Structural characterisation and DFT calculations of three new complexes of zinc phthalocyanine with n-alkylamines

Dyes and Pigments 100 (2014) 247e254

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Structural characterisation and DFT calculations of three new complexes of zinc phthalocyanine with n-alkylamines Bartosz Przyby1, Jan Janczak* Institute of Low Temperature and Structure Research, Polish Academy of Sciences, P.O. Box 1410, Okólna 2 Str., 50-950 Wrocław, Poland

a r t i c l e i n f o

a b s t r a c t

Article history: Received 26 July 2013 Received in revised form 11 September 2013 Accepted 12 September 2013 Available online 20 September 2013

Three complexes of zinc phthalocyanine monoaxially ligated by n-alkylamines (n-butylamine, n-amylamine and n-heptylamine) in the crystalline form were obtained and studied. These zinc phthalocyanine ligated by n-alkylamine complexes crystallize with the n-alkylamine molecules as solvates in the centrosymmetric space group. Two of them (with n-butylamine and n-amylamine) crystallize in the P21/ c space group of monoclinic system while the third (with n-heptylamine) in the triclinic system. The zinc centre of these molecules is 4 þ 1 coordinated by four isoindole nitrogen atoms of phthalocyaninate(2-) macrocycle in the equatorial position, and by the nitrogen atom of n-alkylamine in an axial position. Owing to the interaction of electropositive zinc centre of zinc phthalocyanine with the amine nitrogen atom of n-alkylamines, the zinc atom is significantly displaced (w0.5  A) from the plane defined by the four isoindole nitrogen atoms of phthalocyaninate(2-) macrocycle. The monoaxially ligation of zinc centre of zinc phthalocyanine molecule by n-alkylamines leads to distortion of the planar zinc phthalocyanine molecule to the saucer-shape form. X-ray conformations of these molecules are compared with the conformation of that in the gas-phase as obtained by the density functional theory calculations. The calculated three-dimensional molecular electrostatic potential maps are helpful for understanding of the interaction between the zinc phthalocyanine and n-alkylamines molecules forming the monoaxially ligated zinc phthalocyanine complexes. Thermogravimetric analysis and the UVeVis spectroscopy were used for characterisation of these complexes. The Q band of these complexes (at about 670 nm) does not change comparing to that of the parent colorant. The monoaxially ligated by n-alkylamines zinc phthalocyanine dyes are about 5 times more soluble than the parent zinc phthalocyanine pigment. Ó 2013 Elsevier Ltd. All rights reserved.

Keywords: Zinc phthalocyaninate complexes n-Alkylamine Crystal structure UVeVis spectroscopy DFT Molecular electrostatic potential

1. Introduction Phthalocyanine and its metal complexes, in spite of the fact that they have known since several dozen years, still arouses interest because of exhibition of many important features which gives potential application in many fields from industry do medicine [1,2]. Structurally, phthalocyanine is consists of four isoindole units connected by azamethine bridges to form 18-p aromatic macroring (Scheme 1). Zinc phthalocyanine derivatives (ZnPcs) have proved to be promising photosensitizers in photodynamic therapy due to strong absorption in the red region of visible radiation. The advantage of ZnPc over phthalocyanine complexes of transition metals are high triplet quantum yield and long lifetimes, these are required for effective sensitization [3]. Zinc phthalocyanines are also attractive

* Corresponding author. E-mail address: [email protected] (J. Janczak). 0143-7208/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.dyepig.2013.09.020

sensitisers for photodegradation of pollutants, for example the oxidation of chlorinated phenols [4,5], sulphur containing organic compounds [6,7] and 4-nitrophenol [8]. Phthalocyanines are known for their very poor solubility in many solvents because of strong stacking interaction between molecules in the solid-state. This property seriously limits potential applications of these compounds. There are main two methods to increase the solubility: (1) by symmetrical or unsymmetrical substitution on peripheral aromatic rings with different functional groups and/or (2) by axial ligation of central metal ion by different organic or inorganic ligands (Scheme 1). These modifications are made to limit stacking interactions to improve interactions with solvent molecules. Several structures of zinc phthalocyanine with aromatic axial ligands, mainly based on pyridine and its derivatives [9e11], as also 4,40 -dipyridyl [12] and 3,30 -dipyridyl [13] compounds with different linkers, are present in the literature. The first, and only experiment of recrystallization of zinc phthalocyanine from nalkylamine was made by T. Kobayashiet et al., in 1971 [14]. They

