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Dyes and Pigments 100 (2014) 247e254

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Dyes and Pigments

journal homepage: www.elsevier .com/locate/dyepig

Structural characterisation and DFT calculations of three newcomplexes 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

Article history:Received 26 July 2013Received in revised form11 September 2013Accepted 12 September 2013Available online 20 September 2013

Keywords:Zinc phthalocyaninate complexesn-AlkylamineCrystal structureUVeVis spectroscopyDFTMolecular electrostatic potential

* Corresponding author.E-mail address: j.janczak@int.pan.wroc.pl (J. Jancz

0143-7208/$ e see front matter � 2013 Elsevier Ltd.http://dx.doi.org/10.1016/j.dyepig.2013.09.020

a b s t r a c t

Three complexes of zinc phthalocyanine monoaxially ligated by n-alkylamines (n-butylamine, n-amyl-amine and n-heptylamine) in the crystalline form were obtained and studied. These zinc phthalocyanineligated by n-alkylamine complexes crystallize with the n-alkylamine molecules as solvates in thecentrosymmetric space group. Two of them (with n-butylamine and n-amylamine) crystallize in the P21/c space group of monoclinic systemwhile the third (with n-heptylamine) in the triclinic system. The zinccentre 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 nitrogenatom of n-alkylamines, the zinc atom is significantly displaced (w0.5 �A) from the plane defined by thefour isoindole nitrogen atoms of phthalocyaninate(2-) macrocycle. The monoaxially ligation of zinccentre of zinc phthalocyanine molecule by n-alkylamines leads to distortion of the planar zinc phtha-locyanine molecule to the saucer-shape form. X-ray conformations of these molecules are compared withthe conformation of that in the gas-phase as obtained by the density functional theory calculations. Thecalculated three-dimensional molecular electrostatic potential maps are helpful for understanding of theinteraction between the zinc phthalocyanine and n-alkylamines molecules forming the monoaxiallyligated zinc phthalocyanine complexes. Thermogravimetric analysis and the UVeVis spectroscopy wereused for characterisation of these complexes. The Q band of these complexes (at about 670 nm) does notchange comparing to that of the parent colorant. The monoaxially ligated by n-alkylamines zincphthalocyanine dyes are about 5 times more soluble than the parent zinc phthalocyanine pigment.

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1. Introduction

Phthalocyanine and its metal complexes, in spite of the fact thatthey have known since several dozen years, still arouses interestbecause of exhibition of many important features which gives po-tential application in many fields from industry do medicine [1,2].Structurally, phthalocyanine is consists of four isoindole unitsconnected by azamethine bridges to form 18-p aromatic macroring(Scheme 1).

Zinc phthalocyanine derivatives (ZnPcs) have proved to bepromising photosensitizers in photodynamic therapy due to strongabsorption in the red region of visible radiation. The advantage ofZnPc over phthalocyanine complexes of transition metals are hightriplet quantum yield and long lifetimes, these are required foreffective sensitization [3]. Zinc phthalocyanines are also attractive

ak).

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sensitisers for photodegradation of pollutants, for example theoxidation of chlorinated phenols [4,5], sulphur containing organiccompounds [6,7] and 4-nitrophenol [8].

Phthalocyanines are known for their very poor solubility inmany solvents because of strong stacking interaction betweenmolecules in the solid-state. This property seriously limits potentialapplications of these compounds. There are main two methods toincrease the solubility: (1) by symmetrical or unsymmetrical sub-stitution on peripheral aromatic rings with different functionalgroups and/or (2) by axial ligation of central metal ion by differentorganic or inorganic ligands (Scheme 1). These modifications aremade to limit stacking interactions to improve interactions withsolvent molecules.

Several structures of zinc phthalocyanine with aromatic axialligands, mainly based on pyridine and its derivatives [9e11], as also4,40-dipyridyl [12] and 3,30-dipyridyl [13] compounds withdifferent linkers, are present in the literature. The first, and onlyexperiment of recrystallization of zinc phthalocyanine from n-alkylamine was made by T. Kobayashiet et al., in 1971 [14]. They

N

N

N

N

N

N

N

N

M non-peripheralsubstituents

peripheralsubstituents

metal center axialligand(s)

Scheme 1. The ways of possible modifications of metallophthalocyanines showing the18-p electron aromatic macroring.

