Synthesis, Characterization and Structure of the Bis(Methyl-Cyclopentadienyl)Vanadium(IV) Carboxylates

CEJC 3(1) 2005 157–168

Synthesis, characterization and structure of the Bis(methyl-cyclopentadienyl)vanadium(IV) carboxylates

Jarom´ır Vinklárek1∗, Jan Honz´ıˇcek1, Ivana C´ısaˇrová2, Martin Pavliˇsta3, Jana Holubová1 1 The Department of General and Inorganic Chemistry, University of Pardubice, nám. Cs.ˇ legi´ı565, 532 10 Pardubice, Czech Republic 2 Department of Inorganic Chemistry, Charles University, Hlavova 2030, 128 40 Prague 2, Czech Republic 3 Research Centre “New Inorganic Compounds and Advanced Materials”, University of Pardubice, nám. Cs.ˇ legi´ı565, 532 10 Pardubice, Czech Republic

Received 1 July 2004; accepted 18 November 2004

Abstract: The 1,1’-dimethylvanadocene dichloride ((C5H4CH3)2VCl2) reacts in aqueous solution with various carboxylic acids giving two diﬀerent types of complexes. The 1,1’- dimethylvanadocene complexes of monocarboxylic acids (C5H4CH3)2V(OOCR)2 (R = H, CCl3, CF3, C6H5) contain two monodentate carboxylic ligands, whereas oxalic and malonic acids act as chelate compounds of the formula (C5H4CH3)2V(OOC-A-COO) (A= –, CH2). The structure of the (C5H4CH3)2V(OOCCF3)2 complex was determined by single crystal X-ray diﬀraction analysis. The isotropic and anisotropic EPR spectra of all the complexes prepared were recorded. The obtained EPR parameter values were found to be in agreement with proposed structures. c Central European Science Journals. All rights reserved.

Keywords: bent metallocene, 1,1’-dimethylvanadocene dichloride, antitumor agent, EPR spectroscopy, X-ray diﬀraction analysis

∗ E-mail: [email protected] 158 J. Vinkl´arek et al. / Central European Journal of Chemistry 3(1) 2005 157–168

1 Introduction

The titanocene- and vanadocene dichlorides, (C5H5)2MCl2(M = Ti, V), exhibit antitumor activity for a wide variety of human tumors with reduced toxicity [1-4]. The biological experiments showed that both the water solubility and the stability of bent 2+ [(C5H5)2M] fragment are the limiting factors in application of such pharmaceuticals. The bent metallocene dichlorides can be modified either by substitution of the chlo- ride ligands [5,6] or by substitution on the cyclopentadienyl rings [7,8]. Some of the recently prepared titanocene dichloride derivatives showed significantly better activity and stability than corresponding non-substituded counterparts [9-12]. These findings prompted us to study water-soluble vanadocene compounds [13-15]. Here, we report the preparation and structural characterization of 1,1’-dimethylvanadocene complexes with monocarboxylic (C5H4CH3)2V(OOCR2)2 (R=H, CCl3, CF3, C6H5) and dicarboxylic acids

(C5H4CH3)2V(OOC-A-COO) (A= –, CH2).

2 Results and discussion

The reactions of the 1,1’-dimethylvanadocene dichloride ((C5H4CH3)2VCl2) (1) with mono- and dicarboxylic acids in water media yield appropriate 1,1’-dimethylvanadocene carboxylates of the general formulae (C5H4CH3)2V(OOCR)2 (R=H(3), CCl3 (4),

CF3 (5), C6H5 (6)) and (C5H4CH3)2V(OOC-A-COO) (A= – (7), CH2 (8)), respectively (see Scheme 1).

Scheme 1 Proposed structures of carboxylic acid complexes.

