Cite this: DOI: 10.1039/c3ce40754c

Formation of three new metal organic hybrids of Cd(II)with N,N9 donor spacer: an in situ perchlorate tochloride transformation3

Received 30th April 2013,Accepted 24th June 2013

DOI: 10.1039/c3ce40754c

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Biswajit Bhattacharya, Rajdip Dey, Dilip Kumar Maity and Debajyoti Ghoshal*

Three new metal–organic hybrids have been synthesized in a reaction of Cd(II) with 1,4-bis(3-pyridyl)-2,3-

diaza-1,3-butadiene (3-bpdb) and disodium succinate (Na2suc). All three compounds, i.e., {[Cd(3-

bpdb)(Cl)]?ClO4}n (1), {[Cd(3-bpdb)3(H2O)2]?(3-bpdb)(ClO4)2}n (2) and {[Cd(3-bpdb)(suc)(H2O)2]?(H2O)2}n

(3) are characterized by single-crystal X-ray diffraction and other physicochemical methods. Structure

determination reveals that 1 shows an a-polonium type 3D coordination network created by an exactly

perpendicular Cl–Cd–Cl linkage. The framework of 1 contains 1D channels, which are filled with ClO42.

Compound 2 shows a 1D coordination structure with two bridging and two pendent 3-bpdb ligands.

These pendent ligands are involved in H-bonding, p–p and C–H…p interactions with its coordinated water

molecules and lattice 3-bpdb ligands, to form the 3D supramolecular structure. Compound 3 is a 2D

4-connected net with succinate and the 3-bpdb ligand and extended to 3D supramolecular architecture by

H-bonding and p–p interactions. During the syntheses, an in situ chemical transformation of perchlorate to

chloride has occurred along with the oxidation of imine to amide and the chlorides so produced are found

integrated in compound 1, which facilitates the oxidation of imine in a very unprecedented way.

Introduction

The fabrication of metal–organic hybrids has proven to be anefficient approach towards the design of multifunctionalmaterials,1 for their potential application in several importantfields like gas storage,2 heterogeneous catalysis,3 magnetism,4

ion exchange,5 drug delivery,6 and designing sensing7 andconductive materials.8 Apart from the acquired functionality,these materials are also important due to their structuraldiversity. These are obtained by the assembly of smallinorganic clusters and organic linkers to form one-, two-, orthree-dimensional crystalline networks. In this context, differ-ent polycarboxylic ligands having versatile coordination modesare being used as building blocks in the construction of suchmaterials, which helps in their formation with a rich diversityin shape and connectivity.9 Recently, researchers have alsoshown interest in the possibility of the synthesis of metal–organic hybrids, based on a mixed ligand system by usingpolycarboxylates and several pyridyl based N,N9 donor spacerligands with different metal ions.10 The pyridyl based spacer

can act nicely as a pillar to link the metal–carboxylate layersinto higher dimensionality to alter the structural topology.

These frameworks not only show interesting physicalproperties, but also display some unusual chemical behaviorduring their formation. This may be in terms of thestabilization of the uncommon primary and/or secondaryvalency state of the metal ions,11 rare binding mode of theligands,12 interesting behavior of the counter anions,13 oroften easy occurrence of in situ chemical transformation,14

which may be difficult in normal reaction conditions. In thisreport we also observed an in situ perchlorate to chloridetransformation, which has occurred under mild reactionconditions and the chlorides so produced are found integratedin the resulting metal–organic hybrid. Herein we report theformation of two different metal organic hybrids of Cd(II)and 1,4-bis(3-pyridyl)-2,3-diaza-1,3-butadiene (3-bpdb),{[Cd(3-bpdb)(Cl)]?ClO4}n (1) and {[Cd(3-bpdb)3(H2O)2]?(3-bpdb)(ClO4)2}n (2), from a single reaction. The compoundsare synthesized in a chloride free water–methanol medium bythe reaction of Cd(ClO4)2?6H2O and 3-bpdb. However, thesame reaction with disodium succinate also produces a newmetal organic hybrid {[Cd(3-bpdb)(suc)(H2O)2]?(H2O)2}n (3),along with 1 and 2 (Scheme 1).

