Synthesis and structural characterization of three new 1D and 2D zinc(II) azide polymers with some pyridine and pyrazine derivative ligands

Article abstract of DOI:10.1016/j.molstruc.2007.10.030

Three new polymeric zinc(II) azido complexes, namely [Zn(N₃)₂(3-Brpy)]_n (1), [Zn(N₃)₂(4-Etpy)]_n (2) and [Zn₂(N₃)₄(2,5-dmpyz)]_n (3), where Brpy = bromopyridine, Etpy = ethylpyridine and dmpyz = dimethylpyrazine have been prepared and structurally characterized. The IR spectra of these complexes are measured and discussed. The structures of 1 and 2 are similar and feature one-dimensional zigzag chain of [Zn(N₃)₂]_n in which each zinc atom is surrounded by double di-end on (EO) bridging azido ligands forming cyclic Zn₂N₂ units. Furthermore, each zinc atom links a N hetero atom of the pyridine moiety leading to ZnN₅ chromophore. The geometry around the zinc center is best described as distorted trigonal bipyramid. Although complex 3 consists of the 1D chain of [Zn(N₃)₂]_n with double di-EO azido bridges around each zinc center with almost planar Zn₂N₂ cyclic units, the pyrazinic moiety behaves as a bidentate bridging N,N′-ligand that binds the zinc centers across the [Zn₂(N₃)₂]_n chains extending the structure to be two-dimensional sheets. The Zn ... Zn distances within the Zn₂N₂ units are similar, fall within the range of 3.20-3.26 ?, and the azido ligands are asymmetric and linear within experimental error in all of these three complexes.

Full text of DOI:10.1016/j.molstruc.2007.10.030

Available online at www.sciencedirect.com
Journal of Molecular Structure 886 (2008) 32–38
www.elsevier.com/locate/molstruc
Synthesis and structural characterization of three new 1D
and 2D zinc(II) azide polymers with some pyridine
and pyrazine derivative ligands
a
b
b
Mohamed A.S. Goher , Brigitte Bitschnau , Beate Sodin ,
b
b,
*
Christian Gspan , Franz A. Mautner
a
Department of Chemistry, Faculty of Science, Alexandria University, P.O. Box 426 Ibrahimia, 21321 Alexandria, Egypt
b
Institut f u¨ r Physikalische und Theoretische Chemie, Technische Universit a¨ t Graz, A-8010 Graz, Austria
Received 4 September 2007; accepted 22 October 2007
Available online 4 November 2007
Abstract
3 2 n 3 2 n 2 3 4 n
Three new polymeric zinc(II) azido complexes, namely [Zn(N ) (3-Brpy)] (1), [Zn(N ) (4-Etpy)] (2) and [Zn (N ) (2,5-dmpyz)] (3),
where Brpy = bromopyridine, Etpy = ethylpyridine and dmpyz = dimethylpyrazine have been prepared and structurally characterized.
The IR spectra of these complexes are measured and discussed. The structures of 1 and 2 are similar and feature one-dimensional zigzag
chain of [Zn(N
Furthermore, each zinc atom links a N hetero atom of the pyridine moiety leading to ZnN
center is best described as distorted trigonal bipyramid. Although complex 3 consists of the 1D chain of [Zn(N ) ] with double di-EO
3
)
2
]
n
in which each zinc atom is surrounded by double di-end on (EO) bridging azido ligands forming cyclic Zn
2 2
N units.
5
chromophore. The geometry around the zinc
3
2 n
0
azido bridges around each zinc center with almost planar Zn N cyclic units, the pyrazinic moiety behaves as a bidentate bridging N,N -
2
2
ligand that binds the zinc centers across the [Zn
2 3 2 n
(N ) ] chains extending the structure to be two-dimensional sheets. The Zn . . . Zn dis-
˚
tances within the Zn units are similar, fall within the range of 3.20–3.26 A, and the azido ligands are asymmetric and linear within
2 2
N
experimental error in all of these three complexes.
Ó 2007 Elsevier B.V. All rights reserved.
