A structural study of the iminodiacetate moiety conformation in N-(1-adamantyl)-iminodiacetate(2-) copper(II) complexes

Article abstract of DOI:10.1002/zaac.200700364

N,N-bis(carboxymethyl)-1-adamantylamine acid (H₂BCAA) or N-(1-adamantyl)-iminodiacetic acid forms zwitterions that are intra-stabilized by a 'bifurcated' N⁺-H...O(carboxyl)₂ interaction. In the crystal, both half-protonated carboxyl groups of H₂BCAA ^± are involved in linear O-H...O intermolecular bridges of 2.46 A. In the studied BCAA-Cu^II derivatives, the iminodiacetate-moiety of the BCAA chelating ligand exhibits a mer-NO₂ conformation in [Cu(BCAA)(H₂O)₂] (1) and [Cu(BCAA)(Him)]₂ (2), but fac-O₂+N(apical) conformation in Cu(BCAA)(bpy)(H₂O)]·3.5H₂O (3) [Him = imidazole, bpy =2,2′-bipyridine]. In clear contrast, dipyridylamine (dpya), as auxiliary ligand, seems to be unable to promote the fac-O₂+N(apical) conformation in BCAA, as reveal the structures of two new salts with the trinuclear cation [(dpya)₂Cu-μ₂-Cu(BCAA) ₂-Cu(dpya)₂]²⁺ and the anions [Cu(BCAA) ₂]^2- (4) or NO₃^- (5), respectively.

Full text of DOI:10.1002/zaac.200700364

DOI: 10.1002/zaac.200700364
A Structural Study of the Iminodiacetate Moiety Conformation in
N-(1-adamantyl)-iminodiacetate(2-) Copper(II) Complexes
a
a
a
´
´
´
´
˜
Regina Fernandez-Pinar , Celia Sanchez de Medina-Revilla , Alicia Domınguez-Martın ,
a
b
a
´
´
´
´
Marıa Pilar Brandi-Blanco , Duane Choquesillo-Lazarte , Josefa Marıa Gonzalez-Perez , and
Juan Niclos-Gutierrez *
a,
´
´
a Granada/Spain, Department of Inorganic Chemistry, University of Granada
b
´
Granada/Spain, Laboratorio de Estudios Cristalograficos, IACTϪCSIC, P. T. Ciencias de la Salud
Received May 20th, 2007; revised July 11th, 2007.
th
˜
Dedicated to Professor Alfonso Castineiras on the Ocassion of his 65 Birthday
Abstract.
(H2BCAA) or N-(1-adamantyl)-iminodiacetic acid forms
zwitterions that are intra-stabilized by
‘bifurcated’ Nϩ-
N,N-bis(carboxymethyl)-1-adamantylamine
acid
[Cu(BCAA)(bpy)(H2O)]·3.5H2O (3) [Him ϭ imidazole, bpy ϭ2,2Ј-
bipyridine]. In clear contrast, dipyridylamine (dpya), as auxiliary
ligand, seems to be unable to promote the fac-O2ϩN(apical) con-
formation in BCAA, as reveal the structures of two new salts with
the trinuclear cation [(dpya)2Cu-µ2-Cu(BCAA)2-Cu(dpya)2]2ϩ and
a
H···O(carboxyl)2 interaction. In the crystal, both half-protonated
carboxyl groups of H2BCAA are involved in linear O-H···O inter-
molecular bridges of 2.46 A. In the studied BCAA-CuII derivatives,
˚
the anions [Cu(BCAA)2]2Ϫ (4) or NO3 (5), respectively.
Ϫ
the iminodiacetate-moiety of the BCAA chelating ligand
exhibits a mer-NO2 conformation in [Cu(BCAA)(H2O)2] (1) and
[Cu(BCAA)(Him)]2 (2), but a fac-O2ϩN(apical) conformation in
Keywords: Copper; Imidazole; Bipyridine; Dipyridylamine;
Adamantamine; Iminodiacetate; Crystal structure
Introduction
EDTA)Cu(H2O)]·2H2O [6] (EDTA ϭ ethylenediamine-
tetraacetate(4-) ligand). Obviously, the presence of a N-sub-
stituent in the IDA ligand influences the conformation of
the chelating IDA moiety in these binary CuII complexes.
