Unexpected chlorination of a pyrazole ligand. Structural characterisation of a new binuclear Cu(II) complex

Inorganic Chemistry Communications 4 (2001) 610±612

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Unexpected chlorination of a pyrazole ligand. Structural characterisation of a new binuclear Cu(II) complex Jose®na Pons a

a,*

, Arafa Chadghan a, Angel Alvarez-Larena b, Joan Francesc Piniella b, Josep Ros a

Departament de Quõmica, Unitat de Quõmica Inorg anica, Universitat Aut onoma de Barcelona, 08193-Bellaterra, Barcelona, Spain b Departament de Geologia, Unitat de Cristallogra®a, Universitat Aut onoma de Barcelona, 08193-Bellaterra, Barcelona, Spain Received 22 June 2001; accepted 16 July 2001

Abstract Crystallisation of Cu…HL1 †2 Cl2
EtOH …HL1 ˆ 3-phenyl-5-…6-methyl-2-pyridyl†pyrazole† in DMF a€ords ‰Cu2 …ClL1 †2 Cl2 …DMF†2 Š, where the C-chlorination of the pyrazolyl ring and the formation of a dinuclear compound is observed. The deprotonated pyrazolyl ligands have three co-ordination positions (two pyrazole nitrogens and one pyridine nitrogen) and simultaneously act as chelate and bridging ligands. Ó 2001 Elsevier Science B.V. All rights reserved. Keywords: Copper complexes; Dinuclear complexes; Pyrazole complexes; Crystal structures

1. Introduction The chemistry of pyrazole and pyrazolate metal complexes is quite extensive [1±4]. One of the major research areas of interest is the study of metallocycles M…pz†n M0 , where pz is a pyrazole or pyrazolate-derived ligand [1]. Numerous double pz-bridged, bimetallic complexes M…pz†2 M0 , are known, normally with monodentate or bidentate ligand groups completing the co-ordination of the metal ions [5]. With few exceptions, the …D†M…pz†n M0 …D†, (D ˆ donor ligand) complexes display boat con®gurations, the M…pz†2 M0 core not being planar [5]. In the course of our studies on 3,5-substituted pyrazoles as ligands, some polynuclear complexes have been isolated and characterised: the tetramer Cu(II) complex ‰Cu4 …L2 †4 …H2 O†4 Š…NO3 †4
4H2 O [6] and the dinuclear Ni(II) compound ‰Ni2 …L2 †2 …MeOH†4 ŠCl2
2H2 O [7] both with the ligand HL2 ˆ 3; 5-bis…2-pyridyl† pyrazole. With this same ligand, Munakata et al. [8] described the tetramer Cu(II) complex ‰Cu4 …L2 †4 …ClO4 †4 Š
2H2 O. We have also reported [9] the dinuclear Pd(II) complex ‰Pd2 …L1 †4 Š with the ligand * Corresponding author. Tel.: +34-93-581-28-95; fax: +34-93-58131-01. E-mail address: Jose®[email protected] (J. Pons).

HL1 ˆ 3-phenyl-5-…6-methyl-2-pyridyl†pyrazole (Fig. 1). HL1 has been known to act as a simple bidentate ligand in octahedral cobalt(II) [10], octahedral nickel(II) [11], and square planar and tetragonal pyramid copper(II) [12,13] mononuclear complexes. In this paper, we describe the obtention, structural characterisation and spectroscopic properties of a dinuclear copper(II) complex containing a modi®ed HL1 ligand. 2. Results and discussion In a general study on crystalisation of the complex, Cu…HL1 †2 Cl2
EtOH [13], in order to obtain suitable single crystals for X-ray di€raction, a solvent evaporation at room temperature was carried out for a DMF solution of the complex. Unexpectedly, a new dinuclear compound ‰Cu2 …ClL1 †2 Cl2 …DMF†2 Š …ClL1 ˆ 4-chloro-3-phenyl-5 -…6-methyl-2-pyridyl†pyrazolate† was obtained with the ligand HL1 chlorinated in the C-4 position. This product is green and gave satisfactory C, H and N elemental analyses. The Mass spectra of the complex are a valuable tool in the determination of the chlorine atom's presence in the ligand …m=z: 271, 269 …C15 H12 N3 Cl‡ ; 45; 15†; 235 …C15 H12 N3 ; 100††. According to IR data Cu atoms are co-ordinated to nitrogen atoms …m…C@C†; m…C@N† 1606; 1573 cm 1 †, to chlorine atoms

1387-7003/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII: S 1 3 8 7 - 7 0 0 3 ( 0 1 ) 0 0 2 8 5 - 4

J. Pons et al. / Inorganic Chemistry Communications 4 (2001) 610±612

Fig. 1. Pyrazole-derived ligands.