Keywords: Azide; Zinc(II); Pyridine and pyrazine derivative complexes; Synthesis; Spectra; Crystal structures
1
. Introduction
tures with interesting polymeric topologies and/or
magnetic properties [3]. An interesting strategy toward
high dimensional topologies is to incorporate a second
bridging ligand into the metal azido systems. An increasing
number of 2D and sometimes 3D systems have been
obtained by this strategy, and the second bridging ligands
used thus far have been pyridyl-based ditopic ligands such
The azido bridged complexes have attracted intense
interest due to the coordination versatility of the azido
bridge and the magnetic diversity of the complexes [1].
The azido ligand can link two or more metal ions in various
modes; l-1,1 (end-on, EO), l-1,3 (end-to-end, EE), l-1,1,3
and others, and mediate magnetic exchange of different
nature and magnitude. These modes may simultaneously
exist in the same compound in a variety of alternating
sequences [2]. These features in conjunction with the pres-
ence of coligands, have led to a lot of 1D and 2D architec-
0
as pyrazine, 4,4 -bipy and their analogues [4].
Compared to the relatively large number of azido-
bridged polymers with Mn(II) [5], Ni(II) [6] and Cu(II)
[7] reported in the literature, the Zn(II) polymers are still
1
0
very rare [8,9]. Zinc is well suited [10–12] as its d config-
uration permitting a wide variety of symmetries and coor-
dination numbers and it has drawn special attention for its
importance in bio-inorganic chemistry [13,14], in addition
*
Corresponding author. Tel.: +43 316 873 8234; fax: +43 316 873 8225.
E-mail address: mautner@ptc.tu-graz.ac.at (F.A. Mautner).
0
022-2860/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2007.10.030

M.A.S. Goher et al. / Journal of Molecular Structure 886 (2008) 32–38
33
to the relatively appreciable number of reports concerned
with the photoluminescence of some zinc(II) complexes
an aqueous solution of Zn(N ) (30 mL, 26.6 mmol Zn).
3 2
The mixture was heated to 65 °C to obtain a clear solution.
Colorless transparent crystals of complex 2 were deposited
after 1 day at 37 °C. Yield: 1.58 g, 78%. Analysis: found: C,
32.9; H, 3.6; N, 38.8; Zn, 25.2%. Calculated for C H N Zn:
[
15,16]. Previously we have shown that Zn(N ) interacts
3 2
with some pyridine derivatives [17], 4-methylpyrimidine
18], pyridine-, and picoline N-oxides [19]. In the case of
[
7
9
7
ꢀ
1
pyridine-, and 3-picoline-N-oxide we found that these
ligands do not participate in coordination to the zinc atom,
but just consolidate the 1D [Zn(N ) (H O) ] chains
Calc.: C, 32.8; H, 3.5; N, 38.2; Zn, 25.5. IR, KBr (cm ):
3402 vw, 3351 w, 2980 w, 2914 w, 2890 w, 2625 w, 2571
w, 2080 vs, 1618 s, 1557 w, 1503 w, 1458 w, 1433 m,
1345 m, 1288 s, 1204 w, 1066 m, 1031 m, 835 m, 788 w,
664 m, 601 w, 576 w, 497 w, 389 w.
3
2
2
2
through hydrogen bonding formation [19] which is not
the case for 2-picoline N-oxide acting as monodentate
ligand [18]. As an extension of that work we used
3
2
-bromopyridine (3-Brpy), 4-ethylpyridine (4-Etpy) and
,5-dimethyl pyrazine (dmpyz) to compare the type and
2.2.3. [Zn (N ) (2,5-dimethylpyrazine)] (3)
3 4
2
n
Complex 3 was prepared in a similar procedure as com-
plex 1. 2,5-Dimethylpyrazine (0.52 g, 4.8 mmol) was mixed
with an aqueous solution of Zn(N ) (10 mL, 8.9 mmol
topology of the resulting complexes. We isolated 1:1 com-
plexes for the pyridinic ligand and 2:1 in case of dmpyz
ligand. This report concerns the synthesis and structural
characterization of these three new complexes as elucidated
by spectroscopic and crystallographic methods.
