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Journal of Molecular Structure 800 (2006) 93–99

Second-sphere coordination in non-spherical anion binding:Synthesis, characterization and X-ray structure of

cis-diazidobis(ethylenediamine)cobalt(III)2-chloro,5-nitrobenzenesulphonate monohydrate

Rajni Sharma a, Raj Pal Sharma a,*, Ritu Bala a, Loretta Pretto b, Valeria Ferretti b,*

a Department of Chemistry, Panjab University, Chandigarh 160014, Indiab Centro di Strutturistica Diffrattometrica and Dipartimento di Chimica, University of Ferrara via L. Borsari 46, I-44100, Ferrara, Italy

Received 17 February 2006; received in revised form 21 March 2006; accepted 25 March 2006Available online 11 May 2006

Abstract

Dark red coloured single crystals of [cis-Co(en)2(N3)2] C6H3ClNO5SÆH2O were obtained by slowly mixing the separately dissolved cis-diazidobis(ethylenediamine)cobalt(III) nitrate with sodium 2-chloro,5-nitrobenzenesulphonate in aqueous medium in 1:1 molar ratio.The complex salt was characterized by elemental analyses, spectroscopic studies (IR, UV/visible, 1H and 13C NMR) and solubility mea-surements. The compound crystallizes in the triclinic space group P�1 with a = 7.8128(2), b = 8.3219(2), c = 17.4526(2) A, a = 95.224(1),b = 95.759(1), c = 116.636(2)�, V = 997.36(5) A3, Z = 2. Single crystal X-ray structure determination revealed an ionic structure consist-ing of [cis-Co(en)2(N3)2]+, [C6H3ClNO5S]� and one lattice water molecule. In the complex cation [cis-Co(en)2(N3)2]+, the cobalt(III) isbonded to six nitrogen atoms, originating from two ethylenediamine ligands, and two azide groups showing an octahedral geometryaround cobalt(III). Supramolecular hydrogen-bonding networks involving second-sphere coordination like ½NHen

þ � � �Xanion�� and

NHenþ � � �Owater besides electrostatic forces of attraction have been observed to stabilize crystal lattice. This is the first crystal structure

of a salt containing 2-chloro,5-nitrobenzenesulphonate anion and cis-diazidobis(ethylenediamine)cobalt(III) cation.� 2006 Elsevier B.V. All rights reserved.

Keywords: Cobalt(III); Coordination chemistry; 2-Chloro,5-nitrobenzenesulphonate; Second-sphere coordination; Supramolecular chemistry; X-raycrystallography

1. Introduction

Crystal engineering and molecular recognition are thetwo facets of supramolecular chemistry which have acceler-ated the pace of research [1]. The design and synthesis ofsmart molecules that are able to function as sensors orbinding agents for charged species are a challenge forresearchers [2]. Up to now various types of synthetic anion

0022-2860/$ - see front matter � 2006 Elsevier B.V. All rights reserved.

doi:10.1016/j.molstruc.2006.03.093

* Corresponding authors. Tel.: +91 0172 2544433; fax: +91 01722545074 (R.P. Sharma); tel.: +39 0532 291132; fax: +39 0532 240709(V. Ferretti).

E-mail addresses: rpsharma@yahoo.co.in (R.P. Sharma), frt@unife.it(V. Ferretti).

receptors for the binding of anions have been developed,although receptors for the selective binding of non-spheri-cal anions are scarce [3]. Therefore, there is a great need fornovel anion receptors in order to better characterize anionassociation patterns and to obtain novel binding features.A proper understanding of hydrogen bonding [4] andsupramoleular synthons [5] is important in the design ofsolid state architectures with new functional groups [6] orcombination of functional groups. Early studies in crystalengineering have focused on exploiting hydrogen bondingbetween same functional groups or homosynthons, e.g.,COOH� � �COOH, CONH2� � �CONH2, etc. [5]. A recenttrend is to utilize complementary functional groups forcontrolling the organization of molecules in the target