Surprisingly, in ternary CuII complexes with N-bulky-
IDA and one aromatic α,αЈ-diimine as ligands, such as
[Cu(TEBIDA)(bpy)(H2O)]·4.5H2O [5], [Cu(NBIDA)(bpy)]·
3H2O [7] or [Cu(NBIDA)(phen)]·2H2O [7] (NBIDA ϭ N-
(p-nitrobenzyl)-IDA), the IDA moiety of chelating ligands
(TEBIDA or NBIDA) exhibits an unexpected fac-
O2ϩN(apical) conformation, where two O-carboxyl atoms
of the IDA-like ligand are among the four closest CuII do-
nor atoms, whereas the N-amino(IDA-like) atom is in one
apical/distal position of the elongated metal surrounding. It
has been suggested that two features are required to pro-
mote the fac-O2ϩN(apical) conformation in the Cu(IDA-
like) chelate: 1) the presence of a bulky N-substituent in the
IDA chelating agent, and 2) the cooperation of an aromatic
α,α-diimine as auxiliary ligand. In cases where the bulky
arm of the IDA group is of the N-benzyl type, an intra-
molecular interligand π,π-stacking interaction is operative
[7]. Indeed, such kind interaction is unexpectedly operative
between the benzimidazolyl group and the phen ligand in
[Cu(BimIDA)(phen)]·3H2O (BimIDA ϭ N-(2-benzimidazo-
lyl)methyliminodiacetate(2-) ligand, which only acts as tri-
dentate in this case) although this feature seems to be ig-
nored in a recent paper [8]. On the other hand, in related
ternary compounds having a bulky N-alkyl-IDA ligand (un-
able to participate in π,π-stacking) such interaction is devel-
A large amount of structural reports on iminodiacetate
(IDA) or N-substituted IDA-derivatives copper(II) com-
plexes with or without N-heterocyclic auxiliary ligands has
afforded interesting structural correlations. Main obser-
vations to this respect deal on the fac-NOϩO(apical) or
mer-NO2 tridentate conformation of the IDA-moiety in the
used IDA-like chelating agents. In non-substituted IDA-
CuII complexes, the fac-NOϩO(apical) conformation is
found both in the binary compound poly-[Cu(IDA)(H2O)2]
[1] and in related ternary complexes having a N,N-bidentate
aromatic diimines (such as 2,2Ј-bipyridine, bpy [2] or 1,10-
phenantroline, phen [3]) as auxiliary ligands. On the other
hand, the IDA or IDA-like ligand unequivocally exhibits
a mer-NO2 conformation in many ternary complexes with
imidazole (Him) [1] or large variety of monodentate N-het-
erocyclic donors (including the nucleobase adenine [4]).
Noteworthy such mer-NO2 tridentate conformation is also
observed in the binary CuII chelates of N-tert-butyl-IDA,
[Cu(TEBIDA)(H2O)2] [5] as well as in each half of the
binuclear complex of the compound [(H2O)Cu(µ-
´
´
* Prof. J. Niclos-Gutierrez
Department of Inorganic Chemistry, Faculty of Pharmacy
University of Granada
E-18071 Granada, Spain
E-mail: jniclos@ugr.es
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Iminodiacetate Moiety Conformation in N-(1-adamantyl)-iminodiacetate(2-) Copper(II) Complexes
Table 1 Crystal and structure refinement data for compounds 1-5.
Compound
1
2
3
4
5
Empirical Formula
Formula Weight
Temperature / K
C14H23CuNO6
364.87
120(2)
C34H46Cu2N6O8
793.85
100(2)
C48H72Cu2N6O17
1132.20
100(2)
C96H163Cu4N16O41.50
2459.58
100(2)
C68H78Cu3N16O16
1566.08
293(2)
˚
λ / A
0.71073
0.71073
0.71073
0.71073
1.54178
Crystal System
Space Group
orthorhombic
Abm2
monoclinic
P21/c
triclinic
P1
triclinic
P1
monoclinic
P21/c
¯
¯
Unit Cell Dimensions
˚
a / A
15.000(4)
10.644(3)
9.955(3)
90
90
90
1589.4(8)
4
1.525
11.2912(8)
11.4068(8)
12.6174(8)
90
92.5550(10)
90
1623.46(19)
2
1.624
10.4670(5)
14.0620(7)
17.7850(8)
87.7560(10)
85.7890(10)
74.1390(10)
2510.8(2)
2
15.330(5)
16.877(5)
22.856(5)
74.336(5)
85.914(5)
87.714(5)
5678(3)
18.1764(7)
10.7849(4)
18.3297
90
106.6850(19)
90
3441.9(2)
2
1.511
˚
b / A
˚
c / A
α / °
β / °
γ / °
3
˚
Volume / A
Z
2
Density / Mg·m3
µ / mm
1.498
0.926
1.439
0.831
