Charge-transfer interaction of iodine with some polyamidoamines

Spectrochimica Acta Part A 61 (2005) 205–211

Charge-transfer interaction of iodine with some polyamidoamines M.S. Refat a,∗ , S.M. Teleb b , Ivo Grabchev c a

Chemistry Department, Faculty of Education, Suez Canal University, Port-Said, Egypt b Chemistry Department, Faculty of Science, Zagazig University, Zagazig, Egypt c Institute of Polymers, Bulgarian Academy of Science, 1113 Sofia, Bulgaria Received 9 December 2003; accepted 6 April 2004

Abstract The interaction of iodine as a ␴-acceptor with two derivatives of polyamidoamine dendrimers (donor), 1,8-naphthalimide polyamidoamine (PAM1) and 4-piperidino-1,8-naphthalimide polyamidoamine (PAM2) have been investigated spectrophotometrically at room temperature in chloroform. The results indicate the formation of two CT-complexes [(PAM1)I]+ I3 − and [(PAM2)2 I]+ I3 − with molar ratios of 1:2 and 1:1, respectively. The formation of these two complexes are in good agreement with their elemental analysis, infrared measurements and photometric titration plots based on the characteristic absorption bands of I3 − ion around 280 and 360 nm. Moreover the formation of triiodide ion, I3 − , in both of the two complexes was supported by measuring their spectra in the far-infrared region. Three characteristic bands are observed at 125, 110 and 75 cm−1 due to νas (I–I), νs (I–I) and δ(I3 − ), respectively, with C2v symmetry. © 2004 Elsevier B.V. All rights reserved. Keywords: Charge transfer; Dendrimers; Far-infrared; Polyamidoamine; Triiodide

1. Introduction Dendrimers are well defined three-dimensional macromolecules possessing a very large number of surface functional groups. Polyamidoamines (PAMAMs) form a novel class of industrial dendrimers which possess a definite molecular composition with different terminal functional groups [1–4]. At present time the chemistry of dendrimers has faced a growing interest because of the broad spectrum of applications associated with this type of compounds. Dendrimers with electroactive groups are used as components in different sensors and electroluminescent devices [5]. Dendrimers macromolecules with chromophors found many applications in photochemical devices [6–8] and some of these compounds have also been investigated for use as biosensors [9,10]. Charge-transfer complexes in general have much lower activation energies and much higher conductivities than the free components. Hence, this type of compounds especially polyiodide charge-transfer complexes is expected to show a high electrical conductivity [11]. CT-complexes found also

∗

Corresponding author. E-mail address: [email protected] (M.S. Refat).

1386-1425/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2004.04.017

many application in the field of drug interactions [12,13] and analytical chemistry [14,15]. In this paper we report the formation of two new chargetransfer complexes formed in the reaction of iodine as a ␴-acceptor with two derivatives of polyamidoamine dendrimers (electron donors), 1,8-naphthalimide polyamidoamine (PAM1) and 4-piperidino-1,8-naphthal-imide polyamidoamine (PAM2), as shown in Scheme 1. The reactions were carried out in chloroform as a solvent, and the nature of bonding and structure inherent in these complexes were investigated on the basis of the obtained data.

2. Experimental All chemicals used throughout this investigation were of analytical grade. 1,8-Naphthalimide and 4-pipridino-1,8naphthalimide-PAMAM (PAM1 and PAM2, respectively) were prepared [16] and used without further purification. Iodine was obtained from BDH. The solid charge-transfer complexes were isolated as follows. Excess saturated solution (40 ml) of iodine in chloroform was added to a saturated solution (10 ml) of each the donors in chloroform. The reaction mixture in each case was stirred for about 10–20 min. The dark brown [(PAM1)I]+ I3 −

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Scheme 1. A represents H or piperidino.

and the light brown [(PAM2)2 I]+ I3 − solid CT-complexes formed were filtered immediately and washed several times with minimum amounts of chloroform (2–5 ml) and then dried under vacuum over P2 O5 . The obtained complexes were characterised by their elemental analyses, vibrational (mid and far) and electronic absorption spectroscopy. The analysis data were obtained as follows: [(PAM1)I]+ I3 −

