Available online at www.sciencedirect.com

www.elsevier.com/locate/molstruc

Journal of Molecular Structure 886 (2008) 17–23

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

[cis-diazidobis(ethylenediamine)cobalt(III)]-[trans-diamminetetranitrocobaltate(III)]

Rajni Sharma a, Raj Pal Sharma a,*, Paula Brandao b, Vitor Felix b,*

a Department of Chemistry, Panjab University, Chandigarh 160014, Indiab Departamento de Quımica, CICECO, Universidade de Aveiro, 3810-193 Aveiro, Portugal

Received 21 September 2007; received in revised form 21 October 2007; accepted 22 October 2007Available online 4 November 2007

Abstract

Dark maroon coloured single crystals of [cis-Co(en)2(N3)2][trans-Co(NH3)2(NO2)4] were obtained by slowly mixing the separately dis-solved [cis-diazidobis(ethylenediamine)cobalt(III)] nitrate with potassium [trans-diamminetetranitrocobaltate(III)] in aqueous medium in1:1 molar ratio. The complex salt was characterized by elemental analyses, spectroscopic studies (IR, UV/visible, 1H and 13C NMR) andsolubility product measurements. The title complex salt crystallises in triclinic space group P�1 having cell dimensions, a = 7.4210(2),b = 11.0618(3), c = 12.3763(3) A, a = 95.5850(10), b = 91.4400(10), c = 108.9070(10)�, V = 954.853 A3, Z = 2 and R-factor = 5.16%.Single crystal X-ray structure determination revealed an ionic structure consisting of [cis-Co(en)2(N3)2]+ and [trans-Co(NH3)2(NO2)4]�.Supramolecular hydrogen bonding networks involving second sphere coordination like ½NHþen � � �X�anion� besides electrostatic forces ofattraction have been observed to stabilize the crystal lattice. This is the first crystal structure of a salt containing [trans-diamminetetra-nitrocobaltate(III)] anion and [cis-diazidobis(ethylenediamine)cobalt(III)] cation. The formation of complex salt of definite compositionand solubility product measurements show that the cationic cobaltammine [cis-Co(en)2(N3)2]+ is a potential anion receptor for complexanion [trans-Co(NH3)2(NO2)4]� in aqueous medium.� 2008 Published by Elsevier B.V.

Keywords: Cobalt(III); Coordination chemistry; [trans-Diamminetetranitrocobaltate(III)]; Second sphere coordination; Supramolecular chemistry; X-raycrystallography

1. Introduction

An area of interest in supramolecular chemistry thatcontinues to attract attention is the coordination ofanions [1]. A number of rational design and methodolo-gies towards this goal has emerged [2,3]. Reliable supra-molecular synthons based on complementarity of

0022-2860/$ - see front matter � 2008 Published by Elsevier B.V.

doi:10.1016/j.molstruc.2007.10.031

* Corresponding authors. Tel.: +91 0172 2544433; fax: +91 01722545074 (R.P. Sharma); tel.: +351 234 370 729; fax: +351 34 70 084(V. Felix).

E-mail addresses: rpsharma@yahoo.co.in (R.P. Sharma), vitor.felix@ua.pt (V. Felix).

intermolecular interactions have also been identified [4].In this context, the structure directing influence of stronghydrogen bonds such as O–H � � � O, O–H � � � N andN–H � � � O has extensively been used to generate well-rec-ognized association patterns and networks. However, apotential synthetic strategy based on systematic applica-tion of second sphere coordination to build such hydro-gen-bonded networks has not been investigatedelaborately. An important aspect of modern supramolec-ular chemistry [5] is the utilization of ‘‘hydrogen bond-ing” in the development of receptors for therecognition of anions. Solvation effects are also moreprominent for anions than their isoelectronic cations.