3
2
Zn). The mixture was heated to 80 °C to obtain a clear
solution. Colorless transparent crystals of complex 3 were
deposited after 1 day at room temperature. Yield: 1.22 g,
67%. Analysis: found: C, 17.5; H, 1.9; N, 48.4; Zn,
2
. Experimental
32.2%. Calculated for C H N Zn : Calc.: C, 17.7; H,
6
8
14
2
ꢀ
1
2.0; N, 48.2; Zn, 32.1. IR, KBr (cm ): 3572 br, 3361 w,
2
.1. Materials and instrumentation
Elemental analyses were carried out using a Perkin-
3129 w, 3049 w, 2630 w, 2576 w, 2140 s, 2091 vs, 1500
m, 1445 w, 1345 m, 1291 s, 1189 w, 1159 m, 1074 m,
1035 w, 972 w, 900 w, 667 m, 596 w, 529 w, 444 m.
Elmer analyzer and infrared spectra were recorded on a
Perkin-Elmer FTIR Series 1600 spectrophotometer as
KBr pellets. Aminopyrazine has been purchased from
Aldrich Company, other chemicals were of analytical grade
quality and used without further purification. Aqueous
hydrazoic acid was obtained with a modified Kipp’s gener-
ator by decomposition of NaN in H SO /H O (1:3, v:v)
2.3. X-ray crystallography
Single crystal X-ray data for complexes 1 and 2 were
measured at 90(2) K on a modified STOE four circle dif-
fractometer, and for 3 at 100(2) K on a Bruker-AXS
SMART APEX CCD diffractometer, using graphite crys-
3
2
4
2
˚
and subsequent transfer of HN into H O with aid of an
tal-monochromatized Mo-Ka; radiation (k = 0.7107 A).
3
2
inert gas stream [5c,20].
The intensities were corrected for Lorentz-polarisation
effects, intensity decay and for absorption. Crystallo-
graphic data and processing parameters are given in Table
1. The structures were solved by direct methods and subse-
quent Fourier analyses. Anisotropic displacement parame-
ters were applied to non-hydrogen atoms in full-matrix
Caution: Azide compounds and hydrazoic acid (HN3)
are potentially explosive! Only a small amount of material
should be prepared and handled with care.
2
2
.2. Synthesis
2
least-squares refinements based on F . The hydrogen atoms
.2.1. [Zn(N ) (3-bromopyridine)] (1)
3
were assigned with isotropic displacement factors and
included in the final refinement cycles. Geometrical
restraints were applied for all hydrogen atoms and also
for the twofold disordered 4-ethylpyridine molecule of 2.
Analytical expressions of neutral-atom scattering factors
were employed, and anomalous dispersion corrections were
incorporated. The programs DIFABS, SADABS [21] and
SHELXTL/PC program package [22] were used for com-
putations. Selected bond distances and bond angles are
given in Tables 2–4, for complexes 1–3, respectively.
2
n
Complex 1 was prepared by mixing 3-bromopyridine
(
(
0.06 g, 0.4 mmol) with an aqueous solution of Zn(N3)2
22 mL, 8.9 mmol Zn) saturated with hydrazoic acid. The
mixture was heated to 70 °C to obtain a clear solution.
Upon slow cooling transparent crystals of the complex
were deposited after 5 days at room temperature. Yield:
0
.074 g, 60%. Analysis: found: C, 19.3; H, 1.2; N, 32.1;
Zn, 21.5%. Calculated for C H BrN Zn: C, 19.5; H, 1.3;
N, 31.9; Zn, 21.3. IR, KBr (cm ): (v very, s strong, m
medium, w weak, br broad): 3573 br, 3387 vw, 3062 vw,
5
4
7
ꢀ
1
2
160 m, 2086 vs, 1585 w, 1465 w, 1415 w, 1343 w, 1295
3. Results and discussion
w, 1190 w, 1122 w, 1097 w, 1028w, 794 w, 693 m, 664 w,
6
34 w, 408 w.
