Synthesis, structure, and antibacterial properties of ternary rare-earth complexes with o-methylbenzoic Acid and 1,10-phenanthroline1

Article abstract of DOI:10.1134/S1070328409070124

Ternary rare-earth complexes with o-methylbenzoic acid (o-MBA) and 1,10-phenanthroline (Phen) Ln₂(o-MBA)₆(Phen)₂ ? nH₂O(n = 0, 1) (Ln = La, Pr, Y, Yb) were synthesized and characterized by elemental analysis, IR

Full text of DOI:10.1134/S1070328409070124

ISSN 1070-3284, Russian Journal of Coordination Chemistry, 2009, Vol. 35, No. 7, pp. 541–546. © Pleiades Publishing, Ltd., 2009.
Synthesis, Structure, and Antibacterial Properties
of Ternary Rare-Earth Complexes with o-Methylbenzoic Acid
and 1,10-Phenanthroline1
Z. M. Chena, S. P. Wanga, N. Yangc, N. Zhaoa, J. J. Zhangb, R. F. Wanga*, and B. H. Zhaoc
a College of Chemistry & Material Science, Hebei Normal University, Shijiazhuang, 050016 P. R. China
b Experimental Center, Hebei Normal University, Shijiazhuang, 050016 P. R. China
c College of Life Science, Hebei Normal University, Shijiazhuang, 050016 P. R. China
*E-mail: wruifen@mail.hebtu.edu.cn
Received October 14, 2008
Abstract—Ternary rare-earth complexes with o-methylbenzoic acid (o-MBA) and 1,10-phenanthroline (Phen)
Ln2(o-MBA)6(Phen)2 · nH2O (n = 0 , 1) (Ln = La, Pr, Y, Yb) were synthesized and characterized by elemental anal-
ysis, IR, X-ray diffraction, and TG-DTG means. The complex La2(o-MBA)6 (Phen)2 · H2O (I) is composed of two
species of binuclear molecules in which the La3+ ion is coordinated with two nitrogen atoms of Phen and seven ox-
ygen atoms of carboxylate groups. The carboxylate groups were bonded to La3+ in three modes: chelating-bidentate,
bridging-bidentate, and chelating-bridging tridentate. The La3+ ion adopted a vigorous distorted monocapped square
antiprism geometry. Complex I belongs to the triclinic crystal system, P1 space group, lattice parameters: a =
13.058(3), b = 12.7584(11), c = 20.773(4) Å, α = 101.18(3)°, β = 93.88(3)°, γ = 115.82(3)°, V = 3283.0(11)Å3, Z = 2,
ρ
calcd = 1.484 mg/m3, Mr = 1467.06, F(000) = 1476, µ = 1.350 mm–1. The structure was refined to Rl = 0.0631 and
wR2 = 0.1504. The antibacterial activity test indicates that these complexes exhibit better antibacterial ability against
Escherichia coli and Staphylococcus aureus than the corresponding rare–earth chloride or o-MBA.
DOI: 10.1134/S1070328409070124
1
INTRODUCTION
and 1.10-phenanthroline (Phen), Ln2(o-MBA)6(Phen)2 ·
nH2O (n = 0, 1), were synthesized and characterized,
and their antibacterial activities were investigated in
detail.
It is well known that almost all metals enable to gen-
erate reactive oxygen species, and this property is
mainly used for the treatment of cancer and other dis-
eases. Some rare-earth ions may participate in various
physicochemical processes of living systems. They also
show efficient inhibitory properties for O–2• and OH• [1,
2]. So, they exhibit good functions as antibacterial and
antiphlogistic compounds [3–5].
EXPERIMENTAL
Ln2O3 (Ln = La, Pr,Y,Yb), (o-MBA), and Phen were
purchased. All reagents were analytical grade and used
without further purification. LnCl3 · 6H2O were pre-
pared by reacting their oxides in hydrochloric acid, and
then the solutions were dried by water-bath heating.
