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IR absorption spectroscopic characteristics of peripherally substituted thiophenyl phthalocyanine in sandwich bis(phthalocyaninato) complexes
Vibrational Spectroscopy 92 (2017) 105–110
Contents lists available at ScienceDirect
Vibrational Spectroscopy journal homepage: www.elsevier.com/locate/vibspec
IR absorption spectroscopic characteristics of peripherally substituted thiophenyl phthalocyanine in sandwich bis(phthalocyaninato) complexes Jingchao Wei, Xiaobo Li, Chi Xiao, Fanli Lu* Department of Chemistry, School of Science, Tianjin University, Tianjin 300354, PR China
A R T I C L E I N F O
Article history: Received 22 March 2017 Received in revised form 31 May 2017 Accepted 5 June 2017 Available online 9 June 2017 Keywords: Double-deckers IR spectra UV–vis spectra Rare earth Phthalocyanine
A B S T R A C T
The IR spectra data for a series of thirteen rare earth double-deckers M[Pc(SPh)8]2 (M = Y, Ce Lu, except La and Tm) have been collected and detailed characterized. The electronic absorption spectra showed that the Soret and Q bands are blue-shifted, and especially the Q bands at 705–726 nm clearly become stronger along with the decrease of rare earth ion radius. For MIII[Pc(SPh)8]2, the Infrared characteristic absorption peaks for the phthalocyanine anion radical [Pc(SPh)8] were observed at 1311–1323 cm 1 as the strongest absorption bands, which can be ascribed to the pyrrole stretching. As for the Ce[Pc(SPh)8], the marker absorption bands at 1335 cm 1 was observed. In addition, the typical IR absorption bands of phthalocyanine radical anion [Pc(SPh)8] move to the high energy as the decrease of rare earth metal ionic radius. These facts suggest that the p-p electron interaction in these double-deckers becomes stronger along with the lanthanide contraction. © 2017 Elsevier B.V. All rights reserved.
1. Introduction Phthalocyanines (Pcs) were originally used as blue and green dyestuffs and pigments since they were first synthesized by chance last century [1]. These tetrapyrrole compounds have a highly conjugated system with 18 p-electron delocalized on the phthalocyaine macrocycle [2]. Pcs show widely attractive applications in various fields including semiconductor, non-linear optical devices, information storage systems, liquid crystal materials, photodynamic reagents for cancer therapy and germicides and candidates for gas sensors, and so on [3–9]. They are chemically studied for different optics and electron via manipulation of the metal center and substitution of functional groups on the organic ring, which has been attributed to electron donation from the functional groups to increase the p-p electron interaction [10–14]. Sandwich-type rare earth metal phthalocyanines have been comprehensively studied for several decades [15–20]. These complexes have two or three redox centers and strong p-p electron interaction between rings, in which the large conjugated
* Corresponding author. E-mail address: [email protected] (F. Lu). http://dx.doi.org/10.1016/j.vibspec.2017.06.002 0924-2031/© 2017 Elsevier B.V. All rights reserved.
p systems are held in close proximity by rare earth metal ions, have been intensively studied over several decades as prospective advanced functional materials due to their unique optical, electrical, magnetic, and other novel physical properties associated with the intriguing intramolecular inter-ring p-p interactions, such as field effect transistor, molecular information storage materials, nonlinear optics, electrochromic material and liquid crystal materials [15–21]. In the past several decades, the vibrational (IR and Raman) characteristics of phthalocyanine complexes have been mainly investigated by Jiang, Aroca, Tran-Thi, and Homborg [22–27]. Meantime, these investigations basically focused on various alkoxyl and alkyl substituted phthalocyanine derivatives. As far as we know, systematically spectroscopic characteristics of peripherally substituted thiophenyl phthalocyanine in sandwich bis(phthalocyaninato) complexes was not reported. In this paper, a series of 13 rare earth sandwich-type complexes M[Pc(SPh)8]2(M = Y, Ce, . . . ,Lu, except for La and Tm) were prepared, as shown in Scheme 1. We give a detailed investigation of the vibrational spectra to gain a deeper insight of the spectroscopic intrinsic properties. The rare earth ionic radius effect on the IR and UV–vis characteristics of phthalocyanine in bis(phthalocyaninato) rare earth complexes was also studied.
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fragment M(SPh) contains a large number of atoms. In the IR spectra of M[Pc(SPh)8]2, the other IR active modes could be attributed to the related 22A1 and 41E type [27,28]. The vibrational representations are classified as follows:
Gvib = 22A1 (IR, R) + 19A2 + 22B1 (R) + 20B2 (R) + 41E (IR, R) A1 and E modes are both IR- and Raman-active. B1 and B2 modes are Raman-active and A2 modes are spectrally inactive. 3.1. Electronic absorption spectra of M[Pc(SPh)8]2
Scheme. 1. Schematic structures of the rare-earth double-decker complexes with 3, 4, 12, 13, 21,22,30,31-octa(thiophenyl)-2,3-phthalocyanine ligands.
