Synthesis, crystal structures, and deprotonation of cis- and trans-octahedral nickel(II) complexes with a 14-membered tetraaza macrocycle bearing two N-phenacyl pendant arms

Article abstract of DOI:10.1016/j.ica.2012.02.026

The di-N-functionalized macrocycle 2,13-bis(2-phenacyl)-5,16-dimethyl-2,6, 13,17-tetraazatricyclo[16.4.0.^1.180^7.12]docosane (H ₂L²) bearing two N-CH₂COC₆H ₅ groups has been prepared by the reaction of 3,14-dimethyl-2,6,13, 17-tetraazatricyclo[16.4.0.0^7.12]docosane (L¹) with phenacyl bromide. Interestingly, H₂L² reacts with Ni ²⁺ ion to form two geometric isomers, trans-[Ni(H₂L ²)]²⁺ and cis-[Ni(H₂L²)] ²⁺. The axial Ni-O (N-CH₂COC₆H₅ group) bond distance (2.080(2) ) of trans-[Ni(H₂L²)] (ClO₄)₂·2DMSO is shorter than the in-plane Ni-N distances (2.096(2) and 2.100(2) ). However, the Ni-O distances (2.105(2) and 2.124(2) ) of cis-[Ni(H₂L²)](ClO₄) ₂·H₂O are considerably longer than the Ni-N distances (2.053(2)-2.086(2) ). Each N-CH₂COC₆H ₅ group of trans-[Ni(H₂L²)]²⁺ and cis-[Ni(H₂L²)]²⁺ exists as its keto form in the solid state and in various solvents. Two N-CH₂COC₆H ₅ groups of trans-[Ni(H₂L²)]²⁺ are readily deprotonated in basic aqueous solutions, producing the enolate form trans-[Ni(L²)]. On the other hand, cis-[Ni(H₂L ²)]²⁺ undergoes deprotonation to yield cis-[Ni(HL ²)]⁺, in which one N-CH₂COC₆H ₅ group is not deprotonated, under similar conditions.

Full text of DOI:10.1016/j.ica.2012.02.026

Inorganica Chimica Acta 387 (2012) 346–351
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Synthesis, crystal structures, and deprotonation of cis- and trans-octahedral
nickel(II) complexes with a 14-membered tetraaza macrocycle bearing two
N-phenacyl pendant arms
b
Hyunja Kim a, Shin-Geol Kang a, , Chee-Hun Kwak
⇑
a Department of Chemistry, Daegu University, Gyeongsan 712-714, Republic of Korea
b Department of Chemistry, Sunchon National University, Sunchon 540-742, 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 di-N-functionalized macrocycle 2,13-bis(2-phenacyl)-5,16-dimethyl-2,6,13,17-tetraazatricyclo
[16.4.0.1.1807.12]docosane (H2L2) bearing two N-CH2COC6H5 groups has been prepared by the reaction of
3,14-dimethyl-2,6,13,17-tetraazatricyclo[16.4.0.07.12]docosane (L1) with phenacyl bromide. Interestingly,
H2L2 reacts with Ni2+ ion to form two geometric isomers, trans-[Ni(H2L2)]2+ and cis-[Ni(H2L2)]2+. The axial
Ni–O (N-CH2COC6H5 group) bond distance (2.080(2) Å) of trans-[Ni(H2L2)](ClO4)2ꢀ2DMSO is shorter than
the in-plane Ni–N distances (2.096(2) and 2.100(2) Å). However, the Ni–O distances (2.105(2) and
2.124(2) Å) of cis-[Ni(H2L2)](ClO4)2ꢀH2O are considerably longer than the Ni–N distances (2.053(2)–
2.086(2) Å). Each N-CH2COC6H5 group of trans-[Ni(H2L2)]2+ and cis-[Ni(H2L2)]2+ exists as its keto form
in the solid state and in various solvents. Two N-CH2COC6H5 groups of trans-[Ni(H2L2)]2+ are readily
deprotonated in basic aqueous solutions, producing the enolate form trans-[Ni(L2)]. On the other hand,
cis-[Ni(H2L2)]2+ undergoes deprotonation to yield cis-[Ni(HL2)]+, in which one N-CH2COC6H5 group is
not deprotonated, under similar conditions.
