Polyhedron 24 (2005) 1829–1836
www.elsevier.com/locate/poly
Two new 3D network structures: [Cd3(nic)4(N3)2(H2O)]n
and [Zn(nic)(N3)]n (nic = nicotinate anion)
Morsy A.M. Abu-Youssef
*
Department of Chemistry, Faculty of Science, Alexandria University, P.O. Box 426 Ibrahimia, 21321 Alexandria, Egypt
Received 6 February 2005; accepted 31 May 2005
Available online 8 August 2005
Abstract
Two new cadmium(II) and zinc(II) complexes: [Cd3(nic)4(N3)2(H2O)2]n (1) and [Zn(nic)(N3)]n (2) (nic = nicotinate anion) have
been synthesized and characterized by spectroscopic, crystallographic and thermal methods. Both complexes 1 and 2 represent
3D network structures. Complex 1 consists of trinuclear units in which the three Cd centers are held together by four bridging
l-N,O,O 0 -tridentate nicotinate anions, two bridging end-on (EO), (l1,1-N3) groups and two aqua molecules. The water molecule
is further H-bonded to the neighboring unit through an O H–O bond. Complex 2 crystallizes in the non-centrosymmetric space
group P212121, representing a right handed chiral complex. Each zinc(II) atom forms a distorted trigonal bipyramidal structure
linked through l-N,O,O 0 -tridentate nicotinate anions and di-(l1,1-N3) groups. IR, Raman, 1H NMR and 13C NMR spectra of both
complexes have been measured and discussed in comparison to the free ligand, in addition to the discussion of the thermal TGA and
DTA curves.
2005 Elsevier Ltd. All rights reserved.
Keywords: Cd(II); Zn(II); Nicotinate; Azido complexes; Preparation; X-ray structures; Spectra
1. Introduction
Nicotinic acid, also known as pyridine-3-carboxylic
acid, forms different types of metal complexes. It may
act as a neutral ligand, ligating the metal ion through
its N atom, as found in its copper(I) [1] and gold(III)
[2] complexes, or as a nicotinate anion (nic). As an anion it forms complexes of the type [M(nic)2 Æ nH2O]
(n usually equals 2 or 4) (M(II) = Mn [3], Co [4,5] Zn
[6,7], Cr [7]). In these complexes the nicotinate anion
links metal atoms via its hetero N atom only, giving
an unusual zwitterion. The nicotinate anion also forms
complexes with lanthanides of the type [Ln(nic)3 Æ
2H2O]2 (Ln = Pr(III), Gd(III) and Ho(III)), in which it
binds the Ln atom by the two carboxylate O atoms
*
Tel.: +20127866390; fax: +2033911794.
E-mail address: [email protected].
0277-5387/$ - see front matter 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2005.05.026
forming a four-member chelate ring, thus acting as a
bidentate ligand [8]. A few years ago three complexes
in the silver(I)-nicotinic acid system were reported,
namely orthorhombic catena-[pyridine-3-carboxylato(O,O 0 )]silver(I) [9,10], triclinic ammonium bis[pyridine3-carboxylato-(O,N,N 0 )]silver(I)monohydrate [10] and
catena-(hydrogen bis[pyridine-3-carboxylato-(N,N 0 )]silver(I)) [11]. The nicotinate anion links three different
Ag atoms in the first complex, but it binds two Ag atoms
in the last two compounds. Thus catena-[pyridine-3carboxylate-(0,0 0 )]silver(I) is the first example containing
a N,O,O 0 -tridentate bridging nicotinate anion.
We have recently reported a number of cadmium(II)
azido and thiocyanato coordination polymers with some
pyridine derivative ligands containing different bridging
modes of [Cd(N3)2]n and [Cd(NCS)2]n chains [12–20].
We now extend our work to include the reaction of
cadmium(II) and zinc(II) ions with nicotinic acid in the
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M.A.M. Abu-Youssef / Polyhedron 24 (2005) 1829–1836
presence of azide ions, and isolated a 3:4:2 Cd:(nic):azide
(1) and a 1:1:1 Zn:(nic):azide (2) complex.
Caution. Metal azide complexes are potentially explosives. Only a small amount of material should be prepared and handled with caution.