In the last decades, research of rare-earth organic
materials has been a very attractive subject due to their
peculiar properties and wide potential applications as
luminescence probes in biological systems and active
centers for luminescent materials or electroluminescent
devices [6–8]. In particular, their peculiar functions in
life science and clinical medicine have attracted peo-
ple’s great interests [9–11]. For instance, they can be
used as diagnostic imaging agents, antibacterial and
antiphlogistic agents, etc [4, 5, 12]. In this paper, a
series of complexes containing Ln3+ (Ln = La (I), Pr
(II), Y (III), Yb (IV)), o-methylbenzoic acid (o-MBA)
The contents of C, H, and N in the complexes I−IV
were measured by a Flash EA 1112 elemental analyzer.
The FT-IR spectra were recorded on a FT-IR 1730 spec-
trometer in the 3500–350 cm–1 region, using KBr pel-
lets. The single-crystal was determined on a Bruker
XSCANS P4 diffractometer equipped with a graphite
monochromated MoKα radiation.
The antibaterial activity was tested by the disc diffu-
sion method using the Mueller-Hinton agar medium.
Sterile filter paper discs (5 cm in diameter) were soaked
in 20 µl solutions prepared in sterile DMF. Five concen-
trations of the test compounds, viz., 0.004, 0.006, 0.008,
1
The article is published in the original.
541

542
CHEN et al.
Table 1. Analytical data for the complexes Ln2(o-MBA)6(Phen)2 · nH2O
Contents (found/calcd), %
H
Compound
Empirical formula
C72H60O13N4La2
C36H29O6N2Pr
C36H29O6N2Y
C36H29O6N2Yb
C
N
I
II
III
IV
59.49/58.95
59.51/59.02
64.10/63.73
56.99/56.54
4.15/4.12
4.02/4.32
4.33/4.76
3.85/3.89
3.92/3.82
3.86/3.89
4.15/4.14
3.69/3.71
0.010, and 0.012 mol l–1, were prepared and tested
against Escherichia coli and Staphylococcus aureus. The
bacterial concentration was OD600 = 1. The antibacterial
effects were investigated after 18–24 h of incubation at
37°C. The antibacterial activity was classifed as highly
active (diameter (dia) ≥ 15 mm), moderately active
(dia = 10–15 mm), and slightly active (dia = 5–10 mm).
The diameter less than 5 mm was regarded as inactive
[13].
Synthesis of rare-earth complexes. An ethanol solu-
tion containing o-MBA (6.0 mmol) and Phen
(2.0 mmol) was adjusted to pH 6.0–7.0 with a 1.0 mol l–1
NaOH solution and then was added dropwise to the
stirred aqueous solution of LnCl3 (2.0 mmol), while a
white precipitate formed (Pr(III) complex is light
green). The mixture was stirred for 5 h at room temper-
ature, filtered, and dried. The mother liquor was evapo-
rated at room temperature, and a colorless transparent
crystal suitable for X-ray analysis was obtained from
the mother liquor of La(III).
Table 2. Crystallographic data and details of the experiment
and refinement of structure I
Parameter
Formula weight
Value
1467.06
Triclinic
Crystal system
Space group
P1
Unit cell dimensions:
a, Å
13.058 (3)
12.7584 (11)
20.773 (4)
101.18 (3)
93.88 (3)
115.82 (3)
3283.0 (11)
2
b, Å
c, Å
α, deg
β, deg
γ, deg
V, Å3
Z
All four complexes I−IV were synthesized by this
method. The molecular composition of four complexes
is shown in the Table 1.
