Synthesis and structural characterization of nickel(II) complexes of 3,14-diethyl-2,6,13,17-tetraazatricyclo[14,4,01.18,07.12]docosane with inorganic salts

Article abstract of DOI:10.1016/j.poly.2015.07.022

Abstract The square-planar complex [Ni(L3)]Cl₂·2H₂O (1) (L1 = 3,14-diethyl-2,6,13,17-tetraazatricyclo[14,4,0^1.18,0^7.12]docosane) with inorganic salts KNO₃ and NaN₃ yields the octahedral nickel(II) complexes [Ni(L3)(NO₃)₂] (2) and [Ni(L3)(N₃)₂] (3). The structures were characterized by X-ray crystallography, spectroscopic, thermogravimetry and cyclic voltammetry. The crystal structures of compounds 2 and 3 show that each nickel(II) centre has an elongated distorted octahedral geometry with the axial ligands. Electronic spectra and redox potentials of the complexes 2 and 3 reveal a high-spin octahedral environment, which is reflected by the nature of the axial ligands. The TGA behaviors of two compounds 2 and 3 are also significantly affected by the nature of the axial ligands.

Full text of DOI:10.1016/j.poly.2015.07.022

Polyhedron 100 (2015) 43–48
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis and structural characterization of nickel(II) complexes of
3,14-diethyl-2,6,13,17-tetraazatricyclo[14,4,01.18,07.12]docosane with
inorganic salts
In-Taek Lim a, Chong-Hyeak Kim b, Ki-Young Choi a,
⇑
a Department of Chemistry Education, Kongju National University, Kongju 314-701, Republic of Korea
b Center for Chemical Analysis, Korea Research Institute of Chemical Technology, P.O. Box 107, Yuseong, Daejeon 305-600, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
The
square-planar
complex
[Ni(L3)]Cl2Á2H2O
(1)
(L1 = 3,14-diethyl-2,6,13,17-tetraazatricy-
clo[14,4,01.18,07.12]docosane) with inorganic salts KNO3 and NaN3 yields the octahedral nickel(II) com-
plexes [Ni(L3)(NO3)2] (2) and [Ni(L3)(N3)2] (3). The structures were characterized by X-ray
crystallography, spectroscopic, thermogravimetry and cyclic voltammetry. The crystal structures of com-
pounds 2 and 3 show that each nickel(II) centre has an elongated distorted octahedral geometry with the
axial ligands. Electronic spectra and redox potentials of the complexes 2 and 3 reveal a high-spin octahe-
dral environment, which is reflected by the nature of the axial ligands. The TGA behaviors of two com-
pounds 2 and 3 are also significantly affected by the nature of the axial ligands.
Received 12 June 2015
Accepted 8 July 2015
Available online 14 July 2015
Keywords:
Nickel(II) complexes
Diethyl tetraaza macrocycle
Potassium nitrate
Sodium azide
Ó 2015 Elsevier Ltd. All rights reserved.
Octahedral complexes
1. Introduction
[Ni(Me4cyclam)(NCO)](ClO4) (Me4cyclam = 1,4,8,11-tetramethyl-
1,4,8,11-tetraazacyclotetradecane) has a distorted square pyramidal
Polyaza macrocycles with C-alkyl substituents of the macro-
cyclic ring and their metal complexes have attracted considerable
attention because of their structural and chemical properties,
which are often quite different from those of the unalkylated poly-
aza macrocyclic ligands [1–16]. For example, the reaction of
NiCl2Á2H2O with cyclam (1,4,8,11-tetraazacyclotetradecane) leads
to the mononuclear compound [Ni(H2O)2(cyclam)]Cl2Á4H2O [12],
in which the nickel ion has a six-coordinated octahedral geometry
with a N4 basal plane and two aquo ligands in the axial position.
