Bizony, N. M.

Császár, József

English

Császár József

Bizony N. M.

University of Szeged

ISBN 963 481 625 8 Acta Phys. et Chem, Szeged 33 37-51 (1987) 3 7 SPECTROSCOPIC STUDY OF MOLECULAR COMPLEXES OF AROMATIC SCHIFF BASES WITH POLYNITRO COMPOUNDS By J. CSASZAR and N. M. BIZONY Institute of General and Physical Chemistry, J6zsef Attila University, P.O.B. 105, H-6701, Szeged, liungary (Received 1 October 1987) Schiff bases were formed from salicylaldehyde an aminopyridines and their methyl derivatives and molecular complexes of these Schiff bases with 2,4-dinitroaniline, . picric acid and dipicrylamine were prepared. The spectral behaviour of the parent Schiff bases and their molecular com-plexes was studied and discussed. Introduction Molecular complexes of polynitro compounds with Schiff bases as n-donor systems are an interesting group of com-pounds, which have recently been widely studied [1-5]. Issa and El-Essawey [6] found that the type and structure of these complexes may be studied well via UV, IR and ^H NMR-spect-roscopy. As a continuation of our earlier work, we have prepared molecular complexes of Schiff bases as donors (formed from salicylaldehyde and 2-aminopyridine, its methyl derivatives 3 8 and 3-amlnopyridine) with aromatic polynitro compounds as ac-ceptors. The present paper reports a spectral study of the parent Schiff bases and their molecular complexes. Expérimental The donors were Schiff bases having the general structu-res I and II. < 1 Û 1_ X = H 5 X = 5-CH3 3 X = 3-CH3 6 X = 6-CH3 2 4 X = 4-CH3 The acceptors used were 2,4-dinitroaniline (DNA), pic-ric acid (PA) and dipicrylamine (DPA). All chemicals were pure lab. grade BDH products. The preparation of the molecular complexes was described pre-viously [4, 5]. The analytical data are listed in Table I; these data are in good agreement with the expected composi-tions for a donor:acceptor stoichiometric ratio of 1:1 (DNA and PA) or 1:2 (DPA). The UV and visible spectra were recorded on a SPECORD UV-VIS spectrophotometer, using spectroscopically pure sol-vents. The IR spectra were measured on a ZEISS UR-20 spectro-photometer, in KBr discs; the 1H NMR spectra were observed on Table I Analytical data on the. molecular complexes studied c% c% Acceptor Donor M.p.* Colour** ^ ^ F o u n d ^ ^ F o u M 1 178.5 (64.1) LY 56.69 56.48 3.96 3.96 2 120.5 (57.0) LY 56.50 3.91 3 113.5 (80.3) 0 57.72 57.66 4.33 4.30 4 93.5 (99.4) LY 57.69 4,28 5 96.0 (100.5) BY 57.71 4.30 6 178.5 (65.8) LY 57.66 4.26 1 218.5 LY 50.59 50.50 3.07 3.01 2 165.0 LY 50.52 3.05 3 218.5 LY 51.71 51.66 3.43 3.40 4 218.0 LY 51.61 3.38 5 228.5 LY 51.65 3.41 6 202.5 LY 51.60 3.37 1 177.5 R 40.16 40.01 1.87 1.77 2 136.5 R 39.96 1.80 3 197.5 BB 40.75 40.15 2.03 1.98 4 196.5 0 40.33 2,00 5 175.5 SC 40.51 1.88 6 186.5 SC 40.55 1.78 * the data In parentheses are the m.p.s. of the Schiff bases ** LY: lemon-yellow; O: orange; BY: brownish-yellow; R: red; BB:~ bluish-brown; SC: scarlet 4 0 a JEOL 60 MHz instrument in CC14, with TMS as internal