Synthesis, structures and DNA binding of ternary transition metal complexes M(II)L with the 2,2′-bipyridylamine (L = p-HB, M = Co, Ni, Cu and Zn)

Article abstract of DOI:10.1016/j.ica.2005.05.012

New ternary transition metal complexes of formulations [Co(bpa)(p-HB) ₂](bpa = 2,2′-bipyridylamine, p-HB = p-hydroxybenzenecarboxylic acid) (1), [Ni(bpa)(p-HB)(H₂O)₂]⁺(NO ₃)^- ? H₂

Full text of DOI:10.1016/j.ica.2005.05.012

Inorganica Chimica Acta 358 (2005) 3407–3416
www.elsevier.com/locate/ica
Synthesis, structures and DNA binding of ternary transition
metal complexes M(II)L with the 2,20-bipyridylamine
(L = p-HB, M = Co, Ni, Cu and Zn)
a
Yue Wang , Nobuo Okabe
b,
*
a
Lab of Inorganic Chemistry, China Pharmaceutical University, Nanjing 210009, China
Faculty of Pharmaceutical Sciences, Kinki University, Kowakae 3-4-1, Higashiosaka, Osaka 577-8502, Japan
b
Received 28 February 2005; received in revised form 30 April 2005; accepted 11 May 2005
Available online 16 June 2005
Abstract
New ternary transition metal complexes of formulations [Co(bpa)(p-HB)2](bpa = 2,20-bipyridylamine, p-HB = p-hydroxybenzen-
ecarboxylic acid) (1), [Ni(bpa)(p-HB)(H2O)2]+(NO3)ꢀ Æ H2O (2), ½NiðbpaÞ ðp-HBÞꢁ 2þðNO3Þꢀðp-HBÞꢀ ꢂ 5H2O ð3Þ, [Cu(bpa)(p-
2
2
HB)Cl] (4) and [Zn(bpa)(p-HB)2]2 Æ 0.5H2O (5) are prepared, their structural features are characterized by crystal structural studies,
and their DNA binding propensity has been evaluated by fluorescence method. The molecular structure of complex 1 shows the six
coordinate octahedral geometry with one bpa and two p-HB ligands, complex 2 is the cationic complex and has the six coordinate
octahedral structure with one bpa, one p-HB and two aqua ligands, complex 3 is also the cationic complex of octahedral coordi-
nation with two bpa and one p-HB ligands, complex 4 is five coordinate distorted square pyramidal with one bpa, one p-HB
and chloride ligands and complex 5 has the distorted octahedral coordination with two p-HB and one bpa ligands. In all of the
complexes, both bpa and p-HB act as the bidentate N and O-donor ligands, respectively. The intermolecular H-bond networks,
together with p–p interaction in their solid state are also described. The complexes show the competitive inhibition of ethidium bind-
ing to DNA, and the DNA binding propensity can be reflected as the relative order: 3 > 2 > 1 > 5 > 4, in which the cationic charged
Ni(II) complexes 2 and 3 show the most effective inhibition ability.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: X-ray crystal structure; Ternary transition metal complexes; 2,20-Bipyridylamine; p-Hydroxybenzenecarboxylic acid; DNA binding;
Fluorescence
1. Introduction
plexes with heterocyclic ligands such as phen (1,10-phe-
nanthroline), bpy (2,20-bipyridine), dppz (dipyrido [3,2-
a:20,30-c] phenazine) [5–8]. However, there are few
reports concerning DNA binding of the complexes with
2,20-bipyridylamine (bpa) ligand which has a central
aromatic amine. As a result of the high rotational flexi-
bility around its central amine bridging the two pyridine
ring, the two pyridine planes adopt either coplanar or
tilted conformation in the coordination to the metal cen-
ters [9]. Several Pd(II) and Pt(II) complexes with bpa
have been reported [9–12], and some of them have
revealed potential antitumor activity towards leukemia
Among the systems of the biomimetic degradation of
DNA or RNA, transition and/or lanthanide metal com-
plexes have been shown to be most effective [1–4]. A par-
ticular emphasis has been on the use of complexes with
extended planar aromatic ligands so as to enhance non-
covalent binding, especially through intercalation.
Many studies are focused on the transition metal com-
*
Corresponding author. Tel.: +81 6 6730 5880; fax: +81 6 6730 1394.
E-mail address: okabe@phar.kindai.ac.jp (N. Okabe).
0020-1693/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2005.05.012

3408
Y. Wang, N. Okabe / Inorganica Chimica Acta 358 (2005) 3407–3416
cells which is equal or exceed the activity of cisplatin
[13,14]. The interaction studies between these complexes
and calf thymus (CT) DNA suggest the non-covalent
binding via the minor groove. However, few studies
about the interaction between the transition metal com-
plexes of bpa and DNA have been reported, and most of
the studies are limited in the structure characterization
[15–18].
was added drop wise to such mixture and reacted for
no less than 30 min. The solution was placed at the room
temperature and kept for slow evaporation. A week la-
ter pink planelet crystals (complex 1) suitable for X-
ray diffraction studies were obtained from mother
liquor.
Anal. Calc. for [Co(bpa)(p-HB)2]: C, 57.15; H, 3.80;
N, 8.33. Found: C, 57.25; H, 3.92; N, 8.20%.
By these reasons, we aimed to synthesize the ternary
transition metal complexes with bpa and a metabolite li-
gand, p-hydroxybenzenecarboxylic acid (p-HB), and
characterize their structural features. p-HB is used by
the following reasons: (1) Although a large number of
metal complexes with p-HB isomers, o-HB (salicylic
acid) and m-HB have been reported, only a few metal
complexes with p-HB have been recorded [19–21].
Therefore it seems to be important to clarify the coordi-
nation modes of p-HB; (2) It is one of the tyrosine
metabolites in the coenzyme Q (ubiquinone) synthesis
[22,23] and is an active ingredient in an energy-enhancing
supplement for increasing the cellular formation of ATP
[24]. Therefore, it seems to be useful as a low toxic li-
gand suitable for the medicinal use of the metal
complexes.
