Synthesis, structure and hydrolytic properties of a family of new Zn complexes containing hexaazamacrocyclic ligands

Article abstract of DOI:10.1002/ejic.200300381

The synthesis, structure and spectroscopic properties of a family of Zn complexes containing a dinucleating hexaazamacrocyclic ligand (L) and anionic ligands (X) of general formula [Zn₂(X)_4-n(L)]ⁿ⁺ (1-8; L = H2p, H3p, Me2p

Full text of DOI:10.1002/ejic.200300381

FULL PAPER
Synthesis, Structure and Hydrolytic Properties of a Family of New Zn
Complexes Containing Hexaazamacrocyclic Ligands
Miquel Costas,[a] Carmen Anda,[a] Antoni Llobet,*[a] Teodor Parella,[b]
Helen Stoeckli Evans,[c] and Elena Pinilla[d]
Keywords: Zinc / Cooperative effects / Coordination chemistry / Fluxionality / Homogeneous catalysis / Macrocyclic
ligands
The synthesis, structure and spectroscopic properties of a
ligand bonded to the metal centres. The different factors gov-
family of Zn complexes containing a dinucleating hexaazam- erning the relative Zn−Zn disposition are discussed. NMR
acrocyclic ligand (L) and anionic ligands (X) of general for-
mula [Zn2(X)4−n(L)]n+ (1−8; L = H2p, H3p, Me2p, Me2m,
Me3p, Me3m; X = Cl, n = 0; X = NO3, n = 2) have been
investigated. The solid-state structural characterisation has
spectroscopy in solution reveals the presence of fluxional be-
haviour and a completely different structural arrangement
than in the solid state. In particular, evidence for the forma-
tion and breaking of Zn−N bonds involving all the macro-
been performed by means of X-ray diffraction analysis for cyclic ligand aminic N atoms is obtained for the chloride
complexes 3, 5, 7·1/3CH2Cl2 and 8. The Zn complexes 5, 7·1/
3CH2Cl2 and 8 containing chloride ligands present a dis-
torted N2Cl2 tetrahedral coordination with two non-coordin- stants ranging from 0.045 to 0.193
ated N atoms of the macrocyclic ligand. On the other hand, the influence of the ligands over the hydrolytic activity.
complex 3, which contains nitrate ligands, displays an N3O2 ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
complexes 2 and 4−8. Finally, complexes 1, 3, 5 and 7 hydro-
lyse p-nitrophenyl acetate (NA) with second-order rate con-
M
−1s−1, thus manifesting
pentacoordination with all the N atoms of the macrocyclic
Germany, 2004)
Introduction
properties.[6Ϫ8] The ability of macrocyclic ligands to preor-
ganise two metal centres at a particular distance has also
been used in the design of Zn complexes that efficiently
catalyse the hydrolysis of phosphate and carboxy
esters[9Ϫ11] thus mimicking the activity of zinc enzymes that
mediate hydrolytic reactions.[12Ϫ16] However, exhaustive
characterisation of Zn complexes with macrocyclic polyam-
ines is scarce. In this work we have synthesised and charac-
terised a series of Zn complexes with hexaazamacrocyclic
ligands where the metal coordination and the metal-metal
relative disposition are modulated by the characteristics of
the macrocyclic ligand. We have also studied the ability of
these complexes to perform the hydrolysis of p-nitrophenyl
acetate (NA). Our results demonstrate that small changes
in the macrocyclic backbone lead to important changes in
the ZnϪZn distance and in the hydrolytic ability manifested
by the complexes.
Macrocyclic polyamines are well-known to participate in
molecular recognition phenomena with different kinds of
substrates, such as organic and inorganic cations, anions
and neutral molecules.[1] Such interactions have attracted
interest from environmental, catalytic and health-related
domains.[2] Macrocyclic molecules containing two polyam-
ine units linked by a spacer are also capable of ligating two
metal atoms in close proximity. In some cases this leads to
interactions between the two metallic centres that results in
interesting magnetic,[3] electronic[4,5] and/or catalytic
[a]
´
Departament de Quımica, Universitat de Girona,
Campus de Montilivi, 17071 Girona, Spain
Fax: (internat.) ϩ34-972-418-150
E-mail: antoni.llobet@udg.es
[b]
[c]
[d]
`
Servei de RMN, Universitat Autonoma de Barcelona,
Bellaterra 08193, Barcelona, Spain
Fax: (internat.) ϩ34-93/581-2003
E-mail: teo@rmn4.uab.es
´
ˆ
Institut de Chimie, Universite de Neuchatel,
Av. Bellevaux 51, 2007 Neuchatel, Switzerland
Fax: (internat.) ϩ41-32-718-2511
Results and Discussion
E-mail: Helen.Stoeckli-Evans@unine.ch
Synthesis and Solid-State Structure
´
Departamento de Quimica Inorganica, Facultad de Ciencias
´
Quımicas, Universidad Complutense
The six macrocyclic ligands used in this work are shown
in Scheme 1 and were prepared according to literature
procedures.[17Ϫ20] This family of ligands comprises second-
ary amines and their hexamethylated analogues and is
Ciudad Universitaria, 28040 Madrid, Spain,
Fax: (internat.) ϩ34-91-394-4284
E-mail: epinilla@quim.ucm.es
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
Eur. J. Inorg. Chem. 2004, 857Ϫ865
DOI: 10.1002/ejic.200300381
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857

M. Costas, C. Anda, A. Llobet, T. Parella, H. Stoeckli Evans, E. Pinilla
FULL PAPER
Scheme 1. Macrocyclic ligands used in this work
characterised by the number of methylenic units linking the structures of complexes 5 (top right), 7 (bottom left) and 8
amines, which can be two or three, and by the aromatic (bottom right), together with the atom labelling system
substitution that takes place in the meta or para positions.
used.
