Structure and spectroscopic properties of phthalocyaninato zinc(II) complexes fused with different number of 15-crown-5 moieties

Spectrochimica Acta Part A 72 (2009) 627–635

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Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa

Structure and spectroscopic properties of phthalocyaninato zinc(II) complexes fused with different number of 15-crown-5 moieties Xue Cai a,b , Ning Sheng c , Yuexing Zhang a , Dongdong Qi a , Jianzhuang Jiang a,∗ a b c

Department of Chemistry, Shandong University, 27 Shanda Nanlu, Jinan 250100, China Department of Chemistry, Mudanjiang Normal College, Mudanjiang 157012, China Department of Chemistry, Jining University, Jining 273155, China

a r t i c l e

i n f o

Article history: Received 24 July 2008 Received in revised form 29 October 2008 Accepted 5 November 2008 Keywords: Phthalocyanine Crown ether Electronic absorption spectrum Vibrational spectrum Density functional theory (DFT)

a b s t r a c t A series of structurally closely related phthalocyaninato zinc(II) complexes fused with different number and/or disposition of 15-crown-5 groups at the peripheral positions Zn(Pc ) (1–6) [Pc = Pc, Pc(15C5), Pc(opp-15C5)2 , Pc(adj-15C5)2 , Pc(15C5)3 , Pc(15C5)4 ; Pc = unsubstituted phthalocyaninate; Pc(15C5) = 2,3(15-crown-5)phthalocyaninate; Pc(opp-15C5)2 = 2,3,16,17-bis(15-crown-5)phthalocyaninate; Pc(adj15C5)2 = 2,3,9,10-bis(15-crown-5)phthalocyaninate; Pc(15C5)3 = 2,3,9,10,16,17-tris(15-crown5)phthalocyaninate; Pc(15C5)4 = 2,3,9,10,16,17,24,25-tetrakis(15-crown-5)phthalocyaninate] have been designed, prepared, and spectroscopically characterized. The effect of number and dispositions of 15-crown-5 moieties on their electronic and vibrational spectroscopic properties was understood by systematic investigation over the electronic absorption, infra-red (IR), and Raman spectra of this series of phthalocyaninato zinc complexes. In addition, density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations were carried out to comparatively describe the molecular structures, atomic charges, electronic absorption spectra, infrared (IR), and Raman spectra of 1–6, revealing the nature of the main transitions in electronic absorption spectra and identifying the vibration modes in the IR and Raman spectra of the series of six complexes with the assistance of animated pictures produced on the basis of the normal coordinates. © 2008 Elsevier B.V. All rights reserved.

1. Introduction Phthalocyanines have been an important class of dyes and pigments since their first synthesis early in the last century [1]. Crown ethers have found wide applications in molecular electronic devices due to their remarkable recognition and metal binding properties [2]. The combination of these two functional subunits for the purpose of constructing novel supramolecular structures with novel multi-functional properties has attracted research interests since 1980s [3]. The first effort was the preparation of crown ether-substituted phthalocyaninato copper complex Cu[Pc(15C5)4 ] reported in 1986 [3]. Subsequently, corresponding crown ethersubstituted metal-free phthalocyanine and metal phthalocyanines was studied [4]. From that time, significant efforts have been paid in introducing different species of crown-ether substituents onto the phthalocyanine ring [5]. Very recently, this group has successfully incorporated different number of 15-crown-5 groups, from one to four, onto different peripheral positions of the phthalocyanine ligand in the monomeric phthalocyaninato copper complexes

∗ Corresponding author. Fax: +86 531 88565211. E-mail address: [email protected] (J. Jiang). 1386-1425/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2008.11.001

[6] and one of the two phthalocyaninato ligands of heteroleptic bis(phthalocyaninato) europium double-decker compounds [7]. As part of our continuous efforts in this direction, in the present paper, the series of phthalocyaninato zinc(II) complexes with different number of 15-crown-5 moieties at the peripheral positions 1–6 have been designed and prepared following the previous method (Fig. 1). For the purpose of understanding the effect of the number and disposition of the 15-crown-5 substituents on the spectroscopic characteristics of the series of structurally closely related phthalocyaninato zinc(II) complexes, their electronic absorption, IR, and Raman spectroscopic properties have been systematically studied. Nevertheless, density functional theory (DFT) and timedependent density functional theory (TD-DFT) calculations were carried out to comparatively describe the molecular structures, atomic charges, electronic absorption, infrared (IR), and Raman spectra of these phthalocyaninato zinc complexes. 2. Computational details The primal input structure for ZnPc (1) was obtained from our previous calculation result [8]. For the remaining 15-crownf-substituted phthalocyaninato zinc compounds 2–6, the different number of 15-crown-5 groups were introduced onto corresponding

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Fig. 1. Schematic molecular structures of phthalocyaninato znic(II) complexes fused with different number of 15-crown-5 moieties.