Received 13 October 2011
Received in revised form 7 February 2012
Accepted 15 February 2012
Available online 1 March 2012
Keywords:
Macrocyclic compounds
Geometric isomers
Functional pendant arms
Tautomerism
N-Phenacyl groups
Deprotonation
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
In this work, we prepared a new 14-membered tetraaza macro-
cycle H2L2 bearing two N-CH2COC6H5 pendant arms. Interestingly,
Polyaza macrocyclic ligands and complexes bearing additional
functional pendant arms have received much attention because
of their interesting chemical properties and potential applications
in various fields [1–16]. In general, coordination polyhedron and
chemical properties of such complexes are influenced by the nat-
ure of the functional groups. Furthermore, chemical properties of
the functional groups attached to a coordinated macrocycle are
also influenced by the nature of the central metal ion and, there-
fore, are often quite different from those attached to a metal-free
organic compound [11–14].
H2L2 reacts with nickel(II) ion to form both cis-[Ni(H2L2)]2+ and
trans-[Ni(H2L2)]2+ that are readily deprotonated to cis-[Ni(HL2)]+
and trans-[Ni(L2)], respectively, in basic conditions. Synthesis and
characterization of the nickel(II) complexes are reported, together
with crystal structures of cis- and trans-[Ni(H2L2)](ClO4)2. The
formation of cis-[Ni(H2L2)]2+ as well as the trans isomer in the pres-
ent work is interesting, because most other related macrocycles
bearing two N-functional pendant arms, such as L3, L4, and L5, are
reported to form only trans-octahedral nickel(II) complexes [8–10].
2. Experimental
Various types of functionalized macrocyclic compounds have
been prepared and investigated. Some polyaza macrocycles bear-
ing N-COC6H5 pendant arms, such as L6, have also been reported
[15,16]. However, relatively few studies have been devoted to
the synthesis of tetraaza macrocyclic complexes bearing ketone
groups (N-(CH2)nCOR). As far as we know, the preparation of 14-
membered tetraaza macrocycles bearing N-CH2COC6H5 pendant
arms has not been reported.
2.1. Measurements
Electronic absorption spectra were recorded with an Analytic
Jena Specord 200 UV–Vis spectrophotometer, infrared spectra with
a Genesis II FT-IR spectrometer, NMR spectra with a Varian Mercury
300 FT NMR spectrometer, and GC–mass spectra with a Shimadzu a
Z18 Oyster Conductivity/Temperature meter GCMSD-QP5050
spectrometer. Conductance measurements were taken with a Z18
Oyster Conductivity/Temperature meter. Magnetic moments were
calculated from magnetic susceptibility data obtained at 293 K
using a Johnson Matthey MK-1 magnetic susceptibility balance.
⇑
Corresponding author. Tel.: +82 53 850 6443; fax: +82 53 850 6449.
E-mail address: sgkang@daegu.ac.kr (S.-G. Kang).
0020-1693/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2012.02.026

H. Kim et al. / Inorganica Chimica Acta 387 (2012) 346–351
347
product was collected by filtration, washed with methanol, and
dried in air. The crude product contains relatively small amount
(<20%) of an orange solid {cis-[Ni(H2L2)](ClO4)2}. The solubility of
trans-[Ni(H2L2)](ClO4)2 in acetonitrile–water (3:1) was found to
be considerably higher than that of cis-[Ni(H2L2)](ClO4)2. The pure
product was isolated by fractional recrystallizations of the crude
product in acetonitrile–water (3:1). Yield: ꢁ60%. Anal. Calc. for
NR
NH
HN
RN
NH
NR
RN
HN
C
36H52Cl2N4NiO10 (Mw: 830.42): C, 52.07; H, 6.31; N, 6.75. Found:
C, 51.74; H, 6.16; N, 6.48%. FAB mass (m/z): 729.4 for [Ni(H2L2)
+ClO4]+, 629.5 for [Ni(HL2)]+. IR (cmꢂ1): 3223 (mN
L1: R = H
L2: R = X
L3: R = CH2CH2OH
L4: R = CH2CONH2
L6: R = Y
H
C@O
A ), 1631 (
): 2.90
m
),
, ClO ꢂ). Magnetic moment (
at 20 °C.
ClAO
1100 (m
4
eff
l
B
l
2.5. Preparation of cis-[Ni (H2L2)](ClO4)2
To a boiling methanol solution (30 ml) of Ni(OAc)2ꢀ4H2O (ca.
2.0 g) was added H2L2 (0.5 g). The mixture was refluxed for 1 h
and then cooled to room temperature. After the addition of HClO4
(2.0 ml) and water (10 ml), the resulting solution was allowed to
stand at room temperature to produce an orange solid. The product
was collected by filtration, washed with methanol, and dried in air.
