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Inorganic Chemistry Communications 9 (2006) 1075–1078

First X-ray structure of a cis-isomer of cobalt(III) aromaticcarboxylate: Synthesis, and characterization of

[cis-Co(en)2(C8H7O2)2](C8H7O2) Æ 2H2O,where C8H7O2 = p-methylbenzoate

Rajni Sharma a, Raj Pal Sharma a,*, Ritu Bala a, Miguel Quiros b, Juan M. Salas b

a Department of Chemistry, Panjab University, Chandigarh 160014, Indiab Departamento de Quımica Inorganica, Facultad de Ciencias, Universidad de Granada, Granada 18071, Spain

Received 7 June 2006; accepted 3 July 2006Available online 8 July 2006

Abstract

A new cobalt(III) complex salt, [cis-Co(en)2(C8H7O2)2](C8H7O2) Æ 2H2O, has been synthesized and characterized by single crystal X-ray structure determination. This is the first example of a cobalt(III) compound of this type with two p-methylbenzoate groups in cis-configuration. The cations and anions are associated in chains by strong NH . . . O hydrogen bonds. The crystal lattice is stabilized byextensive hydrogen bonding besides electrostatic forces of attraction.� 2006 Elsevier B.V. All rights reserved.

Keywords: Cobalt(III); Coordination chemistry; Crystal structure; Ethylenediamine; p-Methylbenzoate; NMR spectroscopy

Although cis- and trans-isomers of Co(III) complexes,e.g., [Co(en)2(H2O)Cl]2+ [1], [Co(en)2(halogenoacetato)2]+

[2], [Co(en)2(N3)(C2O4)] [3] are known in the literaturebut in the case of [Co(pn)2(p-chlorobenzoato)2]+ [4] aswell as [Co(en)2(benzoate)2] namely, [Co(en)2(p-fluor-obenzoato)2] [5], [Co(en)2)(p-aminobenzoato)2]+ [6], allthe complexes known have trans-configuration wherepn = propylenediamine and en = ethylenediamine. Duringinvestigation of the reactions of [trans-Co(en)2)Cl2]Clwith various sodium benzoate salts, we have isolatedand characterized for the first time a cis-compound,[Co(en)2(C8H7O2)2](C8H7O2) Æ 2H2O (C8H7O2 = p-methyl-benzoate) [7] in continuation of our interest in cobalt(III)

1387-7003/$ - see front matter � 2006 Elsevier B.V. All rights reserved.

doi:10.1016/j.inoche.2006.07.002

* Corresponding author. Tel.: +91 1722534433.E-mail address: rpsharma@pu.ac.in (R.P. Sharma).

salts [8–10]. X-ray structure determination of this com-pound [11] is described here.

[trans-Co(en)2Cl2]Cl + 3NaC8H7O2

[trans-Co(en)2(C8H7O2)2](C8H7O2)(Expected)

[cis-Co(en)2(C8H7O2)2](C8H7O2)(Unexpected)

In the complex cation [cis-Co(en)2(C8H7O2)2]+, thecobalt(III) is bonded to four nitrogen atoms, originatingfrom two ethylenediamine molecules, and two oxygenatoms of two carboxylate groups showing an octahedralgeometry around cobalt.

The coordination of carboxylate to metal ion has beenstudied extensively by infrared spectroscopy. To distin-guish between the various bonding modes of carboxylatepresent in a compound, the magnitude of separation,Dm cm�1 between mas(COO�) and ms(COO�) is often used

1076 R. Sharma et al. / Inorganic Chemistry Communications 9 (2006) 1075–1078

[12,13] as diagnostic for structure elucidation. The infraredabsorption bands in the title complex salt observed at 1602and 1342 cm�1 are assigned to mas(COO�) and ms(COO�),the value of Dm = 260 cm�1 indicated the presence ofmonodentate carboxylate group. For the ionic carboxylategroup, the values of mas(COO�) and ms(COO�) overlap withthe region of m(C@C) and dasNH2, i.e., 1458 and1551 cm�1. It is, therefore, obvious that the characteristicabsorption bands of coordinated carboxylate groups areeasily seen in the IR spectrum (see Fig. 1) but those ofthe non-coordinated carboxylate group are obscured dueto overlap with other groups. In 1H NMR spectrum, thefour NAH signals observed at 4.8, 6.0, 6.2 and 7.3 ppmstrongly indicated the cis-geometry [14] of metal complex.The signals due to coordinated and non-coordinated p-methylbenzoate groups are clearly seen in the 13C NMRbut not in the 1H NMR (see Fig. 2).

