Chelation versus binudeation: Metal complex formation with the hexadentate all-cis-N1,N1-bis(2,4,6-trihydroxy-3,5-diaminocyclohexyl) ethane-l,2-diamine

Article abstract of DOI:10.1002/chem.200902552

The hexadentate ligand allcis-N¹,N²-bis(2,4,6- trihydroxy-3,5-diaminocyclohexy l)ethane-1,2-diamine (L^c) was synthesized in five steps with an overall yield of 39% by using [Ni(taci) ₂]SO₄·4H₂O as starting material (taci = l,3,5-triamino-l,3,5-trideoxy-c/sinositol). Crystal structures of [Na _0.5^- (H₆L^e](Bia)₆Cl _0.5·H₂O (1), [Ni(L^e)]C1 ₂·5H₂O (2), [Cu(L_e)](C1O ₄)·H₂O (3), [Zn(L^e)]CO ₃·7H₂O (4), [Co(L^e)](ClO₄)., (5c), and [Ga(H_-2L^e)]NO₃·2H₂O (6) are reported. The Na complex 1 exhibited a chain structure with the Na ⁺ cations bonded to three hydroxy groups of one taci subunit of the fully protonated H₆(L^e)⁶⁺ ligand. In 2, 3, 4, and 5 c, a mononuclear hexaamine coordination was found. In the Ga complex 6, a mononuclear hexadentate coordination was also observed, but the metal binding occurred through four amino groups and two alkoxo groups of the doubly deprotonated H_-2(L^e)^2-. The steric strain within the molecular framework of various M(L^e) isomers was analyzed by means of molecular mechanics calculations. The formation of complexes of L^e with Mn^II, Cu^II, Zn^II, and Cd^II was investigated in aqueous solution by using potentiometric and spectrophotometric titration experiments. Extended equilibrium systems comprising a large number of species were observed, such as [M(L ^e)]²⁺, protonated complexes [MH_z(L ^e)]^2+z: and oligonuclear aggregates. The pKa values of H₆(L^e)⁶⁺ (25 °C,μ = 0.10 M) were found to be 2.99, 5.63, 6.72, 7.38, 8.37, and 9.07, and the determined formation constants (log β) of [M(L^e)]²⁺ were 6.13(3) (Mn ^II), 20.11(2) (Cu^II), 13.60(2) (Zn^II), and 10.43(2) (Cd^II). The redox potentials (vs. NHE) of the [M(L ^e)]^3+,12+ couples were elucidated for Co (-0.38 V) and Ni (+0.90 V) by cyclic voltammetry

Full text of DOI:10.1002/chem.200902552

DOI: 10.1002/chem.200902552
Chelation versus Binucleation: Metal Complex Formation with the
Hexadentate all-cis-N1,N2-Bis(2,4,6-trihydroxy-3,5-
diaminocyclohexyl)ethane-1,2-diamine
Mark Bartholomꢀ, Sergej Gisbrecht, Stefan Stucky, Christian Neis,
Bernd Morgenstern, and Kaspar Hegetschweiler*[a]
Dedicated to Professor Hans-Jçrg Schneider on the occasion of his 75th birthday
Abstract: The hexadentate ligand all-
cis-N1,N2-bis(2,4,6-trihydroxy-3,5-di-
amine coordination was found. In the
Ga complex 6, a mononuclear hexa-
dentate coordination was also ob-
served, but the metal binding occurred
through four amino groups and two
alkoxo groups of the doubly deproton-
ated Hꢁ2(Le)2ꢁ. The steric strain within
the molecular framework of various
M(Le) isomers was analyzed by means
of molecular mechanics calculations.
The formation of complexes of Le with
MnII, CuII, ZnII, and CdII was investi-
gated in aqueous solution by using po-
tentiometric and spectrophotometric ti-
tration experiments. Extended equilib-
rium systems comprising large
number of species were observed, such
as [M(Le)]2+
protonated complexes
A
a
(Le) was synthesized in five steps with
an overall yield of 39% by using [Ni-
,
A
[MHz(Le)]2+z and oligonuclear aggre-
gates. The pKa values of H6(Le)6+
(258C, m=0.10m) were found to be
2.99, 5.63, 6.72, 7.38, 8.37, and 9.07, and
the determined formation constants
(log b) of [M(Le)]2+ were 6.13(3)
(MnII), 20.11(2) (CuII), 13.60(2) (ZnII),
and 10.43(2) (CdII). The redox poten-
tials (vs. NHE) of the [M(Le)]3+/2+ cou-
ples were elucidated for Co (ꢁ0.38 V)
and Ni (+0.90 V) by cyclic voltamme-
try.
(taci=1,3,5-triamino-1,3,5-trideoxy-cis-
inositol). Crystal structures of [Na0.5-
ACHTUNGTRENNUNG ACHTUNGTRENNUNG
(H6Le)](BiCl6)2Cl0.5·4H2O (1), [Ni(Le)]-
Cl2·5H2O (2), [Cu(Le)]
ACHTUNGTRENNUNG
[Zn(Le)]CO3·7H2O
A
(5c),
and
[GaACHTNUGTRENNNUG
NO3·2H2O (6) are reported. The Na
complex 1 exhibited a chain structure
with the Na+ cations bonded to three
hydroxy groups of one taci subunit of
the fully protonated H6(Le)6+ ligand. In
2, 3, 4, and 5c, a mononuclear hexa-
Keywords: amino alcohols · bridg-
ing ligands · chelates · coordination
modes · N,O ligands
Introduction
chelator that could either form mononuclear hexacoordinat-
ed or dinuclear bis-triscoordinated species. For the triden-
tate 1,4,7-triazacyclononane and its methylated derivative, a
variety of such coupled chelators has been described in the
literature, and a series of mono- and polynuclear metal com-
plexes of several transition metal cations have been charac-
terized.[4] To the best of our knowledge, this approach has
not widely been exploited for other cyclic triamine ligands.[5]
The linking of two all-cis-1,3,5-triaminocyclohexane (tach)
units by an ethylene bridge has been the main focus of a
PhD work.[6] However, the results have not been published
in a scientific journal. More recently, the preparation and
metal binding properties of two dimeric derivatives of the
related 1,3,5-triamino-1,3,5-trideoxy-cis-inositol (taci) have
been reported.[7] In these compounds, rigid and separating
linker units that prevent coordination of six donor atoms to
one metal cation were used.
Triamine ligands with a cyclic backbone that are restricted
to facial coordination have received much interest, owing to
possible applications in catalysis and in particular as mimet-
ics for the modeling of the active site of metalloproteins.[1–3]
The connection of two trinuclear units via a polymethylene
(CH2)n (nꢀ2) linker generates a potentially hexadentate
[a] Dr. M. Bartholomꢀ, Dipl.-Chem. S. Gisbrecht, Dr. S. Stucky,
Dr. C. Neis, Dr. B. Morgenstern, Prof. Dr. K. Hegetschweiler
Anorganische Chemie, Universitꢀt des Saarlandes
Postfach 15 11 50, 66041 Saarbrꢁcken (Germany)
Fax : (+49)681-302-2663
E-mail: hegetschweiler@mx.uni-saarland.de
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.200902552.
3326
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2010, 16, 3326 – 3340

FULL PAPER
Taci is a versatile ligand because of the high number of
functional groups, leading to an N,N,N (i), N,O,N (ii), O,N,O
(iii), or O,O,O (iv) coordination mode (Scheme 1a). In addi-
tion, the oxygen donors can bind a metal ion either as neu-
Scheme 1. Possible coordination modes of 1,3,5-triamino-1,3,5-trideoxy-
cis-inositol.
tral hydroxy groups or in the form of a zwitter ion, as
alkoxo groups (proton transfer from a coordinated oxygen
donor to a non-coordinated nitrogen donor, see Sche-
me 1b).[8] We expected a corresponding dimer bearing a suit-
able linker to be a particularly interesting metal complexing
agent. In view of the different possible interactions of a
metal ion with hydroxy and amino groups, it would be intri-
guing to elucidate whether a mononuclear chelation or a
polynuclear aggregation takes place for a particular metal
cation. CoIII complexes with a bis-taci-ligand have been pre-
pared recently in our laboratory by a template method.[9]
However, in these complexes, the two taci subunits were in-
Scheme 2. Synthetic pathway for Le.
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
terlinked by N=CH NH CH2 NH or NH CH2
C
(NH2)=N
moval of the protecting urea group requires harsh condi-
tions, such as reflux in an ethylene glycol/water mixture at
high NaOH concentration and high temperature. The bis-
taci ligand Le was isolated as a hydrated hydrochloride
Le·6HCl·2.5H2O and was fully characterized by elemental
bridges, which are sensitive to hydrolysis as soon as the
metal center is removed. Herein, we report on the synthesis
of a stable ethylene-bridged bis-taci derivative Le, and on its
complex formation with NaI, NiII, CuII, ZnII, CoIII, and GaIII
in the solid state and in solution.
1
analysis and spectroscopic methods. The H and 13C NMR
spectra of Hx(Le)x+ (0ꢂxꢂ6) all contain five resonances
(Figure 1), which is in agreement with symmetry considera-
1
Results and Discussion
tions.[11] Assignments were established by a series of H–1H
1
and H–13C correlation experiments. The vicinal JCꢁH cou-
Preparation and characterization of the ligand: In view of
the high number of potentially nucleophilic donor groups,
selective alkylation of taci is not trivial. We have previously
described the preparation of the urea derivative P3
(Scheme 2) of taci, which has only one free amino group.[10]
This derivative proved to be particularly suitable for the
coupling reaction required for the tethering of two taci
units. Since sufficient solubility of P3 is only achieved in
water and methanol, a reductive amination reaction with
glyoxal and sodium borohydride, which can be performed in
water, was used. The yield of this reaction was only moder-
ate (68%); however, the unreacted monomer P3 can be
readily separated from the dimer P4 and can be re-used for
the synthetic procedure without significant loss. The final re-
pling interactions H1/C5 and H5/C1 that were observed in
1
the H–13C long-range spectrum are an unambiguous proof
that the linking of the two taci fragments has indeed been
achieved.
The fully protonated H6(Le)6+ reacts as a hexaprotic acid,
and the corresponding pKa values have been determined by
potentiometric measurements (258C) in 0.1m KCl, 1.0m KCl
and 1.0m KNO3 (Table 1). It is known that highly protonat-
ed polyaza macrocycles can bind anions in solution.[12] How-
ever, the pKa values of H6(Le)6+ do not vary significantly for
the 1.0m KCl and 1.0m KNO3 medium, indicating that
H6(Le)6+···anion interactions are mostly negligible. The
marked dependence of the pKa values on the inert electro-
lyte concentration is in accordance with the well-known de-
Chem. Eur. J. 2010, 16, 3326 – 3340
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
3327