The crude product also contains relatively small amount (<20%) of
a pale yellow solid {trans-[Ni(H2L2)](ClO4)2}. The pure product was
isolated by the fractional recrystallizations of the crude product in
acetonitrile–water (3:1). Yield: ꢁ60%. Anal. Calc. for C36H52Cl2
N4NiO10 (Mw: 830.42): C, 52.07; H, 6.31; N, 6.75. Found: C,
52.28; H, 6.26; N, 6.74%. FAB mass (m/z): 729.4 for [Ni(H2L2)
+ClO4]+, 629.5 for [Ni(HL2)]+. IR (cmꢂ1): 3217 (mN
L5: R = CH2CH2COOMe
O
C
O
X = CH2
C
Y =
Molar susceptibilities were corrected for diamagnetism of the
ligand and/or the anions by use of Pascal’s constants. Elemental
analyses were performed at the Research Center for Instrumental
Analysis, Daegu University, Gyeongsan, Korea. FAB-mass spectra
were performed at the Korea Basic Science Institute, Daegu, Korea.
H
NAH
A ), 3261 (
m
),
, ClO ꢂ). Magnetic moment
C@O
C@O
ClAO
4
1660 (
m
), 1640 (
B
m
), 1100 (m
eff
(l
): 2.92
l
at 20 °C.
2.2. Preparation of H2L2
2.6. Preparation of trans-[NiL2]
The macrocycle L1 was prepared by the reported procedure [17].
A chloroform solution (30 ml) of L1 (2.0 g, 6.0 mmol) and phenacyl
bromide (3.5 g, 17.6 mmol) was refluxed for ca. 30 h and then
stored in a refrigerator until a white precipitate formed. The solid
collected by filtration was dissolved in acetonitrile (20 ml). After
the addition of 1.0 M NaOH aqueous solution (20 ml), the mixture
was evaporated at room temperature to precipitate a white solid. It
was collected by filtration and was recrystallized from warm chlo-
roform–methanol (3:1) solution. Yield: ꢁ70%. Anal. Calc. for
To an acetonitrile solution (20 ml) of trans-[Ni(H2L2)](ClO4)2
(0.5 g) was added 0.1 M NaOH aqueous solution (20 ml). The
resulting solution was evaporated at room temperature to precip-
itate a pale purple solid. The product was collected by filtration,
washed with water, and dried in air. It was recrystallized from
chloroform. Yield: ꢁ80%. Anal. Calc. for
629.5): C, 68.69; H, 8.01; N, 8.90. Found: C, 68.02; H, 7.83; N,
8.65%. FAB mass (m/z): 629.5 for [Ni(HL2)]+. IR (cmꢂ1): 3235 (
NAH).
Magnetic moment ( eff): 2.88 lB at 20 °C.
C36H50N4NiO2 (Mw:
m
l
C
36H52N4O2 (Mw: 572.8): C, 75.48; H, 9.15; N, 9.78. Found: C,
75.10; H, 8.82; N, 9.94%. GC–mass (m/z): 573 (M+). IR (cmꢂ1):
2.7. Preparation of cis-[Ni(HL2)]ClO4
3298(mNAH), 1637(m
C@O). 1H NMR (CDCl3): d 1.03 (d, Me), 7.2 (d,
C6H5), 7.3 (d, C6H5), 7.6 (d, C6H5). 13C NMR (CDCl3): 18.0, 21.5,
25.0, 25.6, 29.7, 34.2, 48.5, 50.8, 56.1, 77.5, 106.5, 125.2, 127.3,
127.7, 128.2, 128.9, 129.6, 138.3 (ACH2COC6H5) ppm.
To an acetonitrile solution (20 ml) of cis-[Ni(H2L2)](ClO4)2
(0.5 g) was added 0.1 M NaOH aqueous solution (20 ml). The
resulting solution was evaporated at room temperature to precip-
itate a pale orange solid. The product was collected by filtration,
washed with water, and dried in air. It was recrystallized from
2.3. Preparation of [H4L2](ClO4)2
methanol. Yield: ꢁ80%. Anal. Calc. for
C36H51ClN4NiO6 (Mw:
729.96): C, 59.23; H, 7.04; N, 7.68. Found: C, 59.03; H, 7.16; N,
To an acetonitrile suspension (20 ml) of H2L2 (1.0 g) was added
concentrated HClO4 (1.0 ml) dissolved in water (20 ml). The mix-
ture was stirred for 1 h at room temperature. The white solid,
which had been formed, was collected by filtration, washed with
7.26%. FAB mass (m/z): 729.6 for [Ni(H2L2)+ClO4]+, 629.7 for
[Ni(HL2)]+. IR (cmꢂ1): 3240 (
m
NAH), 3268 (
mNAH), 1660 (mC@O),
A , ClO ꢂ). Magnetic moment (
l
at 20 °C.