18 R. Sharma et al. / Journal of Molecular Structure 886 (2008) 17–23

One of the strategies for the construction of such supra-molecular architecture which can act as reliable anionreceptor is by second sphere coordination[6]; the interac-tion with already coordinatively saturated metal com-plexes and external ligand (anion) through H-bonding.In order to enact second sphere coordination system,some functional group must be appended to the firstsphere ligand. These groups should not coordinate to ametal centre but bind the external ligands, i.e., the anion.Given the inherent intermolecular nature of these interac-tions, their implementation as a means of assemblingmetal complexes is a logical extension of chemistry ofdiscrete species. Therefore, to achieve the desired selectiv-ity, the combination of electrostatic attraction, hydrogenbonding and a suitable framework onto which thesestructural components can be assembled needs to betaken into consideration when designing artificial anionichost [7,8]. During last 30 years, many organic basedanion receptors have been reported, e.g., cationic cyclicpolyamines [9–11], tripodal amines [12], calixarenes [13],sapphyrins [14], azacryptands [15] and azacages or openchain counterparts [16], but sporadic reports are avail-able with cationic transition metal complexes basedanion receptors, i.e., urea based Pt(II) receptor [17] andbipyridine Ru(II) complexes [18]. These anion receptors(cationic metal complexes) are rather difficult to synthe-size or are expensive. We have undertaken an extensiveresearch programme to explore cationic cobaltamminesincluding [Co(en)2X2]+ (X = Cl, NO2 or N3) as anionreceptors (binding agents) in continuation of our interestin cobalt(III) complex salts [19].This is because these cat-ionic metal complex salts could be easily synthesized inexcellent yields from readily available materials andstored for months without any noticeable decomposition.This cation is positively charged, possesses eight N–Hhydrogen bond donor groups and a stable structuralframework onto which anionic components can beassembled. Anions possess different shapes and charges,for example, spherical (halides), octahedral (SiF6

2�), tet-rahedral (PO4

3�, SO42�), triangular (NO3

�), square pla-nar (PtCl4

2�), linear (SCN�, N3�). This paper reports

the utility of [cis-Co(en)2(N3)2]+ present in [cis-Co(en)2(N3)2]NO3 as anion receptor for the monoanion[trans-Co(NH3)2(NO2)4]� which belongs to (i) a rare classof anionic cobaltammines, (ii) played crucial role in earlyconductance measurements and (iii) possesses octahedralshape.

2. Materials

2.1. Caution

Azide salts as well as their complexes should be handledwith care due to their explosive nature.

Technical grade reagents were used throughout thiswork without any further purification. The azido salt,

[cis-Co(en)2(N3)2]NO3 has been prepared according to lit-erature method [20,21].

2.2. Instruments

Cobalt was determined by standard method [22] 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][trans-

Co(NH3)2(NO2)4]

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 (0.5938 g,0.003 mol) of potassium [trans-diamminetetranitrocobal-tate(III)] dissolved in minimum amount of water. The mix-ture, when allowed to evaporate at room temperature, gavethe dark maroon coloured crystals. Crystals, suitable forsingle crystal X-ray structure determination, were collectedafter one day by drawing off the mother liquor and air-dried (yield, 70%). The complex is soluble in water, ethanoland DMSO but insoluble in chloroform. The melting pointof the newly formed complex salt is above 200 �C (dec.).The elemental analysis is consistent with the compositionof [cis-Co(en)2(N3)2][trans-Co(NH3)2(NO2)4]. Found: C,9.1; H, 3.9; N, 41.2; Co, 10.3 for the complex salt, Calcu-lated C, 8.8; H, 4.0; N, 41.4; Co, 10.9. Solubility in waterat room temperature (30 �C): 1 g/100 ml.

2.4. X-ray crystallography

The X-ray data were collected on a CCD Bruker APEXII using graphite monochromatized Mo-Ka radiation(k = 0.71073 A) with the crystal positioned at 35 mm fromthe CCD and the spots were measured using a countingtime of 5 s. Data reduction and empirical absorption werecarried out using the SAINT-NT from Bruker XS. Thestructure was solved by direct methods and by subsequentdifference Fourier syntheses and refined by full matrix leastsquares on F2 using the SHELX-97 system programs [23].Anisotropic thermal parameters were used for all non-hydrogen atoms. Hydrogen atoms bonded to the carbonand nitrogen atoms were included in refinement in calcu-lated positions with isotropic parameters equivalent 1.2times those of the atom to which they are attached. Molec-ular diagrams presented are drawn with graphical packagesoftware PLATON [24]. PLUTON view of the structure isshown in Fig. 1. Crystal data, data collection and refine-ment parameters are summarized in Table 1 and selectedbond lengths and angles are given in Table 2.

Fig. 1. PLUTON view and atom numbering scheme for [cis-Co(en)2(N3)2]+ (left) and [trans-Co(NH3)2(NO2)4]� (right).

