Complexes of zinc(II) halides with N-benzyl- and N-p-tolyl-2-oxo-1- naphthylideneamine - Preparation and characterization

Article abstract of DOI:10.1016/j.poly.2003.12.023

A series of novel complexes, dihalo-bis(N-benzyl-2-oxo-1- naphthylideneamine-O)zinc(II), ZnX₂(bznapH)₂ (1-3), dihalo-bis(N-p-tolyl-2-oxo-1-naphthylideneamine-O)zinc(II), ZnX ₂(tolnapH)₂ (4-6), of the general formula [ZnX ₂(LH)₂] X=Cl, Br, I, have been prepared. The crystal structures of four compounds (1-4) reveal four coordinated zinc centres by two halogen and two oxygen atoms from the Schiff-base in the form of distorted tetrahedra. Complex 4 crystallizes as the one-to-one solvate with ethanol. The tetrahedral distortion is most pronounced in the structure of ZnI ₂(bznapH)₂ complex. X-ray structural data showed that the Schiff-base ligand in the naphthylideneamine tautomeric form is weakly bound to Zn atom in 1-4 (being in the range from 1.952(3) ? in 2 to 2.002(3) ? in 4). The molecular structures of 1-4 are governed by the type of halide and the corresponding Schiff-base. Although the structure comparison of ZnX₂(bznapH)₂ vs. ZnX₂(tolnapH)₂ leads to the conclusion that ligand spatial accomodation (non-planar bznapH with aliphatic interruption vs. aromatic tolnapH) is the dominating factor in the crystal structures. The crystal structures of 2-4 are dominated by van der Waals forces. There is a weak intermolecular hydrogen bond of the C-H?Cl type in 1 (3.710(5) ? joining molecules into endless chains. The UV-Vis and ¹H NMR spectra, obtained in ethanolic and acetone solution indicate that the complexes do not exist in the solutions.

Full text of DOI:10.1016/j.poly.2003.12.023

Polyhedron 23 (2004) 1293–1302
www.elsevier.com/locate/poly
Complexes of zinc(II) halides with N-benzyl- and
N-p-tolyl-2-oxo-1-naphthylideneamine – preparation
and characterization
a,
Zora Popovic , Vibor Roje , Gordana Pavlovic , Dubravka Matkovic-Calogovic ,
a
b
a
*
ꢁ
ꢀ
ꢀ
Masa Rajic , Ivan Leban
ꢀ
ꢀ
c
d
ꢁ
ꢀ
a
Faculty of Science, Laboratory of General and Inorganic Chemistry, Department of Chemistry, University of Zagreb,
Ul. kralja Zvonimira 8, HR-10000 Zagreb, Croatia
b
Faculty of Textile Technology, University of Zagreb, Pierottijeva 6, HR-10000 Zagreb, Croatia
c
Laboratory for Thermal Analysis, Brodarski Institute – Marine Research and Special Technology, Av. V. Holjevca 20, HR-10000 Zagreb, Croatia
d
Laboratory of Inorganic Chemistry, Faculty of Chemistry and Chemical Technology, University of Ljubljana, P.O. Box 537,
1001 Ljubljana, Slovenia
Received 22 July 2003; accepted 8 December 2003
Available online 9 April 2004
Dedicated to Professor Milan Sikirica on the occasion of his 70th birthday
Abstract
A series of novel complexes, dihalo-bis(N-benzyl-2-oxo-1-naphthylideneamine-O)zinc(II), ZnX2(bznapH)2 (1–3), dihalo-bis(N-p-
tolyl-2-oxo-1-naphthylideneamine-O)zinc(II), ZnX2(tolnapH)2 (4–6), of the general formula [ZnX2(LH)2] X ¼ Cl, Br, I, have been
prepared. The crystal structures of four compounds (1–4) reveal four coordinated zinc centres by two halogen and two oxygen atoms
from the Schiff-base in the form of distorted tetrahedra. Complex 4 crystallizes as the one-to-one solvate with ethanol.
The tetrahedral distortion is most pronounced in the structure of ZnI2(bznapH)2 complex. X-ray structural data showed that the
Schiff-base ligand in the naphthylideneamine tautomeric form is weakly bound to Zn atom in 1–4 (being in the range from 1.952(3)
ꢂ
ꢂ
A in 2 to 2.002(3) A in 4). The molecular structures of 1–4 are governed by the type of halide and the corresponding Schiff-base.
Although the structure comparison of ZnX2(bznapH)2 vs. ZnX2(tolnapH)2 leads to the conclusion that ligand spatial accomodation
(non-planar bznapH with aliphatic interruption vs. aromatic tolnapH) is the dominating factor in the crystal structures. The crystal
structures of 2–4 are dominated by van der Waals forces. There is a weak intermolecular hydrogen bond of the C–Hꢀ ꢀ ꢀCl type in 1
1
ꢂ
(3.710(5) A joining molecules into endless chains. The UV–Vis and H NMR spectra, obtained in ethanolic and acetone solution
indicate that the complexes do not exist in the solutions.
ꢀ 2004 Elsevier Ltd. All rights reserved.
Keywords: Zinc complexes; Schiff-bases; Crystal structures; IR; UV and NMR spectroscopy; Thermal analysis
1. Introduction
Schiff-bases play important roles in biological systems;
zinc mainly as a part of metalloenzymes [2] and Schiff-
bases as the intermediates in aminoacid metabolism
[3,4].