2. Experimental
2.2. Synthesis
2.1. Material and instrumentation
2.2.1. [Cd3(nic)4(N3)2(H2O)2] (1)
To an aqueous solution (20 cm3) of 3CdSO4 Æ 8H2O
(0.77 g, 1.0 mmol, 3 mmol in Cd2+) nicotinic acid
(0.74 g, 6 mmol) in methanol/water (15 cm3) was added,
followed by dropwise addition of an aqueous solution of
NaN3(0.65 g, 10 mmol) with continuous stirring. The
mixture was heated, filtered off, boiled again and the final clear mixture was allowed to cool gradually to room
temperature then placed in a refrigerator for several
days. Yellow crystals suitable for X-ray measurement
were collected, dried in air, with a yield of 85%. Anal.
Calc.: C, 30.48; H, 2.13; N, 14.81; Cd, 35.66. Found: C,
30.38; H, 2.23; N, 14.74; Cd, 35.69%. 1H NMR (DMSOd6): d 7.53 (t, 4H), 8.34 (d, 4H), 8.67 (s, 4H), 9.19 (s, 4H);
13
C NMR (DMSO-d6): d 124.24, 131.22, 138.60, 151.24,
151.72 and 170.82.
C, H, N elemental analyses were carried out using a
Perkin–Elmer analyzer, Cd and Zn were analyzed by a
Perkin–Elmer Analyst 300, AAS atomic absorption
spectrometer. Infrared spectra were recorded on a Bruker IFS-125 model FT-IR spectrophotometer as KBr
pellets. Raman spectra were recorded on a BRUKER
IFS 6/s FT-Raman spectrometer with Nd:CYAG laser
wavelength (1064 nm) as the light source. 1H NMR
and 13C NMR (DMSO-d6) spectra were recorded on a
Jeol JNM-ECA 500 MHz spectrometer. TGA and
DTA were carried out on a Shimadzu-50H under a
nitrogen flow rate 30 ml/min. Nicotinic acid was purchased from Aldrich Company and other chemicals
were of analytical grade quality and used as received.
Table 1
Crystallographic data and structure refinement for compounds 1 and 2
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
b (Å)
c (Å)
a ()
a ()
c ()
Volume (Å3)
Z
Dcalc (Mg/m3)
Absorption coefficient (mm)1
F(0 0 0)
Crystal size (mm3)
h range for data collection ()
Index ranges
Reflections collected
Independent reflections [Rint]
Absorption correction
Maximum and minimum transmission
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2r(I)]
R indices (all data)
Largest difference peak and hole (e Å3)
1
2
C24H20Cd3N10O10
945.70
173(2)
0.71073
triclinic
P 1
C6H4ZnN4O2
229.50
173(2)
0.71073
orthorhombic
P212121
6.7224(1)
10.1819(1)
11.7912(2)
75.063(1)
74.514(1)
88.173(1)
750.898(17)
1
2.091
2.177
458
0.08 · 0.06 · 0.04
1.86–30.00.
9 6 h 6 9,
14 6 k 6 14,
16 6 l 6 15
10 696
4350 [0.0481]
multi-scan
0.9180 and 0.8451
full-matrix least-squares on F2
4350/2/223
1.028
R1 = 0.0457, wR2 = 0.0952
R1 = 0.0732, wR2 = 0.1062
1.348 and 1.373
5.9585(1)
10.4445(1)
12.5726(1)
90
90
90
782.437(16)
4
1.948
3.106
