Crystal structure and properties of complex [Eu(m-BrBa)3(H2O)(phen)]2

Article abstract of DOI:10.1016/S0022-2860(03)00017-6

A binuclear europium complex [Eu(m-BrBA)₃(H₂O)(phen)]₂ (1) has been obtained in the ethanol solution and characterized structurally by X-ray diffraction, where m-BrBA = m-bromobenzoate and phen = 1,10-phenanthroline. Each Eu³⁺ ion is eight-coordinated to one 1,10-phenanthroline molecule, one monodentate carboxylate group, one water molecule and four bridging carboxylate groups in which the carboxylate groups are bonded to the europium ion in two modes: the monodentate and the bridging bidentate, Excitation and luminescence data observed at room temperature show that the title complex emits red fluorescence under ultraviolet light. The results of thermal analysis indicate that the complex [Eu(m-BrBA)₃(H₂O)(phen)]₂ is quite stable to heat.

Full text of DOI:10.1016/S0022-2860(03)00017-6

Journal of Molecular Structure 648 (2003) 151–158
www.elsevier.com/locate/molstruc
Crystal structure and properties of complex
[Eu(m-BrBA)3(H2O)(phen)]2
a,
Rui-Fen Wang , Shu-Ping Wang , Jian-Jun Zhang
a
b
*
aCollege of Chemistry, Hebei Normal University, Shijiazhuang 050091, People’s Republic of China
bExperimental Center, Hebei Normal University, Shijiazhuang 050016, People’s Republic of China
Received 16 September 2002; revised 7 December 2002; accepted 18 December 2002
Abstract
A binuclear europium complex [Eu(m-BrBA)3(H2O)(phen)]2 (1) has been obtained in the ethanol solution and characterized
structurally by X-ray diffraction, where m-BrBA ¼ m-bromobenzoate and phen ¼ 1,10-phenanthroline. Each Eu3þ ion is
eight-coordinated to one 1,10-phenanthroline molecule, one monodentate carboxylate group, one water molecule and four
bridging carboxylate groups in which the carboxylate groups are bonded to the europium ion in two modes: the monodentate
and the bridging bidentate. Excitation and luminescence data observed at room temperature show that the title complex emits
red fluorescence under ultraviolet light. The results of thermal analysis indicate that the complex [Eu(m-BrBA)3(H2O)(phen)]2
is quite stable to heat.
q 2003 Elsevier Science B.V. All rights reserved.
Keywords: Europium complex; m-Bromobenzoic acid; 1,10-Phenanthroline; Crystal structure; Luminescence
1. Introduction
is no coordinated water molecules. These complexes
result in strong emission of a red colour and are stable
to light and heat [2–10]. As part of our continuing
study of europium carboxylate complexes, the present
paper reports the crystal structure, luminescence
spectra and thermal analysis of a special complex
[Eu(m-BrBA)3(H2O)(phen)]2, in which there are two
coordinated water molecules.
The rare-earth carboxylic acid complexes have
many special structures and interesting spectroscopic
properties, which are of great interest in extraction,
separation, germicide preparation, catalysis, lumines-
cence and functional material preparation. Therefore
the study of them has been a rich topic for chemical
workers all through [1]. Structural studies of ternary
europium complexes with aromatic acids and nitro-
gen-containing ligands have shown that the rare earth
atoms have several types of coordination, usually with
coordination number of eight or nine, of which there
2. Experimental
2.1. General
All the starting materials were of analytical
grade. Excitation and luminescence spectra were
*
Corresponding author. Tel.: þ86-311-3800378; fax: þ86-311-
3834673.
0022-2860/03/$ - see front matter q 2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0022-2860(03)00017-6