94 R. Sharma et al. / Journal of Molecular Structure 800 (2006) 93–99

architecture because heterosynthons are strong, specificand show greater probability of occurrence in crystal struc-tures [7]. The ideal situation in supramolecular chemistrywould be to use those combinations that exhibit predict-able recognition for a particular synthon pair and almostno bonding with other functional groups that are presentin the self-assembling milieu. A number of packing motifshave been used, charge assistance to hydrogen bonding isthe enhancement to donor and acceptor systems’ polarityby utilizing cationic donors and anionic receptors insteadof neutral systems. Although, several examples of second-sphere complexes with aquo [8] and ammine [9] coordina-tion compounds have appeared in the literature, the sec-ond-sphere interaction as a synthetic strategy has notbeen much exploited for the construction of extended orlayered solid structures. Generation of extended solids byexploiting both primary and secondary sphere interactionsin metal sulphonate complexes has been extensively studiedby Shimizu and co-workers [10,11]. As these interactions(i.e., second-sphere interactions) are essentially intermolec-ular in nature, we reasoned that if cations and anions areproperly functionalised to incorporate hydrogen bondswith the availability of properly oriented hydrogen bonddonors and acceptors, i.e., complementary, novel networkarchitecture may ensue and stabilize the lattice. In thisregard, metal ligand complexes have been exploited as sim-ple pieces of inorganic molecular scaffolding [12].

2-Chloro,5-nitrobenzenesulphonate belongs to the classof commercially important organosulphonates which havelongstanding industrial applications as surfactants, dyes,fuel and lubricant, detergents or antioxidants [13]. Theyhave been studied as potential liquid crystalline [14] andnon-linear optical materials [15,16] besides pharmaceuticalsalt preparation [17] and therefore, the search for new andefficient anion receptors for sulphonate ion. We envisagedthat the presence of eight NAH hydrogen bond donorgroups on each positively charged cation [cis-Co(en)2(N3)2]+ will facilitate the interaction with properlyoriented negatively charged oxygens of oxoanion and thismay result in the formation of a donor–acceptor complexinvolving second-sphere coordination. In the solid state,with all probabilities, these two ions should form an intri-cate network of hydrogen bonds stabilizing the entire lat-tice. Understanding of such network interactions ofjudicially chosen cations and anions would be rewardingas it can provide means of constructing intricate and novelmolecular entities based on second-sphere coordination.We report here the potential use of [cis-Co(en)2(N3)2]+ cat-ion present in diazidobis(ethylenediamine)cobalt(III)nitrate as anion receptor for non-spherical anion2-chloro,5-nitrobenzenesulphonate i.e., synthesis,characterization and X-ray structure determination of cis-diazidobis(ethylenediamine)cobalt(III) 2-chloro,5-nitro-benzenesulphonate, [cis-Co(en)2(N3)2]C6H3NClO5SÆH2Oin continuation of our interest in cobalt(III) complexes[18]. We have already reported the synthesis, characteriza-tion and X-ray structure determination of salts containing

various shapes of anions, viz. [cis-Co(en)2(N3)2]SCN (linear)[19], [cis-Co(en)2(N3)2]N3(linear) [20], [cis-Co(en)2(N3)2]2SiF6(octahedral), [cis-Co(en)2(N3)2]BF4ÆNO3 (tetrahedral)[21] and [cis-Co(en)2(N3)2]picrate (hexagonal) [22]. Inciden-tally, this is the first crystal structure of a salt containingthe anion 2-chloro,5-nitrobenzenesulphonate with cis-diazidobis(ethylenediamine)cobalt(III).

2. Experimental

Caution: Azide salts as well as their complexes should behandled with care due to their explosive nature.

2.1. Materials

Technical grade reagents were used throughout thiswork without any further purification. [cis-Co(en)2(N3)2]NO3 has been prepared according to litera-ture method [23,24].

2.2. Instruments

Cobalt was determined by standard method [25] and C,H, N were estimated micro-analytically by automatic Per-kin Elmer 2400 CHN elemental analyzer. IR spectrumwas recorded as KBr pellets on PERKIN ELMER SPEC-TRUM RXFT-IR system. 1H and 13C NMR spectra wererecorded in DMSO-d6 by using BRUCKER AC 300 F(300 MHz) spectrophotometer with TMS as internal refer-ence. UV/visible spectrum was recorded in H2O using HIT-ACHI 330 SPECTROMETER.

