Ring-ring or nitro-ring π,π-interactions in N-(p-nitrobenzyl)iminodiacetic acid (H2NBIDA) and mixed-ligand copper(II) complexes of NBIDA and imidazole (Him), 2,2′-bipyridine (bipy) or 1,10-phenanthroline (phen). Crystal structures of H2NBIDA, [Cu(NBIDA)(Him)(H2O)], [Cu(NBIDA)(bipy)] · 3H2O and [Cu(NBIDA)(phen)]-2H2O

Article abstract of DOI:10.1016/S0277-5387(03)00089-5

N-(p-nitrobenzyl)iminodiacetic acid (H₂NBIDA) and the mixed-ligand copper(II) complexes with NBIDA and imidazole (Him), 2,2′-bipyridine (bipy) or 1,10-phenanthroline (phen) were prepared and characterised by thermal, spectral, magnetic and X-ray diffraction methods. Our aim is to study various possibilities of the N-(p-nitrobenzyl) arm in the iminodiacetate(2-) ion (IDA) skeleton to be involved in π,π-interactions which contribute to molecular recognition processes and crystal building. Analysis of the shortest aromatic ring-ring interactions were carried out with PLATON program and let us conclude that in free H₂NBIDA acid (1) and [Cu(NBIDA)(Him)(H₂O)] (2) only inter-molecular benzyl-benzyl π,π-stacks occur, whereas in [Cu(NBIDA)(bipy)] · 3H₂O (3) and [Cu(NBIDA)(phen)] · 2H₂O (4) there are both inter-molecular nitro-benzyl π,π-interactions (instead of benzyl-benzyl π,π-stacks) and α,α′-diimine-α,α′-diimine ring-ring π,π-interactions. In compound 2 NBIDA ligand has a typical mer-NO₂ tridentate conformation, whereas in 3 or 4 it exhibits an unusual fac - O₂ + N(apical) conformation. The molecular recognition pathway in 3 and 4 is discussed on a structural basis, considering a variety of interligand interactions involved in molecular recognition processes to build these and closely related crystals. We conclude that both the presence of a non-coordinating N-substituent in the IDA-like ligand and the chelation of Cu(II) by an aromatic α,α′-diimine (bipy or phen) display active roles for promote a fac-O₂ + N(apical) conformation and various modes of interligand π,π-stacking interactions.

Full text of DOI:10.1016/S0277-5387(03)00089-5

Polyhedron 22 (2003) 1039ꢀ1049
/
www.elsevier.com/locate/poly
Ringꢀring or nitro-ring p,p-interactions in N-(p-
/
nitrobenzyl)iminodiacetic acid (H2NBIDA) and mixed-ligand
copper(II) complexes of NBIDA and imidazole (Him), 2,2?-bipyridine
(bipy) or 1,10-phenanthroline (phen). Crystal structures of
H2NBIDA, [Cu(NBIDA)(Him)(H2O)], [Cu(NBIDA)(bipy)]×
/
3H2O
and [Cu(NBIDA)(phen)]×2H2O
/
M.J. Sa´nchez-Moreno a, Duane Choquesillo-Lazarte a, Josefa M. Gonza´lez-Pe´rez a,
Rosa Carballo b, Jose´ D. Mart´ın-Ramos c, Alfonso Castineiras d,
˜
Juan Niclo´s-Gutie´rrez a,*
a Department of Inorganic Chemistry, Faculty of Pharmacy, University of Granada, Campus de Cartuja, s/n, E-18071 Granada, Spain
b Department of Inorganic Chemistry, Faculty of Sciences, University of Vigo, E-36200 Vigo, Spain
c Department of Mineralogy and Petrology, Faculty of Sciences, University of Granada, E-18071 Granada, Spain
d Department of Inorganic Chemistry, Faculty of Pharmacy, University of Santiago de Compostela, E-15706 Santiago de Compostela, Spain
Received 4 October 2002; accepted 20 January 2003
Abstract
N-(p-nitrobenzyl)iminodiacetic acid (H2NBIDA) and the mixed-ligand copper(II) complexes with NBIDA and imidazole (Him),
2,2?-bipyridine (bipy) or 1,10-phenanthroline (phen) were prepared and characterised by thermal, spectral, magnetic and X-ray
diffraction methods. Our aim is to study various possibilities of the N-(p-nitrobenzyl) arm in the iminodiacetate(2ꢁ
skeleton to be involved in p,p-interactions which contribute to molecular recognition processes and crystal building. Analysis of the
shortest aromatic ringꢀring interactions were carried out with PLATON program and let us conclude that in free H2NBIDA acid (1)
and [Cu(NBIDA)(Him)(H2O)] (2) only inter-molecular benzylꢀbenzyl p,p-stacks occur, whereas in [Cu(NBIDA)(bipy)]×3H2O (3)
and [Cu(NBIDA)(phen)]×2H2O (4) there are both inter-molecular nitro-benzyl p,p-interactions (instead of benzylꢀbenzyl p,p-
stacks) and a,a?-diimine-a,a?-diimine ringꢀring p,p-interactions. In compound 2 NBIDA ligand has a typical mer-NO2 tridentate
conformation, whereas in 3 or 4 it exhibits an unusual fac-O2ꢂN(apical) conformation. The molecular recognition pathway in 3
/) ion (IDA)
/
/
/
/
/
/
/
and 4 is discussed on a structural basis, considering a variety of interligand interactions involved in molecular recognition processes
to build these and closely related crystals. We conclude that both the presence of a non-coordinating N-substituent in the IDA-like
ligand and the chelation of Cu(II) by an aromatic a,a?-diimine (bipy or phen) display active roles for promote a fac-O2ꢂ
/
N(apical)
conformation and various modes of interligand p,p-stacking interactions.