2. Experimental These double-deckers were prepared by base-promoted cyclization of 4,5-disubstitued dicyanobenzene in refluxing 1pentanol in the presence of M(acac)3H2O (M = Y, Ce Lu, except La and Tm) and nucleophilic base DBU (1,8-diazabicyclo[5.4.0]undec7-ene) according to the published procedures [22,23]. Under a slow stream of nitrogen, a mixture of M(acac)3nH2O (42 mg, 0.09 mmol), DBU (78 mg, 0.51 mmol) and 4,5-bis(thiophenyl) phthalonitrile (0.36 mmol) was refluxed in 1-pentanol (3 mL) for 10 h to give a dark-green solution. The resulting solution was cooled to room temperature, and then 1-pentanol was removed in vacuo. The residue was chromatographed over a silica gel column (Qingdao, 200–300 mesh) with CHCl3/hexanes (2.5:1) as eluent. The crude product obtained was further purified by the same chromatographic procedure, followed by recrystallization with a mixture of CHCl3 and CH3OH to afford dark blue microcrystals. The UV–vis spectra were obtained for solutions in CHCl3 using a HP 8543 spectrophotometer and the IR spectra were recorded in KBr pellets using a BIORAD FTS-3000 spectrometer. Their sandwich nature has been investigated through a series of spectroscopic methods including UV-vis, IR and ESI mass spectra (Table S1). Mass spectra data of these complexes confirm their identification and purity.
The electronic absorption spectral data of the double-deckers M [Pc(SPh)8]2 in CHCl3 are collected in Table S2. Fig. 1 compares the UV–vis spectra of four complexes MIII[Pc(SPh)8]2 (M = Pr, Sm, Ho and Lu), which are representative for the light, middle and heavy rare earths, respectively. Due to similar structure, these compounds undoubtedly showed the similar electronic absorption characteristics. The obviously splitted absorption bands at 335– 347 nm and 373–386 nm are assigned to the Soret bands, which may be governed by the thiophenyl electron-donating. Another characteristic absorption band is the Q-band observed at 636– 661 nm and 705–726 nm. It is clearly showed that the Soret bands and Q bands are blue-shifted along with the decrease of ion radius in Figs. 2, 3. It should be mentioned that the second Q-bands at 705–726 nm become stronger along with the decrease of ion radius which means that these double-deckers with smaller the rare earth has the stronger p-p electron interaction. Although the structure of MIII[Pc(SPh)8]2 are similar to those of bis(phthalocyaninato) rare earth compounds MIII(Pc)2 [22–24], their spectral features are obviously different from each other. It can be seen in Figs. 1 and 4 that the Q bands of MIII[Pc(SPh)8]2 have a significant red-shift by comparison with those of MIII(Pc)2, which can be attributed to electron donating of the thiophenyl group with the more extended p-p conjugated system.
3. Results and discussion According to the single crystal X-ray diffraction structural analyses of bis(phthalocyaninato) rare earth complexes M(Pc*)2 (Pc* = unsubstituted or substituted Pc) [24–26], the static symmetry is D4 or D4d depending on the twist (skew) angle between the two macrocyclic rings. For Pc(SPh)8 rare earth complexes, D4 or D4d group symmetry is also reasonably assumed due to the symmetrical location of eight thiophenyl groups on the phthalocyaninato rings. Based on the theoretical prediction, the phthalocyanine metal fragment M[Pc(SPh)8] (except PhS-) has 57 atoms and 168 normal vibrational modes, and there are only 22 A1 totally symmetric fundamental vibrations active in the Raman spectra although the
Fig. 1. Electronic absorption spectra of M[2,3-Pc(SPh)8]2 (M = Pr, Sm, Ho and Lu) in CHCl3.
J. Wei et al. / Vibrational Spectroscopy 92 (2017) 105–110
107
Fig. 2. Polt of wavelength of the Q band as a function of the ionic radius of MIII of M [2,3-Pc(SPh)8]2.
3.2. Infrared spectra of M[Pc(SPh)8]2 IR spectroscopy is a powerful technique for investigating the intrinsic properties of the sandwich bis(phthalocyaninato) rare earth complexes M(Pc’)2 and mixed porphyrinato-phthalocyaninato rare earth double-deckers M(Por)(Pc*) (Pc* = unsubstituted or substituted phthalocyanine) [24–37]. It is well known that all MIII(Pc*)2 and M(Por)(Pc*) complexes show a strong marker band at ca. 1310–1323 cm 1 which is diagnostic for phthalocyanine p-radical anions Pc* [24–32]. As for bis(naphthalocyaninato)
Fig. 4. Electronic absorption spectra of the p-radical anion of Tb[2,3-Pc(SPh)8]2 and Tb(Pc)2 in CHCl3.
rare earth analogs, the vibrations at 1316–1330 cm 1 have been assigned as the marker bands for the naphthalocyanine monoanion radical Nc* in bis(naphthalocyaninato) compounds. The frequencies of the IR marker bands are shifted slightly to higher energy along with the rare earth contraction [28–33]. However, the interpretation and understanding of the vibrational spectra of
Fig. 3. Polt of wavelength of the Soret band as a function of the ionic radius of M[2,3-Pc(SPh)8]2.
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Table 1 Characteristic IR bands (cm
1
) of phthalocyanine for M[2,3-Pc(SPh)8]2.