The infrared and Raman spectra of all complexes studied exhibit a number of char- acteristic bands originating from the fundamental vibrations of the η5-bonded methylcy- −1 clopentadienyl ring: C5H4:C-H stretching (3084-3136 cm ), CH3: C-H stretching (2936- −1 −1 2926 cm ), C5H4: C-H bending (IR: 825-863 cm ) [17]. Typical spectral features of all carboxylate complexes are very intensive bands of νa(COO) stretching (IR: 1630-1695 cm−1). In agreement with earlier reports on the coordination behavior of carboxylic acid J. Vinkl´arek et al. / Central European Journal of Chemistry 3(1) 2005 157–168 159

with metals, νa(COO) are shifted to higher wavelengths compared with those for the par- ent carboxylic acids [18]. In the case of complexes 7 and 8 two sharp bands of νa(COO) vibration were found. This coupling of carbonyl vibration can be observed for the dicarboxylic acids with the shortest carbon chain (oxalates and malonates) [19]. Vibrational spectra of complexes 7 and 8 do not show the bands corresponding to free COOH group [20]. These results indicate participation of both carboxylic groups in the bonding to dimethylvanadocene fragment in case of complexes 7 and 8. The paramagnetism of the central metal atom d1V(IV) and its nuclear spin (51V: I=7/2, abundance 99.8 %) make vanadocene(IV) complexes to be a suitable EPR structural probe. As follows from our recent studies, different bonding modes of acidoligands on the vanadium atom induce changes in hyperfine coupling (HFC) tensor of EPR spectra [13,21] and thus account for the isotropic HFC constants of monodentate and chelate ligands substantially differ. That is why they can be considered as a basic evidence of the bonding manner of the ligand. The EPR spectra of all complexes 3-8 give simple eight-line spectra indicating pres- ence of only one paramagnetic species. The values of isotropic and anisotropic EPR parameters of studied compounds are listed in Table 1.

3 4 5 6 7 8

Aiso -220.8 -222.2 -222.5 -221.2 -190.8 -207.6 Tx -24.4 -26.8 -27.8 -22.7 -49.7 -40.6 Ty -137.9 -134.0 -134.8 -147.7 -117.9 -127.6 Tz 162.3 160.8 162.6 170.5 167.6 168.2 giso 1.981 1.980 1.981 1.981 1.984 1.981 gx 1.986 1.988 1.985 1.986 1.990 1.984 gy 1.952 1.952 1.952 1.952 1.963 1.957 gz 2.006 2.001 2.007 2.005 1.999 2.003

Table 1 The HFC tensor [MHz] and g-tensor of 1,1’-dimethyl vanadocene complexes.

The monocarboxylic acids complexes 3-6 show very similar HFC tensors with isotropic HFC constants ranging in the narrow interval (220.8 – 222.5 MHz). The same holds for their anisotropic parts of HFC tensors. X-ray structure determination of 5 (vide infra) shows that monocarboxylic acid ligand is univalent. Thence we can presume that the same bonding manner occurs in the complexes 3-6. On the other hand, the EPR parameters obtained for 1,1’-dimethylvanadocene complexes of dicarboxylic acids (oxalic acid 7 and malonic acid 8) are considerably different. The isotropic HFC constant values for 7 and 8 are much lower than those found for 3-6 indicating different bonding manner of carboxylic acids to the central vanadium atom in comparison with the monocarboxylic acid complexes (see Scheme 1). Although it was not possible to obtain X-ray suitable crystals of the complexes 7 and 8, their structure can be elucidated using anisotropic and isotropic EPR parameters. From the previous investigations [22], it is obvious that the methyl group pendant on 160 J. Vinklárek et al. / Central European Journal of Chemistry 3(1) 2005 157–168

Fig. 1 Frozen solution EPR spectrum of complex 5 (in methanol). (A) experimental spectrum, (B) computer simulation (gx = 1.988, gy = 1.952, gz = 2.001, Ax = 249.1 MHz, Ay = 356.2 MHz, Az = 61.4 MHz, ν = 9.2785 GHz). the cyclopentadienyl rings do not inﬂuence the electron density distribution on the central 51 V(IV) metal atom, hence, the EPR parameter values of (C5H5)2VX2 complexes are identical with those for (C5H4CH3)2VX2 compounds. Indeed, the anisotropic and isotropic parameter values are nearly identical for both 1,1’-dimethylvanadocene carboxylates 7 and 8 and corresponding unsubstituted analogs, the structures of which were previously elucidated on the basis of X-ray analyses, EPR spectra and theoretical calculations [13]. Thus, the complexes 7 and 8 are supposed to retain the same structure as corresponding unsubtituted counterparts.