# 2003 Elsevier Science Ltd. All rights reserved.
Keywords: Copper(II); Mixed-ligand complexes; Crystal structures; p,p-Stacking; Nitro; Benzyl
1. Introduction
Structural comparisons on the catena-poly-[diaqua(i-
minodiacetato)copper(II)], [Cu(IDA)(H2O)2]n [1] and a
variety of mixed-ligand copper(II) complexes having
IDA or IDA derivatives and imidazoles or aromatic
a,a?-diimines (bipyridine, phenanthrolines) or related
ligands (histamine and others) serve as bioinorganic
* Corresponding author. Tel.: ꢂ
219.
E-mail address: jniclos@ugr.es (J. Niclo´s-Gutie´rrez).
/
34-958-243-855; fax: ꢂ34-958-246-
/
0277-5387/03/$ - see front matter # 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0277-5387(03)00089-5

1040
M.J. Sa´nchez-Moreno et al. / Polyhedron 22 (2003) 1039ꢀ1049
/
Scheme 1.
model compounds to illustrate conformational changes
at the protein conformation for metal-protein centres in
Scheme 3.
absence or presence of appropriate substrates [1ꢀ9]. To
/
gous of B is [Cu(NBzIDA)(TMphen)]×
pound C, TMphenꢃ3,4,7,8-tetramethylphe-
nanthroline) [8]. In compounds B and C the NBzIDA
acts as tridentate with an unusual fac-O2ꢂN(apical)
conformation (Scheme 3) which has been explained as a
consequence of the co-operation of intra- and inter-
/
5H2O (com-
this purposes, IDA or IDA-analogues simulate the
‘protein moiety’ and imidazole (Him) and different N-
containing heterocycles play ‘substrate-like’ roles. These
experimental modelling possibilities arise from the
/
/
changes of the fac-NOꢂO IDA conformation in the
/
diaqua-copper(II) complex to a mer-NO2 IDA or IDA-
like (Scheme 1) in ternary complexes with equimolar
ratio Cu(II)/(IDA or IDA-like)/N-heterocyclic donor, to
molecular interligand benzylꢀ
stacks.
/
phen or phen-like p,p-
As a part of our program on this kind of copper(II)
complexes [9] we report structural results concerning the
possibilities of developing p,p-interactions in N-(p-
nitrobenzyl)iminodiacetic acid (H2NBIDA; see Scheme
4) and three new copper(II) derivatives with NBIDA
and imidazole (Him) or 2,2?-bipyridine (bipy) or 1,10-
phenanthroline (phen). The aim of this work is to study
the influence on the p,p-stacking interactions of a p-
nitro group in the N-benzyl-IDA skeleton.
go back for a fac-NOꢂ
2) in compound with 1/1/2 Cu(II)/IDA or IDA-like/N-
heterocyclic donor ratio [1,3ꢀ9]. Expanding these fron-
tiers and on the knowledge of aromatic ringꢀring p,p-
/
O IDA conformation (Scheme
/
/
interaction possibilities in various mixed-ligand cop-
per(II) complexes with aromatic a-amino acids and N-
heterocyclic secondary ligands [2] we considered of
broad interest to introduce aromaticity and ligand
conformational flexibility in the IDA skeleton to
promote interligand p,p-stacking interactions in ternary
Cu(II) complexes [3]. In this context we have proved
that N-alkyl-, N-benzyl- or N-phenethyl-IDA cop-
per(II) complexes display drastically different recogni-
tion modes with the non-substituted adenine, to such a
point that these N-substituents of the IDA chelating
ligand control selectively the metal chelate-nucleobase
recognition process [4,5].
2. Experimental
2.1. Synthesis of the acid H2NBIDA and its copper(II)
complexes
The acid H2NBIDA (1) was prepared by reaction of
4-nitrobenzylamine hydrochloride (25 g, 132.5 mmol,
Aldrich) and potassium chloroacetate in alkaline aqu-
eous solution (KOH necessary for condensation plus 0.1
mol in excess, pH 11) at 90 8C approximately during 2 h.