152
R.-F. Wang et al. / Journal of Molecular Structure 648 (2003) 151–158
performed at room temperature using a MPF-4
fluorescence spectrophotometer. The TG and DTG
experiment for the title complex were performed
using a Perkin–Elmer TGA7 thermogravimetric
analyzer. The heating rate was 10 8C min21 from
ambient to 918 8C under an air atmosphere. The
sample weight was 2.562 mg.
after a month. Anal. Calcd. (%) for C66H44N4O14Br6-
Eu2: C 41.38(41.71), H 2.27(2.33), N 3.06(2.95).
3. Structure determination
Determination of the unit cell and data collection
was performed on a CCD area detector using graphite
ꢀ
monochromated Mo Ka radiation ðl ¼ 0:71073 AÞ at
2.2. Preparation of [Eu(m-BrBA)3(H2O)(phen)]2 (1)
293(2) K. A total of 8009 ½Rint ¼ 0:1193ꢀ indepen-
dent reflections were collected by v-2u scan
technique in the range 2:018 # u # 25:008 from
which 5580 ½I . 2sðIÞꢀ reflections were corrected.
The structure was solved using direct methods in
SHELXS-97 [11] and refined using a full-matrix least-
square procedure on F 2 in SHELXL-97 [12]. All non-
hydrogen atoms were refined with anisotropic
thermal parameters, hydrogen atoms were added
theoretically and refined with riding model position
parameters and fixed isotropic thermal parameters.
A stoichiometric amount of EuCl3·6H2O, m-
bromobenzoic acid and 1,10-phenanthroline were
dissolved in 95% C2H5OH, respectively. The pH of
the m-bromobenzoic acid was adjusted to the range of
6–7 with 1 M NaOH solution. The C2H5OH solutions
of two ligands were mixed and then the mixture was
added dropwise to the ethanolic EuCl3 solution, while
a white precipitate formed. Crystals suitable for X-ray
investigation were obtained from the mother liqour
Table 1
Data collection and processing parameters for complex (1)
Empirical formula
Formula weight
Temperature
C66H44N4O14Br6Eu2
1900.43
293(2) K
˚
0.71073 A
Wavelength
Crystal system
Space group
Triclinic
¯
P1
ꢀ
Unit cell dimensions
a ¼ 8:1061ð10Þ A
a ¼ 94:200ð2Þ8
ꢀ
b ¼ 12:9770ð15Þ A
b ¼ 94:780ð2Þ8
ꢀ
c ¼ 15:5431ð18ÞA
g ¼ 79:903ð2Þ8
ꢀ 3
Volume
1601:2ð3ÞA
Z; Calculated density
Absorption coefficient
Fð000Þ
1, 1.971 Mg/m3
5.753 mm21
916
u range for data collection
Limiting indices
2.01–25.008
29 # h # 8, 214 # k # 15, 2 18 # l # 17
8009/5580 ½RðintÞ ¼ 0:1193ꢀ
98.8 %
Reflections collected/unique
Completeness to theta ¼ 25.00
Absorption correction
Max and min transmission
Refinement method
Sadabs
1.00000 and 0.50964
Full-matrix least-squares on F2
5580/0/415
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices ½I . 2sðIÞꢀ
R indices (all data)
1.068
R1 ¼ 0:0747; wR2 ¼ 0:1920
R1 ¼ 0:0894; wR2 ¼ 0:2015
23
˚
2.737 and 22.843 eA
Largest diff. Peak and hole