Table 1Crystallographic data and refinement parameters of complex salt [cis-Co(en)2(N3)2][trans-Co(NH3)2(NO2)4

Empirical formula C4H22Co2N16O8

Mr 540.24Crystal system TriclinicSpace group P�1a (A) 7.4210(2)b (A) 11.0618(3)c (A) 12.3763(3)a (�) 95.585(1)b (�) 91.440(1)c (�) 108.907(1)V (A3) 954.85(4)Z Z = 2Dc (Mg m�3) 1.879l (mm�1) 1.812Reflections collected 67530Unique reflections, [Rint] 6998, [0.0358]Final R indicesR1, wR2 [I > 2rI] 0.0258, 0.0626R1, wR2 (all data) 0.0328, 0.0665

Table 2Selected bond lengths (A) and angles (�) of complex salt [cis-Co(en)2(N3)2][trans-Co(NH3)2(NO2)4]

[cis-Co(en)2(N3)2]+

Co(1)–N(1) 1.947(1) Co(1)–N(4) 1.965(1)Co(1)–N(5) 1.950(1) Co(1)–N(8) 1.954(1)Co(1)–N(12) 1.954(1) Co(1)–N(15) 1.952(1)N(12)–N(13) 1.200(2) N(13)–N(14) 1.154(2)N(15)–N(16) 1.199(2) N(16)–N(17) 1.153(2)N(1)–Co(1)–N(5) 92.94(4) N(1)–Co(1)–N(12) 90.61(4)N(1)–Co(1)–N(15) 89.30(5) N(5)–Co(1)–N(12) 88.77(5)N(5)–Co(1)–N(15) 175.69(5) N(15)–Co(1)–N(12) 94.89(5)N(1)–Co(1)–N(8) 177.86(4) N(5)–Co(1)–N(8) 85.38(5)N(15)–Co(1)–N(8) 92.46(5) N(12)–Co(1)–N(8) 88.03(4)N(1)–Co(1)–N(4) 85.91(4) N(5)–Co(1)–N(4) 91.21(4)N(15)–Co(1)–N(4) 85.28(5) N(12)–Co(1)–N(4) 176.52(4)N(8)–Co(1)–N(4) 95.44(4)Co(1)–N(12)–N(13) 118.93(9) Co(1)–N(15)–N(16) 120.25(9)N(12)–N(13)–N(14) 176.76(14) N(15)–N(16)–N(17) 176.81(4)

[trans-Co(NH3)2(NO2)4]�

Co(2)–N(23) 1.924(1) Co(2)–N(22) 1.925(1)Co(2)–N(26) 1.938(1) Co(2)–N(24) 1.946(1)Co(2)–N(21) 1.948(1) Co(2)–N(25) 1.951(1)N(23)–Co(2)–N(22) 178.81(4) N(24)–Co(2)–N(21) 178.52(5)N(26)–Co(2)–N(25) 179.45(5) N(23)–Co(2)–N(26) 89.05(4)N(22)–Co(2)–N(26) 90.33(5) N(23)–Co(2)–N(24) 89.76(4)N(22)–Co(2)–N(24) 91.25(5) N(26)–Co(2)–N(24) 89.77(5)N(23)–Co(2)–N(21) 88.85(4) N(22)–Co(2)–N(21) 90.14(5)N(26)–Co(2)–N(21) 90.74(5) N(23)–Co(2)–N(25) 90.62(5)N(22)–Co(2)–N(25) 90.01(5) N(24)–Co(2)–N(25) 89.78(5)N(21)–Co(2)–N(25) 89.70(5)

R. Sharma et al. / Journal of Molecular Structure 886 (2008) 17–23 19

3. Results and discussion

While a large number of azido divalent metal complexeshave been reported, their corresponding cobalt(III) com-plexes are very limited [25–27]. Moreover there are onlyfew reports of X-ray diffraction studies of the azido cobal-t(III) salts in the literature [28–30]. 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 [31].

The chemical composition of the complex salt obtainedby reacting [cis-Co(en)2(N3)2]NO3 with potassium diam-minetetranitrocobaltate in 1:1 molar ratio in aqueous med-

ium is consistent with the formula [cis-Co(en)2(N3)2][trans-Co(NH3)2(NO2)4].

