-z 1-x, 2-y, 1-z x, 1+y, z 1+x, y, z 1-x, 3-y, 2-z 2-x, 3-y, 2-z

N(1)-H(1)‚‚‚Cl(2) N(1)-H(1)‚‚‚Cl(3) N(7)-H(7)‚‚‚Cl(2) N(13)-H(13)‚‚‚Cl(1) N(13)-H(13)‚‚‚Cl(4) C(2)-H(2)‚‚‚Cl(3) C(5)-H(5)‚‚‚Cl(2) C(6)-H(6)‚‚‚Cl(1) C(6)-H(6)‚‚‚Cl(1) C(11)-H(11)‚‚‚Cl(4) C(12)-H(12)‚‚‚Cl(1) C(12)-H(12)‚‚‚Cl(4) C(15)-H(15)‚‚‚Cl(3) C(14)-H(14)‚‚‚O(9)

1.01 1.01 1.01 1.01 1.01 1.08 1.08 1.08 1.08 1.08 1.08 1.08 1.08 1.08

3.10 2.19 2.31 2.64 2.27 2.72 2.79 2.52 2.75 2.59 2.83 2.92 2.81 2.59

2b 3.584(5) 3.116(5) 3.298(5) 3.382(5) 3.141(5) 3.504(6) 3.667(6) 3.494(6) 3.551(6) 3.385(6) 3.479(6) 3.534(6) 3.721(6) 3.534(7)

111 152 166 130 143 129 138 150 130 130 119 116 142 145

x, 1+y, z x, 1+y, z 1-x, 1-y, 1-z 1+x, y, -1+z 1+x, y, -1+z -x, 2-y, 1-z 1-x, 1-y, 1-z x, y, z x, y, z 1+x, 1+y, -1+z 1+x, y, -1+z 1+x, 1+y, -1+z -x, 1-y, 1-z x, -1+y, z

N(1)-H(1)‚‚‚Cl(2) N(7)-H(7)‚‚‚Cl(1) N(13)-H(13)‚‚‚Cl(3) N(13)-H(13)‚‚‚Cl(4) C(4)-H(4)‚‚‚Cl(1) C(4)-H(4)‚‚‚Cl(1) C(5)-H(5)‚‚‚Cl(4) C(6)-H(6)‚‚‚Cl(2) C(11)-H(11)‚‚‚Cl(3) C(12)-H(12)‚‚‚Cl(4)

1.01 1.01 1.01 1.01 1.08 1.08 1.08 1.08 1.08 1.08

2.31 2.30 2.30 2.62 2.89 2.72 2.53 2.62 2.69 2.69

3 3.167(7) 3.293(7) 3.203(7) 3.325(7) 3.590(7) 3.607(7) 3.549(8) 3.467(8) 3.457(8) 3.353(8)

142 166 147 126 123 139 156 135 128 120

x, -1+y, z 1+x, y, z 1-x, -y, 2-z 1-x, -y, 2-z 1-x, -y, 1-z 1+x, y, z 1-x, -y, 1-z 1-x, 1-y, 1-z 1-x, 1-y, 2-z 1-x, -y, 2-z

N(1)-H(1)‚‚‚Cl(4) N(7)-H(7)‚‚‚Cl(1) N(7)-H(7)‚‚‚Cl(4) N(14)-H(14)‚‚‚Cl(2) N(14)-H(14)‚‚‚Cl(3) C(2)-H(2)‚‚‚Cl(3) C(3)-H(3)‚‚‚Cl(1) C(5)-H(5)‚‚‚Cl(1) C(6)-H(6)‚‚‚Cl(3) C(11)-H(11)‚‚‚Cl(4) C(12)-H(12)‚‚‚Cl(1) C(12)-H(12)‚‚‚Cl(2) C(13)-H(13)‚‚‚Cl(1) C(15)-H(15)‚‚‚Cl(4)

1.01 1.01 1.01 1.01 1.01 1.01 1.08 1.08 1.08 1.08 1.08 1.08 1.08 1.08

2.14 2.23 2.97 2.31 3.12 2.77 2.56 2.81 2.76 2.59 2.84 2.42 2.75 2.53

4 3.128(4) 3.193(4) 3.582(4) 3.263(4) 3.811(4) 3.654(5) 3.472(4) 3.689(4) 3.652(5) 3.665(4) 3.532(4) 3.448(4) 3.496(4) 3.605(4)