2.3. Synthesis of [cis-Co(en)2(N3)2]C6H3NclSO5ÆH2O

An aqueous solution of 1 g (0.003 mol) of [cis-Co(en)2(N3)2]NO3 in 100 ml water was taken and filtered.This was added to an equimolar quantity of (0.7897 g) ofsodium 2-chloro,5-nitrobenzenesulphonate dissolved inminimum amount of water. The mixture when allowed toevaporate at room temperature gave the dark maroon colourproduct. Crystals suitable for single crystal X-ray structuredetermination were collected after one day by drawing offthe mother liquor and air-dried (yield, 70%). The complexis soluble in water, ethanol and DMSO but insoluble in ace-tone. The complex salt decomposes at 190 �C. The elementalanalysis is consistent with the composition [cis-Co(en)2(N3)2]C6H3NClO5SÆH2O. Found: C, 25.6; H, 4.0;N, 29.6; Co, 11.2 for the complex salt, calc. C, 25.4; H, 4.0;N, 29.7; Co, 11.3. Solubility in water at 25 �C: 1 g/100 ml.

2.4. X-ray crystallography

Crystal data, data collection and refinement parametersare summarized in Table 1 and a selection of bond lengthsand angles is reported in Table 2. X-ray diffraction datawere collected on a Nonius Kappa CCD diffractometerusing graphite-monochromated MoKa radiation

Table 1Crystal data, data collection and refinement parameters of [cis-Co(en)2(N3)2]C6H3ClNO5SÆH2O

Chemical formula [Co(N3)2(en)2]+ [2-Cl,5-NO2-benzenesulphonate]� hydrate

Mr 517.82Temperature 295 KCell setting, space group Triclinic, P�1a,b, c (A) 7.8128(2),8.3219(2),17.4526(2)a,b,c (�) 95.224(1),95.759(1),116.636(2)V (A3) 997.36(5)Z 2Dx(Mg m�3) 1.724l (MoKa) (mm�1) 1.155Crystal form, colour and size

(mm3)Prism, violet, 0.13·0.23·0.27

Absorption correction Empirical (SORTAV)h range (�) 2.77–28.00No. of measured,

independent and observedreflections

13112, 4689, 4065

Criterion for observedreflections

I > 2r(I)

Rint 0.028Refinement on F2

R[F2 > 2r (F2)], wR (F2),goodness of fit

0.038, 0.102, 1.041

No. of observed reflections/No. of parameters

4065/349

Weighting scheme w = 1/[r2 (Fo2) + (0.0509 P)2 + 0.6133 P],

where P = (Fo2 + 2Fc

2)/3

R. Sharma et al. / Journal of Molecular Structure 800 (2006) 93–99 95

(k = 0.71069 A). Intensities were corrected for Lorentz andpolarization effects. The structures were solved by directmethods with the SIR97 program [26] and refined by full-matrix least squares using the SHELXL-97 [27] program.Non-hydrogen atoms were refined anisotropically andhydrogen atoms isotropically, with the exception of Hatoms belonging to the disordered parts and to C3 atom,which were included on calculated positions, riding on their

Table 2Selected bond lengths (A) and bond angles (�) for [cis-Co(en)2(N3)2]C6H3ClNO5SÆH2O

Co1AN1 1.969(2) N8AN9 1.194(3)Co1AN2 1.962(2) S1AC7 1.792(2)Co1AN3 1.960(2) S1AO1 1.442(2)Co1AN4 1.952(2) S1AO2 1.461(3)Co1AN5 1.952(2) S1AO3 1.435(3)Co1AN8 1.952(2) C11AC8 1.733(3)N5AN6 1.197(3) N11AC5 1.466(3)N6AN7 1.148(3) N11AO4 1.221(3)N9AN10 1.149(4) N11AO5 1.218(4)

N1ACo1AN2 86.03(9) N4ACo1AN8 94.59(9)N1ACo1AN3 93.14(9) N5ACo1AN8 93.36(9)N1ACo1AN4 92.70(9) N5AN6AN7 175.9(2)N1ACo1AN8 87.72(9) N8AN9AN10 176.2(2)N2ACo1AN3 91.28(9) O1AS1AO2 112.9(1)N2ACo1AN5 90.51(9) O1AS1AO3 115.1(2)N2ACo1AN8 88.19(9) O2AS1AO3 112.2(2)N3ACo1AN4 85.97(9) C5AN11AO4 118.3(2)N3ACo1AN5 85.74(9) C5AN11AO5 118.2(2)N4ACo1AN5 90.70(9) O4AN11AO5 123.5(2)

carried atoms. All other calculations were performed usingthe program WinGX [28]. Hydrogen-bonding parametersfor the present structure, including those for CAH� � �Xbonds, are reported in Table 3. In general, we have consid-ered the CAH� � �X (X = N,O) interactions where theH� � �X distance is less than 2.70 A and CAH� � �X angle isgreater than 130� to be significant.