R.-F. Wang et al. / Journal of Molecular Structure 648 (2003) 151–158
153
Table 2
Atomic coordinates ( £ 104) and equivalent isotropic displacement
Table 2 (continued)
2
3
X
Y
Z
UðeqÞ
˚
parameters (A £ 10 ) for complex (1)
X
Y
Z
UðeqÞ
H(8)
9752
11123
10692
7400
5232
3259
3376
10421
8094
6221
6258
6876
9033
10696
10600
5645
6732
7282
6633
7640
9892
9432
8111
6925
9140
8578
7159
2184
154
74
75
51
49
71
82
62
57
123
136
78
47
66
72
61
H(9)
4106
H(10)
H(15)
H(17)
H(18)
H(19)
H(22)
H(24)
H(25)
H(26)
H(29)
H(31)
H(32)
H(33)
2548
Eu
7994(1)
1316(1)
5187(1)
9143(1)
8585(2)
319(1)
22(1)
82(1)
129(1)
79(1)
39(2)
54(3)
39(2)
40(2)
38(2)
35(2)
39(2)
35(2)
39(2)
50(3)
68(5)
73(5)
54(4)
68(5)
68(5)
51(4)
61(4)
63(4)
43(3)
39(3)
45(3)
36(3)
35(3)
41(3)
43(3)
59(4)
68(5)
52(3)
30(2)
41(3)
48(3)
67(5)
103(9)
113(10)
65(4)
37(3)
32(3)
39(3)
46(3)
55(4)
60(4)
51(3)
60
3304
Br(1)
Br(2)
Br(3)
O(1)
8088(3)
4668(2)
4021
11048(4)
6469(3)
23506(2)
1171(2)
3036
2095
6730(10)
4180(12)
7576(10)
9800(10)
7449(10)
9611(10)
5001(10)
6775(12)
9025(13)
5790(18)
5060(20)
5380(20)
6374(18)
6730(19)
7680(20)
8519(17)
9588(18)
10380(20)
10105(17)
8221(15)
7101(15)
5423(15)
5397(15)
6575(16)
6513(18)
5260(20)
4110(20)
4167(19)
8610(14)
8380(16)
9564(19)
9490(20)
8180(40)
7070(40)
7070(20)
8530(15)
8640(14)
7633(16)
7750(18)
8950(20)
9930(20)
9847(17)
5577
2083(6)
6442(5)
6570(6)
5749(5)
5660(5)
3769(5)
3952(5)
4958(5)
4323(7)
5712(7)
3595(9)
3121(11)
3407(12)
4187(10)
4576(14)
5299(14)
5720(11)
6465(12)
6792(11)
6406(8)
5352(9)
4616(10)
6852(8)
7751(8)
8004(8)
8790(8)
9347(9)
9078(10)
8282(9)
6024(7)
6924(8)
7259(8)
8077(10)
8584(12)
8239(13)
7385(10)
3476(8)
2507(7)
1956(8)
1069(8)
747(9)
22511
22161
2865
2343
916
O(2)
1668(8)
O(3)
2267(7)
21529(7)
550(6)
O(4)
O(5)
O(6)
2713(6)
1310(6)
2738
21803
21528
O(7)
1049
2521
N(1)
2926(7)
N(2)
3079(7)
C(1)
2844(11)
3714(14)
4662(15)
4808(11)
5847(10)
5913(11)
4953(10)
5002(12)
4092(13)
3161(10)
3966(9)
C(2)
C(3)
Further details of the structure analysis are given in
Table 1. Positional parameters and selected bond
lengths and angles are presented in Tables 2 and 3,
respectively.
C(4)
C(5)
C(6)
C(7)
C(8)
C(9)
C(10)
C(11)
C(12)
C(13)
C(14)
C(15)
C(16)
C(17)
C(18)
C(19)
C(20)
C(21)
C(22)
C(23)
C(24)
C(25)
C(26)
C(27)
C(28)
C(29)
C(30)
C(31)
C(32)
C(33)
H(1)
4. Results and discussion
3908(10)
2071(9)
2606(9)
4.1. Crystal structure of [Eu(m-BrBA)3(H2O)(phen)]2
3240(10)
3767(10)
3673(12)
3079(14)
2522(12)
21028(8)
21380(11)
22172(11)
22461(14)
21960(20)
21200(20)
2868(14)
2159(9)
2324(10)
361(9)
The molecular structure and atomic numbering of
the complex are shown in Fig. 1. The two Eu3þ ions
are linked by four carboxylate groups through their
bidentate bridging modes, form a dimeric unit with
crystallographic inversion center. Each Europium ion
is coordinated to eight atoms, of which four oxygen
atom are from the bridging carboxylates, one oxygen
atom from the monodentate carboxylate group, one
oxygen atom from the water molecular and two
nitrogen atoms from a 1,10-phenanthroline molecule.
In the binuclear molecule, the Eu–O distances are
˚
in a range of 2.315(8)–2.424(8) A, in which the
220(10)
2625(12)
21251(12)
21104(11)
2184
Eu–O bonds formed by water molecules are
the longest. The Eu–O bond distances formed by
the bridging carboxylates are slightly longer than that
formed by the monodentate carboxylate groups except
for Eu–O(6)#1[Eu#1–O(6)]. The average bond
distances of Eu–O and Eu–N are 2.372 and
1276(10)
2157(10)
3394
H(2)
4373
3632
2621
81
H(3)
4944
5238
3087
87
H(5)
6268
6455
4302
81
H(6)
7836
6568
5546
82
˚
2.598 A, respectively, which slightly shorter than