peripheral positions of phthlalocyanine ligand as the primal inputs. The ground-state structures of the series of phthalocyaninato zinc complexes in vacuum system were optimized using the selfconsistent field (SCF) convergence criteria tightened to at least 10−5 a.u., the default pruned (75, 302) grid, and a default threshold corresponding to a residual mean square (RMS) on residual forces smaller than 3 × 10−4 a.u. at the end of the minimization process. Using the energy-minimized structures generated in the previous step, normal coordinate analyses were carried out. Charge distribution was carried out using natural population analysis method [9] based on the minimized structure obtained with the Gaussian 03 program [10]. The primary calculated vibrational frequencies were scaled by the factor 0.9614 [11]. All calculations were carried out using the B3LYP method and the standard Lanl2dz basis sets. All calculations were performed with the Gaussian 03 program in the IBM P690 system in Shandong Province High Performance Computing Centre. 3. Experimental The series of phthalocyaninato zinc complexes in particular 15-crown-5-substituted compounds 2–6 were prepared according to the published procedures [6]. Electronic absorption spectra were recorded on a Hitachi U-4100 spectrophotometer. IR spectra were recorded in KBr pellets with 2 cm−1 resolution using a BIORADFTS-165 spectrometer. Resonance Raman spectra were recorded on a few grains of the solid samples with ca. 4 cm−1 resolution using a Renishaw Raman Microprobe, equipped with a Spectra Physics Model 127 He–Ne laser excitation source emitting at a wavelength of 458 nm and a cooled charge-coupled device (CCD) camera. The nature of the newly prepared phthalocyaninato

zinc complexes was unambiguously verified by their MALDITOF mass spectroscopic measurement results taken on a Bruker BIFLEX III ultra-high resolution mass spectrometer with ␣-cyano-4hydroxycinnamic acid as matrix. Zn[Pc(15C5)] (2): 768.5 [calculated for C40 H30 N8 O5 Zn(M+ ) 768.13]; Zn[Pc(opp-15C5)2 ] (3): 958.4 [calculated for C48 H44 N8 O10 Zn(M+ ) 958.32]; Zn[Pc(adj-15C5)2 ] (4): 958.4 [calculated for C48 H44 N8 O10 Zn(M+ ) 958.32]; Zn[Pc(15C5)3 ] (5): 1148.3 [calculated for C56 H58 N8 O15 Zn(M+ )1148.52]; Zn[Pc(15C5)4 ] (6): 1338.3 [calculated for C64 H72 N8 O20 Zn 1338.7]. 4. Results and discussion 4.1. Molecular structures and atomic charges Atomic labeling of Zn[Pc(15C5)4 ] (6) as a typical representative is given in Fig. 2. Table 1 compares our calculated structural parameters of the compounds 1–6 with the X-ray crystallographic data of bis(triethylenediamine-N)-[tetrakis(15-crown-5)5-phthalocyaninato] ruthenium(II) complex (TED)2 Ru[Pc(15C5)4 ] [12]. As can be found from the calculated data in Table 1, introduction of different number of 15-crown-5 moieties does not induce significant change in the structural parameters of phthalocyaninato zinc complexes. The bond lengths and bond angles for the of 15-crown-5-substituted complexes 2–6 are very similar to those of ZnPc (1), which also correspond with those revealed experimentally for (TED)2 Ru[Pc(15C5)4 ] [12]. However, the calculated distance from N1 atom to Zn of 6, 2.02 Å, is a little of shorter than that in (TED)2 Ru[Pc(15C5)4 ], 1.98 Å, because of the different ionic radius between Zn(II) and Ru(II). The N1 –C1 bond length of 6, 1.39 Å, is actually very close to that in (TED)2 Ru[Pc(15C5)4 ],

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Table 1 Calculated main structural parameters of ZnPc (1), ZnPc (15C5) (2), ZnPc(opp-15C5)2 (3), ZnPc(adj-15C5)2 (4), ZnPc(15C5)3 (5), and ZnPc(15C5)4 (6). Parametera

1

2

3

4

5

6

(TED)2 Ru[Pc(15C5)4 ]b

Zn–N1 N1 –C1 C1 –C2 C2 –C7 C2 –C3 C3 –C4 C4 –C5 ∠C1 –N1 –C8 ∠N1 –C1 –C2 ∠C1 –C2 –C7 ∠C7 –C2 –C3 ∠C2 –C3 –C4 ∠C3 –C4 –C5 ∠N1 –C1 –N2

2.02 1.39 1.47 1.42 1.40 1.41 1.42 109.52 108.38 106.84 121.11 117.79 121.10 126.95

2.02 1.39 1.47 1.42 1.40 1.40 1.44 109.14 108.45 106.98 121.19 118.18 120.63 126.85

2.02 1.39 1.47 1.42 1.40 1.40 1.44 109.46 108.33 106.94 120.66 118.61 120.59 127.09