After cooling the reaction mixture was filtered and
acidified with HCl 6 N to pH 2.5, which produces the
Several systems Cu(II)/NBzIDA/N-heterocyclic do-
nor have been studied in our laboratories (NBzIDAꢃ
/
N-benzyliminodiacetate(2ꢁ) ion) [6ꢀ8]. An unique
/
/
behaviour was found using 1,10-phenanthroline (phen)
as secondary ligand, which affords [Cu4(phen)4-
(OH)4(H2O)2][Cu(NBzIDA)2]2×
/
20H2O (A) and [Cu(NB-
zIDA) (phen)]×2H2O (B) [7]. Compound A is a salt with
/
many p,p-stacking interactions whereas B is a typical
mixed-ligand complex with molecules arranged in multi-
p,p-stacked chains which involves alternating intra- and
inter-ligand benzylꢀ
/
phen p,p-interactions. An analo-
Scheme 2.
Scheme 4.

M.J. Sa´nchez-Moreno et al. / Polyhedron 22 (2003) 1039ꢀ
/1049
1041
precipitation of a crude product. This was dissolved in
water by a measured amount of NaHCO3 and the acid
H2NBIDA was re-precipitated by addition of the
equivalent amount of HCl 6 N. Single crystals of this
amino acid were grown from water:ethanol or water:-
acetone 30:70. Yield: 18.78 g, 56.7%. Anal. Calc. for
C11H12N2O6: C, 49.26; H, 4.51; N, 10.44. Found: C,
48.79; H, 4.88; N, 10.55. FT-IR relevant frequencies
semi-empirical method [12]. The structures were solved
by direct methods (compounds 1, 3 and 4) or by the
Patterson method (compound 2) using the program
SHELXS-97 [13] and refined by full-matrix least-square
techniques (FMLS below in Table 1) on F2 using
SHELXL-97 [14]. Positional and anisotropic atomic
displacement parameters were refined for all non-
hydrogen atoms. For compounds 1, 3 and 4, hydrogen
atoms were placed geometrically and positional para-
meters were refined using a riding model. For com-
pound 2 all hydrogen atoms were located from
difference Fourier maps and included as fixed contribu-
tions riding on attached C atoms with isotropic thermal
parameters 1.3 times those of the respective C atoms.
Atomic scattering factors were obtained from ‘Interna-
tional Tables for X-ray Crystallography’ [15]. Molecular
graphics and geometrical calculations have been ob-
tained from SHELXTL [16] or PLATON [17]. A summary
of the crystal data, experimental details and refinement
results for studied compounds are listed in Table 1.
(cmꢁ1): 3448 of n(OÃ
1611 and 1382 of nas and ns(COO) in Ã
(HOOCÃ) or ÃCOO. . . N); 3082, 3067, 3027,
(Hꢂ Ã
2977 for n(CÃ H), 1519 and
H) modes, 2529 of n(Nꢂ Ã
1346 as typical bands of nas and ns of ÃNO2 group [10].
1H NMR (300 MHz, D2Oꢂ
KOD, d ppm): broad
singlets at 3.02 of NCH2CO2, 3.66 of arÃCH2ÃN, 7.34
of H-2,6ar and 7.92 of H-3,5ar. 13C NMR (75 MHz,
D2Oꢂd6-acetone): 51.93 arÃCH2ÃN, 57.44 of NÃCH2Ã
carboxyl, 1232.81 of C-2,6ar, 128.59 of C-3,5ar, 146,81
C-1ar, 147.68 of C-4ar and 178.86 of ÃCOO. TG-analysis
in two steps (190ꢀ370 and 370ꢀ625 8C) with production
/
H), 1711 and 1673 of n(CÄ
/
O),
/
COOꢁ
/
. . .
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
of CO2, H2O, CO, N(CH3)3 (only in first step), NH3,
and N2O (first step) or NO2 (only in second step).
Copper(II) complexes were obtained by reaction of
Cu2CO3(OH)2 (0.5 mmol, Aldrich) and H2NBIDA (1
mmol) in 100 ml of water, under controlled vacuum,
stirring and heating with addition of a N-heterocyclic
ligand (Him, 2,2?-bipy or 1,10-phen). The resulting
solution was filtered without vacuum on a crystallisation
device and evaporated at room temperature. When
precipitation initiated, the solution was filtered once
more on an appropriate crystallisation device to obtain
by evaporation many well shaped crystals for diffrac-
trometric purposes. Successive samples of these com-
2.3. Physical measurements
All physical measurements were carried out as de-
scribed in a previous paper [4] except for susceptibility
measurement, which were only made at room tempera-
ture for compounds 2 and 3.
3. Results and discussion
In addition to the data reported in Table 1, bond
distances and angles for H2NBIDA could be obtained
from deposited files or from the authors. This amino
diacid exists as zwitterions (Fig. 1(a)) stabilised by one
pounds were collected to a final yield ꢀ70%. For
/
[Cu(NBIDA)(Him)(H2O)] (C14H16CuN2O7, compound
2, yield: 314.4 mg, 75.6%): Calc.: C 40.44, H 3.88, N
intra-molecular hydrogen bond (N9Ã
/
H9A
2.66(1) A, 114(1)8) between the ammonium proton and
the H-free O(11) atom of the unionised
C(11)O(11)O(12)H group. These zwitterions form zigꢀ
zag chains along the b axis of the crystal by a rather
linear inter-molecular H-bond (O(12)ÃH(12). . .
