X-ray structural characterizations of the reaction products between ZnCl2 and 6-benzylaminopurine derivatives in different acidic conditions

Article abstract of DOI:10.1016/j.molstruc.2009.06.011

The reaction between ZnCl₂ and the corresponding 6-benzylaminopurine derivative, L_n, [where L₁ = 6-(4-fluorobenzylamino)purine, L₂ = 6-(2-fluorobenzylamino)purine or L₃ = 6-(4-chlorobenzylamino)purine

Full text of DOI:10.1016/j.molstruc.2009.06.011

Journal of Molecular Structure 933 (2009) 148–155
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
X-ray structural characterizations of the reaction products between ZnCl2
and 6-benzylaminopurine derivatives in different acidic conditions
a,
a,b
*
ˇ
ˇ
Zdenek Trávnícek , Jaromír Marek
a
ˇ ˇ
´
Department of Inorganic Chemistry, Faculty of Science, Palacky University, Krízkovského 10, CZ-771 47 Olomouc, Czech Republic
b Institute of Experimental Biology, Faculty of Science, Masaryk University, CZ-625 00 Brno, Czech Republic
a r t i c l e i n f o
a b s t r a c t
Article history:
The reaction between ZnCl2 and the corresponding 6-benzylaminopurine derivative, Ln, [where L1 = 6-(4-
fluorobenzylamino)purine, L2 = 6-(2-fluorobenzylamino)purine or L3 = 6-(4-chlorobenzylamino)purine]
in 0.1 M or 2 M HCl afforded various products in dependence on a pH of the reaction medium. X-ray
structures of the reaction products have been determined by a single crystal X-ray analysis. It has been
found that the reaction led to the formation of [Zn(HL1)Cl3]ÁH2O (1) in 0.1 M HCl in which the L1 ligand
acts as the single N1–H protonated N9–H tautomer and is coordinated to Zn through N7 atom of a purine
skeleton. On the other hand, ion-paired compounds of the composition (H2L2)[ZnCl4]ÁH2O (2) and
(H2L3)[ZnCl4] (3) have been formed during the reactions in 2 M HCl. Each of the organic molecules L2
and L3 is twice protonated and its positive charge is compensated by the presence of the [ZnCl4]2À anion.
The cation exists as the N1–H, N7–H protonated N9–H tautomer in (2), and as the N3–H, N7–H proton-
ated N9–H one in (3). It has been found that the extent of protonation has a significant impact on the
coordination ability of the discussed organic molecules, and as a result of this finding, also on selected
interatomic parameters as well as non-bonding interactions present in their crystal structures. Moreover,
the compounds have been characterized by elemental analyses (C, H, N), FTIR and Raman spectroscopies,
and thermogravimetric (TG) and differential thermal (DTA) analyses.
Received 14 January 2009
Received in revised form 5 June 2009
Accepted 5 June 2009
Available online 13 June 2009
Keywords:
Zinc(II) complexes
Tautomerism
Protonation
6-Benzylaminopurine
Crystal structures
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
conditions used during the synthesis such as a medium pH, the
molar ratio of reactants, and solvents used.
The organic compounds bearing the 6-benzylaminopurine (Bap)
moiety, belonging to a group of plant growth hormones, called
cytokinins (CKs), have been studied since the 1960s. The CKs rep-
resent a group of compounds, which can significantly affect some
of physiological functions, e.g. plant cell divisions, senescence,
etc. [1,2]. Moreover, the substitution of the Bap skeleton at the
C2 and N9 positions by suitable side chains may lead to the forma-
tion of compounds having the ability to behave as cyclin-depen-
dent kinase inhibitors (CDKIs). The cyclin-dependent kinases
belong to the family of protein kinases responsible for the regula-
tion of the cell cycle [3]. Moreover, some of the CDKIs involving the
Bap moiety demonstrate considerable both in vitro and in vivo
cytotoxicity against some human cancer cell lines [4]. Based on
our previously published results, we have found that the cytotox-
icity may be increased after the coordination of both CKs and CDKIs
to suitable transition metal ions [5,6]. Moreover, it may be con-
cluded that the coordination ability of Bap derivatives strongly de-
pends on an extent of substitution of the Bap skeleton and reaction
To date, 22 molecular structures of Zn(II) complexes involving
adenine moiety have been deposited within the Cambridge Struc-
tural Database (CSD ver. 5.29, August 2008 update) [7]. One of
three presented X-ray structures of Zn(II) compounds, i.e. complex
(1), represents the first example of a Zn(II) complex containing the
aromatic CKs derived from the Bap skeleton, except for those
involving the CDKIs derived from the same skeleton, i.e. [Zn(O-
lo)Cl2]n, [Zn(HBoh)Cl3]ÁH2O and [Zn(HiprOlo)Cl3]ÁH2O [8], where
Olo = 2-(2-hydroxyethylamino)-6-benzylamino-9-methylpurine
(Olomoucine), Boh = 2-(3-hydroxypropylamino)-6-benzylamino-
9-isopropylpurine (Bohemine), iprOlo = 2-(2-hydroxyethylamino)-
6-benzylamino-9-isopropylpurine (isopropyl-Olomoucine). Both
the [Zn(HBoh)Cl3]ÁH2O and [Zn(HiprOlo)Cl3]ÁH2O mentioned com-
plexes have been found to be significant inhibitors of the CDK2/cy-
clin E kinase with IC50 = 0.40 and 0.50 lM, respectively [8].