Ce
Pr
Nd
Sm
Eu
Gd
Tb
Dy
Y
Ho
Er
Yb
Lu
469w 570w 549w 613w
467w 505w 548w 616w 654sh 690s 744s
466w 508w 551w 615w 659sh 691s 745s
467w 508w 551w 619w 657s 689s 745s
467w 508w 553w 619w 660sh 691s 745s
467w 508w 553w 619w 660sh 691s 745s
832w 896w
834w 896w
834w 896w
468w 507w 549w 619w 654sh 689s 748s 769w 805w 832w 897w
470w
832w 897w
469w 505w 549w 616w 656sh 689s 750s 769w 805w 834w 898w
469w 507w 550w 617w 660sh 690s 749s
800w 831w 898w
469w 506w 550w 615w 656sh 690s 751s 768w 805w 831w 897w
469m
830w 890w
469w 506w 549w 616w 656sh 688s 752s 772s 800w 833w 899w
938w
934w
935w
935w
938w
937w
937w
942m
999sh 1023w 1066s 1134w 1175w
999sh 1023w 1065s 1130w 1172w
999sh 1023w 1065s 1130w 1172w
Pyrrole-N in-plane bending C H bend C-S-C stretching(sym) C H bend Pyrrole breathing
1270s 1313m
1277s 1317m
1275m 1317s
1275m 1317s
1279w 1323m
1000sh 1024m 1065s 1127w 1172w 1213w 1274m 1317s
1000sh 1024w 1067s 1156w 1174w
1270s 1317m
939m 967w 1003sh 1024m 1066s 1131w 1174w 1213w 1278m 1320s
937m
1000sh 1023w 1064s 1131w 1174w
939m 965w 1000sh 1024w 1066s 1133w 1173w 1213w 1278m 1321s
940m 970sh
1001sh 1026w 1064s 1125w 1169w
939w 967w 999sh 1024m 1067s 1135w 1174w 1213w 1279m 1320s
Coupling of isoindole deformation and aza stretching C H bend
1281m 1325s
1363sh 1391s 1437m 1457m
1360sh 1390s 1438m 1474m 1494sh
1360sh 1393s 1439m 1476m 1497w
1360sh 1393s 1439m 1476m 1497w 1500w
1360sh 1393s 1439m 1476m 1497w
1363sh 1395s 1439m 1475m
1363w 1395vs 1440m 1476m
1364sh 1397m 1439w 1476w
1363w 1394s 1440m 1476m
1362sh 1394vs 1438m 1477m
1364w 1397m 1439m 1477m
C-S-C stretching(asym) Pyrrole stretching Pyrrole stretching Isoindole stretching Isoindole stretching Isoindole stretching Isoindole stretching
1502w
1502m
1500w
1499w
1508w
1508m
1582m 1728w
1582m 1725w
1582s 1724w
1583m 1724w
1584w 1725w
1585m 1727w
1583m 1728w
1582w 1736w
690s 745s 768sh
1026sh 1000sh 1022w 1062s 1063s 1103w 1128w 1172w 1174w 1210w 1274w 1265s 1305w 1311m 1335m 1364m 1363sh 1401s 1389s 1438w 1437m 1475w 1476m
1584w 1725w
1584m 1728w
1586m 1725w
1584m 1731w
1582m 1726w
phthalocyanines are indeed more limited compared with porphyrins. The so-far assignments of the vibrational (IR and Raman) bands of phthalocyanine derivatives have been made mainly on the basis of empirical comparison with related macrocycles like benzene, isoindole, pyrrole and porphyrin [1–6]. Due to the existence of strong couplings of some vibrational coordinates of the large conjugated phthalocyanine rings [1–8], It is impossible that one-to-one matching of observed vibrational frequencies to the internal vibrations can be achieved in the vibrational spectra of mixed bis(phthalocyaninato) rare earth compounds. In Table 1, characteristic IR vibrational frequencies of the phthalocyanine ligand of the series of lanthanides are summarized and their interpretation is proposed by analogy with the IR spectra of M(Pc)2 [31]. Fig. 5 compares the IR spectra in the region of fundamental frequencies of 400–1800 cm 1 of four complexes MIII[Pc(SPh)8]2 (M = Ce, Pr, Sm and Er). It can be seen from Table 1 and Fig. 5 that the IR spectra of these double-deckers were relatively simple and show similar IR characteristics due to the high symmetry and similar molecular structure among the whole series of bis(phthalocyaninato) compounds [31]. Four basic vibration absorptions dominated the IR spectra of MIII[Pc(SPh)8]2: Pc breathing at approximately 615 and 690 cm 1, the C H wagging and C H bending at approximately 750 and 930–1160 cm 1, pyrrole stretching at 1305–1325 cm-1and isoindole stretching at 1360–1480 cm 1. In the range of 460– 1000 cm 1, two strong vibrations at 688–691 cm 1 and 744– 752 cm 1 are derived from Pc breathing and C H wagging, meanwhile a medium band at 934–942 cm 1 assigned to C H bending. The rest of the weak absorption peaks can be mainly attributed to the Pc breathing, C H bending, coupling of isoindole deformation and aza stretching and pyrrole-N in-plane bending in the Pc ring. It should be noted that the weak vibration at 1024 cm 1and 1125–1156 cm 1, strong bands at 1062–1068 cm 1 and 1270–1279 cm 1 are tentatively assigned to C-S-C symmetry
550m 654sh 690w 750m 768sh 802w 831w 902w
1068s 1104s
805w 833w 898w
550w 615w 654sh 690m 750m 768w 805w 833w 900w
assignment
Pc breathing Pc breathing C H wag
Benzene stretching Benzene stretching Benzene stretching C H stretching(Benzene, Pc)
and asymmetry stretching. These band assignments are consistent with expectation and support our overall assignment. It should be pointed out that the pyrrole stretching at 1311– 1325 cm 1 (except Ce) shifts to higher energy along with the decrease of rare earth radius, clearly demonstrating the rare earth size effect, which is the typical marker band of phthalocyanine anion radical [Pc(SPh)8] . This fact well corresponds with the
Fig. 5. IR spectra of M[2,3-Pc(SPh)8]2 (M = Ce, Pr, Sm and Er).
