Synthesis, crystal structure and spectroscopic properties of some cadmium(II) complexes with three polyamine and corresponding macroacyclic Schiff base ligands

Article abstract of DOI:10.1016/j.jorganchem.2008.03.025

Three Cd(II) macroacyclic Schiff base complexes [CdL⁴(NO₃)₂] (4), [CdL⁵(NO₃)₂] (5), [CdL⁶(NO₃)₂] (6) were prepared by template condensation of 2-pyridinecarboxaldehyde with N1-(2-nitrobenzyl)-N1-(2-aminoethyl)ethane-1,2-diamine (L¹), N1-(2-nitrobenzyl)-N1-(2-aminoethyl)propane-1,3-diamine (L²) or N1-(2-nitrobenzyl)-N1-(3-aminopropyl)propane-1,3-diamine (L³), in the presence of cadmium metal ion, respectively. Three Cd(II) complexes with L¹, L² and L³ were also synthesized. All complexes have been studied with IR, ¹H NMR, ¹³C NMR, DEPT, COSY, HMQC and microanalysis. Two of these complexes, [CdL⁴(NO₃)₂] (4) and [CdL¹(NO₃)₂] (1) have been characterized through X-ray crystallography. In complex 4, the Cd is in a six-coordinate environment comprised of the ligand N₄-donor set and two oxygen atoms of two nitrate groups. In the polyamine complexes (1, 2 and 3) Cd and ligand are in a ratio of 1:1. Supporting ab initio HF-MO calculations have been undertaken using the standard 3-21G^* and 6-31G^* basis sets.

Full text of DOI:10.1016/j.jorganchem.2008.03.025

Journal of Organometallic Chemistry 693 (2008) 2237–2243
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis, crystal structure and spectroscopic properties of some cadmium(II)
complexes with three polyamine and corresponding macroacyclic Schiff base
ligands
a
a
b
Hassan Keypour a, , Reza Azadbakht , Sadegh Salehzadeh , Hamid Khanmohammadi ,
*
Hamidreza Khavasi c, Harry Adams d
a Faculty of Chemistry, Bu-Ali Sina University, Hamedan 65174, Iran
b Department of Chemistry, Arak University, Arak 38156, Iran
c Department of Chemistry, Shahid Beheshti University, Evin, Tehran, 19839-63113, Iran
d Department of Chemistry, University of Sheffield, Sheffield S3 7HF, UK
a r t i c l e i n f o
a b s t r a c t
Three Cd(II) macroacyclic Schiff base complexes [CdL4(NO3)2] (4), [CdL5(NO3)2] (5), [CdL6(NO3)2] (6) were
prepared by template condensation of 2-pyridinecarboxaldehyde with N1-(2-nitrobenzyl)-N1-(2-amino-
ethyl)ethane-1,2-diamine (L1), N1-(2-nitrobenzyl)-N1-(2-aminoethyl)propane-1,3-diamine (L2) or N1-(2-
nitrobenzyl)-N1-(3-aminopropyl)propane-1,3-diamine (L3), in the presence of cadmium metal ion,
respectively. Three Cd(II) complexes with L1, L2 and L3 were also synthesized. All complexes have been
studied with IR, 1H NMR, 13C NMR, DEPT, COSY, HMQC and microanalysis. Two of these complexes,
[CdL4(NO3)2] (4) and [CdL1(NO3)2] (1) have been characterized through X-ray crystallography. In complex
4, the Cd is in a six-coordinate environment comprised of the ligand N4-donor set and two oxygen atoms of
two nitrate groups. In the polyamine complexes (1, 2 and 3) Cd and ligand are in a ratio of 1:1. Supporting
ab initio HF–MO calculations have been undertaken using the standard 3-21G* and 6-31G* basis sets.
Ó 2008 Elsevier B.V. All rights reserved.
Article history:
Received 31 December 2007
Received in revised form 7 March 2008
Accepted 20 March 2008
Available online 29 March 2008
Keywords:
Schiff base
Macroacycle
Crystal structure
Ab initio
1. Introduction
the formation of polyamine complexes, three cadmium(II) com-
plexes were also synthesized.