Herein, the syntheses and X-ray structures of one Zn(II) com-
plex (1) and two Zn(II) ion-paired compounds (2) and (3) involving
the selected Bap derivatives are presented. One of the motivations
of this study was to make attempts and to find how the composi-
tion of the reaction products can be influenced by a degree of acid-
ity of the reaction medium used during the synthesis.
* Corresponding author. Tel.: +420 585634944; fax: +420 585634954.
ˇ
E-mail address: zdenek.travnicek@upol.cz (Z. Trávnícek).
0022-2860/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2009.06.011

ˇ
Z. Trávnícek, J. Marek / Journal of Molecular Structure 933 (2009) 148–155
149
610m, 577w, 532w. Raman (cmÀ1): 3285w, 3198w, 3114w,
3071s, 3006w, 2946m, 1605s, 1508s, 1471w, 1402s, 1344s,
1291m, 1222m, 1157m, 1121m, 970m, 853s, 827m, 734s, 638m,
576m, 529w, 493m, 422m, 326m, 283s, 234m.
2. Experimental
2.1. Materials and general methods
ZnCl2Á1.5H2O was used as received from Sigma–Aldrich Co.
6-(4-Fluorobenzylamino)purine (L1), 6-(2-fluorobenzylamino) pur-
ine (L2) and 6-(4-chlorobenzylamino)purine (L3), used as ligands in
this study, were prepared by the method described in the literature
[9]. Elemental analyses (C, H, N) were performed on a Flash EA–
1112 Elemental Analyser (Thermo Finnigan). Determinations of the
melting points were performed using a Melting Point B-540 appara-
tus (Büchi) with the gradient of 5 °C per minute and were uncor-
rected. Infrared spectra were obtained on a Nexus 670 FTIR
spectrometer (Thermo Nicolet) using KBr (4000–400 cmÀ1) and
ATR (600–200 cmÀ1) techniques. Raman spectra were recorded on
a NXR FT–Raman Module (ThermoNicolet) in the range of 150–
3750 cmÀ1. Simultaneous thermogravimetric (TG) and differential
thermal (DTA) analyses were carried out using a thermal analyzer Ex-
star TG/DTA 6200 (Seiko Instruments Inc.) with sample weights of
about 10 mg. TG/DTA studies were performed in ceramic pans be-
tween the laboratory temperature and 800 °C with a 5 °C minÀ1 tem-
perature gradient in dynamic air atmosphere (150 mL minÀ1).
2.3.2. Synthesis of (H2L2)[ZnCl4]ÁH2O (2) and (H2L3)[ZnCl4] (3)
The complexes were prepared by mixing of equimolar solutions
of ZnCl2Á1.5H2O (1 mmol) and L2, and L3 (1 mmol), respectively, in
30 ml of 2 M HCl. The reaction mixtures were stirred and heated at
80 °C for 4 h. The resulting solutions were kept in the room tem-
perature for 14 days. Colourless crystals, suitable for a single crys-
tal X-ray analysis, were obtained by slow evaporation of the
solvent from the reaction solutions. The schematic representation
of the synthetic pathways for the preparation of the complexes
(1)–(3) is depicted in Scheme 1.
For (2). Yield: 58%. M.p. 228–230 °C. Anal. Calcd. for
C12H12FN5ÁCl4ZnÁH2O (Mr = 470.5): C, 33.2; H, 3.0; N, 16.1%. Found:
C, 33.1; H, 3.0; N, 15.9%. IR (ATR; cmÀ1): 547s, 520s, 468s, 434m,
378w, 321s, 282vs, 259vs. IR (KBr; cmÀ1): 3443m, 3205m,
3161w, 3112m, 3072m, 2984w, 2936w, 1675vs, 1609vs, 1588s,
1522m, 1493s, 1454m, 1419s, 1353m, 1288w, 1233s, 1215s,
1182w, 1139m, 1107m, 1033m, 999m, 976m, 954w, 899m,
848m, 764vs, 734m, 656m, 635s, 565w, 546m, 521s. Raman
(cmÀ1): 3116m, 3073s, 2949m, 1687m, 1618m, 1594m, 1523w,
1474m, 1422s, 1337s, 1282vs, 1233w, 1159m, 1136w, 1109w,
1033s, 978s, 949m, 894w, 777vs, 737m, 723m, 524s, 436w,
383m, 278s, 223w.