J. Wei et al. / Vibrational Spectroscopy 92 (2017) 105–110
109
Fig. 6. Plots of wavenumber of the pyrrole stretching of M(Pc)2, M(OOPc)2 and M[Pc(SPh)8]2 as a function of the ionic radius of MIII.
change of the unsubstituted bis(phthalocyaninato) compounds M (Pc)2, as shown in Fig. 6. The other important vibrations are the aza and isoindole stretching at 1360–1477 cm 1 and the benzene stretching at approximately 1583 cm 1. Additionally, the typical marker band of phthalocyanine anion radical [Pc(SPh)8] was not observed in the Intra-red spectra of Ce [Pc(SPh)8]2. Instead, a medium band at 1335 cm 1 was observed. Fig. 7 compares the IR spectra of Ce[Pc(SPh)8]2 and Ce(Pc)2 compound in the region of 400–1800 cm 1. It can be seen from Fig. 7 that the phthalocyanine dianion Pc2 band in Ce[Pc(SPh)8]2 at 1335 cm 1 has a light red-shift compared with that of in Ce(Pc)2, which may be caused by its extended conjugation system. These
results suggest that the cerium complex mainly exists as the form of CeIV{[Pc(SPh)8]22 }. 4. Conclusion According to the electronic absorption spectra, the Soret and Q bands move to the high energy as the decrease of rare earth metal ionic radius. On the basis of the IR investigation, typical IR marker band of the thiophenyl phthalocyanine anion radical [Pc(SPh)8] shows the strong band due to pyrrole stretching, whose frequency linearly varies in the range from 1311 cm 1 for Ce to 1325 cm 1 for Lu along with the decrease of rare earth ionic size. As for Ce[Pc (SPh)8]2, the marker IR band of the [Pc(SPh)8]2 around 1335 cm 1 demonstrates that the cerium metal ion is mainly tetravalent, which has a clear red-shift compared with those of other doubledecker rare earth complexes. The IR spectra of these doubledeckers were relatively simple due to the high symmetry. In conclusion, the frequencies of pyrrole stretching, isoindole breathing, and aza stretchings are sensitive to the rare earth ionic size, and shift to the high energy along with the lanthanide contraction. These facts indicate that the p-p interaction in these double-deckers becomes stronger along with lanthanide contraction. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j. vibspec.2017.06.002. References
Fig. 7. IR spectra of Ce(Pc)2 and Ce[2,3-Pc(SPh)8]2(a = Ce(Pc)2, b = Ce[2,3-Pc (SPh)8]2).
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[8] B.S. Alexander, Phthalocyanine metal complexes in catalysis, Chem. Rev. 113 (2013) 8152. [9] F.I. Bohrer, A. Sharoni, C. Colesniuc, J. Park, I.K. Schuller, A.C. Kummel, W.C. Trogler, J. Am.Chem. Soc. 129 (2007) 5640. [10] X. Li, Y. Mao, C. Xiao, F. Lu, Spectrochim. Acta Part A: Mol. Biomol. Spectrosc. 140 (2015) 96. [11] J. Xu, J. Chen, L. Chen, R. Hu, S. Wang, S. Li, J. Ma, G. Yang, Dyes Pigm. 109 (2014) 144. [12] G. de la Torre, P. Vázquez, F. Agulló-López, T. Torres, Chem. Rev. 104 (2004) 3723. [13] D. Dini, M. Meneghetti, M.J.F. Calvete, T. Arndt, C. Liddiard, M. Hanack, Chem. Eur. J. 16 (2010) 1212. [14] N. Kobayashi, Coord. Chem. Rev. 227 (2002) 129. [15] N. Ishikawa, T. Iino, Y. Kaizu, J. Am. Chem. Soc. 124 (2002) 11440. [16] H. Fuhrhop, U. Bindig, U. Siggel, J. Am. Chem. Soc. 115 (1993) 11036. [17] W.E. Bennett, D.E. Broberg, N. C.Baenziger, Inorg. Chem. 12 (1973) 930. [18] P.A. Barrett, C.E. Dent, R.P. Linstead, J. Chem. Soc. 1 (1936) 1719. [19] K. Bott, Angew. Chem. Int. Ed. Engl. 7 (1968) 894. [20] J.W. Buchler, H.G. Kapellmann, M. Knoff, et al., Org. Chem. 38 (1983) 1339. [21] M. Bouvet, J. Simon, Chem. Phy. Lett. 172 (1990) 299. [22] J. Jiang, M. Bao, L. Rintoul, D.P. Arnold, Coord. Chem. Rev. 250 (2006) 424. [23] J. Jiang, K. Kasuga, D.P. Arnold, Supramolecular Photo-sensitive and ElectroActive Materials, in: H.S. Nalwa (Ed.), Academic Press, New York, 2001, pp. 113– 210.