V1-O1 2.0281(18) V-Cg1 a 1.9668(12) O1-V-O1i 89.67(10) Cg1-V-Cg1ia 133.25(6)

a Cg - the centroid of the cyclopentadienyl ring.

Table 2 Selected bond lengths (A)˚ and bond angles (deg) for complex 5.

The X-ray structure of the complex 5 is shown in Fig 2. Selected bond distances and bond angles are listed in Table 2 and crystallographic data are given in Table 3. The

compound 5 has rigorous C2 symmetry. The vanadium central atom exhibits quasitetra- hedral geometry with two η5-bonded methylcyclopentadienyl rings and two monodentate triﬂuoroacetate ligands. The V-ring centroid distance (1.97 A)˚ and ring centroid-V-ring centroid angle (133.3◦) are comparable to those in other 1,1’-dimethylvanadocene complexes [22]. The methylcyclopentadienyl rings have the staggered conformation with the methyl groups positioned at the opposite sides of the molecule, directed away from each other. The bond distances V-O (2.028 A)˚ are close to corresponding distances J. Vinkl´arek et al. / Central European Journal of Chemistry 3(1) 2005 157–168 161

Fig. 2 ORTEP drawing of the molecular structure of complex 5 with atom numbering of sym- metrically independent part. The second part of molecule is related by rotation around the twofold axis along b. (ellipsoids: 30 % probability). For atoms with positional disorder only one set is shown (labeled with suﬃx A).

found in the complexes (C5H5)2V(OOCCCl3)2 (2.031 A)˚ and (C5H5)2V(OOC)2 (2.021 A,˚ 2.038 A)˚ [13] and they are somewhat longer than those in titanocene(IV) complexes

(C5H5)2Ti(OOCCF3)2 (1.979 A,˚ 1.970 A)˚ [23], (C5H5)2Ti(OOCH)2 (1.951 A,˚ 1.952 A)˚ [24]. Unlike the great majority of titanocene(IV) and vanadocene(IV) carboxylate complexes, in which the “carbonyl” oxygen atoms of the COO groups are pointed apart, in the case complex 5 these oxygens are pointed towards the O-V-O angle. This diﬀerent conformation of COO groups manifests both in the higher value of the bite angle (89.7 ◦ ◦ ) compared to that one in complex (C5H5)2V(OOCCCl3)2 (77.6 ) [13] and in the value of the dihedral O(1’)-V(1)-O(1)-C(7) angle (38.2 ◦) which is considerably diﬀerent in comparison with other similar complexes (140-180 ◦) [13,23-26].

3 Conclusion

Two different groups of 1,1’-dimethylvanadocene complexes were prepared and charac- terized. The (C5H4CH3)2V(OOCR)2 (R = H, CCl3, CF3, C6H5) complexes contain two monocarboxylic acids derived ligands that are monodentately bonded to the 1.1’- dimethylvanadocene fragment, while the oxalic and malonic acids give chelate complexes of the type (C5H4CH3)2V(OOC-A-COO) (A= –, CH2). The structure of trifluoroacetate complex (C5H4CH3)2V(OOCCF3)2 was determined by single crystal X-ray analysis. The EPR parameters of all compounds compare well with those found for similar complexes. 162 J. Vinklárek et al. / Central European Journal of Chemistry 3(1) 2005 157–168

It was found that methyl substitution in cyclopentadienyl rings does not considerably decrease water solubility of these complexes. This is an important assumption for their possible cytostatic activity testing.