B. Przybył, J. Janczak / Dyes and Pigments 100 (2014) 247e254248

published structure of ZnPc monoaxially ligated by n-hexylamine,but some structural aspects are ambiguous or unclear. Since thenany crystalline complex of metallophthalocyanines with any n-alkylamine was not published. This fact induced us to synthesis ofcomplexes of ZnPc with n-butylamine, n-amylamine and n-hep-tylamine to examine their crystal structures, thermal stability andspectral properties.

2. Experimental

2.1. Materials and methods

All chemical reagents are commercially available and were usedwithout further purification. The electronic absorption spectrawere carried out at room temperature using a Cary Varian SE UVeViseNIR spectrometer. The spectra of 1, 2 and 3 were recorded insolution of the respective n-alkylamine (10�5 mol/l). Thermogra-vimetric analysis was achieved with TG-DTA Setaram SETSYS 16/18analyser with heating rate 5 �C min�1. The rest of the sample leftafter thermogravimetric analysis was measured on an STOEdiffractometer equipped with a linear PSD detector [15] using CuKa1 radiation (l ¼ 1.54060 �A) at room temperature. The composi-tion of the crystals was checked with energy dispersive spec-trometry (EDS) as well as with a PerkineElmer 240 elementalanalyser. EDS spectra were acquired and analysed using an EDAXPegasus XM4 spectrometer with SDD Apollo 4D detector mountedon a FEI Nova NanoSEM 230 microscope. The NMR spectra ofsaturated ZnPc(n-alkylamine) complexes in deuterated chloroformwere taken on Bruker Avance 500 and AMX 300 spectrometers. Thechemical shifts were referenced to the residual solvent signals. Thevibrational measurements were carried out at room temperature.The Fourier transform infrared spectrum was recorded from nujoland fluorolube mulls between 4000 and 400 cm�1 on a Bruker IFS113 V FTIR. Resolution was set up to 2 cm�1.

2.2. Preparation

2.2.1. n-Butylamine(phthalocyaninato)zinc n-butylamine solvate(1)

Zinc phthalocyanine (pastille, 0.076 g, 0.132 mmol) was placedin glass elongated ampoule and then n-butylamine (6.0 mL) wasadded. Quite good solubility of phthalocyanine in butylamine wasobserved in room temperature. The system was degassed to

pressure 0.15 hPa and the ampoule was sealed. The ampoule washeated in 90 �C in a horizontal position until whole pastille of ZnPcwas dissolved (c.a. 20 h). After this time the ampoule was cooled toroom temperature, opened and the solution was transferred to50 ml beaker covered by Petri dish and left in room temperature.First very small crystals were observed after 1 h. After 24 h well-shaped rectangular single was filtered and washed by diethylether. 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 andH, 5.00%. 1H NMR: (ppm) 8.1 and 9.34 (peripheral and non-peripheral aromatic H of Pc), �0.46 (NH2), 0.51, 0.71, 0.92 and1.23 for eC4H9. IR (cm�1): 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 1with using similar mass of zinc phthalocyanine pastille (0.080 g;0.139 mmol) and n-amylamine (6.0 mL). Heating temperature wasraised to 100 �C. Well-shaped rectangular crystals were also iso-lated 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 andnon-peripheral aromatic H of Pc),�0.83 (NH2), 0.34, 0.54, 0.55, 0.81and 1.23 for eC5H11. IR (cm�1): 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 placedin glass elongated ampoule and then n-heptylamine (6.0 mL) wasadded. Quite good solubility of phthalocyanine in heptylamine wasobserved in room temperature. The system was degassed to pres-sure 0.15 hPa and the amplewas sealed. The ampoule was heated in160 �C in a slightly oblique position this way that the solution didnot reach the top of the ampoule. After 20 h fused crystals wereobserved on the edge of the solution. Crystals were separated fromthe solution, which was transferred into 50 mL beaker covered byPetri dish and left in room temperature.Well-shaped single crystalswere found in the beaker after 3 days. Crystals obtained in hightemperature and these from room temperature solution proved tocrystallize 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 foreC7H15. IR (cm�1): 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 structureanalysis

