Hydrogen bonded perrhenate-azoimidazoles

Crystal Engineering 5 (2002) 95–104 www.elsevier.com/locate/cryseng

Hydrogen bonded perrhenate-azoimidazoles U.S. Ray a, G. Mostafa b, T.H. Lu b, C. Sinha a,∗ a b

Department of Chemistry, The University of Burdwan, Burdwan 713104, India Department of Physics, National Tsing Hua University, Hsinchu 300, Taiwan

Received 10 June 2002; received in revised form 18 September 2002; accepted 22 September 2002

Abstract Reaction in aqueous medium of KReO4 in methanolic solution of RaaiCH2Ph (1-benzyl-2(arylazo)imidazole) (1) in the presence of perchloric acid has isolated brown products of {[1benzyl-2-(arylazo)imidazolium][ReO⫺ 4 ]앫H2O}n, 2. The structural confirmation has been carried out by the single crystal X-ray diffraction study of {[1-benzyl-2(phenylazo)imidazolium][ReO⫺ 4 ]앫H2O}, 2a. The molecules are polymerized via hydrogen bonding and form cross-linked network.  2002 Elsevier Science Ltd. All rights reserved. Keywords: Imidazolyl azo; Perrehenate; Hydrogen bond; π–π stacking; Supramolecular network

1. Introduction The chemistry of materials is a frontier field of research. Designing, synthesizing and exploiting materials with predefined properties become areas of great interest. Emphasis has laid on the materials of optoelectronics, conductivity, superconductivity, charge transfer, magnetism and nano-materials. No matter whether covalent and/or noncovalent interaction, the construction of materials is based on the utilization of crystal-directed synthetic strategies and the field is known as crystal engineering [1–4]. The rational design and preparation of new materials for specific applications is at an evolutionary stage with the current focus mainly on understanding the factors that determine crystal packing. During the last few years, several types of forces, such as coordination bonding, versatile hydrogen bonding, π–π stacking

∗

Corresponding author. Tel.: +91-342-557683; fax: +91-342-564452. E-mail address: [email protected] (C. Sinha).

1463-0184/02/$ - see front matter  2002 Elsevier Science Ltd. All rights reserved. PII: S 1 4 6 3 - 0 1 8 4 ( 0 2 ) 0 0 0 1 3 - 8

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and electrostatic interactions have been recognized in this area in constructing extended networks. Much of the current literature has concentrated on a metal assisted self-assembly process where ligands are tailored for the recognition of the intrinsic stereochemical properties of a particular metal ion [5]. In contrast, there have been relatively few reports in dealing with the anion directed self-assembly process [2] despite the methodology having considerable current interest in the development of molecular and supramolecular systems. These systems utilize hydrogen bonding and electrostatic interactions to bind anions. The real challenge in this field is the design of molecules to have a number of significant basic centers. In this field the heterocyclic molecules are useful and a protonated compound can act as a hydrogen bond donor. Hydrogen bonding interaction of oxoanions has been employed to construct crystal engineering [6,7]. In the field of organic polycarboxylic acids, hydrogen bonded 2D networks are well established [3–8]. One of the important applications of hydrogen bonded receptors is the binding of anionic and neutral guest molecules during their extractions/purification/detection techniques [9]. One such application is the detec3⫺ ⫺ tion of anionic pollutants NO⫺ 3 , PO4 , radioactive TcO4 (produced in the nuclear ⫺ fuel cycle), ReO4 that have been recently recognized [10]. The azole-based hydrogen ion receptor has been shown to be an effective and selective binding agent to oxoanions [10]. We have a tradition of designing heterocyclic azo-compounds and to study their coordination chemistry [11–14]. Arylazoimidazoles can easily be protonated at imidazole-N center and may act as an anion receptor. This has prompted us to undertake a programme of building up hydrogen bonded crystal engineering of oxoanions with arylazoimidazolium ions. In this work we wish to report on the crystal engineering of ReO⫺ 4 with protonated 1-benzyl-2-(arylazo)imidazoles via strong [N–H…O(Re)] and weak [C–H…O(Re), C–H…π(benzyl)] hydrogen bonds and π–π stacking.