However, the reaction of NiCl2Á2H2O with L1 (3,14-dimethyl-
2,6,13,17-tetraazatricyclo[14,4,01.18,07.12]docosane) gives rise to
the mononuclear complex [Ni(L1)]Cl2Á2H2O [9], which reveals a
distorted square-planner environment This fact may be due to
the steric hindrance of the anti methyl groups on the macrocyclic
ring of L1 ligand. Vicente et al. [7] reported that the
[Ni(cyclam)(NCO)(H2O)](ClO4) (cyclam = 1,4,8,11-tetraazacyclote-
tradecane) reveals a distorted octahedral geometry. However,
geometry, which may be due to the steric hindrance of the
Me4cyclam ligand. Furthermore, [Ni(m-Me6cyclam) (OCN)1.5(ClO4)1.5
(m-Me6cyclam = meso-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacy-
clotetradecane) reveals the peculiarity of the cyanato coordination
mode instead of the habitual isocynate mode. In contrast, [Ni(DL-
]
Me6cyclam)2(l-OCN)2](ClO4)2
(DL-Me6cyclam = DL-5,5,7,12,12,
14-hexamethyl-1,4,8,11-tetraazacyclotetradecane) complex shows
that the cyanate ligand acts as an end-to-end bridge with
the nickel(II) ions in an NiN5O octahedral environment [7].
The same synthetic strategy with azido ligand leads to trans-
monobridged 1D systems with cyclam [17] and m-Me6cyclam
[18].
To further investigate the effect of the C-alkyl substituents of
the macrocyclic ring, we report the structures, spectroscopic, ther-
mogravimetric and cyclic voltammetric properties of the octahe-
dral nickel(II) complexes [Ni(L3)]Cl2Á2H2O (1), [Ni(L3)(NO3)2] (2)
and [Ni(L3)(N3)2] (3).
⇑
Corresponding author. Tel.: +82 41 850 8284; fax: +82 41 850 8347.
E-mail address: kychoi@kongju.ac.kr (K.-Y. Choi).
http://dx.doi.org/10.1016/j.poly.2015.07.022
0277-5387/Ó 2015 Elsevier Ltd. All rights reserved.

44
I.-T. Lim et al. / Polyhedron 100 (2015) 43–48
2.4. Synthesis of [Ni(L3)]Cl2Á2H2O (1)
2. Experimental
A methanolic solution (10 ml) of L3 (182 mg, 0.5 mmol) was
added dropwise to a stirred solution of NiCl2Á6H2O (169 mg,
0.5 mmol) in water (10 ml). The mixture was allowed to reflux
for 1 h. The volume of the solution was reduced to 10 ml and yel-
low crystals formed when the solution was allowed to stand at
room temperature for a period of several days. The product was
recrystallized from a hot water/acetonitrile (1:1 v/v, 20 ml) mix-
ture, but unfortunately crystals suitable for X-ray analysis were
not obtained. Yield: 73%. Anal. Found: C, 49.92; H, 9.07; N, 10.64.
Calc. for C22H48N4NiCl2O2: C, 49.83; H, 9.13; N, 10.57%. IR (KBr,
cmÀ1): 3375(m), 3216(s), 2946(m), 1466(m), 1437(m), 1377(w),
1202(w), 1114(m), 1084(m), 1034(m), 970(w), 916(w), 873(w),
712(w), 629(w).
2.1. Materials and physical methods
All chemicals used in syntheses were of reagent grade and were
used without further purification. IR spectra were recorded as KBr
pellets on a Perkin–Elmer Paragon 1000 FT-IR spectrometer. The
solution electronic and diffuse reflectance spectra were obtained
on a Jasco V-550 spectrophotometer. Electrochemical measure-
ments were accomplished with a three electrode potentiostat
BAS-100BW system. A 3-mm Pt disk was used as the working elec-
trode. The counter electrode was a coiled Pt wire and a Ag/AgCl
electrode was used as a reference electrode. Cyclic voltammetric
data were obtained in DMSO solution using 0.1 M tetraethylammo-
nium perchlorate (TEAP) as supporting electrolyte at 20.0 0.1 °C.
The solution was degassed with high purity N2 prior to carrying out
the electrochemical measurements. DSC and TGA were performed
under flowing nitrogen at a heating rate of 10 °C minÀ1 using an
SDT 2960 Thermogravimetric Analyzer. 13C NMR spectra were
recorded at room temperature on a Bruker AVANCE II 500 spec-
trometer. Elemental analyses (C, H, N) were performed on a
Perkin–Elmer CHN-2400 analyzer.