1100 (mCl
O
4
eff
): 2.85
B
l
water, and dried in air. Yield: ꢁ90%. Anal. Calc. for C36H54Cl2N4O10
:
C, 55.88; H, 7.03; N, 7.24. Found: C, 55.52; H, 6.95; N, 7.37%. FAB
2.8. Crystal structure determination
mass (m/z): 673.4 for [H4L2+ClO4]+, 573.5 for [H3L2]+. IR (cmꢂ1):
3230(mNAH), 1640 (mC@O), 1100 (m
ClAO, ClO4ꢂ).
Single crystals of trans-[Ni(H2L2)](ClO4)2ꢀ2DMSO and cis-
[Ni(H2L2)](ClO4)2ꢀH2O suitable for X-ray study were grown from
water–DMSO and water–acetonitrile solutions, respectively. Inten-
sity data were collected on a Rigaku R-AXIS RAPID II-S diffractom-
2.4. Preparation of trans-[Ni(H2L2)](ClO4)2
To a boiling methanol solution (30 ml) of H2L2 (0.5 g) was added
Ni(OAc)2ꢀ4H2O (ca. 2.0 g). The mixture was refluxed for 1 h and
then cooled to room temperature. After the addition of HClO4
(2.0 ml) and water (10 ml), the resulting solution was allowed to
stand at room temperature to produce a pale yellow solid. The
eter equipped with graphite monochromated MoKa (k = 0.71073
Å) radiation source and imaging plate detector (460 ꢃ 256 mm).
A total of 240 oscillation images were collected at 100 k using
widths of 3° in
x the raw data were processed to give structure
factors using the RAPID AUTO program. The structure was solved

348
H. Kim et al. / Inorganica Chimica Acta 387 (2012) 346–351
Table 1
Crystallographic data for trans-[Ni(H2L2)](ClO4)2ꢀ2DMSO and cis-[Ni(H2L2)](ClO4)2ꢀH2O.
Compound
trans-[Ni(H2L2)](ClO4)2ꢀ2DMSO
cis-[Ni(H2L2)](ClO4)2ꢀH2O
Empirical formula (M)
C
40H64Cl2N4NiO12S2 (986.68)
C36H54Cl2N4NiO11 (848.50)
Crystal system (space group)
monoclinic (P21/c)
monoclinic (P21/c)
Unit cell dimensions
a (Å)
b (Å)
c (Å)
Beta (°)
V (Å3)
Z
12.042(2)
10.330(2)
18.148(2)
92.174(3)
2255.7(4)
2
1.453
11.023(2)
16.901(1)
20.777(2)
96.373(2)
3846.8(4)
4
1.462
Dcalc (g cmꢂ3
)
h range for data collection (°)
F(000)
2.99–27.44
1044
0.706
293(2)
3.04–27.44
1784
7.08
293(2)
l
(mmꢂ1
T (K)
)
Index ranges
ꢂ15 6 h 6 15, ꢂ13 6 k 6 13, ꢂ23 6 l 6 23
ꢂ11 6 h 6 14, ꢂ21 6 k 6 21, ꢂ26 6 l 6 26
Independent reflections
Reflections observed (>2
Data completeness
5146
8786
r
)
4063
1.000
6916
1.00
Data/restraints/parameters
5146/0/277
1.060
8786/0/482
1.040
Goodness-of-fit (GOF) on F2
Final R indices [I > 2
R indices (all data)
r
(I)]
R1 = 0.0615, wR2 = 0.1752
R1 = 0.0767, wR2 = 0.1922
0.795 and ꢂ0.955
R1 = 0.0586, wR2 = 0.1556
R1 = 0.0769, wR2 = 0.1703
1.160 and ꢂ0.600
Largest difference in peak and hole (e Åꢂ3
)
by direct method and refined by full matrix least squares against F2
for all data using SHELXL-97 [18]. All non-hydrogen atoms were
anisotropically refined. All other hydrogen atoms were included
in the calculated position. Experimental details for the structure
determinations are listed in Table 1.
chelate rings and the cyclohexane rings of the complex adopt stable
chair conformations.