X-ray crystallographic determination. A colorless
single crystal of complex I was put on a Bruker
XSCANS P4 diffractometer equipped with a graphite
monochromated MoKα radiation (λ = 0.71073 Å) at
293(2) K by using an ω scans technique. The usual Lp
and empirical absorption corrections were applied by
the SADABS program. The structures were solved by
direct methods with SHELXS-97 [14] and refined
using a full-matrix least-squares procedure on F2 in
SHELXL-97 [15]. Hydrogen atoms were added theo-
retically and refined with riding model position param-
eters and fixed isotropic thermal parameters. The final
R = 0.0631, wR = 0.1504 (R = Σ(||Fo| – |Fc||)/|Fo|, wR =
ρ
calcd, mg/m3
1.484
Absorption coefficient mm–1
1.350
F(000)
1476
Crystal size, mm
0.22 × 0.15 × 0.12
1.68–25.00
θ range for data collection, deg
Index ranges
–15 ≤ h ≤ 15
–11 ≤ k ≤ 16
–24 ≤ l ≤ 18
Reflections collected/unique
Completeness to θ = 28.27°, %
Absorption correction
16755/11552 (Rint = 0.0491)
97.6
(Σw(|Fo|2 – |Fc|2)2/Σw|Fo|2)1/2, w = 1/[σ2(F2o ) +
(0.0295P)2 + 0.6213P], where P = (Fo2 + 2F2c )/3),
Empirical
Max and min transmission
Data/restraints/parameters
Goodness-of-fit on F2
0.850 and 0.784
11277/0/834
S = 1.050, (∆ρ)max = 2.344, (∆ρ)min = –1.454 e Å−3, and
(∆/σ)max = 0.026. Crystallographic data and experi-
mental details for structural analyses are summarized in
Table 2.
Supplementary material has been deposited with the
Cambridge Crystallographic Data Centre (no. 705097;
deposit@ccdc.cam.ac.uk or www:http://www.ccdc.
cam.ac.uk).
1.036
Final R indices (I > 2σ (I))
R indices (all data)
Largest diff. peak and hole, e Å–3
R1 = 0.0631 wR2 = 0.1504
R1 = 0.1075 wR2 = 0.1836
2.344 and –1.454
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 35 No. 7 2009

543
C(31)
C(17)
C(21)
C(22)
C(30)
C(29)
C(28)
C(16)
C(18)
C(32)
C(15)
C(19)
C(23)
C(24)
C(25)
C(4)
C(5)
C(6)
C(20)
N(2)
N(1)
C(69)
C(33)
O(12A)
C(27)
C(26)
C(2)
O(8)
O(7)
La(1)
C(3)
C(1)
O(9)
O(7A)
O(10)
O(11)
C(7)
C(8)
C(68)
C(9)
C(10)
C(14)
C(13)
C(67)
C(11)
C(12)
Fig. 1. ORTEP drawing of the dimeric structure for complex I, La(1).
The TG-DTG curves of the four complexes in a bidentate bridging mode, the other two o-MBA adopt
the tridentate bridging mode. Each Ln3+ ion is coordi-
nated to nine atoms, of which two oxygen atoms O(11),
O(12A) are from the bidentate chelating carboxylate,
two oxygen atoms O(8), O(9) from two bidentate bridg-
ing carboxylates, three oxygen atoms O(7), O(7A),
O(10) from two tridentate bridging chelating carboxy-
lates, and two nitrogen atoms N(1), N(2) from a Phen
static air atmosphere are performed on a Perkin-Elmer
TGA-7 thermogravimetric analyzer from room temper-
ature to 930°C with a heating rate of 10°C min–1.
RESULTS AND DISCUSSION
Compared with the IR spectra of o-MBA and Phen ·
H2O, the characteristic peaks of the ligands have obvi- molecule. The five-membered chelate ring containing
two nitrogen atoms and the Ln3+ ion are coplanar to the
Phen plane. In La(1), the distance between two Ln3+
ions is 4.117 Å, the average La–O bond length is
2.545 Å, the average La–N bond length is 2.733 Å. In
La(2), the distance between two Ln3+ ions is 2.733 Å,
the mean La–O bond length is 2.550 Å, the average La–
N bond length is 2.733 Å, which is equal to that of
La(1). These data indicate that the interaction between
the Ln3+ ions and oxygen atoms in La(1) is stronger
than in La(2), but the interactions between the La3+ ions
and nitrogen atoms are identical in La(1) and La(2).