Single crystal X-ray diffraction measurements of 1, 2 and 3werecarried out at 295 K on a four-circle KUMA KM4 diffractometerequipped with two-dimensional CCD area detector. Graphitemonochromatized Mo-Ka radiation (l ¼ 0.71073 �A) and u-scantechnique (Du ¼ 1�) were used for data collection. Data collectionand reduction along with absorption correction were performedusing CrysAlis software package [16]. The structures were solved bydirect methods using SHELXS-97 [17], which revealed the positions

Table 1Crystallographic data for 1, 2 and 3.

1 2 3

Empirical formula C40H38N10Zn C42H42N10Zn C46H50N10ZnFormula

weight(g mol�1)

724.19 752.25 808.35

Crystal system,space group

Monoclinic, P21/c Monoclinic, P21/c Triclinic, P-1

a (�A) 12.4235(7) 12.642(2) 10.2913(6)b (�A) 15.4622(8) 15.159(2) 13.9352(6)c (�A) 18.7898(9) 19.581(3) 15.3241(9)a (�) 90.0 90.0 80.854(4)b (�) 93.509(3) 93.41(1) 73.307(5)g (�) 90.0 90.0 81.197(4)V (�A3) 3602.7(3) 3745.9(1) 2064.8(2)Z 4 4 2Dcalc/Dobs

(g cm�3)1.335/1.33 1.334/1.33 1.300/1.30

m (mm�1) 0.726 0.701 0.641F(000) 1512.0 1576.0 852.0Crystal size (mm) 0.28 � 0.18 � 0.16 0.32 � 0.28 � 0.24 0.37 � 0.33 � 0.21Radiation type,

wavelength,l (�A)

Mo Ka, 0.71073

Temperature (K) 295(2) 295(2) 295(2)q range(�) 2.80O28.50 2.56O28.51 2.80O28.05Tmin/Tmax 0.8266/08983 0.8124/0.9512 0.8036/0.8803Refs collected/

unique/observed

46519/9066/4891 50515/9415/5248 27255/9928/5126

Rint 0.0489 0.0747 0.0622Refinement on F2

R[F2 > 2s(F2)] 0.0607 0.0685 0.0664wR(F2 all

reflections)0.1707 0.1132 0.1149

Goodness-of-fit, S 1.008 1.000 1.002Drmax, Drmin

(e �A�3)þ0.617, �0.422 þ0.477, �0.364 þ0.334, �0.316

50 100 150 200

-30

-25

-20

-15

-10

-5

0

ZnPcAA x AA

ZnPcBA x BA

ZnPcHA x HA

-Mas

s lo

ss [%

]

Temperature [oC]

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

B. Przybył, J. Janczak / Dyes and Pigments 100 (2014) 247e254 249

of almost all non-hydrogen atoms. The remaining atoms werelocated from subsequent difference Fourier syntheses. The struc-ture was refined using SHELXL-97 [17] with the anisotropic thermaldisplacement parameters. Visualization of the structures was madewith the Diamond 3.0 program [18]. Details of the data collectionparameters, crystallographic data and final agreement parametersare collected in Table 1.