O(13i),
zꢂ1/2) linking
/
. . .
/
O11,
˚
13.47. Found: 40.25,
[Cu(NBIDA)(bipy)]×3H2O, (C21H24CuN4O9, compound
3, yield: 390.9 mg, 72.4%): Calc.: C 46.71, H 4.48, N
10.38. Found: 47.12, 4.84, 10.57. For
[Cu(NBIDA)(phen)]×2H2O (C23H22CuN4O8, compound
H
3.82,
N
13.47. For
/
Ã
/
/
C
H
N
/
/
/
/
˚
4, yield: 432.4 mg, 79.2%), Calc.: C 50.60, H 4.06, N
2.50 A, 1728, iꢃ
/
ꢁ
/
xꢂ
/
1, yꢁ
/
1/2, ꢁ
/
/
10.26. Found: C 50.67, H 4.24, N 10.36.
carboxyl-adjacent carboxylate groups. These chains
build up a 2D framework (Fig. 1(b)) by inter-molecular
p,p-stacking interactions (see below, and Table 3). Such
layers fall parallel to the bc plane of the crystal
connected by van der Waals forces. Stacking parameters
2.2. Crystal structure determination
A prismatic crystal of each studied compound was
mounted on a glass fibre and used for data collection.
Crystal data were collected at 233 (compound 2) or 293
K (compounds 1, 3 and 4) using a Bruker SMART CCD
1000 or an Enraf Nonius CAD4 automatic diffract-
hereafter taken into account are dcꢀc (centroidꢀcentroid
/
distance), a (angle between planes containing aromatic
rings), slipping angles b and g (defined by the vector
c1ꢀc2 and the normal to plane P(1) or P(2) from C1 and
/
ometer. Graphite monochromated Mo Ka (lꢃ
/
0.71073
˚
1.54184 A,
C2, respectively).
Compound 2 (Fig. 2(a)) forms molecules which
˚
A, compounds 1, 3 and 4) or CuKa (lꢃ
/
compound 2) radiation was used. The data were
corrected for Lorentz and polarization effects. Absorp-
tion corrections were made with SADABS [11] or using a
exhibits a typical 4ꢂ
data in Table 2), a mer-NO2 tridentate conformation of
NBIDA, with Him in the trans-site to the CuÃ
/1 copper(II) coordination (see t
/

1042
M.J. Sa´nchez-Moreno et al. / Polyhedron 22 (2003) 1039ꢀ1049
/
Table 1
Crystal data and structure refinement for H2NBIDA acid (compounds 1) and copper(II) compounds 2ꢀ4
/
Compound
1
2
3
4
Empirical formula
Formula weight
Temperature (K)
C11H12N2O6
268.23
293(2)
C14H16CuN4O7
415.85
233(2)
C21H24CuN4O9
539.98
293(2)
C23H22CuN4O8
545.99
293(2)
˚
Wavelength (A)
0.71073
Monoclinic
P21/n
1.54184
Orthorhombic
Pbca
0.71073
Triclinic
P-1
0.71073
Triclinic
P-1
Crystal system
Space group
Unit cell dimensions
˚
a(A)
7.225(6)
14.788(1)
10.809(9)
90
12.110(1)
23.160(1)
12.017(1)
90
7.063(7)
12.364(1)
14.087(1)
105.745(2)
100.003(2)
101.550(2)
1125.64(2)
2
7.199(1)
12.054(2)
14.064(2)
102.180(3)
102.938(3)
101.331(3)
1124.00(3)
2
˚
b(A)
˚
c(A)
a(8)
b(8)
g(8)
94.968(2)
90
90
90
3
˚
V (A )
1150.50(2)
4
1.549
3370.4(4)
8
Z
Calculated density (Mg mꢁ3
Absorption Coefficient (mmꢁ1
F(0 0 0)
)
1.639
2.269
1704
1.593
1.032
558
1.613
1.031
562
)
0.128
560
Crystal size (mm)
u Range data collected (8)
Index ranges
0.17ꢄ
2.34ꢀ28.03
90h 06,
190k 019,
140l013
6867/2674 R(int)ꢃ
/
0.43ꢄ
/
0.97
0.15ꢄ
5.30ꢀ64.97
00h 014,
270k 0
140l0
0.073 3152/2855 R(int)ꢃ
/
0.15ꢄ
/
0.10
0.08ꢄ
1.55ꢀ28.05
80h 09,
160k 014,
180l015
0.0426 6714/4662 R(int)ꢃ
/
0.10ꢄ
/
0.18
0.24ꢄ
1.54ꢀ28.08
90h 08,
150k 015,
1401018
0.048 6734/4689 R(int)ꢃ
/
0.10ꢄ
/
0.10
/
/
/
/
ꢁ
/
/
/
/
/
ꢁ
/
/
/
ꢁ
/
/
/
ꢁ
/
/
/
ꢁ
ꢁ/
/
/
/
0,
ꢁ
/
/
/
ꢁ
/
/
/
ꢁ/
/
/
/
/1
ꢁ/
/
/
ꢁ/
/
/
Reflections collected/unique
Absorption correction
Max/min transmission
Refinement method
/
/
/
/
0.054
SADABS
Semi-empirical
0.805/0.727
FMLS a on F2
2855/0/236
1.006
SADABS
SADABS
1.000/0.505
FMLS a on F2
2674/0/177
1.067
1.000/0.762
FMLS a on F2
4662/0/340
0.752
1.000/0.8339
FMLS a on F2
4689/0/325
0.813
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I ꢀ
R indices (all data)
˚
Large difference peak/hole (e A
/
2s(I)]
R1ꢃ
R1ꢃ
0.267/ꢁ
/
0.049, wR2ꢃ
0.064, wR2ꢃ
0.189
/
0.132 R1ꢃ
0.140 R1ꢃ
0.331/ꢁ
/
0.051, wR2ꢃ
0.102, wR2ꢃ
0.641
/
0.119
0.141
R1ꢃ
R1ꢃ
0.346/ꢁ
/
0.048, wR2ꢃ
0.112, wR2ꢃ
0.302
/
0.087 R1ꢃ
0.101 R1ꢃ
0.378/ꢁ
/
0.059, wR2ꢃ
0.160, wR2ꢃ
0.297
/
0.105
0.126
/
/
/
/
/
/
/
/
ꢁ3
)
/
/
/
/
a
FMLSꢃFull-matrix least-squares.