3. Results and discussion

3.1. Synthesis

While a large number of azido divalent metal complexeshave been reported, their corresponding cobalt (III) com-plexes are very limited [29–31]. Moreover there are onlyfew reports of X-ray diffraction studies of the azido cobal-t(III) salts in the literature [32–34]. It is worth mentioninghere that the salts containing one azide group and anotherligand e.g. [cis-Co(en)2(N3)(SO3)]1.5H2O and cis-Co(en)2(N3)(C2O4)H2O could be obtained by using propersynthetic strategies [35].

The chemical composition of the complex salt obtainedby reacting [cis-Co(en)2(N3)2]NO3 with sodium salt of 2-chloro,5-nitrobenzenesulphonic acid in 1:1 molar ratio inaqueous medium is consistent with the formula [cis-Co(en)2(N3)2]C6H3NClO5SÆH2O.

3.2. Measurement of solubility product

Solubility of ionic salts in water differs to a great extentand on the basis of solubility criterion, the salts are classi-fied into three categories (a) solubility >0.1 M (soluble); (b)solubility between 0.01 and 0.1 M (slightly soluble); (c)solubility <0.01 M are (sparingly soluble). The solubilitymeasurements at room temperature show that [cis-Co(en)2(N3)2]NO3 and [cis-Co(en)2(N3)2]C6H3NClO5-SÆH2O are sparingly soluble in water but it is more true forthe former. The solubility product of [cis-Co(en)2(N3)2]

Table 3Hydrogen-bonding parameters (A, �) of [cis-Co(en)2(N3)2]C6H3ClNO5SÆH2O

DAH� � �A DAH D� � �A H� � �A \DAH� � �AN2AH22� � �O3 0.88(3) 3.270(3) 2.54(3) 142(3)N3AH32� � �O2 0.85(3) 3.006(3) 2.16(3) 176(3)N1AH11� � �O1i 0.87(3) 3.015(3) 2.20(3) 155(3)N4AH41� � �N10ii 0.90(4) 3.099(4) 2.23(4) 163(3)N3AH31� � �O4iii 0.77(4) 3.152(3) 2.39(4) 178(3)O6AH61� � �O2iv 0.87(6) 2.875(4) 2.04(6) 162(5)N2AH21� � �N7iv 0.90(4) 3.088(4) 2.31(4) 146(3)O6AH62� � �N6iv 0.66(6) 3.231(4) 2.85(5) 120(6)N1AH12� � �O6v 0.90(3) 3.054(3) 2.29(4) 142(3)N4AH42� � �O6v 0.88(3) 2.885(3) 2.03(3) 165(3)C2AH24� � �O4iii 0.97(3) 3.438(4) 2.58(3) 147(2)C9AH9� � �O5vi 0.90(4) 3.357(4) 2.48(4) 164(3)

Symmetry codes used: (i) x + 1,y + 1,z; (ii) 2 � x, 2 � y, 2 � z; (iii) 2 � x,1 � y, 1 � z; (iv) 2 � x,1 � y, 2 � z; (v) x + 1,y + 1,z; (vi) 3 � x, 2 � y,2 � z; (vii) 9x � 1,y,z.

96 R. Sharma et al. / Journal of Molecular Structure 800 (2006) 93–99

C11H19N11ClSO5ÆH2O is 3.0 · 10�4 as compared to9.0 · 10�4of [cis-Co(en)2(N3)2]NO3 which indicates thatthe affinity or binding of the cation [cis-Co(en)2(N3)2]+ ismore for 2-chloro,5-nitrobenzenesulphonate ion as com-pared to nitrate ion.