X-ray structure determination revealed that there aretwo organic carboxylate anions monodentately coordi-nated to the metal ion and a third non-coordinated car-boxylate anion. The disposition of the ligands aroundthe metal is all-cis. The complex salt is stabilized by intra-molecular H-bonds of ethylenediamine ligands with thenon-coordinated O-atoms of the coordinated anions.The complex cation and the non-coordinated anion are

Fig. 1. Infrared spectrum of [Co(en

associated in ionic pairs through two H-bonds, from eachen molecule towards each oxygen atom of the carboxylate(see Fig. 3).

Bond distances around the cobalt atom are, 1.91 A(CoAO), 1.94, 1.94, 1.95, 1.95 A (CoAN(3E), CoAN(1E),CoAN(4E), CoAN(2E); the coordination octahedron issomewhat distorted, the main distortions being the chelat-ing N(3E)ACoAN(4E) angle (86.10�), N(1E)ACoAN(2E)angle (86.38�) and the O(11A)ACoAO(11B) angle is91.13�. Non-coordinated OACAO angle in methylbenzo-ate is 123.4� and coordinated OACAO angle is 125.0�.The CAO bond lengths in non-coordinated methylbenzo-ate group are 1.24 and 1.27 A while the correspondingaverage values in the coordinated group are 1.24 and1.29 A. The CSD search did not show a single entry of[cis-Co(en)2(benzoate)2] structure which means this is firststructure of its type.

In conclusion, a new cobalt(III) complex [Co(en)2(C8H7-

O2)2](C8H7O2) Æ 2H2O with cis-geometry around cobal-t(III) consisting of discrete ions, has been unexpectedlyisolated and characterized for the first time from the reac-tion of [trans-Co(en)2)Cl2]Cl with sodium p-methylbenzo-ate (1:3 molar ratio) in aqueous medium followed byslow evaporation of its solution in methanol–watermixture.

)2(C8H7O2)2](C8H7O2) Æ 2H2O.

Fig. 3. ORTEP III view and atom numbering scheme for [cis-Co(en)2

(C8H7O2)2] (C8H7O2) Æ 2H2O only one of the alternative positions for C4Eis displayed.

Fig. 2. NMR spectra: (a) 1H NMR and (b) 13C NMR for [cis-Co(en)2(C8H7O2)2] (C8H7O2 Æ 2H2O).

R. Sharma et al. / Inorganic Chemistry Communications 9 (2006) 1075–1078 1077

Appendix A. Supplementary data

Supplementary data associated with this article can befound, in the online version, at doi:10.1016/j.inoche.2006.07.002.

References

[1] (a) E.A. Dittmar, R.D. Archer, J. Am. Chem. Soc. 90 (1968)1468;(b) A. Guerrero-Laverat, A. Ramirez, A. Jeronimo, A. Santos, F.Florencio, S. Martinez-Carrera, S.G. Blanco, Inorg. Chim. Acta128 (1987) 113;(c) V. Janickis, K. Marøy, Acta Chem. Scand. 48 (1994)465.

[2] E.B. Kipp, R.A. Haines, Can. J. Chem. 47 (1969) 1073.[3] M.E. Kastner, D.A. Smith, J.N. Cooper, A.G. Kuzmission, T. Tyree,

M. Yearick, Inorg. Chim. Acta 158 (1989) 185.[4] M.R. Sundberg, R. Uggla, R. Kivekas, Inorg. Chim. Acta 232 (1995)

1.[5] R.P. Sharma, R. Sharma, R. Bala, B.M. Kariuki, J. Mol. Struct.,

submitted for publication.[6] R.P. Sharma, R. Sharma, R. Bala, P. Venugopalan, J. Chem.