456
0.42 · 0.39 · 0.22
2.54–32.80
9 6 h 6 9,
15 6 k 6 15,
18 6 l 6 19
13 250
2803 [0.0280]
multi-scan
0.5482 and 0.3554
full-matrix least-squares on F2
2803/0/122
1.038
R1 = 0.0185, wR2 = 0.0495
R1 = 0.0188, wR2 = 0.0498
0.561 and 0.398
M.A.M. Abu-Youssef / Polyhedron 24 (2005) 1829–1836
Table 2
Selected bond lengths (Å) and bond angles () for complex 1
Cd(1)–N(1)i
Cd(1)–N(1)
Cd(1)–O(2B)ii
Cd(1)–O(2B)iii
Cd(1)–O(2A)iv
Cd(1)–O(2A)v
Cd(2)–O(1B)iii
Cd(2)–N(1)
Cd(2)–O(1)
Cd(2)–O(1A)vi
Cd(2)–N(1A)
Cd(2)–N(1B)
O(1)–H(1)
O(1)–H(2)
N(1)–N(2)
N(2)–N(3)
N(1)i–Cd(1)–N(1)
N(1)i–Cd(1)–O(2B)ii
N(1)–Cd(1)–O(2B)ii
N(1)i–Cd(1)–O(2B)iii
N(1)–Cd(1)–O(2B)iii
O(2B)ii–Cd(1)–O(2B)iii
N(1)i–Cd(1)–O(2A)iv
N(1)–Cd(1)–O(2A)iv
O(2B)ii–Cd(1)–O(2A)iv
O(2B)iii–Cd(1)–O(2A)iv
N(1)i–Cd(1)–O(2A)v
N(1)–Cd(1)–O(2A)v
O(2B)ii–Cd(1)–O(2A)v
O(2B)iii–Cd(1)–O(2A)v
O(2A)iv–Cd(1)–O(2A)v
O(1B)iii–Cd(2)–N(1)
O(1B)iii–Cd(2)–O(1)
N(1)–Cd(2)–O(1)
O(1B)iii–Cd(2)–O(1A)vi
N(1)–Cd(2)–O(1A)vi
O(1)–Cd(2)–O(1A)vi
O(1B)iii–Cd(2)–N(1A)
N(1)–Cd(2)–N(1A)
O(1)–Cd(2)–N(1A)
O(1A)vi–Cd(2)–N(1A)
O(1B)iii–Cd(2)–N(1B)
N(1)–Cd(2)–N(1B)
O(1)–Cd(2)–N(1B)
O(1A)vi–Cd(2)–N(1B)
N(1A)–Cd(2)–N(1B)
N(2)–N(1)–Cd(1)
N(2)–N(1)–Cd(2)
Cd(1)–N(1)–Cd(2)
N(3)–N(2)–N(1)
2.285(4)
2.285(4)
2.315(3)
2.315(3)
2.330(3)
2.330(3)
2.277(3)
2.296(4)
2.304(4)
2.324(3)
2.348(4)
2.351(4)
0.88(2)
0.88(2)
1.211(5)
1.146(5)
180.0
93.35(13)
86.65(13)
86.65(13)
93.35(13)
180.0
91.68(14)
88.32(14)
86.54(13)
93.46(13)
88.32(14)
91.68(14)
93.46(13)
86.54(13)
180.0
95.70(13)
86.67(13)
94.67(14)
174.18(12)
88.95(13)
96.45(12)
89.99(14)
94.25(15)
170.74(14)
86.19(13)
88.47(13)
175.39(13)
87.51(14)
86.76(12)
83.77(15)
123.2(3)
118.3(3)
117.19(16)
179.1(5)
Symmetry transformations used to generate equivalent atoms:
(i) x,y,z; (ii) x, y, z 1; (iii) x,y, z + 1; (iv) x, y 1, z;
(v) x, y + 1, z; (vi) x + 1, y + 1, z; (vii) x, y + 1, z; (viii) x, y,
z + 1.
1831
2.2.2. [Zn(nic)(N3)] (2)
This complex was prepared by mixing zinc sulfate
ZnSO4 Æ 7H2O (0.50 g, 1.74 mmol) in water (30 cm3)
with nicotinic acid (0.43 g, 3.5 mmol) in ethanol/water
(20 cm3). An aqueous solution of NaN3 (0.65 g,
10 mmol) was added dropwise with continuous stirring.
The final mixture was then allowed to stand for several
days to yield pale brown crystals of the complex suitable for X-ray diffraction (65% yield). Anal. data for
the complex C6H4N4O4Zn: Calc.: C, 31.40; H, 1.76;
N, 24.41; Zn, 28.48. Found: C, 31.38; H, 1.82; N,
24.56; Zn, 28.53%. 1H NMR (DMSO-d6): d 7.57 (t,
1H), 8.58 (d, 1H), 8.64 (d, 1H), 9.08 (s, 1H); 13C
NMR (DMSO-d6): d 124.78, 131.41, 139.31, 150.69,
151.51 and 169.65.