Selected bond distances and angles of trans-[Ni(H2L2)]2+ are
listed in Table 2. The Ni–N (2.095(2) and 2.097(3) Å) distances
are comparable with those of other related trans-octahedral nicke-
l(II) complexes, such as trans-[NiL3](ClO4)2 and trans-[NiL4](ClO4)2
[8,9]. One of the most remarkable structural features of the
complex is that the axial Ni–O (N-CH2COC6H5 group) distance
(2.083(2) Å) is shorter than the in-plane Ni–N distances. The
Ni–O distance is distinctly shorter than the axial Ni–O (pendant
N-CH2CH2OH or N-CH2CONH2 group) distances of trans-[NiL3]
(ClO4)2 (2.149(4) Å) and trans-[NiL4](ClO4)2 (2.302(3) Å) [8,9]. This
3. Results and discussion
3.1. Synthesis
The macrocycle H2L2 bearing two N-CH2COC6H5 pendant arms
was prepared by the reaction of L1 with phenacyl bromide. The
mass, 1H NMR, 13C NMR, and IR spectral data of H2L2 and/or
[H4L2](ClO4)2 are listed in Section 2. The di-N-functionalized mac-
rocycle is soluble in chloroform, but is nearly insoluble in methanol
at room temperature.
The reaction of Ni(OAc)2ꢀ4H2O with H2L2 in methanol, followed
by addition of NaClO4 or HClO4, produces a mixture of two geometric
isomers, cis-[Ni(H2L2)](ClO4)2 and trans-[Ni(H2L2)](ClO4)2. Interest-
ingly, the proportion of cis-[Ni(H2L2)](ClO4)2 to trans-[Ni(H2L2)]
(ClO4)2 in the product is dependent on the reaction conditions (see
Section 2). The major product prepared by adding H2L2 to a boiling
methanol solution of Ni(OAc)2ꢀ4H2O was the trans isomer. On the
other hand, the cis isomer could be prepared as the major product
by the addition of Ni(OAc)2ꢀ4H2O to a boiling methanol solution of
H2L2. The addition of a base to an aqueous solution of trans-
[Ni(H2L2)](ClO4)2 yields the enolate form trans-[NiL2], in which two
functional pendant arms are deprotonated. However, the only com-
plex isolated from basic aqueous solutions of cis-[Ni(H2L2)](ClO4)2 is
cis-[Ni(HL2)]ClO4; one of the two pendant arms is not deprotonated.
The deprotonation of the N-CH2COC6H5 group attached to cis-
[Ni(HL2)]ClO4 could not be achieved even in 1.0 M NaOH aqueous
solution.
3.2. Crystal structure of trans-[Ni(H2L2)](ClO4)2ꢀ2DMSO
The isomer trans-[Ni(H2L2)]2+ has slightly distorted trans-octa-
hedral coordination geometry; the axial positions are occupied by
the oxygen atoms of the N-CH2COC6H5 pendant arms (Fig. 1). The
macrocycle adopts a trans-III type N-conformation, and the complex
has an inversion center at the nickel atom. The six-membered
Fig. 1. An ORTEP drawing of symmetric unit of trans-[Ni(H2L2)](ClO4)2ꢀ2DMSO
(symmetry code; ꢂx, 1/2 + y, 1/2 ꢂ z). Lattice DMSO and perchlorate anions are
omitted for clarity.

H. Kim et al. / Inorganica Chimica Acta 387 (2012) 346–351
349
Table 2
Table 3
Bond distances [Å] and angles [°] for trans-[Ni(H2L2)](ClO4)2ꢀ2DMSO.
Bond distances [Å] and angles [°] for cis-[Ni(H2L2)](ClO4)2ꢀH2O.
Ni(1)–N(1)
Ni(1)–O(1)
2.095(2)
2.083(2)
1.508(4)
85.1(1)
180.0(2)
81.5(2)
Ni(1)–N(2)
C(11)–O(1)
C(11)–C(12)
2.097(3)
1.234(4)
1.483(4)
94.9(1)
180.0(2)
93.5(2)
Ni(1)–N(1)
Ni(1)–N(3)
Ni(1)–O(1)
C(20)–O(1)
2.065(2)
2.053(2)
2.105(2)
1.230(4)
1.524(4)
1.511(4)
Ni(1)–N(2)
Ni(1)–N(4)
Ni(1)–O(2)
C(28)–O(2)
2.075(2)
2.086(2)
2.124(2)
1.234(3)
1.483(4)
1.482(4)
C(10)–C(11)
N(1)–Ni–N(2)
N(1)–Ni–N(1)a
N(1)–Ni–O(1)
O(1)–Ni–O(1)a
N(1)–Ni–N(2)a
N(2)–Ni–N(2)a
N(2)–Ni–O(1)
C(10)–C(11)–O(1)
C(19)–C(20)
C(27)–C(28)
N(1)–Ni–N(2)
N(1)–Ni–N(4)
N(2)–Ni–N(4)
N(1)–Ni–O(1)
N(2)–Ni–O(1)
N(3)–Ni–O(1)
N(4)–Ni–O(1)
O(1)–Ni–O(2)
C(9)–N(3)–C(10)
C(20)–C(21)
C(28)–C(29)
N(1)–Ni–N(3)
N(2)–Ni–N(3)
N(3)–Ni–N(4)
N(1)–Ni–O(2)
N(2)–Ni–O(2)
N(3)–Ni–O(2)
N(4)–Ni–O(2)
C(1)–N(1)–C(18)
O(1)–C(20)–C(19)
180.0(2)
120.0(3)
100.9(1)
171.9(1)
86.4(1)
100.9(1)
80.0(1)
171.9(1)
92.3(1)
87.2(1)
82.7(1)
113.0(2)
86.4(1)
95.8(1)
94.9(1)
89.3(1)
81.6(1)
169.4(1)
115.6(1)
118.6(3)
a
Symmetry code; 1 ꢂ x, 2 ꢂ y, ꢂz.