167 158 120 157 127 139 141 138 140 172 122 159 126 172

1+x, 1+y, z 1-x, 1-y, 1-z 1-x, 1-y, 1-z x, 1+y, 1+z x, 1+y, 1+z 1+x, 1+y, z 2-x, 1-y, 1-z 1-x, 1-y, 1-z x, 1+y, z 1-x, -y, 1-z x, y, 1+z x, y, 1+z x, y, 1+z 1-x, 1-y, 1-z

N(1)-H(1)‚‚‚Cl(4) N(7)-H(7)‚‚‚Cl(2) N(10)-H(10)‚‚‚Cl(1) N(10)-H(10)‚‚‚Cl(2) N(14)-H(14)‚‚‚Cl(2) N(14)-H(14)‚‚‚Cl(3) C(2)-H(2)‚‚‚Cl(1) C(2)-H(2)‚‚‚Cl(4) C(3)-H(3)‚‚‚Cl(3) C(3)-H(3)‚‚‚Cl(4) C(6)-H(6)‚‚‚Cl(1) C(13)-H(13)‚‚‚Cl(2) C(15)-H(15)‚‚‚Cl(1) C(12)-H(12)‚‚‚O(9) C(13)-H(13)‚‚‚O(9)

1.01 1.01 1.01 1.01 1.01 1.01 1.08 1.08 1.08 1.08 1.08 1.08 1.08 1.08 1.08

2.15 2.29 2.27 2.85 2.47 2.40 2.53 2.79 2.89 2.90 2.75 2.81 2.82 2.83 2.43

5 3.146(4) 3.167(4) 3.195(4) 3.566(4) 3.244(4) 3.256(4) 3.447(4) 3.538(5) 3.778(5) 3.587(5) 3.538(6) 3.408(6) 3.571(5) 3.384(6) 3.213(6)

171 145 151 129 133 142 143 126 139 122 130 115 127 112 128

-1+x, -1+y, z -x, -1/2+y, 3/2-z -x, -1/2+y, 3/2-z -x, -1/2+y, 3/2-z x, y, z x, y, z -1+x, -1+y, z -1+x, 1/2-y, -1/2+z -1+x, 1/2-y, -1/2+z -1+x, 1/2-y, -1/2+z -1+x, 1/2-y, 1/2+z x, y, z 1-x, 1-y, 2-z x, 1/2-y, -1/2+z x, 1/2-y, -1/2+z



Table 3 (Continued) D-H‚‚‚A

D-H/Å

H‚‚‚A/Å

N(1)-H(1)‚‚‚Cl(1) N(1)-H(1)‚‚‚Cl(3) O(1W)-H(1OW)‚‚‚Cl(1) O(1W)-H(1OW)‚‚‚Cl(3) O(1W)-H(1OW)‚‚‚O(9) O(8)-H(8O4)‚‚‚O(1W) C(5)-H(5)‚‚‚Cl(1) C(6)-H(6)‚‚‚Cl(3) C(6)-H(6)‚‚‚Cl(3)

1.01 1.01 0.99 0.99 0.91 1.08 1.08 1.08 1.08

2.33 2.42 2.62 2.39 1.77 1.54 2.61 2.66 2.82

N(1)-H(1)‚‚‚Cl(2) N(1)-H(1)‚‚‚Cl(4) N(7)-H(7A)‚‚‚Cl(4) N(7)-H(7B)‚‚‚Cl(2) N(1′)-H(1′)‚‚‚Cl(3) N(7′)-H(7A′)‚‚‚Cl(1) N(7′)-H(7B′)‚‚‚Cl(4) C(4)-H(4)‚‚‚Cl(3) C(6)-H(6)‚‚‚Cl(2) C(3′)-H(3′)‚‚‚Cl(2) C(6′)-H(6′)‚‚‚Cl(1)