3.1. Structures
2
.2.2. [Zn(N ) (4-Ethylpyridine)] (2)
2
3.1.1. [Zn(N ) (3-Brpy)] (1)
3 2
3
n
Complex 2 was prepared in a similar procedure as com-
plex 1. 4-Ethylpyridine (0.85 g, 7.9 mmol) was mixed with
Fig. 1a illustrates the principle structural features of
complex 1 along with a labeling scheme, selected bond

34
M.A.S. Goher et al. / Journal of Molecular Structure 886 (2008) 32–38
Table 1
Crystallographic data and processing parameters
Compound
1
2
3
Empirical formula
Formula mass
System
C
5
H
4
BrN
307.44
Monoclinic
P2 /c
7
Zn
C
256.60
Monoclinic
I2/a
7
H
9
N
7
Zn
C
3 4 7
H N Zn
203.52
Monoclinic
P2 /c
Space group
1
1
˚
a (A)
6.038(2)
21.255(7)
7.528(4)
90
98.37(3)
90
955.8(7)
4
6.720
6.109(3)
17.722(5)
9.544(2)
90
101.65(2)
90
1012.0(6)
4
2.405
7.4356(15)
15.585(3)
6.1639(12)
90
102.11(3)
90
698.4(2)
4
3.456
˚
b (A)
˚
c (A)
a (°)
b (°)
c (°)
˚
3
V (A )
Z
ꢀ
1
l (MoKa) (mm
calc (Mg/m )
)
3
D
2.136
1.684
1.936
Crystal size (mm)
h Range (°)
Reflections collected
Independ. refl./Rint
Parameters
0.24 ꢁ 0.12 ꢁ 0.10
2.90–26.99
2669
2086/0.0419
127
0.30 ꢁ 0.25 ꢁ 0.20
3.59–26.98
1367
1105/0.0321
106
0.35 ꢁ 0.28 ꢁ 0.20
2.61–26.37
5322
1421/0.0448
101
2
Goodness of Fit on F
1.063
1.291
1.117
R
R
1
/wR
/wR
2
2
[I > 2r(I)]
(all data)
0.0367/0.0859
0.0447/0.0927
0.721/ꢀ0.702
0.0544/0.1458
0.0557/0.1465
0.667/ꢀ1.835
0.0450/0.1167
0.0528/ 0.1336
1.125/ꢀ1.100
1
˚
3
Residual extrema (e/A )
Table 2
Table 3
˚
˚
Selected bond lengths (A) and angles (°) for 1
Selected bond lengths (A) and angles (°) for 2
Zn(1). . .Zn(1A)
Zn(1)–N(21)
Zn(1)–N(1)
Zn(1)–N(21B)
N(12)–N(13)
N(22)–N(23)
Zn(1A). . .Zn(1)
3.200(1)
2.007(3)
2.033(3)
2.250(3)
1.151(5)
1.139(5)
138.26(3)
Zn(1). . .Zn(1B)
3.262(1)
2.007(4)
2.132(3)
1.206(5)
1.209(5)
1.885(4)
126.9(2)
Zn(1)–N(11)
Zn(1)–N(1)
2.008(5) Zn(1)–N(11A)
2.025(8) Zn(1)–N(1A)
2.203(5) Zn(1)–N(11C)
1.214(7) N(12)–N(13)
3.262(2)
2.008(5)
2.025(8)
2.203(5)
1.134(7)
Zn(1)–N(11)
Zn(1)–N(11A)
N(11)–N(12)
N(21)–N(22)
C(2)–Br(1)
Zn(1)–N(11B)
N(11)–N(12)
Zn(1). . .Zn(1B)
N(11)–Zn(1)–N(11A)
N(11A)–Zn(1)–N(1)
119.8(3) N(11)–Zn(1)–N(1)
124.3(5) N(11)–Zn(1)–N(1A)
116.0(5)
124.3(5)
8.3(10)
N(21)–Zn(1)–N(11)
.
