Spectroscopic properties of N-n-hexyltetrachlorophthalimide and supramolecular interactions in its crystals

Article abstract of DOI:10.1016/j.molstruc.2007.03.046

N-n-hexyltetrachlorophthalimide has been characterized by X-ray diffraction, FTIR, Raman and NMR spectroscopy. Also B3LYP and DFT calculations have been carried out. The optimized bond lengths, bond angles and torsion angles calculated by B3LYP/6-31G(d,p) approach have been compared with the X-ray data. The screening constants for ¹³C and ¹H atoms have been calculated by the GIAO/B3LYP/6-31G(d,p) approach and analyzed. Linear correlations between the experimental ¹H and ¹³C chemical shifts and the computed screening constants confirm the optimized geometry. The supramolecular structure is organized into hydrophilic and hydrophobic segments. The tetrachlorophthalimide moieties of the hydrophilic segments form infinite chains via halogen bonds C{double bond, long}O?Cl. These bonds as well as weak intermolecular hydrogen bonds C{single bond}H?O contribute to the parallel orientation of the chains and to the stabilization of their flat conformation. The intermolecular Cl?Cl interactions stabilize the organization of the hydrophilic segments.

Full text of DOI:10.1016/j.molstruc.2007.03.046

Available online at www.sciencedirect.com
Journal of Molecular Structure 874 (2008) 145–150
www.elsevier.com/locate/molstruc
Spectroscopic properties of N-n-hexyltetrachlorophthalimide
and supramolecular interactions in its crystals
a
a,
a
*
´
Bogumił Brycki , Iwona Kowalczyk , Andrzej Zielinski ,
b
b
Teresa Borowiak , Irena Wolska
a
Laboratory of Microbiocides Chemistry, Faculty of Chemistry, Adam Mickiewicz University, Grunwaldzka 6, 60-780 Poznan´, Poland
b
Department of Crystallography, Faculty of Chemistry, Adam Mickiewicz University, Grunwaldzka 6, 60-780 Poznan´, Poland
Received 6 February 2007; received in revised form 23 March 2007; accepted 26 March 2007
Available online 3 April 2007
Abstract
N-n-hexyltetrachlorophthalimide has been characterized by X-ray diffraction, FTIR, Raman and NMR spectroscopy. Also B3LYP
and DFT calculations have been carried out. The optimized bond lengths, bond angles and torsion angles calculated by B3LYP/6-
1
31G(d,p) approach have been compared with the X-ray data. The screening constants for 13C and H atoms have been calculated by
1
the GIAO/B3LYP/6-31G(d,p) approach and analyzed. Linear correlations between the experimental H and 13C chemical shifts and
the computed screening constants confirm the optimized geometry. The supramolecular structure is organized into hydrophilic and
hydrophobic segments. The tetrachlorophthalimide moieties of the hydrophilic segments form infinite chains via halogen bonds
C@Oꢀ ꢀ ꢀCl. These bonds as well as weak intermolecular hydrogen bonds CAHꢀ ꢀ ꢀO contribute to the parallel orientation of the chains
and to the stabilization of their flat conformation. The intermolecular Clꢀ ꢀ ꢀCl interactions stabilize the organization of the hydrophilic
segments.
Ó 2007 Elsevier B.V. All rights reserved.
Keywords: N-n-Hexyltetrachlorophthalimide; X-ray diffraction; Supramolecular structure; Intermolecular halogen bond; DFT calculations; FTIR;
Raman and NMR spectra
1. Introduction
in the biosynthesis of the N-linked oligosaccharides on the
envelope glycoprotein [1]. N-n-Hexyltetrachlorophthali-
mide is one of a series of N-n-alkyltetrachlorophthalimides
investigated in our laboratory in order to better understand
the mechanism of their biocidal activity against bacteria
and fungi. These compounds will be used as co-microbio-
cides with another group of antimicrobial agents to avoid
the increase of resistance of microorganisms on the biocides
applied. Structure and activity relationship studies on
N-n-alkyltetrachlorophthalimide derivatives indicated that
the hydrophobic groups at the N atom are of crucial
meaning [4,5].