K. Hegetschweiler et al.
Table 1. Equilibrium constants for the stepwise protonation of Le (log
Ki)[a,b] at 258C in aqueous media. Values for Lmx, Lpx and taci (258C) are
shown for comparison.
Le[c]
1.0m
KCl
Lmx[d]
0.1m
NaCl
Lpx[d]
0.1m
NaCl
taci[e]
0.1m
KCl
0.1m
KCl
1.0m
KNO3
logK6
logK5
logK4
logK3
logK2
logK1
2.99
5.63
6.72
7.38
8.37
9.07
3.46
6.10
7.15
7.71
8.63
9.17
3.53
6.14
7.15
7.75
8.63
9.22
4.99
5.67
6.73
7.33
8.39
8.98
5.26
5.65
6.95
7.65
8.87
9.30
5.96
7.42
8.91
[a] Ki =[LHi]ꢃ[H]ꢁ1 ꢃ[LHiꢁ1 ꢁ1. [b] For the sake of comparability, the
]
values are given here as protonation constants Ki; the usual pKa values
are obtained by pKai =log Kn+1ꢁi with n=6 for Le, Lmx, Lpx and n=3 for
taci. [c] This work, estimated standard deviations are 0.01 or less. [d] Ref-
erence [7]. [e] Reference [31].
0.1m KCl) was performed (Figure 2). However, line broad-
ening or splitting of individual resonances have not been ob-
served. Moreover, significant coupling for C4/H2 and C2/H4
on one hand and non-observance of such coupling interac-
tions between C3/H1 and C1/H3 on the other hand
(Figure 1) were found for the entire pH range investigated.
All these observations indicate a single conformation for the
two cyclohexane rings with axial oxygen atoms and equato-
rial nitrogen atoms for the fully and partially protonated
and completely deprotonated species. A similar behavior
has already been found for the Hxtacix+ (0ꢂxꢂ3) mono-
mer.[13] This assignment is further supported by the observed
monotonic decrease of the chemical shifts with increasing
e
x+
ꢁ
Figure 1. Long range C H correlated 2D NMR spectrum of Hx(L ) (x
ꢃ5.6) at pH*=3.0.[43] The significant H2–C4 and H4–C2 coupling (black
arrows) and the non-observance of H1–C3 and H3–C1 coupling (circles)
indicate a chair conformation with axial hydroxy groups; the H1–C5 and
H5–C1 couplings (white arrows) prove the interlinking of the two taci
moieties by an ethylene bridge. The numbering scheme is given in the
structural representation on top. In this representation the observed
long-range C–H interactions indicative of the chair conformation with
axial hydroxy groups are highlighted as bold bonds.
pendence of activity coefficients
on the ionic strength. The fully
protonated H6(Le)6+ dimer is a
considerably stronger acid than
the H3taci3+ monomer and the
6+
dimeric derivatives
and H6A
diamino-cyclohexyl-2,4,6-triol-
(Lmx
H6ACHTUNRGTNEGNU )
CHTUNGTRENNUNG
(Lpx)6+ (Lmx: 1,3-bis(3,5-
amino-methyl)benzene,
Lpx:
1,4-bis(3,5-diamino-cyclohexyl-
2,4,6-triol-amino-methyl)ben-
zene) reported by Mancin
et al.,[7] for which the two taci
units are bridged by a meta- or
Figure 2. pH* dependence[43] of the 1H NMR resonances of Hx(Le)x+ (0ꢂxꢂ6). The points correspond to ex-
perimental values; the lines were calculated (minimization of S[dobsꢁdcalcd]2). The numbering scheme of
Figure 1 is used.
para-xylene
linker
unit
(Table 1). The low pKa1 of
H6(Le)6+ can obviously be ex-
plained by the increased elec-
trostatic repulsions, due to the
relatively short ethylene tether unit. Moreover, the small
DpKa values for the pKai values with iꢀ2 indicate an alter-
nating deprotonation of the two taci subunits in the dimeric
system. To further corroborate the deprotonation process
and to elucidate possible conformational changes upon de-
protonation, an NMR titration experiment in D2O (258C,
pH values. It is well established that protonation of a basic
ꢁ
site causes a deshielding of the neighboring C H protons,
and this effect increases with a decreasing number of bonds
between the basic site and the hydrogen atom under consid-
eration.[14–16] The particularly strong shift observed for H1
and H5 in the range of 2ꢂpHꢂ4 together with the negligi-
3328
www.chemeurj.org
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2010, 16, 3326 – 3340

N,O-Ligand Complexes
FULL PAPER
ble effect observed for H3 in this range, corroborates the
hypothesis of a first selective deprotonation step at the dia-
mino-ethane bridge.
Structure of the metal complexes—molecular mechanics cal-
culations: A large number of structures arise from the dif-
ferent possibilities to wrap the bis-taci molecule around a
metal cation. The different stereoisomers of a mononuclear,
hexacoordinated chelate [M(Le)]z+ can be classified in terms
of the coordination modes adopted by the two taci subunits
(Scheme 1). In addition, cis/trans or mer/fac diastereomers
must be considered for some of these combinations. Further
structural diversity arises from the inequivalence of the al-
kylated and non-alkylated nitrogen donors and the possibili-
ty to adopt an R or S configuration at the coordinated sec-
ondary-nitrogen donors. It is obvious that the ethylene
bridge is too short to span a trans-N-M-N arrangement.
Consequently, the corresponding structures, such as a trans-
bis-typeACHTUNGTRENNUNG(iii) isomer, were not further considered. For similar
reasons, the linking of two non-coordinated nitrogen donors,
as required for a bis-type(iv) structure, for example, was
also neglected. After exclusion of such highly strained struc-
tures, 15 possible isomers M1–M15 were identified (see
Table S1 in the Supporting Information). For some of them,
different conformations were accounted for, owing to a dis-
tinct folding of the chelate rings. Finally, different tautomers
were taken into account, owing to the possibility of adopting
zwitterionic forms. It is far from trivial to judge the stability
of all these species in terms of their free energy of formation
DG. This quantity would depend on solvation effects, the in-
trinsic affinity of the selected metal ion for either nitrogen
or oxygen donors, and on the steric strain within the coordi-
nation sphere and the ligand back bone. As a first screening,
we analyzed the steric contributions by means of molecular
mechanics calculations and chose CoIII as a representative of
relatively small metal cations with defined octahedral coor-
dination geometry. It is clear that large metal cations, such
as the trivalent lanthanides, could give significantly different
results. These calculations revealed a total of six low-energy
structures (Scheme 3), with the trans-bis-type(ii) structure
M6 being the least strained. The additional low-strain iso-
Scheme 3. Schematic representations of the six low-strain structures for a
mononuclear hexacoordinated [M(Le)]z+ complex. The reference sym-
bols, symmetry labels and relative total strain energies, calculated for the
corresponding CoIII complex, are listed. A more comprehensive compila-
tion of all 15 isomers M1–M15 can be found in Table S1 in the Support-
ing Information.
Crystal structure of the sodium complex: A crystal of the
sodium
complex
of
composition
[Na0.5ACHTUNGTRENNUNG
(H6Le)]-
mers have a bis-type(i), type(i)-type(ii), type(i)-type
G
ACHTUNGTRENNUNG
type(i)-type(iv), and type(ii)-type(iv) mode, thus yielding an
MN6, MN5O, MN4O2, MN3O3, or MN2O4 coordination. This
result shows that in terms of strain, the bis-taci ligand Le
should be able to form stable, hexacoordinated chelates
with both oxophilic (M14) and nitrophilic (M1) metal cat-
ions. For the bis-type(i) structure M1, the strain energy was
calculated for the parallel (lel) and oblique (ob) conforma-
tion, and it was found that the latter is slightly less stable
(5 kJmolꢁ1). The low amount of strain for the bis-type(ii)
structure M6 is remarkable, since this type of coordination
the growth of single crystals of the free hexaprotonated
ligand was envisaged. Inspection of the crystal structure of
this compound revealed, however, the incorporation of
some additional NaCl (Figure 3). The amount of only
0.5 equivalents is based on an examination of the electron
density, exhibiting a 50% occupancy of the Na and the cor-
responding Cl sites, and was further confirmed by an induc-
tively coupled plasma optical emission spectrometry (ICP-
OES) analysis (yielding an occupancy of 52(2)%). Although
additional NaCl (up to a 30-fold excess) was added to the
test solutions in further crystallization experiments, the
amount of incorporated NaCl did not increase. We explain
the partial incorporation of NaCl by the large electrostatic
repulsion interactions between Na+ and H6(Le)6+. The bind-
ing of Na+ to the axial hydroxy groups of a fully protonated
is not particularly favorable for the parent MCAHTUNGTRENNNUG
It is also noteworthy that a low-strain bis-typeCAHTUNGTRENNUNG
of [M(Le)]z+ (see M13 in Table S1 in the Supporting Infor-
mation) does not exist according to these calculations.
Chem. Eur. J. 2010, 16, 3326 – 3340
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
3329

K. Hegetschweiler et al.
after prolonged exposure to air.
[Co(Le)]3+ was prepared by
aerial oxidation of the CoII
complex. It was purified by
cation-exchange chromatogra-
phy and was isolated as a hy-
drated trichloride salt [Co-
(Le)]Cl3·5H2O (5a). For struc-
tural studies [Co(Le)]
ACTHNUTRGNEU[GN ZnCl4]Cl
(5b) was prepared, but the crys-
tal structure exhibited some sig-
nificant disorder for the ethyl-
ene bridge,[20] and a satisfactory
description could not be per-
formed.[21] The complex was
therefore converted into the
perchlorate salt [Co(Le)]
ACHTUNGTRENNUNG(ClO4)3
(5c)[22] that could be more suc-
cessfully used for
structure analysis.
a crystal
It has been previously shown
that [Ni
(taci)2]2+, [Cu(taci)2]2+
[Zn
(taci)2]2+ and [Co(taci)2]3+
G
R
,
Figure 3. Structure of the Na-complex 1: a) View of the [NaACTHNUTRGNEUNG
(H6Le)]7+ and [BiCl6]3ꢁ moieties with numbering
G
ACHTUNGTRENNUNG
scheme (displacement ellipsoids drawn for a 50% probability level); b) Section of the zigzag ··H6(Le)6+-Na+-
all adopt a bis-type(i) struc-
ture.[9,23–25] A corresponding he-
xaamine structure with Le
acting as a chelating hexaamine
ligand was also observed in the
crystal structures of 2, 3, 4, and
5c (Figure 4 and Figure S2 in
the Supporting Information). It
H6(Le)6+·· chain structure (carbon skeleton: stick model, N: blue, O: red, Na: green spheres). The C H-hydro-
ꢁ
gen atoms are omitted for clarity, other hydrogen atoms are shown as spheres of arbitrary size. Only half of
ꢁ
ꢁ
the Na positions are occupied. Selected bond lengths [ꢄ] and angles [8]: Na1 O2 2.298(5), Na1 O4 2.245(4),
ꢁ
Na1 O6 2.221(4); O6-Na1-O6A 83.3(2), O6-Na1-O4A 141.7(2), O6-Na1-O4 79.51(11), O4-Na1-O4A 93.3(2),
O6-Na1-O2 77.70(13), O6A-Na1-O2 129.9(2), O4-Na1-O2 79.16(12), O4A-Na1-O2 138.3(2), O2-Na1-O2A
80.0(2).
hexapositive H6(Le)6+ cation is indeed a remarkable and an
unexpected result. In the crystal structure, the H6(Le)6+
entity is placed on a crystallographic center of inversion,
generating the low-energy Ci-symmetric rotamer[11] (see
Chart S1 in the Supporting Information) with an anti-confor-
mation of the diaminoethane subunit. The Na+ cations are
bonded in a bis-type(iv) fashion. The hydroxy groups of the
two taci subunits are thus aligned in opposite directions,
forming a zig-zag chain of the type ··Na+-H6(Le)6+-Na+-
H6(Le)6+··. However, owing to the abovementioned disorder,
only one half of the Na positions are occupied in a statistical
fashion. The Na+ ions are located on a crystallographic
mirror plane and thus exhibit a coordination number of six
is noteworthy that 5c is the only example with an ob orien-
tation of the diaminoethane unit; the other hexaamine com-
plexes adopted a lel orientation. The three nitrogen donors
of each taci subunit define an approximately equilateral tri-
angle. For the parent bis-taci complexes with a bis-type(i)
structure a strictly trigonal antiprismatic structure has been
generally observed. However, of the corresponding hexa-
amine M(Le) complexes, only the CoIII complex 5c showed
an undistorted antiprismatic geometry. For the other M(Le)
complexes, some twisting towards a trigonal prismatic form
was noted. The twist angle f, describing the degree of dis-
tortion between a pure trigonal antiprismatic (f=608) and a
pure trigonal prismatic (f=08) coordination geometry,[26]
was 50.28 for the Ni complex 2, 48.98 for the Cu complex 3,
and 48.68 for the Zn complex 4. This observation has to be
related with the geometry of the diaminoethane bridge. In
contrast to the Na complex where an anti conformation was
observed, all the hexaamine complexes exhibit a synclinal
conformation with torsion N-C-C-N-angles of 56.78 (2),
60.88 (3), 60.38 (4) and 39.38 (5c). The last deviates signifi-
cantly from an ideal gauche geometry. These observations
indicate that the tethering of two taci fragments by an N-
CH2-CH2-N bridge generates some additional strain that can
be partially compensated, either by twisting of the two taci
subunits towards a trigonal prism or by twisting the two
NCH2 fragments in the bridge from an ideal gauche towards
ꢁ
with a strictly trigonal prismatic geometry and average Na
O distance of 2.255 ꢄ. This value is slightly shorter than the
one usually observed for a hexacoordinate NaI.[18] Confor-
mation analysis reveals an almost ideal chair for the cyclo-
hexane ring (see Table S2 in the Supporting Information).[19]
The molecular structure of the NiII, CuII, ZnII, and CoIII
complex: Crystalline samples of [Ni(Le)]Cl2·5H2O (2) and
[Cu(Le)]
ACHTUNGTRENNUNG(ClO4)2·H2O (3) were obtained by the simple com-
bination of aqueous solutions of the free ligand and the cor-
responding metal salt followed by slow evaporation of the
solvent. Single crystals of [Zn(Le)]CO3·7H2O (4) were
grown from an aqueous alkaline [Zn(Le)]
ACTHUNGTRNEUNG(NO3)2 solution
3330
www.chemeurj.org
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2010, 16, 3326 – 3340