2.02 1.39 1.47 1.42 1.40 1.41 1.44 109.46 108.32 106.96 121.42 118.10 120.61 127.08

2.02 1.39 1.47 1.42 1.40 1.40 1.44 109.46 108.35 106.94 120.62 118.65 120.58 127.09

2.02 1.39 1.47 1.42 1.40 1.40 1.42 109.48 108.33 106.94 120.59 118.67 120.60 127.12

1.9831 1.3774 1.4683 1.4008 1.3915 1.3886 1.4204 109.20 109.07 106.91 120.53 118.45 120.57 128.77

a b

See the atomic labeling shown in Fig. 2. Structural parameters taken from the single crystal analysis for (TED)2 Ru[Pc(15C5)4 ] cited from Ref. [11].

1.377 Å, according to the calculations. Similar to the situation for the N1 –C1 bond length, the calculated bond lengths for the C1 –C2, C2 –C7, C2 –C3, C3 –C4, and C4 –C5 bonds in compound 6 are also close to those found in (TED)2 Ru[Pc(15C5)4 ]. The calculated C1 –N1 –C8 bond angle in 6, 109.48◦ , is almost just the same to that found in (TED)2 Ru[Pc(15C5)4 ], 109.20◦ . Actually, the largest difference in the bond angle in the calculated data for 6 from that found in (TED)2 Ru[Pc(15C5)4 ] amounts only 1.6◦ , for N1 –C1 –N2 bond angle. Table S1 (supporting information) lists the atomic charges of the skeleton atoms calculated with NBO population method for 1–6. As can be seen, the charges of Zn, N1 , and N2 atoms for the series of compounds 1–6, about of 1.70, −0.82, and −0.54 e, respectively, remain almost unchanged even with the introduction of different number 15-crown-5 groups onto the phthalocyanine ligand for 2–6. In contrast, the charges of C␦ atoms appear sensitive to the substitution of 15-crown-5 groups, which increase from −0.21 e for 1 to about 0.33 e for 2–6 along with the incorporation of 15-crown-5 moieties, indicating the more effect of 15-crown-5 groups at the peripheral positions of phthaloycanine ligand on the charges of C␦ atoms.

At the end of this section, it is worth noting that the calculated results also reveal that the effect of lowering the molecular symmetry of phthalocyanine derivatives through asymmetric -bonded substitution of the peripheral protons is too small to be reflected in the molecular structure and the atom charges of the complexes 2–6. 4.2. Electronic absorption spectra The electronic absorption spectra of the series of phthalocyaninato zinc complexes 1–6 were recorded in CHCl3 and the data are summarized in Table 2. Fig. 3 displays the electronic absorption spectra in the range of 300–800 nm for 1–6. They are analogous to those reported for related monomeric phthalocyaninato metal complexes in particular Cu(Pc ) [Pc = Pc, Pc(15C5), Pc(opp-15C5)2 , Pc(adj-15C5)2 , Pc(15C5)3 , Pc(15C5)4 ] [6]. The absorption around 340–356 nm can be attributed to the phthalocyaninato Soret band for 1–6. The phthalocyaninato Q bands of 1–6 appear around 669–680 nm as a very strong absorption with two weak satellites around 604–616 and 642–650 nm, respectively. For the 15-crown5-substituted phthalocyaninato zinc complexes 2–6, an additional weak peak was also observed at 422–460 nm, which is absent in the unsubstituted ZnPc (1). Inspection over the results in Fig. 3 and Table 2 indicates that the Soret, Q, and weak absorptions at 422–460 nm show dependence on the number of 15-crown-5 moieties substituted at the peripheral positions of phthalocyanine ligand. Along with increasing the number of 15-crown-5 substituents, the Soret and Q bands shift gradually to the lower energy direction but the weak band at 422–460 nm to the higher energy direction. Apart from the absorption position, the appearance of the electronic spectra of these complexes is also sensitive to the number of 15-crown-5 substituents. For example, the weak absorption in the range of 422–460 nm for 15-crown-5-containing phthalocyaninato zinc complexes 2–6, gradually gets some intensity from 2 to 6 along with the increase in the number of 15-crown-5 sub-

Table 2 Electronic absorption data for phthalocyaninato zinc complexes ZnPc (1), ZnPc (15C5) (2), ZnPc(opp-15C5)2 (3), ZnPc(adj-15C5)2 (4), ZnPc(15C5)3 (5), and ZnPc(15C5)4 (6) recorded in CHCl3 .

Fig. 2. Atom labels of ZnPc(15C5)4 (6).