In this paper the X-ray structure as well as results on
B3LYP calculations, FTIR, Raman and NMR spectros-
copy of N-n-hexyltetrachlorophthalimide [hereafter 1] are
presented. The another aspect of our interest in tetrachlor-
ophthalimides are their supramolecular structures where in
The phthaloyl and tetrachlorophthaloyl groups are
important pharmacophores [1]. Tetrachlorophthalimide
derivatives are good a-glucosidase inhibitors, decreasing
glucose level in blood by delaying digestion of poly- and oli-
gosaccharides to absorbable monosaccharides. Due to that
tetrachlorophthalimides can be potentially valuable for
treatment of diabetes, hyperlipoteinemia, and obesity
[2,3]. Some of tetrachlorophthalimide derivatives show
cytotoxicity and antimicrobial activity, especially anti-
human immunodeficiency virus (HIV) activity. This activity
is thought to arise because of the ability of tetrachlorophral-
imide derivatives to inhibit trimming glucosidases involved
*
Corresponding author. Tel.: +48 61 829 1306; fax: +48 61 865 8008.
E-mail address: iwkow@amu.edu.pl (I. Kowalczyk).
0022-2860/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2007.03.046

146
B. Brycki et al. / Journal of Molecular Structure 874 (2008) 145–150
the absence of strong hydrogen bond donors and/or accep-
tors a significant role in stabilizing the crystal packing play
the other weak intermolecular forces.
tions or in their intensities. The unit cell parameters were
determined by least-squares treatment of setting angles of
3855 highest-intensity reflections chosen from the whole
experiment. Intensity data were corrected for the Lorentz
and polarization effects [7]. The structure was solved by
direct methods with the SHELXS97 program [8] and
refined by the full-matrix least-squares method with the
SHELXL97 program [9]. Six reflections were excluded
2. Experimental
2.1. Synthesis
2
2
from the reflection file due to their large (jFoj ꢁjFcj )
P
A mixture of equimolar amounts of tetrachlorophthalic
anhydride and amine in toluene was heated under reflux for
20 h. After this time the solution was removed under
reduced pressure. The residue was crystallized from hexane
and dried under reduced pressure. Yield 84%, m.p. 145–
146 °C. Analysis: found (calc) %C 45.5 (45.5); %H 4.0
(3.6); %N 3.8 (3.8).
2
2 2
differences. The function w(jFoj ꢁjFcj ) was minimized
with wꢁ1 = [r2(Fo)2 + (0.0251P)2 + 3.2952P], where P ¼
ðF 2o þ 2F 2cÞ=3. All non-hydrogen atoms were refined with
anisotropic thermal parameters. The coordinates of the
hydrogen atoms were calculated in idealized positions
and refined as a riding model with their thermal parameters
calculated as 1.2 (1.5 for methyl group) times Ueq of the
respective carrier carbon atom.
2.2. Instrumentation
The NMR spectra in CDCl3 were measured for 1 with a
Varian Gemini 300VT spectrometer, operating at 300.07
and 75.46 Hz for 1H and 13C, respectively. Infrared spectra
were recorded in the KBr pellets using a FTIR Bruker IFS
113v spectrometer which was evacuated to avoid water
absorption. The Raman spectrum was recorded on a Bru-
ker IFS 66 spectrometer equipped with an FRA 106
Raman module operating at the 1064 nm exciting line of
an Nd:YAG laser.
The calculations were performed using the GAUSSIAN
03 program package [10] at the B3LYP [10,11] levels of the-
ory with the 6-31G(d,p) basis set [12]. The NMR isotropic
shielding constants were calculated using the standard
GIAO (Gauge-Independent Atomic Orbital) approach
[10–13] of GAUSSIAN 03 program package [14].
CCDC 635823 for 1 contains the supplementary crystal-
lographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif,
or by emailing data_request@ccdc.cam.ac.uk, or by con-
tacting The Cambridge Crystallographic Data Centre, 12,
Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223
336033.