154
R.-F. Wang et al. / Journal of Molecular Structure 648 (2003) 151–158
Table 3
˚
Selected bond lengths (A) and angles (8) for complex (1) (Symmetry transformations used to generate equivalent atoms: #1 2x þ 2; 2y;
2z þ 1Þ
Eu–O(6)#1
Eu–O(4)#1
Eu–O(5)
2.315(8)
2.372(8)
2.391(8)
2.572(9)
4.3261(11)
1.858(19)
1.284(14)
1.253(14)
2.372(8)
1.258(15)
1.337(17)
1.341(17)
Eu–O(1)
2.352(8)
2.378(8)
2.424(8)
2.623(9)
1.900(14)
1.875(14)
1.248(15)
1.220(13)
1.242(14)
2.315(8)
1.384(16)
1.353(16)
Eu–O(3)
Eu–O(7)
Eu–N(1)
Eu–N(2)
Eu–Eu#1
Br(1)–C(16)
Br(3)–C(30)
O(2)–C(13)
O(4)–C(20)
O(5)–C(27)
O(6)–Eu#1
N(1)–C(12)
N(2)– C(11)
Br(2)–C(23)
O(1)–C(13)
O(3)–C(20)
O(4)–Eu#1
O(6)–C(27)
N(1)–C(1)
N(2)–C(10)
O(6)#1–Eu–O(1)
O(1)–Eu–O(4)#1
O(1)–Eu–O(3)
88.6(3)
O(6)#1–Eu–O(4)#1
O(6)#1–Eu–O(3)
O(4)#1–Eu–O(3)
O(1)–Eu–O(5)
76.8(3)
139.0(3)
83.1(3)
72.9(3)
126.6(3)
144.0(3)
88.1(3)
O(6)#1–Eu–O(5)
O(4)#1–Eu–O(5)
O(6)#1–Eu–O(7)
O(4)#1–Eu–O(7)
O(5)–Eu–O(7)
122.0(3)
72.2(3)
O(3)–Eu–O(5)
144.0(3)
136.9(3)
71.9(3)
O(1)–Eu–O(7)
72.1(3)
O(3)–Eu–O(7)
74.7(3)
O(6)#1–Eu–N(1)
O(4)#1–Eu–N(1)
O(5)–Eu–N(1)
138.5(3)
75.7(3)
O(1)– Eu–N(1)
O(3)– Eu–N(1)
O(7)–Eu–N(1)
92.2(3)
148.2(3)
73.9(3)
77.4(3)
O(6)#1–Eu–N(2)
O(4)#1–Eu–N(2)
O(5)–Eu–N(2)
78.8(3)
O(1)–Eu–N(2)
68.2(3)
71.4(3)
O(3)–Eu–N(2)
139.9(3)
118.8(3)
101.9(3)
62.4(3)
131.5(3)
63.3(3)
O(7)–Eu–N(2)
N(1)–Eu–N(2)
O(6)#1–Eu–C(27)
O(4)#1–Eu–C(27)
O(5)–Eu–C(27)
N(1)–Eu–C(27)
O(6)#1–Eu–Eu#1
O(4)#1–Eu–Eu#1
O(5)–Eu–Eu#1
N(1)–Eu–Eu#1
C(27)–Eu–Eu#1
C(20)– O(3)– Eu
C(27)–O(5)–Eu
C(1)–N(1)–Eu
O(1)–Eu–C(27)
O(3)–Eu–C(27)
O(7)–Eu–C(27)
N(2)–Eu–C(27)
O(1)–Eu–Eu#1
O(3)–Eu–Eu#1
O(7)–Eu–Eu#1
N(2)–Eu–Eu#1
C(13)–O(1)–Eu
C(20)–O(4)–Eu#1
C(27)–O(6)–Eu#1
C(12)–N(1)–Eu
C(11)–N(2)–Eu
N(1)–C(12)–C(11)
O(2)–C(13)–C(14)
O(4)–C(20)–O(3)
O(3)–C(20)–C(21)
O(5)–C(27)–C(28)
O(5)–C(27)–Eu
C(28)– C(27)– Eu
158.4(3)
82.1(3)
20.1(3)
88.9(3)
92.2(3)
132.0(3)
131.4(2)
65.2(2)
48.5(2)
61.8(2)
73.57(19)
133.9(2)
53.6(2)
127.0(2)
114.2(2)
140.0(7)
141.6(8)
163.1(8)
120.1(8)
117.7(8)
117.4(11)
117.8(10)
127.5(11)
117.2(11)
119.3(11)
41.5(6)
130.9(7)
118.4(8)
121.4(8)
122.7(8)
120.3(10)
125.7(11)
116.5(10)
115.3(11)
122.8(11)
117.8(11)
83.8(7)
C(10)–N(2)–Eu
N(2)–C(11)–C(12)
O(2)–C(13)–O(1)
O(1)–C(13)–C(14)
O(4)–C(20)–C(21)
O(5)–C(27)–O(6)
O(6)–C(27)–C(28)
O(6)–C(27)–Eu
151.7(8)
˚
corresponding average distances 2.389 and 2.599 A
found in the complex [Eu(m-MBA)3phen]2·(H2O)2
[2]. The fact indicates that the interaction of europium
ion with oxygen atom or nitrogen atom in
[Eu(m-MBA)3phen]2·(H2O)2 is weaker than that in
the complex [Eu(m-BrBA)3(H2O)(phen)]2. Compared
with the analogue complexes with aromatic acids and
1,10-phenanthroline ligands [2–6], only the crystal