Table 4
Selected bond lengths (Å) and bond angles () for complex 2
Zn(1)–N(1A)i
Zn(1)–N(1)
Zn(1)–N(1A)
Zn(1)–O(8)ii
Zn(1)–O(9)iii
O(8)–Zn(1)iv
O(9)–Zn(1)v
N(1A)–Zn(1)vi
N(1A)–N(2A)
N(2A)–N(3A)
N(1A)i–Zn(1)–N(1)
N(1A)i–Zn(1)–N(1A)
N(1)–Zn(1)–N(1A)
N(1A)i–Zn(1)–O(8)ii
N(1)–Zn(1)–O(8)ii
O(8)ii–Zn(1)–O(9)iii
N(2A)–N(1A)–Zn(1)vi
N(2A)–N(1A)–Zn(1)
Zn(1)vi–N(1A)–Zn(1)
N(3A)–N(2A)–N(1A)
N(1A)–Zn(1)–O(8)ii
N(1A)i–Zn(1)–O(9)iii
N(1)–Zn(1)–O(9)iii
N(1A)–Zn(1)–O(9)iii
N(2A)–N(1A)–Zn(1)vi
N(2A)–N(1A)–Zn(1)
Zn(1)vi–N(1A)–Zn(1)
N(3A)–N(2A)–N(1A)
2.0325(11)
2.0484(11)
2.0523(11)
2.0651(9)
2.1898(10)
2.0651(9)
2.1898(10)
2.0325(11)
1.2205(14)
1.1443(16)
118.56(4)
128.20(3)
112.30(5)
94.37(4)
94.96(4)
177.82(4)
118.25(9)
120.79(9)
111.96(5)
178.08(16)
90.33(4)
85.59(4)
86.96(4)
87.99(4)
118.25(9)
120.79(9)
111.96(5)
178.08(16)
Symmetry transformations used to generate equivalent atoms:
(i) x 1/2, y + 1/2, z + 1; (ii) x + 1/2, y + 1, z + 1/2; (iii)
x + 1, y 1/2, z + 1/2; (iv) x + 1/2, y + 1, z 1/2; (v) x + 1,
y + 1/2, z + 1/2; (vi) x + 1/2, y + 1/2, z + 1.
Table 3
Hydrogen bonds for [Cd3(nic)4(N3)2(H2O)2]n (1) (Å and )
D–H A
iv
O(1)–H(1) O(2A)
O(1)–H(2) O(2B)ix
d(D–H)
d(H A)
d(D A)
\(DHA)
0.88(2)
0.88(2)
1.87(3)
2.00(2)
2.727(5)
2.874(5)
164(8)
177(8)
Symmetry transformations used to generate equivalent atoms: (i) x, y, z; (ii) x, y, z 1; (iii) x,y, z + 1; (iv) x, y 1, z; (v) x, y + 1, z;
(vi) x + 1, y + 1, z; (vii) x, y + 1, z; (viii) x, y, z + 1; (ix) x + 1, y, z + 1.
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M.A.M. Abu-Youssef / Polyhedron 24 (2005) 1829–1836
2.3. X-ray crystallography
All diffraction data were collected using a Siemens
SMART CCD diffractometer with Mo Ka radiation
(k = 0.71073 Å, graphite monochromator). The crystals
were cooled to 173(2) K by a flow of nitrogen gas using
the LT-2A device. A full sphere of reciprocal lattices
were scanned by 0.3 steps in x with a crystal-to-detector distance of 3.97 cm. Preliminary orientation matrices
were obtained from the first frames using SMART [21].
Fig. 3. A projection along the c-axis of 1. Both ligands and hydrogen
bonds, with the water molecule as a donor, bridging perpendicularly to
the planes of the trinuclear units.
Fig. 1. Numbering scheme of [Cd3(nic)4(N3)2 (H2O)2]n complex 1 and
atomic displacement ellipsoids draw at the 50% probability level. Note
that just a part of the tri-nuclear complex is shown, the rest of it is
symmetry dependent. For symmetry codes see Table 3.
Fig. 2. A 4 · 4 superunit with coordination polyhedra
[Cd3(nic)4(N3)2(H2O)2]n complex 1. Projection along the a-axis.
of
Fig. 4. Numbering scheme of [Zn(nic)(N3)2]n complex 2 and atomic
displacement ellipsoids at the 50% probability level.
M.A.M. Abu-Youssef / Polyhedron 24 (2005) 1829–1836
Fig. 5. Projection of the complex 2 structure along the a-axis.
Coordination polyhedra for Zn atoms are shown.