2.5. Synthesis of [Ni(L3)(NO3)2] (2)
An aqueous solution (10 ml) of [Ni(L2)]Cl2Á2H2O (265 mg,
0.5 mmol) was added to an aqueous solution (10 ml) of potassium
nitrate (51 mg, 0.5 mmol) and the mixture was stirred for 30 min
at room temperature. The solution was filtered and left at room
temperature until the violet crystals formed. The product was
recrystallized from a hot water/acetonitrile (1:1 v/v, 10 ml) mix-
ture. Yield: 65%. Anal. Found: C, 48.35; H, 8.16; N, 15.27. Calc. for
2.2. Synthesis of L2Á2HClO4
C
22H44N6NiO6: C, 48.27; H, 8.10; N, 15.36%. IR (KBr, cmÀ1):
3202(s), 2938(m), 1481(m), 1423(s), 1385(s), 1315(m), 1303(m),
1276(m), 1216(w), 1102(m), 1039(m), 985(m), 963(m), 893(w),
810(w), 707(w), 631(w).
Perchloric acid (60%, 7.14 ml) was added dropwise to an ice-
cooled ethanol (80 ml) solution of 1,2-diaminocyclohexane
(10.0 ml). Ethyl vinyl ketone (8.2 ml) was added 0.13 ml per half
an hour to an ethanolic solution in an ice bath. The mixture was
stirred for 3 days in ice bath, and the color of the solution was
changed from clear yellow to deep brown. The resultant solution
was stirred at room temperature for 7 days. The final product
was filtered off, washed with ethanol, and dried in a vacuum.
Yield: 2.2 g (7.4%). Anal. Found: C, 47.14; H, 7.61; N, 9.91. Calc.
for C22H42Cl2N4O8: C, 47.06; H, 7.54; N, 9.98%.
2.6. Syntheses of [Ni(L3)(N3)2] (3)
This compound was prepared as violet crystals in a reaction
similar to that of 1, using sodium azide (33 mg, 0.5 mmol) instead
of potassium nitrate. Yield: 65%. Anal. Found: C, 52.15; H, 8.66; N,
27.72. Calc. for C22H44N10Ni: C, 52.08; H, 8.74; N, 27.61%. IR (KBr,
cmÀ1): 3241(s), 2937(m), 2020(s), 1483(w), 1449(m), 1379(w),
1328(w), 1301(w), 1213(w), 1151(w), 1099(m), 1007(w), 945(m),
907(w), 891(w), 821(w), 628(w).
2.3. Synthesis of L3
NaOH (0.32 g) and NaBH4 (0.36 g) were added over 2 h to a
methanolic solution (20 ml) of L2Á2HClO4 (2.0 g) in an ice bath.
The mixture was stirred at room temperature for 2 h and refluxed
for 30 min. The filtrate was treated with NaOH (0.96 g) in water
and stirred for 10 min. The white solid was filtered off, washed
with water, and dried in a vacuum. Yield: 90%. Anal. Found: C,
72.54; H, 12.25; N, 15.25. Calc. for C22H44N4: C, 72.47; H, 12.16;
N, 15.37%. 13C NMR (CDCl3): d 56.7, 53.0 (cyclohexane ring carbon),
63.3, 43.7, 42.5 (N–C–C–C–N), 30.5, 30.3, 25.3, 24.6 (cyclohexane
ring carbon), 22.2, 10.6 (–C2H5).
2.7. X-ray crystal structure analysis
Intensity data collected on a Bruker Apex II CCD diffractometer
using graphite-monochromated Mo K
Accurate cell parameters and an orientation matrix were deter-
mined by the least-squares fit of 9905 (compound 2) and 9962
(compound 3) reflections. The intensity data were collected by
a radiation (k = 0.71073 Å).
the
p–x scan and corrected for Lorentz and polarization effects.
An empirical absorption correction was applied with the SADABS
program [19]. The structure was solved by direct methods [20]

I.-T. Lim et al. / Polyhedron 100 (2015) 43–48
45
Table 1
Crystallographic data.
Table 2
Selected bond lengths (Å) and angles (°) for [Ni(L3)(NO3)2] (2).