standard. Discussion Spectra of Schiff bases. The absorption spectra were similar to those of other Schiff bases of salicylaldehyde and aromatic amines [7-10]. Three main bands appear, at 270-280, 300-320 and 320-360 nm (Fig. 1, curves a,c), which may be as-signed to it* 1- it transitions of the aromatic systems. The positions and intensities of the bands measured in chloroform, benzene, hexane, etc. did not vary considerably (Table XX). -4 Figure 1: UV spectra, a: in CHCl-j, c=8.07.10 , b: 1 in conc. H 2S0 4, c=7.57.10~4; cs 2_ in CHC13, c=8.58.10~4; d: 2 in conc. H 2S0 4, c=8.07.10~4 mol/dm3. d=0.1 cm. ( . 4 1 Table II UV and visible spectral data on the Schiff basest measured in different solvents No. Solvent* X/nm (log e) 1 M 270(4.03) 303(4.07) 345(4.02) 450(2.10) Chi 270(4.03) 310(4.12)** 353(4.06) -460 B 270(4.00) 307(4.07) 352(4.04) s — — - 341 (4.26) 419 (3.74) 2 M 276(4.06) 340(3.88) Chi 279(4.17) 344(4.01) B 281(4.04) 343(3.92) S 322(4.14) 398(3.56) 3 M 271(4.04) 315(4.06) 346(4.08) 445(2.47) Chi 274(4.01) 313(4.05)** 355(4.08) -460 B 270(4.12) 320(4.18) 356(4.22) s <-__ 329(4.07) 412(3.60) 4 .M 272(4.04) 302(4.06) 345(4.01) 440(2.20) Chi 274(4.06) 309(4.16)** 352(4.13) -460 B 272(3.95) 305(4.10) 353(4.06) s ' 331 (4 .1 8) 41 4(3.72) 5 M 269(4.04) 310(4.08) 347(4.06) 450(2.20) Chi 272(4.09) _ 320(4.15)** 351(4.17) -460 B 275(3.94) 312(4.06) 353(4.10) s 342(4.26) 414(3.74) 6 M 269(4.07) 310(4.10) 343(4.09) 444(2.30) Chi 273(4.11) . 319(4.14)** 354(4.16) -460 B 275(3.94) 31>(4.06) 353(4.10) s 341(4.29) 415(3.76) * M: methanol; Chi: chloroform; B: benzene; S: concentrated sulphuric acid * * double band / 4 2 We presume that the same transitions are involved in the spectra of all the Schiff bases studied; the wavelength ra-. tios v^/v2 are between 1.10 and 1.16, and the solvent effect does not appreciably influence the relative energies of the ground and excited states of the chromophores. However, -in methanol, or in other hydrogen-bond forming solvents, a band can be detected between 400 and 450 nm, which is absent from the spectra of the benzene or hexane solutions. These medium--intensity bands can be interpreted in terms of a benr-solid state. Totally different spectral behaviour can be observed for 2; the visible band disappears almost completely. The nitro-gen atom in the "meta" position decreases the charge density on the azomethine nitrogen to nearly the same extent as a nitro group; the probability of the above equilibrium is very small. The K values calculated for the methyl derivatives 3-6 vary in the sequence 3 < 6 < _4 < 5; owing to its steric ef-fect, the methyl group in position 3 twists the pyridine ring out of the plane and thereby hinders extension of the quino-idal structure over the entire molecule; the value of K is the lowest. The different behaviour of 2 is also well seen from the low 6CHN and high vCHN frequencies (Table III). In concentratedNsulphuric acid solution, the ^C=8h-protonated forms of the Schiff bases are present, and the molecules have