/
N(NBIDA) bond and an apical/distal aqua ligand.
These structural features are mostly common in
mixed-ligand complexes with equimolar ratio Cu(II)/
tions in metal complexes with N-aromatic heterocycles
has been recently reported by Janiak [18].
IDA or derivative/N-heterocyclic donor [1,3ꢀ9]. Com-
/
pound 2 has a very low distortion toward the trigonal
bipyramid, but a remarkable tetragonality (see Table 2).
˚
The metal atom is at 0.112(2) A from the mean basal
plane P1, and both N and O pairs of donors deviate
Table 2
Coordination bond distances (A) in compounds 2ꢀ
for the distortion of 4ꢂ1 polyhedron
˚
/
4 and parameters
/
˚
0.10(1) A in opposite sense (O donor toward aqua
Compound
2
3
4
ligand). The Him plane defines a dihedral angle of
17.4(2)8 with P1 and the Cu(II) atom is 0.21(1) from the
CuÃ
CuÃ
CuÃ
CuÃ
CuÃ
CuÃ
CuÃ
/
N(NBIDA)
O(NBIDA)
O(NBIDA)
O(aqua)
1.984(3) 2.343(3)
1.962(3) 1.949(3)
1.982(3) 1.986(3)
2.349(3)
2.252(4)
1.945(4)
1.958(4)
/
Him plane, in accordance with the s nature of the CuÃ
/
/
N(Him) bond. The analysis of the shortest ringꢀring
/
/
/N(Him)
1.936(4)
interactions in compound 2 reveals again that side-on
p,p-interactions participate in the molecular recognition
/N(bipy or phen)
2.012(3)
2.016(3)
2.003(4)
2.021(4)
0.88
/N(bipy or phen)
process. That occurs in such a way that two NBIDA
˚
T (tetragonality)
0.l84
1.60
0.85
7.33
benzyl aromatic rings lie parallel (aꢃ0.008) at 3.39 A
/
t (%)
9.98
75.6
and are involved in a ‘complex pair formation’ (Fig.
2(b)). Pairs of stacked molecules build the crystal by
f Chelate rings (8)
NBIDA Conforma-
tion
14.34
mer-
NO2
99.65/80.35
fac-O2ꢂ
cal)
/
N(api- fac-O2ꢂ
/
N(api-
cal)
hydrogen bonds, which link OÃ
/
H bonds of aqua
ligands, imidazole NÃ
/
H groups with O-carboxylate
acceptors from six adjacent complex molecules. A
tꢃ
/
100(uꢁ
/
f)/60, where u ꢀf are the trans-donor-Cu-donor
/
angles for the four closest donor atoms. t is 0 or 100 for ideal SBP
or BPT coordination, respectively [19].
comprehensive and critical account of these p,p-interac-

M.J. Sa´nchez-Moreno et al. / Polyhedron 22 (2003) 1039ꢀ
/1049
1043
Fig. 1. (a) Two zwitterions of H2NBIDA acid showing the intra- and inter-molecular H-bonds. (b) Inter-molecular benzylꢀ
(dashed lines) connecting H-bonded chains of H2NBIDA acid into 2D layers extending parallel to the bc plane of the crystal (stacked rings are
/
benzyl p,p-interaction
related by the symmetry code iꢃ x, 1ꢁy, ꢁz).