. .Zn(1B)
N(11A)–Zn(1)–N(1A) 116.0(5) N(1)–Zn(1)–N(1A)
N(21)–Zn(1)–N(1)
112.90(14) N(11)–Zn(1)–N(1)
98.05(13)
102.80(14) N(21)–Zn(1)–N(21B) 80.12(14)
119.48(14)
N(11)–Zn(1)–N(11A) 78.7(2)
N(11)–Zn(1)–N(11B)
N(1)–Zn(1)–N(11B)
N(11)–Zn(1)–N(11C)
N(1)–Zn(1)–N(11C)
N(11B)–Zn(1)–N(11C) 172.8(3) N(12)–N(11)–Zn(1)
N(12)–N(11)–Zn(1B)
N(13)–N(12)–N(11)
78.5(2)
93.0(4)
97.8(2)
94.2(4)
N(11A)–Zn(1)–N(11B)
97.8(2)
94.2(4)
78.5(2)
93.0(4)
123.1(4)
101.5(2)
N(21)–Zn(1)–N(11A)
N(1)–Zn(1)–N(11A)
N(11)–Zn(1)–N(21B)
N(1A)–Zn(1)–N(11B)
N(11A)–Zn(1)–N(11C)
N(1A)–Zn(1)–N(11C)
91.41(13)
N(1)–Zn(1)–N(21B)
90.36(13)
125.6(3)
N(11A)–Zn(1)–N(21B) 166.25(13) N(12)–N(11)–Zn(1)
N(12)–N(11)–Zn(1A)
N(13)–N(12)–N(11)
N(22)–N(21)–Zn(1B)
N(23)–N(22)–N(21)
133.1(3)
179.8(4)
122.5(3)
178.2(4)
Zn(1)–N(11)–Zn(1A) 101.3(2)
N(22)–N(21)–Zn(1) 121.5(3)
Zn(1)–N(21)–Zn(1B) 99.88(14)
123.3(4) Zn(1)–N(11)–Zn(1B)
178.7(7) Zn(1B). . .Zn(1). . .Zn(1C) 138.88(6)
Symmetry codes: (A) ꢀx + 1/2,y,ꢀz; (B) ꢀx,ꢀy,ꢀz; (C) x + 1/2,ꢀy,z.
Symmetry codes: (A) ꢀx,ꢀy + 1,ꢀz; (B) ꢀx + 1,ꢀy + 1,ꢀz.
˚
Zn–N(23) = 2.252(3) A, respectively, while the other three
˚
are virtually equal to 2.007(3)–2.132(3) A (Table 2) and
distances and bond angles are listed in Table 2. The coor-
dination of the zinc(II) atom by 3-Brpy and azido ligands
may be described as distorted trigonal bipyramid
compare well with corresponding distances in other zinc(II)
azide complexes of pyridine derivative ligands [17]. Both l-1,1
azido ligands are asymmetric [N(11)–N(12) = 1.206(5),
N(12)–N(13) = 1.151(5) A and N(21)–N(22) = 1.209(5),
N(22)–N(23) = 1.139(5) A] and linear within experimental
error [N–N–N angles of 178.2(4) and 179.8(4)°]. The
Zn . . . Zn distances within the cyclic four-membered
Zn N rings are 3.200(1) and 3.262(1) A.
(
s = 0.66) with N(11A) and N(21B) at the apical positions.
In the asymmetric unit, l-1,1 azido groups
N(11)–N(12)–N(13) and N(11A)–N(12A)–N(13A)] lying
˚
˚
[
on the same crystallographic diad bridge a pair of zinc
atoms [Zn(1) and Zn(1A)] related by an inversion center
forming a planar Zn N cyclic ring, whereas l-1,1 azide
˚
2
2
2
2
ligands [N(21)–N(22)–N(23) and N(21B)–N(22B)–N(23B)]
link Zn(1) and Zn(1B) atoms forming another Zn N ring,
3.1.2. [Zn(N ) (4-Etpy)] (2)
3 2 n
2
2
giving rise to zigzag chains of zinc polyhedra along the a-
axis of the unit cell (Fig. 1b). The shortest and longest
metal–ligand bonds are Zn–N(11) = 2.007(3) and
The structural features of complex 2 are shown in
Fig. 2a, and bond parameters are collected in Table 3.
The structure of complex 2 features five coordinate zinc

M.A.S. Goher et al. / Journal of Molecular Structure 886 (2008) 32–38
35
Table 4
Selected bond lengths (A) and angles (°) for 3
atoms, each zinc is surrounded by two di-EO (end-on)
azide bridges; N(11), N(11A), N(11B), N(11C)
[Zn–N = 2.008(5) and 2.203(5) A], and the fifth position
˚
˚
Zn(1). . .Zn(1A)
Zn(1)–N(11A)
Zn(1)–N(1)
Zn(1)–N(21A)
N(12)–N(13)
N(22)–N(23)
Zn(1A). . .Zn(1)
3.256(1)
2.028(3)
2.104(3)
2.179(3)
1.137(5)
1.147(5)
142.39(3)
Zn(1). . .Zn(1B)
Zn(1)–N(21)
Zn(1)–N(11)
N(11)–N(12)
N(21)–N(22)
6.962(1)
2.036(3)
2.142(3)
1.218(5)
1.210(5)
is occupied by
N
atom of 4-Etpy ligand
˚
[
Zn–N = 2.025(8) A]. The 1D chain of polyhedra
(Fig. 2b) is extended along the a-axis of the unit cell. The
Zn. . .Zn distances within the four-member Zn N units
2
2
˚
N(11A)–Zn(1)–N(21)
124.81(14)
are 3.262(2) A. As in complex 1, the l-1,1 azido groups
are asymmetric and almost linear within experimental
error.