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peripheral substituents N N N

N M

N

N

non-peripheral substituents

N N metal center axial ligand(s)

Scheme 1. The ways of possible modifications of metallophthalocyanines showing the 18-p electron aromatic macroring.

published structure of ZnPc monoaxially ligated by n-hexylamine, but some structural aspects are ambiguous or unclear. Since then any crystalline complex of metallophthalocyanines with any nalkylamine was not published. This fact induced us to synthesis of complexes of ZnPc with n-butylamine, n-amylamine and n-heptylamine to examine their crystal structures, thermal stability and spectral properties. 2. Experimental 2.1. Materials and methods All chemical reagents are commercially available and were used without further purification. The electronic absorption spectra were carried out at room temperature using a Cary Varian SE UVe ViseNIR spectrometer. The spectra of 1, 2 and 3 were recorded in solution of the respective n-alkylamine (105 mol/l). Thermogravimetric analysis was achieved with TG-DTA Setaram SETSYS 16/18 analyser with heating rate 5  C min1. The rest of the sample left after thermogravimetric analysis was measured on an STOE diffractometer equipped with a linear PSD detector [15] using Cu Ka1 radiation (l ¼ 1.54060  A) at room temperature. The composition of the crystals was checked with energy dispersive spectrometry (EDS) as well as with a PerkineElmer 240 elemental analyser. EDS spectra were acquired and analysed using an EDAX Pegasus XM4 spectrometer with SDD Apollo 4D detector mounted on a FEI Nova NanoSEM 230 microscope. The NMR spectra of saturated ZnPc(n-alkylamine) complexes in deuterated chloroform were taken on Bruker Avance 500 and AMX 300 spectrometers. The chemical shifts were referenced to the residual solvent signals. The vibrational measurements were carried out at room temperature. The Fourier transform infrared spectrum was recorded from nujol and fluorolube mulls between 4000 and 400 cm1 on a Bruker IFS 113 V FTIR. Resolution was set up to 2 cm1. 2.2. Preparation 2.2.1. n-Butylamine(phthalocyaninato)zinc n-butylamine solvate (1) Zinc phthalocyanine (pastille, 0.076 g, 0.132 mmol) was placed in glass elongated ampoule and then n-butylamine (6.0 mL) was added. Quite good solubility of phthalocyanine in butylamine was observed in room temperature. The system was degassed to

