Intramolecular ether oxygen coordination in the zinc complexes with dipicolylamine (DPA)-derived ligands

Article abstract of DOI:10.1016/j.ica.2011.02.022

The ether oxygen coordination to the zinc center in the complexes with dipicolylamine (DPA)-derived ligands, N-(2-methoxyethyl)-N,N-bis(2- pyridylmethyl)amine (L), N-(3-methoxypropyl)-N,N-bis(2-pyridylmethyl)amine (L′), and N-{3-(2-pyridylmethyloxy)propyl}-N,N-bis(2-pyridylmethyl)amine (L^Py) has been discussed. Upon chelation of the oxygen atom, L forms a five-membered chelate ring with respect to the 2-aminoethyl ether moiety whereas L′ forms a six-membered chelate in 3-aminopropyl ether unit. This difference was highlighted by the crystal structures of ZnCl₂ complexes, in which [Zn(L)Cl₂] (1) exhibited ether oxygen coordination but [Zn(L′)Cl₂] (2) had the ether oxygen non-coordinated. The terminal pyridyl group of L^Py facilitates the ether oxygen atom coordination via a metal binding from the basal plane trans to the aliphatic nitrogen.

Full text of DOI:10.1016/j.ica.2011.02.022

Inorganica Chimica Acta 370 (2011) 420–426
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Intramolecular ether oxygen coordination in the zinc complexes
with dipicolylamine (DPA)-derived ligands
b
b
c
Yuji Mikata a, , Tomomi Fujimoto , Tomomi Fujiwara , Shin-ichi Kondo
⇑
a KYOUSEI Science Center, Faculty of Science, Nara Women’s University, Nara 630-8506, Japan
b Department of Chemistry, Faculty of Science, Nara Women’s University, Nara 630-8506, Japan
c Department of Material and Biological Chemistry, Faculty of Science, Yamagata University, Yamagata 990-8560, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 8 July 2010
Received in revised form 4 February 2011
Accepted 9 February 2011
Available online 16 February 2011
The ether oxygen coordination to the zinc center in the complexes with dipicolylamine (DPA)-derived
ligands, N-(2-methoxyethyl)-N,N-bis(2-pyridylmethyl)amine (L), N-(3-methoxypropyl)-N,N-bis(2-
pyridylmethyl)amine (L0), and N-{3-(2-pyridylmethyloxy)propyl}-N,N-bis(2-pyridylmethyl)amine (LPy
)
has been discussed. Upon chelation of the oxygen atom, L forms a five-membered chelate ring with
respect to the 2-aminoethyl ether moiety whereas L0 forms a six-membered chelate in 3-aminopropyl
ether unit. This difference was highlighted by the crystal structures of ZnCl2 complexes, in which
[Zn(L)Cl2] (1) exhibited ether oxygen coordination but [Zn(L0)Cl2] (2) had the ether oxygen non-
coordinated. The terminal pyridyl group of LPy facilitates the ether oxygen atom coordination via a metal
binding from the basal plane trans to the aliphatic nitrogen.
Keywords:
Zinc complex
Coordination mode
Ligand effect
Ether oxygen
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
processes [16,17]. Thus, a lot of fluorescent zinc sensor molecules
having DPA unit as a zinc-binding site have been reported [18–
Binding of ether oxygen atom to the metal center is commonly
found in metal complex structures. Represented by the crown
ethers, this single metal–oxygen bond is moderate to weak in
strength, however, cooperative binding by accumulating weak
interactions makes metal–ether oxygen bonds strong and specific
[1–4]. Tethering of ether moiety with strong metal binding site is
another effective method to facilitate the ether oxygen coordina-
tion to the metal center [2,3]. This chelation effect becomes maxi-
mal when five-membered ring is formed. The six-membered
chelate structures are also commonly used.
21]. Multidental nitrogen and oxygen ligands bound to zinc center
have been investigated within the field of bioinorganic chemistry
[22–24]. Zinc–DPA complex is also used as model complexes of
hydrolytic enzymes of phosphate esters including nucleic acids
[25,26]. Bis(Zn–DPA) unit is utilized for phosphate binding motif
of fluorescent probe molecules for phosphate anions [27], pyro-
phosphates [28,29], nucleoside polyphosphates [30], and phospho-
proteins [31].