Thus, during the reaction, the chloride containing 1 hasformed along with two other redox-innocent metal–organichybrids. The perchlorate has been accounted as the source ofthe chloride in 1, as the reduction of perchlorate has occurred

Department of Chemistry, Jadavpur University, Jadavpur, Kolkata, 700 032, India.

E-mail: dghoshal@chemistry.jdvu.ac.in

3 Electronic supplementary information (ESI) available: FT-IR data (Fig. S1–S3)and structural figure of compounds reported in this paper along with GC-MS,ESI-MS spectra are available as ESI. CCDC 915228–915230. For ESI andcrystallographic data in CIF or other electronic format see DOI: 10.1039/c3ce40754c

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here with an oxidation of imine to amide. In this context, it isimportant to note that the transformation of perchlorate tochloride is very important in terms of environmental reasons,as nowadays soluble perchlorates are the major source of waterpollution due to the uncontrolled use of perchloric acid and itssalts in several industrial processes.15 Moreover, the reductionof perchlorate has occurred here with an oxidation of imine toamide,16 which is also important in terms organic reactionmethodology. It is interesting to note that here the imine toamide conversion has taken place by using a mild and verytrivial perchlorate with a metal–organic hybrid support.

Experimental section

Materials and methods

1,4-Bis(3-pyridyl)-2,3-diaza-1,3-butadiene (3-bpdb) was synthe-sized by the procedure reported earlier.17 High puritycadmium(II) perchlorate hexahydrate, succinic acid and3-pyridinecarboxaldehyde were purchased from Sigma-Aldrich Chemical Co. Inc. and used as received. All otherchemicals, including solvents, were of AR grade and used asreceived. The methanol used for the synthesis of thecompounds was used after double distillation. Ultrapure waterobtained from a Milliopore water purification system (¢18MV, Milli-Q, millipore) was used in the synthesis as well as inall experiments. Microanalyses (C, H, N) were performed usinga Perkin-Elmer 240C elemental analyzer. Infrared spectra(4000–400 cm21) were taken on KBr pellet, using a Perkin-Elmer Spectrum BX-II IR spectrometer. GC-MS analysis wasperformed using a Perkin Elmer CLARUS 680 instrument. ESI

mass spectra were recorded with Waters QTOF Micro YA263equipment.

Synthesis of {[Cd(3-bpdb)(Cl)]?ClO4}n (1) and {[Cd(3-bpdb)3(H2O)2]?(3-bpdb)(ClO4)2}n (2). Compounds 1 and 2 weresynthesized in one reaction. An aqueous solution (15 mL) ofCd(ClO4)2?6H2O (1 mmol, 0.419 g) was mixed to a methanolicsolution (15 mL) of 1,4-bis(3-pyridyl)-2,3-diaza-1,3-butadiene(3-bpdb) (1 mmol, 0.210 g) and stirred for 24 h. A yellowishcompound separated out on filtration and upon slowevaporation of the filtrate at 4 uC, two different single crystalsviz. hexagonal light yellow (1) and block shaped yellow (2)crystals suitable for single-crystal X-ray diffraction wereobtained after two weeks (Fig. 1). The crystals were washedwith methanol–water (1 : 1) and dried under air and separatedmanually by the shape and color of the crystals with yields of28% for 1 and 45% for 2, respectively, based on Cd(II)consumed. Anal. calcd for C24H20CdCl2N8O4 (1, %): C 43.17; H3.02; N 16.78. Found: C 43.33; H 2.96; N 16.52. IR for 1 (KBrpellet, cm21; Fig. S1, ESI3): n(CLN), 1630; n(ClO4), 1097; n(CH–Ar), 3100–2900 and n(CLC), 1560–1410. Anal. calcd forC48H44CdCl2N16O10 (2, %): C 48.52; H 3.73; N 18.95. Found:C 48.41; H 3.62; N 18.95. IR for 2 (KBr pellet, cm21; Fig. S2,

Scheme 1

Fig. 1 Optical microscopic images of the crystals used for data collection (usingsame magnification for all three crystals).

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ESI3): n(O–H), 3300–3500; n(CLN), 1628; n(ClO4), 1085; n(CH–Ar), 3100–2900 and n(CLC), 1570–1420.