1.402
1.375
1.755
F(000)
764
828
1192
0.30 x 0.25 x 0.08
25836
2598
0.22 x 0.16 x 0.07
133589
1626
0.18 x 0.18 x 0.05
12094
Crystal size / mm
Collected reflections
Unique reflections
Absorption correction
Data / parameters
Goodness of Fit
Final R indices
[I>σ(I)]
0.29 x 0.25 x 0.06
7560
1992
SADABS
1992 / 113
1.194
R1 ϭ 0.0302
wR2 ϭ 0.0875
0.30 x 0.14 x 0.12
8830
3006
SADABS
3006 / 226
1.036
R1 ϭ 0.0322
wR2 ϭ 0.0808
9287
23093
12094
SADABS
9287 / 676
1.079
R1 ϭ 0.0303
wR2 ϭ 0.0819
SADABS
23093 / 1293
1.092
R1 ϭ 0.0664
wR2 ϭ 0.1706
TWINABS
12094/ 473
1.044
R1 ϭ 0.0486
wR2 ϭ 0.1405
oped between aromatic α,αЈ-diimines of adjacent complex
molecules [5]. Thus the intra-molecular π,π-interligand in-
teraction seems not to be a requisite to impose the fac-
O2ϩN(apical) conformation in the IDA-chelating moiety.
Deeping in the role of the bulky aliphatic arm in the confor-
mation of N-alkyl-IDA ligands, the aim of the present work
is to provide a broad structural study on [N-(1-adamantyl)-
IDA]-CuII chelates without or with selected N-heterocyclic
secondary ligands (Him, bpy or dpya ϭ dipyridylamine).
Results and Discussion
As expected for an amino diacid and as is also known for
a large variety of amino polycarboxylic acids, the H2BCAA
acid exists as a zwitterion (figure 1). It is intra-stabilized
by a ‘bifurcated’ H-bonding interaction (N1ϪH1···O4 and
N1ϪH1···O8). In addition, the ‘non-ammonium’ H acid
atom is statistically linked to the O5 and O9 atoms, with
occupancy of 0.5 for each carboxyl group. This feature
enables the formation of H-bonded chains of zwitterions by
means of linear and rather short H-bonds (O5ϪH1···O5#1
Figure 1 Molecular structure of the zwitterionic H2BCAA acid
showing the H-bonding interactions.
˚
and O9-H1···O9#2; 2.46 A, #1 Ϫx,Ϫy,Ϫzϩ1, #2
H atom is only H-bonded to the corresponding car-
boxylate group.
Ϫxϩ2,Ϫy,Ϫzϩ2) with the hydrophobic adamantyl arms
alternatively disposed to each side of chain. Additional
hydrophobic contacts between adamantyl arms from adjac-
ent H2BCAA zwitterion chains build the crystal of this
amino-diacid. This structure is closely related to those of
other N-alkyl-H2IDA acids, such as H2TEBIDA [6] and
H2iPIDA (N-isopropyl-H2IDA) [9] where the ‘ammonium’
Relevant structural parameters of CuII compounds 1 to
5 are given in table 1. Coordination bond lengths are sum-
marized in the legend of the corresponding figures. The
crystal of the binary chelate [Cu(BCAA)(H2O)2] (1) consists
of complex molecules (figure 2) with the metal in a 4ϩ1
type CuII coordination. One H atom of each aqua ligand is
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H bonded to one O(12) atom from two different adjacent
molecules, generating a 2D layered supramolecular struc-
ture, parallel to the bc plane, with adamantyl arms oriented
to the external faces. Hydrophobic interactions connect
these layers perpendicular to the a axis of the crystal (fig-
ure 3).
main in
a
compound of the hypothetical formula
Cu(BCAA)(Him)·nH2O. Indeed, the structure of
[Cu(BCAA)(Him)]2 (2) (figure 4) revealed that in this ter-
nary compound, which consists of centro-symmetric di-
nuclear molecules, the IDA moiety of BCAA exhibits a
mer-NO2 conformation. The 4ϩ1 type CuII coordination of
this compound is the most common coordination poly-
hedron in Cu(IDA-like)(imidazole-like) ternary complexes
(rarely of distorted octahedral type). To the best of our
knowledge, this is the first example of dinuclear complex of
this 1:1:1 Cu/IDA-like/Him-like composition, usually
mononuclear molecules or 1D polymers. In the crystal of 2
the Him ligands are involved in N-H···O interactions build-
ing again 2D frameworks parallel to the bc plane and ori-
enting the adamantyl arms towards their external faces.