Reaction of those ligands at room temperature with two
The cationic part of 3 consists of the macrocyclic ligand,
times the stoichiometric amount of the appropriate ZnII salt which binds to two zinc atoms, and an NO3Ϫ anion bonded
in methanol affords the corresponding dinuclear ZnII com- to each metal adopting an (η2-O,O-NO3) chelating mode
plexes 1Ϫ8 as white microcrystalline solids in modest to (∆rZnϪO ϭ 0.075 A). The whole molecule has an inversion
˚
good yields (ranging from 34 to 77%), as shown in Equa- centre that relates the metal atoms and half of the macro-
tion (1) for the particular case of 5.
cyclic ligand with the other half. The Zn metal centres are
five-coordinate, binding to three N atoms from the macro-
cyclic ligand and two oxygens from the nitrate ligand. The
(1)
˚
ZnϪN distances range from 1.992(6) to 2.054(7) A and the
two ZnϪO bonds are significantly different [ZnϪO1:
˚
˚
The crystal structures of [Zn2(NO3)2(H3p)](NO3)2 (3), 2.206(8) A; ZnϪO2: 2.281(9) A], although all of them com-
[Zn2Cl4(Me2p)] (5), [Zn2Cl4(Me3p)]·1/3CH2Cl2 (7·1/ pare well with the observed values of complexes containing
3CH2Cl2) and [Zn2Cl4(Me3m)] (8) have been determined by an N3ZnO2NO coordination environment.[21] The
means of single-crystal X-ray diffraction analysis. Table 1 NϪZnϪN bond angles range from 92.5(3)° to 128.1(3)°
contains their crystallographic data whereas Table 2 con- whereas the NϪZnϪO angles range from 89.3(3)° to
tains their selected bond lengths and angles. Figure 1 shows 141.0(3)°, reflecting the distortions imposed by the rigidity
the ORTEP diagrams obtained for the cationic molecular of the macrocyclic ligand and the asymmetry of the coordi-
structure of complex 3 (top left) and the neutral molecular nated nitrate anion.
Table 1. Crystallographic data of 3, 5, 7 and 8
Complex
3
5
7·1/3CH2Cl2
8
Empirical formula
Mol. mass (g/mol)
Crystal system
C28H46N10O12Zn2
845.49
orthorhombic
Pbca
0.09 ϫ 0.2 ϫ 0.4
14.1458(12)
15.3309(13)
16.2605(14)
90
3526.4(5)
4
C30H52Cl4N6Zn2
769.42
monoclinic
P21/n
0.05 ϫ 0.3 ϫ 0.4
10.9716(7)
8.0318(5)
20.9911(13)
101.144(8)
1814.9(2)
2
C34.33H58.67Cl4.67N6Zn2
851.71
C34H60Cl4N6OZn2
825.42
monoclinic
P21/c
0.15 ϫ 0.3 ϫ 0.45
10.7508(9)
12.2409(8)
14.8889(13)
95.772(10)
1949.4(3)
2
hexagonal
¯
Space group
R3
Crystal size (mm3)
0.2 ϫ 0.2 ϫ 0.1
22.9991(14)
22.9991(14)
21.7424(15)
120
9960.0(11)
9
˚
a (A)
˚
b (A)
˚
c (A)
β (deg)
Volume (A )
Z
3
˚
Temperature (K)
296(2)
0.71073
1.593
223(2)
0.71073
1.408
223(2)
0.71073
1.278
293(2)
0.71073
1.406
˚
λ(Mo-Kα) (A)
ρcalcd. (g/cm3)
µ (mmϪ1
)
1.436
1.570
1.395
1.537
Meas. reflns.
Unique reflns.
17342
3109
13530
3513
23527
4297
15306
3579
Observed reflns. [I Ͼ 2σ(I)]
Parameters
1713
216
0.076
0.24
2403
194
0.0298
0.0681
1823
211
0.0402
0.0949
1990
211
0.0332
0.0699
R1 [I Ͼ 2σ(I)][a]
wR2 (all data)[b]
[a]
[b]
2
2 2
4
R1 ϭ Σ(||Fo| Ϫ |Fc||)/Σ|Fo|]. wR2 ϭ {Σ[w(Fo Ϫ Fc ) ]/Σ(wFo )}1/2
.
858
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New Zn Complexes Containing Hexaazamacrocyclic Ligands
FULL PAPER
˚
Table 2. Selected bond lengths (A) and bond angles (°) for 3, 5, 7 and 8
3
5
7·1/3CH2Cl2
8
Zn(1)ϪN(1)
Zn(1)ϪN(2)
Zn(1)ϪN(3)
2.042(6)
2.054(7)
1.992(6)
2.100(2)
2.1194(19)
2.088(4)
2.077(3)
2.088(3)
2.108(2)
Zn(1)ϪCl(1)
Zn(1)ϪCl(2)
2.2153(7)
2.2092(7)
2.2395(15)
2.1888(14)
2.2103(9)
2.2266(9)
Zn(1)ϪO1
Zn(1)ϪO2
Zn(1)ϪZn(1Ј)
2.206(8)
2.281(9)
8.73
12.395
87.38(7)
10.744
100.72(14)
6.743
100.95(10)
N(1)ϪZn(1)ϪN(2)
N(1)ϪZn(1)ϪN(3)
N(2)ϪZn(1)ϪN(3)
Cl(2)ϪZn(1)ϪCl(1)
N(1)ϪZn(1)ϪCl(2)
N(2)ϪZn(1)ϪCl(2)
N(1)ϪZn(1)ϪCl(1)
N(2)ϪZn(1)ϪCl(1)
N(1)ϪZn(1)ϪO(1)
N(1)ϪZn(1)ϪO(2)
N(2)ϪZn(1)ϪO(1)
N(2)ϪZn(1)ϪO(2)
N(3)ϪZn(1)ϪO(1)
N(3)ϪZn(1)ϪO(2)
O(1)ϪZn(1)ϪO(2)
92.5(3)
128.1(3)
98.4(3)
121.19(3)
112.49(6)
111.02(6)
108.58(6)
111.08(5)
115.14(6)
119.12(4)
105.49(7)
108.70(7)
113.59(7)
107.42(7)
121.37(12)
107.90(11)
104.74(11)
104.97(11)
94.9(3)
125.2(3)
141.0(3)
89.7(3)
106.6(3)
105.6(3)
55.3(3)
Upon coordination, the macrocyclic ligand generates ported in the literature.[26] The number of atoms that form
four six-membered rings containing the Zn metal, which, in the chelate cycle dramatically affects the N1ϪZnϪN2 and
all cases, adopt a chair conformation. The aromatic rings Cl1ϪZnϪCl2 angles. The six-membered chelate rings of 7
are oriented in a parallel manner and the coordinated ni- and 8 result in N1ϪZnϪN2 angles of 100.72(14)° and
trates are disposed in an anti configuration, as expected 100.95(10)°, slightly smaller than the corresponding
from a steric viewpoint. Finally the Zn···Zn distance is 8.73 Cl1ϪZnϪCl2 angles [115.14(6)° and 119.12(4)°, respec-
˚
A. The structure is completed by two non-coordinating ni- tively], whereas the more constrained five-membered ring
trate anions which could only be refined isotropically. Two formed in the ethylene-based macrocycle 5 forces a more
oxygen atoms of each nitrate are within H-bond range acute N1ϪZnϪN2 angle [87.38(7)°], remarkably smaller
˚
(2.95Ϫ3.1 A) of the N atoms of the macrocyclic ligand, on than the corresponding Cl1ϪZnϪCl2 angle [121.19(3)°].