Synthesis of {[Cd(3-bpdb)(suc)(H2O)2]?(H2O)2}n (3). Theabove reactions, when carried out in the presence of anaqueous solution (15 mL) of disodium succinate (1 mmol,0.162 g), led to the formation of compound 3 (in 20% yield)along with compounds 1 and 2 (in 18% and 40% yield,respectively). Transparent single crystals of 3 (Fig. 1) suitablefor single-crystal X-ray diffraction were obtained after twoweeks. Anal. calcd for C16H22CdN4O8 (3, %): C 37.62; H 3.55; N10.97. Found: C 37.48; H 3.64; N 10.85. IR for 3 (KBr pellet,cm21; Fig. S3, ESI3): n(O–H), 3300–3500; n(CLN), 1632; n(C–O),1300–1220; n(CH–Ar), 3100–2900 and n(CLC), 1560–1410.

Both the reactions lead to the same products (Scheme 1)with almost similar yields even when they are performedunder an inert atmosphere (N2).

Crystallographic data collection and refinement. The singlecrystals of compounds 1–3 were mounted on the tips of glassfibers with commercially available glue. The X-ray datacollections of all three single crystals were performed at roomtemperature using a Bruker APEX II diffractometer, equippedwith a normal focus, sealed tube X-ray source with graphitemonochromated Mo Ka radiation (l = 0.71073 Å). The datawere integrated using SAINT18 program and the absorptioncorrections were made with SADABS.19 All the structures weresolved by SHELXS-9720 using Patterson method and followedby successive Fourier and difference Fourier synthesis. Fullmatrix least-squares refinements were performed on F2 usingSHELXL-9720 with anisotropic displacement parameters for allnon-hydrogen atoms. All the hydrogen atoms were fixedgeometrically by HFIX command and placed in ideal positionsin the cases of all four structures. Calculations were carried out

using SHELXS 97,20 SHELXL 97,20 PLATON v1.15,21 ORTEP-3v2,22 and WinGX system Ver-1.80.23 Data collection andstructure refinement parameters along with crystallographicdata for all compounds are given in Table 1. The selected bondlengths and angles are given in Tables 2, 3 and 6.

Results and discussions

Crystal structure descriptions of {[Cd(3-bpdb)(Cl)]?ClO4}n (1)

Compound 1 crystallizes in the tetragonal P4/n space groupand the structure analysis reveals a 3D a-polonium typecoordination network of Cd(II) connected by the bent bis(3-pyridyl) N,N9 linker (3-bpdb) and perpendicular bridgingchloride ions, which may have originated from the reductionof perchlorate. In the asymmetric unit, each hexa-coordinatedCd(II) with a CdN4Cl2 chromophore shows a nearly perfectoctahedral geometry (Fig. 2a) satisfied by four symmetry

Table 1 Crystallographic and structural refinement parameters for 1–3

1 2 3

Formula C24H20CdClN8?ClO4 C48H44CdN16O2?2ClO4 C16H18CdN4O6?2H2OFormula weight 667.79 1188.30 510.79Crystal system Tetragonal Triclinic TriclinicSpace group P4/n P1 P1a/Å 16.1284(2) 10.6965(5) 7.4763(1)b/Å 16.1284(2) 10.9917(5) 8.3707(1)c/Å 5.2134(1) 11.8093(5) 9.0121(1)a (u) 90 99.715(2) 93.246(1)b (u) 90 98.778(2) 113.291(1)c (u) 90 92.825(2) 105.230(1)V/Å3 1356.14(4) 1348.49(11) 491.575(12)Z 2 1 1Dc/g cm23 1.635 1.463 1.725m/mm21 1.049 0.575 1.163F(000) 668 606 258h range/u 1.8–27.6 1.8–27.6 2.5–27.6Reflections collected 20 021 21 757 8278Unique reflections 1566 6189 2274Reflections I . 2s(I) 1505 5592 2258Rint 0.025 0.023 0.019Goodness-of-fit (F2) 1.07 1.04 1.10R1

a (I . 2s(I)) 0.0243 0.0447 0.0178wR2

a (I . 2s(I)) 0.0686 0.1399 0.0477Dr max/min/e Å3 20.40,0.73 20.75,0.95 20.24,0.34

a R1 = S||Fo| 2 |Fc||/S|Fo|, wR2 = [S(w(Fo2 2 Fc

2)2)/Sw(Fo2)2]K.