R.-F. Wang et al. / Journal of Molecular Structure 648 (2003) 151–158
155
Fig. 1. The molecular structure of complex (1).
for the title complex and [Eu(m-MBA)3phen]2 ·2H2O
contain water molecules, and water molecules are not
coordinated in the complex [Eu(m-MBA)3phen]2·
2H2O. Because of the coordination effect of water
molecules, the unbridging bidentate carboxylate
groups become monodentate in the title complex.
These are possibly caused by the electronic effect of
different substituent on the benzene ring and the steric
effect.
carboxylate group is 125.7(11)8. The O(3)–C(20)–
O(4) [O(5)–C(27)–O(6)] angle in the bidentate
bridging carboxylate group is 127.5(11)8
[122.8(11)8]. The five atoms of the chelated ring
containing two chelated nitrogen atoms and euro-
pium ion are coplanar in the dimer since the
molecule of 1,10-phenanthroline is rigid.
4.2. Thermal decomposition
In the carboxylate groups, C–O distances differ
significantly; coordination causes lengthening of
˚
C–O[1.284(14) A] for the monodentate carboxylate
The TG and DTG curves of the [Eu(m-BrBA)3(-
H2O)(phen)]2 are shown in Fig. 2. The thermoanaly-
tical data for the complex are given in Table 4. The
Eu(III) complex decomposed via intermediates to give
the europium oxide as an end product. The percentage
groups in comparison to the bidentate-bridging
˚
carboxylate groups[1.220(13)–1.258(15) A].
The O(1)–C(13)–O(2) angle in the monodentate

156
R.-F. Wang et al. / Journal of Molecular Structure 648 (2003) 151–158
Fig. 2. Thermogravimetric curves (DTG and TG) for complex (1).
of mass loss and probable composition of the expelled
groups are also indicated in Table 4.
the DTG curve. The first stage start from 107 to
156 8C with a mass loss 2.15 wt% which corresponds
to the loss of 2 mol H2O (theoretical loss is 1.90 wt%).
The second stage degradation temperature is in the
range of 264–464 8C with the mass loss of 23.28 wt%,
in which 2 mol C12H8N2 and 1 mol Br are removed
with theoretical loss of 23.17 wt%. This degradation
can be explained based on the bond distances of the
structure (Table 3): Eu–N distance is longer than any
The results of thermal analysis indicate that title
complex begins to decompose at the temperature of
107 8C and its decomposition ends at 918 8C. The TG
degradation of [Eu(m-BrBA)3(H2O)(phen)]2 reveals
four decomposition stages, as predicted by the DTG
curve(Fig. 2), and there are weight losses with
maximum rate at 139, 381, 564 and 699 8C in
Table 4
Thermal decomposition data for complex (1) in air atmosphere from TG and DTG analysis
Stage
Temperature
DTG peak
Loss of mass (wt%)
Probable composition
of expelled groups
Intermediate
range (8C)
temperature (8C)
TG
Theory
I
107–156
264–464
464–607
607–918
139
381
564
699
2.15
1.90
23.17
25.40
31.01
81.48
2H2O
[Eu(m-BrBA)3(phen)]2
Eu2(m-BrBA)5(–C6H4COO)
Eu2 (–C6H4COO)5.2O0.8
Eu2O3
II
23.28
25.19
32.18
82.80a
2C12H8N2 þ Br
5Br þ 0.8(–C6H4CO)
5.2 (–C6H4COO)–2.2O
III
IV
a
Tatal loss of mass.