[24] M.L. Rodriguez-Mendez, R. Aroca, J.A. Desaja, Spectrochim. Acta A 49 (1993) 965. [25] R.E. Clavijo, D. Battisti, R. Aroca, G.J. Kovacs, C.A. Jennings, Langmuir 8 (1992) 113. [26] T.H. Tran-Thi, T.A. Mattioli, D. Chabach, A. De Cian, R. Weiss, J. Phys. Chem. 98 (1994) 8279. [27] G. Ostendorp, H. Homborg, Z. Anorg, Allg. Chem. 622 (1996) 1358. [28] X. Zhang, Y. Zhang, J. Jiang, J. Mol. Struct.: Theochem. 673 (2004) 103. [29] X. Sun, X. Xui, D.P. Arnold, M.T.M. Choi, D.K.P. Ng, J. Jiang, Eur. J. Inorg. Chem. (2003) 1555. [30] F. Lu, M. Bao, C. Ma, X. Zhang, D.P. Arnold, J. Jiang, Spectrochim. Acta Part A 59 (2003) 3273. [31] J. Jiang, L. Rintoul, D.P. Arnold, Polyhedron 19 (2000) 1381. [32] M.L. Rodriguez-Mendez, R. Aroca, Chem. Mater. 5 (1993) 933. [33] K.M. Kadish, G. Moninot, Y. Yu, D. Dubois, A. Ibnlfassi, J.-M. Barbe, R. Guilard, J. Am. Chem. Soc. 115 (1993) 8153. [34] K. Takahashi, J. Shimoda, M. Itoh, Y. Fujita, H. Okawa, K. Nojima, Chem. Lett. (1998) 173. [35] N. Ishikawa, T. Okubo, Y. Kaizu, Inorg. Chem. 38 (1999) 3173. [36] W. Liu, J. Jiang, D.P. Arnold, N. Pan, Inorg. Chim. Acta 310 (2000) 140. [37] N. Ishikawa, T. Iino, Y. Kaizu, J. Am. Chem. Soc. 124 (2002) 11440.
Contents lists available at ScienceDirect
Vibrational Spectroscopy journal homepage: www.elsevier.com/locate/vibspec
IR absorption spectroscopic characteristics of peripherally substituted thiophenyl phthalocyanine in sandwich bis(phthalocyaninato) complexes Jingchao Wei, Xiaobo Li, Chi Xiao, Fanli Lu* Department of Chemistry, School of Science, Tianjin University, Tianjin 300354, PR China
A R T I C L E I N F O
Article history: Received 22 March 2017 Received in revised form 31 May 2017 Accepted 5 June 2017 Available online 9 June 2017 Keywords: Double-deckers IR spectra UV–vis spectra Rare earth Phthalocyanine
A B S T R A C T
The IR spectra data for a series of thirteen rare earth double-deckers M[Pc(SPh)8]2 (M = Y, Ce Lu, except La and Tm) have been collected and detailed characterized. The electronic absorption spectra showed that the Soret and Q bands are blue-shifted, and especially the Q bands at 705–726 nm clearly become stronger along with the decrease of rare earth ion radius. For MIII[Pc(SPh)8]2, the Infrared characteristic absorption peaks for the phthalocyanine anion radical [Pc(SPh)8] were observed at 1311–1323 cm 1 as the strongest absorption bands, which can be ascribed to the pyrrole stretching. As for the Ce[Pc(SPh)8], the marker absorption bands at 1335 cm 1 was observed. In addition, the typical IR absorption bands of phthalocyanine radical anion [Pc(SPh)8] move to the high energy as the decrease of rare earth metal ionic radius. These facts suggest that the p-p electron interaction in these double-deckers becomes stronger along with the lanthanide contraction. © 2017 Elsevier B.V. All rights reserved.
1. Introduction Phthalocyanines (Pcs) were originally used as blue and green dyestuffs and pigments since they were first synthesized by chance last century [1]. These tetrapyrrole compounds have a highly conjugated system with 18 p-electron delocalized on the phthalocyaine macrocycle [2]. Pcs show widely attractive applications in various fields including semiconductor, non-linear optical devices, information storage systems, liquid crystal materials, photodynamic reagents for cancer therapy and germicides and candidates for gas sensors, and so on [3–9]. They are chemically studied for different optics and electron via manipulation of the metal center and substitution of functional groups on the organic ring, which has been attributed to electron donation from the functional groups to increase the p-p electron interaction [10–14]. Sandwich-type rare earth metal phthalocyanines have been comprehensively studied for several decades [15–20]. These complexes have two or three redox centers and strong p-p electron interaction between rings, in which the large conjugated
* Corresponding author. E-mail address: [email protected] (F. Lu). http://dx.doi.org/10.1016/j.vibspec.2017.06.002 0924-2031/© 2017 Elsevier B.V. All rights reserved.