pressure 0.15 hPa and the ampoule was sealed. The ampoule was heated in 90  C in a horizontal position until whole pastille of ZnPc was dissolved (c.a. 20 h). After this time the ampoule was cooled to room temperature, opened and the solution was transferred to 50 ml beaker covered by Petri dish and left in room temperature. First very small crystals were observed after 1 h. After 24 h wellshaped rectangular single was filtered and washed by diethyl ether. Yield: 0.089 g, 93%. Anal. Calc. for C40H38N10Zn: C, 66.35; N, 19.34; Zn, 9.02 and H, 5.29%. Found: C, 66.54; N, 19.41; Zn, 9.05 and H, 5.00%. 1H NMR: (ppm) 8.1 and 9.34 (peripheral and nonperipheral aromatic H of Pc), 0.46 (NH2), 0.51, 0.71, 0.92 and 1.23 for eC4H9. IR (cm1): 3361, 3285, 3048, 2954, 2926, 2856, 2547, 1653, 1608, 1584, 1487, 1455, 1408, 1378, 1331, 1264, 1181, 1164, 1115, 1091, 1061, 1003, 951, 886, 875, 827, 776, 749, 728, 633, 569, 499. 2.2.2. n-Amylamine(phthalocyaninato)zinc n-amylamine solvate (2) The procedure was strictly the same as in the case of complex 1 with using similar mass of zinc phthalocyanine pastille (0.080 g; 0.139 mmol) and n-amylamine (6.0 mL). Heating temperature was raised to 100  C. Well-shaped rectangular crystals were also isolated after 24 h. Yield: 0.100 g, 96%. Anal. Calc. for C42H42N10Zn: C, 66.07; N, 18.62; Zn, 8.69 and H, 5.63%. Found: C, 66.24; N, 18.71; Zn, 8.75 and H, 5.33%. 1H NMR: (ppm) 8.07 and 9.27 (peripheral and non-peripheral aromatic H of Pc), 0.83 (NH2), 0.34, 0.54, 0.55, 0.81 and 1.23 for eC5H11. IR (cm1): 3359, 3283, 3047, 2952, 2923, 2855, 2547, 1747, 1607, 1583, 1486, 1455, 1408, 1377, 1331, 1285, 1181, 1165, 1116, 1091, 1061, 1004, 951, 896, 874, 827, 776, 750, 728, 634, 570, 500. 2.2.3. n-Heptylamine(phthalocyaninato)zinc n-heptylamine solvate (3) Zinc phthalocyanine (pastille 0.121 g; 0.209 mmol) was placed in glass elongated ampoule and then n-heptylamine (6.0 mL) was added. Quite good solubility of phthalocyanine in heptylamine was observed in room temperature. The system was degassed to pressure 0.15 hPa and the ample was sealed. The ampoule was heated in 160  C in a slightly oblique position this way that the solution did not reach the top of the ampoule. After 20 h fused crystals were observed on the edge of the solution. Crystals were separated from the solution, which was transferred into 50 mL beaker covered by Petri dish and left in room temperature. Well-shaped single crystals were found in the beaker after 3 days. Crystals obtained in high temperature and these from room temperature solution proved to crystallize in the same space group. Yield: 0.154 g, 91%. Anal. Calc. for C46H50N10Zn: C, 68.35; N, 17.33; Zn, 8.09 and H, 6.23%. Found: C, 68.54; N, 17.45; Zn, 8.05 and H, 5.96%. 1H NMR: (ppm) 8.09 and 9.32 (peripheral and non-peripheral aromatic H of Pc), 0.38 (NH2), 0.49, 0.54, 0.75, 0.87, 0.97, 1.10 and 1.24 for eC7H15. IR (cm1): 3336, 3280, 3052, 2945, 2921, 2849, 2536, 1609, 1584, 1484, 1454, 1406, 1375, 1331, 1284, 1181, 1162, 1114, 1090, 1061, 1003, 951, 887, 854, 796, 775, 750, 724, 679, 634, 570, 499. 2.3. X-ray single crystal measurements and crystal structure analysis Single crystal X-ray diffraction measurements of 1, 2 and 3 were carried out at 295 K on a four-circle KUMA KM4 diffractometer equipped with two-dimensional CCD area detector. Graphite monochromatized Mo-Ka radiation (l ¼ 0.71073  A) and u-scan technique (Du ¼ 1 ) were used for data collection. Data collection and reduction along with absorption correction were performed using CrysAlis software package [16]. The structures were solved by direct methods using SHELXS-97 [17], which revealed the positions

B. Przybył, J. Janczak / Dyes and Pigments 100 (2014) 247e254 Table 1 Crystallographic data for 1, 2 and 3.

0

1

2

3

C40H38N10Zn 724.19

C42H42N10Zn 752.25

C46H50N10Zn 808.35

Monoclinic, P21/c

Monoclinic, P21/c

Triclinic, P-1

12.4235(7) 15.4622(8) 18.7898(9) 90.0 93.509(3) 90.0 3602.7(3) 4 1.335/1.33

12.642(2) 15.159(2) 19.581(3) 90.0 93.41(1) 90.0 3745.9(1) 4 1.334/1.33

10.2913(6) 13.9352(6) 15.3241(9) 80.854(4) 73.307(5) 81.197(4) 2064.8(2) 2 1.300/1.30

-5

-Mass loss [%]