a planar or nearly planar conformation [16, 17]. Table II shows that the intensity of the third band is III. zoid/quinoid tautomeric equilibrium (Structure III) [10]. Similar phenomena can be observed in the photochromic [11, 12] and thermochroraic [e.g. 13-15] transformations of the Schiff bases in the J 4 3 increased considerably compared, for example, to the spectra of the methanolic solutions (Pig. 1, curves b, d). Ont the basis of the intensity differences, the twist angle 0 N of the aniline ring can be calculated [18-20] (Table III); the values differ only slightly, and the different positions of the methyl group scarcely influence the conformation. The OH proton signals are in the interval 12.4-13.7 ppm; the lowest value is observed for We found that the ppm values and the intensities of-the advanced visible bands change in .parallel. The 6.5-9.5 ppm region is extremely com-plicated, the signals of the aldehyde and pyridine ring protons apjiear with significant couplings in this range. Spectra of the molecular complexes. DNA, PA and DPA dif-fer considerably in their acidic character (pK = 15.0, 2.68 cl and 1.0, respectively). The donors have a basic character, and thus their behaviour towards the acceptors used differs. In the case of DNA and DPA, only a charge-transfer (CT) in-teraction is expected, but in the case of PA proton-transfer is also possible theoretically. The three groups of molecular complexes studied show different spectral behaviour; characteristic data on the com-plexes DNA/1^-6 and PA/^-6 are presented in Table IV. The absorption spectra of DNA/^-6 display two high-in-tensity bands, at around 260-265 and 330-335 nm; in the longer-wavelength region, an inflection is also found. On the basis of the positions and intensities of the main bands, we assigned these to i* <- n transitions in the aromatic systems, while the inflection is due to CT°processes between the aromatic rings of the donor and acceptor. Table IV shows that the solvent effect is not so important. It is remarkable that the spectra of DNA and its com-plexes are practically the same. However, the formation of molecular complexes is supported by the facts that the inten-4 4 Table III Characteristics of the Schiff bases No 60H a 6CHNa ÔCH3 vCHN13 K c e N d 1 13.11 9.47 1618s 4.0 81 2 12.46 8.60 1629s 3 13.69 9.40 2.49 1620s 2.0 74 4 13.23 9.50 2,38 1603s 5.7 80 5 13.19 9.43 2.33 1619s 8.6 80 6 13.26 9.47 2.55 1619s 4.6 79 a: measured in CC14; b: in KBr discs; c: in methanol/benzene mixtures see e.g. [8,9]; d: calculated via the intensity of the protonated form. sities are higher than that of DNA and the predicted one, and the analytical data also correspond to the formation of 1 :1 complexes. Ross and Labes [21] suggested that in the molecular complexes of aniline with 1,3,5-trinitrobenzene the two aromatic rings are parallel to each other. We propose an analogous structure (Structure IV), in which the DNA mole-cule and the pyridine ring of thé Schiff base lie parallel, and only a it - it* interaction need be taken into account. IV The high similarity of the meas-ured spectra to the one calcu-lated on the basis of the ad-ditivity suggests that in solu-tions corresponding to the equilibrium D.A«=*D+ + A the sum of the spectra of the donor and acceptor is measurable (Fig.2), 4.5 Table IV UV and visible spectral data on the molecular complexes of DNA and PA Donor Solvent* X/nm (log E) 1 Chi 2 6 2 ( 4 . 