the opposite side of the N3Zn(η2-O,O)NO3 unit.
These parameters indicate a significant distortion from a
The molecular structures of 5, 7 and 8 consist of a neutral tetrahedral geometry in 5, which is further evidenced by the
Zn2Cl4L unit. The macrocyclic molecules are again centro- dihedral angle of 80.80° formed between the planes de-
symmetric. In sharp contrast to the previous structure and scribed by N2ϪZn1ϪCl2 and N1ϪZn1ϪCl1. It is interest-
related complexes described in the literature
—
ing to note here that in all the structures described in the
[Pd2Cl2(Me2p)](ClO4)2·H2O,[22]
[Cu2Cl2(Me2p)](BPh4)- present work the aromatic rings are disposed in a parallel
(ClO4)·CH3CN,[23] [Cu2(Me2p)(CO)2](ClO4)2·2H2O and manner. Finally, complex 7 cocrystallises with a third of a
[24]
[Cu2(Me2m)(tBuNC)2](CF3SO3)2
— the Zn atoms ad- molecule of severely disordered CH2Cl2.
opt a distorted tetrahedral geometry coordinated to only
For dinuclear complexes containing hexaazamacrocyclic
four of the six available N atoms of the macrocyclic ligand; ligands, such as the ones described here, the ‘‘internal cav-
each Zn coordinates to two chlorine atoms and two adjac- ity’’ of the complex can be defined as the smallest macrocy-
ent N atoms of the macrocycle, leaving two benzylic amines cle containing the two metals. For complexes with all N
of the macrocycle as non-coordinating. Binding of the me- atoms coordinated to the metal centre, as in 3, the cavity
tal ion to only two N atoms of the macrocycle in 5, 7 and dimension, expressed in terms of the number of member
8 probably reflects that formation of the second ZnϪCl units, is dependent on the aromatic substitution (the para
bond, in combination with the release of the strain imposed case having an internal cavity with two more units than the
by the macrocyclic ligand, can overcome the breakage of a meta) and independent of the number of methylenic units
rather weak ZnϪNtertiary bond.[25]
within the amines. On the other hand, with a partial coordi-
The coordination of Zn1 to two adjacent macrocyclic N nation of the macrocyclic ligand, such as that obtained in
atoms results in a five- (5), or six-membered (7 and 8) che- complexes 5, 7 and 8, the internal cavity will now depend
late ring where the six-membered ring always adopts a chair on both factors. Thus, complex 7, containing the Me3p li-
conformation. The Zn bond lengths and angles are within gand, will have a larger internal cavity than 3, its H3p ana-
the expected range for Zn polyaza complexes previously re- logue, due to the enlargement produced by the partial coor-
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M. Costas, C. Anda, A. Llobet, T. Parella, H. Stoeckli Evans, E. Pinilla
FULL PAPER
Figure 1. ORTEP diagram (50% probability) of the cationic part of complex 3 (top left), complex 5 (top right), complex 7 (bottom left)
and 8 (bottom right)
dination of the former ligand. As a consequence the com- which produces the largest internal cavity, presents the
plex with the tertiary amine has a Zn···Zn distance larger shortest Zn···Zn distance. This is due to the different ar-
than the corresponding secondary amine. Complex 5, con- rangement that the meta aromatic substitution provokes
taining the Me2p ligand, has a smaller internal cavity than with regard to the para, the former being more compact.
complex 7, containing the analogous ligand but with pro- As a consequence of this, in complex 8 (meta substitution)
pylene linkers instead of ethylene. In sharp contrast, 5 has two of the Cl ligands bonded to the metal centres are di-
a larger Zn···Zn distance than 7, due to the relative dispo- rected towards the inside the cavity, whereas in complexes
sition of the metal complexes produced by the methylene 5 and 7 (para substitution) all Cl ligands are clearly oriented
linkers. Finally, complex 8, containing the Me3m ligand, outside the cavity and are pointing in opposite directions.
860
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New Zn Complexes Containing Hexaazamacrocyclic Ligands
FULL PAPER
the complex. However, the singlet structure of the signals
strongly suggests again the presence of fluxional behaviour
and that each of the signals does not belong to a single
species but to a number of inter-exchanging isomers. The
solvent strongly influences the nature of the fluxional be-
haviour, as deduced from the sharpening of the resonances
when using D2O instead of CD2Cl2 or [D6]DMSO. Even
though the signals do not totally resolve, it is obvious that
in aqueous solution the speed of the process is enhanced.
Another interesting aspect of the chemistry of these com-
NMR Spectroscopy and Solution Structure
The 1H and 13C NMR spectra of complexes 1Ϫ7 at room
temperature in different deuterated solvents are presented
as Supporting Information and are assigned in the Exp.
Sect. No NMR spectra could be obtained for complex 8
due to its low solubility.
In the spectra, the resonances are shifted downfield rela-
tive to the free ligand demonstrating that the metal ion re-
mains bound to the macrocycle in solution. However, it is
interesting to point out here that the fine structure of the
spectra of these complexes is not well resolved either due
to poor resolution of multiple superimposed signals or,
more likely (vide infra), the presence of fluxional behaviour.