Empirical formula Formula weight (g mol1) Crystal system, space group a ( A) b ( A) c ( A) a ( ) b ( ) g ( ) V ( A3) Z Dcalc/Dobs (g cm3) m (mm1) F(000) Crystal size (mm) Radiation type, wavelength, l ( A) Temperature (K) q range( ) Tmin/Tmax Refs collected/ unique/ observed Rint Refinement on F2 R[F2 > 2s(F2)] wR(F2 all reflections) Goodness-of-fit, S Drmax, Drmin (e  A3)

249

-10 -15

ZnPcBA x BA

-20 -25

ZnPcAA x AA

-30

ZnPcHA x HA 50

100

150

200

o

Temperature [ C] Fig. 1. Thermograms for ZnPcBA∙BA (B), ZnPcAA∙AA (>) and ZnPcHA∙HA (,).

0.726 0.701 0.641 1512.0 1576.0 852.0 0.28  0.18  0.16 0.32  0.28  0.24 0.37  0.33  0.21 Mo Ka, 0.71073

295(2) 2.80O28.50 0.8266/08983 46519/9066/4891

295(2) 2.56O28.51 0.8124/0.9512 50515/9415/5248

295(2) 2.80O28.05 0.8036/0.8803 27255/9928/5126

0.0489

0.0747

0.0622

0.0607 0.1707

0.0685 0.1132

0.0664 0.1149

1.008 þ0.617, 0.422

1.000 þ0.477, 0.364

1.002 þ0.334, 0.316

which are present in the crystals as a solvent molecules, were performed with the Gaussian03 program package [19]. All calculations were carried out with the DFT level using the Becke3-LeeYang-Parr correlation functional (B3LYP) [20,21] with the 6-31 þ G* basis set assuming the geometry resulting from the X-ray diffraction study as the starting structure. As convergence criterions the threshold limits of 0.00025 and 0.0012 a.u. were applied for the maximum force and the displacement, respectively.

3. Results and discussion

of almost all non-hydrogen atoms. The remaining atoms were located from subsequent difference Fourier syntheses. The structure was refined using SHELXL-97 [17] with the anisotropic thermal displacement parameters. Visualization of the structures was made with the Diamond 3.0 program [18]. Details of the data collection parameters, crystallographic data and final agreement parameters are collected in Table 1. 2.4. Theoretical calculation Theoretical calculations with geometry optimization of 1, 2 and 3 as well as the n-butylamine, n-amylamine and n-heptylamine,

3.1. Synthesis and characterisation Our preparation method of the single crystals of 1, 2 and 3 is very simple. The suspension of b-ZnPc in respective n-alkylamine (n-butylamine, n-amylamine and n-heptylamine) was heated in degassed and evacuated glass ampoule. The respective n-alkylamine with the electron pair at the N atom amine group is nucleophilic. During the heating process the electronegatively polarised nitrogen atom of the rescpective n-alkylamine with the lone pair of electron interacts with electropositively polarised Zn centre of ZnPc molecule forming coordinating ZneN bond yielding the 4 þ 1 coordinated ZnPc(n-alkylamine) complexes (Scheme 2). During the cooling process to the room temperature the 4 þ 1 coordinated ZnPc(n-alkylamine) complexes crystallise with the solvent molecules yielding blue-violet well-developed single crystals of 1, 2 and 3. The obtained crystals are about 5 times more soluble in the most organic solvents than the parent ZnPc due to the

( )n

NH2 N N N

N

N Zn

N

N N

+ 2

( )n

NH2

N N

N Zn

N

N

N N

N n = 2 (n-butylamine) n = 3 (n-amylaminine) n = 5 (n-heptylamine) Scheme 2. Synthetic route of ZnPc(n-alkylamine) n-alkylamine.