4 Experimental section

4.1 Methods and materials

All reactions and manipulations were performed under an inert atmosphere of argon using the standard Schlenk techniques. Water was deionized, double distilled and thoroughly saturated with argon. Other solvents were dried by standard methods and saturated with argon.

4.2 Spectroscopic measurements

The EPR spectra were recorded on the ERS 221 (ZWG Berlin) spectrometer at X-band.

Isotropic spectra were measured in solutions (CH2Cl2, CH3OH or water) at 293 K. The anisotropic spectra were obtained from frozen solutions (CH3OH) at 77 K. They showed two well resolved sets of hyperﬁne features. The third components of g- and A tensors were obtained from computer simulation (SimFonia v.1.2, Bruker). The second-order perturbation theory for the interaction of unpaired electronic spin with vanadium nuclear spin, the anisotropic linewidths and the mixed Lorentzian/Gaussian lineshapes were used.

The isotropic (Aiso) and anisotropic (T ) components of the experimentally obtained HFC tensors were calculated using the equation A = Aiso + T . The IR 4000-350 cm−1 region spectra were recorded on a Perkin-Elmer 684 using Nujol mulls between KBr windows. Raman spectra were recorded on a Bruker IFS 55 s with extension FRA 106 (λ = 1064 nm, 180 deg, 30 mW) in the 50 - 3500 cm−1region at the resolution 2 cm−1. Elemental analyses were performed on the automatic analyzer EA 1108 FISONS.

4.3 Preparation of compounds

The complexes 3-8 were prepared by reaction of 1 and appropriate carboxylic acid. The complex 1 was prepared from vanadium tetrachloride and sodium methylcyclopentadi- enide in toluene according the standard method [22] (EPR (CH2Cl2): Aiso = 74.5 G; giso = 1.988). The water solution of 1 exhibits a simple eight-line EPR spectrum with 2+ parameters Aiso = 79.5 G; giso = 1.9805 that correspond to [(C5H4CH3)2V(OH2)2] (2) species as it was found in the case of its non-substituted counterpart [16]. The purity of the prepared complexes was checked by elemental analysis and EPR, IR, and Raman spectroscopy. J. Vinkl´arek et al. / Central European Journal of Chemistry 3(1) 2005 157–168 163

4.3.1 Synthesis of (C5H4CH3)2V(OOCH)2 (3)

0.5 g (1.78 mmol) of 1 was dissolved in 50 ml formic acid (98 %). 0.61 g (2.21 mmol)

Ag2CO3 was added into this solution and the formed suspension was stirred for 10 minutes. The suspension was filtered off and the filtrate was evaporated to dryness. The

crude product was recrystallized from 25 ml CH2Cl2 and dried in vacuo.

Complex (C5H4CH3)2V(OOCH)2 (3). Yield: 0.26 g; 0.96 mmol; 48.4 %; Calc. for

C14H16O4V (MW 299.21): C 56.20, H 5.39 Anal. Found: C 56.01, H 5.24; EPR (CH2Cl2 solution): Aiso = 79.6 G, giso = 1.981; EPR (frozen CH3OH solution): Ax = 88.2 G, Ay = 131.3 G, gx = 1.986, gy = 1.952; IR (KBr, nujol mull): 3102w, 2725w, 2524w, 2481m, 1736w, 1636w, 1615w 1588w 1565s, 1340vw, 1321vw, 1283w, 1180vw, 1083w, 1024vw, 970m, 933vw, 850m, 804vw, 774w, 753wv, 723m, 665w, 519w; Raman: 3767w, 3163w, 3029w, 2933m, 503m, 433w, 339m, 257m.