R.-F. Wang et al. / Journal of Molecular Structure 648 (2003) 151–158
157
Fig. 3. Luminescence spectrum of complex (1) (excited by 313 nm).
other bond distance, so the bond is less stable and easy
to be broken down theoretically. The third stage start
from 464 to 607 8C with a mass loss of 25.19 wt%
which corresponds to the loss of 5 mol Br and
0.8 mol(–C6H4CO)(theoretical loss is 25.40 wt%).
The degradation can also be demonstrated by the
bond distances of the structure (Table 3): C(13)–O(1)
distance is longer than any other C–O bond distance,
so this bond is less stable and easy to be broken down.
The fourthly stage degradation temperature is in the
range of 607–918 8C with the mass loss of 32.18 wt%,
in which [5.2 mol(–C6H4COO)–2.2 mol O] are
removed with theoretical loss of 31.01 wt%. Up to
now, water-1,10-phenanthroline-tris(m-bromobenzo-
ate) europium(III) was completely degraded into
Eu2O3 with a total loss of 82.80 wt% (theoretical loss
is 81.48 wt%). The thermal decomposition of [Eu(m-
BrBA)3(H2O)(phen)]2 can be described as follow:
The luminescence spectrum is shown in Fig. 3. The
excitation of complex [Eu(m-BrBA)3(H2O) (phen)]2
was effected in a range of 240–400 nm. The
fluorescence was observed in a range of 550–
650 nm by selective excitation at 313 nm. The
emission spectrum composed of the characteristic
emission peaks arising from the transition of Eu3þ
:
7
7
5D0 ! F0(579 nm), 5D0 ! F1(589, 592, 595 nm),
5D0 ! F2(612, 618, 619, 620 nm). The intensity of
7
5
7
the luminescence band arising from the D0 ! F2
transition is most intense.
Acknowledgements
This work was supported by the Natural Science
Foundation of Hebei Province (No. 202140), P.R.
China.
[Eu(m-BrBA)3(H2O)(phen)]2 ! [Eu(m-BrBA)3
(phen)]2 ! Eu2(m-BrBA)5(–C6H4COO) ! Eu2
(–C6H4COO)5.2O0.8 ! Eu2O3
References
[1] Gmelin Handbook of Inorganic Chemistry, eighth ed., System.
No. 39, Part D5, 1984.
4.3. Luminescence properties
[2] L.P. Jin, R.F. Wang, M.Z. Wang, G.L. Cai, S.X. Liu, J.L.
Huang, Chem. J. Chin. Univ. 14 (1993) 1195.
The excitation and luminescence spectra of the title
complex were recorded at room temperature.
[3] L.P. Jin, M.Z. Wang, G.L. Cai, S.X. Liu, J.L. Huang, R.F.
Wang, Sci. China (Ser. B) 38 (1995) 1.

158
R.-F. Wang et al. / Journal of Molecular Structure 648 (2003) 151–158
[4] R.F. Wang, L.S. Li, L.P. Jin, S.Z. Lu, Chem. J. Rare Earths 16
(1998) 149.
[9] R.F. Wang, L.S. Li, L.P. Jin, S.Z. Lu, J.H. Zhang, J. Coord.
Chem. 47 (1999) 279.
[5] S.Y. Niu, B. Yang, J.Q. Cao, G.D. Yang, W.M. Bu, Chem.
J. Chin. Univ. 18 (1997) 1917.
[10] L.P. Jin, R.F. Wang, L.S. Li, S.Z. Lu, S.H. Huang, Polyhedron
18 (1998) 487.
[6] L.P. Jin, R.F. Wang, L.S. Li, S.Z. Lu, Chem. J. Rare Earths 14
(1996) 161.
[11] G.M. Sheldrick, SHELXS-97: Program for the Solution of
¨
Crystal Structures, University of Gottingen, Germany,
[7] R.F. Wang, L.P. Jin, M.Z. Wang, S.H. Huang, X.T. Chen, Acta
Chim. Sin. 53 (1995) 39.
1997.
[12] G.M. Sheldrick, SHELXL-97: Program for the Refinement of
Crystal Structures, University of Go¨ttingen, Germany, 1997.
[8] L.P. Jin, S.X. Lu, S.Z. Lu, Polyhedron 15 (1996) 4069.