x

( )n

NH2

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steric hindrance of respective axial n-alkylamine that lowering the pep interaction in solid. 3.2. Thermal stability In order to determine the thermal stability of these complexes investigated here, the thermal analyses of 1, 2 and 3 were carried out on the samples of w50 mg with the same heating rate of 5  C/ min. The thermogravimetric analyses of the solid-state samples are shown in Fig. 1. Crystal 1 is stable up to w90  C, and at higher temperature loses the solvated n-butylamine molecules. After loss of the solvent n-butylamine molecules, the starting compound transforms into ZnPc(n-butylamine) complex, which during further heating loses the coordinated n-butylamine molecule (at w 125  C) and finally transforms into ZnPc in b-form that was confirmed by the X-ray powder diffraction experiment. The respective weight losses correspond well to the weight decrease by 10.12% due to release the solvated n-butylamine molecules (w92  C) and coordinated n-butylamine molecule from crystal 1. The calculated total weight loss is equal to 20.19% and agrees well with the weight loss observed in TG experiment (Fig. 1). Crystal 2 loses its solvated n-amylamine molecules at w95  C. After loss of solvent n-amylamine molecules the starting compound transforms into ZnPc(n-amylamine) complex, which during further heating loses the coordinated n-amylamine molecule (w128  C) and finally transforms into b-ZnPc (confirmed by the Xray powder diffraction experiment). The respective mass loss on the heating are w11.5% (solvated n-amylamine) and w23% (both solvated and coordinated n-amylamine molecule), and are in agreement with the calculated values of 15.58% and 23.17%, respectively. Crystal 3 loses both n-heptylamine molecules (solvated and coordinated) at the same temperature (w122  C). The total mass loss of w28% is in agreement with the calculated value of 28.06%. Two steps of the thermal decomposition of the solid state complex 1 and 2 and one step for complex 3 correlate well with boiling point of respective amines (n-butylamine 77  C, n-amylamine 104  C and n-heptylamine 155  C). Probably, in complex 3 the NeH$$$N hydrogen bond breaks at a similar temperature to 1 and 2, but its too low to observe the first step due to relatively high boiling point of n-heptylamine. Therefore, in 3 both solvated and coordinated nheptylamine molecules are removed simultaneously at the same temperature. The thermal analyses of these pentacoordianted ZnPc-complexes axially ligated by n-alkylamines show similar strength of the axial ZneN bonds and are in agreement with the Xray crystal structure analysis. 3.3. Description of the structures and molecular arrangement Complexes 1 and 2 crystallize in centrosymmetric space group P21/c of monoclinic system, while complex 3 in triclinic centrosymmetric group. Asymmetric unit of 1, 2 and 3 contains zinc phthalocyanine monoaxially ligated by n-butylamine, n-amylamine and n-heptylamine, respectively (Fig. 2a, b and c). In every case the amino group of coordinated n-alkylamine plays role of NeH$$$N hydrogen bond donor to second molecule of n-alkylamine. In complexes 1, 2 and 3 Zn(II) centre is pentacoordinated forming a distorted square pyramid. Interaction between lone pairs, localized on nitrogen atoms of ligands, and electropositive Zn centre of ZnPc molecule lead displacement of Zn(II) from the plane defined by the four isoindole N atoms of Pc(2-) macrocycle by 0.4945(4), 0.4976(4) and 0.4771(4)  A in 1, 2 and 3 respectively. Owing to the interaction between the Zn centre of ZnPc with amine N atom of n-alkylamine the approximate D4h symmetry of planar ZnPc molecule undergoes distortion and exhibits a saucer-like

Fig. 2. View of the asymmetric unit of 1 (a), 2 (b) and 3 (c).