/
ꢁ
/
/
/
Compounds 3 and 4 also exhibit a square base
pyramidal coordination (see Fig. 3 and t data in Table
2). The four closest donors of the metal atoms are both
N atom of aromatic a,a?-diamine (bipy or phen) and
two O carboxylate atoms from NBIDA acetate arms,
whereas the N amino donor of this chelate ligand lies at
the apical/distal coordination site. That represents an
interligand nitro-benzyl p,p-interactions (Fig. 4(b)) are
used to give infinitive chains of pairs of complex
molecules (Fig. 4(c)). The molecular recognition pattern
in compound 4 is very different. Data of Table 4 and
Fig. 5(a) show that phen ligands lie parallel (aꢃ
/0.00)
and are involved in both complex pairs (stacked at 3.41
˚
A) and in the formation of an infinite chain (stacked at
˚
unusual fac-O2ꢂ
/
N(apical) conformation for NBIDA in
3.46 A) by means of inter-molecular p,p-stacking
interactions between C6-phen ring (Table 4). Moreover
these inter-molecular stacks are still unequally slipped
compounds 3 and 4 (Table 2). As far as concerns to
molecular recognition processes and building of crystals,
data of Table 3 reveal that p-nitro-benzyl rings fall
˚
0.03 A. However they
for base pairing (bꢃ
/
gꢃ
/
15.08) and for chain (bꢃ
/
gꢃ
/
parallel (aꢃ
/
0.008) and at 3.569
/
23.88) formation. In addition infinite chains are involved
to each other side in ‘nitro-adjacent benzyl’ p,p-interac-
tions (Fig. 5(b)) giving a supramolecular 2D framework
(Fig. 5(c)). These layers are connected by H-bonding
interactions involving non-coordinated water molecules.
are too slipped (angles b and g ꢁ
/
458) to enable
effective ringꢀring p,p-stacking interactions between
/
the ‘benzyl ring moieties’ of compound 3 and 4 (see
below). On the other hand, data of Table 4 reveal
possibilities for such p,p-stacking interactions between
aromatic rings of a,a?-diimines. In compound 3 that
indeed represents the formation of ‘pairs of complex
molecules’ with 2,2?-bipy planes defining a dihedral
The fac-O2ꢂN(apical) NBIDA conformation in
/
compounds 3 and 4 cannot be attributed to the
contribution of intra-molecular p,p-stacking interligand
interactions, as has been argued in compounds
angle aꢃ
/
4.438. In this case both pyridyl rings of each
[Cu(NBzIDA)(phen)]×
[Cu(NBzIDA)(TMphen)]×
and inter-molecular p,p-stacks seem to co-operate in
/
2H2O
[7]
and
bipy ligand are involved in the stack for complex pair
/5H2O [8] where both intra-
formation (Fig. 4(a)) and, in addition, inter-molecular

1044
M.J. Sa´nchez-Moreno et al. / Polyhedron 22 (2003) 1039ꢀ1049
/
Fig. 2. (a) Molecular structure of [Cu(NBIDA)(Him)(H2O)] (2). (b) A plot showing the inter-molecular benzylꢀ
forming pairs of molecules in the crystal of compound 2.
/
benzyl p,p-stacking interaction
multi-stacked chains. On the basis of the present
knowledge we could consider that the lack of p,p-
fac-NOꢂ
/
O(apical) conformation) as well as the struc-
ture of [Cu(TEBIDA)(bipy)]×
contrast the N-(tert-butyl)-iminodiacetato ligand (TE-
BIDA) adopts a fac-O2ꢂN(apical) conformation and
/4.5H2O [21] where in
stacking interactions in [Cu(IDA)(bipy)]×
/6H2O [20]
(where the non-N-substituted IDA ligand exhibits a
/

M.J. Sa´nchez-Moreno et al. / Polyhedron 22 (2003) 1039ꢀ
/1049
1045
Fig. 3. (a) Asymmetric unit of [Cu(NBIDA)(bipy)]×
/
3H2O (3). (b) Asymmetric unit of [Cu(NBIDA)(phen)]×2H2O (4).
/
once more ‘pairs of complex molecules are formed by a
p,p-stacking interaction between bipy ligands (dcꢀc
has significant similarities with that now reported for
compound 3. Consequently, it seems clear that two
features are required to promote a change from fac-
ꢃ
/
˚
˚
3.78 A, dpꢀp
ꢃ
/
3.41 A, aꢃ
/
4.748, bꢃ
/
20.278, gꢃ
/
24.958). Indeed the structure of the latter compound
NOꢂ
/
O(apical) to fac-O2ꢂN(apical) in IDA-like li-
/

1046
M.J. Sa´nchez-Moreno et al. / Polyhedron 22 (2003) 1039ꢀ1049
/
Fig. 4. (a) Inter-molecular p,p-stacking interaction between bipy ligands forming a pair of complex molecules in 3. (b) p,p-Interactions between
adjacent p-nitro groups and benzyl rings of NBIDA ligands in 3. (c) Fragment of a chain of 3 formed by alternating bipyꢀ
interactions.