Complexes

max (nm)

1 2 3 4 5 6

340 340 350 350 356 356

460 436 436 430 422

604 606 606 607 616 616

643 642 643 643 648 650

669 671 671 672 678 680

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parison with that for complexes 2–6, at 598–610 nm, according to the calculation results. This is in good agreement with the experimentally recorded electronic absorption spectroscopic results as detailed above (Table 2). Comparison between the calculated and recorded electronic absorption spectroscopic results reveals that the calculated Soret band for 1–6 agrees well with the observed one in energy. However, the calculated Q band of 1–6 is at the higher energy side in comparison with the experimental one, indicating that the TDDFT method overestimates the energy level of both the LUMO and LUMO+1 orbitals and/or underestimates the energy level of HOMO. As expected, a common band expected in the range of 428–437 nm for 15-crown-5-substituted complexes 2–6 due mainly to the electron transition from the orbital 188–190 LUMO is corresponding well with the observed absorption at 422–460 nm for 2–6. To get information about the composition of the orbital 188, the isosurface plot of the orbital 188 for 2 is given in Fig. 5 and the atomic composition compared in Table S2 (supporting information). Accordingly, the orbital 188 of 2 is mainly composed of 5Pz orbital of O1 and O2 atoms, 4Pz orbital of N1 atom, and 4Pz and 5Pz orbitals of C2 –C7 atoms of benzene ring. As a consequence, the observed absorption at 422–460 nm for 15-crown-5-substituted complexes 2–6 is therefore be attributed to the n → * transitions arising from the lone pairs of electrons of the O atoms. This also rationalizes the observation of a similar absorption band for other 15-crown-5-substituted phthalocyanine compounds as well as alkoxy-substituted phthalocyanine derivatives [3,14]. It is noteworthy that the expected absorption of the n → * transition gradually blue-shifts from 437 nm for 2 to 428 nm for 6 along with the increase in the number of 15-crown-5 substituents, which is in good accordance with the experimental findings. Fig. 3. Recorded electronic absorption spectra of ZnPc (1), ZnPc (15C5) (2), ZnPc(opp-15C5)2 (3), ZnPc(adj-15C5)2 (4), ZnPc(15C5)3 (5), and ZnPc(15C5)4 (6) in CHCl3 .

stituents. This result clearly reveals the origin of this absorption, which should be associated with the 15-crown-5 substituents. It is noteworthy that for the isometric compounds 3 and 4, a very slight shift is observed for some of the absorption bands, indicating that the electric absorption properties are more or less dependent on the substituent positions. Table 3 summarizes the calculated wavelength, oscillator strength, and molecular orbital excitations for the most relevant transitions of electronic absorption bands for the whole series of complexes 1–6, obtained in vacuum system using TD-DFT method. The electronic absorption spectra were simulated by fitting to Lorentzian line with a half-width at half-maximum of 10 [13]. In the Soret band region between 300 and 400 nm and Q band region between 600 and 700 nm, compounds 1–6 displays very intense absorptions in the simulated electronic absorption spectra (Fig. 4). For example, the expected band at 337 nm in the simulated electronic absorption spectrum of 2, which mainly involves electron transfer from the orbital 185 to LUMO (orbital 191), corresponds with the observed band at 340 nm of the same compound in CHCl3 . The simulated bands centered at 600 and 598 nm due to the electronic transitions from HOMO to LUMO and LUMO + 1, respectively, with small energy difference for 2 should combine together to correspond with the observed Q absorption at 671 nm. According to our calculation results, the energy gap between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) for ZnPc (1) is a bit of bigger, 2.20 eV, than that of the series of phthalocyanino zinc complexes substituted with different number of 15-crown-5 moieties 2–6, about 2.18 eV. As a consequence, the Q band of 1 appears at the higher energy side, 581 nm, in com-

Fig. 4. Simulated electronic absorption spectra of ZnPc (1), ZnPc (15C5) (2), ZnPc(opp-15C5)2 (3), ZnPc(adj-15C5)2 (4), ZnPc(15C5)3 (5), and ZnPc(15C5)4 (6).

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Table 3 Calculated wavelength (, nm), oscillator strength (f), and composition in terms of molecular orbital excitations for the most relevant transitions of ZnPc (1), ZnPc (15C5) (2), ZnPc(opp-15C5)2 (3), ZnPc(adj-15C5)2 (4), ZnPc(15C5)3 (5), and ZnPc(15C5)4 (6) by TD-DFT. 1

2

Wavelengtha

Transitionb

Wavelengtha

Transitionb

581 nm (f = 0.40)

(0.56)138HOMO → 139LUMO (0.20)138 → 140 (0.57)138HOMO → 140 (0.20)138 → 139 LUMO

600 nm (f = 0.42)

(0.49)189HOMO → 190LUMO

598 nm (f = 0.39)

(0.49)189HOMO → 191

437 nm (f = 0.14) 337 nm (f = 0.42)

(0.61)188 → 190 LUMO (0.32)185 → 191 (0.28)181 → 191

336 nm (f = 0.40)

(0.27)178 → 191 (0.26) 185 → 190 LUMO

581 nm (f = 0.40)