.
. .Zn(1B)
N(11A)–Zn(1)–N(1)
N(11A)–Zn(1)–N(11) 100.47(14) N(21)–Zn(1)–N(11)
N(1)–Zn(1)–N(11) 95.45(11)
N(21)–Zn(1)–N(21A) 97.88(13)
N(11)–Zn(1)–N(21A) 174.13(12) N(12)–N(11)–Zn(1C)
128.29(12) N(21)–Zn(1)–N(1)
106.45(12)
78.45(13)
N(11A)–Zn(1)–N(21A) 77.76(13)
N(1)–Zn(1)–N(21A)
89.97(11)
125.0(3)
102.64(14)
127.8(3)
3.1.3. [Zn (N ) (2,5-dmpyz)] (3)
2 3 4 n
Crystal structure analysis has revealed that the ratio of
Zn(N ) to 2,5-dmpyz is exactly 2:1 as inferred from the
N(12)–N(11)–Zn(1)
N(13)–N(12)–N(11)
N(22)–N(21)–Zn(1C) 128.3(3)
N(23)–N(22)–N(21) 178.7(4)
131.0(3)
179.0(4)
Zn(1C)–N(11)–Zn(1)
N(22)–N(21)–Zn(1)
Zn(1)–N(21)–Zn(1C)
3
2
101.09(14)
elemental analysis. A view of the asymmetric unit along
with a labeling scheme is given in Fig. 3a, and selected
bond lengths and bond angles are given in Table 4. The
structure consists of a chain of Zn(N ) in which each zinc
Symmetry codes: (A) x,ꢀy + 3/2,z + 1/2; (B) ꢀx,ꢀy + 1,ꢀz; (C)
x,ꢀy + 3/2,z ꢀ 1/2.
3
2
atom binds two di-EO bridging azides and extended along
the c-axis of the unit cell. The fifth position is occupied by a
nitrogen atom from 2,5-dmpyz ligand forming ZnN chro-
5
mophore having distorted trigonal bipyramid (TBP) geom-
etry (s = 0.76) with N(11), and N(21A) at the axial
positions. The Zn–N(N ) distances are variable from
3
˚
2
.026(3) to 2.142(3) A, which are more or less similar to
corresponding values given for complexes 1 and 2. Each
Fig. 1. (a) Perspective view with atom labeling scheme of (1). Symmetry
codes according Table 2. (b) Packing plot of (1) viewed along the a-axis of
the unit cell.
Fig. 2. (a) Perspective view with atom labeling scheme of (2). Symmetry
codes according Table 3. (b) Packing plot of (2) viewed along the a-axis of
the unit cell.

36
M.A.S. Goher et al. / Journal of Molecular Structure 886 (2008) 32–38
of 123.1(4) and 123.3(4)°, respectively, in complex 1, are
2
within the 120° angle of sp hybridized nitrogen atom of
the azido ligands, whereas the corresponding angles
Zn(1)–N(11)–N(12) and Zn(1A)–N(11)–N(12) in complex
2
of 125.6(3) and 133.1(3)° are greater than the 120° angle.
Both complexes however, differ from the structure of com-
plex 3, with the 2D sheet structure and bridging bidentate
0
N,N -dmpyz ligand. The structure of complex 3 differs also
from that of [Zn (N ) (ampyz) ] 4 (ampyz = aminopyr-
3
3 6
2 n
azine), also having 2D sheet structure [23]. Complex 4 con-
tains two crystallographically different zinc centers: Zn(1) is
octahedrally coordinated by two di-EO azido bridges and
two trans ampyz ligands giving ZnN6 chromophore,
whereas Zn(2) is five coordinated by two di-EO bridging
azides and one ampyz forming ZnN chromophore, and
5
each ampyz links another zinc center. Complex 4, thus hav-
ing chains of alternate ZnN /ZnN .