3 4 ) 3 3 1 ( 4 . 4 7 ) ~ 3 8 0 AcCN 2 6 1 ( 4 . 3 0 ) 3 3 3 ( 4 . 4 9 ) ~ 3 8 0 2 Chi 2 6 3 ( 4 . 4 7 ) 3 3 4 ( 4 . 4 8 ) ~ 3 8 0 AcCN 2 6 3 ( 4 . 4 2 ) 3 3 5 ( 4 . 4 3 ) - 3 7 0 3 Chi 2 6 2 ( 4 . 4 3 ) 3 3 3 ( 4 . 5 3 ) ~ 3 8 0 AcCN 2 6 4 ( 4 . 4 4 ) 3 3 1 ( 4 . 5 0 ) - 3 8 0 4 Chi 2 6 3 ( 4 . 4 2 ) 3 3 4 ( 4 . 5 2 ) - 3 7 0 AcCN 2 6 3 ( 4 . 4 3 ) 3 3 3 ( 4 . 5 3 ) ~ 3 8 0 5 ' Chi 2 6 3 ( 4 . 4 2 ) 3 3 3 ( 4 . 5 4 ) , - 3 8 0 AcCN 2 6 1 ( 4 . 4 2 ) 3 3 5 ( 4 . 5 0 ) - 3 8 0 6 Chi 2 6 2 ( 4 . 4 2 ) 3 3 1 ( 4 . 5 3 ) - 3 8 0 AcCN 2 6 1 ( 4 . 4 5 ) 3 3 0 ( 4 . 5 1 ) - 3 8 0 I MeOH - 3 1 5 3 5 4 ( 4 . 4 1 ) - 3 9 0 Chi - 3 1 8 3 4 4 ( 4 . 2 8 ) 4 1 1 ( 4 . 0 1 ) AcCN 3 1 0 ( 4 . 0 6 ) 3 6 9 ( 4 . 2 9 ) - 4 1 0 2 MeOH 2 5 2 ( 4 . 4 7 ) 3 4 9 ( 4 . 4 4 ) - 4 0 0 Chi 2 5 2 ( 4 . 0 8 ) 3 4 1 ( 3 . 9 4 ) ~ 4 1 0 AcCN 2 4 3 ( 4 . 4 9 ) 3 7 4 ( 4 . 4 5 ) - 4 2 0 3 MeOH 3 1 4 ( 4 . 2 8 ) 3 5 7 ( 4 . 4 0 ) - 4 1 0 Chi 3 2 3 ( 4 . 3 0 ) 3 4 6 ( 4 . 3 2 ) 4 1 2 ( 4 . 0 2 ) AcCN 3 0 7 ( 4 . 1 1 ) 3 6 7 ( 4 . 3 4 ) - 4 2 0 4 MeOH 3 1 1 ( 4 . 1 1 ) 3 5 8 ( 4 . 3 2 ) - 4 2 0 Chi - 3 1 5 3 5 0 ( 4 . 2 8 ) 4 1 4 ( 4 . 0 1 ) AcCN 3 0 3 ( 4 . 0 1 ) 3 6 9 ( 4 . 3 4 ) - 4 1 0 5 MeOH - 3 2 5 3 5 7 ( 4 . 3 3 ) - 4 0 0 Chi 3 3 8 ( 4 . 2 5 ) - 3 5 0 4 1 4 ( 3 . 9 3 ) AcCN - 3 1 8 3 6 9 ( 4 . 3 3 ) - 4 1 5 6 MeOH 3 2 0 ( 4 . 2 4 ) 3 5 8 ( 4 . 3 0 ) - 4 0 0 Chi 3 2 6 ( 4 . 2 9 ) - 3 4 0 4 0 6 ( 4 . 0 6 ) AcCN 3 1 3 ( 4 . 1 2 ) 3 7 2 ( 4 . 3 5 ) - 4 2 0 *MeOH: methanol; Chi: chloroform; AcCN: acetonitrile. 4 6 It must be mentioned that the possibility for intermolecular n - n* bonding between the amino and nitro groups should not pears and an inflection is observed in the same region. If the spectral data and the changes are taken into account, it may be presumed that the structures of the molecular com-plexes are similar to those discussed above; only the n - n* CT process is possible; the intramolecular hydrogen-bond in the Schiff bases prevents intermolecular proton-transfer [e.g. 1-3]; the characteristic frequencies of the yC=0H- group are absent from the solid-state IR spectra. It has long been known that DPA yields slightly-soluble compounds with, for example, quaternary ammonium compounds [23] and different organic bases [24, 25]. While the complexes discussed above are yellow or orange, the molecular complexes of DPA are brick-red, scarlet or violet. Since it is obvious from the structure of DPA that donor *- acceptor proton trans-be excluded [22], but our results do not support this possibility. Figure 2: UV spectra of DNA/1_ in CHClj. 1: measured, 2: cal-culated spectrum. 