/
bipy and nitro-benzyl p,p-
gands. These are the presence of non-coordinating N-
substituent in the IDA skeleton and the binding of an
aromatic and chelating a,a?-diimine (such as 2,2?-bipy or
1,10-phen). We can note that if the N-substituent of
IDA skeleton has appropriate conformational flexibility
(as the benzyl arm), a p-electron rich group (as nitro)
and/or an aromatic ring (as the phenyl moiety in the
benzyl substituent), a variety of interligand p,p-stacking
interactions could be displayed. Then such interactions
take part of molecular recognition processes involved in
crystal building. In this connection, we can appreciate
that the binding of copper(II) to an aromatic chelating
a,a?-diimine modifies the p,p-stacking pattern of the
NBIDA p-nitro-benzyl arm. In fact, H2NBIDA acid
and [Cu(NBIDA)(Him)(H2O)] (compound 2) gives
its implication in inter-molecular recognition processes.
Both Cu-bipy derivatives with TEBIDA or NBIDA
display very similar bipyꢀbipy stacks, but they are
/
clearly different to those observed in Cu-phen deriva-
tives with NBzIDA [7,8] or NBIDA (compound 4).
Unfortunately, until the present the crystal structure of
other hypothetical ternary complexes (such as Cu(II)ꢂ
/
IDAꢂphen or Cu(II)ꢂTEBIDAꢂphen) remain un-
/
/
/
known. Additional researches should be carried out to
accomplish fundamental structural co-relations and
increase our present knowledge on the molecular
recognition processes in these mixed-ligand copper(II)
complexes.
As it is show in Table 5, the studied compounds have
thermal, spectral and magnetic properties in accordance
with the reported structures. Its should be outlined that
in dry-air atmosphere the compound 2 loosely retains
the aqua apical ligand in a molar H2O:Cu ratio 0.94/1,
but compounds 3 and 4 loss a significant amount of
‘benzylꢀbenzyl’ inter-molecular stacks, whereas com-
/
pounds 3 and 4 produces ‘nitro-benzyl’ inter-molecular
p,p-interactions. Finally it is also interesting to note that
the own skeleton of the aromatic a,a?-diimine influences

M.J. Sa´nchez-Moreno et al. / Polyhedron 22 (2003) 1039ꢀ
/1049
1047
Fig. 5. (a) Fragment of a multi-stacked chain by inter-molecular p,p-interaction between phen ligands of 4 (see text). (b) Detail of the overlapping
between pairs of p-nitrobenzyl groups in 4. (c) 2D framework in the crystal of 4 build up by both phenꢀ
/
phen and (p-nitrobenzyl)-(p-nitrobenzyl)
p,p-interactions.
Table 3
Analysis of short benzylꢀ/benzyl interaction between molecules of H2NBIDA and ternary Cu(II) complexes with NBIDA and N-heterocyclic donors
˚
dc ꢀ c(A)
˚
Compound
a(8)
b(8)
g(8)
dp,p (A)
Angle NO2/Bz-ring (8)
1
2
3
4
3.68
3.72
5.10
5.01
0.03
0.00
0.00
0.00
25.3
24.3
45.3
45.2
25.3
24.3
45.3
45.2
3.33
3.39
3.59
3.53
5.3
9.1
6.5
3.7

1048
M.J. Sa´nchez-Moreno et al. / Polyhedron 22 (2003) 1039ꢀ1049
/
Table 4
Analysis of short ringꢀ
2H2O (4)
/
ring inter-molecular p,p-interactions between bipy or phen ligands in [Cu(NBIDA)(bipy)]×
/
3H2O (3) and [Cu(NBIDA)(phen)]×
/
˚
dc ꢀ c (A)
˚
Compound
a(8)
b(8)
g(8)
dp,p (A)
Comment
3 (both pyridyl rings)
3.98
3.98
4.43
4.43
28.6
24.4
24.4
28.6
3.56
3.56
Pairs of molecules
Stacking the two rings of bipy
4 (C6-rings)
3.53
3.78
0.00
0.00
15.0
23.8
15.0
23.8
3.41
3.46
Forming pairs
Linking pairs
Table 5
Summary of thermal, spectral and magnetic properties of Cu(II) compounds 2ꢀ4
/
Copper(II) compound
2
3
4
TG analysis
H2O in formula
H2O on starting TG
N8 Steps
1
3
2
0.94
4
0.88
3
1.60
2
Temperature (8C)
Loss in 1st step
Other steps loss a
Final residue
108ꢀ
H2O
CH4
CuO
/
490
50ꢀ
H2O
/
500
40ꢀ490
H2O
/
CuO
CuO
IR spectrum (cmꢁ1
H2O nas
)
3419
1621
3145
3486, 3403
1625
3485
1617
d
ImH nas(NH)
d(NÃ
/
H)
ꢁ/1500
Carboxylate nas
b
ns
ꢁ
1397
/
1600
ꢁ
1381
/
1600
1592
1383
Electronic spectrum
nmax (cmꢁ1
)
14 165
12 920
15 550, 10 050 (shoulder)
12 000
16 050, 10 000 (shoulder)
nbaricenter (cmꢁ1
)
ꢁ/
ꢁ/12 500
ESR spectrum
Type
Axial
2.24
2.06
Axial
2.30
2.05
Axial
2.25
2.05
g
Š
ꢁ
/
ꢁ
/
gÞ
Magnetic properties
(293 K)
m (B.M.)