This paper reports the synthesis, IR, NMR and UV
characterization as well as thermal studies of a series of
1:2 complexes of zinc(II) halides with N-benzyl-, N-p-
tolyl-2-oxo-1-naphthylideneamine. The crystal struc-
tures of the complexes 1–4 have been determined by
crystal X-ray diffractometry.
In the context of our investigation of mercury(II)
compounds with Schiff-bases [1], we undertook the in-
vestigation of the analogous zinc(II) compounds in or-
der to make more complete the coordination chemistry
of the group 12 metals. It is well known that zinc and
* Corresponding author. Tel.: +385-1-4606652; fax: +385-1-4611191.
ꢀ
E-mail address: zpopovic@chem.pmf.hr (Z. Popovic).
0277-5387/$ - see front matter ꢀ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2003.12.023

1294
Z. Popoviꢀc et al. / Polyhedron 23 (2004) 1293–1302
Scheme 1.
Schiff-bases derived from O-hydroxy aromatic alde-
in parts per million (ppm), are referred to TMS. Digital
resolution was 0.32 Hz per point. The thermal mea-
surements were performed using a simultaneous TGA–
DTA analyser (TA Instruments, SDT Model 2960
coupled with MS). The samples were placed in small
alumina sample pans. The TGA and DTA curves were
obtained by placing the samples of about 2 mg in mass,
in open sample pans, with a heating rate of 10 ꢁC minꢁ1
and argon (purity above 99.996%) flowing at the rate of
50 ml minꢁ1. The SDT was calibrated with indium.
hydes such as salicylaldehyde and 2-hydroxy-1-naph-
thaldehyde with the N,O-donor set react with the zinc
ion to yield two different types of compounds, i.e. metal
chelates and adducts of general formulas ZnL2 and
ZnX2 Æ 2LH, respectively, both containing a four-coor-
dinated zinc metal centre [5]. The chelate zinc complexes
of the ZnL2 type where L ¼ salicylaldiminato ligand are
well known, but according to the Cambridge Structural
Database [6a,6b] there are only two zinc(II) complexes
with the Schiff-bases derived from 2-hydroxy-1-naph-
thaldehyde that are structurally characterized. One of
them (refcode: POGJAW) [7] contains a five-coordi-
nated zinc atom (three nitrogen atoms, one oxygen atom
and one bromine atom) and the other has a tetrahedrally
coordinated zinc atom (refcode: SUQWOK) [8]. Ac-
cording to our best knowledge, there is only one more
zinc(II) complex with a Schiff-base derived from 2-hy-
droxy-1-naphthaldehyde and that has only been char-
acterized spectroscopically [9]. There is no structural
characterization of zinc adducts with the naphthaldi-
mine type of Schiff-bases.
The crystal structures of these non-coordinated li-
gands have not been determined up until now. The
tautomeric equilibrium of the Schiff-bases derived from
2-hydroxy-1-naphthaldehyde and amines (1:1 molar
ratio), in the solid state [10–12] as well as in solution [3],
is usually shifted toward the keto-amine tautomeric
form (Scheme 1). There are also examples of the struc-
tures of this Schiff-base type that in the solid state exist
in the enol-imine tautomeric form [13].
2.1. Preparation of the ligands and basic analytical data
The Schiff-bases N-benzyl-2-oxo-1-naphthylidene-
amine (bznapH) [14] and N-p-tolyl-2-oxo-1-naphthylid-
eneamine (tolnapH) were prepared by the conventional
condensation method.
[bznapH]. Chemical analysis: found (required for
C18H15NO) C, 82.73 (82.89); H, 6.18 (5.79); N, 5.66
(5.36). Melting point: 98.5 ꢁC. Selected IR-max (KBr
disc, cmꢁ1): 1629vs (C@O), 1542s and 1209m-s (C–N).
Selected UV–Vis absorptions (EtOH): kmax/nm (e/dm3
molꢁ1 cmꢁ1) 231 (45370), 307 (10920) and 420 (11010).
1H NMR peaks (d6-acetone): 14.98 (s, 1H, –OH), 9.36
(s, 1H, HC@N), 8.14-6.92 (m, 11H, Ar–H), 4.91 (s, 2H,
–CH2–).
[tolnapH]. Chemical analysis: found (required for
C18H15NO) C, 82.05 (82.89); H, 5.77 (5.79); N, 5.46
(5.36). Melting point: 131 ꢁC. Selected IR-max (KBr
disc, cmꢁ1): 1619vs (C@O), 1543s and 1211m-s (C–N).
Selected UV–Vis absorptions (EtOH): kmax/nm (e/dm3
molꢁ1 cmꢁ1) 233 (47420), 318 (13810) and 440 (16370).
1H NMR peaks (d6-acetone): 15.73 (s, 1H, –OH), 9.68
(s, 1H, HC@N), 8.44-7.06 (m, 10H, Ar–H), 2.36 (s, 3H,
–CH3).