p systems are held in close proximity by rare earth metal ions, have been intensively studied over several decades as prospective advanced functional materials due to their unique optical, electrical, magnetic, and other novel physical properties associated with the intriguing intramolecular inter-ring p-p interactions, such as field effect transistor, molecular information storage materials, nonlinear optics, electrochromic material and liquid crystal materials [15–21]. In the past several decades, the vibrational (IR and Raman) characteristics of phthalocyanine complexes have been mainly investigated by Jiang, Aroca, Tran-Thi, and Homborg [22–27]. Meantime, these investigations basically focused on various alkoxyl and alkyl substituted phthalocyanine derivatives. As far as we know, systematically spectroscopic characteristics of peripherally substituted thiophenyl phthalocyanine in sandwich bis(phthalocyaninato) complexes was not reported. In this paper, a series of 13 rare earth sandwich-type complexes M[Pc(SPh)8]2(M = Y, Ce, . . . ,Lu, except for La and Tm) were prepared, as shown in Scheme 1. We give a detailed investigation of the vibrational spectra to gain a deeper insight of the spectroscopic intrinsic properties. The rare earth ionic radius effect on the IR and UV–vis characteristics of phthalocyanine in bis(phthalocyaninato) rare earth complexes was also studied.
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J. Wei et al. / Vibrational Spectroscopy 92 (2017) 105–110
fragment M(SPh) contains a large number of atoms. In the IR spectra of M[Pc(SPh)8]2, the other IR active modes could be attributed to the related 22A1 and 41E type [27,28]. The vibrational representations are classified as follows:
Gvib = 22A1 (IR, R) + 19A2 + 22B1 (R) + 20B2 (R) + 41E (IR, R) A1 and E modes are both IR- and Raman-active. B1 and B2 modes are Raman-active and A2 modes are spectrally inactive. 3.1. Electronic absorption spectra of M[Pc(SPh)8]2
Scheme. 1. Schematic structures of the rare-earth double-decker complexes with 3, 4, 12, 13, 21,22,30,31-octa(thiophenyl)-2,3-phthalocyanine ligands.
2. Experimental These double-deckers were prepared by base-promoted cyclization of 4,5-disubstitued dicyanobenzene in refluxing 1pentanol in the presence of M(acac)3H2O (M = Y, Ce Lu, except La and Tm) and nucleophilic base DBU (1,8-diazabicyclo[5.4.0]undec7-ene) according to the published procedures [22,23]. Under a slow stream of nitrogen, a mixture of M(acac)3nH2O (42 mg, 0.09 mmol), DBU (78 mg, 0.51 mmol) and 4,5-bis(thiophenyl) phthalonitrile (0.36 mmol) was refluxed in 1-pentanol (3 mL) for 10 h to give a dark-green solution. The resulting solution was cooled to room temperature, and then 1-pentanol was removed in vacuo. The residue was chromatographed over a silica gel column (Qingdao, 200–300 mesh) with CHCl3/hexanes (2.5:1) as eluent. The crude product obtained was further purified by the same chromatographic procedure, followed by recrystallization with a mixture of CHCl3 and CH3OH to afford dark blue microcrystals. The UV–vis spectra were obtained for solutions in CHCl3 using a HP 8543 spectrophotometer and the IR spectra were recorded in KBr pellets using a BIORAD FTS-3000 spectrometer. Their sandwich nature has been investigated through a series of spectroscopic methods including UV-vis, IR and ESI mass spectra (Table S1). Mass spectra data of these complexes confirm their identification and purity.
The electronic absorption spectral data of the double-deckers M [Pc(SPh)8]2 in CHCl3 are collected in Table S2. Fig. 1 compares the UV–vis spectra of four complexes MIII[Pc(SPh)8]2 (M = Pr, Sm, Ho and Lu), which are representative for the light, middle and heavy rare earths, respectively. Due to similar structure, these compounds undoubtedly showed the similar electronic absorption characteristics. The obviously splitted absorption bands at 335– 347 nm and 373–386 nm are assigned to the Soret bands, which may be governed by the thiophenyl electron-donating. Another characteristic absorption band is the Q-band observed at 636– 661 nm and 705–726 nm. It is clearly showed that the Soret bands and Q bands are blue-shifted along with the decrease of ion radius in Figs. 2, 3. It should be mentioned that the second Q-bands at 705–726 nm become stronger along with the decrease of ion radius which means that these double-deckers with smaller the rare earth has the stronger p-p electron interaction. Although the structure of MIII[Pc(SPh)8]2 are similar to those of bis(phthalocyaninato) rare earth compounds MIII(Pc)2 [22–24], their spectral features are obviously different from each other. It can be seen in Figs. 1 and 4 that the Q bands of MIII[Pc(SPh)8]2 have a significant red-shift by comparison with those of MIII(Pc)2, which can be attributed to electron donating of the thiophenyl group with the more extended p-p conjugated system.
3. Results and discussion According to the single crystal X-ray diffraction structural analyses of bis(phthalocyaninato) rare earth complexes M(Pc*)2 (Pc* = unsubstituted or substituted Pc) [24–26], the static symmetry is D4 or D4d depending on the twist (skew) angle between the two macrocyclic rings. For Pc(SPh)8 rare earth complexes, D4 or D4d group symmetry is also reasonably assumed due to the symmetrical location of eight thiophenyl groups on the phthalocyaninato rings. Based on the theoretical prediction, the phthalocyanine metal fragment M[Pc(SPh)8] (except PhS-) has 57 atoms and 168 normal vibrational modes, and there are only 22 A1 totally symmetric fundamental vibrations active in the Raman spectra although the
Fig. 1. Electronic absorption spectra of M[2,3-Pc(SPh)8]2 (M = Pr, Sm, Ho and Lu) in CHCl3.