…m…Cu±Cl† 272; 258 cm 1 † and to oxygen atoms …m…Cu±ODMF † 283 cm 1 † [14±17]. The pyrazole is deprotonated because the band m…N±H† is not observed. 1 The chlorination of pyrazole is most surprising. Some cases of chlorination of pyrazolate ligands have been described [18±20], but strong oxidising media were present in these reactions, and were considered responsible for generating the actual chlorination agent, t BuOCl or Cl2 [20]. In our case, the experimental conditions are very soft and a non-reaction mechanism was tentatively established. Together with the chlorination, a deprotonation of the ligand occurs and a dinuclear complex is obtained. In relation to deprotonation, it is known that one very weak base such as the acetate ion can deprotonate the HL1 ligand [9]. The structure of the new complex was unequivocally determined by single crystal X-ray di€raction. 2 The molecular structure of Cu2 …ClL1 †2 Cl2 …DMF†2 is illus1

For Cu2 …ClL1 †2 Cl2 …DMF†2 : Yield: 82%. Anal. Found: C, 48.8; H, 4.0; N, 12.5;. Calc. for C18 H18 N4 CuCl: C, 49.0; H 4.1; N 12.7%. IR (KBr): m…C±H†ar 3090; m…C@C†, m…C@N† 1606, 1573; d…C±H†oop 761; m…Cu±N†as 380; m…Cu±O† 283; m…Cu±Cl† 272, 258; m…Cu±N†s ˆ 234 cm 1 . MS…CI; CH4 † m=z: 271, 269 …C15 H12 N3 Cl‡ , 45, 15), 235 …C15 H12 N3 ; 100†. 2 X-ray structure determination of complex Cu2 …ClL1 †2 Cl2 …DMF†2 crystal data: C36 H36 Cl4 Cu2 N8 O2 , M ˆ 881:61, green, crystal size 0:4  0:3  0:2; monoclinic, space group P21 =c (No. 14);  a ˆ 9:487…7†, b ˆ 9:523…3†, c ˆ 20:915…8† A, b ˆ 99:00…3†°, 3 (by least-squares re®nement on di€ractometer 25 V ˆ 1866:3…17† A automatically centered re¯ections), Z ˆ 2; Dc ˆ 1:569 g cm 3 ; F …0 0 0† ˆ 900; l…Mo-Ka† ˆ 1:471 mm 1 . Data collection and processing: data collected on an Enraf-Nonius CAD4 di€ractometer using  and graphite-monochromated Mo-Ka radiation (k ˆ 0:71069 A) x±2h scan, x scan width ˆ 0:80 ‡ 0:35 tan h, x scan speed 1.3±5.5°. Re¯ections ranges for the data collection were 1:97° < h < 24:97°, 11 6 h 6 11, 0 6 k 6 11, 0 6 l 6 24. Lp and empirical absorption corrections [26] were applied, Tmin ˆ 0:739, Tmax ˆ 0:990. 3273 unique re¯ections, 2210 with I > 2r…I†. Structure solution and re®nement: the structure was solved by direct methods (S H E L X S -86) [27] and re®ned by full-matrix least-squares procedures on F 2 for all re¯ections (S H E L X L -97) [28]. All non-hydrogen atoms were re®ned with anisotropic thermal parameters and hydrogen atoms were placed in calculated positions with isotropic temperature factors 1.5 times (methyl hydrogens) or 1.2 times (the rest) the Ueq values of corresponding carbons. The weighting scheme was w ˆ 1=‰r2 …F02 † ‡ …0:2174P †2 Š where P ˆ ‰max…F02 ; 0† ‡ 2Fc2 Š=3. RW …F 2 † ˆ 0:288 for all re¯ections and R…F † ˆ 0:095 for observed re¯ections.