N,O-Ligand Complexes
FULL PAPER
decay in acidic media (vide infra), the inert hexaamine
structure of [Co(Le)]3+ is, as expected, unaffected for pro-
longed periods of time even in 6m HCl.
Molecular structure of [Ga
colorless complex
GaIII
(Hꢁ2Le)]NO3·2H2O (6) were obtained by slow evaporation
of an aqueous solution that was obtained by the simple com-
bination of Ga
(NO3)3 and Le. Although the ligand Le coordi-
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
nates as the doubly deprotonated anion (Hꢁ2Le)2ꢁ, addition
of base to the reaction mixture was not necessary. A single-
crystal X-ray analysis revealed a bis-type(ii) structure of the
complex cation (M6 in Scheme 3) with a trans-GaN4O2 coor-
dination (Figure 5). In the crystal structure, the [Ga-
Figure 4. Molecular structures of a) [Ni(Le)]2+ and b) [Co(Le)]3+ of 2 and
5c, respectively. Displacement ellipsoids are drawn for a 50% probability
level. Hydrogen atoms are omitted for clarity. The drawings show the dif-
ferent orientation of the ethylene bridge (lel for Ni, ob for Co) in the two
complexes. Corresponding pictures of the Cu and Zn complex are provid-
ed in Figure S2 in the Supporting Information. Selected bond lengths [ꢄ]
ꢁ
ꢁ
ꢁ
and angles [8], Ni-complex 2: Ni1 N13 2.091(1), Ni1 N4 2.103(1), Ni1
ꢁ
ꢁ
ꢁ
N2 2.115(1), Ni1 N9 2.130(1), Ni1 N11 2.144(2), Ni1 N6 2.161(2); N13-
Ni1-N4 168.49(5), N13-Ni1-N2 97.27(6), N4-Ni1-N2 92.06(5), N13-Ni1-N9
88.18(5), N4-Ni1-N9 83.36(5), N2-Ni1-N9 171.51(5), N13-Ni1-N11
91.82(6), N4-Ni1-N11 95.19(6), N2-Ni1-N11 88.34(6), N9-Ni1-N11
84.98(6), N13-Ni1-N6 88.77(6), N4-Ni1-N6 85.14(6), N2-Ni1-N6 86.08(5),
ꢁ
N9-Ni1-N6 100.59(5), N11-Ni1-N6 174.42(5); Co-complex 5c: Co1 N3
ꢁ
ꢁ
1.966(4), Co1 N1 1.969(4), Co1 N2 1.987(4); N1-Co1-N2 90.5(2), N3-
Co1-N3A 180.0, N3-Co1-N1A 90.0(2), N3-Co1-N1 90.0(2), N1A-Co1-N1
180.0, N3-Co1-N2 88.5(2), N3A-Co1-N2 91.5(2), N1A-Co1-N2 89.5(2),
N2-Co1-N2A 180.0.
Figure 5. Molecular structure of [GaACTHNUTRGNEUNG
(Hꢁ2Le)]+ of 6. Displacement ellip-
ꢁ
ꢁ
soids are drawn for a 30% probability level. H O and H N hydrogen
ꢁ
atoms are shown as spheres of arbitrary size; H C hydrogen atoms are
ꢁ
omitted for clarity. Selected bond lengths [ꢄ] and angles [8]: Ga1 O11
1.942(3), Ga1 O12 1.947(4), Ga1 N11 2.119(4), Ga1 N12 2.085(4),
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
an eclipsed orientation. The observed structures can be re-
Ga1 N31 2.077(4), Ga1 N32 2.061(4); O11-Ga1-O12 177.2(2), O11-Ga1-
N32 97.8(2), O12-Ga1-N32 83.5(2), O11-Ga1-N31 84.2(2), O12-Ga1-N31
98.0(2), N32-Ga1-N31 102.9(2), O11-Ga1-N12 93.9(2), O12-Ga1-N12
83.7(2), N32-Ga1-N12 86.2(2), N31-Ga1-N12 170.9(2), O11-Ga1-N11
83.0(2), O12-Ga1-N11 95.4(2), N32-Ga1-N11 171.2(2), N31-Ga1-N11
86.0(2), N12-Ga1-N11 85.0(2).
garded as
a compromise between these two effects.
[Co(Le)]3+ with its high ligand-field stabilization exhibits a
lower amount of distortion in the coordination sphere, but
more twisting in the ligand backbone. For ZnII, which is
devoid of a ligand-field effect, the geometry of the diamino-
ethane bridge is almost ideal, whereas the coordination ge-
ometry is somewhat distorted towards a trigonal prism.[27]
A
chair conformation was observed for the cyclohexane rings
of all hexaamine M(Le)-complexes. However, for 2, 3, and 4,
a slight but significant distortion towards a half-boat (for
one of the rings) or towards a half-chair (for the other ring)
was noted (see Table S2 in the Supporting Information).[19]
Metal–nitrogen bond lengths are as expected.[9,24,25,28]
[Cu(Le)]2+ exhibited the usual tetragonally elongated 4+2
Jahn—Teller geometry.[29] In solution, the hexaamine struc-
ture of these complexes was retained as indicated by the
UV/Vis parameters for [Co(Le)]3+ (lmax =340 and 471 nm),
[Ni(Le)]2+ (lmax =321, 511 and 799 nm) and [Cu(Le)]2+
(Hꢁ2Le)]+ cation is placed on a general position and is thus
ACHTUNGTRENNUNG
devoid of any crystallographically imposed symmetry. How-
ever, deviation from C2 symmetry is not significant; a
pseudo twofold rotational axis is running through the Ga
center and the center of the ethylene bridge. It is notewor-
thy that the parent bis-taci complex [GaACTHNUTRGNEUNG
(taci)2]3+ adopted a
type(i)-type(iv) structure with a mixed GaN3O3 coordina-
tion.[31] As shown in Scheme 3, the corresponding zwitterion-
ic bis-adamantane-[Ga(Le)]3+ isomer M10 would also
belong to the low-strain structures. However, the bis-type(ii)
coordination M6 is even less strained, and deprotonation of
the two oxygen donors would result in a further release of
strain. The adoption of this low-strain structure is apparently
one of the driving forces for this particular geometry. The
(lmax =603 nm), and the NMR characteristics of [Co(Le)]3+
.
The 13C NMR and the 1H NMR spectra exhibited six and
eight resonances,[30] respectively, with two separate signals
for the CH2 hydrogen atoms of the ethylene bridge, indicat-
ing a chiral C2 symmetry for the solution structure. In con-
trast to the labile NiII, CuII and ZnII complexes, that readily
ꢁ
ꢁ
Ga N and Ga O bond distances in [Ga
AHCTUNGTRENNUNG
(Hꢁ2Le)]+ and [Ga-
ACHTUNGTRENNUNG
(taci)2]3+ are in close agreement.
Chem. Eur. J. 2010, 16, 3326 – 3340
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
3331

K. Hegetschweiler et al.
Hydrogen bonding: Owing to the high number of amino
and hydroxy groups of the ligand Le, hydrogen bonding is
one of the principal structural motives in the crystal struc-
ꢁ
tures of 1–6. The N H hydrogen atoms of the ammonium
ꢁ
groups of 1 and the N H hydrogen atoms of the coordinat-
ed amino groups of 2–6 generally act as hydrogen donors;
also the coordinated hydroxy groups of 1 serve exclusively
as hydrogen donors, whereas the non-coordinated hydroxy
groups of 2–6, as well as the water molecules, serve as hy-
drogen donors and hydrogen acceptors. The two coordinated
alkoxo oxygen groups of 6 act as strong hydrogen acceptors,
and the non-coordinated primary amino groups of 6 accept
ꢁ
an N H hydrogen atom of the coordinated amino groups by
intra-molecular hydrogen bonding. This type of intra-molec-
ular hydrogen bond formation is well established for the
type(ii) coordination mode.[9,17] Some of the counter anions
are also involved as hydrogen acceptors in the hydrogen
bonding networks. A complete overview of the explicit hy-
drogen bond interactions in 1–6 is given as supporting infor-
mation (Table S3).
Formation constants: The formation constants of Le with
MnII, CuII, ZnII, and CdII were determined in aqueous media
by potentiometric titrations. For all metal cations, a large va-
riety of species of general composition [Mx(Le)yHz]2x+z had
to be taken into account. As a matter of fact, the selection
of a proper and unambiguous speciation model proved to be
difficult, because the analysis of one single titration curve
often allowed the assignment of more than one set of spe-
cies with a similar goodness of fit. In terms of a case study,
we will describe here the treatment of the CuII-Le system in
detail. This system is particularly suited for such an investi-
gation, since the potentiometric study can be combined with
spectrophotometric measurements. For this purpose, the ti-
tration cell was equipped with an immersion probe, connect-
ed to a diode array spectrophotometer, allowing the record-
ing of spectra during the titration (Figure 6a). The UV/Vis
data of the blue CuII-complexes provided valuable inde-
pendent information that could be used to corroborate the
validity and accuracy of the selected model (Table 2). The
additional data also allowed the calculation of individual
spectra (Figure 6b) for each species, which could be used
for structural assignments (Scheme 4).[32] In a first step, a set
of 12 titration curves were used for the evaluation with
sample solutions having total Cu to total ligand ratios of 1:1
and 2:1. In the 2:1 solutions, dinuclear species
Figure 6. a) Spectral changes for the CuII-Le system during a titration ex-
periment with equimolar concentrations (10 mm) of total Cu and total Le
(1m KCl, 258C). b) The calculated spectra for the individual species of
composition CuxLe Hz (labeled as xyz). The spectrum of CuII was mea-
y
sured separately and kept constant in the refinement.
Table 2. Summary of the evaluated formation constants of the CuII-(Le)
system (258C, inert electrolyte as indicated) with estimated uncertainties
(3s) in parentheses. Values are shown for the evaluation of the potentio-
metric (pot) and spectrophotometric (spec) titrations.
[a]
logbxyz
0.1m KCl
pot
1.0m KCl
pot
1.0m KNO3
spec[b]
spec[c]
pot
logb110
logb111
logb112
logb113
logb11ꢁ1
logb210
logb21ꢁ1
logb21ꢁ2
logb21ꢁ3
20.11(2)
25.64(2)
30.46(1)
33.23(6)
9.86(3)
26.09(2)
19.82(3)
13.16(2)
2.11(3)
19.85(2)
25.72(2)
31.04(2)
33.95(6)
9.36(3)
19.80(2)
25.57(2)
30.97(2)
34.05(4)
9.41(3)
20.56(1)
26.36(1)
31.56(1)
34.30(3)
30.49(2)
A
pH 5, and a first estimate for their formation constants
could be obtained. The titration experiments with the 1:1
solutions were evaluated with the previously determined
constants of the dinuclear species treated as fixed values,
26.12(4)
19.54(4)
13.52(6)
26.23(5)
26.30(2)
26.42(7)
yielding
a set of constants for mononuclear species
[a] bxyz =[Cux(Le)yHz]ꢃ[Cu]ꢁx ꢃ[(Le)]ꢁy ꢃ[H]ꢁz
. [b] Measured for total
[Cu(Le)Hz]2+z (ꢁ1ꢂzꢂ3). Finally, all 12 titration curves
were combined into one single data set for a last concluding
evaluation. In this final evaluation the formation constants
of all metal containing species were simultaneously refined.
Additional titrations with sample solutions where the ligand
Cu=2 mm, total Le =1 mm. [c] Measured for total Cu and total Le =
10 mm.
was present in excess have then been performed. They were
consistent with the previous results and did not provide evi-
3332
www.chemeurj.org
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2010, 16, 3326 – 3340

N,O-Ligand Complexes
FULL PAPER
Figure 7. pH-dependent species distribution plot for the CuII-Le system
a) with equal total concentrations (1 mm) of Cu and Le, b) with excess Cu
(total Le =1 mm, total Cu=2 mm). The distributions were calculated
using the formation constants listed in Table 2 (0.1m KCl). The percent-
age refers to the abundance of each species; that is, the amount of Cu is
twice the one shown for dinuclear complexes. Charges are omitted for
clarity; possible structures of the CuII complexes are shown in Scheme 4.
618 nm). The uncharged doubly deprotonated [Cu(Le)Hꢁ2]
is only observed as a minor species at high pH (the pKa of
[Cu(Le)Hꢁ1]+ is>12). Only one dinuclear complex,
[Cu2(Le)]4+ (lmax =649 nm), appears to a minor degree
around pH 4. Based on the lmax value of 675 nm, we as-
signed a mono-type(i) structure to the triply protonated
[Cu(Le)H3]5+ with the other taci subunit remaining proton-
ated;[16,32] this assignment is in agreement with lmax =683
and 658 nm observed for the corresponding facial CuII-tria-
Scheme 4. Possible structures for the various CuII complexes formed in
aqueous solution. Only the Cu-Le moieties are depicted, additional water
molecules which may be coordinated to the Cu centers are omitted for
clarity.
mine chromophore of [CuACTHNUGTRENNUG ACHUTNGTRENNGUN
(tach)]2+ and [Cu(tacn)]2+, re-
spectively.[6,33] The observed monotonic shift of lmax to lower
values indicates that the progressive deprotonation of
[Cu(Le)H3]5+ is coupled with a coordination of further nitro-
gen donors. Such a conclusion is also supported by the rela-
tively low values of the apparent pKa values of [Cu(Le)H3]5+
(2.77, 4.82, 5.53) that are lower than the pKa values of the
dence for the formation of further species with more than
one ligand entity (y>1).
Species distribution plots for the CuII-Le system are
shown in Figure 7. For equimolar concentrations of Le and
CuII, complex formation starts around pH 3. At this pH a
small amount of the triply protonated [Cu(Le)H3]5+ (lmax
=
fully protonated H6(Le)6+. It should be noted that a lmax
=
675 nm) is formed. Stepwise deprotonation leads to
645 nm, observed for [Cu(Le)H2]4+ (which will receive a tet-
raamine coordination according to these considerations), is
only compatible with a cis-CuN4O2 configuration; the trans
[Cu(Le)H2]4+ (lmax =645 nm), [Cu(Le)H]3+ (lmax =626 nm),
[Cu(Le)]2+ (lmax =602 nm), and [Cu(Le)Hꢁ1]+ (lmax
=
Chem. Eur. J. 2010, 16, 3326 – 3340
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
3333