(FW = 1743.6); C, 48.12% (48.18%); H, 3.64% (3.67%); N, 7.93% (8.03%); I, 29.03% (29.11%). [(PAM2)2 I]+ I3 − (FW = 3531.6); C, 61.09% (61.16%); H, 5.61% (5.66%); N, 10.97% (11.10%); I, 14.17% (14.37%) (the calculated values are shown in parenthesis). The electronic spectra of the donors, 1,8-naphthalimide polyamido-amine (PAM1) and 4-piperidino-1,8-naphthalimide polyamido-amine (PAM2), acceptor (iodine) and the formed CT-complexes in chloroform were recorded in the region of 700–200 nm using a Shimadzu UV-spectrophotometer model 1601 PC with quartz cell of 1 cm path length. The mid-infrared spectra of the reactants and the formed CT-complexes were recorded from KBr discs using a Genesis II FT-IR, while the far-infrared spectra for the donors and their polyiodide complexes were recorded from Nujol mulls dispersed on polyethylene windows in the region 50–300 cm−1 using a Mattson infinity series FT-IR spectrometer. Photometric titration were performed [17] at 25 ◦ C for the reactions of PAM1 and PAM2 with iodine in chloroform as follow. The concentration of the donors in the reaction mixtures was kept fixed at 5 × 10−6 M, while the concentration of the iodine was changed over a wide range from

Fig. 1. Electronic absorption spectra of (A) [(PAM1)]–I2 reaction in CHCl3 and (B) [(PAM2)]–I2 reaction in CHCl3 : (a) acceptor (1 × 10−5 M); (b) donor (1 × 10−5 M); (c) donor–acceptor CT-complex.

M.S. Refat et al. / Spectrochimica Acta Part A 61 (2005) 205–211 Table 1 The electronic absorption spectral data for [(PAM1)I]+ I3 − [(PAM2)2 I]+ I3 − complexes, respectively in CHCl3 X ml of iodine

0.25 0.50 0.75 1.00 1.50 2.00 2.50 3.00 3.50 4.00

0.25 0.50 0.75 1.00 1.50 2.00 2.50 3.00 3.50 4.00

PAM1:iodine ratio

and

Absorbance at 280 (nm)

362 (nm)

1:0.25 1:0.50 1:0.75 1:1.00 1:1.50 1:2.00 1:2.50 1:3.00 1:3.50 1:4.00

0.020 0.048 0.068 0.090 0.138 0.181 0.203 0.228 0.255 0.275

0.023 0.043 0.095 0.138 0.210 0.308 0.342 0.387 0.432 0.481

PAM2:iodine ratio

Absorbance at

1:0.25 1:0.50 1:0.75 1:1.00 1:1.50 1:2.00 1:2.50 1:3.00 1:3.50 1:4.00

207

284 (nm)

330 (nm)

0.055 0.095 0.138 0.175 0.205 0.223 0.230 0.248 0.263 0.268

0.026 0.050 0.065 0.085 0.105 0.125 0.143 0.150 0.163 0.175

1 ml base (5 × 10−5 M) + X ml of iodine (5 × 10−5 M) + Y ml solvent = 10 ml.

1.25 × 10−6 to 20.00 × 10−6 M. These produced solutions with donor:acceptor molar ratios varying from 1:0.25 to 1:4 as shown in Table 1.

3. Results and discussion The electronic absorption spectra of the donor bases (PAM1 and PAM2), acceptor (iodine) and their 1:2 and 1:1 iodine CT-complexes are shown in Fig. 1A and B, respectively. The spectrum of the PAM1–iodine system shows two strange absorption bands at 280 and 362 nm due to the formation of [(PAM1)I]+ I3 − CT-complexes, while the corresponding absorption bands associated with the formation of the complex [(PAM2)2 I]+ I3 − are observed at 284 and 330 nm in the spectrum of PAM2–iodine system. The stoichiometry of the PAM1–iodine and PAM2–iodine were shown to be of 1:2 and 1:1 ratios, respectively. These values were proposed on the bases of the obtained elemental analysis data of the isolated solid complexes, infrared spectra, Fig. 2 and Table 2 and greatly supported by photometric titration measurements. These measurements were based on the CT-absorption bands exhibited by the spectra of the two systems (mentioned above) and given in Fig. 3A and B. The equivalence point of the PAM1–iodine system indicate that the donor–acceptor ratios is 1:2, while the corresponding