2. Experimental Imidazole (Loba-Chemie Indo-Austranal Co., India), Aniline, benzyl chloride (PhCH2Cl) (Merck) and KReO4 (Aldrich) and HClO4 (Sisco Research Lab, India) were reagent grade. 2.1. 2-(Phenylazo)imidazole (PaiH) To an aqueous solution of imidazole (3.4 g, 53 mmol) and Na2CO3 (7.0 g, 66 mmol) at 0 to ⫺5 °C, a diazotized solution of aniline (53 mmol) (prepared by adding a NaNO2 (3.7 g, 53 mmol) solution into a 1 M HCl (50 ml) suspension of aniline at 0 to –5 °C and filtered) was added drop wise with continuous stirring. The temperature was controlled at ice cold conditions. The orange compound thus precipitated was filtered, washed with cold water and extracted with 2N HCl (4×15 ml). The solution was neutralized with Na2CO3 and the pH regulated to 7. The precipitate

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was filtered, washed and dried. Yield: 86%. 2-(p-Tolylazo)imidazole, TaiH is also prepared following an identical procedure in the yield of 80%. 2.2. 1-Benzyl-2-(phenylazo)imidazole (PaiCH2Ph), 1a To a dry THF solution (30 ml) of 2-(phenylazo)imidazole (PaiH) (2.0 g, 11.6 mmol), NaH (50% paraffin) (0.8 g) was added in small portions and stirred at cold conditions for 1 h. Benzyl chloride (1.47 g, 11.62 mmol) was added slowly for a period of 1 h and then refluxed over a steam bath for an additional 3 h. The solution was filtered, evaporated, extracted with CHCl3 solution (3×15 ml), washed with 10% NaOH solution and finally with distilled water (3×20 ml). It was chromatographed over silica gel prepared in benzene and the desired compound was eluted by CH3CN– C6H6 (1:11 v/v). Orange crystalline needles were separated on slow evaporation. Yield: 44%. (Found: C, 73.1; H, 5.0; N, 21.5. [C16H14N4] requires C, 73.3; H, 5.3; N, 21.4%); FTIR (KBr) 1410 m, 1590 s, 1495 s, 1480 m, 1365 s, 1295 b,m, 1200 vs. δH (500 MHz; CDCl3) 7.13 d (4 H), 7.20 d (5 H), 7.90 d (7, 11H), 7.41 (8, 10 H), 7.45 (9 H). 2.3. 1-Benzyl-2-(p-tolylazo)imidazole (TaiCH2Ph), 1b To a dry THF solution (30 ml) of 2-(p-tolylazo)imidazole (TaiH) (2.16 g, 11.6 mmol) NaH (50% paraffin) (0.8 g) was added in small portions and stirred at cold conditions for 1 h. Benzyl chloride (1.47 g, 11.62 mmol) was added slowly for a period of 1 h and then refluxed over a steam bath for an additional 3 h. Extraction procedure and purification is the same as before. Yield: 55%. (Found: C, 73.7; H, 5.9; N, 20.4. [C17H16N4] requires C, 73.9; H, 5.8; N, 20.3%); FTIR (KBr) 1405 m, 1595 s, 1490 s, 1480 m, 1365 s, 1295 b, m, 1195 vs. δH (500 MHz; CDCl3) 7.12 d (4 H), 7.18 d (5H), 7.88 d (7, 11 H), 7.00 (8, 10 H). + 2.4. {[1-Benzyl-2-(phenylazo)imidazolium][ReO⫺ 4 ]앫H2O}, [PaiCH2PhH ] ⫺ [ReO4 ]앫H2O, 2a

An aqueous solution of KReO4 (0.10 g, 0.35 mmol) is slowly added into warm methanolic solution of PaiBz in the presence of HClO4 (0.1 M, three drops). Brown solution was left in air for a week and brown needle shaped crystals were deposited on the wall of beaker. The yield was 0.101 g (60%). (Found: C, 36.3; H, 3.2; N, 10.4. [C16H15N4O4ReH2O] requires C, 36.1; H, 3.2; N, 10.5%); FTIR (KBr) 3450 b, 3360 m, 1587 s, 1400 m, 925 b, s (cm⫺1). δH (500 MHz; CD3CN) 7.93 d (4 H), 7.95 d (5 H), 7.98 d (7,11 H), 7.49 (8, 10 H), 7.51 (9 H). 2.5. {[1-Benzyl-2-(p-tolylazo)imidazolium][ReO⫺ 4 ]앫H2O}, ]앫H O, 2b [TaiCH2PhH+][ReO⫺ 2 4 An aqueous solution of KReO4 (0.10 g, 0.35 mmol) is slowly added into warm methanolic solution of TaiBz in the presence of HClO4 (0.1 M, three drops). Brown