The latter may be attributed to fast exchange between dif-
ferent conformers in solution, although these phenomena
alone cannot explain the apparent simplicity of the spectra,
which is not consistent with the more asymmetric structure
of the complexes in the solid state, as determined by X-ray
crystallography. If retained in solution, the structure deter-
mined in the solid state should give rise to two different
signals (assuming fast aromatic ring rotation) for the aro-
matic protons in the complexes containing para-substituted
macrocycles (5 and 7). In addition, the benzylic protons in
5, 6 and 7 should also give rise to at least two different
1
plexes emerges when comparing the H NMR spectra of
complex 2 or 4 with 5 or 7, respectively, in the same sol-
vent — the comparison of the spectra of Zn complexes
bearing secondary or tertiary amine macrocyclic ligands,
showing a sharp narrowing for the latter. This observation
favours the description of the fluxional behaviour as bond
formation and breaking rather than a unique structure since
it indicates that the breaking of the weaker ZnϪNtertiary
bonds[25] requires lower activation energies. Thus
ZnϪNtertiary bonds can form and break faster than the
stronger ZnϪNsecondary analogues, finally resulting in the
narrowing of the resonances.
Hydrolytic Activity
The Zn complexes containing para-substituted ligands (1,
3, 5 and 7) described in the present work were tested in the
hydrolysis of 4-nitrophenyl acetate (NA) [Equation (2)]. The
meta derivatives could not be used due to their low solu-
bility in water. Figure 2A shows the linear dependency of
the initial rate constant kin (defined as vin/[NA]) with regard
to [ZnCl4(Me2p)] (5) at different pH values ranging from
7.31 to 8.40; more-detailed kinetic data related to the hy-
drolysis of NA in the presence of different Zn complexes is
included as Supporting Information in Table S1. As ex-
pected, the increase in pH results in a monotonical increase
of kin. This behaviour can be interpreted in terms of the
generation of the nucleophilic LZnϪOH species which has
been shown to be the active species in previous works with
related ligands.[11,28] This behaviour also rules out the pos-
sibility of the free metal ion being the active species since,
as the pH is increased, its concentration strongly decreases.
On the other hand blank experiments with only free ligand
or free metal ion under similar conditions display a much
smaller hydrolytic capacity. Furthermore, the free ligand is
not observed in the NMR spectra of the complexes re-
ported here. It is interesting to point out here that the rate
constants observed for [ZnCl4(Me3p)] (7) and for its nitrate
analogue [Zn(NO3)2(Me3p)](NO3)2 (data not shown) are
1
signals in a 1:1 ratio. However, the H NMR spectra of 5 in
CD2Cl2 (D2O) and 7 in DMSO (D2O) show only one broad
singlet at δ ϭ 7.39 (7.56) and 7.24 (7.47) ppm, respectively,
indicating that all the aromatic protons are equivalent on
the NMR timescale. The benzylic protons also appear as a
broad singlet at δ ϭ 3.78 (3.99) for 5, 3.77 for 6 and 3.46
(3.91) ppm for 7, which implies that the four benzylic
groups are again equivalent. Thus, these symmetric spectra
could either indicate the presence of a symmetric structure
in solution, where the six N atoms participate in the simul-
taneous binding of the Zn atoms, or, alternatively, it may
suggest the presence of two or more species in solution,
such as the one determined by X-ray crystallography, un-
dergoing fast inter-exchange. This process supposes rapid
ZnϪN bond formation and breaking involving all the am-
ino nitrogen atoms of the ligand. This type of behaviour is
not uncommon for d10 metal ions probably due to the lack
of ligand field stabilisation.[27] Further support for the
fluxional behaviour of the complexes is provided by variable
temperature NMR spectroscopy of 5 in CD2Cl2 (Figure
S10). The initially simple room temperature 1H NMR spec-
tra become complicated upon lowering the temperature.
For example, the aromatic and benzylic protons, which ap-
pear as singlets at 295 K, convert into multiple poorly re-
solved signals. The higher complexity of the low tempera-
ture spectra is consistent with the freezing-out of the
fluxional processes, although even at 160 K the signals do
not became completely resolved, thus precluding a com-
plete assignment of the spectra.
The spectra of 3 and 4, which show two broad singlet
signals, with a 5:3 integration ratio that are assigned to the
benzylic protons, are also unusual. The data are consistent
with at least two dramatically different isomeric forms of
(2)
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M. Costas, C. Anda, A. Llobet, T. Parella, H. Stoeckli Evans, E. Pinilla
FULL PAPER
virtually the same within experimental error. These results ditions,[28,29] although the low solubility of our complexes
manifest the strong dependency of the rate constant with at pH’s higher than 8.4 precludes a fair comparison.
regard to the ligand system and, in contrast, the weak influ-
ence of the labile chloride and nitrate ligands.
Our results for the second-order rate constants are in
agreement with tertiary amines generating more nucleo-
philic LZnϪOH species than secondary amines due to the
hydrophobicity of the former,[30] which precludes charge de-
localisation among solvated species. When comparing com-
plexes 5 and 7, both with tertiary amines, at a given pH it
is found that 5 has higher kNA values than 7 even though
the latter has four more methylenic groups. This is due to
the fact that at the same pH the Me2p ligand generates a
much higher concentration of LZnϪOH species than
Me3p, as has been previously shown in the literature for
similar complexes.[31] Finally, for complexes bearing sec-
ondary amines the tendency is just the opposite than in
the case of the tertiary amines just discussed. In particular,
complex 1 presents significantly lower kNA values than the
rest of the studied complexes. At this moment it is not obvi-
ous to us why 1 has such a low hydrolytic activity, although,
presumably, the structure of the ligand does not favour the
interaction between the electrophile (ZnϪOPO2R) and nu-
cleophile (ZnϪOH) units.