The present ligand library includes L with aminoethyleneoxy
moiety that forms five-membered chelate ring, L0 with aminoprop-
yleneoxy moiety that forms six-membered chelate ring, and LPy
having aminopropyleneoxy and 2-pyridylmethyloxy moieties at
the same ether oxygen atom, spawning six- and five-membered
chelate upon metal binding (Chart 1). The structures of zinc com-
plexes with these ligands were investigated by X-ray crystallogra-
phy and 1H NMR spectroscopy. The ligand structure as well as
anion of the metal salt controls the ether oxygen coordination to
the zinc center in these complexes.
Dipicolylamine (2,20-dipyridylmethylamine, DPA) is one of the
most studied tridentate metal-binding units in the coordination
chemistry [5–9]. As described above, linking an ether pendant
chain to the DPA moiety would enhance the ether oxygen binding
to the metal center [10]. Strong binding of the DPA unit to the cop-
per(II) [5–9,11] assists the coordination of the anomeric oxygen
atom of the sugar unit to the metal center, generating an asymmet-
ric oxygen [12,13]. Similar idea for the improvement of ether oxy-
gen coordination was employed by Sigel using a phosphate group
in place of DPA [14,15]. With this respect, here we prepared zinc
complexes with a DPA-pendant ether ligand to evaluate the intra-
molecular metal-coordination ability of oxygen atom in solid and
solution state. Zinc plays a lot of important roles in biological
2. Experimental
2.1. General
2.1.1. Equipments
⇑
Solvents and reagents used for the preparative procedures were
Corresponding author. Tel./fax: +81 742 20 3095.
E-mail address: mikata@cc.nara-wu.ac.jp (Y. Mikata).
obtained from commercial sources. 1H NMR (300.07 Hz) and 13C
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.02.022

Y. Mikata et al. / Inorganica Chimica Acta 370 (2011) 420–426
421
Chart 1.
(75.45 Hz) NMR spectra were recorded on a Varian GEMINI 2000
spectrometer and referenced to internal TMS or solvent signals.
Elemental analyses were recorded on J-Science JM-10 micro cor-
der. X-ray crystallography was performed on a Rigaku Mercury
CCD system.
Anal. Calc. for C15H19Cl2N3OZn (1): C, 45.77; H, 4.87; N, 10.68.
Found: C, 45.50; H, 4.79; N, 10.53%.
2.2.2.2. [Zn(L0)Cl2] (2). Methanolic solution (1.0 mL) of L0 (40.7 mg,
0.15 mmol) was mixed with ZnCl2 (20.6 mg, 0.15 mmol) in the
same solvent (1.0 mL) at room temperature. After 2 days, single
crystals suitable for X-ray crystallography were obtained directly
from the reaction mixture (44.5 mg, 0.11 mmol, 73% yield). Table
1 summarizes the crystallographic parameters.
2.1.2. Materials
N-(2-methoxyethyl)-N,N-bis(2-pyridylmethyl)amine (L) [32] and
N-(3-methoxypropyl)-N,N-bis(2-pyridylmethyl)amine (L0) [32] were
prepared from 2-chloromethylpyridine and corresponding amines
and characterized by 1H and 13C NMR spectroscopies. Caution:
Perchlorate salts of metal complexes with organic ligands are
potentially explosive. All due precautions should be taken.
1H NMR (CD3OD): d 8.93 (d, J = 4.5 Hz, 2H, py-6), 8.16 (ddd,
J = 1.5, 7.8, 7.8 Hz, 2H, py-4), 7.6–7.7 (m, 4H, py-3,5), 4.31 (s, 4H,
py-CH2–N), 3.29–3.39 (m, 2H, CH2–O), 3.26 (s, 3H, CH3), 2.81–
2.87 (m, 2H, CH2–N), 1.7–1.8 (m, 2H, C–CH2–C).
13C NMR (CD3OD): d 156.4, 149.7, 142.1, 125.9, 125.3, 71.5, 58.8,
58.4, 53.6, 25.6.
2.2. Synthesis
Anal. Calc. for C16H21Cl2N3OZn (2): C, 47.14; H, 5.19; N, 10.31.