2.2.2. Preparation of [Ni(bpa)(p-HB)(H2O)2]þ(NO3)ꢀꢂ
H2O (2)
Five milligrams (0.035 mmol) p-HB was dissolved in
5 ml water and was mixed with the methanol solution
of 6 mg (0.035 mmol) bpa. Then 10.2 mg (0.035 mmol)
Ni(NO3)2 Æ 6H2O dissolved in a small amount of water
solution was added drop wise to such mixture and re-
acted for no less than 30 min. The solution was placed
at the room temperature and kept for slow evaporation.
Two weeks later some very clear blue prismatic crystals
(complex 2) suitable for X-ray diffraction studies were
obtained from mother liquor.
Anal. Calc. for ½NiðbpaÞðp-HBÞðH2OÞ ꢁþðNO3Þꢀꢂ
2
H2O: C, 42.27; H, 4.17; N, 11.60. Found: C, 42.29; H,
4.00; N, 11.46%.
In this study, we report the synthesis, crystal struc-
tures, and DNA binding properties of Co(II), Ni(II),
Cu(II) and Zn(II) ternary complexes of bpa with p-
HB. The current topic focuses on the construction of
the novel crystal engineering in the solid state, and the
corresponding DNA interaction in the solution.
2.2.3. Preparation of [Ni(bpa)2(p-HB)]22þ(NO3)ꢀ
(p-HB)ꢀ ꢂ 5H2O (3)
In the same condition as complex 2 mentioned above,
some violet planet crystals (complex 3) appeared in the
same vessel.
Anal. Calc. for ½NiðbpaÞ ðp-HBÞꢁ 2þðNO3Þꢀðp-HBÞꢀꢂ
2
2
5H2O: C, 53.65; H, 4.50; N, 13.34. Found: C, 53.99;
H, 4.66; N, 13.55%.
2. Experimental
Although the two different crystals (complex 2 and 3)
were coexisting as polymorphism in the same vessel,
they could be separated easily by their different colors
and shapes from each other.
2.1. General remarks
Analytical grade of 2,20-bipyridylamine (bpa),
p-hydroxybenzenecarboxylic acid (p-HB), CoCl2 Æ
6H2O, Ni(NO3)2 Æ 6H2O, CuCl2 Æ 2H2O and ZnCl2 were
obtained from Wako Pure Chemicals, Industries Ltd.
(Osaka, Japan). Fluorescence measurements were per-
formed with a Hitachi 850 spectrofluorometer at 25
ꢁC. Element analysis was done on YANACO CHN Co-
der MT-3. The X-ray measurements were made on a
Rigaku RAXIS RAPID diffractometer with a graphite
2.2.4. Preparation of [Cu(bpa)(p-HB)Cl] (4)
Five milligrams (0.035 mmol) p-HB was dissolved in
5 ml water and was mixed with the methanol solution of
3 mg (0.017 mmol) bpa. Then 1.5 mg (0.008 mmol)
CuCl2 Æ 2H2O dissolved in a small amount of water solu-
tion was added drop wise to such mixture and reacted
for no less than 30 min. The solution was placed at
the room temperature and kept for slow evaporation.
Ten days later clear blue prismatic crystals (complex 4)
suitable for X-ray diffraction studies were obtained from
mother liquor.
˚
monochromatised Mo Ka radiation (k = 0.71069 A)
using scan mode.
2.2. Preparation of the complexes
Anal. Calc. for [Cu(bpa)(p-HB)Cl]: C, 50.13; H, 3.47;
N, 10.32. Found: C, 50.12; H, 3.52; N, 10.39%.
2.2.1. Preparation of [Co(bpa)(p-HB)2] (1)
Five milligrams (0.035 mmol) p-HB was dissolved in
3 ml 50% (v/v) methanol–water solution and was mixed
with the methanol solution of 6 mg (0.035 mmol) bpa.
Then 8.3 mg (0.035 mmol) CoCl2 Æ 6H2O dissolved in a
small amount of 50%(v/v) methanol–water solution
2.2.5. Preparation of [Zn(bpa)(p-HB)2]2 Æ 0.5H2O (5)
Five milligrams (0.035 mmol) p-HB was dissolved in
5 ml water and was mixed with the methanol solution of
6 mg (0.035 mmol) bpa. Then 5 mg (0.035 mmol) ZnCl2

Y. Wang, N. Okabe / Inorganica Chimica Acta 358 (2005) 3407–3416
3409
solution was added drop wise to such mixture and re-
acted for no less than 30 min. The solution was placed
at the room temperature and kept for slow evaporation.
A week later colorless prismatic crystals (complex 5)
suitable for X-ray diffraction studies were obtained from
mother liquor.
refined for all non-hydrogen atoms. Selected bond dis-
tances and angles are listed in Tables 2–5, respectively.
3. Results and discussion
Anal. Calc. for [Zn(bpa)(p-HB)2]2 Æ 0.5H2O: C, 55.94;
H, 3.81; N, 8.16. Found: C, 56.10; H, 3.86; N, 8.25%.
3.1. Crystal structures
3.1.1. Complex 1
2.3. X-ray crystallography
The structure of complex 1 contains four asymmetric
CoN2O4 units. Each unit has the similar coordination
mode with a slightly different bond distances and angles
listed in Table 2. Only Co1 complex unit is shown in Fig.
1(a) in order to clarify the geometry around the central
metal. In Co1 unit, Co(II) atom is bonded to two N
atoms from bpa ligand and four carboxylato O atoms
from two p-HB molecules. The central metal is located
in a distorted octahedron with the N11, N12, O11 and
O14 atoms constructing the equatorial plane and the
other two O12 and O15 atoms in the axial direction.