indicates that the N-CH2COC6H5 groups in trans-[Ni(H2L2)]2+ bind
the metal more strongly than those of the N-CH2CH2OH or
N-CH2CONH2 groups in trans-[NiL3](ClO4)2 and trans-[NiL4](ClO4)2.
The C(11)–O(1) distance (1.234(4) Å) is corresponding to the C@O
double bond of a ketone group. The N(1)–Ni–N(2) angle (85.1(1)°)
involved in the five-membered chelate ring is smaller than the
N(1)–Ni–N(2)# angle (94.9(1)°) involved in the six-membered
chelate ring, as usual. The Ni–O(1) bond is not perpendicular to
the NiN4 plane with N(1)–Ni–O(1) angle of 81.5(2)°. The C(10)–
C(11)–O(1) angle is 120.0(3)°.
along the N(1)–Ni–N(3) axis. The N(1)–Ni–N(2) and N(3)–Ni–
N(4) angles (95.8(1)–100.9(1)°) involved in the six-membered
chelate rings are considerably larger than the N(1)–Ni–N(4) and
N(2)–Ni–N(3) angles (86.4(1)°) involved in the five-membered
chelate rings. The N(1)–Ni–O(1) and N(3)–Ni–O(2) angles
(80.0(1)–81.6(1)°) are smaller than the N(1)–Ni–N(4) and N(2)–
Ni–N(3) angles. It is also seen that the O(1)–Ni–O(2) angle
(82.7(1)°) is much smaller than 90°. The C(19)–C(20)–O(1) angle
is 118.6(3)°.
3.3. Crystal structure of cis-[Ni(H2L2)](ClO4)2ꢀH2O
The ORTEP drawing (Fig. 2) of cis-[Ni(H2L2)]2+ cation shows that
the N-CH2COC6H5 pendant arms as well as the four nitrogen atoms
are involved in coordination. In contrast to trans-[Ni(H2L2)]2+, the
ketone groups in this isomer are cis to each other. The macrocycle
is folded along the N(1)–Ni–N(3) axis and adopts cis-II type
N-conformation.
3.4. Spectra and properties of trans-[Ni(H2L2)](ClO4)2 and trans-
[Ni(L2)]
As described above, the coordinated N-CH2COC6H5 groups in
trans-[Ni(H2L2)]2+ are readily deprotonated in basic aqueous solu-
tions, yielding trans-[Ni(L2)] bearing two N-CH@C(Oꢂ)C6H5 groups
that are protonated in acidic solutions (Eq. (1)). However, both
trans-[Ni(H2L2)](ClO4)2 and trans-[Ni(L2)] are quite stable in the
solid states or in various pure solvents.
Selected bond distances and angles of cis-[Ni(H2L2)]2+ are listed
in Table 3. The Ni–N distances (2.053(2)–2.086(2) Å) are not quite
different from the Ni–N distances of trans-[Ni(H2L2)]2+. However,
the Ni–O distances (2.105(2)–2.124(2) Å) of cis-[Ni(H2L2)]2+ are
distinctly longer than the Ni–N distances and are P0.02 Å longer
than those (2.083(2) Å) of trans-[Ni(H2L2)]2+. The N(1)–Ni–N(3) an-
gle (171.9(1)°) is slightly deviated from 180°. The N(2)–Ni–O(1)
and N(4)–Ni–O(2) angles (171.9(1) and 169.4(1)°, respectively)
are also deviated from 180°. The N(2)–Ni–N(4) angle (100.9(1)°)
is even smaller than 120°, showing that the macrocycle is folded
2+
-
O
O
H
H
N
N
N
N
OH-
H+
N
N
N
N
Ni
(1)
Ni
H
H
-
O
O
ð1Þ
The complex trans-[Ni(H2L2)](ClO4)2 is soluble in acetonitrile
and nitromethane. On the other hand, trans-[Ni(L2)] is soluble in
chloroform, but is nearly insoluble in acetonitrile or nitromethane.