Found: C, 46.71; H, 5.15; N, 10.18%.
2.2.1. N-{3-(2-pyridylmethyloxy)propyl}-N,N-bis(2-
pyridylmethyl)amine (LPy
)
2.2.2.3. [Zn(L0)2](ClO4)2 (3). Methanolic solution (0.5 mL) of L0
(27.1 mg, 0.10 mmol) was mixed with Zn(ClO4)2 (26.4 mg, 0.10
mmol) in the same solvent (0.5 mL) at room temperature. After
3 days, single crystals suitable for X-ray crystallography were ob-
tained directly from the reaction mixture (16.4 mg, 0.020 mmol,
40% yield). Table 1 summarizes the crystallographic parameters.
Anhydrous tetrahydrofuran solution of 3-hydroxypropyl-N,
N-bis(2-pyridylmethyl)amine [5] (563 mg, 2.19 mmol) was added
1.78 mL (2.85 mmol) of n-butyllithium in hexane solution (1.6 M)
at 0 °C, and the resulting red solution was stirred for 20 min. Then,
2-chloromethylpyridine (364 mg, 2.85 mmol) in tetrahydrofuran
(10 mL) was added dropwise and the reaction mixture was stirred
at 0 °C for 30 min, at room temperature for 1 h, and under reflux
for 2 days. After cooled to room temperature, water was added
and the organic material was extracted with chloroform. After
removal of the solvent, the residual oily crude product was puri-
fied by column chromatography (Alumina, eluent: chloroform/
methanol = 100/1) to afford N-{3-(2-pyridylmethyloxy)propyl}-N,
Table 1
Crystallographic data for [Zn(L)Cl2] (1), [Zn(L0)Cl2] (2), and [Zn(L0)2](ClO4)2 (3).
[Zn(L)Cl2] (1)
[Zn(L0)Cl2] (2)
[Zn(L0)2](ClO4)2
(3)
Formula
C
15H19Cl2N3OZn C16H21Cl2N3OZn C32H42Cl2N6O10Zn
N-bis(2-pyridylmethyl)amine (LPy
) as a brown oil (336 mg,
Formula weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
393.62
407.65
monoclinic
P21/n
8.0633(5)
8.8955(6)
25.1516(17)
90
96.411(4)
90
1792.8(2)
4
807.00
orthorhombic
Pbcn
0.964 mmol, 44% yield).1H NMR (CDCl3): d 8.50–8.53 (m, 3H, py-
6), 7.59–7.68 (m, 3H, py-4), 7.52 (d, J = 7.8 Hz, 2H, py-3), 7.31 (d,
J = 7.8 Hz, 1H, py0-3), 7.10–7.19 (m, 3H, py-5), 4.56 (s, 2H, py0-
CH2–O), 3.83 (s, 4H, py-CH2–N), 3.59 (t, J = 6.6 Hz, 2H, CH2–O),
2.70 (t, J = 7.2 Hz, 1H, CH2–N), 1.91 (m, 2H, C–CH2–C).13C NMR
(CDCl3): d 160.2, 159.1, 149.3, 136.9, 136.7, 123.2, 122.6, 122.2,
121.5, 74.0, 69.4, 60.8, 51.5, 27.8.
triclinic
ꢀ
P1
7.4162(8)
8.6223(10)
14.2351(18)
82.875(4)
81.916(4)
68.504(3)
835.93(17)
2
1.564
17.924
55.0
173
20.308(3)
10.6095(18)
17.139(3)
90
90
90
3692.8(11)
4
1.451
8.722
57.4
a
(°)
b (°)
c
(°)
V (Å3)
Anal. Calc. for C21H25N4O1.5 (LPyꢀ0.5H2O): C, 70.56; H, 7.05; N,
15.67. Found: C, 70.98; H, 6.96; N, 15.60%.
Z
Dcalc (g cmꢁ3
)
1.510
16.744
55.0
l
(cmꢁ1
)
2hmax (°)
T (K)
2.2.2. Preparation of complexes
123
173
2.2.2.1. [Zn(L)Cl2] (1). Methanolic solution (0.5 mL) of L (38.6 mg,
0.15 mmol) was mixed with ZnCl2 (20.5 mg, 0.15 mmol) in the same
solvent (0.5 mL) at room temperature. After 2 days, single crystals
suitable for X-ray crystallography were obtained directly from the
reaction mixture (21.5 mg, 0.055 mmol, 36% yield). Table 1 summa-
rizes the crystallographic parameters.