2.2. X-ray crystallography
Diffraction data for single crystals of complexes (1), (2) and (3)
were collected at 100 K on an Xcalibur2 diffractometer (Oxford
For (3). Yield: 53%. M.p. 234–236 °C. Anal. Calcd. for
C12H12ClN5ÁCl4Zn (Mr = 468.9): C, 30.7; H, 2.6; N, 14.9%. Found: C,
30.5; H, 2.6; N, 15.0%. IR (ATR; cmÀ1): 543vs, 528m, 480s, 403m,
313vs, 277vs, 253s. IR (KBr; cmÀ1): 3446m, 3302m, 3212m,
3174w, 3129m, 1654vs, 1625s, 1568s, 1493s, 1477m, 1464s,
1440s, 1408s, 1395m, 1343s, 1263m, 1209s, 1190w, 1169m,
1121s, 1108m, 1095m, 1015s, 983m, 967w, 908w, 883w, 801s,
778w, 722vs, 637w, 610s, 544s, 527w, 481s. Raman (cmÀ1):
3129w, 3065s, 2926m, 1656m, 1623s, 1599w, 1567w, 1512s,
1478m, 1441w, 1396m, 1373vs, 1344vs, 1263w, 1204m, 1170w,
1124vs, 1107vs, 982m, 843s, 765s, 684s, 639m, 542m, 403w,
304s, 288s, 234w.
Diffraction, Ltd.) with Mo K (monochromator Enhance, Oxford
a
Diffraction, Ltd.) radiation and
x-scan rotation techniques. The
data were reduced using the CrysAlis software package (Oxford Dif-
fraction, Ltd.) [10]. A multi-scan absorption correction integrated
in the CrysAlis software was applied on the data of all three com-
pounds. All three structures were determined by direct methods
using SHELXS-97 and refined anisotropically on F2 using a full-
matrix least-squares procedure by SHELXL-97 [11] with weight:
w = 1/[
r
2(Fo)2 + (0.035P)2 + 1.500P]
for
r
(1),
w = 1/[r
2(Fo)2 +
(0.025P)2 + 1.500P] for (2) and w = 1/[
2(Fo)2 + (0.035P)2 + 1.500P]
for (3), where P = (Fo2 + 2Fc2)/3. All H-atoms were found from Fou-
rier maps and refined with a riding model, with C—H distances of
0.95–0.99 Å and N—H distances of 0.88 Å, and with Uiso(H) values
of 1.2 Ueq C,N. The H-atoms of water molecules of crystallization
were refined with the O—H distances restrained to 0.95(2) Å. All
structural figures were made with DIAMOND [12].
3. Results and discussion
3.1. X-ray molecular and crystal structures
2.3. Synthesis of the complexes
Crystallographic data and refinement details for compounds (1),
(2) and (3) are summarized in Table 1, while the selected bond
lengths and angles are given in Table 2. All important hydrogen-
bonding interactions are given in Table 3.
2.3.1. Synthesis of [Zn(HL1)Cl3]ÁH2O (1)
The complex was prepared by mixing of equimolar solutions of
ZnCl2Á1.5H2O (1 mmol) and the L1 ligand (1 mmol) in 30 ml of
0.1 M HCl. The reaction mixture was stirred and heated at 80 °C
for 4 h. The resulting solution was kept at room temperature for
several days. Colourless crystals of (1), suitable for a single crystal
X-ray analysis, were obtained by slow evaporation of the solvent
from the reaction solution. As for the FTIR, Raman and TG/DTA
studies, the complex was prepared by the same procedure in the
form of [Zn(HL1)Cl3]Á(HL1Cl)ÁMeOH (1a).
3.1.1. Molecular and crystal structures of [Zn(HL1)Cl3]ÁH2O (1)
The molecular structure of (1) together with the atom number-
ing scheme is shown in Fig. 1. The central Zn(II) ion is tetrahedrally
coordinated by three chlorido ligands and one HL1 molecule
through the N7 atom of an adenine moiety. The Zn—Cl and Zn—N
bond lengths (see Table 2) are comparable with the average bond
length of 2.316(13) and 2.091(7) Å, respectively, as found in 50
compounds containing a ZnCl3N motive which are deposited in
CSD [7]. As for the Zn—Cl and Zn—N distances in the complex (1),
these are also comparable to those found in [Zn(HBoh)Cl3]ÁH2O
and [Zn(HiprOlo)Cl3]ÁH2O for which Zn—Cl and Zn—N distances
range from 2.2269(14) to 2.2719(14) Å, and from 2.045(4) to
2.0311(18) Å, respectively [8]. It is well known that molecules
involving an adenine skeleton may behave as ligands suitable for
coordination to transition metals owing to five nitrogen atoms to
be present within their molecules. Based on the search within
For (1). Yield: 73%. Anal. Calcd. for C12H11Cl3FN5ZnÁH2O
(Mr = 434.0): C, 33.2; H, 3.0; N, 16.1%. Found: C, 33.1; H, 3.0; N,
15.9%.