K. Hegetschweiler et al.
configuration with four nitrogen donors in the equatorial
positions of an elongated octahedron would absorb in the
range of 540–580 nm.[32,34,35] A bis-type(ii) mode (i.e. a
doubly protonated structure of M6 in Scheme 3) can thus be
tional hydroxy groups. However, the electron-withdrawing
effect also reduces basicity, and in terms of conditional sta-
bility, Le is an effective chelator in slightly acidic and neutral
media.
excluded for this particular complex. The value of lmax
=
A final comment should be made on the difference of the
formation constants in a 1.0m KCl and 1.0m KNO3 medium.
In the chloride medium, the formation constants are gener-
ally smaller, which is indicative of chloro complex forma-
602 nm, calculated for [Cu(Le)]2+ is in close agreement with
lmax =603 nm observed for a solution of a crystalline sample
of 3. [Cu
ACHTUNGTRENNUNG
(tach)2]2+ absorbs at lmax =635 nm and [Cu-
ꢁ
T
tion. Assuming negligible NO3 ···Cu2+ interactions, we have
Obviously, the presence of two secondary nitrogen donors
results in some increase of the ligand field. The dinuclear
[Cu2(Le)]4+ exhibited a lmax of 649 nm. For the proposed
facial type(i) coordination, this value is relatively low. It
compares, however, very well with lmax =647 nm, reported
by Mancin et al. for a related dinuclear species of the bis-
taci ligands Lmx and Lpx , which have a meta- or para-xylene
linker, respectively.[7] Above pH 5, deprotonation of
[Cu2(Le)]4+ yields [Cu2(Le)Hꢁ1]3+ and [Cu2(Le)Hꢁ2]2+ (Fig-
ure 7b). The apparent pKa values are 6.27(3) and 6.66(3).
The relatively low numbers (particularly for the second de-
protonation step) can be explained by an additional stabili-
zation due to Cu-OH-Cu bridging (Scheme 4).[7]
calculated a value of 0.58(2) for log K of the reaction Cu2+
ACTHNUTRGNEUNG
+Clꢁ =CuCl+. For the series [Cu(HxLe)]2+x +Clꢁ =[Cu-
A
x=2, +0.35(7) for x=3, and +1.34(5) for the dinuclear spe-
cies, that is, for [Cu2(Le)]4+ +Clꢁ =[Cu2(Le)Cl]3+. Interest-
ingly, no significant chloride binding was observed for
ACTHNUTRGNEUNG
[Cu(Le)]2+ and [Cu(HLe)]3+, an observation that further
supports the hexacoordinated structures shown in Scheme 4.
The significant chloride binding of [Cu
AHCTUNGTRENNUNG
evidence for an open rather than a closed structure of this
particular complex (see box in Scheme 4).
Complex formation of Le with MnII is generally weak. Sig-
nificant metal binding was only observed above pH 7. At
these conditions, the sample solutions proved to be highly
sensitive towards oxidation, especially when the metal
cation was present in excess. The formation constant of
[Mn(Le)]2+ could be established (log b=6.1, see Table 3),
but an unambiguous verification of dinuclear species, such
as [Mn2(Le)]4+, was not possible. Protonated species of com-
position [Mn(Le)Hx]2+x play, if at all, only a minor role. The
weak tendency of Le to bind to MnII coincides with the low
stability of the corresponding taci complexes (log b110 =4.0,
log b120 <7).[38]
The formation constant of [Cu(Le)]2+ (log b=20.11) is
only slightly higher than the formation constant of the
parent [CuACHTUNGTRENNUNG
(taci)2]2+ (log b2 =18.79).[24] Thus it appears that
the chelate effect of the hexadentate ligand is partially out-
weighed by the additional strain within the CuLe-structure.
Comparison with other hexaamine analogues confirmed that
the [Cu(Le)]2+-complex is not of particularly high stability
(Table 3). This is true not only for the mononuclear, but also
In aqueous solutions containing an equimolar ratio of ZnII
and Le, the mononuclear [Zn(Le)]2+ is the predominant spe-
cies around pH 7 (log b110 =13.6). At lower pH, a series of
Table 3. Formation constants log bML[a] for the bis-taci ligand (Le) in com-
parison with some other hexaamine ligands previously reported in the lit-
erature.[b,c]
MnII
CuII
ZnII
CdII
e
ꢁ
protonation products [Zn
(HxLe)]2+x is formed. The Cd L -
Le[d]
6.13(3)
–
–
20.11(2)
–
–
13.60(2)
7.75
8.05
10.43(2)
–
–
system behaves similarly (log b110 =10.4). A complete list of
the evaluated formation constants together with some struc-
tural representations of the complexes are provided in the
Supporting Information (Table S4 and Chart S2). It is note-
worthy that for ZnII and CdII, the maximum amount of pro-
tonation (x=5) is higher than for CuII (x=3). In [M-
Lmx[e]
Lpx[e]
penten[f]
3,2,2,2,3-hex[g]
3,3,2,3,3-hex[h]
[18]aneN6[i]
bis-tacn[j]
9.24
–
–
10.50
–
22.15
21.74
19.35
24.40
27.82
16.15
14.45
10.53
18.70
–
16.15
–
9.46
18.80
–
AHCTUNGTRENNUNG
(H5Le)]7+ only one amino group can be coordinated to the
[a] bML =[ML]ꢃ[M]ꢁ1 ꢃ[L]ꢁ1. [b] Reference [37], unless otherwise noted.
[c] 258C, m=0.10m, unless otherwise noted. [d] This work; estimated un-
certainties (3s) in parentheses. [e] Systematic names: see section: prepa-
ration and characterization of the ligand, data from reference [7]. [f] 4,7-
Bis(2-aminoethyl)-1,4,7,10-tetraazadecane. [g] 1,5,8,11,14,18-Hexaazaoc-
tadecane; 258C, 0.15m NaClO4. [h] 1,5,9,12,16,20-Hexaazaicosane; 258C,
0.15m NaClO4. [i] 1,4,7,10,13,16-Hexaazacyclooctadecane. [j] 1,2-Di(1,4,7-
triazonan-1-yl)ethane.
metal ion, and for electrostatic reasons, the H5(Le)5+ unit
probably adopts a chair conformation with equatorial nitro-
gen atoms. Additional coordination of the metal cation to
two axial hydroxy groups by a typeACTHNUGTRNEUNG(iii) binding is feasible.
The individual formation constants log Ki of 2.27 (Zn) and
2.67 (Cd), expressed by the reaction H5(Le)5+ +M2+ =M-
AHCTUNGTERNNUNG AHCTUNGTRENNUNG ]
(H5Le)7+, Ki =[M(H5Le)7+]ꢃ[H5(Le)5+ ꢁ1 ꢃ[M2+]ꢁ1, compare
well with the stability (log b1) of the corresponding mono-
ammine complexes M
(NH3)2+, which are reported to be 2.3
and 2.62, respectively.[39] In the course of deprotonation of
(H5Le)7+, a chair conversion must occur and this confor-
mational change possibly explains the non-observance of the
partially protonated complexes [Zn
(H4Le)]6+ and [Cd-
(H2Le)]4+. A further interesting difference to the CuII-Le-
AHCTUNGTRENNUNG
[36]
for dinuclear species, such as [Cu2(Le)]4+
.
The comparably
low stability can thus not only be attributed to the strain in-
troduced by the ethylene bridge. It also seems to be a result
of the reduced nucleophilicity of the amino groups of Le,
caused by the electron-withdrawing properties of the addi-
MACHTUNGTRENNUNG
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
3334
www.chemeurj.org
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2010, 16, 3326 – 3340

N,O-Ligand Complexes
FULL PAPER
system is the non-observance of the dinuclear [M2(Le)]4+
.
log bMLe ¼ 1:73ð1Þ ꢄ log bMðtaciÞꢁ0:8ð1Þ
ð1Þ
ð2Þ
ð3Þ
ð4Þ
Titration experiments with a total metal to total ligand ratio
of 2:1 unambiguously established that ZnII and CdII do not
form such a species under the conditions employed (see Fig-
ure S3 in the Supporting Information). In solutions with an
excess of the metal cation, we observed, however, formation
of trinuclear complexes of composition [M3(Le)2]6+ together
with corresponding deprotonation products. Moreover, if
the ligand is applied in excess, the formation of additional
components can be observed. For Zn, we have not yet suc-
ceeded in establishing a conclusive model for explaining the
experimental data. However, for Cd the potentiometric data
are in excellent agreement, assuming formation of a series
of dinuclear species of composition [Cd2(Le)3Hx]4+x (see
Table S4 and Chart S2 in the Supporting Information).
log bMLe ¼ 1:24ð1Þ ꢄ log bMðtmcaÞ ꢁ3:1ð1Þ
2
log bMLe ¼ 1:69ð4Þ ꢄ log bMðtmcaÞꢁ4:5ð4Þ
log bMLe ¼ 1:24ð3Þ ꢄ log bMðtmcaÞ ꢁ9:2ð7Þ
2
Redox properties: The redox behavior of the Mn, Ni and
Co complexes was investigated in aqueous media by cyclic
voltammetry. The free ligand Le was found to be redox-inac-
tive over the entire pH range. Cyclic voltammograms of
[Ni(Le)]3+/2+ and [Co(Le)]3+/2+ exhibited quasi-reversible
redox behavior in the range 7<pH<10 with redox poten-
tials of +0.90 V and ꢁ0.38 V vs. NHE, respectively. Similar
potentials have been observed for [Ni
(tmca)2]3+/2+ (both 0.97 V), [Co
(taci)2]3+/2+ (ꢁ0.39 V), and
[Co
(taci)2]3+/2+ and [Ni-
ACHTUNGTRENNUNG
Our findings for the ZnII–Le system differ from the obser-
vations of Mancin et al., who observed mononuclear [Zn-
A
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
ACHTUNGTRENNUNG ACHTUNGTRENNUNG
(Lmx)]2+ and [Zn(Lpx)]2+ complexes with a remarkably low
not depend on pH, but, in acidic solutions, an irreversible
reaction was observed attributed to the decay of the com-
plexes in the divalent stage. The peak separations were 76
and 68 mV, respectively (pH 9, scan rate of 10 mVsꢁ1). A
strictly linear dependence of the peak current on the square
root of the scan rate was observed for both systems, as ex-
pected for a diffusion-controlled process. All these observa-
tions confirm the presence of a mononuclear hexaamine
complex in solution, as observed in the corresponding crys-
tal structures 2 and 5c. Also the Mn-Le system displayed
redox activity in aqueous alkaline media. However, cyclic
voltammetry exhibited a strongly irreversible behavior and
an unambiguous assignment of the corresponding electron
transfer processes was not possible.
stability of log b110 =7.75 and 8.05, respectively.[7] These
values rather correspond to log b110 =8.40, observed for [Zn-
[24]
(taci)]2+
,
thus indicating tridentate coordination. Obvious-
ly the rigidity of the xylene bridge impedes a hexadentate
chelation of Lmx and Lpx. Mancin et al. also reported forma-
tion of the dinuclear [Zn2ACHTNUTRGENNUG 2HCATUNGTRENNUGN
(Lmx)]4+ and [Zn (Lpx)]4+, whereas
in our study such species could not be observed (vide
supra). This latter difference between the ethylene- and the
xylene-bridged ligands is obviously less trivial.
The lower stability of [Cd(Le)]2+compared to [Zn(Le)]2+
is in accordance with the behavior of the corresponding taci
complexes.[40] In general, the stability of MLe complexes can
be well reproduced by linear free energy relations, such as
Equations (1)–(4) with correlation coefficients of 0.999 or
higher (Figure 8).
Conclusion and Outlook
The potentially hexadentate, ethylene-bridged bis-taci ligand
Le offers the possibility of mononuclear hexacoordinate che-
lation or metal bridging. In this paper, we provided ample
evidence for both types of interactions. Formation of mono-
nuclear chelates in the solid state could be characterized for
CoIII, NiII, CuII, ZnII, and GaIII by crystal-structure analyses.
An extended solution study verified that such species were
also formed in dilute solution, provided that an equimolar
ligand to metal ratio is applied. However, as exemplified for
CuII, the chemistry of such solutions is much more diverse,
comprising formation of a series of partially protonated
[Cu(Le)Hx]2+x species in equilibrium with the dinuclear
[Cu2(Le)]4+. If the metal cation is present in excess, the di-
nuclear [Cu2(Le)]4+ becomes the predominant species. We
tentatively assign binding of each of the two CuII centers to
one of the two taci subunits resulting in a fac-CuN3-coordi-
nation. The dinuclear as well as the protonated species de-
serve additional interest as possible catalysts for the hydrol-
ysis of biopolymers.[7,41] For ZnII and CdII formation of a
[M2(Le)]4+ dimer was not observed. The two cations form,
however, trimeric aggregates, which can be regarded as a
Figure 8. Graphical representations of the Linear-free-energy relations
log b
A
R
the Equations (1)ꢁ(4) discussed in the text (taci=1,3,5-triamino-1,3,5-tri-
deoxy-cis-inositol, tmca=all-cis-2,4,6-trimethoxycyclohexane-1,3,5-tria-
mine). The formation constants of the taci and tmca complexes are from
references [13], [24], [38], and [40].
Chem. Eur. J. 2010, 16, 3326 – 3340
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
3335