ousely shifts in all spectra of complexes I−IV. The
characteristic absorption of v(C=O) (1690 cm–1) in
o-MBA disappeared completely while vas (1609–
1639 cm−1) and vs (1400–1410 cm–1) of the carboxyl
group appeared, suggesting that the carboxyl group was
coordinated to Ln3+ ions [16, 17]. In addition, the
absorption band of v(C=N) (1560 cm–1) in Phen shifts to
1518 cm–1 in the spectra of the complexes, exhibiting
the coordination of the two nitrogen atoms with Ln3+
ion [18]. Furthermore, the broad peak around 3447 cm–
1
is ascribed to the stretching vibration of the crystal
water molecule [19]. The peak of 475 cm–1 was
assigned to v(Ln–O), further testifying that the oxygens
of the carboxyl group coordinate to Ln3+ ions [20, 21].
The crystal of complex I contains two independent
dimeric molecules La2(o-MBA)6(Phen)2 · H2O, noted as
La(1) and La(2), respectively. The structure for La(1) is
shown in Fig. 1. Selected bond lengths and angles are
listed in Table 3. La(1) and La(2) are identical in com-
position with similar structures. In each molecule, two
Ln3+ ions are linked by four bridging carboxylate
groups forming a dimer with a crystallographic inver-
The central Ln3+ adopts vigorous distorted mono-
capped square antiprism in both La(1) and La(2)
(Fig. 2). In La(1), the cap position is occupied by N(1)
(the longest bond in the polyhedron of La3+). The four
positions of the upper square are occupied by O(7),
O(9), O(11), N(2), the lower square is formed by O(8),
O(10), O(7A), O(12A). In La(2), the cap position is
occupied by N(4) (the longest bond in polyhedron of
La3+). The four positions of the upper square are occu-
pied by O(2), O(5), O(6), and N(3), and the lower
sion center. Two of the bridging o-MBA adopt the square is formed by O(1), O(3), O(4), and O(6A).
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 35 No. 7 2009

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CHEN et al.
Table 3. Bond lengths and bond angles for complex I*
Bond
d, Å
Bond
d, Å
La(1)–O(11)
La(1)–O(7)
2.446(6)
2.476(5)
2.487(6)
2.558(6)
2.577(6)
2.594(6)
2.689(6)
2.712(8)
2.753(7)
La(2)–O(5)
2.455(6)
2.476(6)
2.489(6)
2.536(6)
2.549(6)
2.610(6)
2.706(7)
2.734(6)
2.760(7)
La(2)–O(4)
La(2)–O(6)
La(2)–O(1)
La(2)–O(2)
La(2)–O(3)
La(2)–N(3)
La(1)–O(12)#1
La(1)–O(9)
La(1)–O(8)
La(1)–O(10)
La(1)–O(7)#1
La(1)–N(2)
La(1)–N(1)
La(2)–O(6)#2
La(2)–N(4)
Angle
ω, deg
Angle
ω, deg
O(11)La(1)O(7)
O(11)La(1)O(12)#1
O(7)La(1)O(12)#1
O(11)La(1)O(9)
O(7)La(1)O(9)