3.1. Measurement of solubility product

Solubility of ionic salts in water differs to a great extentand on the basis of solubility criterion, the salts are

Fig. 2. Plot of square root of concentration versus molar conductance of[cis-Co(en)2(N3)2][trans-Co(NH3)2(NO2)4].

Fig. 3. FT-IR spectrum of [cis-Co(en)2(N3)2][trans-Co(NH3)2(NO2)4].

20 R. Sharma et al. / Journal of Molecular Structure 886 (2008) 17–23

classified into three categories: (a) soluble >0.1 M (soluble),(b) solubility between 0.01 and 0.1 M (slightly soluble) and(c) solubility <0.01 M (sparingly soluble). The solubilitymeasurements at room temperature show that [cis-Co(en)2

(N3)2]NO3 and [cis-Co(en)2(N3)2][trans-Co(NH3)2(NO2)4]are sparingly soluble in water but it is more true for theformer. The solubility product of [cis-Co(en)2(N3)2][trans-Co(NH3)2(NO2)4] is 3.2 � 10�4 as compared to 9.0 � 10�4

of [cis-Co(en)2(N3)2]NO3 which indicates that the affinityor binding of the cation [cis-Co(en)2(N3)2]+ is more for[trans-diamminetetranitrocobaltate(III)] ion as comparedto nitrate ion.

3.2. Molar conductance

The conductance measurement studies were carried out at30 �C in aqueous medium and a plot of K (molar conduc-tance) versus concentration is presented in Fig. 2. When theconcentration was extrapolated to zero, it gave valueKo = 49.2 Sm2 mol�1 for [cis-Co(en)2(N3)2][trans-Co(N-O2)4(NH3)2] which is within the range reported for 1:1 electro-lyte [32] and is comparable to that of other similar cobalt(III)complex salts, e.g., Ko = 51.3 for [cis-diazidobis(ethylenedia-mine)cobalt(III)]2,4-dinitrophenolate, Ko = 69.9 for [cis-diazidobis(ethylenediamine)cobalt(III)]mesitylenesulphonate,Ko = 55.7 for [cis-diazidobis(ethylenediamine)cobalt(III)]-saccharinate, Ko = 51.3 Sm2 mol�1 for [cis-diazidobis(ethy-lenediamine)cobalt(III)]thiocyanate. It is obvious that thenitrate salt behaves as 1:1 electrolyte in aqueous mediumbut title complex salt is much less ionized in the solution. Thismay be ascribed to ion pair formation.

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 literature [33]. The IR absorption band at 828 cm�1

(Fig. 3) is assigned to CH2 rocking region and a band at1564 cm�1 is assigned to NH2 asymmetric deformation[34], which also indicates the cis-geometry of the complex.The IR absorption bands at 2019 and 2089 cm�1 areassigned to asymmetric stretching frequency of azidegroup. The antisymmetric stretching modes of NH3 andNO2 appear at 3263 and 1430 cm�1. The symmetricstretching mode of NO2 appears at 1326 cm�1.

The electronic spectrum of the complex salt has beenrecorded in H2O. The UV/visible absorption spectrum ofthe title complex salt is comparable to that of the similar com-plex cation which shows three absorptions. The complex saltsabsorbs strongly at 511 and 305 nm corresponding to d–dtransitions [35] typical for octahedral low spin cobalt(III)complexes. These electronic transitions are from 1A1g groundstate of cobalt(III) to singlet state 1T1g (low energy) and from1A1g ground state to 1T2g (higher energy). But a specialabsorption band due to nitro radical [35a] appears in theregion 254 nm since this band is extremely bathochromic.

NMR spectra (1H and 13C) of the newly synthesizedcomplex salt were recorded in DMSO-d6. The chemicalshift values are expressed as d value (ppm) downfield fromtetramethylsilane as internal standard. In 1H NMR, thetwo signals at 4.2 and 4.8 ppm are attributed to nitrogenprotons [36] of ethylenediamine ligand while CH2 protonsof ethylenediamine groups were observed at 2.6 ppm. 13CNMR spectrum showed the characteristic signal at44.3 ppm for carbon atoms of ethylenediamine group inthe title complex salt.