1.01 1.01 0.97(5) 0.98(4) 1.01 0.99(4) 1.00(5) 1.08 1.08 1.08 1.08

2.42 2.86 2.36(6) 2.35(4) 2.19 2.33(5) 2.34(4) 2.85 2.93 2.93 2.82

N(1)-H(1)‚‚‚Cl(1) N(1)-H(1)‚‚‚Cl(3) N(4)-H(4A)‚‚‚Cl(4) N(4)-H(4B)‚‚‚Cl(1) N(1′)-H(1′)‚‚‚Cl(4) N(4′)-H(4A′)‚‚‚Cl(4) N(4′)-H(4B′)‚‚‚Cl(2) C(2)-H(2)‚‚‚Cl(1) C(2)-H(2)‚‚‚Cl(4) C(6)-H(6)‚‚‚Cl(3) C(2′)-H(2′)‚‚‚Cl(1) C(5′)-H(5′)‚‚‚Cl(3) C(6′)-H(6′)‚‚‚Cl(2)

1.01 1.01 0.98(5) 1.00(3) 1.01 0.99(4) 0.99(4) 1.08 1.08 1.08 1.08 1.08 1.08

2.96 3.06 2.32(6) 2.36(4) 3.00 2.37(4) 2.29(4) 2.37 2.81 2.86 2.91 2.12 2.81

D‚‚‚A/Å

D-H‚‚‚A/°

6

symmetry operation for A

3.179(5) 3.205(5) 3.431(4) 3.224(4) 2.667(6) 2.616(6) 3.649(5) 3.644(6) 3.397(6)

141 134 139 142 171 178 162 151 113

-1+x, y, z -x, 1-y, -z x, y, z x, y, z 1-x, 1-y, 1-z 1+x, -1+y, z x, -1+y, z x, -1+y, z -x, 1-y, -z

3.230(5) 3.722(5) 3.289(5) 3.333(5) 3.174(5) 3.268(6) 3.334(6) 3.764(6) 3.479(6) 3.920(6) 3.631(6)

137 143 161(5) 174(5) 163 159(4) 173(5) 140 112 152 132

1+x, y, z 1+x, y, z 1+x, y, z 1+x, y, z -x, -y, -z -x, -y, -z x, y, z 1-x, 1-y, 1-z 1+x, y, z x, y, z -1-x, -1-y, -z

3.485(4) 3.757(4) 3.289(4) 3.344(4) 3.729(5) 3.330(4) 3.260(4) 3.241(3) 3.726(3) 3.757(4) 3.894(4) 3.167(3) 3.621(5)

113 127 168(4) 172(4) 130 163(4) 168(5) 137 142 141 152 163 132

x, y, z 1-x, 1-y, 1-z x, y, z x, 1+y, z -1+x, -1+y, z x, y, z 1-x, 1-y, -z x, y, z x, y, z 1-x, 2-y, 1-z x, y, z 1-x, 1-y, -z -x, -y, -z

7

8

and amide nitrogen display supramolecular synthon A with the adjacent anion moiety. The pyridinium proton of 4-aminopyridine moiety shows N-H‚‚‚Cl-Cu interactions. The supramolecular architecture in this hybrid may be best described as a 1-D zigzag ribbon arising from the hydrogen-bonded interactions between the cations and anions (Figure 4a). The zigzag ribbons further pack in a parallel fashion in the crystal structure (Figure 4b) via several C-H‚‚‚Cl interactions (Table 3). [H2-N,N′-bis(4-pyridyl)urea][CuCl4] (5). In this crystal structure, the anion moiety exists as a dimer wherein each metal center may be considered as having a slightly distorted square-pyramidal geometry displaying all ∠Cl-Cu-Cl angles of the equatorial plane close

to 90.0°. Each metal in the dimer is found to be coordinated with five Cl atoms with four short (ca. 2.30 Å) and one long (ca. 2.90 Å) Cu-Cl bonds. The molecular structure of the organic cation is slightly distorted (C(8)-N(10)-C(11)-C(12) ) 175.41; C(8)-N(7)-C(4)C(3) ) 179.3°). The ring nitrogen protons form two different types of hydrogen-bonding interactions with the dimeric anion; one is bifurcated (synthon A) and the other is simple N-H‚‚‚Cl-Cu type of interaction. These interactions result into a 1-D ribbon architecture (Figure 5a). Interestingly, each proton of the urea backbone is involved in an N-H‚‚‚Cl2-Cu type of bifurcated hydrogen bonding with an adjacent anion dimer, and this

Figure 3. (a) 1-D ribbon in 3 displaying cyclic network and synthon A; (b) parallel self-assembly of the 1-D ribbons in 3.