These layers connect along the a axis by hydrophobic con-
tacts to build the 3D crystal (figure 5).
˚
Figure 2 Molecular structure of the 1. Bond lenghts /A: Cu1-
O11 ϭ Cu1-O11#1 1.918(2), Cu1-O1 1.948(2), Cu1-N1 2.037(2),
Cu1-O2 2.349(3). Symmetry code #1: x, Ϫyϩ3/2, z.
Figure 4 Molecular structure of dinuclear unit of 2. Bond
˚
lenghts /A: Cu1-O8 1.928(1), Cu1-O4 1.936(1), Cu1-N20 1.945(2),
Cu1-N1 2.038(2), Cu1-O9#1 2.751(2). Symmetry code #1: Ϫx,
Ϫy, Ϫz.
The asymmetric unit of compound 3 contains two sym-
metry-independent molecules (3-1 and 3-2) and seven water
molecules, according to a simplified chemical formula
[Cu(BCAA)(bpy)(H2O)]·3.5H2O (figure 6). Both complex
molecules have a 4ϩ1ϩ1 type CuII coordination and are
close similar to each other. In clear contrast to that ob-
served for compounds 1 or 2, the IDA moiety exhibits a
fac-O2ϩN(apical) conformation in the molecules of 3. In
Figure 3 Crystal packing of 1 viewed along the c axis. Hydrogen
atoms ommited for clarity.
The mer-NO2 IDA-moiety conformation of 1 is con-
sistent with the also observed in the related binary
complexes [Cu(TEBIDA)(H2O)2] [5] and [(H2O)Cu(µ-
EDTA)Cu(H2O)]·2H2O [6]. This conformation could re-
˚
the crystal, pairs of molecules 3-1 (dππ ϭ 3.40 A, α ϭ 1.52°,
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Iminodiacetate Moiety Conformation in N-(1-adamantyl)-iminodiacetate(2-) Copper(II) Complexes
Figure 7 View of 3 showing a chain built by π,π-stacking interac-
tions.
Figure 5 A view of 2 showing hydrophobic contacts between 2D
layers built by H-bonding interactions. Hydrogen atoms ommited
for clarity.
Using dipyridylamine (dpya) instead of 2,2Ј-bpy, we have
prepared the compound of formula: [(dpya)2Cu-µ2-[Cu-
(BCAA)2]-Cu(dpya)2][Cu(BCAA)2]·25.5H2O (4). The
asymmetric unit contains two times the above referred for-
mula as two symmetry-independent structural units. Unex-
pectedly, we can appreciate that this compound is a hy-
drated salt of the bis-chelate anion [Cu(BCAA)2]2Ϫ and a
centrosymmetric trinuclear cation [(dpya)2Cu-µ2-[Cu-
(BCAA)2]-Cu(dpya)2]2ϩ. The bis-chelate counter-anion ex-
hibits a 4ϩ2 type CuII coordination with BCAA only as
tridentate ligand in a fac-NOϩO(apical) conformation. In
the trinuclear cation, the central CuII ion also takes part
of an octahedral bis-chelate [Cu(BCAA)2] moiety, but each
BCAA ligand acts both as tridentate and as bridging ligand
(figure 8). Again, the µ-BCAA adopts a fac-NOϩO(apical)
configuration respect to the central CuII surrounding. The
µ-BCAA role implies that the bridging carboxyl group sup-
plies one O(apical) donor to the central CuII ion and one
O(equatorial) donor of a terminal CuII ion. Both symmetry
related terminal CuII ions exhibit a CuN3OϩN(apical)
chromophore (coordination type 4ϩ1). Thus, to each ter-
minal CuII ion of the cation, one dpya ligand supplies two
N-basal donors and the other dpya ligand gives one N-ba-
sal and the N-apical donors. Both referred dpya-chelating
behaviours are well documented in the abundant structural
literature on dpya-CuII complexes deposited in the struc-
tural CSD database. We can also appreciate that the trinu-
clear cation of 4 is indeed a ternary ‘mixed-ligand Cu-com-
plex’, but its structure is far away from that expectable for
a ‘ternary complex molecule’ in a typical compound of
formula Cu(BCAA)(dpya)·nH2O, similar in composition to
the bpy-derivative compound 3. Unfortunately, the crystal
structure of compound 4 cannot provide concluding in-
sights on the modulating role of the 1-adamantyl arm in
the conformation of BCAA when dpya acts as a secondary
ligand. Surprisingly and from an essay where accidentally
we introduced a hazardous nitrate contamination in syn-
thesis, we have obtained a few single crystals of the hydrated
salt [(dpya)2Cu-µ2-[Cu(BCAA)2-Cu(dpya)2](NO3)2·2H2O
(5) (figure 9). The most interesting structural feature of this
compound is the presence of the centro-symmetric trinu-
clear cation [(dpya)2Cu-µ2-[Cu(BCAA)2]-Cu(dpya)2]2ϩIn
the crystal, pairs of symmetry related cations stack their
˚
β or γ ϭ 21.24° or 22.76°) and 3-2 (dππ ϭ 3.41 A, α ϭ
4.07°, β or γ ϭ 23.04° or 19.01°) involve both bpy rings in
a π,π-stacking interaction. Furthermore, pairs of symmetry
independent molecules are linked to each other by two
O(aqua)-H···O(carboxy) bridges. The referred π,π-stacking
and H-bonding interactions reinforce ribbon chains of the
complex molecules along the c axis (figure 7). Additional
H-bonds built a 3D array, where the water fills channels
extending along the b axis of the crystal.