2. Experimental
All reagents used were purchased from Aldrich, sol-
vents from Kemika-Zagreb and were used without fur-
ther purification. C, H and N analysis was provided by
the Analytical Services Laboratory of the Rudꢃer
2.2. Preparation of the complexes and basic analytical
data
ꢄ
ꢀ
Boskovic Institute. The IR spectra of all mentioned
compounds were recorded in a Perkin–Elmer Fourier
Transform 1600 spectrometer in the range of 4000–450
cmꢁ1 as KBr discs. The UV–Vis spectra were recorded
using a Varian Cary 300 operating in the range 190–900
2.2.1. General procedure
Ethanolic solutions of the corresponding zinc(II)
salts and the appropriate Schiff-base in a 1:2 molar ratio
were refluxed for several hours. The reaction mixture
was then left to stand for two days. The compounds
were filtered off, washed with ethanol and dried in va-
cuo. After standing for a few days, the filtrates 1–4
1
nm. The H NMR spectra were recorded in a Varian
Gemini 300 spectrometer, at 20 ꢁC. All chemical shifts,

Z. Popoviꢀc et al. / Polyhedron 23 (2004) 1293–1302
1295
Table 1
General and crystal data and summary of intensity data collection and structure refinement for 1, 2, 3 and 4
Compound
1
2a
3b
4
Formula
Mr
C36H30Cl2N2O2Zn
658.91
C36H30Br2N2O2Zn
747.81
C18H15INOZn0:5
420.90
C36H30Cl2N2O2Zn Æ EtOH
698.93
Colour and habit
Crystal system
Space group
colourless, prism
monoclinic
Cc (No. 9)
0.596 · 0.498 · 0.284
293
yellow, plate
monoclinic
P21=n (No. 14)
0.29 · 0.28 · 0.09
200
yellow, needle
monoclinic
P2=c (No. 13)
0.10 · 0.05 · 0.01
200
yellow, plate
triclinic
ꢃ
P1 (No. 2)
Crystal dimensions (mm)
Temperature (K)
Unit cell parameters
0.40 · 0.20 · 0.01
293
ꢂ
a (A)
13.4309(15)
19.7654(19)
12.049(4)
12.6821(1)
38.3182(4)
13.1555(2)
12.1548(3)
8.6508(2)
17.7188(4)
10.089(5)
11.571(3)
16.318(5)
108.758(19)
102.52(3)
92.76(2)
1746.5(12)
2
ꢂ
b (A)
ꢂ
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
93.33(2)
94.179(1)
92.452(2)
3
ꢂ
V (A )
3193.2(12)
4
1.371
6375.99(13)
8
1861.40(8)
4
Z
Dcalc (g cmꢁ3
)
1.558
3.3
1.502
2.348
824
1.329
0.9
l (mmꢁ1
F ð000Þ
)
0.971
1360
3–30
3008
3–55
h range for data collection (ꢁ)
h; k; l range
4–54
2–27
)18 to 18; 18 to 27; )11
to 16
)16 to16; )46 to 48; )15 to 15; )11 to 10; )22 )12 to 12; )14 to 13;
)17 to 17
Nonius Kappa CCD Nonius Kappa CCD
to 22
0 to 20
PW 1100 upgraded by
Stoe
Diffractometer
PW 1100 upgraded by
Stoe
area-detector
diffractometer
x
area-detector
diffractometer
x
Scan type
x
6321
x
7519
Number of measured
reflections
Number of independent
16243
6713
6137 (0.031)
388 (two restraints)
3532
9606 (0.026)
792
3895 (0.024)
199
7519 (0.00)
421
reflections ðRint
Þ
Number of refined
parameters
Number of observed
reflections I P 2rðIÞ
Range of transmission
factors minimum,
maximumc
6507
2571
1812
0.6117; 0.7776
Crystal face indices,
(1 0 0; )1 0 0) 0.298
distances from centroid (mm) (1 0 )1; )1 0 1) 0.249
(0 1 0; 0 )1 0) 0.142
Rd wRe I P rðIÞ]
R, wR (all data)
g1, g2 in wf
0.043; 0.124
0.094; 0.106
0.0844; 0
0.91
0.046; 0.089
0.088; 0.078
0.0227; 6.8592
1.08
0.047; 0.151
0.078; 0.128
0.0805; 1.2948
1.002
0.048; 0.1396
0.099; 0.257
0.0624; 0
0.705
Goodness-of-fit on F 2,
Sg
Maximum and minimuꢁm3
0.44 and )0.28
)0.40 and 0.44
0.652 and )0.69
0.34 and )0.60
ꢂ
electron density (e A
)
Flack parameter
Maximum D=r
Extinction coefficent
0.006(14)
0.001
0.001
0.00025(8)
0.001
0.001
a The asymmetric unit contains two crystallographically independent molecules.
b The iodine atom lies on the twofold axis.
c Absorption correction type: numerical Gaussian for 1; only scaling for 2 and 3; not applied for 4.
P
P
d R ¼ jjFoj ꢁ jFcjj= jFoj:
h
.
i
1=2
P
P
2
2
e wR ¼
ðFo2 ꢁ Fc2Þ
wðFo2Þ
:
2
f w ¼ 1=½r2ðFo2Þ þ ½ðg1PÞ þ g2Pꢂ where P ¼ ðFo2 þ 2Fc2Þ=3:
P
2
1=2
g S ¼ ½wðFo2 ꢁ Fc2Þ =ðNobs ꢁ NparamÞꢂ
:
yielded crystals of good quality for X-ray diffraction
experiment.
C36H30Cl2N2O2Zn): C, 64.78 (65.62); H, 4.85 (4.59); N,
4.20 (4.25); Zn, 10.17 (9.92%). Selected IR-max (KBr
disc, cmꢁ1): 1634vs (C@O), 1548s (C@C) and 1212m-s
(C–N).
[ZnCl2(bznapH)2] (1). Reaction time: 4 h. Colour:
yellow-brownish Yield: 60%. Anal. Found (required for

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Z. Popoviꢀc et al. / Polyhedron 23 (2004) 1293–1302
[ZnBr2(bznapH)2] (2). Reaction time: 4 h. Colour:
3 only scaling based on all symmetrically dependent
reflections were applied.
yellow. Yield: 76%. Anal. Found (required for
C36H30Br2N2O2Zn): C, 57.85 (57.82); H, 4.00 (4.04); N,
3.75 (3.75); Zn, 8.43 (8.74%). Selected IR-max (KBr
discs, cmꢁ1): 1633vs (C@O), 1548s (C@C) and 1211m-s
(C–N).