335 nm (f = 0.48)

324 nm (f = 0.38)

(0.13) 136 → 139 LUMO (0.20) 137 → 140 (0.52)130 → 139 LUMO (0.38)129 → 140 (0.24)125 → 139 LUMO

3

4

Wavelengtha

Transitionb

Wavelengtha

Transitionb

606 nm (f = 0.50) 601 nm (f = 0.37) 437 nm (f = 0.31) 350 nm (f = 0.51) 345 nm (f = 0.26)

(0.46)240HOMO → 241LUMO (0.46) 240 HOMO → 242 (0.55) 239 → 241 LUMO (0.51)230 → 242 (0.45)230 → 241 LUMO

603 nm (f = 0.43) 603 nm (f = 0.43) 435 nm (f = 0.16) 337 nm (f = 0.42) 336 nm (f = 0.30)

(0.59)240HOMO → 241LUMO (0.59) 240HOMO → 242 (0.51)239 → 241 LUMO (0.30)234 → 242 (0.28)228 → 242

Wavelengtha

Transitionb

Wavelengtha

Transitionb

608 nm (f = 0.48)

610 nm (f = 0.48)

(0.60)342HOMO → 343LUMO

610 nm (f = 0.48)

(0.60)342HOMO → 344

431 nm (f = 0.25)

(0.46)291HOMO → 292LUMO (0.40) 291 HOMO → 293 (0.46)291HOMO → 293 (0.39)291HOMO → 292LUMO (0.51)288 → 293

428 nm (f = 0.40)

353 nm (f = 0.16) 350 nm (f = 0.24)

(0.41)281 → 293 (0.33)278 → 292 LUMO

352 nm (f = 0.35) 339 nm (f = 0.55)

(0.51)338 → 343 LUMO (0.39) 338 → 344 (0.58)329 → 343 LUMO (0.39)330 → 344

5

6

605 nm (f = 0.42)

a b

Calculated wavelength (, nm) by TD-DFT. Corresponding oscillator strength(f) is given in parentheses. The nature of the electronic transition and contribution of each transition are shown in parentheses.

4.3. Infrared spectra

Fig. 5. The isosurface plot of the molecular orbital 188 for ZnPc(15C5) (2).

Fig. 6 shows the recorded IR spectra of 1–6, which also resemble those of analogous Cu(Pc ) [Pc = Pc, Pc(15C5), Pc(opp-15C5)2 , Pc(adj-15C5)2 , Pc(15C5)3 , Pc(15C5)4 ] [6]. As expected, the presence of one, two, three, and four 15-crown-5 moieties on the peripheral positions of phthalocyanine ring in the molecules of compounds 2–6 increases the number of IR-active modes in comparison with 1. It is worth noting that despite of several additional peaks observed for 6 compared with 1, the characteristic pattern of the IR spectrum for 6 still remains relatively simple compared with those of 2–5, revealing the relatively higher molecular symmetry for 6. The molecular point group symmetry for 1, 6, and 3, is D4h , C4 , and C2 point group while 2, 4, and 5 have C1 point group, respectively. This is clearly revealed by the larger number of vibrational modes observed in the IR spectra of 2–5 compared with those of either 1 or 6 in Table 4. Two common absorptions at about 940 and 1200 cm−1 were observed in the IR spectra of 5-crown-5-substituted complexes 2–6, the intensity of which increases along with the increase in the number of 15-crown-5 moiety from 2 to 6. Combination with the absence of these two bands in the IR spectrum of the unsubstituted compound ZnPc (1) clearly reveals the origin of these two absorptions of the 15-crown-5 groups. This point is supported by the calculation results shown in Fig. 7 and Table 4. On the basis of our calculations with the assistance of animated pictures produced on the base of normal coordinates, the former peak at 940 cm−1 is attributed to the C–O, C–C stretching, and C–H swing vibrations of 15-crown-5 groups, while the latter one at 1200 cm−1 due to the C–H swing of 15-crown-5 groups. Due to the pure 15-crown-5 origin of the former band with main contribution from the C–O stretching, the observed peak at about 940 cm−1 for compounds 2–6 can there-

632

Table 4 Experimental and calculated (scaled by 0.9614) IR active frequencies (cm−1 ) for ZnPc (1), ZnPc (15C5) (2), ZnPc(opp-15C5)2 (3), ZnPc(adj-15C5)2 (4), ZnPc(15C5)3 (5), and ZnPc(15C5)4 (6). 1

2 Assignmenta

Freq. Ex.

Cal. 567 740 788 856

Pc ring def., Zn–N str. C–H OPB C–H OPB C–N symstr., ben. def.

1058 1084 1114 1157

1057 1102

C–H sw., C–N asymstr. C–H sw., C–C str.

1153

C–H sw., C–N asymstr.

1281 1324

1279 1336

C–H sw., C–N symstr. C–H sw., C–C, C–N str.