Figure 6 Molecular structure of one of two crystallographically
independent but chemically equivalent structural units in 3. Non
coordinated water molecules omitted for clarity. Bond lenghts /A,
averaged: Cu-O(BCAA) 1.959, Cu-O(BCAA) 1.984, Cu-N(BCAA)
2.485, Cu-N(bpy) 2.021, Cu-N(bpy) 2.026, Cu-Ow 2.328.
˚
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Figure 8 Molecular structure of one of two crystallographically independent but chemically equivalent structural units in 4. Hydrogen
˚
atoms and water molecules omitted for clarity. Bond lenghts /A: Complex anion: Cu5-O113 1.929(3), Cu5-O93 1.931(3), Cu5-N6 2.120(4),
Cu5-N5 2.129(4), Cu5-O111 2.431(3), Cu5-O91 2.519(3). Trinuclear cation (averaged): Central: Cu-O(BCAA) 1.969, Cu-O(BCAA) 2.432,
Cu-N(BCAA) 2.093. Terminal: Cu-N(dpya1) 1.987, Cu-N(dpya1) 2.005, Cu-N(dpya2) 2.022, Cu-N(dpya2) 2.159, Cu-O(BCAA) 1.969.
˚
Figure 9 Centrosymmetric molecular structure of the 5. Hydrogen atoms omitted for clarity. Bond lenghts /A: Cu2-O34 1.950(2), Cu2-
N27 2.125(2), Cu2-O30 2.436(2), Cu1-N1 2.019(2), Cu1-N13 1.990(2), Cu1-O31 1.986(2), Cu1-N14 2.060(2), Cu1-N26 2.186(2).
˚
N1-pyridine rings (dππ ϭ 3.51 A, α ϭ 0.00°, β ϭ γ 24.33°)
generating a chain that extends along the a axis.
ν(CϭO) and νas(COO) of the groups ϪCOOH and
ϪCOOϪ···(H-Nϩ), respectively. In this spectrum, an ab-
sorption at 1398 will be assigned to the combined mode
ν(C-O)ϩδ(O-H) and to νs(COO) of the referred carboxyl
groups. The presence of aqua ligands in 1 is shown by the
bands due to the modes νas (3420), νs (ϳ3160) and δ (1627).
The carboxylate group of the binary compound 1 gives
bands of the modes νas (1593) and νs (1384). The IR spectra
The IR spectrum (cmϪ1) of the H2BCAA zwitterion
shows bands of the stretching modes νas(CH2) at 2971, 1956
and 2944,ν(CH) at 2936 and νs(CH2) at 2852. A similar
pattern is observed in the region of the C-H stretching
bands in the IR spectra of compounds 1-5. The amino-di-
acid also gives two bands at 1733 and 1645 of the modes
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Iminodiacetate Moiety Conformation in N-(1-adamantyl)-iminodiacetate(2-) Copper(II) Complexes
Figure 10 TG curves of compounds 1 to 4.
of compounds 2, 4 and 5 exhibit, among others, a band of
the δ(N-H) in-plane deformation mode at 1551 (Him, 2) or
1533 (dpya, 4 and 5). This weak but easily identifiable band
has a remarkable diagnostic value to observe the presence
of ligands such as Him or dpya and it is absent in the
spectrum of 3 with bpy as secondary ligand. The presence
of bridging and monodentate carboxylate groups in 5 is
featured by two bands for the νs(COO) mode at 1400 and
1383, respectively. The IR spectra of metal complexes
with aromatic auxiliary ligands (2-5) show one or more
sharp bands of the π(C-H)arom out-of-plane mode near to
700-750. The IR spectrum of 5 shows a sharp and very
intense band due to the overlap to the νs(COO) of BCAA
and a ν(NO3) modes.