Schiff base complexes have been amongst the most widely
studied coordination compounds in the past few years [1–8]. This
is due to the fact that Schiff bases offer opportunities for inducing
substrate chirality, tuning the metal centred electronic factor,
enhancing the solubility and stability of either homogeneous or
heterogeneous catalysts [9–14]. They are also becoming increas-
ingly important as biochemical, analytical and antimicrobial re-
agents [15]. The environment around the metal centre ‘‘as
coordination geometry, number of coordinated ligands and their
donor group” is the key factor for metalloproteins to carry out spe-
cific physiological functions [16]. We have been interested in the
design and synthesis of a range of amines, polyamine complexes
and Schiff base macrocyclic and macroacyclic complexes [17–20].
The variety of possible Schiff base metal complexes with a wide
choice of ligands, and coordination environments, has prompted
us to undertake research in this area. We wish to report the results
of our investigations on the cadmium ion ability to act as a tem-
plate in synthesizing macroacyclic complexes. Furthermore, to
study the effect of existence of a 2-nitrobenzyl pendant arm on
2. Experimental
2.1. Starting materials
All solvents were of reagent grade quality and purchased
commercially.
2-diaminetrishydrochloride (I) N1-(2-nitrobenzyl)-N1-(2-amino-
ethyl)propane-1,3-diaminetrishydrochloride (II), N1-(2-nitroben-
zyl)-N1-(3-aminopropyl)propane-1,3-diaminetrishydrochloride
(III) were synthesized according to the literature method [21].
N1-(2-nitrobenzyl)-N1-(2-aminoethyl)ethane-1,
2.2. Instrumentation
NMR spectra were obtained using a Bruker A V 300 MHz spec-
trometer. Infrared spectra were recorded in KBr pellets using
BIO-RAD FTS-40A spectrophotometer (4000–400 cmÀ1).
2.3. X-ray crystal structure determination
X-ray data for [CdL1(NO3)2] were measured on a STOE IPDS-II
two circle diffractometer at 150 °C, using graphite monochromated
* Corresponding author. Tel.: +98 811 8257407.
E-mail address: Keypour@basu.ac.ir (H. Keypour).
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.03.025

2238
H. Keypour et al. / Journal of Organometallic Chemistry 693 (2008) 2237–2243
Mo Ka X-ray radiation (k = 0.71073 nm). X-ray data for
[CdL4(NO3)2] were also measured on a Bruker SMART-1000 diffrac-
tometer. Other crystallographic data are summarized in Table 1.
core potential (ECP) standard basis set LanL2DZ [23], was utilized
for cadmium. The full-electron standard basis sets 3-21G* and
6-31G* [24] were used for all other atoms. A starting semi-empir-
ical structure for the ab initio calculations was obtained using the
HYPERCHEM 5.02 program [25].
2.4. Ab initio molecular-orbital calculations
A full minimization of the structure of each macrocyclic com-
plex was performed at the ab initio HF level of theory using gradi-
ent techniques with the GAUSSIAN-98 set of programs [22], on a
Pentium-PC computer with a 3000 MHz processor. The effective
2.5. Synthesis
2.5.1. Preparation of complexes
2.5.1.1. [CdL1(NO3)2] (1). All syntheses of polyamine complexes
were performed under similar conditions. To a solution of (L1, L2
or L3), cadmium nitrate (0.5 mmol) was added. The reaction was
carried out for 1 h at room temperature a white precipitate formed.
This was filtered off and dried under vacuo. Yields 82–85%.