6
5
It is noteworthy at this point to compare complexes 1
and 2 with known zinc(II) azide complexes of the same for-
mula [Zn(N ) L] for L = 2-picoline [17c], 3-picoline [17b],
3
2
n
4-picoline [17d], lutidines [17a] and 4-methylpyrimidine
[
18]. All these structures are very similar adopting ZnN5
geometries with distorted trigonal bipyramids. The asym-
metric end-on (l-1,1) azide bridges form 1D chains with
common edges, with one equatorial Zn–N bond [from
˚ ˚
1
.99 to 2.05 A, mean value 2.02 A] and one longer axial
˚
˚
Zn–N bond [range from 2.11 to 2.28 A, mean 2.22 A],
respectively. Due to low steric hindrance of the azido
bridges the difference of axial and equatorial Zn–N bonds
of 0.20 A is in good agreement with theoretical calculation
done for d systems by Gillespie [24]. In all the above eight
Fig. 3. (a) Perspective view with atom labeling scheme of (3). Symmetry
codes according Table 4. (b) 2D arrangement of (3). The sheets are
extended along the b- and c-axes of the unit cell.
˚
10
˚
complexes the Zn–N(pyridine) bond range is 1.99–2.06 A
of the dmpyz ligands binds another zinc atom in adjacent
Zn(N ) chains via its second nitrogen extending the struc-
˚
(
mean value 2.02 A), the Zn. . .Zn distances range from
˚
3
2
3.03 to 3.31 A, and Zn. . .Zn. . .Zn angles from 134° to
40°. Metal azide complexes similar to 1 and 2, featuring
ture along the b-axis to form 2D sheets (Fig. 3b). The pyr-
1
˚
azine ligand has a Zn–N(pyz) bond distance of 2.104(3) A,
which is a little longer than corresponding values found in
complexes 1 and 2 with monodentate pyridine ligands,
five coordinate metal centers, two di-EO azido bridges
forming zigzag chains, and distorted trigonal bipyramid
or distorted square pyramid have been reported previously
in numerous structures of copper(II) azido complexes of
pyridine derivatives, e.g. [Cu(N ) (3-picoline)] [25],
whereas the Zn. . .Zn distance within the Zn N units of
2
2
˚
3
.256(1) A, is very close to those found in complexes 1
3
2
n
and 2.
[
Cu(N ) (2-chloropyridine)]
[26] and [Cu(N ) (2,5-
3 2
3
2
n
dimethyl pyridine)] [27].
n
3
.2. Discussion
The IR spectrum of complex 1, shows a very strong
ꢀ1
band at 2086 cm
,
and another strong band at
ꢀ1
The reaction between Zn(N ) and 3-Brpy, 4-Etpy and
2042 cm , in addition to two medium to strong bands at
3
2
ꢀ
1
2
,5-dmpyz afforded 1:1 zinc(II) azide to ligand in case of
1343 and 1286 cm , due to m (N ) and m (N ) vibration
as 3 s 3
the first two pyridine derivatives and 2:1 in case of the pyr-
azinic ligand. Maybe this is related to the ability of the
third ligand to behave as a bridging bidentate. Although
the structures of complexes 1 and 2 are similar: both crys-
tallize in monoclinic, features 1D chains consisting of two
di-EO azido bridges around each zinc center which is fur-
ther connected to the monodentate pyridine derivative
modes. The high frequency vibrations are consistent with
the crystal structure determination that the complex con-
tains two l-1,1 azido bridges with different degrees of
˚
˚
asymmetry [Dd = 0.070 A for one, and 0.055 A for the
other (Dd is the difference between the N–N distances
ꢀ
1
within the azide group)], and the 1350–1280 cm bands
confirm the asymmetric nature of the azides. Complex 2
with two l-1,1 azido bridges having the same degree of
ligand having therefore ZnN chromophore, there are sub-
5
˚
tle differences. Crystals of complex 1 are monoclinic, space
asymmetry [Dd = 0.080 A] only one very strong band asso-
ꢀ1
group P2 /c, whereas the space group of complex 2 is I2/a.
ciated with m (N ) vibration mode appears at 2080 cm ,
as 3
1
ꢀ
1
The Zn(1)–N(11)–N(12) and Zn(1B)–N(11)–N(12) angles
in addition to two strong bands at 1345 and 1288 cm

M.A.S. Goher et al. / Journal of Molecular Structure 886 (2008) 32–38
37
due to m (N ). The IR spectrum of complex 3, exhibits a
ner, G. Reiss, R. Vicente, Angew. Chem. Int. Ed. Eng. 39 (2000)
1624.