The Co1(II) deviates from the equatorial plane by
A summary of the crystallographic data and structure
refinements is given in Table 1. The data were corrected
for Lorentz and polarization effects. The structure was
solved by direct methods [25] using the CRYSTAL STRUC-
TURE [26] software package. The refinement was per-
formed using SHELXL-97 [27]. All H atoms including
water molecule were located from difference Fourier
maps and placed at idealized positions and treated as
riding, with C–H distance of 0.93 and Uiso(H) values
equal to 1.2Ueq(C) and Uiso(water H) values equal to
1.5Ueq(C) (Ueq is the equivalent isotropic displacement
parameter for the pivot atom).
˚
0.057(1) A towards O12 atom.
The basic coordination structures are almost the
same for the four independent units, therefore, the de-
tailed description for the others is neglected here. In con-
clusion, the average Co–O bond and Co–N distances are
P
2
The function of
using the weight scheme of w ¼ 1=½r2ðF o2Þþ
wðF 2o ꢀ F 2cÞ was minimized by
2
ðaPÞ þ bPꢁ; where P ¼ ðF 2o þ 2F c2Þ=3.
Final
R½¼
P
P
P
P
2
˚
ðjF oj ꢀ jF cjÞ= jF ojꢁ; Rw½¼ ð wðjF oj ꢀ jF cj Þ=
w
2.154(3) and 2.051(3) A, respectively, and both of them
P
2
1=2
jF oj Þ ꢁ and S ðGoodness ꢀ of ꢀ fitÞ ½¼ ð wðjF ojꢀ
are within the reported values for the Co analogues
complexes with the same ligand atoms [18,28]. The mean
dihedral angle of the two pyridine rings is 11.6(1)ꢁ indi-
cating bpa ligand adopts nearly coplanar conformation.
2
1=2
jF cjÞ =ðM ꢀ NÞ Þ, where M = no. of reflections and
N = no. of variables used for the refinement] are given
in Table 1. Anisotropic displacement coefficients were
Table 1
Crystal data and structure refinement for compound 1–5
1
2
3
4
5
Formula
C
504.35
24H19N3O6Co
C17H20N4O9Ni
483.06
C61H61N13Ni2 O17
1365.61
C17H14Cl1N3 O3Cu
407.31
C48H39N6O12.5 Zn2
1030.63
Formula weight
Crystal System
Space group
triclinic
ꢀ
monoclinic
P21/c
monoclinic
P21/c
orthorhombic
P212121
monoclinic
P2/c
P1
Unit cell dimensions
˚
a (A)
˚
11.020(6)
17.72(1)
24.69(1)
81.79(3)
85.64(2)
73.28(2)
4567(4)
8
9.9763(3)
17.1052(5)
12.0469(3)
90.00
20.44(4)
15.01(2)
21.60(5)
90.00
6.904(2)
7.940(2)
30.867(9)
90.00
19.9163(6)
11.0087(4)
21.4208(5)
90.00
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
105.351(2)
90.00
110.19(7)
90.00
90.00
90.00
98.188(2)
90.00
3
˚
V (A )
1982.4(1)
4
1.618
6220(21)
4
1.458
1692.1(8)
4
1.599
4648.7(2)
4
1.472
Z
Dcalc (g/cmꢀ3
T (K)
F(000)
)
1.467
296.1
2072
296.1
1000
296.1
296.1
828
296.1
2116
2840.0
0.40 · 0 · .15 · 0.05
0.687
Crystal size (mm)
Absorption coefficient (mmꢀ1
Unique reflections
R (F2 > 2r(F2))
0.40 · 0.10 · 0.05
0.797
7981
0.30 · 0.30 · 0.15
1.039
3544
0.30 · 0.20 · 0.10
1.470
3101
0.10 · 0.10 · 0.10
1.103
2837
)
2352
0.0460
0.1370
0.920
0.0420
0.1310
1.112
0.0900
0.2680
0.814
0.0310
0.0890
1.064
0.0570
0.1520
0.860
wR (F2)
Goodness-of-fit
Number of variables
1234
282
873
228
623

3410
Y. Wang, N. Okabe / Inorganica Chimica Acta 358 (2005) 3407–3416
Table 2
Table 3
˚
˚
Selected bond distances (A) and angles (ꢁ) for complex [Co(bpa)(p-
HB)2] (1)
Selected bond distances (A) and angles (ꢁ) for complex [Ni(bpa)(ꢀp-
HB)(H2O)] (2) and complex ½NiðbpaÞ ðp-HBÞꢁ 2þðNO3Þꢀðp-HBÞ ꢂ
2
2
5H2O ð3Þ
Bond distances
Co1–O11
Co1–O12
Co1–O14
Co1–O15
Co1–N11
Co1–N12
Co2–O21
Co2–O22
Co2–O24
Co2–O25
Co2–N21
Co2–N22
Co3–O31
Co3–O32
Co3–O34
Co3–O35
Co3–N31
Co3–N32
Co4–O41
Co4–O42
Co4–O44