For (1a). Yield: 80%. Anal. Calcd. for C12H11Cl3FN5ZnÁ
C12H11ClFN5ÁCH3OH (Mr = 727.7): C, 41.3; H, 3.6; N, 19.2%. Found:
C, 40.9; H, 3.9; N, 18.9%. IR (ATR; cmÀ1): 576vs, 551m, 535s,
518s, 485s, 432m, 419m, 329s, 288vs, 209w. IR (KBr; cmÀ1):
3422w, 3274w, 3121w, 3066w, 2971w, 1656vs, 1606s, 1510s,
1447w, 1432w, 1403m, 1349m, 1295m, 1223s, 1159m, 1126w,
1097w, 1041w, 1015w, 971w, 825m, 793w, 779w, 765w, 637w,

ˇ
150
Z. Trávnícek, J. Marek / Journal of Molecular Structure 933 (2009) 148–155
Scheme 1. A schematic representation of the synthetic pathways for the preparation of the complexes (1)-(3).
Table 1
Crystallographic data and refinements for (1), (2) and (3).
(1)
(2)
(3)
Formula
M (g molÀ1
T (K)
C12H11Cl3FN5Zn.H2O
433.99
100(2)
C12H12FN5.Cl4Zn.H2O
470.45
100(2)
C12H12ClN5.Cl4Zn
468.89
100(2)
)
k (Å)
0.71073
0.71073
0.71073
Crystal system
Space group
a (Å)
b (Å)
c (Å)
monoclinic
P21/c
8.98995(19)
9.66082(19)
19.0579(4)
90
monoclinic
P21/n
9.92791(18)
17.4231(4)
10.3673(2)
90
monoclinic
P21/c
18.9463(8)
6.04673(18)
16.0349(4)
90
a
(°)
b (°)
103.034(2)
90
1612.54(6)
4
1.788
2.040
92.5434(17)
90
1791.52(6)
4
1.744
1.987
107.970(4)
90
1747.40(10)
4
1.782
2.173
c
(°)
V (Å3)
Z
Dc (g cmÀ3
)
l
(Mo K ) (mmÀ1
)
a
Crystal size (mm)
Crystal shape and color
TMin/TMax
0.35 Â 0.35 Â 0.30
Colourless prism
0.448/0.542
12316
0.30 Â 0.20 Â 0.20
Colourless prism
0.630/0.671
9163
0.30 Â 0.20 Â 0.20
Colourless prism
0.524/0.648
8567
No. data measured
Unique data (Rint
Observed data [I > 2
)
2850 (0.0146)
2677
3149 (0.0139)
2824
3077 (0.0112)
2905
r
(I)]
Final R1, wR2 (obs. data)
Final R1, wR2 (all data)
0.0198, 0.0616
0.0215, 0.0623
0.462, À0.223
0.0210, 0.0507
0.0255, 0.0519
0.783, À0.194
0.0198, 0.0536
0.0219, 0.0657
0.497, À0.416
qmax, )
qmin (e ÅÀ3
the CSD regarding compounds involving the Zn-adenine moiety, 22
molecular structures meeting the above-mentioned structural cri-
terion have been deposited in the database. By interpreting these
results, it may be concluded that the adenine moiety is coordinated
to zinc, depending mainly on a degree of adenine moiety substitu-
tion, as a monodentate ligand via the N1-atom [13], N3-atom [14],
N7-atom [15] and N9-atom [16], or as a bridging ligand via N1, N7-
atoms [17].
The HL1 ligand is protonated at the N1 position and represents
the N1–H protonated N9–H tautomer. The ligand contains three
different aromatic rings, i.e. benzene (A), pyrimidine (B) and imid-
azole (C). Each of these rings deviates slightly from planarity, with
the maximum deviations from the mean planes being 0.009(2) Å
for the atom C11 (ring A), 0.011(2) Å for the atom C5 (ring B) and
0.0015(19) Å for the atoms C4 and C5 (ring C) [12]. The dihedral
angle between the ring A and the purine skeleton (rings B and C)
is 80.51(4)°, while the B and C rings are nearly coplanar, with a
dihedral angle of 0.98(6)°. Generally, it may be concluded that a
degree of deformation within the purine moiety strongly depends
on the protonation of the molecule and its coordination mode to a
transition metal. Thus, significant changes in interatomic parame-
ters should be noticeable in the vicinity of nitrogen atoms meeting
the above-mentioned conditions, mainly in C–N–C angles (see Ta-
ble 2).
The crystal structure of (1) is stabilized by the N–H. . .Cl,
N–H. . .O, O–H. . .Cl and N–H. . .F hydrogen bonds, and C–H. . .F
[C(14)...F(1) = 3.114(3) Å] and C–H. . .N [C(12)...N(3) = 3.579(2) Å]
non-bonding intermolecular interactions. Some of the mentioned
contacts are depicted in Figs 2 and 3, while their parameters are
summarized in Table 3.