Fig. 2. Infrared spectra of (a) PAM1; (b) [(PAM1)I]+ I3 − complex; (c) PAM2; (d) [(PAM2)2 I]+ I3 − complex.

ratio for the system PAM2–iodine is 1:1, in good agreement with the elemental data and infrared spectra of the solid CT-complexes. The appearance of two absorption bands in the electronic spectra of the two complexes are well known [18–20] to be characteristic for the formation of polyiodide ions, In ; n = 3, 5 or 7. This was also supported by measuring the far-infrared spectra for both of the two complexes (Table 3). The spectra show that a group of three bands do not exist in the spectra of the donors around 125, 110 and 75 cm−1 . These bands are known to be characteristic for the triiodide ion and can be assigned to νas (I–I), νs (I–I) and δ(I3 − ), respectively. The assignment of these bands to these vibrations are in good

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Table 2 Infrared frequenciesa (cm−1 ) and tentative assignments for PAM1, PAM2; [(PAM1)I]+ I3 − and [(PAM2)2 I]+ I3 − complexes PAM1

PAM2

[(PAM1)I]+ I3 −

[(PAM2)2 I]+ I3 −

Assignmentsb

3428 vs, br 3343 sh 3257 sh

3529 vw 3471 vw 3443 s, br 3414 vw

3540 vw 3470 vw 3414 w 3243 w, sh

3543 w 3471 vw 3485 vw 3414 vs 3243 w

ν(O–H) ; H2 O of KBr

3086 ms 2971 ms

3100 w, sh 2928 s

2957 w 2915 ms

2957 w 2928 vs

νas(C–H) ; CH2 ν(C=C) ; CH-aromatic

2843 vw 2814 w 2786 vw

2824 ms 2814 w, sh

2857 ms

2857 vs

νs(C–H) ; CH2

1771 vw 1700 ms 1671 vs 1640 vw

1657 vs 1686 w

1772 ms 1743 vw 1700 s 1657 vs 1614 ms

1786 w 1743 w 1700 w 1640 vs

ν(C=O) δ(H2 O); H2 O of KBr

1586 s 1557 s

1586 vs 1514 w

1586 s 1543 vw

1571 vw 1529 vw 1514 vw

ν(C=C) ; CH-aromatic

1500 vw 1443 vs 1414 vw 1386 s

1457 w 1428 w 1385 vs 1357 vw

1500 vw 1428 s 1371 vs

1485 vw 1471 s 1386 vw 1371 w, sh

δ(CH) ; CH-deformation

1342 s 1286 s 1243 vs 1186 vs 1128 ms

1257 vw 1228 vs 1171 s 1140 w 1128 w

1342 s 1271 vw 1228 vs 1186 s

1343 sh 1271 w 1228 ms 1157 vw

νas (C–N)

1100 w 1057 ms 1045 vs 1014 vw

1114 ms 1086 s 1043 ms 1014 w

1114 ms 1057 vw 1043 w 1028 vw

1140 vw 1086 w 1043 vw 1014 vw

νs (C–N)

985 vw 914 vw 886 vs 857 vs

985 vw 957 vw 886 w 842 w 814 w

1000 vw 886 vw 871 vw 857 vw 843 s

843 vw 814 vw

δ(CH) ; in-plane bend

786 vs 743 ms 686 vw

786 vs 757 vs 728 w 671 vw

771 vs 728 vw

757 ms 743 vw 700 vw

δ(CH) ; CH-rock δ(N–H) ; NH-deformation

671 vw 614 vw 571 vw 530 s 485 vw 455 vw

657 vw 586 w 500 mw

600 s, br 530 w 470 s, br

614 vs 430 s

δ(CH) ; out-of-plane bend

a b

448 w 432 ms

s: strong; w: weak; m: medium; sh: shoulder; v: very; br: broad. ν, stretching; δ, bending.