1400 1448 1481 1595 2856 2926 3038

1384 1451 1462 1595

C–H sw., C–C, C–N str. C–H sw., C–N asymstr., C–C str., C–H sw., C–N asymstr., C–C str., Ben. def., Ben. C–H str. Ben. C–H str. Ben. C–H str.

3114

Ex.

Cal.

Ex.

Cal.

573 734 774 866 940 1057 1109

558 749 788 856 933 1067 1095

Pc, crown def., Zn–N str. C–H OPB C–H OPB C–N symstr., C–O str., ben. def., crown C–O, C–C str., C–H sw. C–H sw., C–N asymstr., crown C–O, C–H str. C–H sw., C–C, C–N str., crown C–O, C–C str.

578 736 772 866 938 1058 1103

557 750 788 856 933 1058 1102

Pc, crown def, Zn–N str. C–H OPB C–H OPB C–N symstr., C–O str., ben. def., crown C–O, C–C str., C–H sw. crown C–O, C–C str., C–H sw. C–H sw., C–N asymstr., crown C–O, C–H str. C–H sw., C–C, C–N str., crown C–O, C–C str.

1204 1284 1335 1382 1407 1461 1488 1610 2854 2922

1202 1278 1336 1403 1423 1442 1461 1567 2884 2903

Crown C–H sw. C–H sw., C–N symstr., C–O str. C–H sw., C–C, C–N str., crown C–H sw. C–H sw., C–C, C–N str., crown C–H sw. C–H sw., C–C, C–N str., crown C–H sw. C–H sw., C–N asymstr., C–C str., crown C–H sw. C–H sw., C–N asymstr., C–C str., crown C–H str. Ben. def., C–O str. C–H str. C–H str.

1202 1287 1335 1381 1409 1461 1490 1609 2856 2922

1190 1278 1336 1365 1394 1442 1461 1557 2893 2922

Crown C–H sw. C–H sw., C–N symstr., C–O str. C–H sw., C–C, C–N str., crown C–H sw. C–H sw., C–C, C–N str., crown C–H sw. C–H sw., C–C, C–N str., crown C–H sw. C–H sw., C–N asymstr., C–C str., crown C–H sw C–H sw., C–N asymstr., C–C str., crown C–H str. ben. def., C–O str. C–H str. C–H str.

4

5 a

Freq.

Assignment

Ex.

Cal.

574 737 772 867 937 1056 1105 1201 1281 1336 1380 1404 1462 1488 1607 2853 2922

557 755 789 884 926 1028 1067 1191 1268 1346 1352 1384 1422 1461 1557 2894 2923

a

Assignmenta

Freq.

Pc, crown def., Zn–N str. C–H OPB C–H OPB C–H OPB Crown C–O, C–C str., C–H sw. C–H sw., C–N asymstr., crown C–O, C–H str. C–H sw., C–N asymstr., crown C–O, C–H str. Crown C–H sw. C–H sw., C–N symstr., C–O str. C–H sw., C–C, C–N str., crown C–H sw. C–H sw., C–C, C–N str., crown C–H sw. C–H sw., C–C, C–N str., crown C–H sw. C–H sw., C–N asymstr., C–C str., crown C–H sw. C–H sw., C–N asymstr., C–C str., crown C–H sw. Ben. def., C–O str. C–H str. C–H str.

6 a

Freq.

Assignment

Ex.

Cal.

575 738 776 866 939 1056 1104 1199 1280 1340 1383 1404 1461 1490 1610 2855 2923

577 759 788 874 933 1028 1067 1192 1230 1346 1371 1384 1423 1461 1596 2893 2922

Pc, crown def., Zn–N str. C–H OPB C–H OPB C–H OPB Crown C–O, C–C str., C–H sw. C–H sw., C–N asymstr., crown C–O, C–H str. C–H sw., C–N asymstr., crown C–O, C–H str. Crown C–H sw. C–H sw., C–N symstr., C–O str. C–H sw., C–C, C–N str., crown C–H sw. C–H sw., C–C, C–N str., crown C–H sw. C–H sw., C–C, C–N str., crown C–H sw. C–H sw., C–N symstr., C–C str., crown C–H sw. C–H sw., C–N asymstr., C–C str., crown C–H sw. Ben. def., C–O str. C–H str. C–H str.

Assignmenta

Freq. Ex.

Cal.

583 743 812 867 938 1054 1102 1198 1281 1360

577 762 790 887 935 1019 1067 1192 1227 1356

Pc, crown def., Zn–N str. C–H OPB C–H OPB C–H OPB Crown C–O, C–C str., C–H sw. C–H sw., C–N asymstr., crown C–O, C–H str. C–H sw., C–N asymstr., crown C–O, C–H str. Crown C–H sw. C–H sw., C–N symstr., C–O str. C–H sw., C–C, C–N str., crown C–H sw.