400 300 Vnm 200 The chloroform solu-tions of complexes PA/1_-([ also show two intense bands; a well-defined band appears at around 400 nm (Fig. 3). This band cor-responds unambigously to the molecular complex, and is also due with high probability to n - n* proc-esses. In methanol or in acetonitrile, the long--wavelength band disap-4 7 250 300 J50 WO ynm 300 150 «00 Figure 3s UV and visible spectra, a) PA/£ in 1: CHClj, c=5.89.10~4; 2s CH-jOH, c=5.89.10~4; 3s AcCN, c=5.44.10~4. b) PA/5 in 1: CHC13, c=6.12.10~4; 2s CH3OH, c=5.89.10~4; 3s AcCN, c=5.89.10~4 3 1 mol/dm . d=0.1 cm. fer is impossible, in this case only CT processes need be taken into account; typical spectra are shown in Fig. 4, In methanol or acetonitrile the molecular complexes DPA/1^-6 show a broad high-intensity band between 420 and 430 nm; this band corresponds to the characteristic 383 rati band of DPA (Table V) [26]. The longer-wavelength side of this band is asymmetric, which indicates the presence of a covered band. In chloroform or dioxane solutions, the maximum is situated at around 3 80 nm, with an inflection in the interval 440-460 nm. The higher-energy band appears at 290-320 nm. 4 8 Figure 4: UV spectra of DPA/2 in 1: CH3OH, c=1.02.10~4; 2: CHCl3, c=8.82.10~5; 3: 1,4-dioxane, c=1.10.10~4 mol/dm3, d=0.1 cm. We presume that the inflection appearing next to the 383 ran band (loge = 3.5-4.0) corresponds to n - n* CT proces-ses; the CT bands occur in a similar range in the spectra of molecular complexes of other Schiff bases [1, 2]. According to Issa [27], the aniline ring is primarily the centre contributing to the intermolecular CT interaction, but in the case of 1:2 donor:acceptor complexes the aldehyde ring, takes also part in the formation of complexes. On the basis of these findings, the analytical data, the intensity relations and the intense colours, we assume that 1:2 donor:acceptor complexes are formed, i.e. the aniline and aldehyde rings of the Schiff bases bind two acceptor molecules via n - n* CT (Structure V). The formation of a 2:1 donor:ac-ceptor complex is improbable, because iof the steric inhibition. The structural considerations are very problematic, because 4 9 Table Spectral data on the molecular complexes of DPA Donor Solvent* X/nm (log e) 1 MeOH 310(4.62) 421(4.92) Chi ~280 384(a) -460 Diox 295(4.58) 380(4.51) -460 ACCN 298(4.43) 423(4.83) 2 MeOH 305(4.45) 419(4.79) Chi ~280 386(4.60) -460 Diox 294(4.82) 383(4.81) -460 AcCN 300(4.26) 423(4.70) 3 MeOH 315(4.46) 422(4.74) Chi ~280 389 (4 .42) -440 Diox 297(4.64) 380(4.58) -460 AcCN 304(4.32) 426(4.72) 4 MeOH 318(4.41)- 420(4.73) Chi ~2 80 385(4.33) -460 Diox 300(4.52) 381(4.49) -480 AcCN 313(4.34) 425(4.79) 5 MeOH • 311(4.68) 420(5.02) Chi -280 384(a) -470 Diox 296(4.62) 382(4.57) -460 AcCN 302(4.26) 425(4.72) 6 MeOH 261(4.72) 350(4.59) 420(4.58) Chi 278(4.78) .,350(4.66) ~390 Diox 278(4.80) 346(4.69) -390 AcCN 273 (4.69) 347(4.63) 423(4.60) * * MeOH: methanol; Chi; chloroform; Diox: 1,4-dioxane; AcCN: Acetonltrile; a) very low solubility