Crystals suitable for X-ray analysis were grown by slow
evaporation from hexane solution. All details of the mea-
surements, crystal data and structure refinement are given
in Table 1. The data were collected on an Oxford Diffrac-
tion KM4CCD diffractometer [6] at 180 K (a phase transi-
tion at 156 K), using graphite-monochromated MoKa
radiation. A total of 1072 frames were measured in six sep-
arate runs. The x-scan was used with a step of 0.75°, two
reference frames were measured after every 50 frames, they
did not show any systematic changes either in peak posi-
Table 1
Crystal data, data collection and structure refinement for 1
Empirical formula
Formula weight
T (K)
C14H13Cl4NO2
369.05
180(2)
0.71073
˚
Wavelength (A)
ꢀ
Crystal system, space group
Unit cell dimensions
Triclinic, P1
˚
a (A)
5.0009(4)
6.1160(5)
27.036(2)
87.974(6)
88.199(6)
75.300(7)
799.1(1)
2,1.534
0.742
376
3.45–29.87
ꢁ6 6 h 6 6
ꢁ8 6 k 6 8
ꢁ36 6 l 6 37
˚
b (A)
˚
c (A)
a (°)
b (°)
c (°)
3. Results and discussion
3
3.1. The crystal structure of 1
˚
Volume (A )
Z, Dx(Mg/m3)
l (mmꢁ1
F(000)
)
A view of the molecular structure together with the
atom numbering scheme is shown in Fig. 1. The phthali-
mide moiety is approximately planar, the bond lengths
and angles are comparable to those reported in the litera-
ture [15–19].
The supramolecular structure of 1 is particularly inter-
esting when compared with that of the other derivative,
N-n-butyltetrachlorophthalimide [hereafter (2)], [19]. The
both molecules differ by two CH2 groups in the substituent
at N(1) and this steric factor causes substantial differences
in the modes of packing. The crystal structure of 1 consists
of hydrophobic and hydrophilic segments (Fig. 2) and in
each of them the consecutive inversion centers connect
h Range for data collection (°)
hklRange
Reflections
Collected
10,565
3988 (0.039)
3421
3988/0/190
1.053
0.0643
0.1386
0.737/ꢁ0.503
Unique (Rint
)
Observed (I > 2r((I))
Data/restraints/parameters
Goodness-of-fit on F2
R(F) (I > 2r(I))
wR(F2) (all data)
3
˚
Max/min. (e/A )

B. Brycki et al. / Journal of Molecular Structure 874 (2008) 145–150
147
Fig. 1. A view of the molecule of 1. Displacement ellipsoids are drawn at
the 30% probability level and H atoms are depicted as spheres of arbitrary
radii.
either the hydrophobic or the hydrophilic molecular
fragments. If the main driving forces for the supramolecu-
lar structure formation for (2) are the CAClꢀ ꢀ ꢀO,
CAClꢀ ꢀ ꢀClAC and Cd+ꢀ ꢀ ꢀCldꢁ intermolecular interactions,
in 1 the diversity of interactions in the hydrophilic segment
is higher and encompasses also the CAHꢀ ꢀ ꢀO weak hydro-
gen bonds. Thus, in 1 the hydrophilic segment is organized
into two blocks of infinite chains (Fig. 2) which expand in
the [110] direction (Figs. 2 and 3). The tetrachlorophthal-
imide moieties of each chain are coplanar (Fig. 4). Only
one carbonyl group of the phthalimide moiety participates
Fig. 3. One molecular chain which expands in the [110] direction.
˚
to 3.380(3) and 3.421(3) A, respectively. The hydrophilic
blocks are joined via Clꢀ ꢀ ꢀCl interactions (Table 2, Fig. 5)
[20].
3.2. B3LYP calculations
The optimized geometry parameters were computed by
using the B3LYP and compared with the X-ray diffraction
data in Table 4. The experimental and calculated bond
lengths and bond angles are comparable in the most cases.
Some discrepancies in the values of torsion angles
between the X-ray and theoretical data concern mainly
the n-hexyl substituent and are caused by the packing
forces.
in the chain formation via
a
halogen bond
C9@O9ꢀ ꢀ ꢀCl4AC4 (Table 2, Figs. 3 and 4). The second car-
bonyl group, C2@O2 is involved in a bifurcated weak
hydrogen bond CAHꢀ ꢀ ꢀO to the n-hexyl substituent which
belongs to a molecule from the other molecular chain
(Table 3 and Fig. 4). These bonds fulfill two functions: they
contribute to the parallel orientation of chains and stabilize
their flat conformation. The n-hexyl substituents of one
block are oriented in the same direction like antennas being
almost perpendicular to the phthalimide planes [the torsion
angle C(9)AN(1)AC(10)AC(11) is ꢁ92.5(4)° in 1, the same
angle in (2) is ꢁ73.3(2)°). Molecules of two parallel chains
are stacked with no overlap, the molecules of one chain are
positioned over gaps of the other one (Fig. 4) in a conse-
quence of electrostatic interactions C(5)d+ꢀ ꢀ ꢀCl(7)dꢁ and
C(8)d+ꢀ ꢀ ꢀCl(4)dꢁ, the both distances are shorter than the
sum of the respective van der Waals radii and are equal
3.3. FTIR and Raman spectra
Room-temperature solid-state FTIR and Raman spec-
tra of 1 are shown in Fig. 6. The observed and calculated
harmonic frequencies and their tentative assignments are
listed in Table 5. These assignments are partly based on
the calculated spectrum of N-tetrachlorophthalimide [21].