Conclusion
A family of new dinuclear Zn complexes bearing hexaaz-
amacrocyclic and chloride or nitrate ligands have been pre-
pared and characterised from the corresponding metal salt
and ligand as the starting materials. In the solid state, the
metal coordination geometry as well as the ligand coordi-
nation mode are strongly dependent on the Zn starting ma-
terial. Thus, ZnCl2 generates a Cl2N2 tetrahedrally distorted
environment for Zn with a coordination number (CN) of
four whereas the Zn(NO3)2 salt generates an N3O2 environ-
ment with a CN of five. Furthermore the macrocyclic li-
gand in the former case coordinates through only four of
Figure 2. Kinetic data for the hydrolysis of 4-nitrophenyl acetate the six possible N atoms, whereas in the latter case it coor-
(NA) by the macrocyclic Zn complexes: A) initial rate constant
dinates through all its N atoms. These different coordi-
kin relative to [ZnCl4(Me2p)] at different pH; B) second-order rate
nation modes, together with the flexibility of the macro-
cyclic ligands, allows a certain control of the relative spatial
ZnϪZn disposition.
constants, kNA, relative to [OH] for different macrocyclic Zn com-
plexes
NMR spectroscopy clearly indicates that the solution
structure of these macrocyclic complexes is radically differ-
ent from their structure in the solid state. In the case of the
chloride complexes 2 and 4Ϫ8, NMR spectroscopy reveals
the presence of a fluxional behaviour that presumably in-
volves exchange between conformational isomers and the
formation and breaking of ZnϪN bonds including all N
atoms of the macrocyclic ligand.
Finally, complexes 1, 3, 5 and 7 have been shown to be
capable of hydrolyzing p-nitrophenyl acetate (NA). Their
different hydrolysis rates reveal how small variations in the
ligand can significantly influence hydrolytic activity.
Unfortunately, in our case, at higher pH values the com-
plexes start to precipitate out of the solution, preventing
further kinetic analysis. A similar linear dependency is also
found for complexes 1, 3 and 7 and is presented as Support-
ing Information.
Second-order rate constants, kNA, were obtained at a
given pH from a plot of kin vs. complex concentration. The
linear dependency of this second-order rate constant
against [OH] is shown in Figure 2B for the four para com-
plexes. As can readily be seen, at a given pH complexes 5
(for instance at pH 8.4, kNA ϭ 0.193 Ϫ1sϪ1) and 7 (0.158

Ϫ1sϪ1), bearing tertiary amine ligands, give higher rate val-
ues than complexes 1 (0.045 Ϫ1sϪ1) and 3 (0.123 Ϫ1sϪ1
)
Experimental Section
containing secondary amines. These values are about an or-
der of magnitude lower than the best complexes reported
Physical Methods: IR spectra were recorded on a Mattson-Galaxy
in the literature for the same reaction under similar con- Satellite FT-IR spectrophotometer as solid KBr pellets. Elemental
862  2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim www.eurjic.org
Eur. J. Inorg. Chem. 2004, 857Ϫ865

New Zn Complexes Containing Hexaazamacrocyclic Ligands
FULL PAPER
analyses were conducted on a CarloϪErba Instrument, Mod.
found C 38.08, H 5.43, N 10.93. FT-IR (KBr): ν˜, 3217, 2930, 2874
1
CHNS 1108. UV/Vis spectra were recorded on a Varian Cary-50 and 1445 cmϪ1. H NMR (200 MHz, D2O, 25 °C): δ ϭ 2.50Ϫ3.20
spectrophotometer, using quartz cuvettes. NMR spectra were re-
corded at 298 K on a Bruker DPX200 Model Avance (4.7 T) op-
erating at 200 MHz for proton. Spectra were referenced to the re-
sidual protio solvent peaks or TMS (tetramethylsilane).
(m, 16 H, NCH2) 3.85 (m, 8 H, ArCH2) 7.34 (s, 8 H, arom.) ppm.
13C NMR (50 MHz, D2O, 25 °C): δ ϭ 47.8 (NCH2), 55.3 (ArCH2),
132.4 (arom. tert.), 139.3 (arom. quat.) ppm.
[Zn2(NO3)2(H3p)](NO3)2·4/3CH3OH (3·4/3CH3OH): A methanol
(5 mL) solution of Zn(NO3)2·6H2O (297 mg, 1 mmol) was added
Electrospray ionisation mass spectra were acquired using a Navi-
gator quadrupole instrument (MassLab Group, Finnigan, Manch-
ester, UK) equipped with an Aqua system for atmospheric pressure
chemical ionisation (APCI) and electrospray (ESI). The samples
were introduced either with a liquid chromatographic pump
(P2000, Thermo Separation Products) at a flow rate of 0.3 mL/min
using different proportions of H2O/methanol as the mobile phase,
or by direct infusion by the Aqua system. Positive ion spectra were
acquired in full scan 2Ϫ1600 m/z in continuum mode.
dropwise to
a vigorously stirred solution of H3p (233 mg,
0.50 mmol) in methanol (10 mL). A white precipitate rapidly ap-
peared. The mixture was stirred for 30 min and then cooled down
in an ice bath. The white solid that precipitated was then filtered,
washed with methanol and dichloromethane and dried under vac-
uum. (328 mg, 0.39 mmol, 77%). FT-IR (KBr): ν˜, 3223, 2933, 2878
and 1383 cmϪ1. C28H46N8O6Zn2·4/3CH3OH (888.2): calcd. C
1
39.67, H 5.83, N 15.77; found C 39.84, H 5.86, N 15.73. H NMR
(200 MHz, D2O, 25 °C): δ ϭ 1.40Ϫ2.00 (m, 8 H, CH2CH2CH2),
2.86 (s, 16 H, NCH2), 3.31 (s, CH3OH) 3.97 (s, 5 H, ArCH2), 3.77
(s, 3 H, ArCH2), 7.41 (s, 8 H, arom.) ppm. 13C NMR (50 MHz,
D2O, 25 °C): δ ϭ 22.9 (NCH2) 44.7, 45.4 (CH2CH2CH2), 49.5
(CH3OH), 50.7 (ArCH2) 129.9 (arom. tert.), 133.9, 136.1 (arom.