Yield (83%). Anal. Calc. for C11H18CdN6O8: C, 27.83; H, 3.82;
N, 17.20. Found: C, 28.01; H, 4.11; N, 17.43%. IR (KBr) 3273,
Table 1
Crystal data and structure refinement for [CdL4 (NO3)2] and [CdL1(NO3)2]
Compound
[CdL4(NO3)2]
[CdL1(NO3)2]
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
b (Å)
c (Å)
a (°)
b (°)
C
23H24CdN8O8
C11 H18Cd1N6O8
474.72
120(2)
3336, 3064, 1604, 1530, 1341 cmÀ1 1H NMR dH (DMSO-d6, ppm)
;
2.35 (bt, 4H), 2.67 (bt, 4H), 4.22 (s, 2H), 3.23 (NH2, 4H) 7.56–7.93
(Ar, 4H); 13C NMR dC (DMSO-d6, ppm) 36.91, 49.06, 51.13,
124.76, 127.14, 129.97, 132.97, 134.64, 151.91.
652.9
150(2)
0.71073
Monoclinic
P2(1)/c
0.71073
Triclinic
ꢀ
P1
2.5.1.2. [CdL2(NO3)2] (2). Yield (80%). Anal. Calc. for C12H20CdN6O8:
16.0337(7)
12.1555(5)
13.4025(6)
90
104.160(2)
90
7.8761(6)
8.0679(7)
14.5785(12)
91.649(7)
94.098(7)
115.628(6)
831.26(12)
2
C, 29.49; H, 4.12; N, 17.20. Found: C, 29.21; H, 4.14; N, 17.42%. IR
(KBr) 3288, 3349, 3070, 1603, 1530, 1342 cmÀ1 1H NMR dH
;
(DMSO-d6, ppm) 1.71 (bp, 2H), 2.24 (bt, 2H), 2.49(bt, 2H),
2.71(bt, 2H), 2.86 (bt, 4H), 4.26 (s, 2H), 3.4 (NH2, 4H), 7.49–7.91
(Ar, 4H); 13C NMR dC (DMSO-d6, ppm) 25.61, 36.72, 43.1, 48.41,
51.66, 54.18, 124.63, 125.7, 130.1, 132.74, 134.64, 152.41.
c (°)
Volume (Å3)
Z
2532.75(19)
4
Calculated density
1.712
1.897
(Mg/mÀ3
)
2.5.1.3. [CdL3(NO3)2] (3). Yield (77%). Anal. Calc. for C13H22CdN6O8:
Absorption coefficient
(mmÀ1
F(000)
0.928
1.37
)
C, 31.06; H, 4.41; N, 16.72. Found: C, 31.23; H, 4.32; N, 17.02%. IR
1320
476
(KBr) 3264, 3330, 3064, 1604, 1517, 1350 cmÀ1 1H NMR dH
;
Crystal size (mm)
h Range for data
collection (°)
0.28 Â 0.16 Â 0.14
0.35 Â 0.33 Â 0.20
(DMSO-d6, ppm) 1.59 (bp, 4H), 2.34 (bt, 4H), 3.34 (bt, 4H), 3.76
(s, 2H), 7.65–7.86 (Ar, 4H); 13C NMR dC (DMSO-d6, ppm) 28,
49.05, 51.34, 55.28, 124.52, 128.8, 131.7, 133.18, 134.35, 150.07.
1.31–27.54
2.81–29.21
Limiting indices
À20 6 h 6 20,
À10 6 h 6 10,
À11 6 k 6 10,
À18 6 l 6 19
À15 6 k 6 15,
À17 6 l 6 17
2.5.1.4. General synthesis (Schiff base macroacyclic complexes). All
syntheses of the Schiff base macroacyclic complexes were per-
formed under similar conditions. A solution of NaOH (1.5 mmol)
in methanol (10 cm3) was added to a suspension of the appropriate
triaminetrishydrochloride (I, II or III) (0.5 mmol) in methanol
(10 cm3). The mixture was stirred at room temperature for a few
minutes then filtered, and the precipitate was washed well with
methanol (10 cm3). The washings and the filtrate were combined
and to this solution (L1, L2 or L3) and 2-pyridinecarboxaldehyde
(1 mmol) in methanol (50 mL), nitrate cadmium (0.5 mmol) was
added. The reaction was carried out for 6 h at room temperature.
The solution volume was then reduced to 10 mL by roto-evapora-
tion and a yellow precipitate formed on addition of a small amount
of diethyl ether. This was filtered off, washed with ether, and dried
under vacuo. Yields 69–72%.