O(12)#1La(1)O(9)
O(11)La(1)O(8)
O(7)La(1)O(8)
O(12)#1La(1)O(8)
O(9)La(1)O(8)
73.9(2)
134.4(2)
74.0(2)
79.8(2)
142.4(2)
141.8(2)
127.4(2)
156.7(2)
92.0(2)
50.0(2)
92.1(3)
122.1(2)
78.5(3)
84.7(2)
71.3(2)
67.7(2)
74.4(2)
73.0(2)
119.3(2)
119.9(2)
48.94(19)
135.9(2)
88.8(2)
74.3(2)
91.9(2)
69.2(2)
130.5(2)
146.2(2)
76.3(2)
74.3(2)
123.7(2)
73.8(2)
99.7(2)
157.0(2)
137.4(2)
59.8(2)
O(5)La(2)O(4)
O(5)La(2)O(6)
O(4)La(2)O(6)
O(5)La(2)O(1)
O(4)La(2)O(1)
O(6)La(2)O(1)
O(5)La(2)O(2)
O(4)La(2)O(2)
O(6)La(2)O(2)
O(1)La(2)O(2)
O(5)La(2)O(3)
O(4)La(2)O(3)
O(6)La(2)O(3)
O(1)La(2)O(3)
O(2)La(2)O(3)
O(5)La(2)N(3)
O(4)La(2)N(3)
O(6)La(2)N(3)
O(1)La(2)N(3)
O(2)La(2)N(3)
O(3)La(2)N(3)
O(5)La(2)O(6)#2
O(4)La(2)O(6)#2
O(6)La(2)O(6)#2
O(1)La(2)O(6)#2
O(2)La(2)O(6)#2
O(3)La(2)O(6)#2
N(3)La(2)O(6)#2
O(5)La(2)N(4)
O(4)La(2)N(4)
O(6)La(2)N(4)
O(1)La(2)N(4)
O(2)La(2)N(4)
O(3)La(2)N(4)
N(3)La(2)N(4)
134.12(18)
73.46(19)
75.38(19)
141.7(2)
73.6(2)
144.7(2)
96.92(19)
125.08(19)
152.3(2)
51.6(2)
72.37(19)
96.7(2)
121.00(18)
79.4(2)
78.42(19)
130.7(2)
77.0(2)
O(11)La(1)O(10)
O(7)La(1)O(10)
O(12)#1La(1)O(10)
O(9)La(1)O(10)
O(8)La(1)O(10)
O(11)La(1)O(7)#1
O(7)La(1)O(7)#1
O(12)#1La(1)O(7)#1
O(9)La(1)O(7)#1
O(8)La(1)O(7)#1
O(10)La(1)O(7)#1
O(11)La(1)N(2)
O(7)La(1)N(2)
83.5(2)
73.4(2)
83.7(2)
152.7(2)
71.39(18)
68.66(19)
75.24(19)
108.15(18)
127.22(19)
48.83(17)
143.1(2)
73.3(2)
131.1(2)
78.4(2)
110.3(2)
73.8(2)
O(12)#1La(1)N(2)
O(9)La(1)N(2)
O(8)La(1)N(2)
O(10)La(1)N(2)
O(7)#1La(1)N(2)
O(11)La(1)N(1)
O(7)La(1)N(1)
O(12)#1La(1)N(1)
O(9)La(1)N(1)
O(8)La(1)N(1)
O(10)La(1)N(1)
O(7)#1La(1)N(1)
N(2)La(1)N(1)
132.2(2)
59.5(2)
140.6(2)
O(6)#2La(2)N(4)
#1
#2
Note: *Symmetry transformations used to generate equivalent atoms: –x, –y + 1, –z + 2; –x + 1, –y + 1, –z + 1.
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 35 No. 7 2009

545
N(1)
O(7)
N(2)
O(11)
O(9)
La(1)
O(12A)
O(8)
O(7A)
O(10)
3+
Fig. 2. Coordination polyhedron of the La ion in complex I, La(1).
These complexes show similar stepwise thermal
decomposition processes (Table 4). The thermal
decomposition process of La2(o-MBA)6(Phen)2 · H2O (I)
can be divided into four steps as follows:
Based on the above thermal decomposition pro-
cesses, the Phen is degraded from the complex firstly,
this can be explained by the fact that the Ln–N bond
lengths are less stable and easy to be broken down by
the crystal data of La3+ [22]. From the data of Table 4,
one can conclude that these complexes exhibit fine sta-
blity to heating.