In the FTIR spectra of N-n-hexyltetrachlorophthalimide
the stretching vibrations mCH2 and mCH3 groups are
Fig. 2. The supramolecular structure of 1. Hydrophilic and hydrophobic segments have been shown.

148
B. Brycki et al. / Journal of Molecular Structure 874 (2008) 145–150
Fig. 4. Mutual orientation and stacking of molecules of two chains which belong to one block.
Table 4
Table 2
Weak intermolecular interactions in crystals of 1
Selected X-ray and B3LYP parameters for N-n-hexyltetrachlorophthali-
mide 1
˚
Cl(4)ꢀ ꢀ ꢀO(9)(i)
2.917(3) A
˚
C(4)ACl(4)ꢀ ꢀ ꢀO(9)(i)
Cl(5)ꢀ ꢀ ꢀCl(5)(ii)
Cl(5)ꢀ ꢀ ꢀCl(6)(ii)
Cl(6)ꢀ ꢀ ꢀCl(6)(iii)
Cl(6)ꢀ ꢀ ꢀCl(7)(iii)
156.3(3) A
Parameters
X-ray
B3LYP 6-31G(d,p)
˚
3.527(2) A
˚
Bond lengths (A)
N(1)AC(2)
N(1)AC(9)
N(1)AC(10)
C(2)AO(2)
C(9)AO(9)
C(4)ACl(4)
C(5)ACl(5)
C(6)ACl(6)
C(7)ACl(7)
˚
3.636(1) A
1.392(5)
1.398
1.398
1.461
1.212
1.212
1.732
1.733
1.733
1.732
˚
3.559(2) A
1.398(5)
1.462(5)
1.202(4)
1.195(4)
1.723(3)
1.718(3)
1.714(3)
1.721(3)
˚
3.589(1) A
Symmetry codes: (i) x ꢁ 1, y ꢁ 1, z; (ii) ꢁx, ꢁy, 1 ꢁ z; (iii) 1 ꢁ x, 1 ꢁ y,
1 ꢁ z.
Table 3
˚
Weak intermolecular hydrogen bonds CAHꢀ ꢀ ꢀO in crystals of 1 (A, °)
Bond angles (°)
D–H
Hꢀ ꢀ ꢀA
2.50
Dꢀ ꢀ ꢀA
3.397(5)
<D–Hꢀ ꢀ ꢀA
153
C(9)AN(1)AC(10)
N(1)AC(10)AC(11)
O(9)AC(9)AN(1)
C(3)AC(4)AC(5)
C(5)AC(6)AC(7)
C(6)AC(7)AC(8)
122.5(3)
127.4
109.5
124.5
117.9
117.9
120.6
112.0(3)
125.5(3)
118.3(3)
118.1(3)
120.2(3)
C(11)AH(11B)ꢀ ꢀ ꢀO(2)(i)
C(13)AH(13B)ꢀ ꢀ ꢀO(2)(i)
0.97
0.97
2.71
3.554(7)
146
Symmetry codes: (i) x, 1 + y, z.
Torsion angles (°)
C(2)AN(1)AC(10)AC(11)
C(9)AN(1)AC(10)AC(11)
C(8)AC(9)AN(1)AC(10)
N(1)AC(10)AC(11)AC(12)
O(2)AC(2)AN(1)AC(9)
84.6(5)
ꢁ92.5(4)
177.5(3)
165.7(4)
176.8(4)
ꢁ88.96
ꢁ88.96
ꢁ177.7
180.0
ꢁ167.1
The CAC skeletal vibrations of benzene ring and the
CAN stretching vibrations of 1 are observed at 1650–
1350 cmꢁ1 and at 1187–1178 cmꢁ1, respectively.