Materials and Synthesis: Solvents were purchased from SDS as syn-
thesis grade. Acetonitrile was distilled from over P2O5 (Prolabo)
and stored over molecular sieves. Diethyl ether and THF were dis-
tilled from over Na (Panreac) or benzophenone (Fluka), respec-
tively, just previously to their use. CH2Cl2 was distilled from over
CaH2 (Aldrich) and stored over molecular sieves. Methanol was
distilled from over Mg (Aldrich) and stored in the dark over molec-
ular sieves. Acetone was dried over CaCl2 (Panreac) and stored
over molecular sieves.
quat.) ppm. MS: m/z
ϭ 783.66 [Zn2(NO3)3(H3p)], 656.19
[Zn(NO3)2(H3p)], 594.19 [Zn(NO3)(H3p)].
[Zn2Cl4(H3p)]·7/3H2O (4·7/3H2O): A methanol (5 mL) solution of
ZnCl2 (27 mg, 0.20 mmol) was added dropwise to a vigorously
stirred solution of H3p (47 mg, 0.10 mmol) in methanol (3 mL). A
white precipitate rapidly appeared. The mixture was stirred for 2 h
and then cooled down in an ice bath. The white solid that precipi-
tated was then filtered, washed with methanol and dried under vac-
uum. (25 mg, 0.34 mmol, 34%). FT-IR (KBr): ν˜, 3212, 2933, 2874
and 1431 cmϪ1. C28H46N6Zn2Cl4·7/3H2O (781.3): calcd. C 43.04,
H 6.54, N 10.76; found C 43.01, H 6.59, N 10.80. 1H NMR
(200 MHz, D2O, 25 °C): δ ϭ 1.74 (m, 8 H, CH2CH2CH2), 2.89 (m,
16 H, NCH2), 3.96 (s, 5 H, ArCH2), 3.80 (s, 3 H, ArCH2), 7.46
(s, 8 H, arom.) ppm. 13C NMR (50 MHz, D2O, 25 °C): δ ϭ 22.2
(CH2CH2CH2), 43.2, 43.9 (NCH2), 50.5 (ArCH2), 128.0, 128.2
(arom. tert.), 132.4, 133.5, 134.3 (arom. quat.) ppm. MS: m/z ϭ
704.01 [Zn2Cl3(H3p)], 603.09 [ZnCl2(H3p)], 567.64 [ZnCl(H3p)].
The macrocyclic ligands 3,6,9,16,19,22-hexaazatricyclo[22.2.2.211,14]-
triaconta-1(27),11(30),12,14(29),24(28),25-hexaene (H2p), 3,7,11,18,
22,26-hexaazatricyclo[26.2.2.213,16]tetratriaconta-1(31),13(34),
14,16(33),28(32),29-hexaene
(H3p),
3,6,9,16,19,22-hexamethyl-
3,6,9,16,19,22-hexaazatricyclo[22.2.2.211,14]triaconta-1(27),11(30),
12,14(29),24(28),25-hexaene (Me2p) 3,6,9,17,20,23-hexamethyl-3,6,9,
17,20,23-hexaazatricyclo[23.3.1.111,15]triaconta-1(29),11,13,15(30),
25,27-hexaene (Me2m), 3,7,11,18,22,26-hexamethyl-3,7,11,18,22,26-
hexaazatricyclo[26.2.2.213,16]tetratriaconta-1(31),13(34),14,16(33),
28(32),29-hexaene
(Me3p)
and
3,7,11,19,23,27-hexamethyl-
3,7,11,19,23,27-hexaazatricyclo[27.3.1.113,17]tetratriaconta-1(33),
13,15,17(34),29,31-hexaene (Me3m) were prepared according to the
published procedures or slight modifications thereof.[17Ϫ20] (for
structural drawing see Scheme 1).
[Zn2Cl4(Me2p)] (5): Me2p (50 mg, 0.10 mmol) was dissolved in
MeOH (2 mL). A solution of ZnCl2 (28 mg, 0.20 mmol) dissolved
in acetone (2 mL) was added to this solution. A white solid rapidly
precipitated. The mixture was stirred for 30 min and the white solid
filtered. The solid was collected and dissolved in CH2Cl2 (3 mL),
filtered through celite and the solvent removed under vacuum. The
residue that remained was washed with acetone and methanol to
obtain the product as a white solid (56 mg, 0.07 mmol, 72%). FT-
IR (KBr): ν˜ ϭ 1467 cmϪ1. C30H50Cl4N6Zn2 (767.3): calcd. C 46.96,
H 6.57, N 10.95; found C 46.84, H 6.82, N 10.75. 1H NMR
(200 MHz, CD2Cl2, 25 °C): δ ϭ 2.41 (s., 12 H, NCH3), 2.50Ϫ3.10
(m, broad, 22 H, NCH2 and NCH3), 3.78 (s, 8 H, ArCH2), 7.39 (s,
8 H, arom.) ppm. 13C NMR (50 MHz, CD2Cl2, 25 °C): δ ϭ 32.7,
44.9, 43.3 (NCH3), 56.0 (NCH2), 63.7 (ArCH2), 131.2 (arom. tert.),
[Zn2(NO3)2(H2p)](NO3)2·11/3H2O (1·11/3H2O):
A
methanol
(3 mL) solution of Zn(NO3)2·6H2O (179 mg, 0.60 mmol) was ad-
ded dropwise to a vigorously stirred solution of H2p (123 mg,
0.30 mmol) in methanol (6 mL). A white precipitate rapidly ap-
peared. The mixture was stirred for 30 min and then cooled down
in an ice bath. The white solid that precipitated was then filtered,
washed with methanol and dichloromethane and dried under vac-
uum. (168 mg, 0.21 mmol, 71%). FT-IR (KBr): ν˜, 3223, 2933, 2878
and 1383 cmϪ1. C24H38N8O6Zn2·11/3H2O (855.5): calcd. C 33.70,
H 5.34, N 16.37; found C 33.87, H 5.36, N 16.31. 1H NMR
(200 MHz, D2O, 25 °C): δ ϭ 2.50Ϫ3.20 (m, 16 H, NCH2),
3.80Ϫ4.20 (m, 8 H, ArCH2), 7.36 (s, 8 H, arom.) ppm. 13C NMR
(50 MHz, D2O, 25 °C): δ ϭ 45.9 (NCH2), 52.0 (ArCH2), 129.8
(arom. tert.), 136.6 (arom. quat.) ppm. MS: m/z ϭ 727.56
[Zn2(NO3)2(H2p)], 538.08 [Zn(NO3)(H2p)].