The collected frames were integrated using the preliminary orientation matrices which were updated every 100
frames. Final cell parameters were obtained by refinement of the positions of reflections with I > 10r(I) after
integration of all the frames using SAINT [21]. The data
were empirically corrected for absorption and other effects using the SADABS [22] program. The structures were
solved by direct methods and refined by full-matrix least
squares on all F2 data using SHELXTL software [23]. The
non-H atoms were refined anisotropically, while hydrogen atoms were refined isotropically with use of geometrical restrains. The crystallographic and refinement data
are summarized in Table 1. Selected bond distances and
bond angles are given in Tables 2 and 4 for complexes 1
and 2, respectively. Molecular graphics (Figs. 1–5) were
prepared using the DIAMOND [24] program Table 3.
3. Results and discussion
The reaction between cadmium(II) and zinc(II) ions
and nicotinic acid in the presence of the azide ion afforded 3:4 and 1:1 complexes, respectively. Complexes 1
and 2 are insoluble in non-polar solvents, e.g., benzene,
CCl4, etc. and in polar solvents, e.g., H2O, MeOH,
EtOH, CHCl3, acetone, etc. indicating their polymeric
nature. Both complexes are slightly soluble in DMSO.
The 1H NMR spectra of these complexes in DMSO suggest a partial substitution of the azido ligands by
DMSO.
3.1. Structures
3.1.1. [Cd3(nic)4(N3)2(H2O)2]n (1)
X-ray single crystal structure determination reveals
that complex 1 has a 3D network structure consisting
of a novel linear, trinuclear unit containing three Cd(II)
1833
atoms, four nicotinate anions, two azide ions and two
aqua molecules as shown in Fig. 1. All the three cadmium atoms are hexa-coordinated in a distorted octahedral environment. The central cadmium atom Cd1 is
surrounded by two N atoms of two l1,1-azido groups
at [Cd–N 2.285(4) Å] and four O atoms of four different
l-N,O,O 0 -nicotinate anions [Cd–O 2.330(3) and 2.315(3) Å], having a CdN2O4 chromophore. Each of the
other two Cd atoms (Cd2) is surrounded by two hetero
nitrogen atoms of two bridging l-N,O,O 0 -tridentate nicotinate anions [Cd–N 2.348(4) and 2.351(4) Å]; one N
atom of a bridging (l1,1-N3) group [Cd–N 2.296(4) Å]
and three O atoms from two bridging carboxylate
groups of two different nicotinate anions [Cd–O
2.277(3) and 2.324(3) Å] and one aqua molecule [Cd–O
2.304(4) Å]. Fig. 2 presents a 4 · 4 superunit with coordination polyhedra of the complex illustrating each nicotinate anion bridging one unit through its hetero
nitrogen atom and other units through its carboxylate
oxygen, assembling a sheet structure. The water molecule is further H-bonded to a neighboring unit [H OH,
1.87(3) and 2.00(2) Å], Fig. 3. The Cd–O distances are
shorter than those reported in other Cd(II) carboxylate
structures, Cd–O 2.502(7) and 2.732(7) Å [25].
3.1.2. [Zn(nic)(N3)]n (2)
Complex 2 crystallizes in the non-centrosymmetric
space group P212121, representing a right handed chiral
complex from achiral molecules. The atom labelling
scheme for complex 2 is shown in Fig. 4. The absolute
structure was determined with Flacks parameter [26]
being so good (0.001(8)) as to indicate that it has been
unequivocally determined. The structure of 2 reveals a
Zn(II) to nicotinate anion ratio of 1:1 as predicted from
the elemental analysis. In this structure, the zinc atom is
located at the center of a trigonal bipyramidal structure.