2
3
Bond lengths (Å)
Ni–N(1)
Ni–N(3)
2.092(4)
2.084(4)
2.162(4)
1.289(6)
1.241(4)
8.032(1)
Ni–N(2)
Ni–N(4)
Ni–O(4)
N(5)–O(2)
N(6)–O(4)
N(6)–O(6)
2.064(4)
2.049(4)
2.183(4)
1.229(7)
1.249(4)
11.327(1)
Empirical formula
Formula weight
Temperature (K)
Crystal color/habit
Crystal system
Space group
C
22H44N6NiO6
C22H44N10Ni
507.38
296(2)
Violet/block
Monoclinic
P21/n
547.34
100(2)
Violet/block
Triclinic
P1
Ni–O(1)
N(5)–O(1)
N(5)–O(3)
N(6)–O(5)
Bond angles (°)
N(1)–Ni–N(2)
N(1)–Ni–N(4)
N(2)–Ni–N(4)
N(1)–Ni–O(1)
N(3)–Ni–O(1)
N(1)–Ni–O(4)
N(3)–Ni–O(4)
Ni–O(1)–N(5)
Unit cell dimensions
84.75(17)
95.24(17)
179.8(2)
96.49(18)
84.16(17)
83.75(17)
95.58(18)
135.0(3)
N(1)–Ni–N(3)
N(2)–Ni–N(3)
N(3)–Ni–N(4)
N(2)–Ni–O(1)
N(4)–Ni–O(1)
N(2)–Ni–O(4)
N(4)–Ni–O(4)
Ni–O(4)–N(6)
178.4(2)
a (Å)
b (Å)
c (Å)
7.9359(2)
9.1473(2)
9.6672(2)
73.4690(10)
73.6750(10)
71.1100(10)
622.56(3)
1
9.3388(5)
13.6788(7)
9.6934(5)
96.67(16)
83.34(19)
95.13(15)
84.70(16)
85.75(15)
94.41(16)
135.7(3)
a
(°)
b (°)
96.554(2)
c
(°)
V (Å3)
1230.18(11)
2
1.370
0.820
548
Z
Dcalc (Mg mÀ3
)
1.460
0.829
294
Absorption coefficient (mmÀ1
F(000)
)
Crystal size (mm)
h range (°)
Limiting indices
0.22 Â 0.20 Â 0.12
2.25 to 28.62
À9 6 h 6 10,
À11 6 k 6 12,
0 6 l 6 12
3152/3152(0.0000)
0.28 Â 0.22 Â 0.18
2.59 to 28.37
À12 6 h 6 12,
À17 6 k 6 18,
À12 6 l 6 12
32,545/
and the least-squares refinement of the structure was performed
by the SHELXL-97 program [21]. All atoms except for all hydrogen
atoms were refined anisotropically. Hydrogen atoms were placed
in calculated positions, allowing them to ride on their parent C
or N atoms with Uiso(H) = 1.2Ueq(C or N). Crystal parameters and
details of the data collections and refinement are summarized in
Table 1.
Reflection collected/unique
(Rint
)
3076(0.0226)
SADABS
Absorption correction
Maximum and minimum
transmission
SADABS
0.9070 and 0.8386
0.8664 and 0.8028
Data/restraints/parameters
3152/3/296
1.095
3076/0/159
1.038
Goodness-of-fit (GOF) on F2
Final R indices (I > 2
r(I))
R1a = 0.0234,
wR2b = 0.0682
R1 = 0.0236,
wR2 = 0.0684
0.574 and À0.514
R1 = 0.0208,
wR2 = 0.0567
R1 = 0.0219,
wR2 = 0.0575
0.382 and À0.213
3. Results and discussion
R indices (all data)
3.1. Crystal structures
Largest difference peak and
hole (e ÅÀ3
3.1.1. Description of the structure
)
The macrocyclic ligand skeleton of the present compounds
adopts the most stable trans-III (R,R,S,S) configuration with two
chair six-membered and two gauche five-membered chelate rings.
The N–Zn–N angles of the six-membered chelate rings for the
a
R1 = ||Fo| À |Fc||/
R|Fo|.
b
wR2 = [
R
[w(F2o À F2c)2]/
R .