4.3.2 Synthesis of (C5H4CH3)2V(OOCCCl3)2 (4)

0.5 g (1.78 mmol) of 1 was dissolved in 10 ml water. 1 ml (9.91 mmol) of trichloroacetic acid was added to the solution. The formed suspension was stirred for 10 minutes, ﬁltered oﬀ and washed twice with 20 ml water. The solid residuum was dried in vacuo. The crude

product was recrystallized from 25 ml CH2Cl2 and dried in vacuo.

Complex (C5H4CH3)2V(OOCCCl3)2 (4). Yield: 0.71 g; 1.40 mmol; 70.9 %; Calc. for

C16H14Cl6O4V (MW 533.95): C 35.99, H 2.64, Cl 39.84; Anal. Found: C 36.12, H 2.54,

Cl 40.05; EPR (CH3OH solution): Aiso = 80.2 G, giso = 1.980; EPR (frozen CH2Cl2 solution): Ax = 89.5 G, Ay = 130.4 G, gx = 1.988, gy = 1.952; IR: 3418s,br, 3110m, 2723w, 2378vw, 1678vs, 1560w, 1495m, 1333s, 1319vs, 1262vw, 1142vw, 1090w, 1025vw, 950vw, 922vw, 863w, 833s, 744s, 683s, 607w, 513m, 449w; Raman: 3787w, 3218w, 3101w, 2926m, 1985m, 1678w, 1495m, 433m, 403m, 343m, 339s, 249s.

4.3.3 Synthesis of (C5H4CH3)2V(OOCCF3)2 (5)

0.5 g (1.78 mmol) of 1 was dissolved in 25 ml water and 1 ml (13.46 mmol) of trifluo- roacetic acid was added to the solution. The formed suspension was stirred for 10 minutes then filtered off and the solid residuum was dried in vacuo. The crude product was re-

crystallized from 25 ml CH2Cl2 and dried in vacuo.

Complex (C5H4CH3)2V(OOCCF3)2 (5). Yield: 0.45 g; 1.11 mmol; 55.8 %. Calc.

for C16H14F6O4V (MW 435.22): C 44.16, H 3.24, Anal. Found: C 44.03, H 3.16; EPR

(CH2Cl2 solution): Aiso = 80.3 G, giso = 1.981; EPR (frozen CH3OH solution): Ax = 90.1 G, Ay = 130.8 G, gx = 1.985, gy = 1.952; IR (KBr, nujol mull): 3653w, 3362vw, 3136m, 2720w, 2672vw, 2379vw, 2345w, 1720s, 1704s, 1572m, 1500m, 1407s, 1195vs, 1139s, 1073w, 1037m, 929w, 915w, 835s, 782s, 715s, 668w, 604m, 563w, 520w, 505w, 439w; Raman: 275m, 337w, 409m, 473m, 970m, 1077s, 1641m, 2943m, 3101w, 3131w, 3454m, 3773s. 164 J. Vinkl´arek et al. / Central European Journal of Chemistry 3(1) 2005 157–168

4.3.4 Synthesis of (C5H4CH3)2V(OOCC6H5)2 (6) 0.5 g (1.78 mmol) of 1 was dissolved in 25 ml of water. 0.44 g (3.60 mmol) of benzoic

acid was dissolved in 20 ml of CH2Cl2 and then was added to the solution of 1. The mixture was vigorously stirred and solution of NaOH (3.50 mmol) in water (7 ml) was added. The CH2Cl2 phase was separated and dried over sodium sulfate. The solvent was evaporated and the crude product was recrystallized from CH2Cl2.