The two axial positions of the trigonal bipyramidal
structure are occupied by two oxygen atoms of two carboxylate groups [Zn–O 2.0651(9) and 2.1898(10) Å]
from two different nicotinate anions with an O–Zn–O
angle of 177.82(4). This is different from the bidendate
O,O 0 -nicotinate anion in [Ln2(nic)6(H2O)4] complexes,
in which the two O atoms of the carboxylate group bind
the same Ln atom, forming a four membered ring [8]. At
the equatorial positions the zinc atom is linked by three
nitrogen atoms, one N hetero atom [Zn–N 2.0484(11) Å]
of the nicotinate anion and two N atoms of 2 (l1,1-N3)
groups [Zn–N 2.0325(11) and 2.0523(11) Å]. The nicotinate anion, therefore behaves as a N,O,O 0 -tridentate
bridging ligand, as in complex 1, giving rise to a 3D
structure for complex 2, Fig. 5. The Zn–N and Zn–O
bond lengths fall within the range found for other similar complexes, Zn–N 2.040(8) Å and Zn–O 2.152 Å for
[Zn(H-pic)(pic)Cl] [12]. It is also comparable to the
bonds in the dimeric Zn2N2 unit of the structure of
1834
M.A.M. Abu-Youssef / Polyhedron 24 (2005) 1829–1836
[Zn(dpa)(N3)(NO3)]2 (dpa = 2,2 0 -dipyridylamine) [Zn–
N 2.090(2) and 2.130(2) Å] [27]. The larger N(1A)i–
Zn(1)–N(1A) bond angle [128.20(3)] is due to the
Zn2N2 unit which has a Zn(1)vi–N(1A)–Zn(1) bond angle of 111.96(5). The reported [Zn3(bpy)3(hip)2] Æ 5H2O
complex has two different penta coordinated Zn(II) ions
in a trigonal bipyramidal geometry with Zn–L (L = O,
N) distances in the range of 1.997(9)–2.257(14) Å and
bond angles in the equatorial plane in the range of
98.2(5)–142.3(5) [28]. The bridging azide ion is asymmetric [N(1A)–N(2A) 1.2205(14) Å and N(2A)–N(3A)
1.1443(16) Å] and linear [N(3A)–N(2A)–N(1A) 178.08(16)].
3.2. Spectra
The room temperature IR spectra of the crystalline
nicotinic acid and the sodium salt of nicotinic acid,
and also the IR and Raman spectra of [Cd3(nic)4(N3)2(H2O)2]n complex 1 and [Zn(nic)(N3)]n complex 2, are given with tentative assignments of the bands in Table 5.
In the high energy region complex 1 exhibits a strong
broad band around 3400 cm1 corresponding to the
water molecules coordinated to the Cd(II) ions bridging
the trinuclear units. Hydrogen bonding of the type
N H–O is indicated in the free acid by the presence
of broad, medium strong bands near 2450 and
1880 cm1 (IR) [29]. These bands are completely absent
in the spectra of the solid complexes 1 and 2, as well as
the corresponding sodium salt [30]. The vibration frequencies of the free nicotinic acid in a KBr pellet at
1715 vs, br, m(C@O) and 1640 s cm1, mas(–COO)
(IR) [31,32] disappeared in both IR and Raman spectra
of the complexes 1 and 2. Instead the spectra of 1 and 2
show strong peaks around 1609 vs, (IR) and 1612 w
cm1 (Raman) and 1617 vs, (IR) and 1610 w cm1 (Raman), respectively. These results indicate that only the
nicotinate anions are coordinated to the Cd(II) and
Zn(II) ions through their carboxylate oxygen atoms.
The bands related to the pyridine ring in the IR spectra
of 1 and 2 show systematic shifts in accordance with
those found for pyridine complexes [33]. Thus, the nicotinate anions in both complexes 1 and 2 are coordinating
via their carboxylate O atoms and the hetero N atoms.