Co4–O45
Co4–N41
Co4–N42
2.164(2)
2.138(3)
2.282(3)
2.101(3)
2.047(3)
2.067(3)
2.113(3)
2.177(2)
2.076(2)
2.303(3)
2.051(3)
2.058(3)
2.059(3)
2.028(3)
2.062(2)
2.279(3)
2.041(3)
2.028(3)
2.230(3)
2.062(2)
2.127(2)
2.257(3)
2.058(3)
2.058(3)
Complex 2
Bond distance
Ni1–O1
2.099(1)
2.142(2)
2.089(1)
2.117(1)
2.010(2)
2.012(2)
Ni1–O2
Ni1–O3
Ni1–O4
Ni1–N1
Ni1–N2
Bond angles
O1–Ni1–O2
O1–Ni1–O3
O1–Ni1–O4
O1–Ni1–N2
N1–Ni1–O2
N1–Ni1–O3
N1–Ni1–O4
N1–Ni1–N2
61.89(6)
93.09(5)
88.70(5)
165.86(7)
162.66(6)
91.05(6)
89.87(6)
92.93(7)
Hydrogen bonds
N3–H1ꢂ ꢂ ꢂO7*
O6–H61ꢂ ꢂ ꢂO5**
O6–H62ꢂ ꢂ ꢂO7
O5–H51ꢂ ꢂ ꢂO9i
O4–H41ꢂ ꢂ ꢂO1ii
O4–H42ꢂ ꢂ ꢂO8
O3–H31ꢂ ꢂ ꢂO2#
O3–H32ꢂ ꢂ ꢂO6##
D–H
0.86
0.82
0.82
0.82
0.82
0.82
0.82
0.82
Dꢂ ꢂ ꢂA
D–Hꢂ ꢂ ꢂA
162
157
2.950(2)
2.910(4)
2.898(3)
2.720(4)
2.815(2)
2.835(3)
2.850(1)
2.687(3)
150
170
169
159
177
161
Bond angles
O12–Co1–O15
O11–Co1–O15
O15–Co1–N12
N11–Co1–N12
O22–Co2–O24
O21–Co2–O24
O24-Co2–N21
N21–Co2–N22
O12–Co1–O15
O32–Co3–O35
O31–Co3–O35
O35–Co3–N32
N31–Co3–N32
O42–Co4–O44
O42–Co4–O45
O45–Co4–N41
N41–Co4–N42
O32–Co3–O35
160.16(9)
101.6(1)
91.3(1)
Complex 3
Bond distance
Ni1–O11
Ni1–O12
Ni1–N11
Ni1–N12
Ni1–N14
Ni1–N15
Ni2–O21
Ni2–O222
Ni2–N21
Ni2–N22
Ni2–N24
Ni12–N25
92.7(1)
2.143(5)
2.121(6)
2.069(7)
2.047(7)
2.049(7)
2.039(5)
2.150(5)
2.115(6)
2.050(7)
2.081(7)
2.037(6)
2.086(8)
156.4(1)
97.8(1)
92.0(1)
91.8(1)
160.16(9)
120.1(1)
164.28(8)
89.5(1)
92.6(1)
158.4(1)
102.4(1)
102.5(1)
91.3(1)
Bond angles
120.1(1)
O11–Ni1–O12
N11–Ni1–N15
N12–Ni1–O11
N12–Ni1–N15
N14–Ni1–O11
O11–Ni1–O12
N11–Ni1–N15
N12–Ni1–O11
N12–Ni1–N15
N14–Ni1–O11
61.8(2)
98.8(2)
86.4(2)
100.3(2)
90.3(2)
61.8(2)
98.8(2)
86.4(2)
100.3(2)
90.3(2)
Hydrogen bonds
N13–H1ꢂ ꢂ ꢂO12*
N23–H4ꢂ ꢂ ꢂO42
N33–H7ꢂ ꢂ ꢂO35**
N43–H10ꢂ ꢂ ꢂO22
O13–H2ꢂ ꢂ ꢂO25i
O23–H5ꢂ ꢂ ꢂO14ii
O33–H8ꢂ ꢂ ꢂO44i
O43–H11ꢂ ꢂ ꢂO32
O16–H3ꢂ ꢂ ꢂO24
O26–H6ꢂ ꢂ ꢂO15#
O36–H9ꢂ ꢂ ꢂO45
O46–H16ꢂ ꢂ ꢂO31##
D–H
0.86
0.86
0.86
0.86
0.82
0.82
0.82
0.82
0.82
0.82
0.82
0.82
Dꢂ ꢂ ꢂA
D–Hꢂ ꢂ ꢂA
159
161
2.784(4)
2.814(4)
2.774(4)
2.838(4)
2.670(4)
2.662(4)
2.709(4)
2.669(4)
2.723(4)
2.710(3)
2.678(4)
2.758(4)
164
158
141
176
160
174
Hydrogen bonds
N13–H1ꢂ ꢂ ꢂO43*
N23–H4ꢂ ꢂ ꢂO2
D–H
0.86
0.86
0.86
0.86
0.82
0.82
Dꢂ ꢂ ꢂA
D–Hꢂ ꢂ ꢂA
160
145
142
162
2.993(12)
2.941(2)
2.956(8)
2.89(1)
167
173
N16–H16ꢂ ꢂ ꢂO1**
N26–H26ꢂ ꢂ ꢂO5i
O3–H31ꢂ ꢂ ꢂO8**
O13–H131ꢂ ꢂ ꢂO4##
154
169
2.74(1)
2.676(9)
109
162
Symmetry code: *: 1;ꢀ x, ꢀy, ꢀz, **: 2 ꢀ x, ꢀy, 1 ꢀ z; i: x, ꢀ1 + y, z;
ii: x, 1 + y, z; #: 1 + x, y, z; ##: ꢀ1 + x, 1 + y, z.

Y. Wang, N. Okabe / Inorganica Chimica Acta 358 (2005) 3407–3416
3411
Table 3 (continued)
Table 5
˚
Selected bond distances (A) and angles (ꢁ) for complex [Zn(bpa)(p-
HB)2]2 Æ 0.5H2O (5)
Complex 3
O23–H231ꢂ ꢂ ꢂO13
O4–H42ꢂ ꢂ ꢂO2**
O5–H51ꢂ ꢂ ꢂO43ii
O5–H52ꢂ ꢂ ꢂO23
O6–H61ꢂ ꢂ ꢂO1
O6–H62ꢂ ꢂ ꢂO7
O7–H71ꢂ ꢂ ꢂO21
O7–H72ꢂ ꢂ ꢂO3#
O8–H81ꢂ ꢂ ꢂO6
O8–H82ꢂ ꢂ ꢂO12#
0.82
0.97
0.98
0.98
0.98
0.98
0.97
0.96
0.96
0.98
2.697(8)
2.93(1)
2.94(1)
2.80(1)
2.73(1)
2.55(1)
2.702(9)
2.68(1)
2.72(1)
2.70(1)
157
113
130
122
176
108
154
126
116
115
Bond distances
Zn1–O111
Zn1–O112
Zn1–O121
Zn1–O122
Zn1–N11
Zn1–N12
Zn2–O211
Zn2–O212
Zn2–O221
Zn2–O222
Zn2–N21
Zn2–N22
1.978(3)
2.565(3)
2.071(3)
2.384(4)
2.044(4)
2.024(4)
2.477(4)
2.057(3)
2.222(3)
2.096(3)
2.051(4)
2.040(4)
Symmetry code for complex 2: *: x, 1/2 ꢀ y, 1/2 + z; **: 2 ꢀ x, 1/2 + y,
1/2 ꢀ z; i: x, ꢀ1/2 ꢀ y, 1/2 + z; ii: 1 ꢀ x, ꢀy, 1 ꢀ z; #: 2 ꢀ x, ꢀy, 1 ꢀ z;
##: 2 ꢀ x, ꢀy, 1ꢀz.