Number of
reflections
collected
6445
17 201
29 575
Number of
reflections used
Number of
parameters
Final R1 (I > 2h(I))
wR2 (all data)
Goodness-of-fit
(GOF)
3645
276
4111
293
4736
232
1H NMR (CD3OD): d 9.00 (d, J = 5.1 Hz, 2H, py-6), 8.11 (ddd,
J = 1.8, 7.8, 7.8 Hz, 2H, py-4), 7.6–7.7 (m, 4H, py-3,5), 4.35 (s, 4H,
py-CH2–N), 3.16 (s, 3H, CH3), 2.9–3.0 (m, 4H, CH2CH2).
13C NMR (CD3OD): d 156.1, 149.1, 142.1, 125.8, 125.1, 68.4, 61.2,
59.1, 57.9.
0.0209
0.0560
1.042
0.0324
0.0991
1.077
0.0411
0.1092
1.058
P
P
P
P
2
2
1=2
R1 ¼ ð jjFoj ꢁ jFcjjÞ=ð jFojÞ. wR2 ¼ f½ wðF2o ꢁ Fc2Þ ꢂ=½ wðFo2Þ ꢂg
.

422
Y. Mikata et al. / Inorganica Chimica Acta 370 (2011) 420–426
Table 2
Anal. Calc. for C21H24BrClN4O5Zn (5): C, 42.52; H, 4.08; N, 9.45.
Found: C, 42.28; H, 4.08; N, 9.33%.
Crystallographic data for [Zn(LPy)Cl](ClO4) (4) and [Zn(LPy)Br](ClO4) (5).
[Zn(LPy)Cl](ClO4) (4) [Zn(LPy)Br](ClO4) (5)
2.3. X-ray crystallography
Formula
Formula weight
Crystal system
Space group
a (Å)
C
21H24Cl2N4O5Zn
C21H24BrClN4O5Zn
593.18
monoclinic
P21/c
13.009(3)
10.573(2)
16.811(3)
97.681(3)
2291.3(8)
4
548.73
monoclinic
P21/c
12.7997(4)
10.6600(3)
16.6604(6)
98.7858(19)
2246.55(12)
4
1.622
13.733
55.0
123
Single crystals of 1–5 were covered by paraffin oil and mounted
on a glass fiber. All data were collected at 123 or 173 K on a Rigaku
Mercury CCD detector, with monochromatic MoKa radiation, opa-
b (Å)
c (Å)
rating at 50 kV/40 mA. Data were processed on a PC using Crystal-
Clear Software (Rigaku). Structures were solved by direct methods
(SIR-92) [33] and refined by full-matrix least-squares methods on
b (°)
V (Å3)
Z
F2
(SHELXL-97) [34].
Dcalc (g cmꢁ3
)
1.719
29.793
55.0
l
(cmꢁ1
)
2hmax (°)
T (K)
3. Results and discussion
123
Number of reflections collected 17 132
17 484
5125
395
0.0299
0.0748
1.070
3.1. Preparation and structure determination of complexes
Number of reflections used
Number of parameters
Final R1 (I > 2h(I))
wR2 (all data)
Goodness-of-fit (GOF)
5135
395
0.0340
0.0898
1.094
Single crystals of complexes 1–5 were prepared from methanol
solutions of ligand and metal salts in some cases under slow ether
diffusion conditions in the presence of sodium perchlorate. Crystal-
lographic data and X-ray diffraction conditions are summarized in
Tables 1 and 2. ORTEP diagrams of complexes 1–5 are shown in
Figs. 1, 2 and 5–7. Selected bond distances were listed in Table 3.
All solved structures exhibit meridional coordination geome-
tries for the DPA moiety [5–9,11,35,36]. The complexes, [Zn(L)Cl2]
(1), [Zn(LPy)Cl](ClO4) (4), and [Zn(LPy)Br](ClO4) (5), exhibit the
coordination of the ether oxygen atom to the zinc center with
Zn–O bond lengths between 2.2742 and 2.6384 Å.