Figure 4. (a) 1-D zigzag ribbon present in 4; (b) parallel packing of the ribbons in 4.

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Figure 5. (a) 1-D ribbon in 5; (b) angular arrangements of 1-D ribbons in 5.

Figure 6. (a) Water-mediated 2-D corrugated sheet in 6; (b) parallel packing of the 2-D sheets in 6.

interaction allows each ribbon to arrange in an angular fashion (Figure 5b). However, the oxygen atom of the urea moiety is involved in significant C-H‚‚‚O contacts. The packing of these hydrogen-bonded ribbons in the crystal structure is found be 3-D further stabilized by several C-H‚‚‚Cl types of interactions (Table 3). [H-isonicotinic Acid]2[CuCl4]2H2O (6). The coordination sphere of the metal center, which is sitting on a center of symmetry, is square planar. The protonated ring nitrogen of isonicotinic acid is involved in N-H‚‚‚Cl2-Cu bifurcated (synthon A) hydrogen bonding with the anion moiety. The COOH group of the isonicotinic acid moiety does not form the typical R22(8) cyclic hydrogen-bonded dimer. Instead, water molecules are incorporated in the network in such a way that two water molecules form a bridge through O-H‚‚‚O hydrogen bonding with COOH groups of two adjacent isonicotinic acid moieties resulting in the ribbon motif B. Moreover, the solvate water molecules also play a significant role in stabilizing the crystal structure further by providing hydrogen-bonding interactions with the Cl atoms of the anion moieties of adjacent ribbon network thereby generating a corrugated 2-D sheet (Figure 6a). The 2-D sheets are packed in a parallel fashion (Figure 6b) involving several C-H‚‚‚Cl interactions (Table 3). It is worth mentioning here that 6 displays an exactly identical supramolecular network


Figure 7. (a) 1-D tape architecture in 7 displaying various hydrogen- bonding interactions including synthon A; (b) packing of the 1-D tapes in 7.

Figure 8. (a) [CuCl4]2- anion surrounded by six cations via N-H‚‚‚Cl-Cu hydrogen bonding in 8; (b) packing of the ions in 8.

that is observed in the corresponding chloroplatinate salt reported by Orpen et al.12a [2-Aminopyridinium]2[CuCl4] (7). The anionic part is in a distorted tetrahedral (∠Cl-Cu-Cl ) ∼99.00) geometry. The ring nitrogen proton and one of the amine protons both show N-H‚‚‚Cl2-Cu (synthon A) hydrogenbonded interactions. The other amine proton is also involved in N-H‚‚‚Cl-Cu interaction probably because of its proximity to the anion. Each anion is found to hold four cations via these interactions resulting in a 1-D tape architecture (Figure 7a). The 1-D tapes are packed in the crystal structure in a parallel fashion (Figure 7b) involving significant π-π stacking interactions (shortest aromatic-aromatic contact ) 3.380 Å) and several C-H‚‚‚Cl type hydrogen-bonding interactions (Table 3). [3-Aminopyridinium]2[CuCl4] (8). The anion moiety displays a distorted tetrahedral geometry (∠Cl-CuCl ) ∼99.0°). Each anion is involved in N-H‚‚‚Cl-Cu type hydrogen-bonded contacts with six neighboring cations (Figure 8a). The supramolecular network in this crystal structure can be best described as a 3-D network (Figure 8b) involving N-H‚‚‚Cl-Cu, C-H‚‚‚Cl, and π-π stacking interactions (shortest aromatic-aromatic contact ) 3.367 Å). Interestingly, in this case, N-H‚‚‚Cl2Cu (synthon A) is not observed.



Scheme 1. Typical 1-D Hydrogen-Bonded Network in (A) Urea17 and (B) Secondary Amide18

Figure 9. Space-filling model of synthon A observed in the crystal structures reported in this work.

