Structure studies of Ni(II) complexes with picolinaldehyde N-oxide thiosemicarbazone

Article abstract of DOI:10.1016/j.molstruc.2006.01.036

Two nickel(II) complexes [Ni(Hpiotsc)₂(NO₃)₂] (1), [Ni(Hpiotsc)₂(NO₃)₂]·H₂O (2) were synthesized and characterized by single crystal X-ray diffraction, IR, and thermal analyses. The geometry of the nickel(II) atom in two complexes is a distorted octahedron with ONS atoms of two neutral ligands. The antimicrobial activities of complex 1 were evaluated by the MIC (minimum inhibitory concentration) against five bacteria. The six-coordinate complex 1 did not inhibit the growth of the test organisms.

Full text of DOI:10.1016/j.molstruc.2006.01.036

Journal of Molecular Structure 794 (2006) 71–76
www.elsevier.com/locate/molstruc
Structure studies of Ni(II) complexes with picolinaldehyde
N-oxide thiosemicarbazone
Yu Qing a, Deng Ji Hua a, Zhu Li Gang a,b, Zhang Xiu Qing a, Bian He Dong a, Liang Hong a,
*
a College of Chemistry and Chemical Engineering, Guangxi Normal University, No. 15 Yucai Road, Guilin, Guangxi 541004, China
b Department of Chemistry and Chemical Engineering, Yulin Teachers’ College, Yulin, Guangxi 573000, China
Received 21 December 2005; received in revised form 20 January 2006; accepted 24 January 2006
Available online 6 March 2006
Abstract
Two nickel(II) complexes [Ni(Hpiotsc)2(NO3)2] (1), [Ni(Hpiotsc)2(NO3)2]$H2O (2) were synthesized and characterized by single crystal X-ray
diffraction, IR, and thermal analyses. The geometry of the nickel(II) atom in two complexes is a distorted octahedron with ONS atoms of two
neutral ligands. The antimicrobial activities of complex 1 were evaluated by the MIC (minimum inhibitory concentration) against five bacteria.
The six-coordinate complex 1 did not inhibit the growth of the test organisms.
q 2006 Elsevier B.V. All rights reserved.
Keywords: Schiff base; Nickel(II) complex; Picolinaldehyde N-oxide; Thiosemicarbazone; Crystal structure
1. Introduction
Each copper(II) atom is coordinated in a slightly distorted
planar arrangement by an ONS-bonded deprotonated ligand
and one coordinated water. Each planar ‘Cu(piotsc)(H2O)’
entity is linked by an out-of-plane N-oxide bridging bond to a
second equivalent entity producing five-coordinate square
pyramidal bonding to each copper(II). Herein, we reported the
structure of Ni(II) complex by the same ligand and the MIC test
was performed to study the antimicrobial activity.
The heterocyclic thiosemicarbazones and their metal
complexes are among the most widely studied compounds
for their potential therapeutic uses, such as antitumoral [1,2],
fungicidal [3,4], bactericidal [5] or antiviral [1] activity. The
biological activities of thiosemicarbazones are considered to be
due to their ability to form chelates with heavy metals [6,7].
Biological activities of metal complexes differ from those of
either ligands or the metal ions and increased and/or decreased
biological activities are reported for several transition metal
complexes, such as nickel(II) and zinc(II) [8,9]. Thiosemi-
carbazone containing a pyridine ring give rise to NNS
tridentate systems, which have been extensively investigated
[8–10]. Kasuga et al. reported that antimicrobial activities of
nickel(II) complexes were significantly influenced by the
molecular structure [8]. However, thiosemicarbazones with
picolinaldehyde N-oxide have not been exhaustively studied.
To our knowledge, only Lu Qin et al. [11] have previously
reported structural study on Cu(II) complex of picolinaldehyde
N-oxide thiosemicarbazone (Hpiotsc). The Cu(II) complex has
a centrosymmetric out-of-plane N-oxide-bridged structure.
2. Experimental
2.1. Materials and instrumentation
2-Pyridinecarboxaldehyde-N-oxide was prepared according
to Ref. [12], Schiff base derived from picolinaldehyde N-oxide
and thiosemicarbazide (Hpiotsc) was prepared according to
Refs. [11,13]. All reagents and other solvents were obtained
from standard commercial sources and were used as received.
The infrared spectrum was taken on a Perkin–Elmer
Spectrum One FT-IR spectrometer in the 4000–400 cmK1
region by using KBr pellets. TG–DTA was carried out in N2
with 10 8C/min heating in the temperature range of 30–900 8C.