The peaks at 2070 (vs), 1289 (m) cm1 (IR) and 2110 (s),
1294 (vs) cm1 (Raman) for 1 and 2100 (vs), 1292 (m) cm1
(IR) and 2070 (m), 1290 (w) cm1 (Raman) for 2 were assigned as (mas-N3) and (ms-N3), respectively. This is in agreement with the asymmetric nature of the bridging (l1,1-N3)
groups [N(1)–N(2), 1.211(5) and N(2)–N(3), 1.146(5) Å for
Table 5
Selected vibrational frequencies (cm1) in the IR and Raman spectra of nicotinic acid, sodium nicotinate and complexes 1 and 2
HNic
NaNic
[Cd3(nic)4(N3)2(H2O)2]n
[Zn(nic)(N3)]n
IR
IR
IR
Raman
IR
3329 s,b
3250 s,b
3064 vs
Assignments
Raman
mOH water
mN H–O
2450 m,b
1880 s,b
1708 s,b
1645 s
1600 s
1380 ms
1330 m
700 wm
700 wm
1585 sh
1550 m
1484 sh
1190 m
1130 m
1095 w
1035 s
951 m
830 m
750 vs
630 ms
500 wm
390 wm
2070 vs
1289 m
2110 s
1294 vs
2100 vs
1292 s
2070 m
1290 w
1602 vs
1609 vs
1612 s
1617 vs
1610 w
1396 vs
1387 vs
1396 vs
1334 w
1401 vs
702 vs
696 s
669 m
1587 vs
1562 vs
1469 m
1196 s
1156 ms
1119 ms
1093 m
1046 s
963 vw
841 m
758 s
641 m
593 m
538 m
425 m
1394 s
1351 w
700 w
640 s
1590 vs
1551 w
1474 vw
1196 s
1140 w
1112 w
1089 w
1043 s
970 w
849 s
1558 vs
1483 vs
1466 s
1194 s
1152 s
1102 s
1089 s
1040 m
968 wm
843 s
759 vs
638 s
593 s
508 s
392 m
656 s
1582 s
1571 s
1476 w
1193 m
1134 vs
1034 vs
965 w
854 s
441 w
696 vs
654 m
1591 vs
1569 vs
1467 wm
1194 s
1163 m
1113 s
1091 s
1056 s
971 w
851 s
757 vs
599 wm
545 m
431 ms
Abbreviations. w, weak; m, medium; s, strong; v, very; b, broad; sh, shoulder; st, stretching.
570 w, b
406 w
mas -N3 ms -N3 mC=O st
mas(–COO)
ms(COO)
d(COO)
pyridine ring
vibrations
M.A.M. Abu-Youssef / Polyhedron 24 (2005) 1829–1836
complex 1 and N(1A)–N(2A), 1.2205(14) and N(2A)–
N(3A), 1.1443(16) Å for complex 2].
3.3. Thermal analysis
The TGA and DTA curves for complexes 1 and 2 are
given in Fig. 6. As these complexes are expected to be
explosives we used small amounts for such thermal analyses, as suggested previously for thermal decomposition
measurements of azido compounds. [34] Complex 1 is
stable until 180 C, after which it decomposes (180–
230 C), losing one H2O molecule (Exp. 1.95%, Theor.
1.91%), followed by the loss of the other H2O molecule
and one N3 group (Exp. 6.6%, Theor. 6.3%), and then a
third stage (305–350 C), with a weight loss of 4.9%, corresponds to loss of the second N3 group. These three
stages are successive and appear as stages of one step
ending at 350 C. This appears in the DTA curve as a
very weak endothermal peak at 241 C. In the next step
(350–440 C) the weight loss is 38.73%, which corresponds to the loss of three nicotinates, (Theor.
38.69%), the loss of the forth nicotinate molecule starts
at 440 C (Exp. 12.8%, Theor. 12.9%). This last step appears in the DTA curve as two overlapped exotherms at
450 and 458 C (Fig. 6). The weight of the final residue
of 35.6% suggests that some explosion occurred since
the residue is found to be CdO, as indicated by X-ray
powder diffraction. Accordingly the residue should be
40.6%, which is much higher than the experimental
value.
1835
The TGA curve for complex 2 shows only two steps;
the first step starts around 120 C, followed by a long
plateau. The weight loss of 8.9% in this step corresponds
to the loss of a half N3 ion (Theor. 9.1%). This step appears as an endotherm at 135 C in the DTA curve. The
second step starts at 375 C with a weight loss of 57%
suggesting a loss of the other half N3 ion, CO and pyridine radical (Theor. 55.3%), leaving a ZnO residue of
35% (Theor. 35.6%).
Acknowledgments
This work was supported by the Swedish Research
Council through the SIDA-Swedish Research Links
Program (Grant No. 348-2002-6879). We are grateful
to Prof. Vratislav Langer (Department of Environmental Inorganic Chemistry, Chalmers University of Technology) for his advice, the use of his equipment and
computational facilities. Thanks to Prof. Yehia Badr,
Cairo University, Egypt for the Raman measurements.
Appendix A. Supplementary data
Supplementary data are available from the CCDC, 12
Union Road, Cambridge CB2 1EZ, UK on request,
quoting the deposition numbers: CCDC 258680 and
258681 for 1 and 2, respectively. Supplementary data
associated with this article can be found, in the online
version, at doi:10.1016/j.poly.2005.05.026.
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