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trated in Fig. 2, and selected bond lengths and angles are listed in Table 1. The molecular structure consists of a centrosymmetrical dinuclear Cu(II) complex containing two coordinated 4-chloro-3-phenyl-5-(6-methyl-2-pyridyl)pyrazolate ligands …ClL1 †. The co-ordination around Cu is a distorted square pyramid (trigonality index s ˆ 0:3168 [21]). The apical site is occupied by a Npz of a ClL1 ligand whose Npy is in the basal plane. Npz of the other ClL1 ligand, a chloride and oxygen of a DMF solvent molecule, de®ne the other three basal positions. The Cu±Npz and Cu±Npy distances are similar to those found previously [6,8,22,23]. However, it is interesting to point out that the existence of a square pyramidal co-ordination with a Npz in apical position implies a Cu±Npz distance longer than the Cu±Npy. Usually, in octahedral, square planar and tetragonal pyramid co-ordinations, we have always found that the Cu±Npz distances were shorter than the Cu±Npy ones. The copper atom forms a ®ve-membered chelate ring [Cu±N11±C16±C23±N22]. The N11±Cu±N22 bite angle is 79.7(3)°, which is comparable to the angles found for mononuclear copper(II) compounds with the ligand HL0 , i.e. 80.4(8)° in ‰Cu…HL0 †…NO3 †…H2 O†2 Š…NO3 † [13] and 80.95(6)° in Cu…L0 †2 [12] and with the dinuclear palladium(II) compound of ligand HL1 , ‰Pd2 …L1 †4 Š, with bite angles 80.2(5)° and 79.2(4)° [9].  is slightly shorter The Cu±Cu distance of 3:917…3† A, than that observed in the complexes ‰Cu4 …L2 †4  [6] and ‰Cu4 …L2 † …H2 O4 †Š…NO3 †4
4H2 O (4.044 A) 4  …ClO4 †4 Š
2H2 O (4.05 A) [8].

Fig. 2. An ORTEP view of the structure ‰Cu2 …ClL1 †2 Cl2 …DMF†2 Š. The displacement ellipsoids enclose 50% probability.

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J. Pons et al. / Inorganic Chemistry Communications 4 (2001) 610±612

Table 1  and angles (°)a Selected distances (A) Cu±Cui Cu±Cl1 Cu±N11 N22±Cu±O41 N11±Cu±O41 N11±Cu±N22 N21i ±Cu±N11 N21i ±Cu±O41 a

iˆ

3.917(3) 2.295(2) 2.010(7) 93.9(2) 86.4(3) 79.7(3) 174.4(3) 88.3(3)

Cu±N21i Cu±N22 Cu±O41 Cl1±Cu±O41 Cl1±Cu±N22 Cl1±Cu±N11 N21i ±Cu±N22 N21i ±Cu±C11

1.940(6) 2.110(7) 2.187(6) 155.40(18) 109.9(2) 91.9(2) 102.3(3) 92.3(2)

x; y; z.

In the new complex, the Cu2 N4 ring is plane and  biggest deviation from the mean plane is (0.028(7) A) and the complex shows two very di€erent Cu±N±N angles. The angle Cu±N22±N21 is 139.6(5)° whereas Cui ±N21±N22 is 117.9(5)°. This di€erence was found in other complexes with a plane Cu2 N4 ring ‰fCu…pt†…D†…NO3 †…H2 O†g2 Š
4H2 O [Hpt ˆ 3-pyridyn2-yl-1,2,4-triazole] [D can be N-methylimidazol, pyrazole or 4; 40 -bipyridineŠ [24] and ‰Cu2 …H2 L†2 ŠCl2 ‰H3 L ˆ 1; 10 -…4-methylpyrazole-3; 5-diyl†diacetaldehydeŠ [25]. In these cases the di€erence between angles is less, 12.7°± 15.9°. The ligand ClL1 is not planar. The pyridyl group is slightly twisted with respect to the pyrazole ring, the py± pz dihedral angle being 4.2(5)°, whereas in the more twisted phenyl group, the ph±pz dihedral angle is 44:2…5†°. The py±pz angle is comparable to those found in the structures Cu…L0 †2 [12] and ‰Cu…HL0 †2 …NO3 † …H2 O†2 Š…NO3 † [13]. The pz±ph angle is larger and comparable to those reported for the compound Pd2 L14 [9].

References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16]

3. Supplementary material Additional material, consisting of fractional atomic co-ordinates, displacement parameters, observed and calculated structure factors and complete list of bond distances and bond angles are available from CCDC, deposition number 166472. Copies of the data can be obtained free of charge on application to Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK (fax: +44-1223-336033; e-mail: [email protected]).

[17] [18] [19] [20] [21] [22] [23] [24]

Acknowledgements We thank MCYT project BQU 2000-0238 for ®nancial support. A. Chadghan is grateful for a grant from the Spanish Ministerio de Asuntos Exteriores: Agencia Espa~ nola de Cooperaci on Internacional (Instituto de cooperaci on con el mundo  arabe).

[25] [26] [27] [28]

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