Discussion It is interesting to note that the crystal structures described here belong to the same space group (P1 h) except for 5 (P21/c). The structures fall into three categories based on their local supramolecular network: (1) salts with linear cations, i.e., 1, 2a, 2b, 5, and 6, (2) salts with angular cations i.e., 3 and 4, and (3) salts with isomeric monocations, i.e., 7 and 8. In category (1), linear ribbon motif B is formed through N-H‚‚‚Cl2-Cu (synthon A) except in 5 wherein either end of the cationic centers are assembled with the anions via synthon A and more simpler N-H‚‚‚ClCu interactions. The different backbones of the cations (unsaturated moiety, amide, urea, and supramolecular hydrogen-bonded dimer) and various anion geometries (square planar, distorted tetrahedron, and dimeric distorted square pyramid) do not seem to have much effect on the local supramolecular network. The assemblies of the cations and anions seem to have been dictated by the electrostatic interactions between the protonated cationic center (ring nitrogen) and halogen coordinated metal center. It is interesting to note that in none of these structures do the hydrogen-bonding capable backbones display their typical hydrogen-bonding network. Thus, the amide backbone in 2a and 2b and urea backbone in 5 do not show a typical 1-D hydrogen-bonding network17 (Scheme 1). Instead, the N-H protons of amide and urea moieties are involved in an N-H‚‚‚Cl-Cu type of hydrogen bonding with the adjacent anion. This could be because of the fact that the acidic condition of the crystallization might prevent the hydrogen-bond acceptor atom oxygen (in both amide and urea moieties) to participate in its usual hydrogenbonding interactions due to partial protonation during crystallization. In category (2), both synthon A and N-H‚‚‚Cl-Cu interactions involving the cationic center are observed. In case of 3, a cyclic network of cation and anion is formed via these interactions. The cyclic assemblies of cation and anion propagate in one dimension involving N-H‚‚‚Cl-Cu interactions between amide protons and anions resulting into a 1-D tape architecture. On the other hand, in case of 4, a zigzag 1-D network is formed between alternating cations and anions via both synthon A and N-H‚‚‚Cl-Cu interactions, and two such 1-D zigzag chain packed in an antiparallel fashion via

N-H‚‚‚Cl-Cu interactions involving the amide protons. It is worth noting here that in this case also the amide backbone does not show the typical 1-D hydrogenbonded network involving a secondary amide18 (Scheme 1) presumably due to partial protonation of the acceptor oxygen atom in the acidic conditions of crystallization. However, it is interesting to note that the angular orientation of the cationic centers in these salts has a direct influence on the local supramolecular architecture resulting in different assemblies (not ribbon motif B) compared to that observed in salts with linear cationic topology (category 1). In category (3), both the crystal structures of 7 and 8 are isostructural having almost identical unit cell and space group (Table 2), indicating that both have essentially same crystal structures (see packing, Figures 7b and 8b). In these structures, N-H‚‚‚Cl-Cu interactions are observed. It is interesting to note that cationic center in 7 shows synthon A, whereas 8 displays only N-H‚‚‚Cl-Cu interactions. Considering the fact that shape fit and electrostatic interactions between the ions around the synthon A are important in providing the access of the crystal structures observed in this work, it is worthwhile to examine the occurrence, various interactions, and shape fit of synthon A observed in these structures. It should be noted here that either end of the linear bipyridinium cations (1, 2a, 2b, and 6) display synthon A except in 5 wherein only one end adopts synthon A and the other end is involved in a much simpler N-H‚‚‚Cl-Cu interaction with the dimeric distorted square pyramidal anion. On the other hand, only one end of the angular bipyridinium cations (3 and 4) shows synthon A. Among the isomeric monocations (7 and 8), only in 7 is synthon A observed. Figure 9 displays the space filling diagrams of synthon A observed in this work. It is clear that in most of the cases, synthon A displays a good shape fit between the pyridinium cation and perchlorocuprate anion except in case of 4 wherein one of the H‚‚‚Cl nonbonded distances of synthon A falls in the “long” range of interacting distances (Table 3).11 It is also notable that in the cases of 2a and 2b, the relative orientations of the cationic and anionic moieties are almost perpendicular to each other displaying another alternative shape fit of the ions. It should be noted that the overall supramolecular architecture in a given crystalline solid arises from a balance of intermolecular forces. Although stronger forces such as electrostatic interactions, strong hydrogen