3.1.2. Molecular and crystal structures of (H2L2)[ZnCl4]ÁH2O (2) and
(H2L3)[ZnCl4] (3)
The molecular structure of (2) together with the atom
numbering scheme is depicted in Fig. 4. The structure consists of
the twice-protonated H2L2 cation, [ZnCl4]2À anion and one crystal
water molecule. The cation exists as the N1–H, N7–H protonated
N9–H tautomer and contains benzene (A), pyrimidine (B) and
imidazole (C) aromatic rings. Each of these rings deviates slightly
from planarity, with the maximum deviations from the mean
planes being 0.006(2) Å for the atom C15 (ring A), 0.013(2) Å for
the atom C4 (ring B) and 0.007(2) Å for the atom C8 (ring C). The

ˇ
Z. Trávnícek, J. Marek / Journal of Molecular Structure 933 (2009) 148–155
151
Table 2
Selected bond lengths (Å) and angles (°) for (1), (2) and (3).
(1)
(2)
(3)
Bond lengths
Zn–Cl(1)
Zn–Cl(2)
Zn–Cl(3)
Zn–Cl(4)
2.2414(5)
2.2389(5)
2.2401(5)
–
2.2783(6)
2.2650(5)
2.2564(5)
2.2839(5)
–
1.368(3)
1.363(2)
1.299(3)
1.357(3)
1.329(3)
1.381(2)
1.329(3)
1.370(3)
1.411(3)
2.2735(6)
2.2754(6)
2.2665(6)
2.2868(5)
–
1.303(3)
1.368(3)
1.347(3)
1.354(3)
1.318(3)
1.383(3)
1.340(3)
1.357(3)
1.415(3)
Zn–N(7)
2.0708(17)
1.365(3)
1.365(3)
1.298(3)
1.354(3)
1.321(3)
1.390(3)
1.346(3)
1.361(3)
1.410(3)
N(1)–C(2)
N(1)–C(6)
N(3)–C(2)
N(3)–C(4)
N(7)–C(8)
N(7)–C(5)
N(9)–C(8)
N(9)–C(4)
C(5)–C(6)
Bond angles
Fig. 1. The molecular structure of complex (1), showing the atom numbering
scheme. Dashed line indicates the intramolecular N(6)–H. . .Cl(1) hydrogen bond.
Thermal ellipsoids are drawn at the 50% probability level.
N(7)–Zn–Cl(1)
N(7)–Zn–Cl(2)
N(7)–Zn–Cl(3)
Cl(2)–Zn–Cl(1)
Cl(3)–Zn–Cl(1)
Cl(4)–Zn–Cl(1)
Cl(3)–Zn–Cl(2)
Cl(4)–Zn–Cl(2)
Cl(3)–Zn–Cl(4)
C(8)–N(7)–Zn
C(5)–N(7)–Zn
C(2)–N(1)–C(6)
C(2)–N(3)–C(4)
C(8)–N(7)–C(5)
C(8)–N(9)–C(4)
N(3)–C(2)–N(1)
N(3)–C(4)–N(9)
N(3)–C(4)–C(5)
N(9)–C(4)–C(5)
C(4)–C(5)–N(7)
C(4)–C(5)–C(6)
N(7)–C(5)–C(6)
N(1)–C(6)–C(5)
N(7)–C(8)–N(9)
111.99(5)
108.98(5)
101.60(5)
110.51(2)
110.77(2)
–
112.72(2)
–
–
114.64(14)
140.27(14)
123.52(18)
112.13(18)
104.42(17)
107.36(17)
125.35(19)
126.47(19)
127.5(2)
106.00(18)
109.56(18)
117.96(18)
132.45(18)
113.48(17)
112.67(19)
–
–
–
–
–
–
103.89(2)
108.04(2)
114.20(2)
114.30(2)
109.43(2)
107.155(19)
–
109.83(2)
115.18(2)
106.05(2)
106.69(2)
112.05(2)
107.12(2)
–
–
–
124.13(17)
111.71(17)
107.68(16)
107.90(16)
125.50(18)
125.61(18)
126.97(18)
107.41(17)
106.87(17)
119.74(17)
133.33(18)
111.90(17)
110.13(17)
119.75(19)
116.11(18)
108.72(18)
107.68(17)
126.0(2)
130.18(19)
121.50(19)
108.31(19)
105.67(18)
119.4(2)
134.78(19)
117.12(18)
109.60(19)
Table 3
Hydrogen bonding geometry and intermolecular: and intramolecular interactions for
(1), (2) and (3).
Fig. 2. A part of the crystal structure of (1), showing the N–H. . .Cl, N–H. . .O and O–
H. . .Cl hydrogen bonds (dashed lines) [Symmetry codes: (ii): x, ½ À y, À½ + z, (iii):
2 À x, ½ + y, 3/2 À z]. Some of the H-atoms are omitted for clarity.