3.3. Spectroscopy

Infrared spectrum of the newly synthesized complex hasbeen recorded in the region 4000–400 cm�1 and tentativeassignments have been made on the basis of earlier reportsin the literature [36]. The IR absorption band at 896 cm�1

is assigned to CH2 rocking region and a band at 1568 cm�1

is assigned to NH2 asymmetric deformation [37], whichalso indicates the cis-geometry of the complex. The IRabsorption bands at 2029 and 2051 are assigned to asym-metric stretching frequency of azide group. The strongabsorption bands at 1216, 1110 cm�1and a weak band at670 cm�1 are assigned for mas (ASO3

�), ms (ASO3�) and

m(CAS), respectively [38]. The corresponding bands appearat 1172 cm�1, 1134 cm�1, 680 cm�1 in [cis-Co(en)2(N3)2](C9H11SO3) [39] and at 1202 cm�1, 1112 cm�1 and at666 cm�1 in Tl(m-NO2C6H4 SO3) [40]. It can be observedthat the presence of an electron withdrawing group on ben-zenesulphonate group shifts the mas(ASO3

�) towards a low-er frequency whereas the presence of an electron releasinggroup shifts it to higher frequency. The IR absorptionbands at 1349 and 1517 are attributed to mas(ANO2

�)and ms(ANO2

�), respectively. The absorption IR band at428 is assigned to CoAN.

The electronic spectrum of the complex salt has beenrecorded in H2O. The UV/visible absorption spectrum ofthe title complex salt is similar to that of the complex cat-ion present in the nitrate salt [23]. The cobalt (III) complexsalts absorb strongly at 520, 289 nm corresponding to d–dtransitions [41] typical for octahedral low spin cobalt(III)complexes. These transitions are from 1A1g ground stateof cobalt(III) to singlet state 1T1g (low energy) and from1A1g ground state to 1T2g (higher energy).

NMR spectra (1H and 13C) of the newly synthesizedcomplex salts are recorded in DMSO-d6. The chemical shiftvalues are expressed as d value (ppm) downfield from tetra-methylsilane as internal standard. In 1H NMR, the two sig-nals at 4.2 and 4.8 ppm are attributed to nitrogen protons[42] of ethylenediamine while CH2 protons of ethylenedia-mine group are observed at 2.6 ppm. For 2-chloro,5-nitro-benzenesulphonate group, aromatic protons are observedin the range 7.4–8.2. 13C NMR spectrum shows the charac-

SO3

Cl

O2N

1 2

34

5

6

S

1

45

6

C

H3C

Scheme

teristic signal at 44.3 ppm for carbons of ethylenediaminegroup in the title complex salts. In the 2-chloro,5-nitro-benzenesulphonate group, signal at 122.0 ppm is assignedto C-2, 124.1 for C-5, 128.4 for C-4, 129.3 for C-6,145.1 ppm for C-1 and 146.2 for C-3 as shown in Scheme1. These values appear at 127.0 ppm for C-3 and 5, 136.0for C-2 and 6, 137.3 for C-1, 142.1 for C-4 in [cis-Co(en)2(N3)2](C9H11SO3) and at 144.1, 121.4, 130.7,127.4, 149.7 and 132.4 ppm corresponding to C-1, C-2,C-3, C-4, C-5, C-6 of the benzene ring in Tl(3-NO2C6H4

SO3), respectively. The observed trend could be easilyrationalized on the basis of electron withdrawing/releasinggroups on aromatic ring of the sulphonate ion.

3.4. Crystal structure

3.4.1. Coordination geometry and bonding

To determine the structure unambiguously, the singlecrystal X-ray crystallography was carried out. The asym-metric unit is formed by a Co(III) complex cation, a 2-chlo-ro,5-nitrobenzenesulphonate anion, linked by two NH� � �Ohydrogen bonds, and a co-crystallized water molecule,interacting with N8 atom of the azido group. ORTEPIII[43] view of the title compound is shown in Fig. 1. Thecobalt(III) cation adopts the usual slightly distorted octa-hedral geometry, being coordinated to two ethylenedia-mine and two azide molecules. The bond angles, reportedin Table 2, show that NACoAN angles involving the ethy-lenediamine nitrogens are less than 90�, because of the biteof the bidentate ligand. CoAN bond lengths are in therange of 1.952(2)–1.969(2) A for nitrogens of ethylenedia-mine, and equal to 1.952(2) A for nitrogens of azidogroups. These bond distances are in agreement with thoseobserved in other cobalt complexes recently reviewed.The C4 atom is disordered over two non-equivalent alter-native orientations, the occupancy factor refining to 0.70for the major component. The geometry of the azidoligands is nearly linear, NANAN angle being of 175.9(2)and 176.2(2)�. The interior NAN bond lengths of1.197(3) and 1.194(3) A are longer than the terminalNAN distances of 1.148(3) and 1.149(3) A, as normallyobserved in monodentate non-bridging azido ligands.