Reflections collected/
unique [R(int)]
50012/5835 [0.0351]
9562/4377 [0.0218]
Completeness to
h = 25.00° (%)
100.0
97.1
Absorption correction
Semi-empirical from
equivalents
Numerical
0.750 and 0.625
Maximum and minimum 0.8811 and 0.7811
transmission
Refinement method
Full-matrix least-squares
Full-matrix least-squares
on F2
on F2
Data/restraints/
5835/0/361
4377/0/251
parameters
Goodness-of-fit on F2
Final R indices [I > 2r(I)]
R indices (all data)
Largest difference peak
1.044
1.08
R1 = 0.0195, wR2 = 0.0470 R1 = 0.0172, wR2 = 0.0428
R1 = 0.0229, wR2 = 0.0504 R1 = 0.0180, wR2 = 0.0431
0.359 and À0.344
0.415 and À0.520
and hole (e AÀ3
)
O2N
O
H2N
N
(CH2)m
NH2
(CH2)n
N
N
(CH2)n
N
Cd2+
Cd2+
N
+
2
(CH2)m
NO2
N
N
n=2 m=2 L4
n=2 m=3 L5
n=3 m=3 L6
n=2 m=2 L1
n=2 m=3 L2
n=3 m=3 L3
Scheme 1.

H. Keypour et al. / Journal of Organometallic Chemistry 693 (2008) 2237–2243
2239
2.5.1.5. [CdL4(NO3)2] (4). Yield (72%). Anal. Calc. for C23H24CdN8O8:
phy. The infrared spectra of the complexes confirm the formation
of the macroacyclic compounds by the absence of bands character-
istic of carbonyl and primary amine groups of the starting
materials and exhibit a Schiff base m(C@N) vibration in the range
of 1652–1659 cmÀ1. The complexes exhibit bands at approxi-
mately 1522–1530 and 1349–1353 cmÀ1 associated with a nitro
group. In complexes of [CdLn(NO3)2] (n = 4,5,6) bands about
1595 cmÀ1 have been seen that attributed to pyridine group. The
NMR studies of the cadmium complexes also provides strong evi-
dence for the formation of the macroacyclic complexes.
C, 42.31; H, 3.71; N, 17.16. Found: C, 42.62; H, 3.75; N, 17.05%. IR
(KBr) 3054, 1659, 1591, 1522, 1352 cmÀ1 1H NMR dH (DMSO-d6,
;
ppm) 2.83 (bt, 4H), 3.87 (bt, 4H), 4.27 (s, 2H), 7.58–8.46 (Ar,
12H), 8.89 (s 2H); 13C NMR dC (DMSO-d6, ppm) 51.39, 53.1, 54.6,
124.83, 129.38, 129.54, 133.02, 133.55, 141.29, 147.21, 150.25,
151.23, 163.19.
2.5.1.6. [CdL5(NO3)2] (5). Yield (70%). Anal. Calc. for C24H26CdN8O8:
C, 43.22; H, 3.93; N, 16.80. Found: C, 43.63; H, 4.12; N, 16.75%. IR
(KBr) 3068, 1652, 1592, 1522, 1353 cmÀ1 1H NMR dH (DMSO-d6,
;
ppm) 1.85 (bp, 2H), 2.41 (bt, 2H), 3.00 (bt, 2H), 3.52 (bt, 2H),
3.83 (bp, 2H), 3.90 (s, 2H), 7.54–8.08 (Ar, 12H), 8.68 (s, 1H), 8.70
(s, 1H); 13C NMR dC (DMSO-d6, ppm) 27, 51.82, 52.96, 54.98,
55,44, 56,94, 124.70, 129.48, 129.15, 132.58, 132.7,133.15,
141.55, 141.77, 149.4, 150.03,150.61, 162.16, 164.61.