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crystalline products are obtained. The yield was 0.101 g (60%). (Found: C, 36.5; H, 3.6; N, 10.4. [C16H15N4O4ReH2O] requires C, 37.4; H, 3.5; N, 10.3%); FTIR (KBr) 3450 b, 3358 m, 1589 s, 1402 m, 920 b, s (cm-1). δH (500 MHz; CD3CN) 7.92 d (4 H), 8.02 d (5 H), 7.97 d (7,11 H), 7.10 (8, 10 H), 7.51 (9 H). 2.6. Structure determinations A crystal of 2a suitable for X-ray analysis was mounted on the Siemens SMART CCD diffractometer equipped with graphite monochromator and Mo Kα radiation ( ˚ ). Data were collected at 295 K. The crystal size was 0.48×0.20×0.08 l ⫽ 0.71073 A mm3. Unit cell parameters were determined from least-squares refinement of setting angles of 2692 reflections with 2q ranges 4–56°. A summary of the crystallographic data and structure refinement parameters is given in Table 1. Of 11,187 collected reflections 4255 unique reflections were recorded using the ω-scan technique. Data were corrected for Lorentz polarization effects and for linear decay. Semi-empirical absorption correction based on ψ-scans was applied. The structure was solved by heavy atom methods using SHELXS-97 and successive difference Fourier syntheses. All non-hydrogen atoms were refined anisotropically. The hydrogen atoms were fixed geometrically and refined using riding model. In the final difference Fourier map the Table 1 Summarized crystallographic data for [PaiCH2PhH+][ReO⫺ 4 ]앫H2O (2a) Crystal parameters Chemical formula Formula weight Crystal system Space group ˚ a/A ˚ B/A ˚ C/A a/° b/° g/° ˚3 V/A Z Dcalc/[g/cm3] T (K) ˚] Radiation [A Reflections collected Independent reflections/Rint Observed data [I⬎2.0s(I)] Nref/Npar R/wR2/S w ⫽ 1 / [s 2(Fo2) ⫹ (0.0795P)2 ⫹ 7.1630P] where P ⫽ (Fo2 ⫹ 2Fc2)/ 3 ˚ ⫺3 Largest difference peak and hole/e A

C16 H15 N4, O4 Re, H2 O 531.55 Monoclinic P21/C 7.2235(12) 23.424(4) 11.1928(18) 90 90.976(3) 90 1893.6(5) 4 1.865 295 0.71073 11,187 4255/0.055 2692 4255/235 0.0584/0.1752/1.05

2.09/-2.20

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˚ ⫺3 those are quite high. All residual maxima and minima were 2.09 and ⫺2.20 e A calculations were carried out using SHELXL-97.