1402 1458 1495 1611 2872 2922

1384 1422 1461 1557 2893 2922

C–H sw., C–C, C–N str., crown C–H sw. C–H sw., C–N symstr., C–C str., crown C–H sw. C–H sw., C–N asymstr., C–C str., crown C–H sw. Ben. def., C–O str. C–H str. C–H str.

OPB: out-of-plane bending; IPB: in-plane bending; def.: deformation; str.: stretching; bre.: breathing; sw.: swing; symstr.: symmetry stretching; asymstr.: asymmetry stretching; ben.: benzene ring; crown: 15-crown-5 groups.

X. Cai et al. / Spectrochimica Acta Part A 72 (2009) 627–635

566 728 775 881

3 Assignmenta

Freq.

X. Cai et al. / Spectrochimica Acta Part A 72 (2009) 627–635

633

1448, and 1481 cm−1 are clearly due to the contribution of the C–H swing as well as C–N and C–C stretching, without any contribution from 15-crown-5 group. Additional peak observed in the range of 1607–1611 cm−1 for 2–6 (Fig. 6) can be attributed to the deformation modes of the benzene ring and C␦ –O stretching with the help of calculation results. Corresponding absorption for unsubstituted compound 1 due to the deformation modes of the benzene ring appears at 1595 cm−1 , which corresponds well with the calculated band just at 1595 cm−1 . In comparison with ZnPc (1), the additional peaks with relatively strong or strong intensity were observed at 2853–2872 and 2922–2923 cm−1 , respectively, for 2–6 (Table 4). According to the calculations, these bands are corresponding to the C–H swing of the 15-crown-5 groups expected at 2884–2894 and 2903–2923 cm−1 , respectively, for these compounds, which agree well with previous results [16,17]. This assignment is supported by such a fact that the intensity of these two peaks for 2–6 gradually increases along with the increase in the number of 15-crown-5 moiety. It is worth noting that in the similar region, three relatively weak peaks at 2856, 2926, and 3038 cm−1 due to the C-H stretching of benzene ring have also been observed for ZnPc (1). It can be found that despite of the complexity in the IR spectra of the 15-crown-5-substituted phthalocyanine compounds, most of the vibration modes can be identified and assigned by comparison with the unsubstituted analogue. To ensure our calculation results, Fig. S1 (supporting information) gives the correspondence relationship of the calculated and experimental data by fitting them to a linear function. The slope of the line is 0.998 and the intercept only 4.55, showing good consistency between the calculated and the Fig. 6. Recorded IR spectra of phthalocyaninato zinc complexes 1–6 in the region of 500–1800 cm−1 .

fore be assigned as the marker IR band for the 15-crown-5 groups. As displayed in Fig. 6, in the range of 1000–1200 cm−1 , four peaks at 1058, 1084, 1114, and 1157 cm−1 are recorded for 1, whereas two peaks at 1054–1058 and 1102–1109 cm−1 are present in the recorded spectra of compounds 2–6. Our calculation results predict three peaks appearing at 1057, 1102, and 1153 cm−1 for 1, while two peaks at 1019–1067 and 1067–1102 cm−1 for 2–6 (Fig. 7 and Table 4). Nevertheless, according to the calculation results the first peak for 1 is revealed to result from the C–H swing together with C–N asymmetric stretching, the second from C–H swing, and C–C stretching, and the third one due to C–H swing and C–N stretching. While for 2–6, the two bands are additionally contributed from the C–O, C–C, and C–H stretching of the 15-crown-5 moieties (Table 4). A common medium peak at 1281–1287 cm−1 was observed for 1–6, which is contributed from the C–H swing, and C–N symstretching but with additional contribution from the C␦ –O stretching for 2–6. In addition, a common peak in the higher energy range of 1324–1360 cm−1 was also observed for 1–6 (Fig. 6), which appears to correspond well with the band observed at 1329 cm−1 for Pb[Pc(␣-OC5 H11 )4 ] [15]. Along with increasing the number of 15crown-5 substituents, this absorption gradually shifts to the higher energy direction. Calculation results indicate that this vibration is due to the C–H swing, C–C, and C–N stretching (Table 4), which is also the marker IR band for phthalocyanine dianion [15]. It is worth noting that the fact that the weak peak observed at about 1380 cm−1 due to the combination of the C–H swing of 15-crown-5 groups and C–H swing and C–C stretching of phthalocyanine ligand in 2–5 was not found in the IR spectrum of 1 and 6. In the region from 1400 to 1500 cm−1 , all the six complexes 1–6 show similar vibrational peaks. However, the three peaks observed at 1402–1409, 1458–1462, and 1488–1495 cm−1 for 15-crown-5-substituted complexes 2–6 are assigned to the C–H swing, C–N and C–C stretching, and C–H swing of the 15-crown-5 groups on the basis of calculation results (Table 4). In contrast, the three peaks observed for 1 at 1400,

Fig. 7. Simulated IR spectra of phthalocyaninato zinc complexes 1–6 in the region of 500–3500 cm−1 .