[ZnI2(bznapH)2] (3). Reaction time: 6 h. Colour:
yellow. Yield: 76%. Anal. Found (required for
C36H30I2N2O2Zn): C, 51.27 (51.36); H, 3.78 (3.59); N,
3.39 (3.33); Zn, 7.97 (7.77%). Selected IR-max (KBr
discs, cmꢁ1): 1633vs (C@O), 1548s (C@C) and 1211m-s
(C–N).
[ZnCl2(tolnapH)2] (4). Reaction time: 4 h. Colour:
yellow. Yield: 90%. Anal. Found (required for
C36H30Cl2N2O2Zn): C, 65.31 (65.62); H, 4.75 (4.59); N,
4.17 (4.25); Zn, 9.60 (9.92%). Selected IR-max (KBr
discs, cmꢁ1): 1626vs (C@O), 1548s (C@C) and 1216m-s
(C–N).
The structures were solved by direct methods imple-
mented in the SHELXS [18] program. The applied re-
finement procedure based on the F 2 values against
all reflections included the anisotropic model for all
non-H atoms using the SHELXL [19] program. The
hydrogen atoms were generated at ideal geometrical
2
3
3
ꢂ
ꢂ
positions [Csp –H 0.93, Csp –H 0.97 A, Csp –H 0.96 A
for phenyl, methylene and methyl carbon atoms with
UisoðHÞ ¼ 1:2 or 1.5 Ueq(C)] and refined applying the
riding model. In the structure of compound 1 the
hydrogen atoms belonging to the nitrogen atoms of
the C@N group were found, but finally refined at ide-
ꢂ
alized stereochemical positions (N–H 0.86 A) by the
riding model procedure. Structurally identical hydrogen
atoms in 2 and 3 were found in the electron density
difference Fourier maps and refined freely [N1–H1N
ꢂ
ꢂ
[ZnBr2(tolnapH)2] (5). Reaction time: 1 h. Colour:
yellow. Yield: 89%. Anal. Found (required for
C36H30Br2N2O2Zn): C, 57.76 (57.82); H, 4.26 (4.04); N,
3.87 (3.75); Zn, 8.53 (8.74%). Selected IR-max (KBr
discs, cmꢁ1): 1626vs (C@O), 1548s (C@C) and 1217m-s
(C–N).
[ZnI2(tolnapH)2] (6). Reaction time: 4 h. Colour:
yellow. Yield: 86%. Anal. Found (required for
C36H30I2N2O2Zn): C, 51.74 (51.36); H, 4.27 (3.59); N,
3.21 (3.33); Zn, 7.87 (7.77%). Selected IR-max (KBr
discs, cmꢁ1): 1622vs (C@O), 1547s (C@C) and 1216m-s
(C–N).
0.74(4) A and N2–H2N 0.83(4) A in 2 and N1–H1N
ꢂ
0.64(4) A in 3].
In the structure of compound 4, due to the poorer
quality X-ray diffraction data (data-to-parameter ratio
is less than 4.5), the positional disorder of the atoms C1,
C2 and O3 of the ethanol molecule could not be refined,
thus hydrogen atoms belonging to C1, C2 and O3 were
not modelled. The hydrogen atom which belongs to the
N2 atom is found in the electron density difference
Fourier map and is refined freely, but the hydrogen
atom which belongs to N1 atom could not be found and
it was generated at an ideal position and refined by the
ꢂ
riding model procedure (N–H 0.86 A). The standard
deviations of the molecular geometry of 4 are signifi-
cantly larger than in 1, 2 and 3 making the comparison
of its geometry to the other ones impossible. Only the
main stereochemical features of the solid state structure
of 4 could be obtained, but not the fine structural de-
tails. Graphical work has been performed by the pro-
gram PLATON-98 [20].
2.3. X-ray single crystal analyses of the compounds 1, 2, 3
and 4
Relevant data on the summary of intensity data col-
lection for the structures 1–4 are given in Table 1. Data
collection for 1 and 4 were controlled by the STADI4
program [15]. Lattice constants were obtained by the
least-squares refinement from the settings of 46 reflec-
tions (10ꢁ 6 h 6 16ꢁÞ for
1
and 21 reflections
3. Results and discussion
ð8ꢁ 6 h 6 15ꢁÞ for 4. 7383 reflections with 1ꢁ 6 h 6 28ꢁ
and 3409 reflections with 1ꢁ 6 h 6 28ꢁ were used for unit
cell refinement for structures 2 and 3, respectively. Two
sets of 311 frames and one of 167 frames were collected
at the crystal-detector distance of 70 mm, 0.6o scans, 12
s per frame for structure 2 and two sets of 187 and 62
frames at the crystal-detector distance of 45 mm, 1.0o
scans, 30 s per frame for structure 3.
3.1. General aspects
The reactions of zinc(II) halides with N-benzyl-2-oxo-
1-naphthylideneamine and N-p-tolyl-2-oxo-1-naphthy-
lideneamine in ethanolic solution, give complexes of the
general formula [ZnX2(HL)2] (X ¼ Cl, Br, I) (Scheme 2).