J. Wei et al. / Vibrational Spectroscopy 92 (2017) 105–110
107
Fig. 2. Polt of wavelength of the Q band as a function of the ionic radius of MIII of M [2,3-Pc(SPh)8]2.
3.2. Infrared spectra of M[Pc(SPh)8]2 IR spectroscopy is a powerful technique for investigating the intrinsic properties of the sandwich bis(phthalocyaninato) rare earth complexes M(Pc’)2 and mixed porphyrinato-phthalocyaninato rare earth double-deckers M(Por)(Pc*) (Pc* = unsubstituted or substituted phthalocyanine) [24–37]. It is well known that all MIII(Pc*)2 and M(Por)(Pc*) complexes show a strong marker band at ca. 1310–1323 cm 1 which is diagnostic for phthalocyanine p-radical anions Pc* [24–32]. As for bis(naphthalocyaninato)
Fig. 4. Electronic absorption spectra of the p-radical anion of Tb[2,3-Pc(SPh)8]2 and Tb(Pc)2 in CHCl3.
rare earth analogs, the vibrations at 1316–1330 cm 1 have been assigned as the marker bands for the naphthalocyanine monoanion radical Nc* in bis(naphthalocyaninato) compounds. The frequencies of the IR marker bands are shifted slightly to higher energy along with the rare earth contraction [28–33]. However, the interpretation and understanding of the vibrational spectra of
Fig. 3. Polt of wavelength of the Soret band as a function of the ionic radius of M[2,3-Pc(SPh)8]2.
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Table 1 Characteristic IR bands (cm
1
) of phthalocyanine for M[2,3-Pc(SPh)8]2.
Ce
Pr
Nd
Sm
Eu
Gd
Tb
Dy
Y
Ho
Er
Yb
Lu
469w 570w 549w 613w
467w 505w 548w 616w 654sh 690s 744s
466w 508w 551w 615w 659sh 691s 745s
467w 508w 551w 619w 657s 689s 745s
467w 508w 553w 619w 660sh 691s 745s
467w 508w 553w 619w 660sh 691s 745s
832w 896w
834w 896w
834w 896w
468w 507w 549w 619w 654sh 689s 748s 769w 805w 832w 897w
470w
832w 897w
469w 505w 549w 616w 656sh 689s 750s 769w 805w 834w 898w
469w 507w 550w 617w 660sh 690s 749s
800w 831w 898w
469w 506w 550w 615w 656sh 690s 751s 768w 805w 831w 897w
469m
830w 890w
469w 506w 549w 616w 656sh 688s 752s 772s 800w 833w 899w
938w
934w
935w
935w
938w
937w
937w
942m
999sh 1023w 1066s 1134w 1175w
999sh 1023w 1065s 1130w 1172w
999sh 1023w 1065s 1130w 1172w
Pyrrole-N in-plane bending C H bend C-S-C stretching(sym) C H bend Pyrrole breathing
1270s 1313m
1277s 1317m
1275m 1317s
1275m 1317s
1279w 1323m
1000sh 1024m 1065s 1127w 1172w 1213w 1274m 1317s
1000sh 1024w 1067s 1156w 1174w
1270s 1317m
939m 967w 1003sh 1024m 1066s 1131w 1174w 1213w 1278m 1320s
937m
1000sh 1023w 1064s 1131w 1174w
939m 965w 1000sh 1024w 1066s 1133w 1173w 1213w 1278m 1321s
940m 970sh
1001sh 1026w 1064s 1125w 1169w
939w 967w 999sh 1024m 1067s 1135w 1174w 1213w 1279m 1320s
Coupling of isoindole deformation and aza stretching C H bend
1281m 1325s
1363sh 1391s 1437m 1457m
1360sh 1390s 1438m 1474m 1494sh
1360sh 1393s 1439m 1476m 1497w
1360sh 1393s 1439m 1476m 1497w 1500w
1360sh 1393s 1439m 1476m 1497w
1363sh 1395s 1439m 1475m
1363w 1395vs 1440m 1476m
1364sh 1397m 1439w 1476w
1363w 1394s 1440m 1476m
1362sh 1394vs 1438m 1477m
1364w 1397m 1439m 1477m
C-S-C stretching(asym) Pyrrole stretching Pyrrole stretching Isoindole stretching Isoindole stretching Isoindole stretching Isoindole stretching
1502w
1502m
1500w
1499w
1508w
1508m
1582m 1728w
1582m 1725w
1582s 1724w
1583m 1724w
1584w 1725w
1585m 1727w
1583m 1728w
1582w 1736w
690s 745s 768sh
1026sh 1000sh 1022w 1062s 1063s 1103w 1128w 1172w 1174w 1210w 1274w 1265s 1305w 1311m 1335m 1364m 1363sh 1401s 1389s 1438w 1437m 1475w 1476m
1584w 1725w
1584m 1728w
1586m 1725w
1584m 1731w
1582m 1726w
phthalocyanines are indeed more limited compared with porphyrins. The so-far assignments of the vibrational (IR and Raman) bands of phthalocyanine derivatives have been made mainly on the basis of empirical comparison with related macrocycles like benzene, isoindole, pyrrole and porphyrin [1–6]. Due to the existence of strong couplings of some vibrational coordinates of the large conjugated phthalocyanine rings [1–8], It is impossible that one-to-one matching of observed vibrational frequencies to the internal vibrations can be achieved in the vibrational spectra of mixed bis(phthalocyaninato) rare earth compounds. In Table 1, characteristic IR vibrational frequencies of the phthalocyanine ligand of the series of lanthanides are summarized and their interpretation is proposed by analogy with the IR spectra of M(Pc)2 [31]. Fig. 5 compares the IR