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X. Cai et al. / Spectrochimica Acta Part A 72 (2009) 627–635

experimental data. The full set of calculated IR vibration modes for 1–6 are compared mode by mode with the assistance of animated pictures (Table 4). 4.4. Raman spectra The Raman spectra of 1–6 were recorded with excitation at 458 nm (Fig. 8). As can be seen, there are less obvious Raman peaks than IR for 1–6 probably due to the complex coupling of the Raman peaks. In line with the observation of their IR spectra, the Raman spectra for 2–5 also appear more complicated than those of 1 and 6 due to their diminished molecular symmetry. As expected, actually only frequencies corresponding to the characteristic fingerprint of the phthalocyanine macrocycle were observed and the 15-crown-5 substituent vibrations were very weak and absent in the Raman spectra of 2–6 [18]. As a result, only the Raman spectrum of compound 2 substituted with one 15-crown5 moiety is theoretically calculated as the typical representative of the series of substituted phthalocyaninato zinc complexes 2–5. The observed Raman spectroscopic frequencies of 1–6 as well calculated ones for 1 and 2 were partially assigned in Table S3 (supporting information). The Raman band observed in the range of 1503–1520 cm−1 for 1–6 maintains intensity, appearing as the most intense band in all cases, which is the marker Raman band for phthalocyanine dianion. In line with the previous point [17,19], this strongest Raman band for 1–6 is indeed due to the C–N asymmetric and C–C stretching, which contains no contribution from

the 15-crown-5 moiety vibration, according to our calculations. At the higher energy side of the most intense band, two separated peaks with medium intensity at 1581–1594 and 1601–1610 cm−1 for 1–6, respectively, contributed mainly from the isoindole ring stretching and aza group stretchings were observed in their Raman spectra. They should correspond with the two expected bands at 1586 and 1597 cm−1 , respectively. However, according to the calculation results, these two vibration bands neighboring at the most intense calculated band at 1519 cm−1 appears very weak in intensity for 2 (Fig. S2 (supporting information)). In addition, a common band with medium intensity was observed at 1403–1419 for the series of complexes 1–6. This peak corresponds with the one expected at 1422 and 1403 cm−1 for 1 and 2, respectively, due to the C–H swing, C–C, and C–N stretching for the former compound 1, while with additional contribution from C–O stretching vibration for the latter 15-crown-5-substituted complex 2. In the range of 1200–1400 cm−1 , three medium bands are observed. The peak observed at 1337–1351 cm−1 for 1–6 is assigned to the isoindole ring stretching and the aza group stretchings on the basis of the calculation results, which is expected at about 1350 cm−1 for 1 and 2. The Raman absorption band observed at 1280–1283 cm−1 for 2–6, shifted to higher energy side at 1306 cm−1 for 1, is assigned to the isoindole ring stretching and the aza group stretchings. The Raman band observed at 1194–1208 cm−1 for 2–6 is due to the C–H swing and C–N asymmetric vibration. In the range of 1000–1200 cm−1 , there are one medium and one weak bands lying at 1110–1124 and 1010–1023 cm−1 , respectively, for 1–6. The former one is assigned to the C–N symmetric stretching, C–C stretching, and C–H swing, whereas the latter contributed mainly from the benzene ring breathing and C–H swing vibration. The medium band observed at 748–751 cm−1 for 1–6 is due to the C–H swing of phthalocyanine macrocycle and Zn–N stretching. In line with previous results [17], the weak Raman band observed at 584–591 nm for 1–6 is attributed to the phthalocyanine ring breathing, which corresponds with the calculated peak at 576 nm for 1. 5. Conclusion Summarizing briefly above, a series of six of phthalocyaninato zinc complexes containing different number of 15-crown-5 moieties at the peripheral positions of phthalocyanine ligand have been designed and prepared. Their electronic structures and in particular electronic absorption, infrared (IR), and Raman spectra were comparatively studied by spectroscopic techniques and DFT calculations, revealing the nature of the main transitions in their electronic absorption spectra. With the assistance of animated pictures produced on the basis of the normal coordinates, the vibration modes in the IR and Raman spectra of the series of phthalocyaninato zinc complexes have also been identified. Acknowledgements Financial support from the Natural Science Foundation of China and Ministry of Education of China, and Shandong University is gratefully acknowledged. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.saa.2008.11.001. References

Fig. 8. Recorded Raman spectra of ZnPc (1), ZnPc (15C5) (2), ZnPc(opp-15C5)2 (3), ZnPc(adj-15C5)2 (4), ZnPc(15C5)3 (5), and ZnPc(15C5)4 (6) with laser excitation source emitting at a wavelength of 458 nm.

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