K. Hegetschweiler et al.
(13.4 mmol, 78%). 1H NMR (CDCl3): d=2.92 (s, 6H), 3.19 (t, J=4 Hz,
3H), 3.77 (t, J=4 Hz, 3H), 4.67 (s, 6H), 7.37 ppm (m, 15H); 13C NMR
(CDCl3): d=51.8, 70.3, 75.1, 127.7, 127.8, 128.4, 137.8 ppm; IR: n˜ =608,
641, 697, 734, 910, 1029, 1070, 1209, 1286, 1391, 1453, 1495, 1585, 2873,
3027, 3386 cmꢁ1; elemental analysis calcd (%) for C27H33N3O3 (447.57): C
72.46, H 7.43, N 9.39; found: C 72.10, H 7.37, N 9.27.
starting point for the formation of 1D polymers. The binding
of more than one metal cation to Le also opens interesting
possibilities for the design of extended frameworks in the
solid state.[42] The Na complex 1 is a first example for this
type of structure. Moreover, this complex is remarkable be-
cause of the coordination of the Na+ ion to the fully hexa-
protonated H6(Le)6+. Considering the significant electrostatic
repulsion between the cation and the ligand, the formation
of such a structure is far from trivial. In this sodium com-
plex, the cation is bonded to the hydroxy groups of Le, and
the interplay O versus N coordination is a further fascinat-
ing aspect of this molecule. As demonstrated by the molecu-
lar mechanics study, the question which type of structure
will be adopted by a metal cation may be less evident than
expected at a first glance. Late transition metal cations with
their high affinity for nitrogen donors exhibit a hexaamine
structure in their mononuclear stage. However, the Ga com-
plex 6 is an example which demonstrates that further coor-
dination modes must also be taken into account. The ob-
served M6 structure also demonstrates that with regard to
N-[6,8,9-Tris(benzyloxy)-3-oxo-2,4-diazabicycloACTHNUTRGNEUG[N 3.3.1]non-7-yl]acetamide
(P2):[10] The triamine P1 (9.0 g, 20 mmol) was dissolved in CHCl3
(120 mL, purified prior to use by column chromatography over alumina
to remove traces of EtOH). Under an atmosphere of N2, 1,1’-carbonyldi-
imidazole (3.36 g, 21 mmol) was added. The solution was stirred for
30 min, and AcOAc (5.82 mL, 61.6 mmol) was added. The solution was
stirred for another 120 min. The solvent was then removed under re-
duced pressure and the residue was dissolved in CH2Cl2 (50 mL). The or-
ganic layer was washed twice with 1m NaOH (100 mL) and 1m HCl
(100 mL) and was then evaporated to dryness. The solid was dried in
vacuo for 24 h. It was dissolved in CH2Cl2 (50 mL) and purified by
column chromatography (SiO2, EtOAc/MeOH 8:1). The solvent of the
main fraction was then removed under reduced pressure and the result-
ing solid was dried in vacuo to yield a white voluminous powder of the
amide P2 (9.85 g, 19.1 mmol, 96%). 1H NMR (CDCl3): d=1.96 (s, 3H),
3.29 (m, 3H), 3.76 (m’, 2H), 4.42 (d, J=12 Hz, 2H), 4.46 (s, 2H), 4.68 (d,
J=12 Hz, 2H), 5.15 (m, 1H), 5.97 (d, J=10 Hz; NH), 6.62 (m’, 2NH),
7.21–7.34 ppm (m, 15H); 13C NMR (CDCl3): d=23.5, 45.0, 52.9, 65.5,
70.0, 70.9, 74.6, 127.7, 127.8, 128.0, 128.2, 128.6, 128.7, 136.5, 137.1, 156.4,
171.7 ppm; IR: n˜ =601, 696, 869, 912, 1025, 1074, 1228, 1276, 1312, 1360,
1453, 1495, 1667, 2358, 2866, 3061, 3325, 3447 cmꢁ1; elemental analysis
calcd (%) for C30H33N3O5 (515.60): C 69.88, H 6.45, N 8.15; found: C
68.94, H 6.48, N 7.74.
the coordination mode, a simple extrapolation from M
ACHTUNGERTN(NUNG taci)2
to MLe is not always conclusive.
7-Amino-6,8,9-trihydroxy-2,4-diazabicycloACTHNUTRGNE[NUG 3.3.1]nonan-3-one (P3): The
Experimental Section
amide P2 (10 g, 19.4 mmol) was dissolved in 6m aqueous HCl (500 mL)
and refluxed for 3 h. The reaction mixture was concentrated to a total
volume of 100 mL and allowed to cool to 258C. The resulting solution
was extracted twice with Et2O (100 mL). The aqueous layer was evapo-
rated to dryness and dried in vacuo for 48 h to give the amine as the hy-
drochloride P3·HCl·2H2O (white powder, 5.24 g, 19.0 mmol, 98%).
1H NMR (D2O, pH*<2):[43] d=3.73 (m, 2H), 3.81 (t, J=6 Hz, 1H), 3.93
(t, J=2.5 Hz, 1H), 4.10 ppm (dd, J1 =2.5, J2 =6 Hz, 2H); 13C NMR (D2O,
pH*<2):[43] d=55.3, 58.2, 61.7, 68.8, 159.9 ppm; IR: n˜ =709, 752, 823,
859, 926, 969, 996, 1027, 1052, 1071, 1111, 1155, 1199, 1265, 1299, 1326,
1371, 1474, 1562, 2904, 3158 cmꢁ1; elemental analysis calcd (%) for
C7H18ClN3O6 (275.69): C 30.50, H 6.58, N 15.24; found: C 30.45, H 5.73,
N 15.24.
General: Commercially available chemicals used for the synthetic work
were of reagent grade quality. Unless otherwise noted, chemicals were
used as obtained. Dowex 50W-X2 (H+ form) and Dowex 2-X8 (Clꢁ
form) were from Sigma Aldrich. The anion exchange resin was converted
into the OHꢁ form by elution with 0.3m aqueous NaOH and extensive
rinsing with H2O until a neutral eluent was obtained. For the potentio-
metric and spectrophotometric titrations, metal salts of the highest avail-
able quality (>99.95%) were used. H2O was distilled twice (quartz appa-
ratus). UV/Vis spectra of individual samples were measured by using an
Uvikon 941 spectrometer (H2O, 25 ꢅ38C). IR spectra were recorded by
using a Bruker Vector 22 FT IR spectrometer equipped with a Golden
Gate ATR unit. 1H and 13C NMR spectra were measured in CDCl3 or
D2O at 218C by using a Bruker DRX Avance 400 MHz NMR spectrome-
ter (resonance frequencies: 400.13 MHz for 1H and 100.6 MHz for 13C).
The 2D spectrum displayed in Figure 1 was performed as a gradient-se-
lected (gs) 1H–13C HMBC experiment. Chemical shifts are given relative
to [D4]sodium (trimethylsilyl)propionate (D2O) or tetramethylsilane
(CDCl3) as internal standards (d=0 ppm); m’ denotes broad unresolved
multiplets. C, H, N analyses were performed by H. Feuerhake and A.
Zaschka (Universitꢀt des Saarlandes); the Na and Bi analyses (ICP-
OES) were performed by T. Allgayer (Universitꢀt des Saarlandes).
The free amine P3·0.5H2O was obtained in quantitative yield as a white
solid by ion-exchange chromatography on Dowex 2-X8 (OHꢁ form).
1H NMR (D2O, pH*=11):[43] d=3.38 (t, J=6 Hz, 1H), 3.61 (m’, 2H),
3.78 (dd, J1 =6, J2 =2 Hz, 2H), 3.88 ppm (m, 1H); 13C NMR (D2O, pH*>
12):[43] d=55.1, 58.4, 62.1, 71.7, 160.1 ppm; IR: n˜ =607, 691, 759, 825, 856,
976, 995, 1038, 1053, 1075, 1167, 1188, 1227, 1282, 1328, 1401, 1505, 1642,
3264, 3322 cmꢁ1; elemental analysis calcd (%) for C7H14N3O4.5 (212.20): C
39.62, H 6.65, N 19.80; found: C 40.37, H 6.65, N 19.82.
7,7’-(Ethane-1,2-diylbis(azanediyl))bis(6,8,9-trihydroxy-2,4-diazabicyclo-
AHCTUNGTRE[GNNNU 3.3.1]nonan-3-one) (P4): The amine P3·0.5H2O (1.0 g, 4.71 mmol) was
all-cis-2,4,6-Tris(benzyloxy)-1,3,5-cyclohexanetriamine
ACHTUNGTRENNUNG
(P1):[13]
[Ni-
(taci)2]SO4·4H2O[23] (5.0 g, 8.6 mmol) was suspended in DMF (400 mL).
suspended in H2O (10 mL), and an aqueous 40% solution of glyoxal
(290 mL, 357 mg, 2.46 mmol) was added. The resulting suspension was
stirred at room temperature. A slow color change to yellow was ob-
served. After 24 h, the unreacted P3 was filtered off (this material may
be regenerated and used in a further experiment, see below). NaBH4
(from Alfa Aesar GmbH, ꢃ97% purity; 1 g, ꢃ25 mmol) was then slowly
added in small portions to the yellow solution. The mixture was stirred
for 2 h. The solution was then acidified to pH 1 with 1m aqueous HCl
and evaporated to dryness under reduced pressure. The residue was dis-
solved in a few mL of an aqueous 0.5m HCl solution and sorbed on
Dowex 50W-X2. The column was successively eluted with H2O (0.5 L),
aqueous 0.5m HCl (1.0 L) and aqueous 3m HCl (1.0 L). The last fraction
was evaporated to dryness and dried in vacuo for 24 h. The product was
isolated as a white, hydrated trihydrochloride P4·3HCl·5H2O (1.01 g,
1.60 mmol, 68%). 1H NMR (D2O, pH*<2):[43] d=3.59 (s, 4H), 3.74 (t,
NaOH (11.8 g, 0.295 mol) and benzylbromide (35 mL, 0.295 mol) were
added, and the reaction mixture was stirred for 24 h at room tempera-
ture. Concentrated ammonia (10 mL) was added to destroy the excess
benzylbromide. The reaction mixture was stirred for 30 min, and H2O
(1.5 L) was then added. Precipitation was observed. The suspension was
allowed to stand at 08C for 10 h. The pink residue was filtered off and
washed twice with H2O (100 mL). The solid was dissolved in EtOH, and
the free trihydrochloride was precipitated by addition of aqueous conc.
HCl (100 mL). The suspension was allowed to stand at 08C for another
10 h. The white residue was then filtered off and dissolved in H2O
(150 mL). An excess of NaOH (10 mL of a 40% aqueous solution) was
added, and the resulting free triamine was extracted with CHCl3. The or-
ganic solution was evaporated to dryness under reduced pressure, and
the resulting white solid was dried in vacuo for 24 h. Yield: 6.0 g
3336
www.chemeurj.org
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2010, 16, 3326 – 3340