Symmetry code for complex 3: *: x, 1/2 ꢀ y, 1/2 + z; **: 1 ꢀ x, 1/2 + y,
1/2 ꢀ z; i: 2 ꢀ x, ꢀ1/2 + y, 1/2 ꢀ z; ii: 2 ꢀ x, 1/2 + y, 1/2 ꢀ z; #: 1 ꢀ x,
ꢀ1/2 + y, 1/2 ꢀ z; ##: x, 3/2 ꢀ y, 1/2 + z; $: x, 3/2 ꢀ y, ꢀ1/2 + z.
Bond angles
O111–Zn1–O121
O111–Zn1–N11
O111–Zn1–N12
O121–Zn1–N11
O121–Zn1–N12
N11–Zn1–N12
O212–Zn2–O222
O212–Zn2–N22
O222–Zn2–N21
O212–Zn2–N21
O222–Zn2–N22
N21–Zn2–N22
106.8(1)
100.9(1)
140.4(1)
92.2(1)
109.5(1)
93.0(2)
Table 4
˚
˚
Selected bond distances (A) and angles (A) for complex [Cu(bpa)(p-
HB)Cl] (4)
102.4(1)
102.4(1)
100.4(1)
94.4(2)
Bond distances
Cu1–Cl1
Cu1–O1
Cu1–O3
Cu1–N1
Cu1–N2
2.5876(7)
2.008(2)
2.024(2)
1.959(2)
1.953(2)
151.4(1)
91.7(2)
Hydrogen bonds
D–H
0.82
0.82
0.82
0.80
0.80
0.80
0.86
0.86
Dꢂ ꢂ ꢂA
D–Hꢂ ꢂ ꢂA
166
159
O113–H1ꢂ ꢂ ꢂO122*
O123–H2ꢂ ꢂ ꢂO212**
O213–H3ꢂ ꢂ ꢂO121i
O3–H31ꢂ ꢂ ꢂO223ii
O3–H31ꢂ ꢂ ꢂO223#
O3–H32ꢂ ꢂ ꢂO211
2.674(5)
2.710(5)
2.738(5)
2.755(5)
2.755(5)
2.627(4)
2.791(6)
2.793(6)
Bond angles
Cl1–Cu1–O1
Cl1–Cu1–O3
Cl1–Cu1–N1
Cl1–Cu1–N2
O3–Cu1–O1
O1–Cu1–N1
O1–Cu1–N2
O3–Cu1–N1
O3–Cu1–N2
N1–Cu1–N2
99.51(6)
100.23(7)
94.91(7)
93.27(7)
65.22(9)
98.22(9)
160.93(9)
159.10(9)
98.71(9)
94.7(1)
171
121
121
154
N13–H131ꢂ ꢂ ꢂO221##
N23–H231ꢂ ꢂ ꢂO112$
157
165
Symmetry code: *: 1 ꢀ x, y, 1/2 ꢀ z; **: x, ꢀy, ꢀ1/2 + z; i: x, 1 ꢀ y,
1/2 + z; ii: ꢀx, ꢀy, ꢀz; #: x, ꢀy, 1/2 + z; ##: x, 1 + y, z; $: x, ꢀ1 + y, z.
Hydrogen bonds
C8–H8ꢂ ꢂ ꢂCl1*
D–H
0.93
0.82
0.86
Dꢂ ꢂ ꢂA
D–Hꢂ ꢂ ꢂA
129
172
bpa, the neighboring molecules are linked to three-
dimensional extensions. The selected bond distances
and angles including H-bonds data are listed in Table 2.
3.525(3)
3.069(2)
3.180(3)
O2–H21ꢂ ꢂ ꢂCl1**
N3–H31ꢂ ꢂ ꢂCl1#
154
Symmetry code: *: 1 ꢀ x, ꢀ1/2 + y, 3/2 ꢀ z; **: 1 + x, ꢀ1 + y,z; #:
ꢀ1 + x, y, z.
3.1.2. Complex 2
The structure of complex 2 consists of discrete [Ni(p-
HB)(bpa)(H2O)2]+ cation unit and one nitrate anion and
one free water molecule. The Ni(II) atom is bonded to
two carboxylato O atoms from p-HB ligand, two aqua
O atoms and two N atoms from bpa ligand (Fig.
2(a)). The coordination geometry around central Ni
atom is a slightly distorted octahedron. The bite angle
of N2–Ni1–N1, 92.93(7)ꢁ is wider than that of
O2–Ni1–O1, 61.89(6)ꢁ and Ni1–O4 distance is slightly
longer than Ni1–O3 in axial direction. The maximum
deviation of Ni atom from the mean plane passing
through the equatorial plane constructed by the O1,
Two bidentate p-HB molecules are lying on the reverse
side of the equatorial square plane, with the mean inter-
plane angle of two benzene rings being 84.9(1)ꢁ. As
shown in packing view of Fig. 1(b), by this ligand
arrangement, the whole complex molecules are easily
to avoid the steric hindrance to intersect with each
other. In the packing, bpa plane of Co2 unit stacks to
that of Co4 unit with the strong p–p interaction as indi-
˚
cated by the interplane distance of 3.546(4) A. More-
over, with the participation of the H-bonding network
provided by phenol O atom and the amine group of
˚
O2, N1 and N2 is only 0.0202(9) A. The coordination

3412
Y. Wang, N. Okabe / Inorganica Chimica Acta 358 (2005) 3407–3416
Fig. 1. (a) ORTEP II drawing of Co1 unit of complex 1, showing 50% probability displacement ellipsoids. (b) A view of packing pattern in complex
1, including H-bond network indicated by thin dashed lines. The p–p interaction is shown by double arrow line.