2.4. Theoretical calculation

Theoretical calculations with geometry optimization of 1, 2 and3 as well as the n-butylamine, n-amylamine and n-heptylamine,

N

NN

N

N

N

NN Zn + 2 NH2n

n = 2 (n-butylamine)n = 3 (n-amylaminine)n = 5 (n-heptylamine)

( )

Scheme 2. Synthetic route of ZnPc

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

3. Results and discussion

3.1. Synthesis and characterisation

Our preparation method of the single crystals of 1, 2 and 3 isvery simple. The suspension of b-ZnPc in respective n-alkylamine(n-butylamine, n-amylamine and n-heptylamine) was heated indegassed and evacuated glass ampoule. The respective n-alkyl-amine with the electron pair at the N atom amine group is nucle-ophilic. During the heating process the electronegatively polarisednitrogen atom of the rescpective n-alkylamine with the lone pair ofelectron interacts with electropositively polarised Zn centre of ZnPcmolecule forming coordinating ZneN bond yielding the 4 þ 1 co-ordinated ZnPc(n-alkylamine) complexes (Scheme 2).

During the cooling process to the room temperature the 4 þ 1coordinated ZnPc(n-alkylamine) complexes crystallise with thesolvent molecules yielding blue-violet well-developed singlecrystals of 1, 2 and 3. The obtained crystals are about 5 times moresoluble in themost organic solvents than the parent ZnPc due to the

N

NN

N

N

N

NN

NH2

Znx

NH2n

n

( )

( )

(n-alkylamine) n-alkylamine.

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

B. Przybył, J. Janczak / Dyes and Pigments 100 (2014) 247e254250

steric hindrance of respective axial n-alkylamine that lowering thepep interaction in solid.

3.2. Thermal stability

In order to determine the thermal stability of these complexesinvestigated here, the thermal analyses of 1, 2 and 3 were carriedout on the samples of w50 mg with the same heating rate of 5 �C/min. The thermogravimetric analyses of the solid-state samples areshown in Fig. 1. Crystal 1 is stable up to w90 �C, and at highertemperature loses the solvated n-butylamine molecules. After lossof the solvent n-butylamine molecules, the starting compoundtransforms into ZnPc(n-butylamine) complex, which during furtherheating loses the coordinated n-butylamine molecule (atw 125 �C)and finally transforms into ZnPc in b-form that was confirmed bythe X-ray powder diffraction experiment. The respective weightlosses correspond well to the weight decrease by 10.12% due torelease the solvated n-butylamine molecules (w92 �C) and coor-dinated n-butylamine molecule from crystal 1. The calculated totalweight loss is equal to 20.19% and agrees well with the weight lossobserved 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 com-pound transforms into ZnPc(n-amylamine) complex, which duringfurther heating loses the coordinated n-amylamine molecule(w128 �C) and finally transforms into b-ZnPc (confirmed by the X-ray powder diffraction experiment). The respective mass loss onthe heating are w11.5% (solvated n-amylamine) and w23% (bothsolvated and coordinated n-amylamine molecule), and are inagreement with the calculated values of 15.58% and 23.17%,respectively.

Crystal 3 loses both n-heptylamine molecules (solvated andcoordinated) at the same temperature (w122 �C). The total massloss of w28% is in agreement with the calculated value of 28.06%.Two steps of the thermal decomposition of the solid state complex1 and 2 and one step for complex 3 correlatewell with boiling pointof respective amines (n-butylamine 77 �C, n-amylamine 104 �C andn-heptylamine 155 �C). Probably, in complex 3 the NeH$$$Nhydrogen bond breaks at a similar temperature to 1 and 2, but itstoo low to observe the first step due to relatively high boiling pointof n-heptylamine. Therefore, in 3 both solvated and coordinated n-heptylamine molecules are removed simultaneously at the sametemperature. The thermal analyses of these pentacoordiantedZnPc-complexes axially ligated by n-alkylamines show similarstrength of the axial ZneN bonds and are in agreement with the X-ray crystal structure analysis.

3.3. Description of the structures and molecular arrangement

Complexes 1 and 2 crystallize in centrosymmetric space groupP21/c of monoclinic system, while complex 3 in triclinic centro-symmetric group. Asymmetric unit of 1, 2 and 3 contains zincphthalocyaninemonoaxially ligated by n-butylamine, n-amylamineand n-heptylamine, respectively (Fig. 2a, b and c). In every case theamino group of coordinated n-alkylamine plays role of NeH$$$Nhydrogen bond donor to second molecule of n-alkylamine.