Crystallog. 35 (2005) 595.[7] Synthesis of the title compound: An aqueous solution of one gram

(0.003 mol) of [trans-Co(en)2Cl2]Cl in 25 ml water was added to0.42 g sodium hydroxide mixed with 1.40 g (0.01 mol) of p-toluic aciddissolved in minimum amount of water. The mixture, when allowedto evaporate at room temperature for one day, gave violet coloredpowder. Crystals suitable for single crystal X-ray structure determi-nation were obtained from methanol–water mixture which werecollected by drawing off the mother liquor and air-dried (yield, 70%).The complex is soluble in water, ethanol and DMSO. The complexsalt decomposes at 210 �C. The elemental analysis is consistent withthe composition [Co(en)2(C8H7O2)2] (C8H7O2) Æ 2H2O. Found: C,54.3; H, 6.5; N, 9.1. Calculated, 54.1; H, 6.6; N, 9.0. 0.46 in 100 mlKsp 4 · 10�5. FT-IR (KBr pellet): (CH2) rocking 891, m(C@C)/ms(COO�) 1458, DasNH2/mas(COO�) 1551 cm�1 which are compara-ble with the literature values [2]. Electronic spectrum (in H2O): kmax

503, 360 and 238 nm corresponding to d–d transitions typical foroctahedral low spin cobalt(III) salts. 1H NMR d (ppm) = 4.8, 6.0, 6.2and 7.3 [8H, NH2(en)], 2.3 [3H, CH3(methylbenzoate)], 2.4–2.8 [8H,CH2(en)], 7.1,7.7 [4H, aromatic]. 13C NMR d (ppm) = 43.4 and 44.8[CH2(en)], 21.0 [CH3, (methylbenzoate)], 129.1, 133.6, 140.1, 175.9[non-coordinated aromatic (methylbenzoate)], 128.0, 129.6, 138.4,170.2 [coordinated aromatic (methylbenzoate)].

[8] R.P. Sharma, R. Bala, R. Sharma, P. Venugopalan, CrystEngComm.8 (2006) 215.

[9] R. Bala, R.P. Sharma, R. Sharma, B.M. Kariuki, Inorg. Chem.Commun. 9 (2006) 852.

[10] R. Sharma, R.P. Sharma, R. Bala, J.M. Salas, M. Quiros, Inorg.Chem. Commun. 9 (2006) 782.

[11] Crystal data for the title compound: [Co(en)2(C8H7O2)2](C8H7O2).2H2O, monoclinic, space group C2/c, a = 36.332(2) A,b = 9.1289(5) A, c = 19.2431(11) A, b = 103.487(1)�, V = 6206.4(6)A3, Z = 8, Dc = 1.328 Mg/m3, l = 0.605 mm�1, R (for reflectionswith I > 2r(I)) = 0.0497, wR2 (for all data) = 0.1321. Data werecollected at room temperature for a crystal with dimensions0.54 · 0.46 · 0.24 mm in a Bruker SMART APEX CCD systemwith Mo Ka radiation. 14874 independent reflections were used forstructure solution and refinement in F2 by means of the SHELX-97[15] package. One of the carbon atoms of one of the en ligands(C4E) has been disordered between two equally populated positionsand isotropically refined with restrained CAC and CAN distances.Void spaces of ca. 37 A3 are detected by means of the PLATON [16]package on positions at the binary axis. Nevertheless the integrationof the residual electron density at these spaces suggest that they are‘‘real voids’’, so no further action has been taken about it. Completecrystallographic data have been deposited at the CambridgeCrystallographic Data Centre (CCDC No. 609653) and may beobtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html.

1078 R. Sharma et al. / Inorganic Chemistry Communications 9 (2006) 1075–1078

[12] A.M. Greenaway, T.P. Dasgupta, K.C. Koshy, G.G. Sadler, Spec-trochim. Acta A 42 (1986) 949.

[13] K.C. Patil, G.V. Chandrashekhar, M.V. George, C.N.R. Rao, Can. J.Chem. 46 (1967) 233.

[14] I.R. Lantzke, D.W. Watts, Aust. J. Chem. 20 (1967) 35.

[15] G.M. Sheldrick, SHELXL-97. Program for the Refinementof Crystal Structures, University of Gottingen, Germany,1997.

[16] A.L. Speek, PLATON. A Multipurpose Crystallographic Tool,University of Utrecht, The Netherlands, 2003.