agreement with the presence of a non-linear triiodide ion with C2v symmetry and also with the previously [18,21–23] observed three infrared bands for other related complexes, as shown in Table 3. According to the foregoing discussion, the formed CT-complexes upon the reaction of the investigated dendrimers PAM1 and PAM2 as donors with iodine

in chloroform were formulated as [(PAM1)I]+ I3 − and the [(PAM2)2 I]+ I3 − , respectively. It should be indicated here that the iodine:PAM1 molar ratio of 2:1 is twice higher than that of the iodine in the other system with PAM2. This occurs in spite of the presence of additional four electron-donating piperidino groups

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209

Fig. 3. (A) Photometric titration curves for the PAM1–iodine reactions in CHCl3 at () 280 and () 362 nm. (B) Photometric titration curves for the PAM2–iodine reactions in CHCl3 at () 284 and () 330 nm.

in the donor PAM2 increasing its electron donation power compared with the donor PAM1. The steric hindrance placed by the four piperidino groups and the possibility to stabilize the rotations of the molecule of PAM2 make the conformational changes are smaller in PAM2 than in PAM1 [16]. This may restrict the extent of PAM2 interaction with iodine to the molar ratio 1:1, as the CT-forces usually hold the components in the complex together in a specific orientation. The 1:1 modified Benesi–Hildebrand equation (1) [24] was used to calculate the values of the equilibrium constants, K (l mol−1 ), and the extinction coefficient, ε (l mol−1 cm−1 ), for the complexes [(PAM2)2 I]+ I3 − : Ca0 Cd0 l C0 + Cd0 1 = + a A Kε ε

(1)

Table 3 Fundamental vibrations for some triiodide compounds Compounds

KI3 CsI3 (CH3 )4 NI3 (C2 H5 )4 NI3 (TACPD)I+ I3 − (HMTACTD)I+ I3 − [Ni(acac)2 ]2 I+ I3 − [Fe(acac)3 ]2 I+ I3 − [(PAM1)I]+ I3 − [(PAM2)2 I]+ I3 − a

Assignmentsa

References

ν1

ν2

ν3

111 103 111 104 109 110 101 102 110 112

69 74 72, 66 60 61 84 76 73 75

143 149 138 132 132 144 132 150 126 124

ν1 , νs (I–I); ν2 , δ(I3 − ); ν3 , νas (I–I).

[18] [21] [21,22] [22] [26] [26] [23] [27] Present work Present work

The corresponding spectral parameters for the complex [(PAM1)I]+ I3 − were calculated using the known [25] Eq. (2) of 1:2 complexes: (Ca0 )2 Cd0 1 1 = + Ca0 (4Cd0 + Ca0 ) A Kε ε

(2)

where Ca0 and Cd0 are the initial concentrations of the iodine and the donor, respectively, while A is the absorbance at the mentioned CT-bands. The data obtained throughout these calculation are given in Table 4. Plotting the values of Ca0 Cd0 /A against Ca0 + Cd0 values of Eq. (1) and plotting the values (Ca0 )2 Cd0 /A versus Ca0 (4Cd0 + Ca0 ) values of Eq. (2), straight lines are obtained with a slope of 1/ε and intercept of 1/Kε as shown in Fig. 4A and B, respectively. The values of both K and ε associated with these two complexes are given in Table 5. These complexes show high values of both the formation constants (k) and the extinction coefficients (ε). The high values of (k) in general reflects high stabilities of the formed CT-complexes as a result of the expected high donation of such dendrimers which contain a very high number of oxygen and nitrogen atoms. The high values of ε agree quite well with the existence of triiodide species which is known to have a high absorbability values [18–20]. It should be mentioned here that the very high order of the formation constant associated with the complex [(PAM1)I]+ I3 − compared with the complex [(PAM2)2 I]+ I3 − does not mean that the former complex is necessary of higher stability with the same order than the latter. This is simply because application of Eq. (2) in calculating the values of k leads to obtaining quite high values which is sometimes not acceptable for a CT-complex.