B. Przybył, J. Janczak / Dyes and Pigments 100 (2014) 247e254

shape. Distortion of pyramidal coordination environment of the zinc ion is expressed by inclination angle between the axial ZneN bond and line normal to the N4-plane and is equal 3.82(9), 3.31(8) and 1.91(8) for 1, 2 and 3, respectively. More selected geometrical parameters of the complexes are shown in Table 2. According to literature [10,11,22], the deviation of the zinc ion from N4 plane, as well as the axial ZneN bond length exhibits slightly different values in comparison with the axial ZneN bond of aromatic pyridinebased ligands. The displacement of Zn centre of a planar ZnPc in the 1, 2 and 3 complexes is c.a. 0.1  A greater and the bond length is about 0.1  A shorter than typical for N-aromatic ligands. These differences are probably caused due to steric effect of hydrogen atoms of pyridine in positions 2,6 interact with the electron cloud of Pc(2-) which limits the minimal distance of the ligand from the Pc(2-) macroring. The lack of this interaction is not observed in the case of aliphatic amines, which explains shortening of the axial ZneN bond. The outer coordination shell in reported complexes consists of the secondmolecule ofn-alkylamine that acts an acceptor of weak hydrogen bond. The weakest NeH$$$N hydrogen bond is observed for complex of zinc phthalocyanine with n-butylamine (1) and the strongest in the case of n-heptylamine (3) which is almost linear (full hydrogen bonds geometry parameters are contained in Table 3). A mutual arrangement of coordinated and solvated molecules of amines in 3 are quite different in relative to 1 and 2. The least square lines drawn through all non - hydrogen atoms of nalkylamines form an angle 164.3(1) in 3 relatively to 69.7(4) and 58.5(1) in 1 and 2, respectively. The arrangement of complex molecules in crystals is mainly determined by the pep interactions between Pc(2-) macrorings. Strong pep interactions are a common feature in the crystal structures of phthalocyanine and its metal complexes. Molecules of complexes are arranged in back-to-back fashion around inversion centres (see Fig. 3a, b and c). Distances between N4 planes of back-to-back interacting Pc(2-) macrorings are equal 3.638(7), 3.623(9) and 3.407(7)  A (3.134(8), 3.126(9) and 3.259(8)  A between mean planes of Pc(2-) macrorings), respectively for structure 1, 2 and 3. Back-to-back interacting phthalocyanine macrorings are shifted relative to each other inducing not full overlapping. The value of shift was calculated as: d ¼ dZneZn$sina, where dZneZn is the distance between Zn atoms of two back-toback interacting molecules and a is an angle between normal to the N4 plane and line drawn through two Zn atoms (see Table 4.). The calculated shifting values for the complexes 1, 2 and 3 are equal 5.395(23), 5.531(18) and 3.815(15)  A, respectively. The smallest value of the shift in case of n-heptylamine complex

251

Table 3 Geometry of the hydrogen bonds for 1, 2 and 3 ( A,  ). DeH$$$A

Compound

DeH

H$$$A

D$$$A

DeH$$$A

N9eH92$$$N10

1 2 3

0.90(2) 0.90(2) 0.90(2)

2.34(2) 2.23(1) 2.11(1)

3.175(10) 3.051(6) 3.004(4)

153.08(14) 150.88(21) 174.02(18)

causes the best overlapping of Pc(2-) macrorings which allows to suppose that interaction between the macrorings are the strongest in 3 (Fig. 3). 3.4. UVeVis spectroscopy To investigate further the structures of reported complexes electronic absorption spectra of 1 in n-butylamine, 2 in n-amylamine and 3 n-heptylamine were recorded. The absorption spectra of all complexes are very similar (Fig. 4) and are characteristic for monoaxially ligated ZnPc. Characteristic intense Q band at 669 nm (logε ¼ 8.62), 670 nm (logε ¼ 8.57) and 671 nm (logε ¼ 8.53) for 1, 2 and 3, respectively, originates from HOMO to LUMO transition, is well apparent on every spectrum. With additional broad B band spectra are in agreement with spectrum of ZnPc published by A.B.P. Lever [23]. Spectra exhibit characteristic splitting of the Q band because of the vibronic coupling in the excited state, which was well described in the literature [24,25]. 3.5. Gas-phase structure and molecular electrostatic potential The gas-phase structures of ZnPc(n-butylamine), ZnPc(n-amylamine) and ZnPc(n-heptylamine) molecules were obtained by the DFT full-optimised molecular orbital calculations starting from the geometry obtained from the X-ray analysis. The bond lengths and angles of the optimised gas-phase conformation of these molecules, in general, are in good agreement with those obtained by the single crystal analysis (Table 2, Table S1 and Fig. S1eS3). As can be seen from the Fig. S1eS3, the gas-phase conformation of the whole molecules obtained by DFT is slightly different than that in the crystals. Noticeable differences between the X-ray and DFT results are observed in the coordination environment of the central Zn atom as well as in the conformation of the axial n-alkylamie ligands. In the crystals the displacement of Zn from the plane defined by the four N isoindole atoms of the Pc macrocycle of these molecules is greater by w0.05  A than that observed in the gas-phase