1
135.7 (arom. quat.) ppm. H NMR (200 MHz, D2O, 25 °C,): δ ϭ
1.98 (s, 6 H, NCH3), 2.68 (s, 12 H, NCH3), 2.85 (m, 8 H, NCH2),
2.99 (m, 8 H, NCH2), 3.99 (s, 8 H, ArCH2), 7.56 (s, 8 H, arom.)
ppm. 13C NMR (50 MHz, D2O, 25 °C): δ ϭ 42.0, 43.9, (NCH3),
53.7, 54.4, (NCH2), 63.0 (ArCH2), 134.1 (arom. tert.), 136.4 (arom.
[Zn2Cl4(H2p)]·4H2O (2·4H2O): A methanol (3 mL) solution of
ZnCl2 (28 mg, 0.20 mmol) was added dropwise to a vigorously
stirred solution of H2p (41 mg, 0.10 mmol) in methanol (2.5 mL).
A white precipitate rapidly appeared. The mixture was stirred for
30 min and then cooled down in an ice bath. The white solid that
precipitated was then filtered, washed with methanol and dichloro-
methane and dried under vacuum. (25 mg, 0.04 mmol, 37%).
quat.) ppm. MS: m/z
ϭ
631.14 [ZnCl2(Me2p)], 595.69
[ZnCl(Me2p)].
[Zn2Cl4(Me2m)]·2H2O·CH3OH (6·2H2O·CH3OH): Me2m (78 mg,
0.16 mmol) was dissolved in MeOH (2 mL), and ZnCl2 (43 mg,
C24H38Cl4N6Zn2·4H2O (755.3): calcd. C 38.17, H 6.14, N 11.13; 0.32 mmol) dissolved in MeOH (2 mL) was added. A white precipi-
Eur. J. Inorg. Chem. 2004, 857Ϫ865
www.eurjic.org  2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 863

M. Costas, C. Anda, A. Llobet, T. Parella, H. Stoeckli Evans, E. Pinilla
evaporation of CD2Cl2 solution. Suitable crystals of
FULL PAPER
tate rapidly appeared which redissolved upon stirring. The solvent
was removed under vacuum and the residue was then dissolved in
warm MeOH (5 mL). Upon standing, the product crystallised as
a
[Zn2Cl4(Me3p)]·1/3CH2Cl2 (7·1/3CH2Cl2) were obtained as colour-
less blocks by slow evaporation of a CH3OH/CH2Cl2 (1:1 v:v) solu-
tion. Suitable crystals of [Zn2Cl4(Me3m)] (8) were obtained as
white blocks (81 mg, 0.11 mmol, 67%). FT-IR (KBr): ν˜, 1467 cmϪ1
.
C30H50N6Zn2Cl4·2H2O·CH3OH (835.4): calcd. C 44.57, H 7.00, N colourless blocks by recrystallisation of the crude reaction mixture
10.06; found C 44.44, H 6.89, N 10.23. 1H NMR (200 MHz, from a CHCl3/MeOH/benzene/THF (2:1:1:1 v:v) mixture.
[D6]DMSO, 25 °C): δ ϭ 2.32 (s, 12 H, NCH3), 2.41 (s, 9 H, NCH3
For 3, data were collected on a Bruker Smart CCD diffractometer,
using Mo-Kα (λ ϭ 0.71073 A) radiation. A summary of the funda-
and DMSO) 2.50Ϫ2.571 (m, 16 H, NCH2), 3.43 (s, CH3OH), 3.77
(s, 8 H, ArCH2), 4.16 (s, broad, OH), 7.38 (m, 6 H, arom.), 7.77
(s, broad, 2 H, arom.) ppm. 13C NMR (50 MHz, [D6]DMSO, 25
°C): δ ϭ 42.8, 43.4 (NCH3), 48.7 (CH3OH), 53.3, 54.7 (NCH2),
60.3 (ArCH2), 127.8, 129.1 (arom. tert.), 136.4 (arom. quat.).
˚
mental crystal data and refinement data are given in Table 1. Data
were collected over a hemisphere of the reciprocal space by combi-
nation of three exposure sets. Cell parameters were determined and
refined by a least-squares fit of all reflections collected (θ range ϭ
2.33 to 25°, hkl from Ϫ16, Ϫ17, Ϫ19 to 13, 18, 19, respectively).
Each frame exposure time was of 20 s, covering 0.3° in ω. The first
50 frames were recollected at the end of the data collection to moni-
tor crystal decay. No appreciable decay in the intensities of stand-
ard reflections was observed. The structure was solved by direct
methods and refined by full-matrix least-squares on F2 (SHELXS-
97).[32] Anisotropic parameters were used in the last cycles of refine-
[Zn2Cl4(Me3p)]·1/3CH2Cl2
(7·1/3CH2Cl2):
Me3p
(65 mg,
0.12 mmol) was dissolved in MeOH/CH2Cl2 (2:1 v:v; 3 mL) and a
solution of ZnCl2 (32 mg, 0.24 mmol) in MeOH (3 mL) was added.