N,O-Ligand Complexes
FULL PAPER
J=2 Hz, 4H), 3.93 (t, J=2 Hz, 2H), 3.96 (t, J=6 Hz, 2H), 4.21 ppm (dd,
J1 =6, J2 =2 Hz, 4H); 13C NMR (D2O, pH*<2):[43] d=48.6, 57.9, 61.3,
62.3, 69.0, 159.6 ppm; IR: n˜ =583, 884, 909, 1053, 1177, 1393, 1506, 1644,
3192 cmꢁ1; elemental analysis calcd (%) for C16H41Cl3N6O13 (631.89): C
30.41, H 6.54, N 13.30; found: C 30.38, H 6.56, N 13.69.
C14H34Cl2N6NiO7 (528.06): C 31.84, H 6.49, N 15.92; found: C 32.41, H
6.59, N 15.81.
[Cu(Le)]
ACHTUNGTRENNUNG
H2O (1 mL). Solid CuAHCTUNGTRENNUNG
evaporation of the solvent at ambient temperature yielded crystals that
could be used for single-crystal X-ray analysis. IR: n˜ =597, 620, 750, 784,
823, 858, 885, 904, 928, 1037, 1210, 1236, 1289, 1348, 1392, 1458, 1567,
2359, 2886, 3238, 3271, 3316, 3348 cmꢁ1; UV/Vis (H2O): lmax =603 nm; el-
emental analysis calcd (%) for C14H34Cl2CuN6O15 (660.90): C 25.44, H
5.19, N 12.72; found: C 25.89, H 5.05, N 12.50.
Regeneration of the unreacted P3: The filtered solid was dissolved in a
minimal amount of H2O and acidified to a pH of 1 with aqueous HCl.
This solution was sorbed on Dowex 50W-X2, and the column was eluted
with H2O, 0.2m aqueous HCl and 0.5m aqueous HCl. The last fraction
was evaporated to dryness and dried in vacuo. This product could be
used as starting material for the synthesis of additional P4·3HCl·5H2O
without further purification.
[Zn(Le)]CO3·7H2O (4): Le·6H2O (40 mg, 82 mmol) was dissolved in H2O
(1 mL). Solid ZnACTHNUGTRNEUNG(NO3)2·6H2O (24 mg, 81 mmol) was added. The solution
The free amine P4·3H2O was obtained in quantitative yield (white solid)
by ion-exchange chromatography on Dowex 2-X8 (OHꢁ form). 1H NMR
(D2O, pH*> 12):[43] d=2.71 (s, 4H), 3.12 (t, J=6 Hz, 2H), 3.58 (m’, 4H),
3.81 (dd, J1 =6, J2 =2 Hz, 4H), 3.85 ppm (t, J=2 Hz, 2H); 13C NMR
(D2O, pH*> 12):[43] d=54.6, 58.4, 62.1, 62.4, 71.8, 159.8 ppm; IR: n˜ =
873, 1044, 1219, 1338, 1397, 1508, 1636, 1716, 2858, 3246, 3735 cmꢁ1; ele-
mental analysis calcd (%) for C16H34N6O11 (486.47): C 39.50, H 7.04, N
17.28; found: C 40.04, H 6.97, N 17.34.
was exposed to air, thus allowing the uptake of atmospheric CO2. Slow
evaporation of the solvent resulted in the formation of a small amount of
colorless crystals that could be used for single-crystal X-ray analysis.
[Co(Le)]Cl3·5H2O (5a): Le·6HCl·2.5H2O (0.46 g, 715 mmol) was dissolved
in H2O (60 mL). The pH of the solution was adjusted to 8.5 by adding
0.1m NaOH. Solid CoCl2·6H2O (170 mg, 715 mmol) was added, resulting
in a red-orange solution that was aerated with a steady stream of air for
24 h. The solution was sorbed onto Dowex 50W-X2, and the column was
successively eluted with H2O (150 mL), aqueous 0.5m HCl (150 mL),
aqueous 1m HCl (150 mL) and aqueous 3m HCl (150 mL). The last frac-
tion was evaporated to dryness, and the resulting orange solid was dried
in vacuo (orange powder, 359 mg, 565 mmol, 79%). 1H NMR (D2O,
pH*=3.80):[43] d=2.81 (m’, 2H), 2.94 (m’, 2H), 3.03 (m’, 2H), 3.24 (d,
J=8 Hz, 2H), 3.98 (d, J=8 Hz, 2H), 4.09 (m’, 2H), 4.166 (m’, 2H)
4.174 ppm (m’, 2H); 13C NMR (D2O, pH*=3.80):[43] d=52.5 (2 C), 56.5,
61.1, 65.4, 67.0, 67.5 ppm;[30] IR: n˜ =553, 803, 861, 930, 1062, 1238, 1339,
1557, 3120; UV/Vis (H2O): lmax (e)=340 (94), 471 nm (87mꢁ1 cmꢁ1); ele-
mental analysis calcd (%) for C14H42Cl3CoN6O11 (635.81): C 26.45, H
6.66, N 13.22; found: C 26.57, H 6.41, N 13.13.
[Co(Le)]
ACTHNUTRGNE[UNG ZnCl4]Cl (5b): A sample of 5a (50 mg, 79 mmol) was dissolved
in H2O. Solid ZnCl2 (11 mg, 81 mmol) was added, and the solution was
acidified to pH <1 with 3m aqueous HCl. Orange crystals appeared after
slow evaporation of the solvent.[21]
[Co(Le)] (5c):[22] A sample of 5a (20 mg, 31 mmol) was dissolved
ACHTNUTRGENN(UG ClO4)3 ACHTUTGNRENNUGN
in 0.5 mL of aqueous 17.5% HClO4. Slow evaporation of the solvent at
ambient temperature over a period of two weeks gave orange crystals
(80%) suitable for single-crystal X-ray analysis.
all-cis-N1,N2-Bis(2,4,6-trihydroxy-3,5-diaminocyclohexyl)ethane-1,2-di-
ACHTUNGTRENNUNG
amine (Le): The solid bis-urea-amine P4·3H2O (0.40 g, 0.82 mmol) and
solid NaOH (4.0 g, 0.10 mol) were dissolved in an ethyleneglycol/H2O
mixture (3:1) and heated to 1258C (temperature of the reaction mixture)
for 24 h. A color change from light yellow to dark brown was observed.
The reaction mixture was then allowed to cool to room temperature. It
was acidified to a pH 1 with 1m aqueous HCl. Some precipitation oc-
curred around pH 7, but the precipitate redissolved by addition of the re-
maining acid. The resulting clear, yellow solution was sorbed on Dowex
50W-X2, and the column was successively eluted with H2O (1 L), aque-
ous 1m and 3m HCl (each 1 L) and aqueous 6m HCl (2 L). The last frac-
tion was evaporated under reduced pressure to a total volume of about
100 mL. A yellowish solid precipitated. It was filtered off and dried in
vacuo for 24 h. This product (0.414 g, 0.64 mmol, 78%) was characterized
as Le·6HCl·2.5H2O. 1H NMR (D2O, pH*<2):[43] d=3.75 (t, J=3 Hz,
4H), 3.79 (s, 4H), 3.88 (t, J=3 Hz, 2H), 4.47 (t, J=3 Hz, 2H), 4.61 ppm
(t, J=3 Hz, 4H); 13C NMR (D2O, pH*<2):[43] d=43.6, 53.3, 60.5, 67.3,
68.7 ppm; IR: n˜ =568, 645, 763, 848, 896, 948, 1037, 1114, 1139, 1285,
1361, 1422, 1480, 1568, 2838 cmꢁ1; elemental analysis calcd (%) for
C14H43Cl6N6O8.5 (644.24): C 26.10, H 6.73, N 13.04; found: C 26.09, H
6.67, N 12.79.
[Ga
ray analysis were obtained following the protocol of the Cu complex 3,
using solid, hydrous Ga
(NO3)3 and Le·6H2O as starting materials.
(Hꢁ2Le)]NO3·2H2O (6): Single crystals of 6 that were suitable for X-
ACHTUNGTRENNUNG
Regeneration of unreacted P4: The 3m HCl fraction of the abovemen-
tioned cation-exchange chromatography was evaporated under reduced
pressure to a total volume of a few mL. Addition of MeOH (20 mL) re-
sulted in the precipitation of a white solid that was filtered off and dried
in vacuo. It could be used as starting material for the synthesis of addi-
tional Le·6HCl·2.5H2O without further purification.
The free amine Le·6H2O was obtained quantitatively as a white solid by
ion-exchange chromatography on Dowex 2-X8 (OHꢁ form). 1H NMR
(D2O, 1 m KOD): d=2.60 (t, J=2.5 Hz, 2H), 2.68 (t, J=2.5 Hz, 4H), 2.84
(s, 4H), 3.84 (m’, 2H), 4.03 ppm (m’, 4H); 13C NMR (D2O, 1 m KOD):
d=47.5, 55.8, 61.5, 76.3, 79.9 ppm; IR: n˜ =770, 798, 888, 916, 951, 996,
1074, 1091, 1127, 1166, 1250, 1353, 1446, 1571, 1669, 2699, 2894, 3071,
3344, 3447 cmꢁ1; elemental analysis calcd (%) for C14H44N6O12 (488.53):
C 34.42, H 9.08, N 17.20; found: C 34.32, H 8.25, N 17.22.
AHCTUNGTRENNUNG
Cyclic voltammetry: Scans were recorded at ambient temperature (25ꢅ
28C) in a BAS C2 cell by using a BAS 100B/W2 potentiostat, a Au (Mn
complex) or a Pt (Co and Ni complex) working electrode, a Pt counter
electrode and a Ag/AgCl reference electrode. 0.1m KCl was used as sup-
porting electrolyte. Samples of the Co and Ni complexes were prepared
by dissolving solid [Co(Le)]Cl3·5H2O (5a) or [Ni(Le)]Cl2·5H2O (2) in
H2O, respectively, and by adjusting the pH to 9 using 0.1m KOH. Sam-
ples of the Mn complex were prepared in situ using MnCl2 and
Le·6HCl·2.5H2O. 0.5m KOH was then added to adjust the pH to a value
of 12. The metal concentration of all samples was 1 mm.
Molecular mechanics calculations: Considering the four different binding
sites shown in Scheme 1, a total of 10 combinations must be considered
for the two subunits in a metal complex MLe. This number increases to
more than 200, if additional cis–trans diastereomers, as well as the vari-
ous possible linking interactions, are taken into account. However, owing
to the relatively short tether length of the ethylene bridge, some of these
structures are obviously not meaningful. A total of 15 relevant isomers
were finally selected for the calculations. Some of them could exist in a
zwitterionic or non-zwitterionic form (Scheme 1b), and both forms were
considered when appropriate. In addition, different conformations of the
ethylene bridge were taken into account for some of the structures. A
first draft of each structure was generated using the program Hyper-
chem.[44] The energy minimization was performed using the program
Momec97[45] with an extension of the force field as described in refer-
ence [9]. All metal complexes were modeled with CoIII. A validation of
A
0.5ACHTUNGTRENNUNG ACHTUNGTRENNUNG
(H6Le)](BiCl6)2Cl0.5·4H2O (1): Le·6HCl·2.5H2O (40 mg, 62 mmol)
ACHTUNGTRENNUNG
08C for several days to give colorless needles that were suitable for
single crystal X-ray analysis. The Na/Bi ratio of this compound deter-
mined by ICP-OES was 3.83ꢅ0.08.
[Ni(Le)]Cl2·5H2O (2): Le·6H2O (41 mg, 84 mmol) was dissolved in H2O
(1 mL). Solid NiCl2·6H2O (20 mg, 84 mmol) was added. Slow evaporation
of the solvent at ambient temperature yielded pink crystals that could be
used for a single-crystal X-ray analysis. The dried product analyzed for
[Ni(Le)]Cl2·H2O. IR: n˜ =551, 559, 580, 744, 772, 829, 857, 904, 1004, 1049,
1122, 1166, 1225, 1267, 1326, 1359, 1569, 2358, 2897, 3193, 3355 cmꢁ1
UV/Vis (H2O): lmax =321, 511, 799 nm; elemental analysis calcd (%) for
;
Chem. Eur. J. 2010, 16, 3326 – 3340
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
3337