Table 2 Selected bond lengths (Å) and bond angles (u) for 1a

Cd1–Cl1 2.6041(10) Cd1–N1 2.3410(18)Cd1–Cl1d 2.6093(10) Cd1–N1a 2.3410(18)Cd1–N1b 2.3410(18) Cd1–N1c 2.3410(18)Cl1–Cd1–N1 90.22(4) Cl1–Cd1–Cl1d 180.00Cl1–Cd1–N1a 90.22(4) Cl1–Cd1–N1b 90.22(4)Cl1–Cd1–N1c 90.22(4) Cl1d–Cd1–N1 89.78(4)N1–Cd1–N1a 90.00(6) N1–Cd1–N1b 179.56(6)N1–Cd1–N1c 90.00(6) Cl1d–Cd1–N1a 89.78(4)Cl1d–Cd1–N1b 89.78(4) Cl1d–Cd1–N1c 89.78(4)N1a–Cd1–N1b 90.00(6) N1a–Cd1–N1c 179.56(6)N1b–Cd1–N1c 90.00(6)

a a = x, K 2 y, z; b = K 2 x, K 2 y, z; c = K 2 x, y, z; d = x, y, 1 +z.

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related nitrogen atoms (N1, N1a, N1b and N1c where a = x, K 2

y, z; b = K 2 x, K 2 y, z; c = K 2 x, y, z) of 3-bpdb linkers,which creates the basal plane. The axial positions are occupiedby two symmetry related bridging chloride ions (Cl1, Cl1d

where d = x, y, 1 + z). The Cd–N and Cd–Cl bond lengthsaround Cd1 are 2.3410(18) Å and 2.6041(10)–2.6093(10) Å,respectively, and the other selected bond lengths and bondangles are reported in Table 2. Here, four 3-bpdb ligandsconnected to each Cd(II) centre to form a two dimensional (4,4)net in the crystallographic ab plane (Fig. 2b). These 2D sheetsare pillared perfectly by the straight Cd–Cl–Cd linkage in thecrystallographic c-axis, resulting in the a-polonium type 3Dnetwork (Fig. 2c and 3a). Each Cd(II) centre is bound by twochloride ions in an exactly perpendicular manner forming aCl–Cd–Cl rod (Cl1–Cd1–Cl1d angle 180u), which is one of theunique features of this structure (Fig. 3b). This chloro-bridged3D framework forms 1D channels along the c-axis, which areoccupied by ClO4

2 counter anions (Fig. 3a).

Crystal structure descriptions of {[Cd(3-bpdb)3(H2O)2]?(3-bpdb)(ClO4)2}n (2)

Compound 2 crystallizes in the triclinic system with spacegroup P1 and the single crystal structure analysis reveals theformation of a one-dimensional coordination framework ofCd(II), connected by 3-bpdb linkers only. Here, each hexa-coordinated Cd(II) shows a distorted octahedral geometry witha CdN4O2 chromophore (Fig. 4a). The equatorial positionsaround the Cd(II) atoms are occupied by four nitrogen atoms(N1, N1a, N5 and N5a where a = 2 2 x, 2y, 2 2 z) of twobridging and two pendent 3-bpdb ligands with Cd–N distancesranging from 2.353(2) to 2.382(2) Å (Table 3). Two symmetryrelated water molecules (O1W, O1Wa) are in the axial positionswith a Cd–O distance of 2.286(2) Å (Table 3). The structureshows a 1D pattern, which is extended in the a direction withthe help of bridging 3-bpdb (Fig. 4b). There are perchloratecounter anions as well as un-coordinated 3-bpdb ligandspresent in the lattice and held within the space between theone dimensional chains. In the crystal packing, these 1Dchains are stitched with the help of coordinated watermolecules, by means of H-bonding with the N-atom (N4) ofpendent 3-bpdb ligands (Table 4). Furthermore, the lattice3-bpdb molecules, along with the coordinated pendent 3-bpdb