3] (a) Z. Shen, J.-L. Zuo, Z. Yu, Y. Zhang, J.-F. Bai, C.-M. Che, H.K.
Fun, J.J. Vittal, X.-Z. You, Dalton Trans. (1999) 3393;
s
3
ꢀ
1
very strong band at 2091 cm related to m (N ), although
as
3
[
[
[
[
the structure contains two l-1,1 bridging azides of different
˚
˚
degrees of asymmetry [Dd = 0.081 A for one and 0.063 A
(
b) A. Escuer, R. Vicente, M.A.S. Goher, F.A. Mautner, Dalton
for the other]. The appearance of two strong bands at
Trans. (1997) 4431;
(c) S.S. Tandon, L.R. Thompson, J.S. Miller, Chem. Commun. (1995)
ꢀ1
1
345 and 1291 cm , however is a strong evidence of the
1
907.
4] (a) E.-Q. Gao, Z.-M. Wang, C.-H. Yan, Chem. Commun. (2003)
748;
b) E.-Q. Gao, S.-Q. Bai, Z.-M. Wang, C.-H. Yan, Dalton Trans.
asymmetric nature of the azido groups in this complex.
Although the positions of the m (N ) mode for complexes
as
3
1
(
1
and 2 are consistent with the relationship pointed out
previously that the larger the difference between the two
N–N distances within the azido group (Dd), the higher is
the energy of m (N ) [28], the position of the m (N ) for
(2003) 1759;
(c) E.-Q. Gao, Z.-M. Wang, C.-S. Liao, C.-H. Liao, New J. Chem. 26
(
2002) 1069.
as
3
as
3
5] (a) E.-Q. Gao, S.-Q. Bai, C.-F. Wang, Y.-F. Yue, C.-H. Yan, Inorg.
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(
b) E.-Q. Gao, Y.-F. Yue, S.-Q. Bai, Z. He, C.-H. Yan, Chem. Mater.
16 (2004) 1590;
c) B. Bitschnau, A. Egger, A. Escuer, F.A. Mautner, B. Sodin, R.
4
. Conclusion
(
Vicente, Inorg. Chem. 45 (2006) 868, and references therein.
6] (a) M.A.S. Goher, A. Escuer, F.A. Mautner, N.A. Al-Salem,
Polyhedron 21 (2002) 1871;
We isolated three zinc(II) azido polymers with 3-bromo-
pyridine, 4-ethylpyridine and 2,5-dimethylpyrazine, with
:1 molar ratio for pyridine derivative ligands and 2:1 ratio
1
(
b) Molecule-based magnets from Ni(II), Mn(II) azido bridging
in case of the pyrazinic ligand, and studied their spectra
and crystal structures. As the pyridine ligands contain only
one coordination site; the hetero nitrogen, the structures of
both 1:1 complexes confined to 1D chain. As the pyrazine
derivative ligand can behave as a bidentate bridge, allows
the structure of complex 3 to extend to be 2D sheets. The
IR spectral results confirm the asymmetric nature of azido
groups in the three complexes.
ligands and related compounds, in: J.S. Miller, M. Drillon (Eds.),
Molecular magnetism and magnetic properties of extended systems,
Wiley-VCH, Germany, 2001, pp. 307–337.
[
[
7] A. Escuer, M.A.S. Goher, F.A. Mautner, R. Vicente, Inorg. Chem. 39
(
2000) 2112, and references therein.
8] (a) J.-L. Tian, W. Gu, S.-P. Yan, D.-Z. Liao, Z.-H. Jiang, P. Cheng, J.
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(
c) P. Mukhopadhyay, B. Sarkar, P.K. Bharadwaj, K. Nattinen, K.
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Appendix A. Supplementary data
(
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