The H2BCAA zwitterion is rather stable and decom-
poses between 210 and 505 °C, in two pyrolytic steps, with
production of CO2, H2O, CO, H2CO, N2O and NO (and
probably trace amounts of ethylene). The formation of
H2CO has always been observed in the pyrolysis of studied
Cu-BCAA derivatives (1-5). In general, the pyrolytic steps
of the studied Cu-BCAA complexes produces CO2, H2O,
CO, H2CO, N2O and NO (among other gases) and a resi-
due of CuO. Figure 10 shows the TG behaviour of com-
pounds 1 to 4. The TG behaviour of 1 (figure 10-1) shows
the loss of the apical aqua ligand (105Ϫ175 °C, exp.
10.668 %, calc. 9.875 %) followed of three pyrolytic steps
(175-220, 220-340, 340-490 °C) to produce a residue of
CuO. The loss of the apical aqua ligand represents an endo-
thermic effect (∆H ϭ Ϫ0.44 kJ/g) with maximum intensity
at 138 °C. The pyrolysis of 2 (figure 10-2) also gives trace
amounts of NH3, NO2 and CH4 (figure 11). This anhydrous
compound initiates its decomposition with an exothermic
effect (230 °C, 0.92 kJ/g). Under air-dry flow, compound 3
losses all water prior to initiate the pyrolysis of the Cu(B-
CAA)(bpy) residue at 215 °C (figure 10-3), with a sharp
first step (215-240 °C, exp. loss 61 %). A fresh sample loss
water under 100 °C with an endothermic effect around
70 °C, followed of other at 209 °C which corresponds to the
melting-decomposition of the anhydrous sample. Com-
pounds 4 (figure 10-4) and 5 initiate their decomposition at
r.t. with water loss. In addition of CO2, H2O, CO, H2CO,
their pyrolysis produces various N-oxides (N2O, NO, NO2)
but not NH3 (as is observed for the Him derivative).
The electronic spectra of 1 and 2 show a d-d band with
νmax at 14470 and ϳ16000 cmϪ1 according to their
chromophores CuNO3ϩO and CuN2O2ϩO. Compounds 4
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Figure 11 Selected FT-IR spectra for the identification of gasses produced during the two pyrolitic steps of 2.
diacid shows a sharp endothermic peak at 233 °C (Ϫ0.20 kJ/g °C).
Crystals of this amino diacid were grown by slow evaporation of a
50:50 ethonol:water solution. Crystal data for H2BCAA:
and 5 have averaged electronic spectra with two bands at
νmax near 15500 and 10500 cmϪ1, with the overlapped con-
tributions of their different CuII chromophores. The spec-
trum of 3 exhibits an unsymmetrical band with νmax at
15150 cmϪ1 and a shoulder around 12500 cmϪ1, a typical
spectrum of CuII complexes with 4ϩ1ϩ1 coordination
surrounding.
˚
C14H21NO4, fw 267.32, 100(2) K, λ ϭ 0.71073 A, monoclinic sys-
˚
˚
tem, space group P21/n, a ϭ 6.2864(5) A, b ϭ 17.3134(14) A, c ϭ
Ϫ3
˚
11.2349(9) A, β ϭ 94.7300(10)°, Z ϭ 4, Dcalc ϭ 1.457 Mg·m
ϭ
0.106 mmϪ1, collected/unique reflections ϭ 7583/2771 for 175
parameters, GOF ϭ 1.041, R1 ϭ 0.0434, wR2 ϭ 0.1065.
We can conclude that the presence of the N-(1-ada-
mantyl) arm in the IDA skeleton of BCAA ligand displays
an expectable steric factor in the binary Cu-BCAA chelate,
and the related ternary compounds with imidazole and 2,2Ј-
bipyridine ligands. That is summarized in the mer-NO2 IDA
moiety conformation in the binary and Him ternary com-
pounds as well as in the fac-O2ϩN(apical) IDA-like confor-
mation in the related bpy derivative. However, the behavior
observed for bpy cannot be applied to the dipyridyl ligand,
which has proved a unique trend to build the linear tri-
nuclear cation [(dpya)2Cu-µ2-[Cu(BCAA)2]-Cu(dpya)2]2ϩ in
salts with [Cu(BCAA)2]2Ϫ or nitrate as counter-anions.