658


bonding, etc. may dominate the overall supramolecular structure, the weak forces such as donor-acceptor interactions, dispersion forces, etc. are also important and may be a structure-determining factor if the number of such interactions are plenty. Therefore, it is important to consider weak forces such as C-H‚‚‚Cl interactions19 in these solids. Data listed in Table 3 indicate that C-H‚‚‚Cl interactions must contribute significantly to the overall supramolecular network observed in these solids. Thus, the crystal lattice is further stabilized by multiple C-H‚‚‚Cl interactions in all the solids. It should also be mentioned here that the hydrogen-bonding acceptor capability of the amide/urea oxygen atom present in 2a, 3, and 4 is not satisfied by weak C-H‚‚‚O interactions, whereas the oxygen atom of these moieties is found to be involved in weak C-H‚‚‚O interactions in 2b and 5. It is therefore clear from the results that although metal bound chlorine atoms do recognize pyridinium cations through N-H‚‚‚Cl-Cu hydrogen-bonding interactions, the overall supramolecular architectures are probably governed by stronger, less directional electrostatic interactions between the cationic and anionic centers, weak interactions such as C-H‚‚‚Cl-Cu and the Coulombic elements of the lattice energy. It may be noted here that recently Valde´s-Martine´z et al. have studied perhalometalate (Cu and Zn) salts based on sterically hindered nonisomeric cations to demonstrate the importance of N-H‚‚‚Cl-M hydrogen-bonding interactions as structure-directing tools.20 It should be noted that the anion in these structures reported here adopts various types of metal coordination geometry, e.g., square planar in 1 and 6, distorted tetrahedral in 2a, 2b, 3, 4, 7, and 8, dimeric square pyramidal in 5. It is known that the geometry adopted by Cu2+ is quite flexible,13 and therefore the coordination geometry of Cu2+ can be influenced by less dominant interactions such as hydrogen bonding. It appears that the type of cation and its hydrogen-bonding capability must have an influence on the anion geometry. The fact that [CuCl4]2- anion adopts a square planar geometry in 1 and 6 is probably due to the cation’s structural resemblance to 4,4′-H2bipy or supramolecularly linked protonated isonicotinic acid cation for which coplanar ribbon motif B containing square planar PtCl42- is obtained in the corresponding perhalometalate salts.12a,12d Conclusions Single-crystal structures of a series of perchlorocuprate based on various pyridinium cations indicate that the occurrence of the bifurcated hydrogen-bonding interaction N-H‚‚‚Cl2Cu (synthon A) appears to be dependent on the topology of the cations, geometry of the anions, and other weak interactions such as C-H‚‚‚Cl. The hydrogen-bonding-capable backbone (amide and urea moieties) of the cations does not display the typical self-assembly mode. Instead, the protons associated with amide or urea nitrogen are involved in N-H‚‚‚Cl-Cu interactions with the neighboring anions presumably because of the partial protonation of the acceptor oxygen atom under acidic crystallization conditions. Presence of numerous weak interactions such as C-H‚‚‚Cl in all these solids suggests that these weak