D–H. . .A
d(D–H)
d(D. . .A)
d(H–A)
<(DHA)
For (1)
dihedral angle between the ring A and the purine skeleton (rings B
and C) is 78.39(5)°, while the B and C rings are nearly coplanar,
N(1)–H(1A). . .O(1)
N(6)–H(6A)...Cl(1)
N(9)–H(9C)...F(1)i
O(1)–H(1V)...Cl(2)ii
O(1)–H(1W)...Cl(1)iii
0.88
0.88
0.88
0.88(2)
0.88(2)
2.772(2)
3.236(2)
2.895(2)
3.366(2)
3.490(2)
1.93
2.36
2.13
2.50(2)
2.61(2)
159
174
144
170(3)
172(3)
with
a dihedral angle of 3.14(7)°. The Zn—Cl bond lengths
[2.2564(5)–2.2839(5) Å] are comparable with the average bond
length of 2.270(1) Å found in 329 compounds containing a ZnCl4
motive deposited in CSD [7].
The N–H. . .O and O–H. . .Cl hydrogen bonds and C. . .C non-
bonding (plane-to-plane distance is ca 3.35 Å) intermolecular con-
tacts contribute to the stabilization of the crystal structure of (2).
These interactions are depicted in Figs. 5 and 6, while the parame-
ters of hydrogen bonds are summarized in Table 3.
For (2)
N(1)–H(1A). . .Cl(4)iv
N(6)–H(6A)...Cl(2)v
N(7)–H(7A)...Cl(2)v
N(7)–H(7A)...Cl(1)v
N(9)–H(9C)...O1
0.88
0.88
0.88
0.88
0.88
0.892(18)
0.878(18)
3.160(2)
3.196(2)
3.369(2)
3.308(2)
2.681(2)
3.3227(15)
3.2268(15)
2.39
2.33
2.56
2.76
1.81
2.50(2)
2.39(2)
146
170
152
121
168
154(3)
159(3)
O(1)–H(1 V)...Cl(4)vi
O(1)–H(1 W)...Cl(3)vii
The molecular structure of (3) together with the atom number-
ing scheme is depicted in Fig. 7. Similarly as in the case of (2), the
structure of (3) consists of the twice-protonated H2L3 cation and
[ZnCl4]2À anion. The cation exists as the N3–H, N7–H protonated
N9–H tautomer and contains benzene (A), pyrimidine (B) and
imidazole (C) aromatic rings. Each of these rings deviates slightly
from planarity, with the maximum deviations from the mean
planes being 0.010(2) Å for the atom C15 (ring A), 0.015(2) Å for
the atom C5 (ring B) and 0.008(2) Å for the atom C8 (ring C). The
dihedral angle between the ring A and the purine skeleton (rings
B and C) is 84.08(5)°, while the B and C rings are nearly coplanar,
with a dihedral angle of 2.12(7)° [0.98(6)° in (1), 3.14(7)° in (2)].
For (3)
N(6)–H(3)...Cl(1)
N(3)–H(3)...Cl(4)
N(3)–H(3)...Cl(3)viii
N(6)–H(6A)...Cl(3)ix
N(7)–H(7)...Cl(2)x
N(7)–H(7)...Cl(3)ix
N(9)–H(9)...Cl(4)xi
N(9)–H(9)...Cl(4)
0.88
0.88
0.88
0.88
0.88
0.88
0.88
0.88
3.239(2)
3.225(2)
3.364(2)
3.208(2)
3.052(2)
3.246(2)
3.142(2)
3.245(2)
2.52
2.61
2.95
2.62
2.28
2.73
2.52
2.66
139
128
111
126
146
118
129
125
Symmetry codes: (i) x À 1, Ày + 1/2, z À 1/2; (ii) x, Ày + 1/2, z À 1/2; (iii) Àx + 2, y + 1/
2, Àz + 3/2; (iv) x + 1/2, Ày + 3/2, z + 1/2; (v) x + 1/2, Ày + 3/2, z À 1/2; (vi) Àx + 1,
Ày + 1, Àz + 1; (vii) Àx + 1/2, y À 1/2, Àz + 1/2; (viii): x, y À 1, z; (ix) x, Ày + 3/2,
z + 1/2; (x) x, Ày + 1/2, z + 1/2; (xi) Àx + 1, y À 1/2, Àz + 1/2.

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Z. Trávnícek, J. Marek / Journal of Molecular Structure 933 (2009) 148–155
152
Fig. 3. A part of the crystal structure of (1), showing the N–H. . .F, C–H. . .F and C–H. . .N intermolecular contacts (dashed lines) [Symmetry codes: (i): À1 + x, ½ À y, À½ + z,
(xii): 1 + x, ½ À y, ½ + z, (xiii): 2 À x, 1 À y, 2 À z].