[w(F2o)2]]1/2
Fig. 1. An ORTEP diagram of [Ni(L3)(NO3)2] (2) with the atom-numbering scheme (30% probability ellipsoids shown). The hydrogen atoms and water molecules are omitted
for clarity.

46
I.-T. Lim et al. / Polyhedron 100 (2015) 43–48
Table 3
complexes are larger than those of the five-membered chelate
rings. The ethyl group on a six-membered chelate ring is anti with
respect to the N4 plane.
Hydrogen bonding parameters (Å, °) for [Ni(L3)(NO3)2] (2).
D–HÁ Á ÁA
D–H (Å)
HÁ Á ÁA (Å)
DÁ Á ÁA (Å)
D–HÁ Á ÁA (°)
150.5
150.2
149.3
An ORTEP drawing of [Ni(L3)(NO3)2] (2) with the atomic num-
bering scheme is shown in Fig. 1 and the selected bond lengths
and angles are listed in Table 2. The nickel(II) ion is coordinated
by four nitrogen atoms of the macrocyclic ligand and two oxygen
atoms of the nitrate ligand in a six-coordinated octahedral geome-
try. The average Ni–N distance of 2.072(4) Å is significantly longer
than in the square-planar geometry of [Ni(L1)]Cl2Á2H2O
[1.948(4) Å] [9], but is similar to that observed for high-spin octa-
hedral nickel(II) complexes with 14-membered tetraaza macro-
cyclic ligands [10–16]. The average Ni–O distance of 2.173(4) Å is
longer than the equatorial Ni–N distances, giving an axially elon-
gated octahedral environment and comparable to the previously
reported values in the related systems {[Ni(L1)(tp)]Á2H2O [22]:
Ni–O = 2.116(3) Å; [Ni(L1)(pdc)]ÁH2O [22]: Ni–O = 2.121(9) and
2.137(10) Å; [Ni(cyclam)(tp)]Á4H2O [18]: Ni–O = 2.129(5) Å}. Also,
The axial Ni–O(1) and Ni–O(4) linkages are bent slightly off the
perpendicular to the NiN4 plane by 5.30–6.49° and 4.41–6.25°,
respectively. The Ni–O(1)–N(5) and Ni–O(4)–N(6) angles related
to the nitrate ligand are 135.0(3)° and 135.7(3)°. The secondary
amines of the macrocycle are hydrogen bonded to the oxygen
atoms of the nitrate ligands [N(1)Á Á ÁO(2)#1 3.036(6) Å, 150.5°;
N(2)Á Á ÁO(3) 2.946(6) Å, 150.2°; N(3)Á Á ÁO(6)#2 3.066(6) Å, 149.3°;
symmetry codes: (#1) x + 1, y, z; (#2) x À 1, y, z]. Interestingly,
the uncoordinated oxygen atom, O(3), of the nitrate ligand forms
the intramolecular hydrogen bond with the secondary amine
N(2) of the macrocycle [N(2)Á Á ÁO(3) 2.946(6) Å, 150.2°].
Furthermore, uncoordinated oxygen atoms, O(2) and O(6), of the
nitrate ligand form the intermolecular hydrogen bonds to an adja-
cent secondary of the macrocycle [N(1)Á Á ÁO(2)#1 3.036(6) Å,
150.5°; N(3)Á Á ÁO(6)#2 3.066(6) Å, 149.3°; symmetry codes: (#1)
N(1)–H(1NA)Á Á ÁO(2)#1
N(2)–H(2NA)Á Á ÁO(3)
N(3)–H(3NA)Á Á ÁO(6)#2
0.93
0.93
0.93
2.19
2.10
2.23
3.036(6)
2.946(6)
3.066(6)
Symmetry codes: (#1) x + 1, y, z; (#2) x À 1, y, z.
Fig. 3. An ORTEP diagram of [Ni(L3)(N3)2] (3) with the atom-numbering scheme
(30% probability ellipsoids shown). The hydrogen atoms and water molecules are
omitted for clarity.
x + 1, y, z; (#2) x À 1, y, z]. This interaction gives rise to a one-di-
mensional hydrogen-bonded polymer (Fig. 2 and Table 3).