The values of molar conductance (Table 4) for trans-[Ni(H2L2)](-
ClO4)2 measured in nitromethane (148
nitrile (260
X
ꢂ1 molꢂ1 cm2) and aceto-
X
ꢂ1 molꢂ1 cm2) indicate that the complex is a 1:2
electrolyte. The enolate form trans-[Ni(L2)] was found to be a non-
electrolyte in chloroform. FAB mass spectrum of trans-[Ni(H2L2)](-
ClO4)2 shows two groups of peaks at m/z 729.4 {[Ni(H2L2)+ClO4]+}
and 629.5 {[Ni(HL2)]+}. The spectrum of trans-[Ni(L2)] shows a peak
at m/z 629.5. The magnetic moments of trans-[Ni(H2L2)](ClO4)2 and
trans-[Ni(L2)] in the solid states were found to be 2.90 and 2.88 lB
,
respectively, at room temperature, showing the d8 electronic con-
figuration of octahedral geometry. The IR spectrum of trans-
Fig. 2. An ORTEP drawing of symmetric unit of cis-[Ni(H2L2)](ClO4)2ꢀH2O. Lattice
water and perchlorate anions are omitted for clarity.
[Ni(H2L2)](ClO4)2 shows mC
@
O
of the coordinated N-CH2COC6H5

350
H. Kim et al. / Inorganica Chimica Acta 387 (2012) 346–351
Table 4
the solid states and in various solvents. The values of molar con-
ductance (Table 3) for cis-[Ni(H2L2)](ClO4)2 and cis-[Ni(HL2)]ClO4
measured in nitromethane or acetonitrile show that they are 1:2
and 1:1 electrolytes, respectively. FAB mass spectrum of cis-
[Ni(H2L2)](ClO4)2 is nearly identical with that of trans-[Ni(H2L2)](-
ClO4)2. The spectrum of cis-[Ni(HL2)]ClO4 shows two groups of
peaks at m/z 729.6 and 629.7. The magnetic moments of cis-
Molar conductance and electronic absorption spectral data of the nickel(II)
complexes.
Complex
kmax, nma
(e
, Mꢂ1 cmꢂ1
)
kM, X
ꢂ1 molꢂ1 cm2
trans-[Ni(H2L2)](ClO4)2
594(3.3)
605(3.5)b
585(3.3)c
570(6.4)d
511(56)
515(57)b
517(60)c
505(sh)
735(3.2)
740(3.6)b
732(3.3)c
805(3.6)d
825(16)
140 260b
60c
trans-[NiL2]
0d
[Ni(H2L2)](ClO4)2 (2.92 B) and cis-[Ni(HL2)]ClO4 (2.85
l lB) mea-
cis-[Ni(H2L2)](ClO4)2
135 245b
55c
830(16)b
845(18)c
805(11)
sured in the solid states also support the fact that the complexes
have octahedral coordination geometry. The IR spectrum of cis-
cis-[Ni(HL2)]ClO4
60 90b
[Ni(H2L2)](ClO4)2 shows
mNAH of the secondary amino groups at
525(sh)b
516(7.2)
525(6.9)
795(10)b
3261 and 3217 cmꢂ1. The spectrum also shows two bands corre-
sponding to mC@O of the coordinated N-CH2COC6H5 groups at
1640 and 1660 cmꢂ1. In the spectrum of cis-[Ni(HL2)]ClO4, one
peak corresponding to mC
trans-[NiL3](ClO4)2
e
trans-[NiL4](ClO4)2
f
a
b
c
d
e
f
Measured in nitromethane at 20 °C unless otherwise specified.
In acetonitrile.
In DMSO.
In chloroform.
Ref. [8].
O
2
6
5
@
ꢂo1f the coordinated N-CH COC H
NAH
m
group is observed at 1660 cm . Two peaks of
are also ob-
served at 3268 and 3240 cmꢂ1. The electronic absorption spectrum
2
2
4 2
of cis-[Ni(H L )](ClO ) measured in nitroꢂm1ethane shows the d–d
transition bands at 511 (e e = 16
= 56 Mꢂ1 cm ) and 825 nm (
Ref. [9].