spectra in the region of fundamental frequencies of 400–1800 cm 1 of four complexes MIII[Pc(SPh)8]2 (M = Ce, Pr, Sm and Er). It can be seen from Table 1 and Fig. 5 that the IR spectra of these double-deckers were relatively simple and show similar IR characteristics due to the high symmetry and similar molecular structure among the whole series of bis(phthalocyaninato) compounds [31]. Four basic vibration absorptions dominated the IR spectra of MIII[Pc(SPh)8]2: Pc breathing at approximately 615 and 690 cm 1, the C H wagging and C H bending at approximately 750 and 930–1160 cm 1, pyrrole stretching at 1305–1325 cm-1and isoindole stretching at 1360–1480 cm 1. In the range of 460– 1000 cm 1, two strong vibrations at 688–691 cm 1 and 744– 752 cm 1 are derived from Pc breathing and C H wagging, meanwhile a medium band at 934–942 cm 1 assigned to C H bending. The rest of the weak absorption peaks can be mainly attributed to the Pc breathing, C H bending, coupling of isoindole deformation and aza stretching and pyrrole-N in-plane bending in the Pc ring. It should be noted that the weak vibration at 1024 cm 1and 1125–1156 cm 1, strong bands at 1062–1068 cm 1 and 1270–1279 cm 1 are tentatively assigned to C-S-C symmetry
550m 654sh 690w 750m 768sh 802w 831w 902w
1068s 1104s
805w 833w 898w
550w 615w 654sh 690m 750m 768w 805w 833w 900w
assignment
Pc breathing Pc breathing C H wag
Benzene stretching Benzene stretching Benzene stretching C H stretching(Benzene, Pc)
and asymmetry stretching. These band assignments are consistent with expectation and support our overall assignment. It should be pointed out that the pyrrole stretching at 1311– 1325 cm 1 (except Ce) shifts to higher energy along with the decrease of rare earth radius, clearly demonstrating the rare earth size effect, which is the typical marker band of phthalocyanine anion radical [Pc(SPh)8] . This fact well corresponds with the
Fig. 5. IR spectra of M[2,3-Pc(SPh)8]2 (M = Ce, Pr, Sm and Er).
J. Wei et al. / Vibrational Spectroscopy 92 (2017) 105–110
109
Fig. 6. Plots of wavenumber of the pyrrole stretching of M(Pc)2, M(OOPc)2 and M[Pc(SPh)8]2 as a function of the ionic radius of MIII.
change of the unsubstituted bis(phthalocyaninato) compounds M (Pc)2, as shown in Fig. 6. The other important vibrations are the aza and isoindole stretching at 1360–1477 cm 1 and the benzene stretching at approximately 1583 cm 1. Additionally, the typical marker band of phthalocyanine anion radical [Pc(SPh)8] was not observed in the Intra-red spectra of Ce [Pc(SPh)8]2. Instead, a medium band at 1335 cm 1 was observed. Fig. 7 compares the IR spectra of Ce[Pc(SPh)8]2 and Ce(Pc)2 compound in the region of 400–1800 cm 1. It can be seen from Fig. 7 that the phthalocyanine dianion Pc2 band in Ce[Pc(SPh)8]2 at 1335 cm 1 has a light red-shift compared with that of in Ce(Pc)2, which may be caused by its extended conjugation system. These
results suggest that the cerium complex mainly exists as the form of CeIV{[Pc(SPh)8]22 }. 4. Conclusion According to the electronic absorption spectra, the Soret and Q bands move to the high energy as the decrease of rare earth metal ionic radius. On the basis of the IR investigation, typical IR marker band of the thiophenyl phthalocyanine anion radical [Pc(SPh)8] shows the strong band due to pyrrole stretching, whose frequency linearly varies in the range from 1311 cm 1 for Ce to 1325 cm 1 for Lu along with the decrease of rare earth ionic size. As for Ce[Pc (SPh)8]2, the marker IR band of the [Pc(SPh)8]2 around 1335 cm 1 demonstrates that the cerium metal ion is mainly tetravalent, which has a clear red-shift compared with those of other doubledecker rare earth complexes. The IR spectra of these doubledeckers were relatively simple due to the high symmetry. In conclusion, the frequencies of pyrrole stretching, isoindole breathing, and aza stretchings are sensitive to the rare earth ionic size, and shift to the high energy along with the lanthanide contraction. These facts indicate that the p-p interaction in these double-deckers becomes stronger along with lanthanide contraction. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j. vibspec.2017.06.002. References
Fig. 7. IR spectra of Ce(Pc)2 and Ce[2,3-Pc(SPh)8]2(a = Ce(Pc)2, b = Ce[2,3-Pc (SPh)8]2).
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