the DPA acceptor molecule, as discussed previously [22], is a twisted one due to the high steric interference of the nitro groups in the 2,2', 6,6' positions. Detailed investigations of DPA complexes by means of different physico-chemical methods are in progress. c 5 0 References [1] Issa, R.M., M. Gaber, A.I. El-Ansary, H.F. Rizk: Bull, Soc. Chlm. France, No.2., 173 (1985). [2] Hindawey, A.M., Y.M. Issa, R.M. Isea, H.F, Rizk'. Acta Acad. Sci. Hung., 112, 415 (1983). [3] Issa, Y.M. , A.E. El-Viholy, A. L. El-Ansary. Acta Acad. Sci. Hung., 118, 43 (1985). [4] CBdszdr, J.i Acta Phys. Chem. Szeged, in press. [5] Dale, B., R. Foster, D. LL. Hammicki J. Chem. Soc., 3986 (1954); R. Foster, D. LL. Hammick, P.J. Placito: J. Chem. Soc., 3881 (1956). [6] Issa, R.M., M.M. El-Essawey. Z. physik. Chem., 253, 96 (1973) . [7] Csdszdr, J.: Acta Phys. Chem., Szeged, 28, 135 (1982). [8] Csdszdv, J.i Acta Phys. Chem., Szeged, 27, 47 (1981). [9] Csdszdr, J.i Acta Phys. Chem., Szeged, 25, 137 (1979). [10] Csdszdr, 'J., J. Balog, A. Makdry. Acta Phys. Chem., Szeged, 24, 473 (1978). [11] Lewis, J.V., C. Sdndorfy: Canad. J. Chem., 60, 1738 (1982). 5 1 ! [12] Yoshida, M., M. Kobayashit Bull. Chem. Soc. Japan, 54, 2395 (1981). [13] Cohen, M.D., G.M.T. Schmidt'. J. Phys. Chem., 66, 2442 (19.62). [14] Cohen, M.D., G.M.T. Schmidt, S. Flavian'. J. Chem. Soc., 2041 (1964). [15] Cohen, M.D., G.M.T. Schmidt'. In Reactivity of Solids., Ed. j.H. de Boer, Elsevier, Amsterdam, 1961. p. 556. [16] Brocklehurst, P.: Tetrahedron, 18, 299 (1961), [17] Minkin, V.I., Yu. A. Zhdanov, E.A. Megyantzeva, Yu. A. Ostroumov: Tetrahedron, 23, 3651 (1967). [18] Braude, E.A., F. Sondheimer: J. Chem. Soc., 3754 (1955). [19] Kraszovickij, B.M., B.M. Bolomin, R.N. Nurmahatmetev:-Zh. Obsch. Khim., 34, 3786 (1964), [20] Csdezdr, J.: Acta Phys. Chem. Szeged, 29, 133 (1983); 32, 17 (1986) . [21] Ross, S., M. Labes: J. Amer. Chem. Soc., 77, 4916 (1955), [22] Hindawey, A.M., A,M.G. Nassar, R.M. Iesa'. Acta Acad. Sci., Hung., 88, 341 (1976). [23] Ackerman, D., H. Maner: Z. physik. Chem., 279, 114 (1943). [24] Kertes, S.'. Anal, Chim. Acta, 15, 73 (1956). [25] Kertes,.S., V. Kertes: Anal, Chim. Acta,' 15.,. 154 (1956) [26] Csdszdr, J. s Acta Phys. Chem,, Szeged, 33, 11 (1987). [27] Issa, Y.M.t Spectrochim, Acta, 40A, 137 (1984), СПЕКТРОСКОПИЧЕСКОЕ ИЗУЧЕНИЕ МОЛЕКУЛЯРНЫХ КОМПЛЕКСОВ АРОМАТИЧЕСКИХ ШИФФОВЫХ ОСНОВАНИЙ С ПОЛИ-НИТРОСОЕДИНЕНИЯМИ Й. Часар и Н.М. Бизонь Синтезированы молекулярные комплексы Шиффовых оснований образованные из салицилальдегида, амино пиридонов, а также их метиловых производных с 2,4-динитроанилином, пикриновой кислотой и дипикриламином^ Изучены и обсуждены спектральные свойства исходных оснований и их молекулярных комплексов. о 

Spectroscopic study of molecular complexes of aromatic schiff bases with polynitro compounds

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Spectroscopic study of molecular complexes of aromatic schiff bases with polynitro compounds

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