K. Hegetschweiler et al.
this force field for such complexes is found in reference [46]. In a first
step, geometry optimization was performed with the full-matrix Newton–
Raphson algorithm. To avoid location of false (local) minima, a search
for further low-energy conformers was performed using the “Random
Kick” option of Momec97. In many cases this procedure did not reveal
any conformation of lower energy. However, in a few cases structures of
considerably lower energy were found and those were once more energy
minimized. The calculated structures generally exhibited bond distances
Calculations of equilibrium constants: Equilibrium constants were gener-
ally calculated as concentration quotients (pH=ꢁlog [H+]) by using the
computer programs Hyperquad2000 and Specfit.[49,50] The total concen-
trations of the reactants and the pKw (13.78 for m=0.1m, 13.77 for m=
1.0m) were not refined.[37] The protonation constants of the ligand Le
were evaluated separately and were kept fixed when refining formation
constants of the metal-containing species. The UV/Vis spectrum of the
free Cu2+ was recorded separately and was imported as a fixed data set
for the evaluation of the formation constants of the Cu complexes. The
free ligand and its protonation products were treated as nonabsorbing
species. The stability of CuII-chloro complexes of composition
[Cux(Le)yHzClq]2x+z–q was calculated from the titration experiments per-
formed in 1.0m KCl. The formation constants of these species were re-
fined, whereas the formation constants of the corresponding Cl-free
[Cux(Le)yHz]2x+z species, that were determined in a 1.0m KNO3 medium
were considered as fixed values. The evaluated value of 0.58(2) for
log bCuCl is in reasonable agreement with the literature[51] and thus sup-
ports the reliability of this method.
ꢁ
ꢁ
and bond angles as expected, with the exception of some Co O and Co
N bond lengths in oxygen-rich coordination spheres (CoOxN6ꢁx, xꢀ3)
that seem to be slightly underestimated (1.92–1.94 ꢄ). All energy minimi-
zation calculations reached convergence (<0.005 ꢄ). A detailed presen-
tation of the results of these calculations is given in Table S1 in the Sup-
porting Information.
NMR titration: A solution of Le·6HCl·2.5H2O (total Le =26 mm) and
KCl (0.1m) in D2O (30 mL) was neutralized stepwise by adding small in-
crements of a NaOD/D2O solution (0.1m). After each addition of base,
the pH* was measured,[43] and a 0.6 mL aliquot was taken for the record-
ing of a 1H NMR spectrum. A total of 41 spectra were recorded. Least
Single-crystal X-ray diffraction studies: Data sets were collected by using
the following diffractometers: Bruker X8-APEX (1, 2, 6), STOE Stadi4
(3, 4), and Bruker Smart (5c). Graphite-monochromated MoKa radiation
(l=0.71073 ꢄ) was used in all experiments. The data were collected at
90(2) K (5c), 100(2) K (1, 2, 6) or ambient temperature (3, 4). Further
details of data collection and structure solutions are summarized in
Tables 4 and 5. The structures were solved by direct methods (SHELXS-
97) and refined by full-matrix, least-squares calculations on F2
(SHELXL-97).[52] Disorder: Na1 and Cl11 of 1 were refined with site oc-
squares calculations S(dobsꢁdcalcd)2 =min were performed assuming
a
rapid equilibrium between the differently protonated species Hx(Le)x+
(0ꢂxꢂ6), using the computer program NMR-Tit.[47] The calculations re-
vealed an excellent fit (Figure 2) with meaningful and robust values for
pKa1 (3.23) and pKa6 (9.02). However, the calculations also showed that
the intermediate values could vary over a wide range without a signifi-
cant influence on the accuracy of the fit. In contrast to the potentiometric
measurements (see next section), the high number of species, that all co-
exist in significant proportions around
5<pH<8, did not allow an unambigu-
ous determination of the intermediate
pKax values (2ꢂxꢂ5) by this method.
Table 4. Crystallographic data for [Na0.5ACHTNUTRGENNUG HCATUNGTRENNGUN
(H6Le)](BiCl6)2Cl0.5·4H2O (1), [Ni(Le)]Cl2·5H2O (2), and [Cu(Le)]-
AHCTUNGTRENNG(UN ClO4)2·H2O (3).
Potentiometric and spectrophotomet-
ric titrations: Titration experiments
were performed at 25.08C under N2
(scrubbed with an aqueous solution of
the pure inert electrolyte) as described
previously.[48] For the determination of
the pKa values of H6(Le)6+, several al-
kalimetric titrations were carried out
with analytically pure samples of
Le·6HCl·2.5H2O (total Le =1.0 mm),
using KCl (0.1 or 1.0m) or KNO3
(1.0m) as inert electrolyte. The forma-
tion constants of metal complexes
were determined using solutions that
contained Le·6HCl·2.5H2O and the
metal salt in 2:1, 1:1 or 1:2 molar
ratios (total Le and total M varied be-
tween 0.5 and 2 mm) at an ionic
strength of 0.1m (KCl). In the case of
CuII, titrations with an equimolar ratio
were also performed in 1m KCl and
1m KNO3 with a total metal and a
total ligand concentration of 10 mm.
Standardized stock solutions of
Le·6HCl·2.5H2O and of the corre-
sponding metal salts were used for
sample preparations. Complete equili-
bration was ensured by back titrations
1
2
3
chemical formula
formula weight
space group
crystal system
a [ꢄ]
b [ꢄ]
c [ꢄ]
a [8]
b [8]
C14H46Bi2Cl
1331.15
N6Na0.5O10
C14H42Cl2N6NiO11
600.15
C14H34Cl2CuN6O15
660.91
Pnma (No.62)
orthorhombic
14.7530(10)
12.5057(9)
21.2619(15)
90.00
90.00
90.00
3922.7(5)
0.55ꢃ0.21ꢃ0.12
2.254
9.867
4
100(2)
0.3839, 0.0741
50.00
3624, 293
0.0161
0.0424
1.157/ꢁ0.680
P21/c (No.14)
monoclinic
13.086(3)
13.259(3)
14.374(3)
90.00
96.98(3)
90.00
2475.7(9)
0.30ꢃ0.25ꢃ0.20
1.610
1.064
4
100(2)
0.8153, 0.7407
52.00
P21/c (No.14)
monoclinic
19.500(4)
9.171(2)
14.430(3)
90.00
107.58(3)
90.00
2460.1(9)
0.30ꢃ0.20ꢃ0.20
1.784
g [8]
V [ꢄ3]
dimensions [mm]
1calcd [gcmꢁ3
]
m [cmꢁ1
Z
]
1.191
4
T [K]
293(2)
[a]
max., min. transmission
2qmax
48.00
3801, 407
0.0422
0.1138
0.673/ꢁ0.540
data, parameters
4864, 411
0.0261
0.0690
1.050/ꢁ0.535
R1 [I> 2s(I)][b]
wR2 (all data)[c]
max/min res. e-density, [eꢄꢁ3
]
2
4
[a] An absorption correction was not performed. [b] R1 =SjjFo jꢁjFc jj/SjFo j. [c] wR2 =[Sw
ACHTUNGTRENNUNG
2
.
for all metal-containing solutions. A Metrohm piston burette was used
for the addition of the titrant (KOH, HCl or HNO3), and the pH was re-
corded using a Metrohm glass electrode with an incorporated Ag/AgCl
reference connected to a Metrohm 713 pH meter. The stability of the
electrode was checked by a calibration titration prior to and after each
measurement. For spectrophotometric measurements, the titration cell
was equipped with an immersion probe (HELLMA), that was connected
to a spectrophotometer equipped with a diode array detector (J&M,
TIDAS-UV/NIR/100–1). A PC was used to trigger the recording of a
spectrum just prior to the addition of each new aliquot of base.[48]
cupancies of 50%. It was further noted that the anisotropic displacement
ellipsoid of Cl11, which is placed on a mirror plane, deviates significantly
from a spherical shape. Attempts were made to resolve this disorder in
terms of a superstructure considering the space groups P21/m, Pmc21 or
ꢁ
Pmn21, but were not successful.[53] One of the oxygen atoms of a ClO4
counter ion of 3 was distributed over two positions having a site occupan-
ꢁ
cy of 50%. One of the ClO4 counter ions of 5c was located in proximity
of a two fold rotational axis and was refined in terms of a superposition
of two half occupied moieties (Cl1, O8, O9), having the fully occupied
O10 and O10A in common. In addition, the ethylene bridge (C1, C2 and
3338
www.chemeurj.org
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2010, 16, 3326 – 3340

N,O-Ligand Complexes
FULL PAPER
Table 5. Crystallographic data for [Zn(Le)]CO3·7H2O (4), [Co(Le)]
(6).
G
N
3584–3593;
c) J. W.
de Boer,
W. R. Browne, J. Brinksma, P. L.
Alsters, R. Hage, B. L. Feringa,
Inorg. Chem. 2007, 46, 6353–
6372; d) V. B. Romakh, B. Ther-
rien, G. Sꢁss-Fink, G. B. Shul’pin,
Inorg. Chem. 2007, 46, 3166–
3175; e) F. H. Fry, A. J. Fisch-
mann, M. J. Belousoff, L. Spiccia,
J. Brꢁgger, Inorg. Chem. 2005, 44,
941–950; f) Q.-X. Li, Q.-H. Luo,
Y.-Z. Li, M.-C. Shen, Dalton
Trans. 2004, 2329–2335.
4
chemical formula
formula weight
space group
crystal system
a [ꢄ]
b [ꢄ]
c [ꢄ]
a [8]
C15H46N6O16Zn
631.95
C14H32Cl3CoN6O18
737.74
Pbcn (No.60)
orthorhombic
13.542(3)
14.476(3)
26.680(5)
90.00
C2/c (No.15)
monoclinic
16.2096(9)
11.0975(6)
14.6272(8)
90.00
b [8]
90.00
90.00
5230.2(19)
0.30ꢃ0.15ꢃ0.10
1.605
104.3480(10)
90.00
2549.2(2)
0.40ꢃ0.30ꢃ0.20
1.922
g [8]
[3] a) Y. Kajita, H. Arii, T. Saito, Y.
Saito, S. Nagatomo, T. Kitagawa,
Y. Funahashi, T. Ozawa, H.
Masuda, Inorg. Chem. 2007, 46,
3322–3335; b) A. K. Nairn, S. J.
Archibald, R. Bhalla, B. C. Gil-
bert, E. J. MacLean, S. J. Teat,
P. H. Walton, Dalton Trans. 2006,
172–176; c) E. A. Lewis, H. H.
Khodr, R. C. Hider, J. R. Lindsay
Smith, P. H. Walton, Dalton
Trans. 2004, 187–188.
[4] a) K. Wieghardt, I. Tolksdorf, W.
Herrmann, Inorg. Chem. 1985,
24, 1230–1235; b) D. Hanke, K.
Wieghardt, B. Nuber, R.-S. Lu,
R. K. McMullan, T. F. Koetzle, R.
V [ꢄ]3
dimensions [mm]
1calcd [gcmꢁ3
]
m [cmꢁ1
Z
]
1.025
8
1.087
4
T [K]
293(2)
90(2)
0.8120, 0.6703
56.54
[a]
max., min. transmission
2qmax
47.0
data, parameters
3865, 395
0.0785
0.2272
0.933/ꢁ0.766
3164, 217
0.0784
0.1850
0.858/ꢁ1.192
R1 [I> 2s(I)][b]
wR2 (all data)[c]
max/min res. e-density [eꢄꢁ3
]
[a] An absorption correction was not performed. [b] R1 =SjjFo jꢁjFc jj/SjFo j. [c] wR2 =[Sw
2
.
the corresponding hydrogen atoms) of the Le-ligand that is duplicated by
an inversion center was also refined with a 50% occupancy. Inspection of
interatomic distances clearly indicated that the two disorder problems
Bau, Inorg. Chem. 1993, 32, 4300–4305; c) R. Haidar, M. Ipek, B.
DasGupta, M. Yousaf, L. J. Zompa, Inorg. Chem. 1997, 36, 3125–
3132.
ꢁ
are dependent on each other. Two oxygen atoms (O1, O3) of the NO3
[5] D. Parker, K. Senanayake, J. Vepsailainen, S. Williams, A. S. Batsa-
nov, J. A. K. Howard, J. Chem. Soc. Perkin Trans. 2 1997, 1445–
1452.
[6] H. Egli, PhD Thesis, ETH Zꢁrich (Zꢁrich), 1975.
[7] F. Mancin, E. Rampazzo, P. Tecilla, U. Tonellato, Eur. J. Org. Chem.
2004, 281–288.
[8] K. Hegetschweiler, Chem. Soc. Rev. 1999, 28, 239–249.
[9] D. Kuppert, P. Comba, K. Hegetschweiler, Eur. J. Inorg. Chem.
2006, 2792–2807.
counter ion of 6 were found to be equally distributed over two sites.
These were considered with 50% site occupancies. Anisotropic displace-
ꢁ
ment parameters were refined for all non-hydrogen atoms. All O H and
ꢁ
N H hydrogen atoms of 1, 2 and 3 were located and refined with varia-
ble isotropic displacement parameters. The OH hydrogen atoms of 4
were located and refined with isotropic displacement parameters fixed at
1.5Ueq of the parent oxygen atoms; however, only one hydrogen atom
ꢁ
could be located for the water oxygen atom O400. For 6, the O H and
ꢁ
N H hydrogen atoms were also located and refined with a variable Uiso
,
[10] M. Weber, B. Morgenstern, K. Hegetschweiler, H. W. Schmalle,
ꢁ
except the N H hydrogen atoms H3NA and H3NB that were refined
Helv. Chim. Acta 2001, 84, 571–578.
with Uiso fixed at 1.2Ueq of N31. All other hydrogen atomic positions
were calculated (riding model). CCDC-747720 (5b), CCDC-747721 (5c),
CCDC-747722 (3), CCDC-747723 (6), CCDC-747724 (1), CCDC-747725
(2), and CCDC-747726 (4) contain the supplementary crystallographic
data for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif.
ꢁ
ꢁ
[11] Rotation around the N C and C C bonds of the diaminoethane
bridge of H6(Le)6+ generates a series of conformers with a C2- and a
Ci-symmetric rotamer being of lowest energy (see Chart S1 in the
Supporting Information). These two conformers have either two ho-
motopic or two enantiotopic cyclohexane rings with six different
carbon atoms per ring. The Ci-symmetric conformer was observed in
the crystal structure of the sodium complex (see Figure 3). Addition-
al conformers with C2h or C2v symmetry, having either a transoid or
cisoid arrangement of the N-C-C-N fragment, are of slightly higher
energy. Due to rapid interconversion of all these rotamers within
the NMR time scale, an averaged structure with two homotopic cy-
clohexane rings was observed. Within each ring, four of the six
carbon atoms (C2, C2’; C3, C3’) belong to two constitutionally heter-
otopic pairs of enantiotopic CH groups. Thus, the two cyclohexane
Acknowledgements
We thank Dr. Volker Huch (Universitꢀt des Saarlandes) for the acquisi-
tion of the X-ray data and Dr. Thomas Weyhermꢁller (Max-Planck-Insti-
tut fꢁr Bioanorganische Chemie, Mꢁhlheim), Dr. Holger Kohlmann
(Universitꢀt des Saarlandes), and Prof. Jon Zubieta (Syracuse University)
for help and advice.
1
residues exhibit four resonances in the 13C and in the H NMR spec-
tra. The ethylene bridge leads to one additional resonance in both
spectra. For the terminology of topicity, see: a) H. Hirschmann,
K. R. Hanson, Eur. J. Biochem. 1971, 22, 301–309; b) K. Mislow,
Bull. Soc. Chim. Belg. 1977, 86, 595–601. A comprehensive discus-
sion of the symmetry properties of such non-rigid molecules can be
found in: c) H. C. Longuet-Higgins, Mol. Phys. 1963, 6, 445–460;
d) H. C. Longuet-Higgins, Mol. Phys. 2002, 100, 11–20.
[1] a) K. F. Sibbons, K. Shastri, M. Watkinson, Dalton Trans. 2006, 645–
661; b) R. Hage, A. Lienke, J. Mol. Catal. A-Chem 2006, 251, 150–
158.
[12] a) A. Bianchi, M. Micheloni, P. Paoletti, Coord. Chem. Rev. 1991,
110, 17–113; b) S. Kubik, C. Reyheller, S. Stꢁwe, J. Inclusion
Phenom. Macrocyclic Chem. 2005, 52, 137–187.
[2] a) B. R. Bodsgard, R. W. Clark, A. W. Ehrbar, J. N. Burstyn, Dalton
Trans. 2009, 2365–2373; b) M. Scarpellini, J. Gꢀtjens, O. J. Martin,
J. W. Kampf, S. E. Sherman, V. L. Pecoraro, Inorg. Chem. 2008, 47,
Chem. Eur. J. 2010, 16, 3326 – 3340
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
3339