An ORTEP drawing of [Ni(L3)(N3)2] (3) with the atomic number-
ing scheme is shown in Fig. 3 and the selected bond lengths and
angles are listed in Table 3. An inversion center exists on the cen-
tral nickel(II) ion. The crystal structure of 3 conforms a six-coordi-
nated octahedral geometry with bonds from the nickel(II) ion to
the secondary amines of the macrocycle and to the two axial azide
ligands. The average bond distance of 2.088(1) Å, between
nickel(II) atom and secondary amines, which is closed to that
found for [Ni(L1)(N3)2] (2.085(2) Å) [11] and shorter than the axial
Ni–N(3) distance of 2.176(1) Å indicates an axially elongated octa-
hedral geometry. The axial Ni–N(3) bond distance and Ni–N(3)–
N(4) angle [116.8(1)°] are similar to the observed for
[Ni(L1)(N3)2] [11] and catena-(
l
-N3)[Ni(cyclam)](ClO4)ÁH2O [17].
The axial Ni–N(3) linkages are bent slightly off the perpendicular
to the NiN4 plane by 1.27–6.07°. Both azide ligands which act mon-
odentate ligands are slightly asymmetric [N(3)–N(4) = 1.191(1)
and N(4)–N(5) = 1.171(1) Å] are linear within the experimental
error [N(3)–N(4)–N(5) angle = 178.7(1)°] (see Table 4).
3.2. Characterization of the complexes
The IR spectra of these complexes show bands at 3202–
3241 cmÀ1, indicating the
m(NH) of the coordinated secondary
amines. An absorption band at 1385 cmÀ1 in 2 is assigned to the
Table 4
Selected bond lengths (Å) and angles (°) for [Ni(L3)(N3)2] (3).
Bond lengths (Å)
Ni–N(1)
Ni–N(3)
N(4)–N(5)
2.105(1)
2.176(1)
1.171(1)
Ni–N(2)
N(3)–N(4)
2.070(1)
1.191(1)
Bond angles (°)
N(1)–Ni–N(2)
N(1)–Ni–N(3)
N(2)–Ni–N(3)
Ni–N(3)–N(4)
83.51(3)
96.07(3)
91.27(3)
116.8(1)
N(1)–Ni–N(2)#3
N(1)#3–Ni–N(3)
N(2)#3–Ni–N(3)
N(3)–N(4)–N(5)
96.49(3)
83.93(3)
88.73(3)
178.7(1)
Fig. 2. Crystal packing of [Ni(L3)(NO3)2] (2), showing the hydrogen bonds as dotted
Symmetry codes: (#3) Àx + 2, Ày + 2, Àz + 1.
lines.

I.-T. Lim et al. / Polyhedron 100 (2015) 43–48
47
Table 5
Electronic spectral data.a
Complex
State
kmax/nm (e )
/MÀ1 cmÀ1
[Ni(L3)]Cl2Á2H2O (1)
Solid
CH3CN
H2O
252, 460
465(65)
461(68)
[Ni(L3)(NO3)2] (2)
Solid
CH3CN
H2O
246, 340, 522, 682(268, 523)
260(7.6 Â 102) 524(8.5)
257(6.4 Â 103), 462(72)
[Ni(L3)(N3)2] (3)
Solid
CH3CN
H2O
266, 330, 532, 724(270, 532)
262(2.4 Â 103), 533(9.4)
258(5.8 Â 103), 463(76)
a
Solution = CH3CN and H2O at 20 0.1 °C; solid = diffuse reflectance.
Fig. 4. Solid state electronic absorption spectra of [Ni(L3)]Cl2Á2H2O (1),
[Ni(L3)(NO3)2] (2) and [Ni(L3)(N3)2] (3) by the diffuse reflectance method at
20.0 0.1 °C.
Fig. 5. Thermogravimetric curves of [Ni(L3)]Cl2Á2H2O (1), [Ni(L3)(NO3)2] (2) and
[Ni(L3)(N3)2] (3).