The isolated compounds are stable in air at room tem-
perature, but do not exist in DMSO, DMF, pyridine,
chloroform, acetone or ethanol solutions, i.e. they un-
dergo decomposition, which is revealed by 1H NMR
and UV spectra. Compound 4 crystallizes as an ethan-
olic solvate, but its crystals, losing the ethanol, slowly
decompose into the unsolvated compound at room
temperature.
Reference reflections were monitored periodically
showing no significant intensity decay for all four
structures. The data were corrected for Lorentz-polari-
zation by the X-RED [16] program for 1 and 4 and by
DENZO-SMN [17] for 2 and 3. The Gaussian absorp-
tion correction based on the crystal dimensions by the
X-RED [16] program was performed for 1, but for 2 and

Z. Popoviꢀc et al. / Polyhedron 23 (2004) 1293–1302
1297
15.73 ppm, respectively. The signals corresponding to
Ar–H appear in the region 6.9–8.2 ppm and 7.0–8.5 ppm
for bznapH and tolnapH, respectively. At 4.91 ppm the
signal corresponding to the two methylene protons for
bznapH have been observed and that at 2.36 ppm cor-
responds to the three methyl protons for tolnapH
[8,26,27].
3.3. X-ray structural studies
The structural study of the four zinc complexes 1–4
was undertaken in order to establish the general mode of
ligating of this type of Schiff-base, dependence of the
zinc coordination sphere geometry on the type of zinc
halide (chloride, bromide and iodide) and to compare
results with the 1:1 mercury halide adducts of the same
Schiff-base which have been previously structurally
characterized by us [1].
Scheme 2.
In the ZnX2 Æ 2LH adducts or in the [ZnX2(LH)2]
complexes zinc retains Xꢁ ions in the coordination
sphere and thus neutral LH Schiff-base completes the
coordination sphere bonding monodentately by either
oxygen or nitrogen ligating centre, but not with both
donor atoms. Contrary to the ZnL2 complexes where
the Schiff-base is bound in an anionic form, the intra-
molecular hydrogen bond of the O–Hꢀ ꢀ ꢀN or N–Hꢀ ꢀ ꢀO
type is preserved in the adducts or in the [ZnX2(LH)2]
type of complexes. Usually, the type of intramolecular
hydrogen bond found in the adduct or in the
[ZnX2(LH)2] complexes and non-coordinated Schiff-
base is different, thus leading to the change of the
tautomeric form of the Schiff-base ligand upon com-
plexation [5]. Adducts of the type ZnX2 Æ 2LH are only
known for salicylaldimine Schiff-bases and according to
the Cambridge Structural Database [6a,6b] there are
three such adducts: N-isopropylsalicylaldimine with
ZnI2 (refcode: VATROX) [28], dichloro-bis(2-(o-toly-
liminomethyl)phenolato-O)-zinc(II) (refcode: XAXVIB)
[29] and bis(1-anilinomethylidene-2-oxo-1H,2H-naph-
thalene-chloro)-zinc (refcode: VIRVUN) [30]. The
common feature of these three adducts is stronger Zn–X
3.2. Spectroscopic studies
The IR spectra of the free Schiff-bases and com-
pounds 1–6 are quite similar in the ‘‘finger print’’ region.
The common feature of all these spectra is a very weak
and broad stretching band in the 3000–1800 cmꢁ1 region
that can be assigned as the m(NH) stretching band. The
very strong absorption band in the region of 1630–1610
cmꢁ1, is due to the C@O stretching vibrations and in-
dicates the presence of the keto-amine tautomeric form
of the Schiff-base, both in the free ligand and in the
complexes. Furthermore, the strong absorption bands in
the region of 1550–1540 cmꢁ1 that can be assigned to the
C@C stretching accompanied with that in the region of
1220–1210 cmꢁ1 that suggests C@N stretching, confirm
the existence of the keto-amine tautomeric form of the
Schiff-base [21–23], suggesting metal-to-ligand coordi-
nation via the carbonyl oxygen atom.
The UV–Vis absorption spectra measured for the
absolute ethanolic solution of the zinc complexes (1–6)
suggest that they decompose when dissolved. Such a
conclusion can be drawn because of the similarity of the
spectra of the free ligands with those measured for the
solution of the complexes. Moreover, that is quite con-
sistent with the our previous results obtained for the
mercury(II) halide adducts with the same ligand [1]. The
spectra reveal a predominance of the keto-amine tau-
tomeric form of both ligands [24,25].
ꢂ
bonds (2.564(1)–2.587(1) A range for the Zn–I bond in
ꢂ
VATROX, 2.2401(7) A for the Zn–Cl bond in XAXVIB
ꢂ
and 2.203(7), 2.226(7), 2.201(7) and 2.217(8) A for the
Zn–Cl bonds in VIRVUN) and weaker Zn–O bonds
ꢂ
being in the range from 1.955 A (mean value) in VAT-
ꢂ
ROX to 2.00(1) A in VIRVUN. These Zn–O bond dis-
tances are longer than in the chelate ZnL2 complexes
(the average Zn–O bond distance value in the ZnL2
ꢂ
complexes with salicylaldimine Schiff bases is 1.926 A).
1
We also measured the H NMR spectra in acetone.
The NMR measurements show that complexes 1–6 are
not stable in acetone either. This conclusion was drawn
from the fact that there are no significant changes in
the 1H NMR chemical shifts of the dissolved com-
pounds in comparison with those of the free ligands. In
the 1H NMR spectrum of bznapH the signals of
azomethine and hydroxyl protons appear at 9.36 and
14.98 ppm, while in tolnapH they appear at 9.68 and
This elongation is the consequence of the Schiff-base
ligation in the neutral form in the adducts and the
participation of N,O-donor atoms in the intramolecular
hydrogen bond formation. The length of the N–Hꢀ ꢀ ꢀO
ꢂ
intramolecular hydrogen bond varies from 2.499 A in
ꢂ
VIRVUN to 2.636 A in VATROX.