3.4. Crystal structure

3.4.1. Coordination geometry and bonding

To determine the structure unambiguously, X-raycrystallography was carried out. The asymmetric unit iscomposed of [cis-Co(en)2(N3)2]+ and [trans-Co(NH3)2

(NO2)4]� linked by N–H � � � O and N–H � � � N hydrogenbonds. The molecular structures of [cis-Co(en)2(N3)2]+

(left) and Co(NH3)2(NO2)4]� (right) are presented inFig. 1 with the atomic numbering scheme employed. Bondlengths and angles subtended at metal centre reported inTable 2 show that in these two complexes, the cobalt(III)metal center adopts the usual slightly distorted octahedralgeometry. The first coordination of complex cation is com-posed of eight nitrogen donors from two ethylendiamineligands and two azide ligands. The N–Co–N angles involv-ing the ethylendiamine nitrogen atoms are less than 90�(c.a. 85�) because of the bite of the bidentate ligand. Theazide ligands are coordinated in a bending fashion with

R. Sharma et al. / Journal of Molecular Structure 886 (2008) 17–23 21

Co–N–N angles 118.93(9) and 120.25(9)�, but the geometryof the azide ligands is nearly linear with N–N–N angle of176.76(14)� The interior N–N bond lengths of 1.120(2)and 1.199(2) A are longer than the terminal N–N lengthsof 1.154(2) and 1.153(2) A, as observed in monodentatenon-bridging azido ligands. The Co–N bond lengths arein the range 1.947(1)–1.965(1) A for nitrogen atoms of eth-ylenediamine ligand and equal to 1.952(1) and 1.954(1) Afor nitrogen atoms of azide ligands. These bond lengthsare in agreement with those observed in other cobalt(III) complexes recently reviewed [37–46] as shown inTable 3a.

Table 3aA comparison of structural parameters (A, �) of azide group in various cation

Formula of the compound Bond lengths

N–N (internal)

[cis-Co(en)2(N3)2][trans-Co(NH3)2(NO2)4] 1.199(2)[cis-Co(en)2(N3)2]C9H11SO3�0.5H2O 1.203(3)[cis-Co(en)2(N3)2]C6H3ClNO5S�H2O 1.197(3)[cis-Co(en)2(N3)2]SCN 1.230(2)[cis-Co(en)2(N3)2]C7H3NClO4�1.25H2O 1.194(2)

Table 3bA comparison of structural parameters (A, �) in [Co(NH3)2(NO2)4]� salts con

Compound Co–NH3 Co–NO2 \H3N–Co(1)–NH3

I 1.94 1.95 180.0II 1.95 1.96 180.0III 1.95 1.95 180.0IV 1.93 1.94 178.0V 1.95 1.96 179.1VI 1.93 1.94 180.0VII 2.00 1.96 180.0VIII 2.01 1.96 –IX 1.94 1.95 178.7

Fig. 4. Packing diagram of [cis-Co(en)2(N3)2][trans-Co(NH3)2(NO2)

A comparison of the Co–N distances for the anion inthe title complex (I) with those found for other relatedcomplexes (Table 3b): [(CH3)4N][trans-Co(NH3)2(NO2)4](II) [41], [(C2H5)4N][trans-Co(NH3)2(NO2)4] (III) [41],[(C3H7)4N][trans-Co(NH3)2(NO2)4] (IV) [42], [(C4H9)4N]-[trans-Co(NH3)2(NO2)4] (V) [43], K[trans-Co(NH3)2-(NO2)4] (VI) [44], NH4[ttrans-Co(NH3)2(NO2)4] (VII)

[35b], [cis-Co(en)2(NO2)2][trans-Co(NH3)2(NO2)4] (VIII)

[45] and [(C2H5)3NCH2C6H5][trans-Co(NH3)2(NO2)4](IX) [46]: shows an appreciable effect of the cation onthe Co–NH3 bond length, while all other structuralparameters of the anion remain unaffected.

ic Co(III) complexes

Bond angles References

N–N (terminal) N–N–N

1.153(2) 176.6(2) This work1.156(3) 173.6(3) [43]1.148(3) 175.9(2) [44]1.181(3) 177.1(2) [45]1.156(3) 176.6(2) [46]

taining different cations

\O2N–Co(1)–NO2 \O2N–Co(1)–NH3 Reference

180.0 90.0 This work180.0 90.0 [37]– 90.0 [37]180.0 90.0 [38]179.6 90.0 [39]180.0 90.0 [40]180.0 90.0 [41]– – [42]179.1 89.9 [35a]

4] showing the hydrogen bond network perpendicular to z axis.