Mꢂ1 cmꢂ1), which are comparable with those of other related octa-
hedral nickel(II) complexes. The wavelengths of the d–d transition
groups at 1631 cmꢂ1. A band corresponding to
mNAH of the second-
2
2
4 2
bands are quite different from those of trans-[Ni(H L )](ClO ) . Fur-
thermore, the molar absorption coefficient of each band for the cis
ary amino groups is observed at 3223 cmꢂ1. In the spectrum of
trans-[Ni(L2)], mNAH of the secondary amino groups is observed at
isomer is distinctly larger than that of the trans isomer. The spec-
3235 cmꢂ1; however, no peak corresponding to
mC@O was observed.
2
4
trum of cis-[Ni(HL )]ClO is not quite different from that of cis-
The electronic absorption spectra (Table 3) of trans-[Ni(H2L2)]
2
2
4 2
[Ni(H L )](ClO ) .
(ClO4)2 measured in various solvents show d–d transition bands
around 600 (e e
= 3.3–3.5 Mꢂ1 cmꢂ1) and 735 nm ( = 3.2–3.6 Mꢂ1
4. Concluding remarks
cmꢂ1). The spectra are quite different from those of various other
related trans-octahedral nickel(II) complexes, such as trans-[NiL3]
(ClO4)2 [8] and trans-[NiL4](ClO4)2 [9]; one (ca. 600 nm) of the bands
is observed at >60 nm longer wavelength than that of trans-[NiL3]
(ClO4)2 (516 nm) or trans-[NiL4](ClO4)2 (525 nm). The spectrum of
trans-[Ni(L2)] measured in chloroform exhibits the bands at 570
This work shows that H2L2 bearing two N-CH2COC6H5 pendant
arms reacts with Ni2+ ion to form cis-[Ni(H2L2)]2+ as well as
trans-[Ni(H2L2)]2+. To our knowledge, cis-[Ni(H2L2)]2+ is a very rare
example of 14-membered tetraaza macrocyclic nickel(II) complex
with two N-functional pendant arms that occupy cis positions of
the octahedron; L3, L4, and L5 react with Ni2+ ion to form only
trans-octahedral complexes [8–10]. The Ni–O (N-CH2COC6H5
groups) bonds of trans-[Ni(H2L2)]2+ are distinctly stronger than
(e e
= 3.3 Mꢂ1 cmꢂ1) and 805 nm ( = 3.6 Mꢂ1 cmꢂ1) that are some-
what shorter and considerably longer, respectively, than those for
trans-[Ni(H2L2)](ClO4)2.
those of cis-[Ni(H2L2)]2+
. The N-CH2COC6H5 groups in trans-
3.5. Spectra and properties of cis-[Ni(H2L2)](ClO4)2 and cis-
[Ni(HL2)]ClO4
[Ni(H2L2)]2+ are readily deprotonated in basic aqueous solutions.
On the other hand, one of the N-CH2COC6H5 groups in cis-
[Ni(H2L2)]2+ does not undergo deprotonation under similar exper-
imental conditions. This may be attributed to the relatively weak
Ni–O interaction in the cis isomer.
The cis isomer cis-[Ni(H2L2)]2+ also undergoes deprotonation in
basic aqueous solutions. However, the only complex isolated from
the solutions is cis-[Ni(HL2)]+ where one of the two pendant arms
is not deprotonated (Eq. (2)). This deprotonation behavior is quite
different from the behavior of trans-[Ni(H2L2)]2+. The deprotona-
tion of the free macrocycle H2L2 was also attempted in 0.1–3.0 M
NaOH aqueous solutions, but failed; the only compound isolated
from the solutions was found to be H2L2. As mentioned above,
the Ni–O interactions of the cis isomer are weaker than those of
the trans isomer. Therefore, it can be suggested that the difference
in the deprotonation behaviors between the two isomers is closely
related to the Ni–O interactions; the stronger the Ni–O interac-
tions, the easer the deprotonation of the N-CH2COC6H5 group.
Acknowledgments
This research was supported in part by Basic Science Research
Program through the National Research Foundation of Korea
(NRF) funded by the Ministry of Education, Science and Technology
(No. 2010-0007251). C.-H. Kwak thanks Non-Directional Fund of
Sunchon National University, 2011.
Appendix A. Supplementary material
+
Supplementary material CCDC 846198 and 846199 contains the
supplementary crystallographic data for cis-[ Ni(H2L2)](ClO4)2ꢀH2O
and trans-[ Ni(H2L2)](ClO4)2ꢀ2DMSO. These data can be obtained
free of charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data_request/cif. Supplementary data
associated with this article can be found, in the online version, at
http://dx.doi.org/10.1016/j.ica.2012.02.026.
2+
-
O
O
N
O
O
N
OH-
H+
ð2Þ
N
Ni
N
N
Ni
N
N
H
N
H
H
H
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acetonitrile and nitromethane. The complexes are quite stable in
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