Elemental analyses for C, H and N atoms were carried out on a
Model 2400 II Perkin–Elmer elemental analyzer.
*
Corresponding author. Tel.: C86 773 5804053; fax: C86 773 5832294.
E-mail addresses: gxnuchem312@yahoo.com.cn (L. Hong), lian-
2.2. Preparation of [Ni(Hpiotsc)2(NO3)2] (1)
ghongby@yahoo.com.cn (L. Hong).
A solution of Ni(NO3)2$6H2O (0.5 mmol) in water (5 mL)
was slowly added to a solution of Hpiotsc (0.5 mmol) in
0022-2860/$ - see front matter q 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2006.01.036

72
Y. Qing et al. / Journal of Molecular Structure 794 (2006) 71–76
Table 1
ethanol (14 mL) under stirring at room temperature. The
mixture was sealed in a 25 mL Teflon-lined stainless steel
vessel and heated under autogenous pressure at 110 8C for
4 days, and then slowly cooled to room temperature. The dark
green crystals obtained were recovered by filtration, washed
with ethanol and dried in air. Yield: 41%. Calcd (%) for
C14H16N10NiO8S2: C, 29.23; H, 2.81; N, 24.36. Found (%): C,
29.42; H, 2.87; N, 24.52.
Crystal data and structure refinement for 1 and 2
Complex
1
2
Empirical formula
Formula weight (M)
Temperature, T (K)
C14H16N10NiO8S2
575.20
C14H18N10NiO9S2
593.21
293(2)
293(2)
˚
Wavelength, Mo Ka (A)
Crystal system
0.71073
Monoclinic
P21/n
0.71073
Orthorhombic
Pca2(1)
20.728(2)
9.5064(8)
11.7113(12)
90
Space group
˚
a (A)
˚
b (A)
13.745(2)
7.8237(12)
20.662(3)
98.750(2)
2196.0(6)
4
2.3. Preparation of [Ni(Hpiotsc)2(NO3)2]$H2O (2)
˚
c (A)
b (8)
Volume, V (A )
The Hpiotsc (0.5 mmol) in 15 mL ethanol was added to a
aqueous solution (5 mL) containing 1 mmol of Ni(NO3)2$6H2O.
The mixture was refluxed for 2 h and then filtered. The dark green
single crystals were obtained by slow evaporation of the filtrate at
room temperature. Calcd (%) for C14H18N10NiO9S2: C, 28.34; H,
3.06; N, 23.62. Found (%): C, 28.50; H, 3.10; N, 23.88.
3
˚
2307.6(4)
4
Z
Dc (mg/m3)
1.740
1.707
Absorption coefficient, m
(mmK1
1.140
1.091
)
F(000)
Crystal size (mm3)
1176
1216
0.38!0.34!0.20
2.79%q%26.40
K17%h%16,
K4%k%9,
0.30!0.23!0.18
3.39%q%27.48
K16%h%26,
K12%k%12,
K14%l%14
15270/5247
q Range for data collection (8)
Limiting indices
2.4. Crystal structure determination and refinement
K25%l%25
12310/4487
[R(int)Z0.0224]
26.40 (99.7%)
4487/6/338
Suitable crystals of complex 1 (dark green, dimensions
0.38 mm!0.34 mm!0.20 mm) and complex 2 (dark green,
dimensions 0.30 mm!0.23 mm!0.18 mm) were used for the
structure determination. Data collection at 293(2) K was
carried out with a Bruker SMART CCD instrument using
Mo Ka radiation. The structures were solved by direct methods
in SHELXS-97 and refined by full-matrix least-squares, based on
F2, using SHELXL-97 [14]. All non-hydrogen atoms were
assigned anisotropic thermal parameters. The coordinates of
the hydrogen atoms were obtained from difference Fourier
maps and refined with a common isotropic thermal parameter.
For the complex 1, convergence was reached at a final R1Z
0.0303 [for IO2s(I)], wR2Z0.0739 (for all data). For the
complex 2, convergence was reached at a final R1Z0.0408 [for
IO2s(I)], wR2Z0.0878 (for all data), with allowance for the
thermal anisotropy for all non-hydrogen atoms. Details of data
collection and processing are given in Table 1.