1298
Z. Popoviꢀc et al. / Polyhedron 23 (2004) 1293–1302
The crystal structures of the two isostructural ad-
ducts, HgX2(bznapH) (X ¼ Cl, Br) revealed dimers
formed by bridging halogen atoms and generated a 2 + 2
effective coordination sphere of the mercury atoms
[1]. The dimers are joined only by the van der Waals
contacts.
Fig. 1. ORTEP drawing of ZnCl2(bznapH)2 (1) with the atom num-
bering scheme. The thermal ellipsoids are at the 50% probability level.
Fig. 4. ORTEP drawing of ZnI2(bznapH)2 (3) with the atom num-
bering scheme. The thermal ellipsoids are at the 50% probability level.
Symmetry code: (a): 1 ꢁ x; y; 3=2 ꢁ z.
Fig. 2. The crystal packing of ZnCl2(bznapH)2 (1) showing the inter-
molecular C212–H21Aꢀ ꢀ ꢀCl1 hydrogen bonds by dashed lines that link
molecules into endless chains parallel to the y-axis. The other hydrogen
atoms are omitted for clarity.
Fig. 3. ORTEP drawing of ZnBr2(bznapH)2 (2) with atom the num-
bering scheme. The thermal ellipsoids are at the 50% probability level.
There are two crystallographically independent molecules within the
asymmetric unit. Only one is shown for clarity.
Fig. 5. ORTEP drawing of ZnCl2(tolnapH)2 Æ EtOH (4) with the atom
numbering scheme. The thermal ellipsoids are at the 50% probability
level.

Z. Popoviꢀc et al. / Polyhedron 23 (2004) 1293–1302
1299
In the zinc complexes 1–4 the common feature is the
distorted tetrahedral coordination sphere of the zinc
atom formed by two halogen atoms [Zn1–Cl1 2.215(2)
values are 118.81(7)ꢁ in 1, 119.49(3)ꢁ in 2, 123.49(4)ꢁ in 3
and 120.94(7)o in 4].
The dihedral angles between planes of the naphtha-
lene rings and phenyl rings of the N-substituents
(Table 3) indicate non-planarity of the ligands in the 1–3
complexes, while in 4 the corresponding dihedral angles
are remarkably smaller, but still the molecules are not
planar [20.3(2)ꢁ and 22.2(3)ꢁ in 4 vs. the range from
56.2(5)ꢁ to 81.7(2)ꢁ for 1, 2 and 3]. The tendency of a
stacking arrangement of planar tolnapH molecules is
observed in the structure of HgCl2(tolnapH) [1] causing
the needle-shaped crystal morphology.
ꢂ
and Zn1–Cl2 2.229(2) A in 1; Zn1–Br1 2.344(1), Zn1–
ꢂ
Br2 2.356(1), Zn2–Br3 2.371(1) and Zn2–Br4 2.355(1) A
ꢂ
in 2 and Zn1–I1 2.564(1) A in 3, Zn–Cl1 2.255 (2) and
Zn–Cl2 2.204 (2) in 4] and two oxygen atoms from two
neutral monodentate Schiff bases [Zn1–O1 1.968(4) and
ꢂ
Zn1–O2 1.982(3) A in 1, Zn1–O1 1.960(3), Zn1–O2
ꢂ
1.975(3), Zn2-O3 1.957(3) and Zn2–O4 1.952(3) A in 2,
ꢂ
Zn1–O1 1.968(4) A in 3, Zn–O1 1.976(3) and Zn–O2
ꢂ
2.002(3) A in 4] (Figs. 1, 3, 4 5). The Zn–O bond dis-
tance values are comparable with those found in zinc
complexes with salicylaldimines (VATROX, XAXVIB,
VIRVUN) and are longer than in the chelate complexes.
In the structures of complexes 1–4 the X1–Zn–X2
bond angles are the most deformed from ideal tetrahe-
dral geometry. The degree of deformation is most pro-
nounced in the iodo derivative [X1–Zn–X2 bond angles
In 2, the rings 1 and 2 are oriented to each other by
approx. 70ꢁ, while other rings (3–8) do not deviate sig-
nificantly from planarity (Table 3).
The molecules are mutually connected only by van
der Waals interactions, except in 1 where weak inter-
molecular hydrogen bonds of the C–Hꢀ ꢀ ꢀCl type link
molecules into endless chains parallel to the y-axis.