Table 3 Selected bond lengths (Å) and bond angles (u) for 2a

Cd1–O1W 2.286(2) Cd1–N1 2.353(2)Cd1–N5 2.382(2) Cd1–O1Wa 2.286(2)Cd1–N1a 2.353(2) Cd1–N5a 2.382(2)O1W–Cd1–N1 93.17(8) O1W–Cd1–N5 88.76(8)O1W–Cd1–O1Wa 180.00 O1W–Cd1–N1a 86.83(8)O1W–Cd1–N5a 91.24(8) N1–Cd–N5 88.78(8)O1Wa–Cd1–N1 86.83(8) N1–Cd1–N1a 180.00N1–Cd1–N5a 91.22(8) O1Wa–Cd1–N5 91.24(8)N1a–Cd1–N5 91.22(8) N5–Cd1–N5a 180.00O1Wa–Cd1–N1a 93.17(8) O1Wa–Cd1–N5a 88.76(8)N1a–Cd1–N5a 88.78(8)

a a = 2 2 x, 2y, 2 2 z.

Fig. 2 (a) View of the coordination environment of Cd(II) in 1 with the atomlabeling scheme. (b) Two-dimensional arrangement in 1 constructed by themetal–3-bpdb moiety. (c) a-Polonium type network in compound 1.

Fig. 3 (a) View of the 3D network of 1 showing the channels occupied by theClO4

2 anions lying in the crystallographic ab plane. (b) Three-dimensionalnetwork of 1 showing the Cl–Cd–Cl rod in the crystallographic c-axis.

Fig. 4 (a) View of the coordination environment of Cd(II) in 2. (b) A fragment ofthe one-dimensional chain of 2 viewed along the b axis. (c) Supramolecular 3Darrangement in 2 (p–p interactions: pink dotted lines, C–H…p interactions andH-bonding. Cyan dotted lines and bridging 3-bpdb ligands are omitted forclarity).

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ligands are involved in p–p and C–H…p interactions (Fig. S4,ESI3 and Table 5). These cooperative H-bonds and p-interac-tions are responsible for the generation of the overallsupramolecular three-dimensional structure, which is shownin Fig. 4c.

Crystal structure descriptions of {[Cd(3-bpdb)(suc)(H2O)2]?(H2O)2}n (3)

Compound 3 crystallizes in the triclinic P1 space group andthe X-ray structure determination reveals the formation of a 2Dcoordination framework of Cd(II) connected by the bridgingsuccinate and 3-bpdb. Each Cd(II) center is located in a specialposition (1, 0, 1) and shows hexa-coordination with a CdN2O4

chromophore and represents a distorted octahedral geometry(Fig. 5a). The equatorial plane of the octahedron is created bythe two N (N1, N1a where a = 2 2 x, 2y, 2 2 z) atoms of thebridging 3-bpdb and two symmetry related oxygen atoms ofthe bridging succinate (O1, O1a); whereas two symmetryrelated water oxygen atoms (O1W, O1Wa) occupy the axialpositions. The Cd–O bond lengths are in the range of2.3110(15)–2.3570(16) Å and the Cd–N bond length is2.3334(16) Å (Table 6). Here, the succinate dianion binds ina bridging monodentate fashion and each succinate connectstwo different Cd(II) centers. The bridging succinate and 3-bpdbcreate the 2D arrangement in the crystallographic ac plane

(Fig. 5b). The topology of the 2D framework suggests a 4-c netwith Schlafli symbol {44.62} (Fig. 5b and 5c).24 In the crystalpacking, the adjacent sheets are held together by means ofH-bonding, mediated through lattice water molecules, coordi-nated waters and oxygen atoms of carboxylates (Fig. 6a). Oneof the H atoms of the lattice water is also H-bonded, with the Natom (N2) of the 3-bpdb ligand to give a supramolecular 3D

Table 4 Hydrogen bonding interactions (Å, u) of 2 and 3a

D–H…A D–H H…A D…A /D–H…A

2 O1W–H1WA…N4i 0.9700 1.7800 2.729(4) 165.00O1W–H1WB…N8ii 0.9300 1.8500 2.754(4) 162.00

3 O1W–H1WA…O2Wiii 0.93(2) 1.95(2) 2.876(2) 170(3)O1W–H1WB…O2iv 0.91(3) 1.86(3) 2.748(2) 165(2)O1W–H1WB…O2ii 0.91(3) 2.52(2) 2.988(2) 112.3(18)O2W–H2WA…O1 0.90(3) 1.92(3) 2.817(2) 172(3)O2W–H2WB…N2v 0.90(3) 2.32(3) 3.161(3) 156(3)

a (i) = 2 2 x, 2y, 1 2 z; (ii) = 2 2 x, 2y, 2 2 z; (iii) = 2 2 x, 21 2 y,2 2 z; (iv) = 1 + x, y, z; (v) = x, 21 + y, z.