Table 4Hydrogen bonding parameters of [cis-Co(en)2(N3)2][trans-Co(NH3)2(NO2)4]

D–H� � �A* H� � �A/A D� � �A/A D–H� � �A/�

N(1)–H(1A)� � �O(231) 2.20 3.09 163N(1)–H(1A)� � �O(231) 2.58 3.23 138N(1)–H(1A)� � �N(23) 2.70 3.56 156N(1)–H(1B)� � �O(232)i 2.07 2.89 147N(4)–H(4A)� � �O(211)ii 2.49 3.15 129N(4)–H(4A)� � �N(15)iii 2.60 3.32 136N(4)–H(4B)� � �N(17)iv 2.27 3.02 138N(5)–H(5A)� � �O(242) 2.31 3.11 147N(5)–H(5A)� � �O(231) 2.57 3.13 120N(5)–H(5A)� � �N(24) 2.65 3.53 160N(5)–H(5B)� � �N(14)iv 2.14 3.00 156N(8)–H(8A)� � �O(211)ii 2.06 2.94 161N(8)–H(8A)� � �O(212)ii 2.53 3.27 137N(8)–H(8A)� � �N(21)ii 2.58 3.43 154N(8)–H(8B)� � �O(222)v 2.29 3.06 140N(25)–H(251)� � �N(12) 2.41 3.31 173N(25)–H(251)� � �N(13) 2.62 3.47 154N(25)–H(252)� � �O(222) 2.44 2.96 116N(25)–H(253)� � �O(212) 2.17 2.79 124N(26)–H(261)� � �O(241) 2.26 2.71 110N(26)–H(262)� � �O(241) 2.20 2.78 121N(26)–H(262)� � �N(17)vi 2.35 3.17 150N(26)–H(263)� � �O(221)vii 2.13 3.02 164N(26)–H(263)� � �O(221)vii 2.46 2.94 114

Equivalent positions: (i) [�x + 1,�y,�z + 1]; (ii) [x,y + 1,z]; (iii)[�x + 1,�y + 1,�z + 1]; (iv) [x � 1,y,z]; (v) [�x + 1,�y,�z]; (vi)[x � 1,y � 1,z]; (vii) [�x,�y � 1,�z].* A, acceptor; D, donor.

22 R. Sharma et al. / Journal of Molecular Structure 886 (2008) 17–23

3.4.2. Packing and hydrogen bonding

The crystal packing in three dimension shows theformation of a 3-D network of N–H � � � O and N–H � � � Nhydrogen bonds in which chains of [cis-Co(en)2(N3)2]+

Fig. 5. Illustration of the role of N–H(en). . .N(azide) hydrogen bonds in assoccrystal structure of [cis-Co(en)2(N3)2]2 SiF6. Extension of this motif into the (0sides of the ladder.

linked by N–H � � � N hydrogen bonds are linked by [trans-Co(NH3)2(NO2)4]� through N–H � � � O and N–H � � � Nhydrogen bonding interactions forming alternate cationanion layered structures. These structural features are illus-trated in Fig. 4. This involves second sphere coordinationof coordinated NH2 groups of ethylenediamine and nitrogroup of the anion. The hydrogen bond parameters are givenin Table 4. The packing of the title complex salt is quite com-plicated, mainly because of the complexity of the asymmetricunit (formed by two cobalt complexes, one acting as anionand the other as cation), but the layers are still present, inter-connected by N–H � � � O and N–H � � � N hydrogen bonds.We have already reported the structure of [cis-Co(en)2(N3)2]2SiF6 [19a] where this particular three-dimen-sional arrangement is found (Fig. 5), suggesting that it hasto be considered peculiar of the cation irrespective of the nat-ure of the anion.

4. Conclusions

The potential of cationic metal complex [cis-Co(en)2(N3)2]+ as anion receptor for diamminetetranitro-cobaltate(III) ion has been explored by characterizing thenewly synthesized salt obtained by reacting [cis-diazid-obis(ethylenediamine)cobalt(III)] nitrate and potassium[trans-diamminetetranitrocobaltate(III)] in aqueousmedium in 1:1 molar ratio. Single crystal X-ray structuredetermination revealed the composition [cis-Co(en)2(N3)2][trans-Co(NH3)2(NO2)4] consisting of discrete ions. Theformation of definite salt (anhydrous) coupled with solubi-lity product measurements showed that the cationic cobal-tammine is a potential anion receptor for complex anion[trans-Co(NH3)2(NO2)4]�. The crystal lattice is stabilized

iation of the [Co(en)2(N3)2]+ complex cations into the ladder motif in the11) layer is achieved by means of the [SiF6]2� octahedra attached at both

R. Sharma et al. / Journal of Molecular Structure 886 (2008) 17–23 23

by electrostatic forces of attraction and N–H � � � O as wellas N–H � � � N hydrogen bonding interactions involvingsecond sphere coordination.