NOÀ3 ion stretching band, which indicates the coordination of the
oxygen atom between NOÀ3 and Ni(II) atom. A single very strong
band at 2020 cmÀ1 of 3 is associated with the azide stretching
mode, which is agree with the crystal structure of 3. The UV–Vis
spectral data and solid state spectra of the complexes are shown
in Table 5 and Fig. 4. The UV spectra of the complexes reveal an
absorption maximum in the region 252 (1), 246 (2), and 266 (3)
nm attributed to a ligand–metal charge transfer associated with
the nitrogen and oxygen donors [23,24] As shown in Fig. 4, the vis-
ible spectrum of 1 in the solid state shows maximum absorption at
460 nm. The wavelength of the d–d band for 1 is similar to that of
[Ni(L1)](ClO4)2 (463 nm) [25], indication that complex 1 has a low-
spin four coordinated square-planar geometry. In addition, the
solid state electronic spectra of 2 and 3 in the visible region exhibit
three absorption bands at 340–330, 522–532, and 682–724 nm
due to the loss of the macrocycle and two nitrate anions (observed
86.9%, calculated 86.4%). A final residue (observed 13.1%, calcu-
lated 13.6%) was remained above 341 °C with NiO composition.
For 3, weight loss of 85.1% (calculated 85.3%) over ca. 30–418 °C
is observed, corresponding to the losses of the macrocycle and
two azide anions. Final residue (observed 14.9%, calculated
14.7%) was remained above 418 °C with NiO composition.
Cyclic voltammetric data and cyclic voltammograms for com-
pounds 1–3 in 0.10 M TEAP–DMSO solution are given in Table 6
and Fig. 6. The complex 1 exhibits two one-electron waves corre-
sponding to NiII/NiIII and NiII/NiI processes. However, the com-
plexes 2 and 3 reveal one one-electron wave corresponding to
NiII/NiI process. It is of interest to compare the redox potentials
for the nickel(II) complexes with the axial ligands. The reduction
potentials for 2 and 3 are distinctly more positive than those of
complex 1. This may result from the structural geometry (octahe-
dral and square-plane). This is consistent with the crystal struc-
tures and spectroscopic data discussed previously. Although
complexes 2 and 3 have the same geometry, reduction potential
for 3 is considerable more positive than that of 2 indicating that
assignable to the 3B1g ? 3Egc 3B1g ? 3Ebg, 3B1g ? 3B2g + 3B1g ? 3A2ag
,
transitions, which are the characteristic spectrum expected for a
high-spin d8 nickel(II) ion in D4h environment [12,26]. However,
the visible spectra of 2 and 3 in water solution displays the broad
bands 462–463 nm, which have a low-spin d8 nickel(II) ion in a
square-planar environment of [Ni(L3)]Cl2Á2H2O (kmax = 461 nm) (1).
This fact can be understood in terms of dissociation of the azido or
nitrato ligands at water solution.
Table 6
The compounds 1–3 were heated in the temperature range 30–
1000 °C on nitrogen gas. The TGA diagrams of compounds are
shown in Fig. 5. TGA curve for 1 shows a first weight loss of 6.5%
(calculated 6.8%) over ca. 30–186 °C, corresponding two water
molecules. A second weight losses corresponding to the macrocycle
and two chloride anion (observed 91.6%, calculated 93.2%) are
found in the temperature range 186–413 °C. A final weigh loss
was observed above 413 °C corresponding to the NiO residue. For
2, the first weight loss is observed from 30 to 341 °C, which is
Cyclic voltammetric data.a
Complex
Potentials (V) versus Ag/AgCl
Ni(III)/Ni(II)
Ni(II)/Ni(I)
[Ni(L3)]Cl2Á2H2O (1)
[Ni(L3)(NO3)2] (2)
[Ni(L3)(N3)2] (3)
+0.68
À1.54(i)b
À1.50
À1.37
a
Measured in 0.10 M TEAP–DMSO solution at 20.0 0.1 °C.
i = irreversible.
b

48
I.-T. Lim et al. / Polyhedron 100 (2015) 43–48
via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge, CB2 1EZ, UK; fax: +44 1223 336 033; or e-mail:
deposit@ccdc.cam.ac.uk.
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100 mV/s.
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Appendix A. Supplementary data
CCDC 1405662-1405667 contains the supplementary crystallo-
graphic data for 2 and 3. These data can be obtained free of charge