Table 2
ꢂ
Relevant interatomic distances (A) and angles (ꢁ) for the compounds 1, 2, 3 and 4
1
2
3
4
Interatomic distances
Zn1–X1a
Zn1–X2a
Zn2–X3a
Zn2–X4a
Zn1–O1
2.2149(15)
2.2292(18)
2.3435(7)
2.3558(8)
2.3708(8)
2.3551(8)
1.960(3)
1.975(3)
1.957(3)
1.952(3)
1.305(5)
1.298(5)
1.301(5)
1.294(5)
1.298(6)
1.291(5)
1.300(6)
1.302(6)
2.5639(6)
1.968(4)
1.298(6)
1.280(6)
2.255(2)
2.204(2)
1.968(4)
1.982(3)
1.976(4)
2.002(3)
Zn1–O2
Zn2–O3
Zn2–O4
O1–C12b
O2–C22
O3–C32
1.283(6)
1.285(5)
1.310(6)
1.319(7)
O4–C42
N1–C111c
N2–C211
N3–C311
N4–C411
1.294(10)
1.299(5)
1.307(8)
1.327(7)
Bond angles
X1–Zn1–X2ad
X1–Zn1–O1
X1–Zn1–O2e
X2–Zn1–O1f
X2–Zn1–O2
O1–Zn1–O2
Br3–Zn2–Br4
Br3–Zn2–O3
Br3–Zn2–O4
Br4–Zn2–O3
Br4–Zn2–O4
O3–Zn2–O4
118.81(7)
112.37(12)
117.59(10)
112.42(13)
101.01(9)
90.93(14)
119.49(3)
116.03(9)
100.65(8)
109.31(9)
114.53(10)
93.61(12)
116.92(3)
119.66(9)
96.54(11)
107.00(9)
120.70(10)
94.37(14)
123.49(4)
103.06(11)
108.25(11)
110.59(15)
120.94(7)
99.22(13)
98.34(10)
116.32(11)
114.06(12)
105.18(15)
a X1 ¼ Cl1 in 1, Br1 in 2 and I in 3;X2 ¼ Cl2 in 1 and Br2 in 2; X3 ¼ Br3 in 2; X4 ¼ Br4 in 2.
b O1–C2 in 3.
c N1–C11 in 3.
d I–Zn–Ii in 3 (i ¼ 1 ꢁ x; y; 3=2 ꢁ z).
e I–Zn–O1i in 3 (i ¼ 1 ꢁ x; y; 3=2 ꢁ z).
f O1–Zn–O1i in 3 (i ¼ 1 ꢁ x; y; 3=2 ꢁ z).

1300
Z. Popoviꢀc et al. / Polyhedron 23 (2004) 1293–1302
Table 3
Dihedral angles between planes defined by the naphtahlene and phenyl
rings atoms in 1, 2, 3 and 4
So, the conclusion is that the geometry of the zinc
coordination sphere in the three complexes 1–3 is not
affected by the crystal packing forces (i.e. intermolecular
hydrogen bonds). Therefore, the bond distances and
angles values within the coordination sphere are mutu-
ally comparable.
Number of plane Plane defined by atoms
Dihedral angle (ꢁ)
Compound 1
1
2
3
4
C11–C110
C113–C118
C21–C210
C213–C218
1,2 56.2(5)
3,4 62.0(5)
3.4. Description of the ligands
Compound 2
The bznapH and tolnapH Schiff-bases exist in the
keto-amine tautomeric form in all four complexes (1–4)
revealing the N–Hꢀ ꢀ ꢀO resonance assisted intramolecu-
lar hydrogen bond (RAHB) [range for the Nꢀ ꢀ ꢀO dis-
1
2
3
4
5
6
7
8
C11–C110
C113–C118
C21–C210
C213–C218
C31–C310
C313–C318
C41–C410
C413–C418
1,2 70.1(2)
3,4 81.7(2)
5,6 80.5(2)
7,8 80.3(2)
ꢂ
tance is 2.565(5)–2.599(5) A] (Table 4). The same
tautomeric form is found in the crystal structures of the
analogous 1:1 adducts with mercury(II) halides [1].
The C@N bond distance values are in the range from
Compound 3
ꢂ
ꢂ
1.280(6) A in 3 to 1.299(5) A in 1. The C–O bond dis-
ꢂ
1
2
C1–C10
C13–C18
1,2 70.5(4)
tance values (1.283(6)–1.301(5) A) are shortened in re-
lation to the Csp2–OH bond distance value in phenols
Compound 4
ꢂ
(1.36 A) [33]. These two bonds, C@N and Csp–O, are
1
2
3
4
C11–C110
C112–C116
C21–C210
C212–C216
1,2 20.3(2)
3,4 22.2(3)
the most sensitive indicators of the proton location, on
the oxygen or nitrogen site, i.e. on the type of the tau-
tomer. In the mercury analogues the intramolecular
ꢂ
hydrogen bond N–Hꢀ ꢀ ꢀO is 2.58(1) A in the chloro de-
ꢂ
rivative and 2.59(1) A in the bromo derivative.
(Table 4, Fig. 2.) [31,32]. This hydrogen bond does not
influence the Zn–Cl1 bond distance since it is compa-
rable with the Zn–Cl2 bond distance (atom Cl2 does not
participate in hydrogen bond formation) [Zn1–Cl1
The geometry of the ligands in the complexes 1–4 are
comparable with the similar non-coordinated naphtha-
ldimines in the keto-amine form, indicating the labile
bounding of the ligands with the zinc centre.
ꢂ
2.215(2) and Zn1–Cl2 2.229(2) A in 1].
The significant difference of the Zn–Cl1 and Zn–Cl2
bond distances in 4 (Table 2) can indicate the partici-
pation of the Cl1 atom in the O–Hꢀ ꢀ ꢀCl intermolecular
hydrogen bond formation with the O3 atom of an eth-
3.5. Thermal analysis
The samples of the free ligands, bznapH and tol-
napH, as well as the zinc complexes 1–6 were heated
from room temperature up to 700 ꢁC.
ꢂ
anol molecule (Cl1ꢀ ꢀ ꢀO3 distance is 3.266(7) A).
