Adjustment of the structures and biological activities by the ratio of NiL to RE for two sets of Schiff Base complexes [(NiL)nRE] (n = 1 or 2; RE = la or Ce)

Article abstract of DOI:10.1016/j.inoche.2010.12.010

Two sets of 3d-4f complexes [(NiL)_nRE] (n = 1, 2; RE = La and Ce; H₂L = N,N′-bis(3-ethoxysalicylidene)ethylenediamine) were obtained by reacting NiL with RE(NO₃)₃ in the ratios of 1/1 and 2/1, respectively. With

Full text of DOI:10.1016/j.inoche.2010.12.010

Inorganic Chemistry Communications 14 (2011) 396–398
Contents lists available at ScienceDirect
Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
Adjustment of the structures and biological activities by the ratio of NiL to RE for two
sets of Schiff Base complexes [(NiL)nRE] (n=1 or 2; RE=La or Ce)
a
Yan Sui a,b, , Rong-Hua Hu , Dong-Sheng Liu a,b, Qing Wu a
⁎
a
School of Chemistry and Chemical Engineering, The Key Laboratory of Coordination Chemistry of Jiangxi Province, Jinggangshan University, Jiangxi, 343009, PR China
School of Chemistry and Chemical Engineering, Nanjing National Laboratory of Microstructures, Nanjing University, Nanjing 210093, PR China
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Two sets of 3d–4f complexes [(NiL)nRE] (n=1, 2; RE=La and Ce; H2L=N,N′-bis(3-ethoxysalicylidene)
ethylenediamine) were obtained by reacting NiL with RE(NO3)3 in the ratios of 1/1 and 2/1, respectively. With
the NiL/RE ratio changing from 1/1 to 2/1, not only the crystal structures were changed from discrete
dinuclear complexes [(NiL)RE] to sandwich-like trinuclear complexes [(NiL)2RE], but also the biological
activities were greatly influenced. The trinuclear complexes [(NiL)2RE] exhibited higher antimicrobial
activities than the corresponding dinuclear counterpart [(NiL)RE].
Received 28 September 2010
Accepted 10 December 2010
Available online 16 December 2010
Keywords:
Salen-type Schiff base ligand
3d–4f complexes
Crystal structure
© 2010 Elsevier B.V. All rights reserved.
Biological activities
For the past few decades, the biological activities of rare earth
and transition metal complexes containing Schiff base ligands have
been widely studied, but the adjustment of structures and activities is
still a challenging subject [1–4]. Much effort has been devoted to
the design and synthesis of different kinds of Schiff bases and their
metal complexes [5]. Salen-type Schiff base (H2salen=N, N′-bis
(salicylidene) ethylenediamine) is of great interest and importance
for its structural flexibility, special chelating property and easy prep-
aration. Its alkoxy derivatives contain an inner site with N- and O-donor
chelating centers suitable for the linkage to d-block ions. The outer
coordination site with its O-donor atoms is greater than the inner one
and can act as a type of crown ether ligands to incorporate larger ions,
such as rare earth ions [6]. More interestingly, these compartmental
ligands can form not only the classical 3d–4f dinuclear complexes but
also the trinuclear ones between two set of Schiff base oxygen [7]. As far
as 3d–4f complexes were concerned, the main research focus was cen-
tered on their magnetic and electric properties [8], and the antimicrobial
activities had been rarely studied [9].
trinuclear [(NiL)2RE] complexes had higher antimicrobial activities than
the corresponding dinuclear counterpart [(NiL)RE].
N, N′-bis(3-ethoxysalicylidene)ethylenediamine (H2L) was pre-
pared by the 2:1 condensation of 3-ethoxysalicylaldehyde and
ethylenediamine in methanol solution. Both trinuclear complexes
[(NiL)2RE] (1a and 1b) and dinuclear complexes [(NiL)RE] (2a and
2b) could be prepared directly from solutions by controlling the
stoichiometric ratio of NiL/RE to 2/1 and 1/1, respectively. It was
worthy to note that complex 2a could also be obtained from 1a, if
complex 1a was redissolved in the methanol solution containing
lanthanum(III) nitrate hexahydrate and slowly evaporated for several
days. A reverse process from 2a to 1a could also be realized by dis-
solving 2a in the methanol solution containing NiL and after several
days of evaporation. Similar results were found for the transformation
between 1b and 2b. It was not unreasonable to think that these
reversible transformations should be related with the exchange equi-
librium of complexes in solutions [10,11].
Complexes 1a and 1b are isostructure, so only 1a is given and
discussed here (Fig. 1). Complex 1a crystallizes in the space group
P21/n with the lanthanum wrapped up by two NiL entities and two
NO−3 anions to form a sandwich-like structure. Lanthanum is linked
to unusual 12 oxygen atoms, four coming from the phenolato atoms,
four from the ethoxy oxygen atoms and four from NO−3 anions. Three
kinds of La–O bond distances are significantly different in 1a, the
longest being the La–O (ethoxy) separations and the shortest being
the La–O (phenolate). The coordination of two nickel (II) can be
considered as square planar, which is defined by two nitrogen atoms
(N1 and N2) and two oxygen atoms (O1 and O2) from one ligand. The
nickel atom is situated in the mean N2O2 coordination plane. The
separation of Ni1…La1 is 3.532(4) Ǻ which is slightly shorter than
In this paper, N, N′-bis(3-ethoxysalicylidene)ethylenediamine (H2L)
was used to coordinate with nickel and rare earth ions (RE=La and Ce)
to construct 3d–4f heteronuclear complexes (Scheme 1). It was the first
time that trinuclear (NiL)2RE complexes and dinuclear [(NiL)RE]
complexes (RE=La and Ce) could be obtained, respectively, when the
ratios of NiL to RE were 2:1 and 1:1, and their antimicrobial activities
were also greatly influenced with the changes of their structures. The
⁎
Corresponding author. School of Chemistry and Chemical Engineering, The Key
Laboratory of Coordination Chemistry of Jiangxi Province, Jinggangshan University,
Jiangxi, 343009, PR China.
E-mail address: ysui@163.com (Y. Sui).
1387-7003/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2010.12.010