Reflections collected/unique
[R(int)Z0.0378]
27.48 (99.4%)
5247/3/333
Completeness to 2q
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [IO2s(I)]
1.040
1.009
R1Z0.0303,
wR2Z0.0739
R1Z0.0418,
wR2Z0.0810
0.479 and K0.308
R1Z0.0408,
wR2Z0.0878
R1Z0.0528,
wR2Z0.0955
0.277 and K0.253
R indices (all data)
Largest diff. peak and hole
K3
˚
(e A
)
3. Results and discussion
3.1. Crystal structure of [Ni(Hpiotsc)2](NO3)2 (1)
The molecular structure of the complex 1 along with the
atomic numbering scheme is given in Fig. 1, and selected bond
lengths and bond angles are summarized in Table 2. The six-
coordinate octahedral Ni(II) complex containing two neutral
ligands Hpiotsc and two non-coordinating nitrate anions. The
perspective view of the complex 1 shows that the thiosemi-
carbazone is functioning as an ONS donor ligand and it is
coordinated in a meridional arrangement. The O1 and S1 atoms
act as axial ligands and O2, N6, S2, N2 atoms are considered to
˚
form a square plane where the Ni(II) ion lies 0.1104 A under
the plane toward S1 atom. The dihedral angle formed by the
mean planes of the bicyclic chelate nodes of the two ligands is
equal to 60.78. The five- and six-membered chelate rings
formed upon coordination are not planar with dihedral angles
of 24.4 and 21.48 in the two coordinating ligands, respectively.
Fig. 1. The molecular structure of [Ni(Hpiotsc)2](NO3)2 (30% probability
ellipsoids).

Y. Qing et al. / Journal of Molecular Structure 794 (2006) 71–76
73
Table 2
˚
Selected bond lengths (A) and angles (8) for 1 and 2
2-methylidene)-propane-1,2-diamine) [16], aphtsc (2-acetyl-
pyridine-hexamethyleneiminyl-3 -thiosemicabazone) [17] and
Hatsc (2-acetylpyridine thiosemicarbazone) [8]. Coordination
lengthens the thiosemicarbazone moiety’s C7–S1 bond from
Complex 1
Complex 2
Ni(1)–N(2)
Ni(1)–N(6)
Ni(1)–O(1)
Ni(1)–O(2)
Ni(1)–S(1)
Ni(1)–S(2)
C(7)–S(1)
C(14)–S(2)
C(7)–S(1)
C(14)–S(2)
C(6)–N(2)
C(13)–N(6)
N(2)–N(3)
N(6)–N(7)
N(3)–C(7)
N(7)–C(14)
2.0207(17)
2.0266(17)
2.0545(15)
2.0494(15)
2.4054(7)
2.3850(7)
1.697(2)
1.694(2)
1.697(2)
1.694(2)
1.286(3)
1.284(3)
1.362(3)
1.363(2)
1.350(3)
1.356(3)
2.023(3)
2.035(3)
2.041(3)
2.082(3)
2.3768(11)
2.3937(11)
1.686(4)
1.685(3)
1.686(4)
1.685(3)
1.275(4)
1.288(4)
1.366(4)
1.369(4)
1.349(4)
1.349(4)
˚
1.687 to 1.697 A indicating the coordination as thione, and a
˚
weak Ni1–S1 (2.4054 A) bonding. In addition, the bonds C6–
N2, N2–N3, and N3–C7 are similar to those reported for free
Hpiotsc [13], which indicates that the neutral ligands in
˚
complex 1 still keep thione form. The bond N1–O1 (1.309 A) is
˚
also found to be lengthened to 1.337 A, which is consistent
with the C7–S1 and C6–N2 remaining as double bonds. The
Hpiotsc possess an E configuration with respect to the
azomethine double bond. The nitrate counter-ions in complex
1 are not involved in coordination, a feature that is also
observed in [Cu2(piotsc)2(H2O)2](NO3)2$H2O [11]. The mol-
ecules of complex 1 are held together in crystal packing
through hydrogen bonds between the oxygen of the anion with
the thiosemicarbazone hydrogen. The H-bonding parameters
are listed in Table 3. The complex 1 forms 3D network through
hydrogen bond and static electrification (Fig. 2).