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Table 4 The values Cd0 , Ca0 , Ca0 (4Cd0 + Ca0 ) and ((Ca0 )2 Cd0 /A) for [(PAM1)I]+ I3 − , and Cd0 , Ca0 , Cd0 + Ca0 and Cd0 Ca0 /A for [(PAM2)2 I]+ I3 − complex in chloroform PAM1:iodine ratio

Cd0 (×10−6 )

1:0.25 1:0.50 1:0.75 1:1.00 1:1.50 1:2.00 1:2.50 1:3.00 1:3.50 1:4.00

5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0

PAM2:iodine ratio

Cd0 (×10−6 )

1:0.25 1:0.50 1:0.75 1:1.00 1:1.50 1:2.00 1:2.50 1:3.00 1:3.50 1:4.00

5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0

Ca0 (×10−6 )

Absorbance at 280 (nm)

362 (nm)

1.250 2.500 3.750 5.000 7.500 10.00 12.50 15.00 17.50 20.00

0.020 0.048 0.068 0.090 0.138 0.181 0.203 0.228 0.255 0.275

0.023 0.043 0.095 0.138 0.210 0.308 0.342 0.387 0.432 0.481

Ca0 (×10−6 )

Absorbance

1.250 2.500 3.750 5.000 7.500 10.00 12.50 15.00 17.50 20.00

284 (nm)

330 (nm)

0.055 0.095 0.138 0.175 0.205 0.223 0.230 0.248 0.263 0.268

0.026 0.050 0.065 0.085 0.105 0.125 0.143 0.150 0.163 0.175

Cd0 (Ca0 )2 /A (×10−18 )

4Cd0 + Ca0 (×10−6 )

Ca0 (4Cd0 + Ca0 ) (×10−12 )

Cd0 (Ca0 )2 (×10−18 )

21.25 22.50 23.75 25.00 27.50 30.00 32.50 35.00 37.50 40.00

26.563 56.250 89.063 125.00 206.25 300.00 406.25 525.00 656.25 800.00

7.813 31.25 70.313 125.00 281.25 500.00 781.25 1125.0 1531.25 2000.0

Cd0 + Ca0 (×10−6 )

Cd0 Ca0 (×10−12 )

Cd0 Ca0 /A (×10−12 )

6.25 7.50 8.75 10.0 12.5 15.0 17.5 20.0 22.5 25.0

6.25 12.50 18.75 25.00 37.50 50.00 62.50 75.00 87.50 100.0

280 (nm)

362 (nm)

390.65 651.04 1034.0 1388.9 2038.0 2762.4 3848.5 4934.2 6004.9 7272.7

339.69 726.74 740.14 905.79 1339.3 1623.4 2284.4 2907.0 3544.6 4158.0

284 (nm)

330 (nm)

113.64 131.58 135.87 142.86 182.93 224.22 271.74 302.42 332.70 373.13

240.38 250.00 288.46 268.82 357.14 400.00 437.06 500.00 536.81 571.43

Fig. 4. (A) The plot of (Ca0 )2 Cd0 /A values against Ca0 (4Cd0 + Ca0 ) values for the PAM1–iodine reaction in CHCl3 at (䊉) 280 and (䉱) 362 nm. (B) The plot of Ca0 Cd0 /A values against Ca0 + Cd0 values for the PAM2–iodine reaction in CHCl3 at (䊉) 284 and (䉱) 330 nm.

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211

Table 5 Spectrophotometric results of CT-complexes of [(PAM1)I]+ I3 − and [(PAM2)2 I]+ I3 − in CHCl3 Complexes [(PAM1)I]+ I3 − [(PAM2)2 I]+ I3 −