Diaqua(N-(1-adamantyl)-iminodiacetate)copper(II),
[Cu(BCAA)-
(H2O)2] (1). 0.27 g (1 mol) of H2BCAA acid and 0.11 g (0.5 mmol)
of bluish Cu2CO3(OH)2 were reacted in 100 ml of a 50:50 iP-
rOH:water mixture, under vacuum, with heating (50Ϫ60 °C) and
stirring until a clear blue solution of the Cu(BCAA) chelate was
obtained. The heating and stirring were continued for 15 min. After
cooling at r.t., the solution was filtered without vacuum on a crys-
tallization device. First well shaped crystals were observed in one
day. Many other air-stable single crystals were obtained from
mother liquors, although the crystallographic study was carried out
at low temperature. Slow evaporation, controlled with a plastic
film, yields 0.31 g (85 %) of the desired product. Many crystals suit-
able for X-ray crystallography were obtained during the evapor-
ation of mother liquors. Calc. for C14H23CuNO6: C 46.08, H 6.35,
N 3.84 %. Found: C 46.16, H 6.20, N 3.79 %. M.p.(decomp.):
105 °C.
Experimental Section
All chemicals have been purchased from Aldrich or Across and
were used as received.
Bis-[(imidazole)(N-(1-adamantyl)-iminodiacetate)copper(II)], [Cu-
(BCAA)(Him)]2 (2). 0.27 g (1 mmol) of H2BCAA acid and 0.11 g
(0.5 mmol) of bluish Cu2CO3(OH)2 were reacted in 100 ml of a
50:50 iPrOH:water mixture, under vacuum, with heating (50-60 °C)
and stirring,. To the resulting clear blue solution 0.14 g of Him
(2 mmol, 100 % of excess) were added. The heating and stirring
were continued for 15 min. After cooling at r.t., the solution was
filtered without vacuum on a crystallization device. The slow evap-
oration of the dark blue solution, controlled with a plastic film,
yields 0.32 g (80 %) of the desired product. The high solubility of
Him precludes its crystallization until a very low amount of solu-
tion remains to evaporate. Calc. for C34H46Cu2N6O8: C 51.44, H
5.84, N 10.59 %. Found: C 51.37, H 5.81, N 10.55 %. The use of a
stoichiometric mixture (as represents to add 1 mmol of Him in the
reported synthesis) causes the initial formation of crystals of the
N,N-bis(carboxymethyl)-1-adamantylamine acid (H2BCAA) or N-
(1-adamantyl)-iminodiacetic acid. The chelating ligand was pre-
pared in acid form by reaction between potassium chloroacetate
(0.45 mol) and 1-adamantylamine (0.2 mol) in alkaline 50:50 etha-
nol:water media, as described elsewhere [10]. In order to carry out
the appropriate condensation process it is important to maintain
the suitable proportion of ethanol in the reaction mixture. If a
white colour is observed, due to the separation of the 1-adamantyl-
amine, an aliquot of ethanol should be added to re-dissolve the
rather water insoluble alkyl-amine. The product was purified by re-
crystallization in 50:50 ethanol:water. Yield: 21.4 g, 40 %. Calc. for
C14H21NO4 (267.32): C 62.90, H 5.24, N 7.92 %. Found: C 62.85,
H, 5.12, N 7.89 %. M.p.(decomp.): 210 °C. The DSC of this amino-
2664
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 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2007, 2658Ϫ2666

Iminodiacetate Moiety Conformation in N-(1-adamantyl)-iminodiacetate(2-) Copper(II) Complexes
binary complex 1, followed of the crystallization of dark blue crys-
tals of 2. The shape and colour of compounds 1 and 2 is still differ-
ent to permit the handily separation of crystals of both compounds.
Interestingly, working in a 200 % of Him in excess, only compound
2 was obtained, but with a possible contamination of Him, as re-
vealed the elemental analysis of isolated samples. Good crystals
for X-ray diffraction purposes were obtained directly from mother
liquors. M.p.(decomp.): 209 °C.
pounds, using a coupled FT-IR Nicolet Magma 550 spectrometer.
The DSC measurements of 1 to 5 where recorded in a Shimadzu
DSC-500 apparatus. Infrared spectra were recorded by using KBr
pellets on a Jasco FTϪIR 410 spectrometer. Electronic (diffuse re-
flectance) spectra were obtained in a Varian Cary-5E spectrophoto-
meter.