The Zn—Cl bond lengths [2.2665(6)–2.2868(5) Å] are comparable
with the average bond length of 2.270(1) Å found in compounds
containing a ZnCl4 motive deposited in the CSD [7].
The crystal structure of (3) is stabilized by the N–H. . .Cl hydro-
gen bonds (see Fig. 8) and C. . .Cl non-bonding intermolecular con-
tacts (see Fig. 9) with the C(2)...Cl(5) separation of 3.252(2) Å. The
parameters of the former interactions are summarized in Table 3.
3.2. FTIR and Raman spectra
For the FTIR, Raman and TG/DTA studies, the complex of (1) was
prepared in
a
solvated form with the composition of
[Zn(HL1)Cl3]Á(HL1Cl)ÁMeOH (1a), although the same preparative
procedure as described in the Section 2.3.1. was used. FTIR spectra
of the compounds (1a), (2) and (3) were measured in the region of
200–4000 cmÀ1. The spectra clearly confirmed the presence of the
organic molecules Ln in the compounds (1a), (2), and (3). The bands
observed at 3206–3302 cmÀ1 and 3072–3176 cmÀ1 are assignable
to
m
(N–H), and
m
(C–H)ar, respectively, while very strong bands be-
(C@N)ar [18].
tween 1653 and 1675 cmÀ1 may be attributed to
m
The m(C@N) and m(C@C) purine skeletal vibrations were observed
Fig. 4. The molecular structure of complex (2), showing the atom numbering
scheme. Thermal ellipsoids are drawn at the 50% probability level.
at 1606, 1510, 1447 and 1432 cmÀ1 for (1a), 1609, 1588, 1493
and 1454 cmÀ1 for (2) and 1625, 1568, 1464 and 1440 cmÀ1 for
(3). The bands assignable to
for (1a) and at 1233 cmÀ1 for (2), while the band attributable to
(C–Cl)ar was found at 1095 cmÀ1 for (3). The values of the last-
m
(C–F)ar were observed at 1223 cmÀ1
m
mentioned maxima are in good accordance with the literature data
summarized in the literature [18], where it is claimed that fluorine
attached directly to an aromatic ring exhibits a C–F band near
1250 cmÀ1 and a C–Cl band shows maximum between 1000 and
1175 cmÀ1. Moreover, the measured values correlate well with
those of theoretical calculations of vibrational frequencies for
6-(4-fluorobenzylamino)purine, L1, and 6-(4-chlorobenzylami-
no)purine, L3, performed with Spartan06 [19] program package at
the B3LYP/6-311+G(d,p) level of theory. The medium strong band
calculated at 1239.9 cmÀ1 is connected with the stretching Car–F
vibration, while the maximum belonging to the stretching Car–Cl
vibration was calculated at 1098.3 cmÀ1. (Note: Calculated maxima
values were not scaled). Both types of the mentioned vibrations are
coupled with the in-plane benzene ring deformation modes. Strong
bands at 329 cmÀ1 for (1a), 321 cmÀ1 for (2) and 313 cmÀ1 for (3)
are assignable to
attributed to (Zn–N) [20].
m
(Zn–Cl), while that at 288 cmÀ1 for (1a) may be
m
The conclusions supporting the presence of the ligands Ln with-
in the complexes may be also drawn from the Raman spectra. The
most intensive bands, which may be assigned to the stretching
vibration of the purine skeleton, appeared in the
1337–1345 cmÀ1 region [21]. The vibrations of strong intensity
Fig. 5. A part of the crystal structure of (2), showing the N–H. . .Cl, N–H. . .O and O–
H. . .Cl hydrogen bonds (dashed lines) [Symmetry codes: (iv): ½ + x, 3/2 À y, ½ + z,
(v): ½ + x, 3/2 À y, À½ + z, (vi): 1 À x, 1 À y, 1 À z, (vii): ½ À x, À½ + y, ½ À z, (xiv):
À½ + x, 3/2 À y, ½ + z]. Most of the H-atoms are omitted for clarity.

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Z. Trávnícek, J. Marek / Journal of Molecular Structure 933 (2009) 148–155
153
Fig. 6. A part of the crystal structure of (2), showing the C. . .C non-bonding contacts (dashed lines) [Symmetry code: (vi): 1 À x, 2 À y, 1 À z].
assignable to
observed at 278–288 cmÀ1 may be connected with
tions of all compounds, while the peak at 234 cmÀ1 is attributable
to
(ZnÀN) in the case of (1a) [20].
m
(C@N) were detected at 1605–1623 cmÀ1. The peaks
(ZnÀCl) vibra-
m
m
3.3. Thermal studies
The complexes (1a), (2) and (3) were also studied by means of
thermogravimetric (TG) and differential thermal (DTA) analyses.