5. Supplementary data

Crystallographic data for the structural analysis of thetitle compound has been deposited at the Cambridge Crys-tallographic Data Center,12 Union Road, Cambridge, CB21EZ, UK, and are available free of charge from the Direc-tor on request quoting the deposition number CCDC661658 (Fax: +44 1223 336033, email: deposit@ccdc.cam.ac.uk).

Acknowledgment

The authors gratefully acknowledge the financialsupport of UGC vide Grant No. F.12-38/2003(SR) dated31-03-2003.

References

[1] A. Bianchi, K. Bowman-James, E. Garcia-Espana, SupramolecularChemistry of Anions, Wiley-VCH, New York, 1997.

[2] A.P. Cote, M.J. Ferguson, K.A. Khan, G.D. Enright, A.D. Kulynych,S.A. Dalrymple, G.K.H. Shimizu, Inorg. Chem. 41 (2002) 287.

[3] S.A. Dalrymple, G.K.H. Shimizu, Chem. Eur. J. 8 (2002) 3010.[4] V.A. Russell, C.C. Evans, W. Li, M.D. Ward, Science 276 (1997) 575.[5] P.D. Beer, D.K. Smith, Prog. Inorg. Chem. 46 (1997) 1;

P.D. Beer, P.A. Gale, Angew. Chem. Int. Ed. 40 (2001) 487;P.D. Beer, L. Fabbrizzi, M. Liechell, G. Rabaioli, A. Taglietti, Coord.Chem. Rev. 205 (2000) 85.

[6] C. Janiak, CrystEngComm 6 (2004) 126;X.-J. Yang, B. Wu, W.-H. Sun, C. Janiak, Inorg. Chim. Acta 343(2003) 366;X.-J. Yang, B. Wu, C. Janiak, W.-H. Sun, H.-M. Hu, Z. Anorg. Allg.Chem. 630 (2004) 1564.

[7] C.R. Bondy, P.A. Gale, S.J. Loeb, J. Am. Chem. Soc. 126 (2004)5030;S. Nieto, J. Perez, V. Riera, D. Miguel, C. Alvarez, Chem. Commun.(2005) 546.

[8] C.M.G. dos Santos, P.B. Fernandez, S.E. Plush, J.P. Leonard, T.Gunnlaugsson, Chem. Commun. (2007) 3389.

[9] J.M. Llinares, D. Powell, K. Bowman-James, Coord. Chem. Rev. 240(2003) 57.

[10] J.L. Sessler, E. Katayev, G.D. Pantos, Y.A. Ustynyuk, Chem.Commun. (2004) 1276.

[11] C.A. Llioudis, D.A. Tocher, J.W. Steed, J. Am. Chem. Soc. 126(2004) 12395.

[12] M.A. Hosseini, J.A. Liljegren, D. Powell, K. Bowman-James, Inorg.Chem. 43 (2004) 3751.

[13] D.M. Roundhill, H.F. Koch, Chem. Soc. Rev. 31 (2002) 60.[14] J.L. Sessler, J.M. Davis, Acc. Chem. Res. 34 (2001) 989.[15] J. Nelson, V. McKee, G. Morgan, Prog. Inorg. Chem. 47 (1998) 167.

[16] D. Farrell, K. Gloe, K. Gloe, G. Goretzki, V. McKee, J. Nelson, M.Nieuwenhuyzen, I. Pa’l, H. Stephan, R.M. Town, K. Wichmann,Dalton Trans. 1961 (2003).