3.4.2. Packing and hydrogen bonding

The packing diagram is shown in Fig. 2. Organic anionsand the cations form, as usual, alternate layers; they arelinked together by NH� � �O hydrogen bonds, which involveboth the sulphonate and the nitro-oxygens, and weaker

O3

2

3

CH3

H3

SO3

O2N

12

34

5

6

1.

Fig. 1. ORTEPIII view and atom numbering for the title compound. The displacement ellipsoids are drawn at 40% probability.

Fig. 2. Packing diagram of the title compound (view along the a direction).

R. Sharma et al. / Journal of Molecular Structure 800 (2006) 93–99 97

CAH� � �O interactions, which contribute to the crystalarchitecture stability. It is well established that supramolec-ular construction may be achieved with weak CAH� � �Ointeractions because of the electrostatic and therefore longrange character of the hydrogen bonds [44]. The water mol-ecule bridges two adjacent layers, acting both as a H-bondacceptor and donor (see Table 3). In the ‘organic’ layer thebenzenesulphonate anions are stacked, but the C� � �C dis-tance between two adjacent aromatic rings is too long(some 3.9 A) to form the hypothesis of the presence ofp� � �p interactions [45]. A search on the Cambridge data-base (CSD version: November 2004) for Co complexes

having the benzenesulphonate as counterion has shownthat, out of 11 structures retrieved ELAVUI [46]; HEF-SAM [47]; KAGMUB [48]; LIYYAT01,QUKRIX [49];MUNWEY [50]; REZSUK [51]; SUVBUG [52]; TERKIK[53]; TOSWON [54]; WABLIU [55], this anion packingmode is peculiar of the present structure.

Out of the various types of structural motifs found byCSD survey [56], the type of structural motif observed inthe title complex salt is one of the simplest and most com-monly occurring motifs formed between sulphonate oxygenatoms and NAH donor (ethylenediamine), i.e., a bidentatemotif resulting in a 16 membered hydrogen bonded ring

Fig. 3. Packing diagram of [cis-Co(en)2(N3)2]C6H3ClNO5SÆH2O along b-axis.

98 R. Sharma et al. / Journal of Molecular Structure 800 (2006) 93–99

R4,4(16). A view of the packing diagram along b-axis (Fig. 3)shows the formation of a layered structure in the solid state.

4. Conclusions

The potential of cationic metal complex [cis-Co(en)2(N3)2]+ as anion receptor for non-spherical 2-chlo-ro,5-nitrobenzenesulphonate ion has been explored bycharacterizing the newly synthesized salt obtained by react-ing cis-diazidobis(ethylenediamine)cobalt(III) nitrate andsodium 2-chloro,5-nitrobenzenesulphonate in aqueousmedium in 1:1 molar ratio. Single crystal X-ray structuredetermination revealed the composition [cis-Co(en)2(N3)2]C6H3ClNO5SÆH2O. The crystal lattice is stabilized by elec-trostatic forces of attraction and hydrogen-bonding inter-actions involving second-sphere coordination. We havedemonstrated that combination of a large cationic cobal-tammine with arylsulphonate anion leads to the formationof a layered structure in the solid state.

5. Supplementary data

Crystallographic data for the structural analysis of thetitle compound have been deposited at the CambridgeCrystallographic Data Center, 12 Union Road, Cam-bridge, CB2 1EZ, UK, and are available free of chargefrom the Director on request quoting the deposition num-ber CCDC 297877 (Fax: 44 1223 336033, email:deposit@ccdc.cam.ac.uk).

Acknowledgment

The authors gratefully acknowledge the financial sup-port of UGC vide Grant No. F.12-38/2003(SR) dated 31-03-2003.

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