N(2)–Ni(1)–N(6)
N(2)–Ni(1)–O(2)
N(6)–Ni(1)–O(2)
N(2)–Ni(1)–O(1)
N(6)–Ni(1)–O(1)
O(2)–Ni(1)–O(1)
N(2)–Ni(1)–S(2)
N(6)–Ni(1)–S(2)
O(2)–Ni(1)–S(2)
O(1)–Ni(1)–S(2)
N(2)–Ni(1)–S(1)
N(6)–Ni(1)–S(1)
O(2)–Ni(1)–S(1)
O(1)–Ni(1)–S(1)
S(2)–Ni(1)–S(1)
176.09(7)
95.24(7)
84.39(6)
83.20(7)
92.90(6)
82.42(6)
97.55(6)
82.28(5)
164.70(5)
90.76(5)
82.08(5)
101.80(5)
89.08(5)
162.24(5)
100.96(3)
178.20(12)
93.75(11)
84.66(11)
87.14(10)
93.39(10)
79.67(12)
98.80(8)
82.90(8)
164.57(8)
91.97(10)
84.24(8)
94.98(8)
92.49(9)
167.96(9)
97.64(4)
3.2. Crystal structure of [Ni(Hpiotsc)2](NO3)2$H2O (2)
The structure of [Ni(Hpiotsc)2](NO3)2$H2O (2) consists of
isolated mononuclear cation, nitrate anions and a molecule of
crystal water. The geometry of [Ni(Hpiotsc)2]2C in complex 2
is very similar to that of complex 1, as mentioned above in
Table 2. It suggests that the environment of Ni(II) in complex 2
is closer to perfect octahedron than that of complex 1.
The Ni–S, Ni–N and Ni–O bond distances in complex 1 are
comparable with those reported for other nickel(II) complexes
with pioen (N,N0-bis(pyridine N-oxide 2-methylidene)ethyle-
nediamine) [15], piopn (N,N0-bis(pyridine N-oxide
3.3. Infrared spectra
Selected vibration bands of Hpiotsc and of its metal
complexes are given in Table 4 (Fig. 3). In principle, the
Table 3
˚
Hydrogen bond distances (A) and bond angles (8)
D–H/A
ARU
D–H
H/A
D/A
ÐDHA
1
N(3)–H(3A)/O(6)
N(3)–H(3A)/O(8)
N(4)–H(4A)/O(4)
N(4)–H(4A)/O(8)
N(4)–H(4B)/O(5)
N(7)–H(7)/O(3)
N(7)–H(7)/O(4)
N(8)–H(8A)/O(3)
N(8)–H(8B)/O(6)
[4_454]
[4_454]
[1_455]
[4_454]
[2_555]
[4_455]
[4_455]
[4_455]
[3_666]
0.87
0.87
0.87
0.87
0.87
0.87
0.87
0.86
0.87
2.07
2.37
2.42
2.39
2.04
2.38
2.00
2.38
2.17
2.9064
3.1135
3.1424
3.0818
2.8834
3.0302
2.8594
3.0659
3.0228
161
143
141
136
162
132
169
137
168
2
O(1W)–H(1WB)/O(6)
O(1W)–H(1WA)/O(7)
N(7)–H(3AB)/O(8)
N(3)–H(3B)/O(4)
N(8)–H(4AC)/O(1)
N(4)–H(4B)/O(5)
N(4)–H(4C)/O(1W)
N(8)–H(4AB)/O(3)
N(8)–H(4AB)/O(4)
[4_565]
[4_565]
0.86
0.86
0.86
0.86
0.86
0.86
0.86
0.86
0.86
2.27
2.10
1.95
2.02
2.16
2.02
2.01
2.42
2.22
3.0888
2.8201
2.7872
2.8765
2.9375
2.8252
2.8617
3.1004
3.0652
159
141
163
178
150
155
170
137
166
[4_565]
[3_555]
[4_565]
[3_565]
[3_565]
Translation of AUR-code to equivalent position code. 1: [2_555]Z1/2Kx, 1/2Cy, 1/2Kz; [4_454]ZK1/2Cx, 1/2Ky, K1/2Cz; [1_455]ZK1Cx, y, z;
[4_455]ZK1/2Cx, 1/2Ky, 1/2Cz; [3_666]Z1Kx, 1Ky, 1Kz; [2_655]Z3/2Kx, 1/2Cy, 1/2Kz; [3_556]ZKx, Ky, 1Kz. 2: [3_555]Z1/2Kx, y, 1/2Cz;
[3_554]Z1/2Kx, y, K1/2Cz; [4_565]Z1/2Cx, 1Ky, z; [3_565]Z1/2Kx, 1Cy, 1/2Cz.

74
Y. Qing et al. / Journal of Molecular Structure 794 (2006) 71–76
Fig. 2. Packing perspective view of complex 1 (a) and complex 2 (b) showing 3D supramolecular by strong hydrogen-bonding interactions along b-axis.