Table 5 p–p interactions in 2, 3 and C–H…p interaction in 2a,b

Ring(i) A ring(j) Distance of centroid(i) from ring(j) (Å) Dihedral angle (i, j) (u) Distance between the (i, j) ring centroids (Å)

2 R(1) A R(2)i 4.0585 (19) 27.96(16) 3.7996(15)R(1) A R(3)ii 3.6575(18) 7.95(15) 3.4365(14)R(2) A R(1)i 4.0585 (19) 27.96(16) 3.1451(12)R(2) A R(3)iii 4.544(2) 35.92(17) 4.0451(14)R(3) A R(1)ii 3.6575(18) 7.95(15) 3.4638(12)R(3) A R(2)iii 4.544(2) 35.92(17) 2.3003(13)

3 R(1) A R(1)iv 3.8923(12) 0 3.6463(8)R(1) A R(1)v 3.7844(12) 0 3.5347(8)

C–H A ring(j) H…R distance (Å) C–H…R angle (u) C…R distance (Å)2 C(24)–H(24) A R(2)iii 2.88 120 3.443(4)

a Symmetry code: (i) = 2 2 x, 2y, 1 2 z; (ii) = x, y, z; (iii) = 2 2 x, 1 2 y, 1 2 z; (iv) 1 2 x, 2y, 1 2 z; (v) 2 2 x, 2y, 1 2 z. b R(i)/R(j) denotesthe ith/jth rings: R(1) = N(1)/C(1)/C(2)/C(3)/C(4)/C(5); R(2) = N(4)/C(8)/C(9)/C(10)/C(11)/C(12); R(3) = N(8)/C(20)/C(21)/C(22)/C(23)/C(24).

Table 6 Selected bond lengths (Å) and bond angles (u) for 3a

Cd1–O1 2.3110(15) Cd1–O1W 2.3570(16)Cd1–N1 2.3334(16)O1–Cd1–O1W 73.82(5) O1–Cd1–N1 88.74(5)O1–Cd1–O1a 180.00 O1–Cd1–O1Wa 106.18(5)O1–Cd1–N1a 91.26(5) O1W–Cd1–N1 92.14(5)O1a–Cd1–O1W 106.18(5) O1W–Cd1–O1Wa 180.00O1W–Cd1–N1a 87.86(5) O1a–Cd1–N1 91.26(5)O1Wa–Cd1–N1 87.86(5) N1–Cd1–N1a 180.00O1a–Cd1–O1Wa 73.82(5) O1a–Cd1–N1a 88.74(5)O1Wa–Cd1–N1a 92.14(5)

a (a) = 2 2 x, 2y, 2 2 z.

Fig. 5 (a) View of coordination environment of Cd(II) in 3 with atom labelingscheme. (b) Two-dimensional sheet structure in 3 constructed by succinate,3-bpdb ligand and Cd(II). (c) 4-Connected 2D net in 3.

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architecture, which is further stabilized by p–p interactions(Fig. 6b and Tables 4 and 5).

Discussion regarding perchlorate to chloride reduction incompound 1

It is evident from the above discussion that, during theformation of 1, chloride is produced and has been incorpo-rated in the 3D framework, although no chloride salt wasadded to the reaction mixture. To best of our knowledge, thereare no provisions for chloride to have come from the solvent orany other impurity as all the reactions are performed inchloride free water. Moreover, both the reactions have beenchecked in an inert environment using nitrogen atmosphere,which also gives the same product and in almost same yield.This observation clearly indicates that the chloride must beproduced from the reduction of perchlorate used in thisreaction. On account of the electrons, we then searched for theparallel oxidation process and found a very interestingobservation. We have performed a GC-MS experiment (Fig.S5 and S6, ESI3) with the reaction mixture and got a clearindication of the formation of nicotinamide, which may beproduced by the oxidation of 3-bpdb (Scheme S1, ESI3). TheESI-MS data of the reaction mixture gave the signature ofnicotinamide at m/z 122.04 (Fig. S7 and S8, ESI3) and IRspectral data [n(CLO), 1636 cm21 (stretch); n(N–H), 3444 cm21