K. Hegetschweiler et al.
[13] M. Weber, D. Kuppert, K. Hegetschweiler, V. Gramlich, Inorg.
Chem. 1999, 38, 859–868.
[32] A. Zimmer, D. Kuppert, T. Weyhermꢁller, I. Mꢁller, K. Hegetsch-
weiler, Chem. Eur. J. 2001, 7, 917–931.
[14] a) D. Kuppert, J. Sander, C. Roth, M. Wçrle, T. Weyhermꢁller, G. J.
Reiss, U. Schilde, I. Mꢁller, K. Hegetschweiler, Eur. J. Inorg. Chem.
2001, 2525–2542; b) K. Hegetschweiler, O. Maas, A. Zimmer, R. J.
Geue, A. M. Sargeson, J. Harmer, A. Schweiger, I. Buder, G.
Schwitzgebel, V. Reiland, W. Frank, Eur. J. Inorg. Chem. 2003,
1340–1354.
[15] J. W. Pauly, J. Sander, D. Kuppert, M. Winter, G. J. Reiss, F. Zꢁrcher,
R. Hoffmann, T. F. Fꢀssler, K. Hegetschweiler, Chem. Eur. J. 2000,
6, 2830–2846.
[33] M. DeRonde, D. Driscoll, R. Yang, L. J. Zompa, Inorg. Nucl. Chem.
Lett. 1975, 11, 521–523.
[34] E. Prenesti, P. G. Daniele, M. Prencipe, G. Ostacoli, Polyhedron
1999, 18, 3233–3241.
[35] J. Bjerrum, B. V. Agarwala, Acta Chem. Scand. A 1980, 34, 475–481.
[36] For 1,5,9,12,16,20-hexaazaicosane, the formation constant for the di-
nuclear species [Cu2L]4+ is logb210 =27.12 (258C, m=0.15m, from
Ref. [37]). This value has to be compared with 26.09, observed for
Le (Table 2).
[16] J. Romba, D. Kuppert, B. Morgenstern, C. Neis, S. Steinhauser, T.
Weyhermꢁller, K. Hegetschweiler, Eur. J. Inorg. Chem. 2006, 314–
328.
[37] Critically Selected Stability Constants of Metal Complexes, NIST
Standard Reference Database 46, Version 8.0, R. M. Smith, A. E.
Martell, R. J. Motekaitis, Gaithersburg, 2004.
[17] a) K. Hegetschweiler, M. Wçrle, M. D. Meienberger, R. Nesper,
H. W. Schmalle, R. D. Hancock, Inorg. Chim. Acta 1996, 250, 35–47;
b) K. Hegetschweiler, A. Egli, E. Herdtweck, W. A. Herrmann, R.
Alberto, V. Gramlich, Helv. Chim. Acta 2005, 88, 426–434; c) A.
Kramer, R. Alberto, A. Egli, I. Novak-Hofer, K. Hegetschweiler, U.
Abram, P. V. Bernhardt, P. A. Schubiger, Bioconjugate Chem. 1998,
9, 691–702.
[38] M. Ghisletta, L. Hausherr-Primo, K. Gajda-Schrantz, G. Machula, L.
Nagy, H. W. Schmalle, G. Rihs, F. Endres, K. Hegetschweiler, Inorg.
Chem. 1998, 37, 997–1008.
[39] b1 =[M
and are from reference [37].
(NH3)2+]ꢃ[NH3]ꢁ1 ꢃ[M2+ ꢁ1, the values refer to 258C, m=1m
ACHTUNGTERNNUNG ]
[40] K. Hegetschweiler, R. D. Hancock, M. Ghisletta, T. Kradolfer, V.
Gramlich, H. W. Schmalle, Inorg. Chem. 1993, 32, 5273–5284.
[41] T. Gajda, Y. Dꢁpre, I. Tçrçk, J. Harmer, A. Schweiger, J. Sander, D.
Kuppert, K. Hegetschweiler, Inorg. Chem. 2001, 40, 4918–4927.
[42] J. J. Perry, J. A. Perman, M. J. Zaworotko, Chem. Soc. Rev. 2009, 38,
1400–1417.
[43] In this paper, the term pH* refers to the direct pH-meter reading
(Metrohm 713 pH meter) for D2O samples using a Metrohm glass
electrode with an aqueous (H2O) Ag/AgCl-reference that was cali-
brated with aqueous (H2O) buffer solutions. For the interconversion
of pH* and pD see: L. Alderighi, A. Bianchi, L. Biondi, L. Calabi,
M. De Miranda, P. Gans, S. Ghelli, P. Losi, L. Paleari, A. Sabatini,
A. Vacca, J. Chem. Soc. Perkin Trans. 2 1999, 2741–2745.
[44] HyperChem, Release 7.51 for Windows, Hypercube Inc., Gainsville,
2002.
[45] a) MOMEC97, a molecular modeling package for inorganic com-
pounds, P. Comba, T. W. Hambley, G. Lauer, N. Okon, University of
Heidelberg, 1997; b) J. E. Bol, C. Buning, P. Comba, J. Reedijk, M.
Strçhle, J. Comput. Chem. 1998, 19, 512–523; c) P. Comba, T. W.
Hambley, Molecular Modeling of Inorganic Compounds, VCH,
Weinheim, 1995.
[46] A. M. T. Bygott, A. M. Sargeson, Inorg. Chem. 1998, 37, 4795–4806.
[47] NMR-Tit, Program for the Simulation of pH Dependent Shifts in
NMR Spectra, Version 2.0, A. Ries, K. Hegetschweiler, Saarbrꢁck-
en, 1999.
[48] S. Steinhauser, U. Heinz, M. Bartholomꢀ, T. Weyhermꢁller, H. Nick,
K. Hegetschweiler, Eur. J. Inorg. Chem. 2004, 4177–4192.
[49] P. Gans, A. Sabatini, A. Vacca, Talanta 1996, 43, 1739–1753.
[50] a) Specfit/32 Version 3.0, Spectrum Software Associates, R. A. Bin-
stead, B. Jung, A. D. Zuberbꢁhler, Marlborough, 2000; b) H.
Gampp, M. Maeder, C. J. Meyer, A. D. Zuberbꢁhler, Talanta 1985,
32, 95–101.
[51] B. Carlsson, G. Wettermark, J. Inorg. Nucl. Chem. 1976, 38, 1525–
1527.
[52] G. M. Sheldrick, Acta Crystallogr. Sect. A 2008, 64, 112–122.
[53] Program used: PowderCell for Windows, Version 2.4, W. Kraus, G.
Nolze, Federal Institute for Materials Research and Testing, Berlin,
2000.
[18] The sum of the ionic radii of a hexacoordinate NaI and a tricoordi-
nate OꢁII is 2.38 ꢄ; see: a) R. D. Shannon, Acta Crytallogr. Sect. A
ꢁ
1976, 32, 751–767. Na O bond lengths of related structures, where
a hexacoordinate NaI cation is bonded to alcoholic oxygen atoms
range from 2.29–2.47 ꢄ: b) F. A. Cotton, M. P. Diebold, W. J. Roth,
Inorg. Chem. 1988, 27, 3596–3600; c) D. Szeymies, B. Krebs, G.
Henkel, Angew. Chem. 1984, 96, 797–798; Angew. Chem. Int. Ed.
Engl. 1984, 23, 804–805; d) M. Capo, J. M. Saa, A. Alvarez, Chem.
Commun. 2002, 1982–1983; e) D. E. Berning, K. V. Katti, C. L.
Barnes, W. A. Volkert, Chem. Ber./Recueil 1997, 130, 907–911.
[19] D. Cremer, J. A. Pople, J. Am. Chem. Soc. 1975, 97, 1354–1358.
[20] The disorder can be explained in terms of a superposition of the lel
and ob isomer; a view of the [Co(Le)]3+ ion is shown in Figure S1 in
the Supporting Information.
[21] C14H32Cl5CoN6O6Zn, monoclinic, space group P21/m, a=9.219(3) ꢄ,
b=13.876(5) ꢄ, c=10.517(3) ꢄ, b=99.054(16)8, Z=2, T=100(2) K,
2377 unique reflections, 203 refined parameters, R1 =0.105, wR2 (all
data)=0.313.
[22] Caution! Perchlorate salts of metal complexes with organic ligands
are potentially explosive.
[23] M. Ghisletta, H.-P. Jalett, T. Gerfin, V. Gramlich, K. Hegetschweiler,
Helv. Chim. Acta 1992, 75, 2233–2242.
[24] K. Hegetschweiler, V. Gramlich, M. Ghisletta, H. Samaras, Inorg.
Chem. 1992, 31, 2341–2346.
[25] G. J. Reiss, W. Frank, K. Hegetschweiler, D. Kuppert, Acta Crystal-
logr. Sect. C 1998, 54, 614–616.
[26] a) E. I. Stiefel, G. F. Brown, Inorg. Chem. 1972, 11, 434–436; b) A.
Avdeef, J. P. Fackler, Inorg. Chem. 1975, 14, 2002–2006.
[27] P. Comba, A. M. Sargeson, L. M. Engelhardt, J. M. Harrowfield,
A. H. White, E. Horn, M. R. Snow, Inorg. Chem. 1985, 24, 2325–
2327.
[28] A. G. Orpen, L. Brammer, F. H. Allen, O. Kennard, D. G. Watson,
R. Taylor, J. Chem. Soc. Dalton Trans. 1989, S1–S83.
[29] M. Melnꢅk, M. Kabesova, L. Macaskova, C. E. Holloway, J. Coord.
Chem. 1998, 45, 31–145.
[30] The two types of diastereotopic carbon atoms, carrying a primary
amino group, exhibited an identical chemical shift of d=52.5 ppm.
[31] K. Hegetschweiler, M. Ghisletta, T. F. Fꢀssler, R. Nesper, H. W.
Schmalle, G. Rihs, Inorg. Chem. 1993, 32, 2032–2041.
Received: September 16, 2009
Published online: February 8, 2010
3340
www.chemeurj.org
ꢂ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2010, 16, 3326 – 3340