Fig. 2. (a) ORTEP II drawing of complex 2, showing 50% probability displacement ellipsoids. (b) A view of packing pattern in complex 2, including
H-bond networks indicated by thin dashed lines. The p–p interaction is shown by double arrow line.
mode around Ni(II) center is very resembled with that of
[Ni(HL)(bpa)(H2O)2]H2O (where HL is the deproto-
nated form of orotic acid) [7].
tion bridged by nitrate O atoms. Besides these bifur-
cated H-bonding networks, the paralleling sheet with
cooperative p–p interaction between bpa and p-HB is
formed along a-axis (Fig. 2(b)). In the p–p interaction,
each individual ring of one bpa stacks to the adjacent
p-HB planes in the upper (1 ꢀ x, ꢀy, 1 ꢀ z) and in the
below (2 ꢀ x, ꢀy, 1 ꢀ z), with the interplane distances
All aromatic planes, as well as the octahedron equa-
torial plane are almost coplanar with the interplane an-
gles between the mean bpa plane and the C11/C16
benzene plane and the O1/O2/N1/N2 equatorial plane
being 7.8(1)ꢁ and 7.1(8)ꢁ, respectively. Moreover, the
dihedral angle of the two pyridine rings of bpa ligand
is 9.4(1)ꢁ.
˚
of 3.332(9) and 3.487(3) A, respectively.
3.1.3. Complex 3
Crystal packing shown in Fig. 2(b) is governed by a
three-dimensional H-bond networks which distances
˚
are in the range of 2.687(3)–2.950(2) A. The two bonded
Complex 3 has two NiN4O2 cation unit, one nitrate
ion, one deprotonated p-HB anion and five free water
molecules. In each inner coordination sphere, Ni(II)
atom is bonded to four N atoms from two bidentate
bpa ligands and two carboxylato O atoms from one p-
HB ligand. The geometry around each Ni1(II) center
(Fig. 3(a)) is essential octahedron with Ni1(II) atom
slightly deviated from the equatorial plane consisting
water molecules act as donors to the corresponding
carboxylato O atom as well as the phenol O atom and
form H-bond chain along a-axis direction. While the sol-
vated water molecule acts as a donor and an acceptor to
link the complex molecules along c-axis direction in the
H-bond networks. Furthermore, the amine group of bpa
is included in the H-bond network through N–Hꢂ ꢂ ꢂO
(nitrate) and the crystal structure is extending to b-direc-
˚
of O11, O12, N11, N15 atoms by 0.006(3) A, while
N12 and N14 atoms completing the octahedron from
the axial direction with the short Ni–N distance. The

Y. Wang, N. Okabe / Inorganica Chimica Acta 358 (2005) 3407–3416
3413
Fig. 3. (a) ORTEP II drawing of the inner coordination sphere of complex 3, showing 50% probability displacement ellipsoids. (b) A view of
complete structure of complex 3, including the nitrate anion and water molecules in the lattice. Thin dashed lines indicate some of H-bonds.
coordination mode of Ni2 moiety is almost the same
with that of Ni1 unit.
As a result of more than one coordinated bpa mol-
ecules in 3, the bpa molecule is somewhat deviated
from the coplanar conformation, indicated by the
mean dihedral angle between the individual pyridine
rings of is 25.6(4)ꢁ. The compatible fact is Ni–N bond
lengths in 3 are much longer than those observed in 2.
These can be considered as the consequent arrange-
ment to minimize the steric hindrance between the
two bulky bpa molecules around each metal center.
Among the structures in this study, 3 is the only
one example in which coordination sphere involves
two bpa ligands.
One free deprotonated p-HB anion also exists in the
lattice to neutralize the whole complex, together with
one nitrate anion. In Fig. 3(b), the complete unit struc-
ture of 3 is shown in the unit cell. The three dimen-
sional H-bonding networks (Table 3) participate in
the stabilization of the whole crystal structure. Some
of them are shown with thin dashed lines in Fig.
Fig. 4. (a) ORTEP II drawing of complex 4, showing 50% probability
displacement ellipsoids. (b) A view of packing pattern in complex 4,
including H-bond networks indicated by thin lines.
3(b). No p–p interaction is observed in the packing be-
cause of the large coordination sphere and tilted bpa
conformation.
˚
3.1.4. Complex 4
Cu atom lies 0.230(1) A above this plane towards the
apical Cl atom, giving the identical N1–Cu–O3 angle
of 159.10(9)ꢁ and N2–Cu–O1 angle of 160.93(9)ꢁ. Two
N atoms of bpa bond to Cu(II) atom with Cu–N dis-
The complex 4 possesses five-coordinated environ-
ment with CuN2O2Cl (Fig. 4(a)). Each of the Cu(II)
atom is coordinated by two N atoms from one bpa
and two O atoms from one bidentate p-HB ligand and
one chloride anion with a weak Cu–Cl apex bond
˚
tance of 1.959(2) and 1.953(2) A and a bite angle of
94.7(1)ꢁ, which is in the range normally observed for
the Cu(II) bpa complexes [15,29]. The Cu–Cl distance
˚
(Cu–Cl: 2.5876(6) A). The molecular structures of pen-
˚
(2.5876(6) A) is intermediate between the known values
˚
from 2.336(2) to 2.733(2) A [30,31].