(stretch) and 1549 cm21 (bending)] also confirms the forma-tion of nicotinamide by the oxidation of imine with per-chlorate (Fig. S9, ESI3). To establish the condition of theperchlorate to chloride transformation we have also performedthe reactions under the same conditions, varying the reactantsas well as their ratios. These reactions are summarized inTable 7. Considering the formation of nicotinamide as asignature of the formation of chloride, hence the formation of1; it is clear from this study that the reduction of perchlorate isindependent of the nature of perchlorate or the presence ofother counter anions. The reactions I and II are alreadydiscussed in experimental section and both the reactionsproduced the chloride-containing 1. In III the use of freeperchlorate along with cadmium nitrate also gives the sameproduct with a similar yield as that of I. But when a higher

concentration of the bridging ligand 3-bpdb is used inreactions IV–VI, the chloride-containing 1 is not produced.This is probably due to the exclusive formation of 2, whichprobably makes Cd(II) unavailable for the formation of thethermodynamically controlled product 1. It is needless tomention that the yield of 2 in reactions IV–VI is better (72%–79%) than in reaction I (45%). In the absence of Cd(II), thestarting material amide is also not formed (reaction VII),which was confirmed by GC-MS and ESI-MS spectra (Fig. S10,ESI3), as the formation of the framework is not possible in thiscase. This clearly indicates the role of the framework in theaforesaid transformation.

Conclusions

The present work represents three new metal organic hybrids,which have been synthesized in a single reaction. Apart fromnumerous significant applications of metal organic hybrids,this report comes up with a possibility of a new functional sidein terms of the utility of such compounds in in situ chemicaltransformation. The perchlorate is a pretty good oxidizing agentbut its use in different organic reactions is not so common dueto the drastic nature of soluble chloride, produced during theoxidation. This affects the reaction condition by changing thepH of the reaction medium.25 But in this case, the chloride soproduced is scavenged by the insoluble metal organic hybrid 1,which successfully allowed the oxidation of imine to produceamide. Thus, here, the production of the pharmaceuticallyimportant molecule nicotinamide26 has been done in a veryunusual way and the metal–organic framework might facilitatethe reaction process by holding the chloride. In summary, thiswork is a nice example of the oxidation of an imine byperchlorate with a metal organic framework support and thisidea of framework support may open up the exploration of newideas in designing the methodology of similar importantorganic reactions.

Acknowledgements

Financial support from UGC, Govt. of India, is gratefullyacknowledged (grant to DG). BB acknowledges UGC for the

Fig. 6 (a) 1D metal carboxylate chains stitched by lattice water molecules in 3.(b) Supramolecular 3D arrangement in 3 (p–p interactions: pink dotted lines & Hbonding: cyan dotted lines).

Table 7 Monitoring for the formation of amide with different reactants andalso varying their ratio

No. ReactionReactantsratio

Formationof amide

I 3-bpdb + Cd(ClO4)2?6H2O 1 : 1 YesII 3-bpdb + Cd(ClO4)2?6H2O + Na2suc 1 : 1 : 1 YesIII 3-bpdb + Cd(NO3)2?4H2O + NaClO4 1 : 1 : 2 Yes

IV 3-bpdb + Cd(ClO4)2?6H2O 2 : 1 NoV 3-bpdb + Cd(ClO4)2?6H2O 3 : 1 NoVI 3-bpdb + Cd(ClO4)2?6H2O 4 : 1 NoVII 3-bpdb + NaClO4 1 : 2 No

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senior research fellowship. The authors are grateful to Prof. S.Bhattacharya, JU and his group for the GCMS study andvaluable discussion during the preparation of the manuscript.The X-ray diffractometer facility under the DST-FIST programof Department of Chemistry (JU) is also gratefully acknowl-edged.

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