Table 2
Selected bond lengths (Å) and angles (°) for [CdL1(NO3)2] (1) and [CdL4(NO3)2] (4)
4
1
Bond
Bond length (Å)
Bond
Bond length (Å)
2.5.1.7. [CdL6(NO3)2] (6). Yield (69%). Anal. Calc. for C25H28CdN8O8:
Cd(1)–N(1)
Cd(1)–N(2)
Cd(1)–N(4)
Cd(1)–N(5)
Cd(1)–O(1)
Cd(1)–O(2)
Cd(1)–O(4)
Cd(1)–O(6)
2.4194(14)
2.2896(13)
2.3417(14)
2.3831(12)
2.4175(12)
2.773
Cd(1)–N(1)
Cd(1)–N(2)
Cd(1)–N(4)
Cd(1)–O(3)
Cd(1)–O(7)
Cd(1)–O(6)
2.2085(12)
2.5609(11)
2.2239(12)
2.3401(10)
2.5598(11)
2.3725(10)
C, 44.10; H, 4.14; N, 16.46. Found: C, 44.21; H, 4.21; N, 16.53%. IR
(KBr) 3100, 2928, 2851, 1650, 1593, 1530, 1349 cmÀ1 1H NMR
;
dH (DMSO-d6, ppm) 1.7 (pb, 2H), 2.4 (tb, 4H), 3.3 (tb, 4H), 4.01
(s, 2H), 7.04–7.98 (Ar, 12H), 8.67 (s, 2H); 13C NMR dC (DMSO-d6,
ppm) 26.61, 51.33, 52.22, 53.11, 161.56, 132.7, 129.15, 129.48,
132.58, 133.15, 141.55, 141.77, 149.4, 150.6.
2.4923(12)
2.322(3)
Bond
Bond angle (°)
Bond
Bond angle (°)
3. Results and discussion
N(2)–Cd(1)–N(1)
N(5)–Cd(1)–N(1)
N(4)–Cd(1)–N(5)
N(2)–Cd(1)–N(4)
N(2)–Cd(1)–O(4)
N(4)–Cd(1)–O(4)
N(5)–Cd(1)–O(4)
N(1)–Cd(1)–O(4)
O(1)–Cd(1)–O(4)
N(5)–Cd(1)–O(1)
O(1)–Cd(1)–N(1)
N(2)–Cd(1)–O(1)
N(4)–Cd(1)–O(1)
70.97(5)
90.86(4)
71.14(5)
134.34(5)
80.94(4)
84.65(5)
117.44(4)
80.24(4)
153.29(4)
83.04(4)
118.54(4)
87.45(4)
86.51(4)
N(2)–Cd(1)–N(1)
O(6)–Cd(1)–N(2)
N(1)–Cd(1)–O(7)
N(2)–Cd(1)–N(4)
N(4)–Cd(1)–O(3)
O(3)–Cd(1)–O(7)
N(4)–Cd(1)–O(7)
N(2)–Cd(1)–O(3)
N(1)–Cd(1)–O(6)
O(6)–Cd(1)–O(7)
77.31(4)
163.16(3)
90.18(4)
77.50(4)
86.65(4)
123.02(4)
90.78(4)
91.01
3.1. Synthesis and characterization
The Schiff base condensation of L1, L2 or L3 and 2-pyridinecar-
boxaldehyde in methanol in the presence of cadmium nitrate and
in 1:2:1 molar ratio, gave good yields of the analytically pure prod-
ucts [CdLn(NO3)2] (n = 4,5,6) (Scheme 1). On the other hand, the
polyamine complexes (1–3) were readily prepared from direct
reaction of L1, L2 or L3 and cadmium nitrate, respectively. All com-
plexes were characterized by spectroscopic methods and in the
case of [CdL4(NO3)2] (4) and [CdL1(NO3)2] (1) by X-ray crystallogra-
99.79
52.07
Fig. 1. ORTEP drawing of the molecular structures of the complexes [CdL1(NO3)2] and [CdL4(NO3)2].

2240
H. Keypour et al. / Journal of Organometallic Chemistry 693 (2008) 2237–2243
3.2. X-ray crystal structure
bond length is too long to be considered as a bond (3.26 Å). In
complex 1, the three nitrogen donor of amine and three oxygen
donor of two different nitrate groups are coordinated to the me-
tal ion.