In the crystal packing (Fig. 4(b)), the molecules are
cross-linked to each other through H-bonds of C8–
H8ꢂ ꢂ ꢂCl1(1 ꢀ x, ꢀ1/2 + y, 3/2 ꢀ z), N3–H31ꢂ ꢂ ꢂCl1
(ꢀ1 + x, y, z) and O2–H21ꢂ ꢂ ꢂCl1(1 + x, ꢀ1 + y, z). No
p–p interaction is observed in the packing.
ta-coordinated copper (II) complexes show a trigonal-
bipyramidal or a square-pyramidal geometry. The bond
distances and the angles around the Cu(II) center shown
in Table 4 indicate that the coordination geometry of 4
is a slightly distorted square pyramidal.
The ligand atoms which are involved in the coordina-
tion (N1, N2, O1 and O3) are nearly coplanar, and the

3414
Y. Wang, N. Okabe / Inorganica Chimica Acta 358 (2005) 3407–3416
3.1.5. Complex 5
The weak interactions are shown with bold dashed
lines in Fig. 5(a) to be distinguished from the others.
The similar weak Zn–O interactions were reported in
[(g-TpPh) Zn (anthranilate)] (TpPh = Hydrotris (3-
phenylpyrazol-1-yl) borate) [33]. The Zn–N distances
Complex 5 contains two crystallographically inde-
pendent [Zn(C7H5O3)2(C10H9N3)] molecules. A view of
the structure is given in Fig. 5(a). The bond lengths
and angles in both molecules differ only slightly and they
are summarized in Table 5.
˚
are in the range 2.024(4) to 2.051(4) A.
In each ZnN2O4 core unit, Zn(II) atom is octahe-
drally coordinated by two bidentate p-HB molecules
and one bpa molecule. The octahedron around the zinc
center is highly distorted due to the presence of a kind of
relatively weak Zn–O interaction, such as Zn1–O112,
Zn1–O122 and Zn2–O211 with the distance of
In each independent molecule, a similar coordination
mode is observed. Three carboxylato O atoms and one
N atom of bpa occupy the equatorial plane and the
fourth carboxylato O atom and another N atom are lo-
cated at the apical direction. Zn1 and Zn2 each deviates
from the deformed equatorial plane by 0.196(2) and
˚
˚
2.566(3), 2.382(4) and 2.475(4) A, respectively. These
values are much shorter than the distance of the uncoor-
dinated O atoms from the Zn atom (2.847(1)–2.946(1)
0.170(2) A, respectively. Two pyridine rings of each
bpa adopt almost coplanar conformation with the dihe-
dral angle of 2.9(2)ꢁ for Zn1 moiety and 10.1(2)ꢁ for Zn2
moiety. In each case, two benzene ring planes of two
coordinated p-HB molecules are dispersed around Zn
center with the interplane angle of 84.5(1)ꢁ in Zn1 moi-
ety and 75.8(1)ꢁ in Zn2 moiety. This arrangement of li-
gands is facile to avoid the steric encumbrance to allow
the neighboring unit intersecting with each other, leav-
ing the p-HB molecules lying on the reverse side and
face-to face stacking of bpa molecules. As shown in
Fig. 5(b), there is strong-interaction between the bpa
pyridine ring of Zn1 moiety and the related one of
Zn2 moiety at (x, 1 + y, z) with the interplane distance
˚
A) [32] but longer than the normal Zn–O coordination
˚
distances ranging from 1.978(3) to 2.222(3) A.
˚
of 3.399(5) A. A weak C@Cꢂ ꢂ ꢂp interaction exist be-
tween C125@C126 edge of p-HB and C221–C226 plane
˚
of p-HB with the edge-to plane distance of 4.210(7) A
and between C212@C213 edge and C111–C116 plane
˚
with 4.268(7) A [34].
The overall structure is also stabilized by the N–
Hꢂ ꢂ ꢂO and O–Hꢂ ꢂ ꢂO hydrogen bond networks which
is indicated by the thin dashed lines in Fig. 5(b).
Except Cu(II) complex, all the other ternary com-
plexes exhibit a distorted octahedral geometry. Both
the Zn(II) and Co(II) complexes have the similar neutral
M(II)N2O4 core unit, while Ni(II) complexes show
either [NiO4]+ or [NiN4O2]+cation core. It can be ex-
plained with the rather variable coordination chemistry
of the d10-Zn(II) ion, in that there is no strong energetic
preference for any coordination polyhedron because of
the filled d-orbital. The inner coordination sphere of
Co(II) complex is quite similar with that of Zn(II).
With the tilted angle of the two pyridine rings of bpa
ligand in the range of 2.9(2)–14.6(1)ꢁ except complex 3,
the preferential conformation of bpa ligand is thought
to be nearly coplanar. In all compounds, the mean coor-
dination bond lengths of M(II)–N (pyridine nitrogen)
and M(II)–O (carboxylato) are arranging in following
˚
order: Co(II) complex (1) [Co–N = 2.051(3) A and
˚
Co–O = 2.154(3) A] > Ni(II) complex (2) [Ni–
˚
N = 2.011(2) A and Ni-O = 2.120(2) A] < Zn(II) com-
˚
Fig. 5. (a) ORTEP II drawing of complex 5, showing 50% probability
displacement ellipsoids. (b) A view of packing pattern in complex 5,
including H-bond networks indicated by thin dashed lines. The p–p
interaction is shown with double arrow line.
˚
˚
plex (5) [Zn–N = 2.039(4) A and Zn–O = 2.231(3) A].
The reverse of this order coincides well with the
Irving–William [35] series which indicates the general

Y. Wang, N. Okabe / Inorganica Chimica Acta 358 (2005) 3407–3416
3415
100
stability sequence of octahedral metal complexes as
being in the order Co< Ni > Zn. In this case, Cu(II)
complex is excluded from the comparison for its differ-
ent penta-coordination mode. The other Ni(II) complex
(3) is also out of the discussion for its unique two coor-
dinated bpa ligands.