[17] A.B. Ellis, D.R. Walt, Chem. Rev. 100 (2000) 2477.[18] C.R. Bondy, S.J. Loeb, Coord. Chem. Rev. 240 (2003) 77.[19] (a) R.P. Sharma, R. Bala, R. Sharma, U. Rychlewska, B. Warzajtis,

V. Ferretti, J. Mol. Struct. 753 (2005) 182;(b) R.P. Sharma, R. Sharma, R. Bala, P. Venugopalan, J. Mol.Struct. 789 (2006) 133;(c) R.P. Sharma, R. Sharma, R. Bala, P. Venugopalan, J. Mol. Struct.787 (2006) 69;(d) R.P. Sharma, R. Sharma, R. Bala, K.N. Singh, L. Pretto, V.Ferretti, J. Mol. Struct. 784 (2006) 109;(e) R. Sharma, R.P. Sharma, R. Bala, B.M. Kariuki, J. Mol. Struct.826 (2007) 177.

[20] P.J. Staples, M.L. Tobe, J. Chem. Soc. (1960) 4812.[21] J.N. Cooper, D.A. Smith, M.E. Kastner, J. Chem. Educ. 66 (1989)

968.[22] A.I. Vogel, A Text Book of Quantitative Inorganic Analysis,

Longmans, London, 1961.[23] SHELX-97, G.M. Sheldrick, University of Gottingen, 1997.[24] PLATON program, A.L. Spek, J. Appl. Cryst. 36 (2003) 7.[25] W.G. Jackson, C.M. Begbie, Inorg. Chim. Acta 60 (1982) 115.[26] J.P. Collman, P.W. Schneider, Inorg. Chem. 5 (1966) 1380.[27] R.G. Pearson, P.M. Henry, F. Basola, J. Am. Chem. Soc. 79 (1957)

5378.[28] R.J. Restivo, G. Ferguson, R.W. Hay, D.P. Piplani, J. Chem. Soc.,

Dalton Trans. (1978) 1131.[29] J. Cho, J.C. Kim, A.J. Lough, Inorg. Chem. Commun. 6 (2003) 284.[30] M.E. Kastner, D. Smith, J.N. Cooper, A. Kuzmission, T. Tyree, M.

Yearick, Inorg. Chim. Acta 158 (1989) 185.[31] R. Hargens, W. Min, R.C. Henny, Inorg. Syn. 14 (1973) 78.[32] S.S. Massoud, Polyhedron 3127 (1994).[33] R.J. Angelici, Synthesis and technique in inorganic chemistry,

Saunders Golden Sunburst series, W.B. Saunders company, 1977.[34] K. Nakamoto, Infrared and Raman Spectra of Inorganic and

Coordination Compounds, fourth ed., John Wiley & Sons, NewYork, 1986.

[35] (a) P. Hendry, A. Ludi, Adv. Inorg. Chem. 35 (1990) 117;(b) Y. Komiyama, Bull. Chem. Soc. Jpn. 30 (1957) 13.

[36] I.R. Lantzke, D.W. Watts, Aust. J. Chem. 20 (1967) 35.[37] R.P. Sharma, R. Sharma, R. Bala, K.N. Singh, L. Pretto, V. Ferretti,

J. Mol. Struct. 784 (2006) 109.[38] R. Sharma, R.P. Sharma, R. Bala, L. Pretto, V. Ferretti, J. Mol.

Struct. 800 (2006) 93.[39] R.P. Sharma, R. Sharma, R. Bala, M. Quiros, J.M. Salas, J. Coord.

Chem. 56 (2003) 1581.[40] R. Sharma, R.P. Sharma, P. Venugopalan, M. Quiros, J.M. Salas, J.

Yu, Y. Du, J. Mol. Struct. 885 (2008) 7.[41] R.P. Sharma, B.K. Vermani, R. Sharma, R. Bala, D.S. Gill, J.M.

Salas, M. Quiros, J. Mol. Struct. 784 (2006) 222.[42] B.K. Vermani, R.P. Sharma, D.S. Gill, L. Pretto, V. Ferretti, Acta

Cryst. E62 (2006) m2412.[43] R.P. Sharma, R. Sharma, R. Bala, D.S. Gill, S. Singh, J.K. Puri, L.

Russo, K. Rissanen, J. Chem. Cryst. 36 (2006) 619.[44] I. Bernal, Inorg. Chim. Acta 96 (1985) 99.[45] I. Bernal, Inorg. Chim. Acta 101 (1985) 175.[46] R.P. Sharma, B.K. Vermani, R. Sharma, R. Bala, D.S. Gill, J.M.

Salas, M. Quiros, J. Coord. Chem. 58 (2005) 309.b.