In complexes 1, 2 and 3 Zn(II) centre is pentacoordinatedforming a distorted square pyramid. Interaction between lone pairs,localized on nitrogen atoms of ligands, and electropositive Zncentre of ZnPc molecule lead displacement of Zn(II) from the planedefined by the four isoindole N atoms of Pc(2-) macrocycle by0.4945(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 amineN atom of n-alkylamine the approximate D4h symmetry of planarZnPc molecule undergoes distortion and exhibits a saucer-like

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

DeH$$$A Compound DeH H$$$A D$$$A DeH$$$A

N9eH92$$$N10 1 0.90(2) 2.34(2) 3.175(10) 153.08(14)2 0.90(2) 2.23(1) 3.051(6) 150.88(21)3 0.90(2) 2.11(1) 3.004(4) 174.02(18)

B. Przybył, J. Janczak / Dyes and Pigments 100 (2014) 247e254 251

shape. Distortion of pyramidal coordination environment of thezinc ion is expressed by inclination angle between the axial ZneNbond 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 geometricalparameters of the complexes are shown in Table 2. According toliterature [10,11,22], the deviation of the zinc ion from N4 plane, aswell as the axial ZneN bond length exhibits slightly different valuesin comparison with the axial ZneN bond of aromatic pyridine-based ligands. The displacement of Zn centre of a planar ZnPc inthe 1, 2 and 3 complexes is c.a. 0.1�A greater and the bond length isabout 0.1 �A shorter than typical for N-aromatic ligands. These dif-ferences are probably caused due to steric effect of hydrogen atomsof 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 ofaliphatic amines, which explains shortening of the axial ZneNbond.

The outer coordination shell in reported complexes consists ofthe secondmolecule ofn-alkylamine that acts an acceptor of weakhydrogen bond. The weakest NeH$$$N hydrogen bond is observedfor complex of zinc phthalocyanine with n-butylamine (1) and thestrongest in the case of n-heptylamine (3) which is almost linear(full hydrogen bonds geometry parameters are contained inTable 3). A mutual arrangement of coordinated and solvated mol-ecules of amines in 3 are quite different in relative to 1 and 2. Theleast square lines drawn through all non - hydrogen atoms of n-alkylamines form an angle 164.3(1)� in 3 relatively to 69.7(4)� and58.5(1)� in 1 and 2, respectively.

The arrangement of complex molecules in crystals is mainlydetermined by the pep interactions between Pc(2-) macrorings.Strong pep interactions are a common feature in the crystalstructures of phthalocyanine and its metal complexes. Moleculesof complexes are arranged in back-to-back fashion around inver-sion centres (see Fig. 3a, b and c). Distances between N4 planes ofback-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 be-tween mean planes of Pc(2-) macrorings), respectively for struc-ture 1, 2 and 3. Back-to-back interacting phthalocyaninemacrorings are shifted relative to each other inducing not fulloverlapping. The value of shift was calculated as: d ¼ dZneZn$sina,where dZneZn is the distance between Zn atoms of two back-to-back interacting molecules and a is an angle between normal tothe N4 plane and line drawn through two Zn atoms (see Table 4.).The calculated shifting values for the complexes 1, 2 and 3 areequal 5.395(23), 5.531(18) and 3.815(15) �A, respectively. Thesmallest value of the shift in case of n-heptylamine complex

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

1

X-ray DFT

ZneN1 2.026(3) 2.053ZneN3 2.031(3) 2.043ZneN5 2.027(3) 2.042ZneN7 2.029(3) 2.054ZneN9 2.073(4) 2.209N1eZneN3 86.48(13) 87.49N3eZneN5 86.04(13) 87.79N5eZneN7 87.10(13) 87.51N1eZneN7 86.76(13) 87.21N1eZneN9 101.92(15) 97.41N3eZneN9 106.78(15) 106.50N5eZneN9 106.82(15) 106.50N7eZneN9 100.87(15) 97.71Displacement of Zn from N4-plane 0.494(4) 0.428

causes the best overlapping of Pc(2-) macrorings which allows tosuppose that interaction between the macrorings are the strongestin 3 (Fig. 3).