3.2. DNA binding studies
50
3.2.1. DNA binding experiment
The binding of the complexes to the calf thymus (CT)
DNA has been studied by fluorescence method. Com-
petitive binding studies have been made by measuring
the emission of ethidium bromide (EB) bound to
DNA which shows the enhanced emission intensity
due to its intercalative binding to DNA [36,37]. The
competitive binding of the complexes to the DNA re-
duces the emission intensity of EB with either a displace-
ment of the bound EB from the bound to the free state
or the bound complex quenching the emission with a
reduction of the emission intensity due to fluorescence
quenching of free EB [5,38].
The concentration of the DNA, used for binding
experiments was determined by measuring the absorp-
tion intensity at 260 nm with the molar extinction coef-
ficient value of 6600 Mꢀ1 cmꢀ1 in Tris–HCl/NaCl buffer
(pH 7.4) [39]. In a typical binding experiment, a 2 L
solution of 1.45 mM ethidium bromide (EB) was added
to a volume of 300 lL of 100 lM DNA solution. All the
fluorescence measurements were taken at kex of 545 nm
and kem of 560 nm. Aliquot of 12 mM solution of the
complexes in DMSO were added to the EB-DNA solu-
tion and the fluorescence intensity had been measured
after each addition. The fluorescence intensities were
plotted against the complex concentration to get a slope
that gave the relative extent of binding of the complexes
to DNA. A control experiment was also done with the
EB in the absence of DNA.
0
0
20
40
60
80
100
120
Concentration of complexes, µM
Fig. 6. The emission intensity of 100 M calf thymus DNA-bonded
ethidium bromide (10 M) at different complex concentrations in 50
mM Tris–HCl buffer (pH 7.4) at 25 ꢁC on addition of complex 1 (m),
complex 2 (j), complex 3 (r), complex 4 ( ), complex 5 (·).The
*
emission intensities of the ethidium bromide in the absence of CT
DNA but at various concentrations of complex 3 are also shown (d).
plex 2 which has a similar square-planar structure with
4 has a second highest propensity to DNA binding. This
may be explained as a role of the metal bound water
molecules in 2. The aqua complex is considered to bind
readily to DNA, because the water ligand is a good leav-
ing group [40]. Hence, the positively charged complex 2
may more easily bind to the negatively charged phoph-
odiester backbone of DNA. At the binding site, an
aquahydroxymetal complex may be produced as an
intermediate [41], because metal must be a strong Lewis
acid in order to generate the hydroxide nucleophile [42].
In the case of the neutral Cu(II) complex 4 with the
weak binding ability, the coordinated chloride anion
may be more difficult to leave as compared to aqua
group, although the antitumor cis-dichloro complexes
of platinum can be activated and bind to DNA by loss
of chloride ion in intracellular conditions [43]. The pos-
itively charged Ni(II) complex 3 shows the highest DNA
binding ability in spite of its largely titled bpa conforma-
tion and nonplanar geometry. Combining its structure
with the DNA binding result, its binding mechanism
may be explained not by intercalation but rather by
binding to the DNA groove. It may be reasonable to
consider that the other two neutral complex 1 and 5
have the similar binding ability according to their resem-
bled structures. In this DNA binding study, the binding
ability of each complex to DNA has been evaluated
from the competitive inhibition of ethidium binding to
DNA, although the exact binding sites on DNA or the
precise binding modes such as the intercalation binding
or DNA groove binding are still not clear.
3.2.2. DNA binding results
Fig. 6 shows the decreasing propensity in the emis-
sion intensity of the EB on addition of the complexes
into the DNA solution. It is apparent from the plot
shown Fig. 6 that EB bound DNA was efficiently
quenched by complex 3, in which displacement process
of complex occurred. Deducing from the slope of the
quenching plot with the complex concentration, the
DNA binding propensity can be reflected as the relative
order: [Ni(p-HB)(bpa)2] (3) > [Ni(p-HB)(bpa)(H2O)2]
(2) > [Co(p-HB)2(bpa)] (1) > [Zn(p-HB)2(bpa)] Æ 0.5H2O
(5) > [Cu(p-HB)(bpa)Cl] (4).
These observations suggest that the complex com-
petes with the intercalative EB binding to DNA in a dif-
ferent degree. The Cu(II) complex 4 exhibits the weakest
DNA binding ability, although it has a relatively square-
planar base structure. On the other hand, Ni(II) com-

3416
Y. Wang, N. Okabe / Inorganica Chimica Acta 358 (2005) 3407–3416
[15] S. Youngme, C. Chailuecha, G.A. Albada, C. Pakawatchai, N.
4. Supplementary material
Chaichit, J. Reedijk, Inorg. Chim. Acta 357 (2004) 2532.
[16] M. Ishaq, A.O. Baghlaf, A. Al-Mouty, M. Al-Dousry, J. Chem.
Soc. Pakistan 14 (1992) 115.
Crystallographic data for the structural analysis has
been deposited with the Cambridge Crystallographic
Data Centre, CCDC 264444 for complex 1, CCDC
264445 for complex 2, CCDC 264446 for complex 3,
CCDC 260812 for complex 4 and CCDC 256475 for
complex 5, respectively. Copies of this information
may be obtained free of charge from The Director,
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK,
fax: +44 1223 336 033, e-mail: deposit@ccdc.cam.ac.uk
or on the web www: http://www.ccdc.cam.ac.uk.
[17] J.Y. Xu, H.D. Bian, Q.L. Wang, W. Gu, S.D. Yan, D.Z. Liao, P.
Cheng, Z.H. Jiang, P.W. Shen, Z. Anorg. Allg. Chem. 629 (2003)
1063.
[18] J. Rogan, D. Poleti, L. Karanovic, G. Bogdanovic, B.A. Spasoj-
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[19] M.L. Tong, H.J. Chen, X.M. Chen, Inorg. Chem. 39 (2000) 2235.
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Acknowledgment
We thank Dr. Odoko M. of Kinki University for
technical assistance.
[26] CRYSTAL STRUCTURE Analysis Package, Rigaku and Rigaku/MSC
(2000–2004), 9009 New Trails Dr. The Woodlands, TX 77381,
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