The symmetric stretching vibration msC@O appears in
the FTIR spectrum as a broad and intensive band at
1711 cmꢁ1 whereas the asymmetric stretching vibrations
of carbonyl group masC@O in a phthalimide moiety is very
small and lies at 1774 cmꢁ1[5]. In the Raman spectrum the
intensity of these bands are converted [22]. Similarly to
FTIR spectra of N-n-butyltetrachlorophthalimide (2) no
split of the carbonyl bands was observed [19]. Even though
both carbonyl groups in 1 are involved in different interac-
tions in the supramolecular structure. These interactions
have to be very weak and are not detectable by infrared
technique.
Fig. 5. Clꢀ ꢀ ꢀCl interactions between two hydrophilic blocks.
observed in the region 2962–2853 cmꢁ1 and the deforma-
tion vibrations dCH2 and dCH3 in the region 1465–
1385 cmꢁ1. The intense deformation band, c(CAH), of
methylene and methyl groups, lie in the range of 721–
1
3.4. H NMR and 13C NMR spectra
The proton chemical shift assignments (Table 6)
are based on 2D COSY experiments, in which the
727 cmꢁ1
.

B. Brycki et al. / Journal of Molecular Structure 874 (2008) 145–150
149
Table 5
100
80
60
40
20
0
Observed and calculated B3LYP/6-31G(d,p) vibrational frequencies,
infrared intensities for 1
a
b
c
Raman
IR
IR(calc.)
INT
Proposed assignment
2958 m
2939 m
2906 m
2892 m
2872 m
2855 m
2728 vw
1775 vs
1711 w
1573 m
2952 m
2925 m
2952
2933
60.0
33.4
mCH2
mCH2
mCH2
mCH2
mCH2
mCH2
mCH2
masCO
msCO
mCC
mCC
mCC
basCH3
bCC
mCC
mCN
bsCH3
mCC, bCH2
bCH2
bCH2
mCC
mCC
mCC
mCN
mCN
mCN
cCH2
cCH2
cCH2
bCH2
bCCC
bCCC
bCO
cCH2
cCH2
2870 m
2852 m
2729 vw
1774 m
1711 vs
1582 w
1513 vw
1464 m
1450 m
1436 s
1406 s
1389 w
1372 s
1360 s
1334 m
1311
1299 m
1224 w
1214 w
1199 m
1181 w
1172 w
1165 w
1076 m
1051 w
1037 w
1019 w
994 w
2889
2876
2866
1759
1715
1522
1520
1451
1442
1438
1409
1359
1356
1346
1334
1310
1308
1265
1264
1201
1158
1150
1112
1084
1041
1016
1008
996
958
907
858
844
770
734
711
705
700
699
670
599
568
515
488
417
34.1
58.5
5.7
66.4
463
5.4
0.1
4.1
0.9
5.7
38.2
102
14.0
9.8
289
141
11.2
48.9
9.3
0.6
0.4
0.2
0.0
80
60
40
20
0
1439 w
1409 w
1388 w
1373 w
1338 w
1301 w
3000 2500 2000
1500
1000
500
1201 m
1171 w
6.8
5.2
Wavenumbers/cm-1
155
13.4
8.2
52.0
0.3
5.2
5.2
7.2
0.7
0.1
6.9
12.3
2.3
19.0
0.1
19.3
93.0
6.7
12.5
2.1
0.1
18.2
3.4
Fig. 6. Spectra of N-n-hexyltetrachlorophthalimide 1: (a) FTIR (KBr
pellet) (b) Raman and (c) Calculated spectrum.
1122 w
1078 vw
1066 vw
1023 vw
1001 vw
947 vw
886 vw
854 vw
819 vw
proton–proton connectivity is observed through the off-
diagonal peaks in the counter plot. The relations between
the experimental 1H and 13C chemical shifts (dexp) and
the GIAO (Gauge-Independent Atomic Orbitals) isotro-
pic magnetic shielding tensors (rcalc) are shown in
Fig. 7. Both correlations are linear, described by the rela-
tionship: dexp = a + b Æ rcalc. The a and b parameters are
given in Table 6. Usually, the correlation between the
experimental chemical shifts and calculated isotropic
screening constants are better for carbon-13 atoms than
for protons [14].