K (l mol−1 ) 4.37 × 1010 1.67 × 1010 53.32 × 104 4.69 × 104

The infrared spectra of the [(PAM1)I]+ I3 − and [(PAM2)2 I]+ I3 − complexes and the free bases PAM1 and PAM2 were recorded and shown in Fig. 2. Table 2 shows the observed frequencies and their assignments. However, the spectra of [(PAM1)I]+ I3 − and [(PAM2)2 I]+ I3 − complexes are quite similar to those of the free bases, but with some changes in their band intensities and shifts of some band frequency values. The infrared band intensities of the free bases PAM1 and PAM2 are in general relatively higher than those associated with the infrared bands of their iodine complexes. This may indicate that the symmetry of the PAM1 and PAM2 are increased upon complexation with iodine implying a smaller change in the dipole moment during the bases vibration in the two complexes form and hence it show relatively weaker band intensities. Finally, the formation of these two complexes upon the reaction of iodine with PAM1 and PAM2 may be understood on the basis of the following reactions: (i) PAM1 + I2 → [(PAM1)I]+ I− , [(PAM1)I]+ I− + I2 → [(PAM1)I]+ I3 − ; (ii) 2PAM2 + I2 → [(PAM2)2 I]+ I− , [(PAM2)2 I]+ I− + I2 → [(PAM2)2 I]+ I3 − .

References [1] M. Fischer, F. Vogtle, Angew. Chem., Int. Ed. 38 (1999) 884. [2] K. Unoue, Prog. Polym. Sci. 25 (2000) 453. [3] F. Vogtle, S. Gesterman, R. Hasse, H. Schwierz, B. Windisch, Prog. Polym. Sci. 25 (2000) 987.

λmax (nm)

εmax (×104 l mol−1 cm−1 )

280 362

11.43 20.00

284 330

7.50 18.52

[4] A.W. Bosman, H.M. Janssen, E.W. Meijer, Chem. Rev. 99 (1999) 1665. [5] P. Froehling, Dyes Pigments 48 (2001) 187. [6] D.M. Jingle, D.V. McGrath, J. Am. Chem. Soc. 121 (1999) 4912. [7] S. Fomie, E. Rivera, L. Fomina, A. Ortiz, T. Ogawa, Polymer 39 (1998) 3551. [8] V. Balzani, P. Ceroni, S. Gestermann, M. Gorka, F. Vogtle, J. Chem. Soc. Dalton Trans. (2000) 765. [9] J. Wang, M. Jiang, J. Am. Chem. Soc. 120 (1998) 8281. [10] A.C. Chang, J. Gillespie, M. Tabacco, Anal. Chem. 73 (2001) 467. [11] E. Mulazzi, I. Pollini, L. Piseri, R. Tubino, Phys. Rev. B 24 (1981) 3555. [12] J. Feng, H. Zhong, B.D. Xuebau, Ziran Kexueban 27 (6) (1991) 691. [13] V.C. Flores, H. Keyzer, C. Varkey-Johnson, K.L. Young, Appl. Phys. NY Org. Conductors (1994), Special Issue, 691. [14] L.I. Bebawy, K. El-Kelani, L. Abdel Fattah, A.S. Ahmed, J. Pharm. Sci. 86 (9) (1997) 1030. [15] M. Luo, Yaowu Fenxi Zazhi 15 (6) (1995) 52. [16] I. Grabchev, X. Qian, V. Bojinov, Y. Xiao, W. Zhang, Polymer 43 (2002) 5731. [17] D.A. Skoog, Principle of Instrumental Analysis, 3rd ed., Saunders College Publishing, New York, USA, 1985 (Chapter 7). [18] W. Kiefer, H.J. Bernstein, Chem. Phys. Lett. 16 (1972) 5. [19] L. Andrews, E.S. Prochaska, A. Loewenschuss, Inorg. Chem. 19 (1980) 463. [20] K. Kaya, N. Mikami, Y. Udagawa, M. Ito, Chem. Phys. Lett. 16 (1972) 151. [21] A.G. Maki, R. Forneris, Spectrochim. Acta A 23 (1967) 867. [22] F.W. Parrett, N.J. Taylor, J. Inorg. Nucl. Chem. 32 (1970) 2458. [23] E.M. Nour, S.M. Teleb, M.A.F. El-Mosallamy, M.S. Refat, South Afr. J. Chem. 56 (2003) 10. [24] R. Abu-Eittah, F. Al-Sugeir, Can. J. Chem. 54 (1976) 3705. [25] A. El-Kourashy, Spectrochim. Acta A 37 (1981) 399. [26] E.M. Nour, L.A. Shahada, Spectrochim. Acta A 45 (1989) 1033. [27] S.M. Teleb, M.S. Refat, Spectrochim. Acta A 60 (2004) 1579.