In solid complexes previously obtained with Cd(II) nitrate with
triamines: dien, 2,3-tri or 3,3-tri of CdL2-type stoichiometry, all six
nitrogen atoms take part in the coordination [27] while in this case
due to steric hindrance caused by the attachment of an extra 2-
nitrobenzyle pendant arm to a secondary amine, only CdL-type
stoichiometry are produced
In complex 1, the tertiary nitrogen atom is coordinated to the
metal ion. But in complex 4, because of displacement of metal
ion towards the nitrogen donors of imine and pyridine groups
due to back donation, only a weak coordinate bond is formed.
The geometry of complex 1 and 4 is best considered as distorted
triangular prism structures (Fig. 2). Charge balances for the com-
plexes are provided by two-coordinated nitrate ions producing
neutral compounds. There are no solvent molecules in these
structures.
The molecular structures of [CdL1(NO3)2] (1) and [CdL4(NO3)2]
(4) are shown in Fig. 1. Selected bond lengths and angles are gi-
ven in Table 2. In macroacyclic complex 1 the four nitrogen do-
nor atoms of the potentially N5 macroacyclic ligand and two
oxygen donor atoms of two monodentate nitrate groups are coor-
dinated to the metal ion. The bond length of Cd–N(3) is 2.84 Å. In
similar cases where there is no pendant arms, secondary amine
can be coordinated [26] while in the presence of 2-nitrobenzyl
pendant arm only a weak coordinative bond can be observed.
When 2-nitrobenzyl pendant arm is attached to a related macro-
cyclic complex then the tertiary nitrogen is strongly coordinated
to the central cadmium [21]. Two nitrate groups are coordinated
to the central cadmium in different manner. In one of Cd–nitrate
bonds, in addition to a strong Cd–O(1) bond the other Cd–O(2)
linkage is considered to be a relatively weak (2.77 Å). But in
the second nitrate group, only one of oxygen atoms, O(4), is
strongly coordinated whereas the other one, e.g. Cd–O(6), the
Fig. 2. The ab initio optimized structures of the [Cd(L5)(NO3)2] and [Cd(L6)(NO3)2].
Table 3
Selected calculated bond distances and angles for optimized structures [Cd(L4)(NO3)2] (4), [Cd(L5)(NO3)2] (5) and [Cd(L6)(NO3)2] (6)
[Cd(L4)(NO3)2] (1) XRD
(4) (HF/3-21G*)
(4) (HF/6-31G*)
(5) (HF/3-21G*)
(5) (HF/6-31G*)
(6) (HF/3-21G*)
(6) (HF/6-31G*)
Bond length (Å)
Cd(1)–N(2)
Cd(1)–N(4)
Cd(1)–N(5)
Cd(1)–O(1)
Cd(1)–O(2)
Cd(1)–N(1)
Cd(1)–O(4)
Cd(1)–O(6)
2.2896(13)
2.3417(14)
2.3831(12)
2.4175(12)
2.773
2.4194(14)
2.4923(12)
3.23
2.37
2.5
2.4
2.6
2.4
2.4
2.5
2.4
2.4
2.416
2.431
2.48
2.412
2.495
2.522
2.391
2.469
2.437
2.431
2.512
2.378
2.469
2.593
2.356
2.478
2.418
2.451
2.454
2.415
2.465
2.503
2.404
2.416
2.518
2.5
2.505
2.37
2.561
2.647
2.5
2.413
2.465
2.408
2.537
2.56
2.408
2.487
2.554
Bond angle (°)
N(2)–Cd(1)–N(1)
N(5)–Cd(1)–N(1)
N(4)–Cd(1)–N(5)
N(2)–Cd(1)–N(4)
O(1)–Cd(1)–N(1)
N(2)–Cd(1)–O(1)
N(4)–Cd(1)–O(1)
N(1)–Cd(1)–O(4)
O(1)–Cd(1)–O(4)
N(2)–Cd(1)–O(4)
N(4)–Cd(1)–O(4)
N(5)–Cd(1)–O(4)
70.97(5)
90.86(4)
71.14(5)
134.34(5)
118.54(4)
87.45(4)
86.51(4)
80.24(4)
153.29(4)
80.94(4)
84.65(5)
117.44(4)
67.12
103.67
68.64
135.12
116.02
76.72
97.92