3.4. UVeVis spectroscopy

To investigate further the structures of reported complexeselectronic absorption spectra of 1 in n-butylamine, 2 in n-amyl-amine and 3 n-heptylamine were recorded. The absorptionspectra of all complexes are very similar (Fig. 4) and are char-acteristic for monoaxially ligated ZnPc. Characteristic intense Qband 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 HOMOto LUMO transition, is well apparent on every spectrum. Withadditional broad B band spectra are in agreement with spectrumof ZnPc published by A.B.P. Lever [23]. Spectra exhibit charac-teristic splitting of the Q band because of the vibronic coupling inthe 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-amyl-amine) and ZnPc(n-heptylamine) molecules were obtained by theDFT full-optimised molecular orbital calculations starting from thegeometry obtained from the X-ray analysis. The bond lengths andangles of the optimised gas-phase conformation of these mole-cules, in general, are in good agreement with those obtained by thesingle crystal analysis (Table 2, Table S1 and Fig. S1eS3). As can beseen from the Fig. S1eS3, the gas-phase conformation of the wholemolecules obtained by DFT is slightly different than that in thecrystals. Noticeable differences between the X-ray and DFT resultsare observed in the coordination environment of the central Znatom as well as in the conformation of the axial n-alkylamie li-gands. In the crystals the displacement of Zn from the plane definedby the four N isoindole atoms of the Pc macrocycle of these mol-ecules is greater by w0.05 �A than that observed in the gas-phase

2 3

X-ray DFT X-ray DFT

2.031(3) 2.055 2.021(2) 2.0542.025(3) 2.054 2.032(2) 2.0552.038(3) 2.042 2.034(2) 2.0422.023(3) 2.041 2.028(2) 2.0432.087(3) 2.208 2.097(2) 2.20986.77(11) 87.21 87.13(10) 87.2185.90(12) 87.51 86.11(10) 87.5086.24(12) 87.89 86.89(10) 87.7987.90(11) 87.49 87.19(10) 87.50

101.51(12) 97.41 103.78(10) 97.21102.21(12) 97.11 101.38(10) 97.60106.44(12) 106.69 104.04(10) 106.69106.59(12) 106.70 105.21(10) 105.590.498(4) 0.428 0.477(4) 0.429

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

B. Przybył, J. Janczak / Dyes and Pigments 100 (2014) 247e254252

molecules (Table 2). Other difference between the X-ray and DFTresults are observed in the axial ZneN bonds linking the respectiven-alkylamie ligands. In the gas-phase molecules the axial ZneNbond is longer (w0.11 �A) than that observed for the molecules in

Table 4Geometry of back-to-back arrangement for 1, 2 and 3 (�A, �).

1 2 3

ZneZn 7.108(4) 7.205(4) 5.794(3)a 49.38(5) 50.14(4) 41.17(4)Shift, d 5.395(23) 5.531(18) 3.815(15)

the crystals. The differences between geometries of molecules ob-tained by the X-ray analysis and by the DFT results from theintermolecular interactions and the crystal packing forces.

The electrostatic potential V(r) that the electrons or nuclei of amolecule create at each point r in the surrounding space can becalculated 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 andthe r(r’) is the electron density function of the molecule. The mo-lecular electrostatic potential (MESP) carry a wealth quantitativeand qualitative information and is widely used as a reactivitymap displaying the most probable regions of molecule for theelectrophilic attack of reagents. The MESP maps are powerful

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

B. Przybył, J. Janczak / Dyes and Pigments 100 (2014) 247e254 253

interpretative tools in several fields of chemistry, biology and thecrystal engineering, for example rational drug design, folding ofsupramolecules, protein-ligand interactions, catalysis, nucleophilicreaction and intermolecular interactions and organisation of mol-ecules in solids [26e29].