943 vw
882 w
867 vw
815 w
803 w
768 w
752 m
735 s
702 w
686 w
627 w
bCCC
bCCC
sring
bCCC
mCCl
bCCC
mCCl
bring
765 vw
752 vw
735 vw
702 vw
687 vw
628 m
588 vw
513 w
491 vw
472 vw
411 vw
383 vw
352 m
332 w
The very good correlation coefficients (r2 = 0.9933) for
1H and (r2 = 0.9954) for 13C correlations confirm the
optimized geometry of 1.
587 w
511 w
490 w
471 w
bNCC
bCCC
sring
sring
409 w
cCCC
Lattice mode
mCCl
Lattice mode
Lattice mode
Lattice mode
Lattice mode
Lattice mode
Lattice mode
386
361
332
306
257
222
188
88.4
25.8
0.2
0.1
2.3
0.2
1.8
0.3
0.9
4. Conclusions
The molecular and crystal structures of N-n-hexyltetra-
chlorophthalimide 1 have been determined by X-ray dif-
301 vw
243 w
229 w
197 vw
93 s
fraction, FTIR, H, 13C NMR spectroscopies and by the
1
B3LYP calculations.
The n-hexyl substituent of the title compound causes
substantial differences in the supramolecular structure in
comparison with that of N-n-butyltetrachlorophthalimide.
FTIR spectra are consistent with the observed structure
in the crystal. The good correlations between the experi-
The abbreviations are: s: strong, m: medium, w: weak, vw; very weak, m:
stretching, b: in plane bending, d: deformation, c: out of plane bending
and s: twisting.
mental 13C and H chemical shifts in CDCl3 solution of 1
and GIAO/B3LYP/6-31G(d,p) calculated isotropic shield-
1
ing tensors (dexp = a + b Æ rcalc) have confirmed the opti-
mized geometry of 1.

150
B. Brycki et al. / Journal of Molecular Structure 874 (2008) 145–150
Table 6
Chemical shifts (d, ppm) in CD3Cl and calculating GIAO nuclear magnetic shielding tensors (rcal) for N-n-hexyltetrachlorophthalimide
dexp.
dcalc
rcalc
34.2
67.1
57.6
dexp.
dcalc
3.74
1.53
1.29
1.29
1.41
0.94
rcalc
C (2,9)
C (3,8)
C (4,7)
C (5,6)
C (10)
C (11)
C (12)
C (13)
C (14)
C (15)
a
163.6
129.5
127.6
140.0
38.9
31.2
28.2
26.4
22.4
158.4
124.4
134.2
143.8
38.1
28.7
27.3
31.4
23.2
H (10)
H (11)
H (12)
H (13)
H (14)
H (15)
3.74
1.66
1.28
1.28
1.28
0.95
28.3
30.2
30.4
30.4
30.3
30.7
48.3
150.5
159.6
161.0
157.0
165.0
175.7
14.0
12.1
193.7361
36.7990
b
ꢁ1.0338
ꢁ1.1680
The predicted GIAO chemical shifts were computed from the linear equation dexp. = a + b Æ rcalc with a and b determined from the fit the experimental data.
a
b
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
150
120
90
60
30
0
0
30 60 90 120 150 180
28
29
30
31
σcalc
σcalc
Fig. 7. The relationship (a) between the experimental 13C chemical shifts (d) and the GIAO computed 13C screening constants (r) and (b) between the
1
experimental 1H chemical shifts (d) and the GIAO computed H screening constants (r).
Li, J.E. Knox, H.P. Hratchian, J.B. Cross, C. Adamo, J. Jaramillo, R.
Gomperts, R.E. Stratmann, O. Yazyev, A.J. Austin, R. Cammi, C.
Acknowledgement
Pomelli, J.W. Ochterski, P.Y. Ayala, K. Morokuma, G.A. Voth, P.
This work was supported by the funds from Adam
Salvador, J.J. Dannenberg, V.G. Zakrzewski, S. Dapprich, A.D.
Daniels, M.C. Strain, O. Farkas, D.K. Malick, A.D. Rabuck, K.
Mickiewicz University, Faculty of Chemistry.
Raghavachari, J.B. Foresman, J.V. Ortiz, Q. Cui, A.G. Baboul, S.
Clifford, J. Cioslowski, B.B. Stefanov, G. Liu, A. Liashenko, P.
Piskorz, I. Komaromi, R.L. Martin, D.J. Fox, T. Keith, M.A. Al-
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