Table 2 Selected geometrical parameters for 1, 2 and 3 ( A,  ). 1

ZneN1 ZneN3 ZneN5 ZneN7 ZneN9 N1eZneN3 N3eZneN5 N5eZneN7 N1eZneN7 N1eZneN9 N3eZneN9 N5eZneN9 N7eZneN9 Displacement of Zn from N4-plane

2

3

X-ray

DFT

X-ray

DFT

X-ray

DFT

2.026(3) 2.031(3) 2.027(3) 2.029(3) 2.073(4) 86.48(13) 86.04(13) 87.10(13) 86.76(13) 101.92(15) 106.78(15) 106.82(15) 100.87(15) 0.494(4)

2.053 2.043 2.042 2.054 2.209 87.49 87.79 87.51 87.21 97.41 106.50 106.50 97.71 0.428

2.031(3) 2.025(3) 2.038(3) 2.023(3) 2.087(3) 86.77(11) 85.90(12) 86.24(12) 87.90(11) 101.51(12) 102.21(12) 106.44(12) 106.59(12) 0.498(4)

2.055 2.054 2.042 2.041 2.208 87.21 87.51 87.89 87.49 97.41 97.11 106.69 106.70 0.428

2.021(2) 2.032(2) 2.034(2) 2.028(2) 2.097(2) 87.13(10) 86.11(10) 86.89(10) 87.19(10) 103.78(10) 101.38(10) 104.04(10) 105.21(10) 0.477(4)

2.054 2.055 2.042 2.043 2.209 87.21 87.50 87.79 87.50 97.21 97.60 106.69 105.59 0.429

252

B. Przybył, J. Janczak / Dyes and Pigments 100 (2014) 247e254

Fig. 3. Projection of the crystal packing of 1 along a-axis (a), 2 along a-axis (b) and along b-axis (c).

molecules (Table 2). Other difference between the X-ray and DFT results are observed in the axial ZneN bonds linking the respective n-alkylamie ligands. In the gas-phase molecules the axial ZneN bond is longer (w0.11  A) than that observed for the molecules in Table 4 Geometry of back-to-back arrangement for 1, 2 and 3 ( A,  ).

ZneZn

a Shift, d

1

2

3

7.108(4) 49.38(5) 5.395(23)

7.205(4) 50.14(4) 5.531(18)

5.794(3) 41.17(4) 3.815(15)

the crystals. The differences between geometries of molecules obtained by the X-ray analysis and by the DFT results from the intermolecular interactions and the crystal packing forces. The electrostatic potential V(r) that the electrons or nuclei of a molecule create at each point r in the surrounding space can be calculated by the equation V(r) ¼ SA (ZA/(RA-r)) e !(r(r’)/jr’erj)dr, where ZA is the charge on nucleus A having a position vector RA and the r(r’) is the electron density function of the molecule. The molecular electrostatic potential (MESP) carry a wealth quantitative and qualitative information and is widely used as a reactivity map displaying the most probable regions of molecule for the electrophilic attack of reagents. The MESP maps are powerful

B. Przybył, J. Janczak / Dyes and Pigments 100 (2014) 247e254

Fig. 4. UVeVis spectra of 1, 2 and 3 in solution; spectra are spaced by 0.15 unit on absorbance scale.

interpretative tools in several fields of chemistry, biology and the crystal engineering, for example rational drug design, folding of supramolecules, protein-ligand interactions, catalysis, nucleophilic reaction and intermolecular interactions and organisation of molecules in solids [26e29].