3. Results and discussion 3.1. Synthesis 2-(Arylazo)imidazole (RaiH) is synthesized by coupling the phenyldiazonium ion with imidazole at pH 7. 1-Benzyl-2-(phenylazo)imidazole (PaiCH2Ph) 1a is synthesized by the benzylation of PaiH with PhCH2Cl in dry THF in presence of NaH. The active function is the azoimine group, –N=N–C=N–, and is designated as an N, N⬘-chelator (N(imidazole) refers to N and N(azo) refers to N⬘). An aqueous solution of KReO4 with methanolic solution of 1-benzyl-2(phenylazo)imidazole and the product is characterized by elemental analyses and IR, 1 H NMR data. The conductance measurement shows that in methanol the molecules are non-conducting (⌳ M ⫽ 15–20 ⍀⫺1 cm⫺1). This supports strong non-separable ion-pair formation in solution phase. Infrared spectra (KBr) exhibit n(N–H) and n(N=N) at 苲3360 and 苲1400 cm⫺1, respectively. The n(ReO4) appears as a strong broad band at 925–935 cm⫺1. The complex 2a exhibits n(H2O) at 3450 cm⫺1. The 1 H NMR spectra exhibit a small degree of downfield shifting (⌬d ⫽ 0.05–0.1 ppm) of aryl-H (7-H to 11-H) while imidazole-H (3-H –5-H) have been affected severely (⌬d ⫽ 0.5–0.9 ppm) compared to free ligand values [11]. 3-H (N(3)-H) shows unusual shifting and may be due to strong H-bonding interaction N–Hδ+ …O(Re) (vide infra) [9c]. The methylene –CH2– appears as a singlet at 5.2–5.3 ppm. The (CH2)Ph protons (14-H–18-H) appear as multiplet at 7.3–7.5 ppm. Both conductance and 1H NMR data support the existence of strong ion interaction following hydrogen bonding in the molecules. The structure has been confirmed by the X-ray structure of [PaiCH2PhH+][ReO⫺ 4 ]앫H2O, 2a.Scheme 1 3.2. Crystal structure of [PaiCH2PhH+][ReO⫺ 4 ]앫H2O, 2a A view of the molecule [PaiCH2PhH+][ReO⫺ 4 ]앫H2O (2a) is shown in Fig. 1 and selected bond length and bond angles are listed in Table 2. In the molecule, the azo group is virtually coplanar with its neighboring phenyl ring and the imidazole ring. The maximum deviation of N2 atom from the mean plane formed by phenyl, azo ˚ . The N–N bond length, 1.254(10) A ˚ , is almost identical and imidazole units is 0.05 A ˚ [11]. The N2(azo)–C7(imidazole) bond distance, with the free ligand data, 1.250(1) A ˚ , is shorter than N1(azo)–C1(phenyl) bond distance, 1.425(11) A ˚ , which 1.394(11) A indicates a stronger intramolecular interaction between azo and imidazole group. The Re atom is in a distorted tetrahedral geometry with Re–O bond lengths in the range ˚ , respectively. A mole of H2O, resides in the ion-pair, acts as 1.652(12)–1.731(11) A donor and acceptor sites to generate a neutral supramolecular ladder. The π-stacked ˚ ; dihedrals 4.66° and 4.66°] aryl [Cg(imidazole)–Cg(aryl) 3.831(6) and 3.937(6) A and imidazole act as rungs and water–ReO4 hydrogen bonds (H(1W)…O(4) 1.895

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Scheme 1.

Fig. 1.

Ortep view of 2a.

O(1)–Re–O(2) N(1)–N(2)–C(7) N(2)–N(1)–C(1) N(1)–C(1)–C(6) N(2)–C(7)–N(3) N(2)–C(7)–N(4)

1.699(8) 1.731(11) 1.715(13) 1.652(12) 1.254(10) 1.425(11) 1.394(11) 1.356(13) 1.326(13)

˚) d(D-H) (A

0.8601 0.8607 0.8605 0.9301

Re–O(1) Re–O(2) Re–O(3) Re-O(4) N(1)–N(2) N(1)–C(1) N(2)–C(7) C(1)–C(6) C(8)–C(9)

Hydrogen-bonds D–H…A

O(1W)–H(1W)…O(4) O(1W)–H(2W)…O(1) N(3)–H(3)…O(1W) C(9)–H(9)….p[(CH2Ph)]

1.8950 2.0114 1.8346 2.938(2)

˚) d(H…A) (A

Angles (°)

˚) Distances (A

2.745(16) 2.868(12) 2.673(12) 3.667(7)

˚) d(D…A) (A

106.3(5) 111.9(7) 114.9(7) 124.5(7) 129.8(8) 121.3(8)

169.45 172.94 164.40 136.46

⬍(DHA) (°)

Table 2 ˚ ) and angles (°) for [PaiCH2PhH+][ReO4⫺]앫H2O 2a along with their estimated standard deviations Selected bond distances (A

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˚ , ⬍O(1W)–H(1W)…O(4) 169.5°; H(2W)…O(1) 2.011 A ˚ ,⬍O(1W)–H(2W)…O(1) A 172.9°) act as support. The π-stacked moieties are linked to water-ReO4 supports ˚ , ⬍N(3)–H(3)…O(1W) 164.4°) via N–H…O hydrogen bond (H(3)…O(1W) 1.835 A to form the ladder (Fig. 2). The C(9)–H(9) of imidazole interacts intermolecularly

Fig. 2.

2D network showing hydrogen bonding of 2a.

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˚ . Phenyl with the (CH2)Ph group showing a C–H…π[(CH2)Ph] distance of 2.938(2) A rings in the (1-CH2)Ph group exhibit weak intermolecular π…π interaction ˚ ] due to a large dihedral angle (⬎70°) and has [Cg(benzyl)….Cg(benzyl), 5.720(2) A not been accounted for in the construction of supramolecular ladder.

Acknowledgements Financial assistance from the University Grants Commission (for fellowship to USR) and the Council of Scientific and Industrial Research, New Delhi, are gratefully acknowledged.

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