74.78
149.01
82.14
81.34
123.65
67
112
65
131
123
79
83
82
150
98
76
67.46
108.36
68.73
132.21
122.26
78.04
90.21
79.47
142.03
84.17
77.34
126.41
66.51
104.71
67.8
68.17
115.31
69.19
126.25
120.58
75.77
93.47
75.66
142.51
81.21
76.78
129.06
65.53
98.43
67.14
114.22
110.61
74.25
113.76
74.69
145.47
77.84
78.89
126.39
137
117.65
76.64
99.28
76.93
146.06
82.96
77.64
124
115

H. Keypour et al. / Journal of Organometallic Chemistry 693 (2008) 2237–2243
2241
In complex 1, the angle between planes of the aromatic ring of
pendant arm and the plane containing N(4), N(2), N(1) and N(6) is
73.33° whereas in complex 4 the angle between plane of the aro-
matic ring of pendant arm and the plane containing N(1), N(2),
N(4) and N(5) is 17.88°.
the lettering scheme shown in Scheme 2. The 1H and 13C signals
were assigned using one- and two-dimensional 1H–1H COSY,
1H–13C HMQC and DEPT spectra.
The 1H NMR spectra of 4, 5 and 6 show three, six and four dis-
tinct signals, respectively, for aliphatic methylene groups. Hi reso-
nance (Scheme 2) for all complexes is appeared as a singlet. The
existence of three, six and four different aliphatic methylene group
in 4, 5 and 6, respectively, was also confirmed by 13C NMR spectra.
In complex [CdL5]2+ (5), there are two signals due to the 1H
imine resonance at ca. 8.68 and 8.70 ppm in 1H NMR spectrum
and two signals (162.16, 164.61 ppm) in 13C NMR spectrum, dem-
onstrating the non-equivalence of the two imine environments. In
the region corresponding to the signals of aromatic rings carbons
(124.70, 129.00, 129.48, 132.58, 132.71, 133.15, 141.77, 141.50,
149.40, 150.32 and 150.60 ppm) 11 peaks instead of 16 expected
peaks are observed, due to high similarity of head unit and low res-
olution of instrument. Unfortunately, since the protons do not
show scalar-coupling, we were not able to assign explicitly the sig-
nals to each of all aromatic systems present in the molecule.
The 1H NMR spectrum of the complex [CdL4]2+ shows only a sin-
gle 1H imine resonance at ca. 8.87 ppm with two satellites (due to
coordinated cadmium) and 13C NMR spectrum shows one imine
carbon Ch (163.19 ppm) that demonstrating the equivalence of
the two imine environments. In the region corresponding to the
signals of aromatic rings carbons (124.83, 129.38, 129.54, 133.02,
3.3. Ab initio modelling studies
We assumed that the same mode that found for [CdL4(NO3)2]
had occurred with other cadmium complexes due to the similarity
of their IR, NMR spectra and microanalyses, and undertook a full
geometry optimization at the HF/3-21G* and HF/6-31G* levels of
theory, using LanL2DZ basis set for cadmium. The resulting struc-
tural diagrams are shown in Fig. 2 and selected calculated bond
distances and angles relating to them are shown in Table 3 along
with the corresponding values obtained for [CdL4(NO3)2] by X-
ray diffraction for comparison. We note that the results of the 3-
21G* calculations for [CdL4(NO3)2] are closer to the experimental
data than those of 6-31G* calculations. There is good agreement
between the calculated and observed distances.