P
P
P
P
2
2
1=2
R1 ¼ ð jjFoj ꢁ jFcjjÞ=ð jFojÞ. wR2 ¼ f½ wðF2o ꢁ Fc2Þ ꢂ=½ wðFo2Þ ꢂg
.
1H NMR (CD3OD): d 8.72 (d, J = 5.4 Hz, 2H), 8.20 (ddd, J = 1.8, 7.8,
7.8 Hz, 2H), 7.7–7.8 (m, 4H), 4.51 (d, J = 16.5 Hz, 2H), 4.19 (d,
J = 16.5 Hz, 2H), 3.40 (t, J = 5.7 Hz, 2H), 3.28 (s, 3H), 2.73–2.79 (m,
2H), 1.8–2.0 (m, 2H).
13C NMR (CD3OD): d 156.5, 149.0, 142.6, 126.4, 126.2, 71.8, 59.0,
58.4, 52.6, 24.0.
Anal. Calc. for C32H42Cl2N6O10Zn (3): C, 47.63; H, 5.25; N, 10.41.
Found: C, 47.76; H, 5.43; N, 10.11%.
3.2. L and L0 complexes
Zinc chloride complexes with L and L0 both afforded single crys-
tals suitable for X-ray crystallography (Figs. 1 and 2). The number
of atoms in chelate chain differentiates the coordination of the
ether oxygen atom. The metal–oxygen interaction affording a
five-membered chelate ring in L–ZnCl2 complex (1) is no more
available in L0–ZnCl2 complex (2), in which six-membered chelate
ring would be formed when the ether oxygen atom coordinates to
the metal center. Complex 1 has two coordinated chloride anions
that cancel out the complex charge, thus the neutral nature of
the complex have a weak ability to form metal–ether oxygen bond
and no examples are found for zinc complexes having three nitro-
gens, two halogens, and metal-bound ether oxygen atoms in the
crystal structure. Most of such a N3O1X2 (X: halogen) system in
Cu/Zn complex includes phenol [37–39] or alcohol [40,41] moiety
as an oxygen donor. Only one example was found for copper com-
plex in N3O(ether)1X2 coordination environment [42].
2.2.2.4. [Zn(LPy)Cl](ClO4) (4). Methanolic solution (0.2 mL) of LPy
(24.4 mg, 0.070 mmol) was mixed with ZnCl2 (9.5 mg, 0.070 mmol)
in the same solvent (0.2 mL) at room temperature. Then,
NaClO4ꢀH2O (9.8 mg, 0.070 mmol) in the same solvent (0.1 mL)
was added and ether vapor was introduced at 4 °C. After 1 day,
single crystals suitable for X-ray crystallography were obtained
directly from the reaction mixture (16.2 mg, 0.030 mmol, 42%
yield). Table 2 summarizes the crystallographic parameters.
1H NMR (CD3OD): d 9.33 (br., 1H), 8.31 (br., 1H), 8.03–8.3 (m,
2H), 7.74–7.81 (br., 4H), 7.45–7.62 (br., 2H), 7.42–7.45 (br., 2H),
4.74 (d, J = 11.7 Hz, 2H), 4.64 (br., 1H), 4.32 (d, J = 11.7 Hz, 2H),
3.53–3.56 (br., 2H), 2.96–2.99 (br., 2H), 1.34–1.36 (br., 2H).
13C NMR (CD3OD): d 156.3, 150.0, 147.2, 142.1, 141.5, 125.9,
125.8, 125.2, 124.1, 74.8, 71.4, 63.1, 60.8, 26.6.
Anal. Calc. for C21H24Cl2N4O5Zn (4): C, 45.96; H, 4.41; N, 10.21.
Found: C, 45.83; H, 4.43; N, 10.11%.
2.2.2.5. [Zn(LPy)Br](ClO4) (5). Methanolic solution (0.4 mL) of LPy
(17.4 mg, 0.050 mmol) was mixed with ZnBr2 (11.2 mg, 0.050
mmol) in the same solvent (0.4 mL) at room temperature. Then,
ether vapor was introduced at 4 °C. The appeared precipitate was
removed by filtration. To the filtrate, NaClO4ꢀH2O (14.0 mg,
0.10 mmol) was added and ether vapor was introduced at 4 °C.