X-Ray diffraction studies: Suitable crystals were mounted on glass
fibers and these samples were used for data collection. Data were
collected with Bruker SMART APEX CCD (H2BCAA, 2 and 3),
Bruker SMART CCD 1000 (2), Bruker Kappa APEX II (4) or
Bruker X8 Proteum (5) diffractometers. The data were processed
with SAINT [11] or APEX2 (5 and 6) [12] and corrected for ab-
sorption using SADABS [13] or TWINABS (6) [14]. The structures
were solved by direct methods [15], which revealed the position of
all non-hydrogen atoms. These atoms were refined on F2 by a full-
matrix least-squares procedure using anisotropic displacement par-
ameters [16]. All hydrogen atoms were located in difference Fourier
maps and included as fixed contributions riding on attached atoms
with isotropic thermal displacement parameters 1.2 times those of
the respective atom. Atom scattering factors were taken from the
International Tables for Crystallography [17]. Geometric calcu-
lations and molecular graphics from PLATON [18]. Crystallo-
graphic data have been deposited at the Cambridge Crystallo-
graphic Data Centre with CCDC Nos. 646522Ϫ646527. Copies of
this information may be obtained free of charge from The
Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK
(Fax: ϩ44-1223-336033; e-mail: deposit@ccdc.cam.ac.uk or
www:http://www.ccdc.cam.ac.uk).
(2,2Ј-bipyridine)(N-(1-adamantyl)-iminodiacetate)copper(II) 3.5-hy-
drate, [Cu(BCAA)(bpy)]·3.5 H2O (3). 0.27 g (mmol) of H2BCAA
acid and 0.11 g (0.5 mmol) of bluish Cu2CO3(OH)2 were reacted in
100 ml of 50:50 iPrOH:water as solvent, working under vacuum,
with heating (50Ϫ60 °C) and stirring,. To the resulting clear blue
solution 0.16 g (1 mmol) of bpy were added. The heating and
stirring were continued for 15 min. After cooling at r.t., the blue-
greenish solution was filtered without vacuum on a crystallization
device. The slow evaporation of the blue greenish solution, con-
trolled with a plastic film, yields 0.51 g (90 %) of compound 3.
Calc. for C24H36CuN3O8.5: C 50.92, H 6.41, N 7.42 %. Found: C
51.07, H 6.35, N 7.36 %. This compound loses water easily and its
anhydrous form decomposes above 215 °C.
Bis-{bis-(dypyridylamine)copper(II)}-µ-bis-(N-(1-adamantyl)-
iminodiacetate)copp-er(II) bis-(N-(1-adamantyl)-iminodiacetate)-
cuprate(II) 25.5-hydrate, [(dpya)2Cu-µ2-[Cu(BCAA)2]-Cu(dpya)2]-
[Cu(BCAA)2]·25.5H2O (4). 0.27 g (mmol) of H2BCAA acid and
0.11 g (0.5 mmol) of bluish Cu2CO3(OH)2 were reacted in 100 ml of
50:50 iPrOH:water as solvent, working under vacuum, with heating
(50Ϫ60 °C) and stirring. To the resulting clear blue solution 0.17 g
(1 mmol) of dpya were added. The colour of the solution changes
to malachite green. The heating and stirring were continued for
15 min. After cooling at r.t., the light green solution was filtered
without vacuum on a crystallization device. The slow evaporation
of the solution, controlled with a plastic film, yields 1.72 g (70 %)
of compound 3. This highly hydrated compound loss water very
easily and its formula was determined by the X-ray diffraction re-
sults, carried out a 100(2) K. Indeed, under an air-dray flow, most
of water content is lost before initiate the thermogravimetric analy-
sis. More well shaped crystals for X-ray diffraction purposes were
formed evaporating a solution having dpya in a 100 % of excess
(where very long needles crystals of dpya are also observed). This
compound loses most of its water very easily and decomposes with
the loss of remaining water at r.t.
Acknowledgements. Financial support from ERDF-EC, MEC-
Spain (Project CTQ2006-15329-C02/BQU) is acknowledged. ADM
thanks for an initiation research grant of the University of Granada
(Plan propio). DChL thanks CSIC-EU for an I3P postdoctoral
´
´
research contract. The project “Factorıa de Cristalizacion,
CONSOLIDER INGENIO-2010” provided X-ray structural facili-
ties for this work.
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Z. Anorg. Allg. Chem. 2007, 2658Ϫ2666