3.4. NMR studies
The 1H as well as 13C{1H} NMR data for [CdLn(NO3)2] (n = 1, 2, 3,
4, 5 and 6) dissolved in DMSO-d6 are shown in Table 4, which uses
Table 4
1H NMR and 13C NMR{1H} spectral assignments for 1–6 recorded in DMSO-d6
[CdL1(NO3)2]
[CdL4(NO3)2]
[CdL2(NO3)2]
[CdL5(NO3)2]
[CdL3(NO3)2]
[CdL6(NO3)2]
Ha
Hb
Hi
NH2
Hn
Hl, Cm,
Ck
Ca
2.67
2.35
4.22
3.23
7.92
7.56–
7.74
49.1
Ha
Hb
Hi
H Ar
Hc
2.87
3.87
4.27
7.58–8.46
8.87
Hq
Hp
Ha
Hr
Hb
Hi
1.71
2.71
2.86
2.24
2.46
4.26
Hq
Hp
Ha
Hr
Hb
Hi
1.79
2.41
3
3.5
3.83
3.9
Ha
Hb
Hc
Hi
NH2
Hn
2.53
Ha
Hb
Hc
Hi
H Ar
Hd
2.4
1.7
3.3
4
7.04–7.98
8.67
1.59
2.34
3.76
3.34
7.85
Ca
53.1
Cb
Ci
54.6
Hk
7.51
Hc
Hs
6.7
Hl, Cm
Hk
7.65–
7.67
7.45
Ca
Cb
51.33
26.61
Cb
36.9
51.39
Hl and
Hm
Hn
NH2
Cq
7.61 or
7.72
7.9
3.4
25.6
6.68
Ci
Cj
Ck
Cl, Cm
51.1
127
124.76
129.97
Ck
Cd
Co, Cj
Ce, Cf, Cg
124.83
151.23
ꢀ133.02
129.38,
129.54
133.55,
141.29
147.21,
150.25
H Ar
Cq
Cp
7.54–8.08
27
51.82
Ca
Cb
Cc
51.3
28.6
49.1
Cc
Ci
Cd
53.11
52.22
161.56
132.97
Ch, Cl
Cp
Ca
48.41
51.66
Ca
Cr
52.96
54.98
Ci
55.28
Ce, Cj, Co
132.7,
129.15
Cm, Cn
129.48,
132.58
133.15,
141.55
141.77,
149.4
Cn
Co
134.64
151.91
Cc
163.19
Cj
128.8
Ck, Cl, Cm,
Cf,
Cg, Ch, Cp
150.6
Cr
Cb
36.72
43.1
Cb
Ci
56.94
55.44
Ck
Cl and
Cm
124.52
131.7 or
133.18
134.34
150
Ci
Cj
Ck
54.18
125.7
125
Ck
Cd
Ct, Co, Cj
124.7
150.03
132.7,
Cn
Co
129.15
129.48,
132.58
133.15,
141.55
141.77,
149.4
130.11
or
Ck, Cl, Cm,
Ce
Cf, Cg, Ch,
Cu
Cl and
Cm
132.74
Cv, Cw, Cx
Cn
Co
134.64
152
Cn
Cs, Cc
150.61
162.16,
164.61

2242
H. Keypour et al. / Journal of Organometallic Chemistry 693 (2008) 2237–2243
n
n
O2N
o
j
O2N
o
j
m
m
H2N
N
N
l
M2+
N
l
Cd2+
N
i
k
i
k
N
a
N
h
a
H2N
c
d
e
b
b
g
f
[Cd L1]2+
[Cd L4]2+
n
O2N
n
v
r
o
j
O2N
u
r
o
H2N
w
m
q
p
s
m
t
q
p
x
N
N
Cd2+
l
N
l
j
M2+
k
N
i
i
k
a
H2N
N
a
N
h
b
c
d
e
b
g
[Cd L2]2+
[Cd L5]2+
f
n
O2N
o
n
O2N
m
o
m
N
N
H2N
i
l
j
M2+
N
i
l
j
N
k
Cd2+
a
k
a
N
N
p
b
b
c
d
e
f
c
H2N
h
g
[Cd L3]2+
[Cd L6]2+
Scheme 2.
133.55, 141.29, 147.21, 150.25 and 151.23 ppm) nine peaks in-
stead of 11 expected peaks are observed, due to high similarity
of head unit and low resolution of instrument.
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