After 2 days, single crystals suitable for X-ray crystallography were
obtained (18.5 mg, 0.031 mmol, 62% yield). Table 2 summarizes
the crystallographic parameters.
1H NMR (CD3OD): d 9.48 (d, J = 5.4 Hz, 1H), 8.34 (dd, J = 7.8,
7.8 Hz, 1H), 8.11 (dd, J = 7.8, 7.8 Hz, 2H), 7.69–7.9 (m, 4H), 7.70
(d, J = 7.8 Hz, 2H), 7.46–7.54 (m, 2H), 4.98 (s, 2H), 4.84 (d,
J = 15.6 Hz, 2H), 4.37 (d, J = 15.6 Hz, 2H), 3.61 (t, J = 5.1 Hz, 2H),
3.02–3.06 (m, 2H), 1.35–1.48 (m, 2H).
13C NMR (CD3OD): d 157.3, 156.5, 150.6, 147.4, 142.4, 141.8,
126.1, 125.5, 124.4, 75.0, 71.5, 62.9, 60.7, 26.5.
Fig. 1. ORTEP for [Zn(L)Cl2] (1) (50% probability).

Y. Mikata et al. / Inorganica Chimica Acta 370 (2011) 420–426
423
between Zn-complex and free ligand is slow compared with NMR
timescales. Although most of signals from Zn-complex appear in
the downfield region compared to those of free ligand, the methy-
lene (CH2-3) and methyl (CH3-4) groups neighboring to the ether
oxygen atom exhibit upfield shift (Dppm = ꢁ0.5 for CH2-3 and
ꢁ0.1 for CH3-4). This is because the ether oxygen-coordinated
structure elucidated by the crystallography ([Zn(L)Cl2] (1), Fig. 1)
is preserved in the methanol solution and the ring current effect
from the pyridine ring causes the upfield shift of those proton sig-
nals. On the other hand, proton signals in ether side chain of the
[Zn(L0)Cl2] complex exhibited negligible metal-induced chemical
shift change (Fig. 4, Dppm = +0.25, ꢁ0.03, ꢁ0.06, and +0.04 for
CH2-2, 3, 4, and CH3-5, respectively), indicating that the ether oxy-
gen is not coordinated to the zinc center as found in the crystal
structure (Fig. 2). Here again, the numbers of chelating atoms
determines the ether oxygen coordination.
For the preparation of zinc complex with L0, replacement of
chloride with perchlorate would yield the cationic complexes that
tend to have ether oxygen-coordinated species because the coordi-
nation ability of perchlorate is weak [10]. The methanol solution of
L0 in the presence of Zn(ClO4)2 afforded [Zn(L0)2](ClO4)2 (3), in
which six nitrogen atoms of cis-orientated two ligand molecules
coordinated to the zinc center even in the presence of 1 eq of li-
gand (Fig. 5). The formation of this complex may be a crystalliza-
tion effect, however, 40% isolated yield of this complex and 1H
NMR spectrum of L0 in the presence of 1 eq. of Zn(ClO4)2 in CD3OD
(data not shown) strongly discourages the coordination of the
ether oxygen atom of L0. In spite of extensive crystallization trials,
the mixture of L and Zn(ClO4)2 in methanol did not afford single
crystals suitable for X-ray crystallography.
Fig. 2. ORTEP for [Zn(L0)Cl2] (2) (50% probability).
The coordination structure of the complexes was further inves-
tigated by 1H NMR spectroscopy in methanol solution (Figs. 3 and
4). Upon addition of ZnCl2 into CD3OD solution of L, a new set of
signals assigned to the zinc complex was appeared (Fig. 3). The
chemical shifts for the proton signals of remaining free ligand were
unchanged during the titration, indicating that the metal exchange
Fig. 3. Zn2+-induced 1H NMR spectral changes of L in the presence of increasing amount of ZnCl2 in CD3OD. Asterisk indicates solvent peak.

424
Y. Mikata et al. / Inorganica Chimica Acta 370 (2011) 420–426
Table 3
Bond lengths around zinc center in complexes 1–5.