Complex (C5H4CH3)2V(OOCC6H5) (6). Yield: 0.27g; 0.95 mmol; 48.2 %; Calc. for

C26H24O4V (MW 317.43): C 60.35, H 5.06; Anal. Found: C 59.97, H 4.89; EPR (CH2Cl2 solution): Aiso = 79.8 G; giso = 1.981; EPR (frozen CH3OH) Ax = 87.8 G, Ay = 135.0 G, gx = 1.986, gy = 1.952; IR (KBr, nujol mull): 3102w, 3065vw, 3023vw, 2727vw, 2678w, 2556vw, 2488vw, 2382vw, 2342vw, 2307vw, 2051w, 1971vw, 1912w, 1829vw, 1696m, 1609vs, 1575s, 1540w, 1498m, 1418m, 1356vs, 1334vs, 1300m, 1260w, 1169m, 1132m, 1101w, 1065m, 1024m, 937m, 847s, 718vs, 691w, 677s, 638vw, 606w, 570w, 430w, 387w; Raman: 3685m, 3277w, 3126m, 3060s, 2922s, 1601s, 1353s, 1259w, 1051w, 1002vs, 492w, 421w, 355m, 288s, 239s, 172m.

4.3.5 Synthesis of (C5H4CH3)2V(COO)2 (7) 0.5 g (1.78 mmol) of 1 was dissolved in the solution of oxalic acid (20 ml water, 15.08 mmol

(COOH)2·2H2O). 1.4 g (5.08 mmol) Ag2CO3 was added into the reaction mixture and resulting suspension was stirred for 10 minutes. The suspension was filtered off and the filtrate was evaporated to dryness. The excess of oxalic acid was removed by extraction with acetone. Then the crude product was recrystallized from 25 ml of methanol and dried in vacuo.

Complex (C5H4CH3)2V(OOC)2(7). Yield: 0.42 g; 1.34 mmol; 67.5 %. Calc. for

C14H14O4V (MW 297.21): C 56.58, H 4.75; Anal. Found: C 56.41, H 4.68; EPR (CH3OH solution): Aiso = 68.7 G; EPR (aqueous solution): Aiso = 68.5 G; giso = 1.984; EPR

(frozen CH3OH solution): Ax= 86.4 G, Ay = 112.4 G, gx = 1.990, gy = 1.963; IR (KBr, nujol mull): 3170vw, 3084m, 2722w, 2438vw, 2372vw, 1754vw, 1698s, 1668vs, 1622w, 1578w, 1559w, 1492w, 1361s, 1259m, 1225w, 1142w, 1093w, 1011m, 924w, 894w, 857w, 825w, 801w, 779s, 736vw, 668w, 634w, 607w, 532m, 455w, 433w; Raman: 3375w, 3249w, 3097s, 2927s, 1695w, 1673w, 1498m, 1359m, 1260w, 1048m, 842m, 637w, 609m, 532w, 431s, 364m, 299vs, 203s, 121m.

4.3.6 Synthesis of (C5H4CH3)2V(OOCCH2COO) (8) 0.5 g (1.78 mmol) of 1 was dissolved in the solution of malonic acid (25 ml water, 14.42 mmol (COOH)2CH2). 1.15 g Ag2CO3 was added to the solution. The formed suspension was stirred for 10 minutes and filtered off. The filtrate was evaporated to dryness. The excess of malonic acid was removed by extraction with acetone. The crude product was recrystallized from 25 ml of methanol and dried in vacuo.

Complex (C5H4CH3)2V(OOCCH2COO) (8). Yield: 0.27 g; 0.95 mmol; 48.2 %; Calc. for C15H16O4V (MW 311.23): C 57.89, H 5.18; Anal. Found: C 57.45, H 5.12; EPR J. Vinkl´arek et al. / Central European Journal of Chemistry 3(1) 2005 157–168 165

(CH3OH solution): Aiso = 74.9 G; giso = 1.981; EPR (aqueous solution): Aiso = 74.7 G; giso = 1.981; EPR (frozen CH3OH solution): Ax = 89.4 G, Ay = 122.4 G, gx = 1.984, gy = 1.957; IR (KBr, nujol mull): 3396vw, 3118s, 2725vw, 2667w, 2488w, 1919w, 1723s, 1708s, 1557vs, 1497w, 1315m, 1271w, 1212s, 1167m, 1085w, 1027,w 978w, 940w, 910w, 857m, 779w, 726m, 647m, 604w, 588vw, 520w, 467w, 436w, 408m; Raman: 3122s, 2977m, 2936s, 2905s, 1498m, 1259w, 1232w, 1046w, 891w, 767w, 435s, 337s, 288vs, 248w, 106m.