Table 4
ꢂ
Hydrogen bond geometry (A, ꢁ) in 1, 2 and 3
D–Hꢀ ꢀ ꢀA
d(D–H)
d(Hꢀ ꢀ ꢀA)
\DHA
d(Dꢀ ꢀ ꢀA)
1
N1–H1ꢀ ꢀ ꢀO1
N2–H2ꢀ ꢀ ꢀO2
C212–H21A ꢀ ꢀ ꢀCl1i
0.86
0.86
0.97
1.984
1.938
2.800
127
133
157
2.591(8)
2.599(5)
3.710(5)
2
N1–H1Nꢀ ꢀ ꢀO1
N2–H2Nꢀ ꢀ ꢀO2
N3–H3Nꢀ ꢀ ꢀO3
N4–H4Nꢀ ꢀ ꢀO4
0.74(4)
0.83(4)
0.90(5)
0.69(4)
1.99(5)
1.91(4)
1.89(4)
2.05(5)
137(5)
135(4)
132(4)
133(5)
2.576(5)
2.565(5)
2.589(5)
2.574(6)
3
N1–H1Nꢀ ꢀ ꢀ O1
0.64(4)
2.13(4)
128(5)
2.571(6)
4
N1–H1ꢀ ꢀ ꢀO1
0.86
0.79(3)
1.856
1.95(3)
2.552(6)
2.602(6)
137
141(4)
N2–H2ꢀ ꢀ ꢀO2
Symmetry code (i): ꢁ1=2 þ x; ꢁ1=2 ꢁ y; ꢁ1=2 þ z.

Z. Popoviꢀc et al. / Polyhedron 23 (2004) 1293–1302
1301
Table 5
Thermoanalytical data for bznapH and tolnapH and its Zn(II) complexes
Compound
Process
Temperature (ꢁC)
Accumulated weight loss (%)
Found
Calculated
BznapH
Melting (endo)
Degradation (endo)
Residue
98.50
150–400
400
88
12
100
TolnapH
Melting (endo)
Degradation (endo)
139.22
100–300
100
100
ZnCl2(bznapH)2 (1)
Degradation of ligand (endo)
Elimination of Cl (exo)
Residue
200–380
340–550
550
70.4
9.83
19.77
79.3
10.77
9.93
ZnBr2(bznapH)2 (2)
ZnI2(bznapH)2 (3)
ZnCl2(tolnapH)2 (4)
Degradation of ligand (endo)
Elimination of Br (exo)
Residue
200–375
330–600
600
61.6
20.37
18.03
69.86
21.64
8.05
Degradation of ligand (endo)
Elimination of Br (exo)
Residue
200–365
325–650
650
54.56
29.43
16.01
62.05
30.17
7.78
Melting (endo)
211.82
200–310
310–365
365–500
500
Degradation of ligand (endo)
Degradation of ligand (endo)
Elimination of Cl (exo)
Residue
31.54
31.35
9.21
39.65
39.65
10.77
9.93
27.9
ZnBr2(tolnapH)2 (5)
ZnI2(tolnapH)2 (6)
Degradation of ligand (endo)
Degradation of ligand (endo)
Elimination of Br (exo)
Residue
200–300
300–370
370–600
600
26.32
27.76
20.54
25.38
34.93
34.93
21.64
8.75
Degradation of ligand (endo)
Degradation of ligand (endo)
Elimination of I (exo)
Residue
200–305
305–385
385–640
640
23.21
24.27
28.96
23.56
31.03
31.03
30.17
7.78
The DTA curves of the complexes 1–3 were domi-
nated by the typical endothermic minima, which corre-
spond to the melting points (Table 5). Degradation of
bznapH (ca. 88%) was observed in the range of 200–400
ꢁC and was characterized by the endothermic peak in
the DTA-curve. On heating the samples 1–3 up to 600
ꢁC elimination of halogen occurred which was deter-
mined by an exothermic peak but still ca. 20% of the
initial mass of the samples was left as a mixture of
carbonated residue and zinc.
lengths and angles have been deposited and allocated
deposition numbers at the Cambridge Crystallographic
Data Centre (CCDC Nos. 198366–198369 for structures
1, 2, 3 and 4, respectively). Copies of this information
may be obtained free of charge from The Director,
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax:
+44-1223-336033; email: deposit@ccdc.caom.ac.uk or
www.ccdc.com.ac.uk). All structural factor tables are
available from the authors upon request.
Thermal analysis of the complexes 4–6 showed that
only the zinc chloride complex 4 melts, while 5 and 6
initially underwent degradation over two consecutive
endothermic processes. Elimination of halogen was
represented by the exothermic peak. As for 1–3, there
was also ca. 25% of the initial mass left in the sample pan.
Acknowledgements
This research was supported by the Ministry of Sci-
ence and Technology of the Republic of Croatia (Grant
Nos. 0119633, 0119632 and 01920202). The crystallo-
graphic data for structures 2 and 3 were collected on the
KappaCCD Nonius diffractometer in the Laboratory of
Inorganic Chemistry, Faculty of Chemistry and Chem-
ical Technology, University of Ljubljana, Slovenia. We
acknowledge with thanks the financial contribution of
the Ministry of Education, Science and Sport, Republic
of Slovenia through grants X-2000 and PO-511-103,
4. Supplementary material
Atomic coordinates and equivalent isotropic dis-
placement parameters, calculated hydrogen atom pa-
rameters, anisotropic thermal parameters and bond

1302
Z. Popoviꢀc et al. / Polyhedron 23 (2004) 1293–1302
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[15] Stoe & Cie, STADI4, Diffractometer Control Program for
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We thank the INA d.d. Zagreb, Division of Strategic
Development, Research and Investment for allowing us
to record the UV–Vis spectra on their instrument.
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