Y. Qing et al. / Journal of Molecular Structure 794 (2006) 71–76
75
Table 4
IR spectral assignments for Hpiotsc and nickel complexes
Compound
n(NH2)
n(NH)
n(CaS)
n(CaN)
n(N–O)
d(N–O)
NOK3
Hpiotsc
3372br, 3263br
3304br
3157br
3107br
3111br
1091s, 760m
1039m, 738w
1048m, 738w
1621s
1626s
1633s
1219s
814m
805m
812m
–
1
2
1201ms
1203ms
1384
1384
3276br
Fig. 3. FT-IR spectra of both the ligand (Hpiotsc) and the two Ni complexes (1 and 2).
ligand can exhibit thione–thiol tautomerism, since it contains a
thioamide –NH–CaS functional group [18]. The n(S–H) band
at 2570 cmK1 is absent from the IR spectra of the Schiff base
but the n(N–H) band at ca. 3150 cmK1 is present, indicating
that in the solid state the ligand remains as the thione tautomer.
The bands appearing around 1091 and 760 cmK1 in the
spectrum of the ligand are shifted to lower wave numbers in
the two complexes [2,19], and this shift can be assigned to the
n(C–S) vibration. On the other hand, the bands in the region
3372–3263 cmK1 attributed to symmetrical and asymmetrical
stretching modes n(NH2) in the spectra of the ligand, undergo
appreciable change in the spectra of the complexes. This is a
consequence of the coordination of the sulfur from the C–
S(NH2) group as reported earlier [2,19]. In the ligand spectrum,
the strong band observed at 1621 cmK1 can be assigned to
n(CaN) vibration mode [19,20]. This band shifts to a higher
region [11,20] in the spectra of all metal complexes, which
indicates the coordination of nitrogen of the azomethine group
to the central metal atoms in these complexes. The Hpiotsc
shows n(N–O) and d(N–O) at 1219 and 814 cmK1, respect-
ively. On complexation, the position of this band is shifted by
ca. 17 cmK1. It indicates that coordination takes place through
the oxygen of N-oxide pyridine [15,16]. In the two complexes,
the band around 1384 cmK1 is assigned to D3h mode of the free
NOK3 group, suggesting the uncoordination of nitrate groups to
Ni(II) cation [21].
3.4. Thermogravimetric analyses
The thermal decomposition data of the complexes were
given in Table 5. The thermal decomposition process of the
complex 2 can be divided into three stages. The first stage is at
72.8–109.7 8C. The TG curve shows that the mass loss
corresponding to this temperature range is 3.6% that roughly
Table 5
Thermal decomposition data of the complexes
Stage
Temp. range (8C)
Loss of mass (%)
TG
Probable composition of
expelled groups
Residual value (%)
Theory
TG
Theory
1
2
1
2
225.6–390.3
442.4–800.0
59.7
27.8
68.2
21.6
–2Hpiotsc
–2NOK3
12.5
13.0
12.6
1
2
3
72.8–109.7
202.5–450.3
510.6–796.1
3.6
62.7
22.4
3.0
66.2
20.9
–H2O
–2Hpiotsc
–2NOK3
11.3

76
Y. Qing et al. / Journal of Molecular Structure 794 (2006) 71–76
coincides with the value of 3.0%, calculated for the loss of
1 mol crystal water from the complex. The second-stage starts
from 202.5 to 450.3 8C with the mass loss of 62.7%, which
corresponds to the loss of 2 mol Hpiotsc. The theoretical mass
loss is 66.2%. The third-stage degradation temperature is in the
range of 510.6–796.1 8C with the mass loss of 22.4%, in which
2 mol NOK3 are removed with theoretical loss of 20.9%. The
main product was NiO with a residual value of 11.3%
(theoretical residual value was 12.6%).
Acknowledgements
We gratefully acknowledge the Nature Science Foundation of
Guangxi Province and the Education Department Foundation of
Guangxi Province for the financial support of this work.
References
[1] P. Tarasconi, S. Capacchi, G. Pelosi, M. Cornia, R. Albertini, A. Bonati,
P.P. Dall’Aglio, P. Lunghi, S. Pinelli, Bioorg. Med. Chem. 8 (2000) 157.
[2] E.M. Jouad, G. Larcher, M. Allain, A. Riou, G.M. Boueta, M.A. Khan,
X.D. Thanh, J. Inorg. Biochem. 86 (2001) 565.
The TG–DTA curve of complex 1 was similar to that of
complex 2. But no endothermic peak appeared during
30–220 8C, which indicated that the complex 1 did not contain
water.