interactions play a significant role in stabilizing the network. Flexibility of the coordination geometry of Cu2+ introduces more complexity in the resultant supramolecular architecture. Other forces such as electrostatic interactions, weak interactions (C-H‚‚‚Cl), and dispersion forces are also important and are probably responsible for the occasional nonoccurrence and distortion of synthon A, and play a significant role in shaping the resultant supramolecular assemblies of these cations and anions. However, occurrence of linear ribbon motif B in the salts of linear cations (1, 2a, 2b, 5, and 6) and zigzag hydrogen-bonded ribbon in salts of angular cations (3 and 4) involving N-H‚‚‚Cl-Cu hydrogenbonded interactions (either synthon A and/or simpler N-H‚‚‚Cl-Cu) clearly indicate that these interactions can be considered as one of the important structuredirecting tools in the supramolecular syntheses of these organic-inorganic hybrid materials. Experimental Section Syntheses. The pyridines in 1, 6, 7, and 8 are commercially available (Aldrich) and used without further purification. N-(4pyridyl)isonicotinamide, N-(3-pyridyl)isonicotinamide, and N-(4pyridyl)nicotinamide, the pyridines used in 2, 3, and 4, respectively, are synthesized following a reported procedure.21a N,N′-bis(4-pyridyl)urea used in 5 is also synthesized following a reported procedure.21b [4,4′-H2diazastilbene][CuCl4] (1). Cu(II) acetate‚H2O (1 g, 5.5 mmol) is dissolved in water (10 mL) by adding concentrated HCl (3 mL). To this pale-yellow solution, a solution of 4,4′-diazastilbene (1.089 mg, 5.5 mmol) in water (10 mL) and concentrated HCl (2 mL) is added. The solution is evaporated to a volume of ∼10 mL and kept for crystallization at room temperature. After few days, blue-colored X-ray quality crystals are obtained. The crystals are filtered and washed with ice cold water and dried (1.72 g, 4.39 mmol, 80% yield). Elemental analysis: C12H12N2CuCl4 Calc (%). C, 36.99; H, 3.10; N, 7.19; Found. C, 36.59; H, 2.63; N, 7.01. [H2-N-(4-pyridyl)isonicotinamide][CuCl4] (2). 2a (Yellow Form). Cu(II) acetate‚H2O (19.8 mg, 0.1 mmol) is dissolved in water (15 mL) by heating at 60 °C for 10 min. A solution of N-(4-pyridly)isonicotinamide (19.9 mg, 0.1 mmol) in methanol (10 mL) is layered over the copper-acetate solution. After 2 days a blue precipitate is obtained, which is dissolved by the addition of concentrated HCl. By adjusting the pH ) 4.0 with 10% sodium bicarbonate solution, a clear yellow colored solution is obtained, which is kept at room temperature, for crystallization. After a period of three weeks, X-ray quality yellow-colored crystals (only a few) are obtained. Elemental analysis: C11H11N3OCuCl4 Calc (%). C, 32.49; H, 2.73; N, 10.34; Found C, 32.20; H, 2.73; N, 10.14. 2b (Bluish-Green Form). A solution of Cu(II) acetate‚H2O (500 mg, 2.52 mmol) in concentrated HCl (5 mL) and water (10 mL) was taken in a 50 mL beaker. A solution of (4-pyridyl)isonicotinamide (502 mg, 2.52 mmol) in methanol (10 mL) was layered carefully over the above solution and allowed to evaporate at room temperature. Bluish-green crystals are collected by filtration and dried at pump (590 mg, 1.45 mmol, 57.8% yield). Elemental Analysis: C11H11Cl4CuN3O Calc (%). C, 32.49; H, 2.73; N, 10.34; Found C 32.20, H 2.33, N 10.14. [H2-N-(3-pyridyl)isonicotinamide][CuCl4] (3). A solution of N-(3-pyridyl)isonicotinamide (502 mg, 2.52 mmol) in methanol (10 mL) is carefully layered over a solution of Cu(II) acetate‚H2O (500 mg, 2.52 mmol) in concentrated HCl (5 mL) and water (10 mL) taken in a 50 mL beaker and evaporated at room temperature. Yellow-colored crystals thus obtained are filtered and dried at the pump (690 mg, 1.70 mmol, yield 67.64%). Elemental Analysis: C11H11Cl4CuN3O Calc (%). C, 32.49; H, 2.73; N, 10.34; Found C, 32.41; H, 2.19; H, 10.05.