Fig. 5. Three-dimensional molecular electrostatic potential (�0.05 eÅ�1, red and þ0.05 eÅ�1

ZnPc (a), n-butylamine, n-amylamine and n-heptylamine (b) and for the ZnPc(n-butylamine)references to colour in this figure legend, the reader is referred to the web version of this

The three-dimensional MESP maps are obtained on the basis ofthe DFT (B3LYP/6-31 þ G(d)) optimised geometries of ZnPc(n-butylamine), ZnPc(n-amylamine) and ZnPc(n-heptylamine) mole-cules as well as for reactants molecules (ZnPc, n-butylamine, n-amylamine and n-heptylamine). The calculated 3D MESP mappedonto the total electron density isosurface (0.008 eÅ�3) for eachmolecule is shown in Fig. 5. The colour code of MESP is in the rangeof �0.05 (red) to 0.05 eÅ�1 (blue). Regions of negative MESP areusually associated with the lone pair of electronegative atoms,whereas the regions of positive MESP are associated with theelectropositive atoms.

The MESP maps give the information about the distribution ofthe charge of the interacting molecules. The 3D MESP maps areobtained on the basis of the DFT optimized geometries of thereacted molecules as well as for molecules of the final products. Forall molecules the calculated 3D MESP is mapped onto the totaldensity isosurface (0.008 e�3). The colour code of MESP is in therange of �0.05 (red) to 0.05 e�1 (blue) as illustrated in Fig. 5.

For ZnPc molecule the calculated 3D MESP map displays theelectrophilic region near the Zn center on both side of the planarZnPc molecule and the nucleophilic regions near the four bridgedazamethine nitrogen atoms (Fig. 5a). In addition, less positive valueof MESP than that near the Zn center and less negative value ofMESP comparing to that of azamethine N atoms are observed onboth sides of the planar ZnPc across the extended 18 p-electron ofthe conjugation in the Pc macrocycle and on the phenyl rings,respectively. The calculated 3D MESP map for the three n-

, blue) mapped on the surface of total electron density (0.008 e�3) for the molecules:, ZnPc(n-amylamine) and ZnPc(n-heptylamine) molecules (c). (For interpretation of thearticle.)

B. Przybył, J. Janczak / Dyes and Pigments 100 (2014) 247e254254

alkylamines displays in each molecule the nucleophilic region nearthe N atom of the amine group containing the lone electron pair(Fig. 5b). The calculated 3D MESP maps are helpful for under-standing the interactions between the reacted molecules yieldingthe 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 forunderstanding why the composition of these complexes in solid-state is 1:2 (the proportion of Zn to n-alkylamine). As can be seenfrom the Fig. 5c upon coordination of the respective n-alkylamineto the ZnPc the region near the H atoms of coordinated n-alkyl-amine displays more positive value of MESP (Fig. 5c) comparing tothat of isolated n-alkylamine molecules (Fig. 5b), therefore duringcrystallization the second n-alkylaminemolecule interacts with theZnPc(n-alkylamine) complex forming crystals with the composi-tion of ZnPc(n-alkylamine) n-alkylamine. In addition, the 3D MESPmaps for the ZnPc(n-alkylamine) complexes are helpful for thebetter understanding of the back-to-back organization of themolecules in the solid-state.

4. Conclusions

Recrystallization of ZnPc pigment in n-alkylamines leads to theformation of the 4 þ 1 coordinated ZnPc-derivatives that crystallizeas solvates. Ligation of ZnPc by n-alkylamines does not change thecolouristic properties compared with the parent ZnPc pigment.However, the [ZnPc(n-alkylamine)] n-alkylamine pigments exhibitbetter solubility than the ZnPc pigment due to the steric hindranceof the axial n-alkylamine ligands that lowers pep interactionsbetween phthalocyaninate macrocycles as well as the aggregationprocess in solution. Thus ligation of ZnPc by n-alkylamines may beof value to improve the technical performance of these colorants.

Acknowledgement

This work was supported by the Ministry of Science and HigherEducation (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.

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