A white precipitate rapidly appeared which was filtered, collected
and dried under vacuum (65 mg, 0.08 mmol, 67%). FT-IR (KBr):
ν˜ ϭ 1467 cmϪ1. C34H58Cl4N6Zn2·1.5CH2Cl2 (950.8): calcd. C
44.84, H 6.47, N 8.84; found C 44.59, H 6.67, N 8.61. 1H NMR
(200 MHz, [D6]DMSO, 25 °C): δ ϭ 1.67 (m, 8 H, CH2CH2CH2),
2.18 (s, 12 H, NCH3), 2.28 (s, 6 H, NCH3), 2.70Ϫ2.30 (m, 16 H,
NCH2), 3.46 (s, 8 H, ArCH2), 7.24 (s, 8 H, arom.) ppm. 13C NMR
(50 MHz, [D6]DMSO, 25 °C): δ ϭ 23.3 (CH2CH2CH2), 42.2
(NCH3), 55.0, 55.2 (NCH2 and CH2Cl2), 61.5, 79.6 (ArCH2), 129.1
Ϫ
ment for all non-hydrogen atoms, with exceptions. For the NO3
counteranion, no resolvable positional disorder of these atoms was
found, and they were isotropically refined. Hydrogen atoms were
included in calculated positions and refined as riding on the re-
spective carbon atoms, with the thermal parameters related to the
bonded atoms, except H1, H2 and H3, bonded to nitrogen atoms,
which were located in a Fourier synthesis, included and their par-
ameters fixed. The largest residual peaks in the final difference
1
(arom. tert.),137.5 (arom. quat.) ppm. H NMR (200 MHz, D2O,
25 °C): δ ϭ 1.89 (m., 8 H, CH2CH2CH2), 2.53 (s, 12 H, NCH3),
2.53 (s, 6 H, NCH3), 2.83, (m, 16 H, NCH2), 3.91 (s, 8 H, ArCH2),
7.47 (s, 8 H, arom.) ppm. 13C NMR (50 MHz, D2O, 25 °C): δ ϭ
23.4 (CH2CH2CH2), 43.4 (NCH3), 56.2, 56.9 (NCH2), 62.8
map, maximum 1.052 e·AϪ3, are close to the non-coordinating
˚
Ϫ
NO3 anion.
(ArCH2), 133.7 (arom. tert.), 136.8 (arom. quat.) ppm. MS: m/z ϭ The intensity data were collected at 298 K (8) or 223 K (5 and 7·1/
687.25 [ZnCl2(Me3p)], 651.80 [ZnCl(Me3p)].
3CH2Cl2) on a Stoe Image Plate Diffraction System[33] using Mo-
Kα (λ ϭ 0.71073 A) graphite-monochromated radiation. Image
˚
[Zn2Cl4(Me3m)]·H2O (8·H2O): Me3m (142 mg, 0.26 mmol) was
dissolved in MeOH (3 mL). ZnCl2 (71 mg, 0.52 mmol) dissolved in
MeOH (1 mL) was added to this solution. The solution was vigor-
ously stirred until a fine white powder precipitated. The solid was
filtered, collected and dried under vacuum (125 mg, 0.15 mmol,
59%). The product was recrystallised from CHCl3 to obtain a white
microcrystalline solid insoluble in most common solvents (42 mg,
plate distance: 70 mm; ϕ oscillation scans: 0Ϫ200°; step ∆ϕ: 1.0°;
2θ range: 3.27Ϫ52.1°; dmaxϪdmin ϭ 12.45Ϫ0.81 A. The structures
˚
were solved by direct methods using the program SHELXS-97.[34]
The H-atoms were included in calculated positions and treated as
riding atoms using the SHELXL default parameters. The refine-
ment and all further calculations were carried out using SHELXL-
97.[34] The non-H atoms were refined anisotropically, using
weighted full-matrix least-squares on F2. For 7·1/3CH2Cl2 a small
amount of residual electron density was located in a final difference
Fourier synthesis at the origin of the unit cell about a threefold
inversion axis. The SQUEEZE routine in PLATON[35] indicated
the presence of a solvent accessible region of ca. 100 electrons for
0.05 mmol, 19.8%). FT-IR (KBr): ν˜
ϭ
1467 cmϪ1
.
C34H58Cl4N6Zn2·H2O (841.5): calcd. C 48.53, H 7.19, N 9.99;
found C 48.61, H 6.85, N 9.94.
Kinetics of p-Nitrophenyl Acetate (NA) Hydrolysis: The hydrolysis
rate of NA in the presence of the Zn complexes was measured in
a H2O/CH3CN (90:10 v:v) solution by an initial-slope method, fol-
lowing the increase in the 402 nm absorption of the released p-
nitrophenolate at 298 K (Ϯ 0.05 K). The molar absorbance of p-
nitrophenolate was determined at the pH of each measurement. The
qionic strength was adjusted to 0.1 with NaNO3. pH was adjusted
with Tris buffer (pH 7Ϫ9; 50 m). In a typical experiment, after
mixing NA (5.15 ϫ 10Ϫ4 ) and the Zn complex (0.1Ϫ0.5 m) in
10% CH3CN solution at appropriate pH (the reference experiment
uses only the ZnII complex), the UV absorption decay was recorded
immediately and was followed generally until 2% decay of NA. This
provided vin values from which pseudo-first-order rate constants,
kin, calculated according to the expression kin ϭ vin/[NA]. Second-
order rate constants, kNA, were obtained at a given pH from the
plot of kin vs. complex concentration.
3
˚
a volume of 1507 A . This was equated to be equal to one third
(1/3) of a highly disordered CH2Cl2 molecule per molecule of com-
plex, and the HKL file was modified accordingly. The molecular
structure and crystallographic numbering scheme are illustrated in
the ORTEP drawing (Figure 1).
Crystallographic data for the structure included in this paper have
been deposited with the Cambridge Crystallographic Data Centre
as supplementary publication nos. CCDC-212656 ... -212659, for
the complexes 3, 5, 7·1/3 CH2Cl2 and 8, respectively. These data
can be obtained free of charge at http://www.ccdc.cam.ac.uk/conts/
retrieving.html [or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (internat.)
ϩ44-1223/336-033; Email: deposit@ccdc.cam.ac.uk].
X-ray Crystallography: Single crystals of [Zn2(NO3)2(H3p)](NO3)2
(3) suitable for X-ray analysis were obtained from a concentrated
methanol solution of the complex upon standing. Suitable crystals
of [Zn2Cl4(Me2p)] (5) were obtained as colourless plates by slow
Supporting Information Available: NMR spectral characterisation
data for the complexes described in the present work and VT-1H
NMR spectra of 5. Kinetic data for the hydrolytic reactions.
864
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2004, 857Ϫ865

New Zn Complexes Containing Hexaazamacrocyclic Ligands
FULL PAPER
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Acknowledgments
This research has been financed by MCYT of Spain through pro-
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Catalunya (Spain) for a Distinction award and the aid SGR2001-
UG-291. M. C. and C. A. are grateful for the award of a doctoral
grant from CIRIT and the University of Girona, respectively.
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