La2(o-MBA)6(Phen)2 · H2O
La2(o-MBA)6(Phen)2
La2(COO)2
La2(o-MBA)6
La2O3
The antibacterial activity results, expressed as the
diameter of the growth inhibition area in millimeters,
are given in Table 5. One can conclude the following:
(1) rare-earths chloride or o-MBA exhibited poor anti-
microbial activities against E. coli and S. aureus;
(2) Phen and their complexes expressed similar anti-
bacterial activity against E. coli andS. aureus; (3) the
antibacterial activity of these complexes will increase
along with the rise of their concentration in the range of
tested concentrations. The antimicrobial mechanism is
presumably that the compounds have a good lipophilic
nature arising from chelation [23]. The action mode of
antimicrobials may involve different targets in patho-
gens, e.g., interference with cell wall synthesis and
damage to the cytoplasmic membrane, as a result of
which cell permeability may be altered leading to cell
death [24].
The thermal decomposition processes of complexes
II–IV are similar to complex I, which may be
expressed by the following schemes:
Pr(o-MBA)3Phen
Y(o-MBA)3Phen
Yb(o-MBA)3Phen
Pr(o-MBA)3
Y(o-MBA)3
Yb(o-MBA)3
1/6 Pr6O11,
1/2 Y2O3,
1/2 Yb2O3.
Table 4. Decompostion temperature range of the com-
plexes I–IV*
Complex
Tl
Ts
Tm
Tf
I
107–220 263–400 400–568 568–744
II
201–397
156–386
188–400
397–621
386–681
400–596
Thus, ternary rare-earth complexes (Ln = La, Pr, Y,
Yb) with o-methylbenzoic acid and 1,10-Phenanthro-
line have been synthesized and structurally character-
ized. According to the antibacterial testing results,
these complexes expressed active antibacterial activitiy
against E. coli and S. aureus.
III
IV
Note: *l – lost solvent molecular, s – start, m – middle, f – final.
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 35 No. 7 2009

546
CHEN et al.
Table 5. Inhibition zone diameter of the compounds (mm) (Escherichia coli/Staphylococcus aureus)
c × 10–3, mol/l
Compound
4.00
6.00
8.00
10.00
12.00
LaCl3 · 6H2O
7.0/7.0
7.0/5.0
7.0/8.0
7.6/9.2
8.0/8.0
8.7/11.1
8.3/11.3
7.0/9.0
8.0/9.0
9.5/11.8
8.5/6.0
9.0/10.0
9.4/11.9
8.8/11.2
8.8/11.2
6.0/7.0
PrCl3 · 6H2O
YCl3 · 6H2O
7.0/5.0
6.0/8.9
YbCl3 · 6H2O
o-MBA
5.4/10.2
6.0/6.0
7.4/9.9
9.4/9.6
6.0/6.0
6.0/6.0
6.0/6.0
Phen
11.0/14.0
12/8.3
12.5/14.70
13.7/11.0
12.7/10.0
14.6/10.0
15.1/12.2
16.0/18.0
15.0/13.3
15.9/15.5
16.2/12.5
17.60/17.3
17.5/19.0
17.7/15.0
17.5/17.5
17.4/15.9
18.3/19.3
19.0/21.0
19.7/19.0
18.6/19.8
21.0/17.6
20.1/21.6
La2(o-MBA)6(Phen)2 · H2O
Pr(o-MBA)3(Phen)
Y(o-MBA)3(Phen)
Yb(o-MBA)3(Phen)
10.4/6.5
13.2/8.9
13.2/10.2
12. Fan, Y.H., He, X.T., Bi, C.F., et al., Russ. J. Coord. Chem.,
2007, vol. 33. no. 7, p. 535.
ACKNOWLEDGMENTS
This work was supported by National Natural Sci-
ence Foundation of China (no. 20773034), the Natural
13. Ravi, K., Amresh K., Chandrashekar, and Anil Kumar, K. S.,
Phosphorus Sulfur, 2008, vol. 183, p. 1410.
Science
Foundation
of
Hebei
Province
(no. B2007000237), Hebei Education Department
(no. 2006125) and Hebei Normal University
(L2005B17), P. R. China.
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