[3] S.G. Teoh, S.H. Ang, H.K. Fun, C.W. Ong, J. Organomet. Chem. 580
(1999) 17.
¨
[4] E. Bermejo, R. Carballo, A. Castin˜eiras, R. Dominguez, C.M. Mossmer,
¨
J. Strahle, D.X. West, Polyhedron 18 (1999) 3695.
¨
[5] S. Abram, C.M. Mossmer, U. Abram, Polyhedron 17 (1998) 131.
3.5. Antibacterial activity
[6] U. Abram, K. Ortner, K. Sommer, J. Chem. Soc., Dalton Trans. (1999)
735.
The antimicrobial activities of the extracts were evaluated
by MIC against five bacteria (Escherichia coliform, Staphylo-
coccus Aureus, b-hemolytic streptococcus, Streptococcus
pneumoniae and Anthrax bacillus) [22]. The test results
indicate that neither the Hpiotsc nor complex 1 show strong
activity. Kasuga et al. [8] had reported that antimicrobial
activities of nickel(II) complexes were significantly influenced
by the molecular structure. The labile four-coordinate
complexes could interact with selected bacteria, while inert
four-coordinate and six-coordinate complexes cannot. Since,
the latter did not undergo ligand replacement easily. In
complex 1, the nickel(II) is six-coordinate with two tridentate
ligands and do not inhibit the growth of the test organisms,
which is consistent with the conclusion reported above [8].
[7] D.X. West, G.A. Bain, R.J. Butcher, J.P. Jasinski, Y. Li, R.Y. Pozdniakiv,
J.V. Martinez, R.A. Toscano, S.H. Ortega, Polyhedron 15 (1996) 665.
[8] N.C. Kasuga, K. Sekino, C. Koumo, N. Shimada, M. Ishikawa,
K. Nomiya, J. Inorg. Biochem. 84 (2001) 55.
[9] N.C. Kasuga, K. Sekino, M. Ishikawa, A. Honda, M. Yokoyama,
S. Nakano, N. Shimada, C. Loumo, K. Nomiya, J. Inorg. Biochem. 96
(2003) 298.
[10] D.X. West, S.B. Padhye, P.B. Sonawane, Struct. Bond. 76 (1991) 1.
[11] Q. Lu, G.X. Wang, Y. Zang, Z.F. Yin, C. Zeng, Z.Y. Zhou, Acta Chim.
Sinica 47 (1989) 1065.
[12] D. Jerchel, J. Heider, H. Wagner, Ann. Chem.-Justus Liebig 153 (1958)
613.
[13] B. Liu, R.X. Hu, H. Liang, K.B. Yu, Chin. J. Struct. Chem. 18 (1999) 414.
[14] G.M. Sheldrick, SHELXL 97, Program for the Refinement of Crystal
¨
Structures, University of Gottingen, Germany, 1997.
[15] Z.F. Yin, G.X. Wang, Y. Ling, F.S. Wang, Y.G. Fan, J. Nanjin Univ. (Nat.
Sci. Ed.) 26 (1990) 256.
[16] Z.Y. Zhou, Z.F. Yin, Y. Zang, G.X. Wang, C. Zeng, A.B. Dai, Acta Phys.-
Chim. Sinica 6 (1990) 556.
4. Supplementary data
[17] A. Sreekanth, S. Sivakumar, M.R.P. Kurup, J. Mol. Struct. 655 (2003) 47.
[18] A.D. Naik, S.M. Annigeri, U.B. Gangadharmath, V.K. Revankar,
V.B. Mahale, J. Mol. Struct. 616 (2002) 119.
Complete listings of bond distances and bond angles,
hydrogen atoms coordinates and isotropic displacement
parameters, anisotropic displacement parameters and least-
squares plans are available either quoting the deposition
number CCDC-290530 and 290531 (12 Union Road,
Cambridge CB2 1EZ, UK) or from the authors on request.
[19] P. Bindu, M.R.P. Kurup, T.R. Satyakeerty, Polyhedron 18 (1999) 321.
[20] E.M. Jouad, A. Riou, M. Allain, M.A. Khan, G.M. Bouet, Polyhedron 20
(2001) 67.
[21] Q. Yu, Y. Tang, M.Y. Tan, J. Rare Earths 20 (2002) 385.
[22] S. Kang, Z.F. Chen, H. Liang, J. Guangxi Normal Univ. (Nat. Sci. Ed.) 20
(2002) 75.