1.78
1.81
1.98 c
a
In addition to H2O, CO2, CO, N2O and NO.
Difference between experimental and calculated residue within 1.0%.
CurieꢀWeiss behaviour (xꢃC/(Tꢁu); 80ꢀ300 K): Cꢃ
0.49 K emu molꢁ1, uꢃ
b
c
/
/
/
/
/
/
ꢁ/5.63 K.
non-coordinated water before starting the TG-analysis.
The three copper(II) compounds produce abundant
N2O and NO oxides, upon the oxidative pyrolysis (but
not N(CH3)3 and NH3 as for H2NBIDA acid) and give a
residue of CuO.
aromatic a,a?-diimines which exhibits a fac-O2ꢂ
/
N(api-
cal) IDA-like conformation. A comparison with other
structural findings reported in previous works reveal
that both the presence of non-coordinating N-substitu-
ent in the IDA skeleton and the chelation of the
copper(II) atom by an aromatic a,a?-diimine contribute
actively to the molecular recognition processes and the
crystal building in compounds with NBIDA in fac-O2ꢂ
/
4. Concluding remarks
N(apical) conformation.
The results of the present study show different modes
of the N-(nitrobenzyl) group to be involved in p,p-
stacking interactions as a N-substituent of IDA chelat-
ing ligand. These modes represent inter-molecular
5. Supplementary material
benzylꢀ
/
benzyl or nitro-benzyl stacks. This latter pattern
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
is found in ternary Cu(II) complexes of NBIDA and

M.J. Sa´nchez-Moreno et al. / Polyhedron 22 (2003) 1039ꢀ
/1049
1049
Gutie´rrez, Inorg. Chim. Acta 339 (2002) 160 (and references
therein).
[5] M.J. Sa´nchez-Moreno, D. Choquesillo-Lazarte, J.M. Gonza´lez-
Data Centre CCDC No. 189626 for H2NBIDA acid
(compound 1), CCDC No. 189627 for [Cu(NBI-
DA)(Him)(H2O)] (compound 2), CCDC No. 189628
Pe´rez, R. Carballo, A. Castineiras, J. Niclo´s-Gutie´rrez, Inorg.
˜
Chem. Commun. 5 (2002) 800.
for [Cu(NBIDA)(2,2?-bipy)]×
/
3H2O (compound 3) and
2H2O
(compound 4). Copies of this information may be
[6] (a) A.G. Sicilia Zafra, E. Bugella Altamirano, J.M. Gonza´lez
Pe´rez, J.D. Mart´ın Ramos, J. Niclo´s Gutie´rrez, VIII Italian-
Spanish Congress on Thermodynamics of Metal Complexes,
Cagliari, Italy, 1997, p. 56.;
CCDC No. 189629 for [Cu(NBIDA)(1,10-phen)]×
/
obtained free of charge from The Director, CCDC, 12
Union Road, Cambridge, CB2 1EZ, UK (fax: ꢂ44-
/
(b) E. Bugella, A.G. Sicilia, J.M. Gonza´lez, A. Castineiras, J.
˜
1223-336033; e-mail: deposit@ccdc.cam.ac.uk or www:
http://www.ccdc.cam.ac.uk).
Niclo´s, IX Spanish-Italian Congress on Thermodynamics of
Metal Complexes, Girona, Spain, 1998, Report P-2.;
(c) E. Bugella-Altamirano, J.M. Gonza´lez-Pe´rez, A.G. Sicilia-
Zafra, A. Castineiras-Campos, J. Niclo´s-Gutie´rrez, XI Spanish-
˜
Italian Congress on Thermodynamics of Metal Complexes,
Valencia, Spain, 2000, Report P-18.
[7] A. Castineiras Campos, J.D. Mart´ın Ramos, E. Bugella Altamir-
˜
Acknowledgements
ano, J.M. Gonza´lez Pe´rez, D. Choquesillo Lazarte, J. Niclo´s
Gutie´rrez, X Italian-Spanish Congress on Thermodynamics of
Metal Complexes, S. Martino al Cimino, Italy, 1999, Report C-
18.
The authors are gratefully indebted to the Direccio´n
de Investigacio´n, MCYT, Spain for financial support
(Research Projects: BQU2002-04523-C02-01/02 and
BQU2002-03543). Doctoral research grants from the
MCYT (Spain) or from the AECI (MAE, Spain) are
grateful acknowledged by M.J.S.M. and D.Ch.-L.,
respectively.
[8] A. Castineiras, E. Bugella Altamirano, J.M. Gonza´lez Pe´rez, J.
˜
Niclo´s Gutie´rrez, Reunio´n Cient´ıfica de Bioinorga´nica 2001,
University of Granada, Granada, 2001. Report P35.
[9] M.J. Sa´nchez Moreno, Ph.D. dissertation, University of Granada,
Granada, 2002.
[10] L.J. Bellamy, The Infrared Spectra of Complex Molecules, vol. 1,
third ed., Chapman and Hall, London, 1975.
[11] G.M. Sheldrick, SADABS: Program for Absorption Corrections,
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