How Robust Is the N-H‚‚‚Cl2-Cu Synthon? [H2-N-(4-pyridyl)nicotinamide][CuCl4] (4). A solution of N-(4-pyridyl)nicotinamide (500 mg, 2.52 mmol) in methanol (10 mL) is layered carefully over a solution of Cu(II) acetate‚ H2O (500 mg, 2.52 mmol) in concentrated HCl (5 mL) and water (10 mL) taken in a 50 mL beaker and left for evaporation at room temperature. Yellow crystals thus formed are filtered and dried at the pump (773 mg, 1.903 mmol, yield 75.78%). Elemental Analysis: C11H11Cl4CuN3O Calc (%). C, 32.49; H, 2.73; N, 10.34; Found C, 31.22; H, 2.55; N, 9.66. [H2-N,N′-bis(4-pyridyl)urea][CuCl4] (5). A solution of N,N′-bis(4-pyridyl)urea (500 mg, 2.34 mmol) in methanol (10 mL) is layered carefully over a solution of Cu(II) acetate‚H2O (464 mg, 2.34 mmol) in concentrated HCl (2 mL) and water (10 mL) taken in a 50 mL beaker After evaporation of the sample at room temperature, good quality yellow crystals are harvested (710 mg, 1.68 mmol, yield ) 72.08%). Elemental Analysis: C11H12Cl4CuN4O Calc (%). C, 31.34; H, 2.87; N, 13.29; Found C, 30.79; H, 2.46; N, 12.77. [H-isonicotinic Acid]2[CuCl4]2H2O (6). Isonicotinic acid (1.24 g, 10 mmol) is dissolved in water (20 mL) by adding concentrated HCl (3 mL). The solution is added to a solution of Cu(II) acetate‚H2O (1 g, 5 mmol) in water (20 mL) under stirring. Evaporation of this solution at room temperature result in blue crystals after a period of three weeks, which are filtered and washed with methanol/water (7:3 v/v) and dried under pump (1.65 g, 3.5 mmol, yield 70.36%). Elemental Analysis: C12H16Cl4CuN2O6 Calc (%). C, 29.44; H, 3.29; N, 5.72; Found C, 29.96; H, 2.90; N, 5.39. [2-Aminopyridinium]2[CuCl4] (7). Cu(II) acetate‚2H2O (198 mg, 1 mmol) was dissolved in water (10 mL) and concentrated HCl (4 mL). To this solution, 2-aminopyridine (188 mg, 2 mmol) in methanol (15 mL) is added and kept for crystallization at room temperature. X-ray quality yellowcolored crystals obtained after a period of one month are filtered, washed with acetone, and dried at the pump (173 mg, 0.438 mmol, yield 43.79%). Elemental Analysis: C10H14Cl4CuN4 Calc (%). C, 30.36; H, 3.57; N, 14.16; Found C, 29.85; H, 3.21; N, 13.85. [3-Aminopyridinium]2[CuCl4] (8). Cu(II) acetate‚2H2O (198 mg, 1 mmol) is dissolved in water (10 mL) and HCl (4 mL). To this solution, 3-aminopyridine (188 mg 2 mmol) in methanol (15 mL) is added and kept for crystallization at room temperature. X-ray quality yellow colored crystals are obtained after a period of 3 weeks (150 mg, 0.405 mmol, yield 40.5%). Elemental Analysis: C10H14Cl4CuN4 Cal (%). C, 30.36; H, 3.57; N, 14.16. Found; C, 30.84; H, 2.33; N, 13.11. Single-Crystal X-ray Diffraction. Data for 1, 2a, 3, 5, 6, 7 are collected using MoKR (λ ) 0.7107 Å) radiation on a CAD-4 diffractometer. Whereas the diffraction data for 2b, 4, and 8 are collected using MoKR (λ ) 0.7107 Å) radiation on a SMART APEX diffractometer equipped with CCD area detector. Data collection, data reduction, structure solution/refinement are carried out using the software package of SMART APEX for 2b, 4, and 8, whereas the corresponding calculations are performed for the data collected on CAD-4 using CAD4PC,22 NRCVAX,23 SHELX97.24 Graphics are generated using PLATON25 and MERCURY 1.1.1.26 All structures are solved by direct methods and refined in a routine manner. In all cases, non-hydrogen atoms are treated anisotropically. Hydrogen atoms are fixed at their geometrically idealized position at a normalized distance (N-H ) 1.01 Å; C-H ) 1.08 Å, see also text) and refined with 1.5 times of the equivalent isotropic thermal parameters of the nonhydrogen atoms to which these hydrogen atoms are attached. This procedure is not followed for the hydrogen atoms attached to -NH2 and -COOH groups. In case of 6, the hydrogen atoms attached to the -COOH group and solvent water molecule are located on a difference Fourier map and in the subsequent refinement, the coordinates and the thermal parameters for these hydrogen atoms (fixed at 1.5 times that of the nonhydrogen atoms to which they are attached to) are kept fixed. On the other hand, the hydrogen attached to the amino groups of 7 and 8 are located on a difference Fourier map and in the subsequent refinement, the N-H distance and thermal pa-

Crystal Growth & Design, Vol. 5, No. 2, 2005 659 rameters are kept fixed at 1.01 Å and 1.5 times of the thermal parameters of the corresponding non-hydrogen atoms, respectively.

Acknowledgment. Department of Science & Technology, New Delhi, is thankfully acknowledged for financial support. We thank Dr. P. K. Ghosh for his support. Supporting Information Available: FT-IR data all the crystals (except 2a), ORTEP diagrams of 1-8 (PDF). This material is available free of charge via the Internet at http://pubs.acs.org.

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