Compound 5

Formula C16H14F6O4V Crystal system Monoclinic Space group C2/c (No. 15) a, A˚ 16.6600(7) b, A˚ 8.2020(4) c, A˚ 12.6650(4) β, ◦ 98.185(3) Z 4 V, A˚3 1712.98(12) −3 Dc, gcm 1.688 Crystal shape green prism Crystal size, mm 0.1 ×.05 ×.05 µ, mm−1 0.661 h range -21,21 k range -10,10 l range -16,16 Reﬂections measured 13660 a - independent (Rint) 1965 (0.056) - observed [I>2σ(I)] 1508 No. of parameters 142 GOFb 1.042 Rc, wRc 0.0487, 0.1315 ∆ρ, e˚A−3 0.802,-0.424

a 2 2 2 Rint =Σ|Fo − Fo,mean|/ΣFo ; b 2 2 2 1/2 GOF = [Σ(w(Fo - Fc ) )/(Ndiffrs - Nparams) ] for all data c R(F )=Σ||Fo| - |Fc||/Σ|Fo| for observed data, wR 2 2 2 2 2 2 1/2 (F ) = [Σ(w(Fo − Fc ) )/(Σ w(Fo ) )]

Table 3 Crystal data of 5, measurements and reﬁnement detailsa.

4.4 X-ray crystallography

Crystal data for 5: C26H14F6O4V, M = 435.21, monoclinic, C2/c(No 15), a = 16.6600(7) A,˚ b = 8.2020(4) A,˚ c = 12.6650(4) A,˚ β = 98.185(3)◦, V = 1712.98(12) A˚3, Z = 4, −3 Dx = 1.688 Mg m . A green crystal of dimensions 0.1x0.05x0.05 mm was mounted on glass capillary with epoxy glue and measured at Nonius Kappa CCD diffractometer by 166 J. Vinklárek et al. / Central European Journal of Chemistry 3(1) 2005 157–168 monochromatized MoKα radiation (λ = 0.71073 A)˚ at 150(2) K. Data reductions were performed with DENZO-SMN [27]. The absorption was neglected (µ = 0.661 mm−1); a total of 13660 measured reflections in the range h = -21 to 21, k = –10 to 10, l = –16 to ◦ 16 (θmax= 27.5 ), from which 1965 were unique (Rint=0.056), 1508 observed according to the I > 2σ(I) criterion. Structure was solved by direct methods (Sir92) [28] and refined 2 by full matrix least-square based on F (SHELXL97) [29]. The -CF3 moieties are heavily disordered into three positions for each of fluorine atom, because of close vicinity of disordered atoms their displacement parameters were mutually constrained. The hydrogen atoms were fixed into idealized positions (riding model) and assigned temperature fac-

tors either Hiso(H) = 1.2 Ueq(pivot atom), or Hiso(H) = 1.5 Ueq(pivot atom) for methyl moiety. The refinement converged (∆/σmax=0.002) to R = 0.049 for observed reflections and wR = 0.131, GOF = 1.042 for 142 parameters and all 1965 reflections. The final difference map displayed no peaks of chemical significance, positive maximum being close −3 to disordered moiety (∆ρmax = 0.802, ∆ρmin-0.424 e.˚A ). Crystallographic data for structural analysis have been deposited with the Cambridge Crystallographic Data Centre, CCDC no. 242949. Copies of this information may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge CB2 1EY, UK (Fax: +44-1223-336033; e-mail: [email protected] or www: http://www.ccdc.cam.ac.uk).

Acknowledgment

This work was supported by grant from the Ministry of Education of the Czech Republic (No. CZ 253100001).

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