Complex
Zn–N1
Zn–N2
Zn–N3
Zn–Xbasal
Zn–O1
Zn–Xap
[Zn(L)Cl2] (1)
2.2846(11)
2.3857(18)
2.3045(16)
2.2042(16)
2.2056(17)
2.1226(13)
2.0879(18)
2.1206(16)
2.1740(15)
2.1098(16)
2.1398(11)
2.082(2)
2.1793(18)
2.1134(16)
2.1704(16)
2.2889(3)a
2.3234(5)a
2.6384(10)
2.3599(3)a
2.2696(6)a
[Zn(L0)Cl2] (2)
[Zn(L0)2](ClO4)2 (3)
[Zn(LPy)Cl](ClO4) (4)
[Zn(LPy)Br](ClO4) (5)
2.0963(15)b
2.1011(16)b
2.2784(14)
2.2742(15)
2.3458(5)a
2.5110(3)c
a
b
c
X = Cl.
X = N.
X = Br.
1
Fig. 4. Zn2+-induced H NMR spectral changes of L0 in the presence of increasing amount of ZnCl2 in CD3OD. Asterisk indicates solvent peak.
3.3. LPy complexes
2-pyridyl group to promote the coordination of ether oxygen atom,
in which six- and five-membered chelate ring would be formed
around 3-aminopropyl 2-pyridylmethyl ether moiety.
Previous works revealed that anchoring group such as hydroxyl
group facilitates the ether oxygen coordination [10,43]. In this
work, a hydrogen atom in the methyl group of L0 was replaced with
The ligand LPy was prepared from N,N-bis(2-pyridylmethyl)-3-
aminopropanol and 2-pyridylmethyl chloride. The zinc complexes

Y. Mikata et al. / Inorganica Chimica Acta 370 (2011) 420–426
425
elemental analysis. No complex was isolated from the reaction
mixture in methanol in the absence of sodium perchlorate.
The LPy complexes 4 and 5 exhibited their ether oxygen atom
bound to the metal center. The Zn–O distances are 2.2784(14) and
2.2742(15) Å for complexes 4 and 5, respectively. These distances
are significantly shorter than that of complex 1 (2.6384(10) Å) by
the effect of anchoring pyridine group. The steric hindrance of
chloride and bromide in complexes 4 and 6 tilts the anchor pyridine
ring, resulting a significant distortion of aminopropyleneoxy chelate
ring.
4. Conclusion
The intramolecular ether oxygen coordination to the metal cen-
ter is strongly perturbed by the ligand structure. In this article, the
first example of crystal structure of ZnN3X2Oether (X = halogen) sys-
tem ([Zn(L)Cl2], 1) is presented. Generally, complexes that have po-
sitive charge exhibit coordination of the ether oxygen atom,
whereas chargeless complexes in which two anions are bound to
the metal center ligated by a neutral ligand tend to dissociate the
ether oxygen. The five-membered chelate ring formation could
hold the ether oxygen coordination in complex 1. On the other
hand, the six-membered chelate ring of L0 is disfavored and zinc
does not coordinate to the oxygen in complex 2 in both solid and
solution. Additional metal binding site, namely pyridine moiety
in LPy, promotes the formation of six-membered ring containing
the ether oxygen coordination. Weak coordinating ability of per-
chlorate yields the ML2 type complex ([Zn(L0)2](ClO4)2, 3) without
ether oxygen coordination. The present information provides
important information about the coordination of oxygen atom to
the metal center in the solid and solution state.
Fig. 5. ORTEP for cationic portion of [Zn(L0)2](ClO4)2 (3) (50% probability). Atoms
generated by symmetric operation are indicated with an asterisk.
Acknowledgements
This work was supported by the Asahi-Glass Foundation, Nara
Women’s University Intramural Grant for Project Research, and
Grant-in Aid for Scientific Research from the MEXT, Japan
(18550059 and 20550065).
Fig. 6. ORTEP for cationic portion of [Zn(LPy)Cl](ClO4) (4) (50% probability).
Appendix A. Supplementary material
CCDC 779482, 779483, 779484, 779485 and 779487 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. Supplemen-
tary data associated with this article can be found, in the online
version, at doi:10.1016/j.ica.2011.02.022.
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