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The three-dimensional MESP maps are obtained on the basis of the DFT (B3LYP/6-31 þ G(d)) optimised geometries of ZnPc(nbutylamine), ZnPc(n-amylamine) and ZnPc(n-heptylamine) molecules as well as for reactants molecules (ZnPc, n-butylamine, namylamine and n-heptylamine). The calculated 3D MESP mapped onto the total electron density isosurface (0.008 eÅ3) for each molecule is shown in Fig. 5. The colour code of MESP is in the range of 0.05 (red) to 0.05 eÅ1 (blue). Regions of negative MESP are usually associated with the lone pair of electronegative atoms, whereas the regions of positive MESP are associated with the electropositive atoms. The MESP maps give the information about the distribution of the charge of the interacting molecules. The 3D MESP maps are obtained on the basis of the DFT optimized geometries of the reacted molecules as well as for molecules of the final products. For all molecules the calculated 3D MESP is mapped onto the total density isosurface (0.008 eÅ3). The colour code of MESP is in the range of 0.05 (red) to 0.05 eÅ1 (blue) as illustrated in Fig. 5. For ZnPc molecule the calculated 3D MESP map displays the electrophilic region near the Zn center on both side of the planar ZnPc molecule and the nucleophilic regions near the four bridged azamethine nitrogen atoms (Fig. 5a). In addition, less positive value of MESP than that near the Zn center and less negative value of MESP comparing to that of azamethine N atoms are observed on both sides of the planar ZnPc across the extended 18 p-electron of the conjugation in the Pc macrocycle and on the phenyl rings, respectively. The calculated 3D MESP map for the three n-

Fig. 5. Three-dimensional molecular electrostatic potential (0.05 eÅ1, red and þ0.05 eÅ1, blue) mapped on the surface of total electron density (0.008 eÅ3) for the molecules: ZnPc (a), n-butylamine, n-amylamine and n-heptylamine (b) and for the ZnPc(n-butylamine), ZnPc(n-amylamine) and ZnPc(n-heptylamine) molecules (c). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

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alkylamines displays in each molecule the nucleophilic region near the N atom of the amine group containing the lone electron pair (Fig. 5b). The calculated 3D MESP maps are helpful for understanding the interactions between the reacted molecules yielding the final ZnPc-complexes axially ligated by the three n-alkylamines. The calculated 3D MESP maps for the three ZnPc(n-alkylamine) complexes are illustrated in Fig. 5c. These maps are helpful for understanding why the composition of these complexes in solidstate is 1:2 (the proportion of Zn to n-alkylamine). As can be seen from the Fig. 5c upon coordination of the respective n-alkylamine to the ZnPc the region near the H atoms of coordinated n-alkylamine displays more positive value of MESP (Fig. 5c) comparing to that of isolated n-alkylamine molecules (Fig. 5b), therefore during crystallization the second n-alkylamine molecule interacts with the ZnPc(n-alkylamine) complex forming crystals with the composition of ZnPc(n-alkylamine) n-alkylamine. In addition, the 3D MESP maps for the ZnPc(n-alkylamine) complexes are helpful for the better understanding of the back-to-back organization of the molecules in the solid-state. 4. Conclusions Recrystallization of ZnPc pigment in n-alkylamines leads to the formation of the 4 þ 1 coordinated ZnPc-derivatives that crystallize as solvates. Ligation of ZnPc by n-alkylamines does not change the colouristic properties compared with the parent ZnPc pigment. However, the [ZnPc(n-alkylamine)] n-alkylamine pigments exhibit better solubility than the ZnPc pigment due to the steric hindrance of the axial n-alkylamine ligands that lowers pep interactions between phthalocyaninate macrocycles as well as the aggregation process in solution. Thus ligation of ZnPc by n-alkylamines may be of value to improve the technical performance of these colorants. Acknowledgement This work was supported by the Ministry of Science and Higher Education (grant No. N N204 397540). Appendix A. Supplementary data Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.dyepig.2013.09.020. References [1] Leznoff CC, Lever ABP. Phthalocyanines: properties and applications, vol. 4. New York: VCH Publishers; 1996. [2] Gregory P. Industrial applications of phthalocyanines. J Porphyrins Phthalocyanines 2000;4(4):432e7. [3] Tedesco AC, Rott JCG, Lunardi CN. Synthesis, photophysical and photochemical aspects of phthalocyanines for photodynamic therapy. Curr Org Chem 2003;7(2):187e96. [4] Ozoemena K, Kuznetsova N, Nyokong T. Photosensitized transformation of 4chlorophenol in the presence of aggregated and non-aggregated metallophthalocyanines. J Photochem Photobiol A: Chem 2001;139(2e3):217e24.

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