Y. Sui et al. / Inorganic Chemistry Communications 14 (2011) 396–398
397
Scheme 1. Synthesis routine of the complexes.
that of Ni2…La1 (3.564(4) Ǻ). The intramolecular distance of Ni1…
Ni2 is 3.958(3) Ǻ.
The nickel ion adopts a square planar coordination mode. The donor
centers are alternatively above and below the mean N2O2 plane, with
an average deviation from the plane of 0.0841(3) Ǻ, while Ni1 is
0.0062(3) Ǻ above this square plane. The dihedral angles between the
planes O1–Ni1–O2 and O1–La1–O2 are equal to 5.9(2) Ǻ, suggesting
that the bridging group is almost coplanar. The lanthanum(III) center
in 2a has a decacoordination environment of O atoms. In addition to
the two phenolate O atoms, the lanthanum(III) achieves its environ-
ment with two ethoxy oxygen atoms from L and six oxygen atoms
coming from three bidentate nitrato ions. The three kinds of La—O
bond distances are significantly different, the shortest being the La—O
(phenolate) and longest being the La—O (ethoxy) separations (Fig. 2).
The anti-microbial activities of NiL, the trinuclear complexes (1a
and 1b) and dinuclear complexes (2a and 2b) against bacteria (E. coli
and S. aureus) and fungi (CA) were tested and the results were
summarized in Table 1. The results indicated that there was no
obvious activity observed by NiL against S. aureus and CA, except for
the weak inhibition to E. coli, whereas complexes 1a, 2a, 1b and 2b
had an obvious inhibition on the culture of E. coli, S. aureus and CA. The
activities of anti-E. coli and anti-CA of 1a were higher than those of
other complexes, with inhibition zones of 20 mm and 8 mm,
respectively. The anti-S. aureus activity of 1a was similar with that
of 1b, but on the whole, the trinuclear complexes (whether 1a or 1b)
had a better inhibition property than the dinuclear complexes (2a or
2b). Compared with these synthesized 3d–4f heteronuclear com-
plexes, pure RE(NO3)3 (RE=La or Ce) showed lower anti-microbial
activities than the trinuclear complexes (1a and 1b), even lower than
the dinuclear complexes (2a and 2b). These results indicated that the
anti-microbial activities of rare earth ions could be improved when
coordinated with NiL ligand, although NiL has no obvious activities in
itself. The reason that the anti-microbial activities of the trinuclear
complexes (1a and 1b) are advantageous over those of the dinuclear
complexes (2a and 2b) may also be attributed to the function of NiL
Complex 2a is isostructural with 2b which has been reported by
others [12]. For 2a, the central region of the dinuclear entity is
occupied by Ni(II) and La(III) that are doubly bridged one to the other
by two phenolato oxygen atoms from the ligand. The nickel
lanthanum separation is 3.452(4) Ǻ which is shorter than that of 1a.
Fig. 1. ORTEP diagram of complex 1a. Thermal ellipsoids are at the 30% probability level.

398
Y. Sui et al. / Inorganic Chemistry Communications 14 (2011) 396–398
Table 1
Zone of inhibition of the compounds.
Compounds
E. coli
S. aureus
CA
NiL
2
–
–
1a
20
10
8
2a
11
6
5
1b
15
11
6
2b
9
7
4
La(NO3)3
Ce(NO3)3
DMSO
4
3
3
3
2
3
–
–
–
Standard drugs
Penicillin 37
Gentamicin 17
Nistatin 26
“–”, indicates that the bacteria are resistant to the compounds. Zones of inhibition are
reported for diameters in mm. Disks were inoculated with 6 mg of the compounds
dissolved in DMSO.
charge 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. Supplementary data to this article can be found online at
doi:10.1016/j.inoche.2010.12.010.
Fig. 2. ORTEP diagram of complex 2a. Thermal ellipsoids are at the 30% probability level.
ligand which can improve the anti-microbial activities of rare earth
ions. These biological activity results may provide us a new way to
adjust the antimicrobial activities of rare earth ions by coordinating
them with different ratios of NiL ligand.
In conclusion, two sets of 3d–4f complexes [(NiL)nRE] (n=1, 2;
RE=La and Ce) containing Salen-type Schiff base ligand were prepared
by adjusting the ratio of NiL/RE in 1/1 and 2/1, respectively. The
trinuclear complexes [(NiL)2RE] exhibited higher antimicrobial activi-
ties than the dinuclear counterpart [(NiL)RE]. The results indicated that
the antimicrobial activities of rare earth ions could be adjusted by
coordinating with adequate ratio of metal complex ligands. It may be
a promising way to explore new types of adjustable antimicrobial
reagents.
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Acknowledgements
This work was supported by the China Postdoctoral Science
Foundation (20090451189), the Natural Science Foundation of Jiangxi
Province (2007GZH1667), the Department of Education of Jiangxi
Province(Grant GJJ10536) and open funds from the State Key laboratory
of Coordination Chemistry of Nanjing University.
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Appendix A. Supplementary material
CCDC 750887, 750888 and 750889 contain the supplementary
crystallographic data for this paper. These data can be obtained free of