The thermal decomposition of complex (1a) is somewhat distinct
from those of complexes (2) and (3) whose decays seem to be
nearly identical. The [Zn(HL1)Cl3]Á(HL1Cl)ÁMeOH (1a) complex
starts to decompose at 96 °C and its thermal decay proceeds in
three main steps [see Fig. 10a]. The first weight loss proceeds with-
in the temperature interval of 97–149 °C and is accompanied by a
small endo-effect on the DTA curve with a minimum at 134 °C. This
step may be connected with the elimination of one MeOH mole-
cule of crystallization (a weight loss calcd./found: 4.4/4.8%). The
complex exists in the form of [Zn(HL1)Cl3]Á(HL1Cl) within the inter-
val of 150–210 °C. Then, the complex decomposes without forma-
tion of any thermally stable intermediates up to 638 °C. This part of
thermal degradation is accompanied by one small endo-effect and
three exo-effects on the DTA curve with a minimum at 326 °C, and
maxima at 342, 443 and 587 °C, respectively. It is supposable that
the last-mentioned endo-effect cannot be connected with the melt-
ing temperature of HL1Cl molecule of crystallization, i.e. 6-(4-fluo-
robenzylamino)purine hydrochloride, which was determined to be
213–214 °C, but it may be associated with melting of some Zn-
complex intermediate. The thermal decomposition is finished at
Fig. 7. The molecular structure of complex (3), showing the atom numbering
scheme. Thermal ellipsoids are drawn at the 50% probability level.

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Z. Trávnícek, J. Marek / Journal of Molecular Structure 933 (2009) 148–155
154
Fig. 8. Part of the crystal structure of (3), showing the N–H. . .Cl hydrogen bonds (dashed lines) [Symmetry codes: (ii): x, ½ À y, À½ + z, (ix): x, 3/2 À y, ½ + z, (xi): 1 À x, À½ + y,
½ À z].
Fig. 9. Part of the crystal structure of (3), showing the alternation of cationic and anionic moieties, and C–H. . .Cl non-bonding contacts (dashed lines) [Symmetry code: (v):
2 À x, 1 À y, 2 À z].

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155
Fig. 10. TG/DTA curves of complexes (1a) (a) and (2) (b).
ca 640 °C and is connected with the formation of ZnO as a final
product of the degradation (a weight loss calcd./found: 88.8/
88.0%).
is gratefully acknowledged. Authors thank Mr. Michal Šipl for help
with the preparation of complexes and their single crystals.
Based on the fact that the courses of thermal decays of com-
plexes (2) and (3) are nearly identical, the decomposition of com-
plex (2) will be depicted as a representative example [see Fig. 10b].
The complex (2) starts to decompose at 33 °C [31 °C for (3)]. This
first step is accompanied by a small endo-effect on the DTA curve
with the minimum at 61 °C [53 °C for (3)] and can be connected
with the elimination of one half of water molecule of crystalliza-
tion (a weight loss calcd./found: 1.9/2.0%). The unsolvated complex
exists between 70 and 200 °C [97–151 °C for (3)]. Then, a broad
endo-effect can be seen on the DTA curve with a minimum at
231 °C [233 °C for (3)]. This effect can be connected with the melt-
ing and decomposition of the unsolvated complex which is accom-
panied by a moderate weight loss (1.7%) on the TG curve. This
conclusion may be supported by a value of melting temperature
of the compound as determined by a melting point apparatus, i.e.
228–230 °C [232–233 °C for (3)]. Consequently, the complex
decomposes in three steps which are connected with three exo-ef-
fects with maxima at 354, 470 and 631 °C [350, 443 and 633 °C for
(3)]. The thermal decomposition is finished at ca 660 °C [690 °C for
(3)]. ZnO may be considered as a final product of the degradation (a
weight loss calcd./found: 88.0/86.8% for 2).
Appendix A. Supplementary material
Supplementary data are available from the CCDC, 12 Union
Road, Cambridge CB2 1EZ, UK on request, quoting the deposition
numbers: CCDC-714074 – CCDC-714076 for (1)–(3), respectively.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.molstruc.2009.06.011.
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4. Conclusions
The reactions between ZnCl2 and the 6-benzylaminopurine
derivative, Ln, in 0.1 M or 2 M HCl afforded two types of products,
i.e. [Zn(HL1)Cl3]ÁH2O (1), and (H2L2)[ZnCl4]ÁH2O (2) and
(H2L3)[ZnCl4] (3), in dependence on a pH of the reaction medium.
It has been confirmed that the extent of protonation, dominantly
depending on the concentration of HCl used, has a significant im-
pact not only on the coordination ability of the discussed organic
molecules to Zn(II) cations but also on the changes in interatomic
parameters within the variously protonated organic molecules.
Moreover, the degree of deformation within the compounds is also
markedly influenced by non-bonding intramolecular and intermo-
lecular interactions.
Acknowledgements
The financial support from The Ministry of Education, Youth
and Sports of the Czech Republic (a Grant No. MSM6198959218)