Diphosphine complexes of nickel: Analogies in molecular structures and variety in crystalline arrangement

Article abstract of DOI:10.1016/S0277-5387(03)00263-8

This work comprised the preparation of six complexes of Ni(II) and their study by spectroscopy and X-ray diffraction. These complexes are: [Ni(dppe)Cl₂]CH₂Cl₂ (I), [Ni(dppen)Cl₂] (II), [Ni(dppm)Br₂]CH₂Cl₂ (III), [Ni(dppe)(NCS)₂] (IV), [Ni(dppen)I₂] (V), [Ni(dppp)Cl₂]CH₂Cl₂ (VI), where dppe = 1,2-bis(diphenylphosphine)ethane, dppen = cis-1,2-bis(diphenylphosphine)ethene, dppm = bis(diphenylphosphine)methane, dppp = 1,3-bis(diphenylphosphine)propane. The structures of complexes II-VI are unknown in the literature. Although the molecular structures of the six complexes present many similarities, their crystalline arrangements vary considerably. This is a feature not presented hitherto in previous work involving complexes of this type. In addition, a systematic spectroscopic study was undertaken on all six complexes.

Full text of DOI:10.1016/S0277-5387(03)00263-8

Polyhedron 22 (2003) 1567Á1573
/
www.elsevier.com/locate/poly
Diphosphine complexes of nickel: analogies in molecular structures
and variety in crystalline arrangement
Joao A.S. Bomfim a, Fabio P. de Souza a, Carlos A.L. Filgueiras a,*,
˜
Alexsandro G. de Sousa b, Maria Teresa P. Gambardella b
a Departamento de Qu´ımica Inorgaˆnica, IQ, Universidade Federal do Rio de Janeiro, 21945-970 Rio de Janeiro, RJ, Brazil
b Departamento de Qu´ımica e F´ısica Molecular, IQSC, Universidade de Sao Paulo, 13560-250 Sao Carlos, SP, Brazil
˜
˜
Received 6 November 2002; accepted 24 March 2003
Abstract
This work comprised the preparation of six complexes of Ni(II) and their study by spectroscopy and X-ray diffraction. These
complexes are: [Ni(dppe)Cl2]CH2Cl2 (I), [Ni(dppen)Cl2] (II), [Ni(dppm)Br2]CH2Cl2 (III), [Ni(dppe)(NCS)2] (IV), [Ni(dppen)I2] (V),
[Ni(dppp)Cl2]CH2Cl2 (VI), where dppeꢀ
/
1,2-bis(diphenylphosphine)ethane, dppenꢀ
/
cis-1,2-bis(diphenylphosphine)ethene,
VI are
dppmꢀbis(diphenylphosphine)methane, dpppꢀ
/
/
1,3-bis(diphenylphosphine)propane. The structures of complexes IIIÁ
/
unknown in the literature. Although the molecular structures of the six complexes present many similarities, their crystalline
arrangements vary considerably. This is a feature not presented hitherto in previous work involving complexes of this type. In
addition, a systematic spectroscopic study was undertaken on all six complexes.
# 2003 Elsevier Science Ltd. All rights reserved.
Keywords: Diphosphine complexes; Nickel complexes; Molecular structures; Crystal packing
1. Introduction
organic chains with several Ni salts, namely NiCl2,
NiBr2, NiI2 and Ni(NCS)2.
Many authors have investigated the modes of co-
ordination of nickel (II) with diphosphines, as well as
the structures and the spectroscopic properties of the
2. Experimental
resulting complexes [1Á7]. These systems are quite
/
attractive in view of their importance in terms of
explaining a series of important features of coordination
compounds, namely p-bonding, lability and trans influ-
ence of ligands, geometry, as well as for their importance
as precursors in catalytic reactions [4]. Although several
complexes have been described in the literature, next to
nothing has been written comparing molecular and
crystalline structures.
Whereas the former can be similar in various com-
pounds, their crystalline arrangements differ to a great
extent. Insofar as most complexes of this kind have been
prepared from NiCl2, we decided to investigate the
complexation of a series of diphosphines of different
All the reactions were carried out under argon in
Schlenk glassware and the solvents were dried by
standard techniques. Commercial Ni halides and dipho-
sphines were used throughout, and Ni(NCS)2 was
obtained in the laboratory from NiCl2 and KNCS.
The complexes were prepared according to the following
scheme:
CH2Cl2ꢂMeOH
NiX2 ꢁdiphosphine 1:1
[Ni(diphosphine)X2]
Ar;
1
h; 50 ꢀC
Replacement of NiCl2 by (Et4N)2[NiCl4] in the
reaction with dppe, and of the solvent by MeNO2,
followed by recrystallisation from CH2Cl2, led to a
mixture of (I) and its unsolvated analogue, previously
reported as forms A (the latter) and B (I), respectively
[8]. All complexes were initially obtained as powders in
approximately 70% yield. Upon recrystallisation in
* Corresponding author.
E-mail address: calf@iq.ufrj.br (C.A.L. Filgueiras).
0277-5387/03/$ - see front matter # 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0277-5387(03)00263-8

1568
J.A.S. Bomfim et al. / Polyhedron 22 (2003) 1567Á1573
/
CH2Cl2 they produced copious crops of crystals suitable
for X-ray work. C, H elemental analysis of the six
complexes were consistent with the proposed formula-
tions, which are: [Ni(dppe)Cl2]CH2Cl2 (I), [Ni(dp-
pen)Cl2] (II), [Ni(dppm)Br2]CH2Cl2 (III), [Ni(dppe)-
(NCS)2] (IV), [Ni(dppen)I2] (V), [Ni(dppp)Cl2]CH2Cl2
(VI). They all decomposed without melting above
140 8C.
3. Results and discussion
All six complexes have the diphosphines chelated to
the Ni atom, which also has, in addition, two halides or
pseudo halides. Table 1 shows the spectroscopic data for
the complexes. The halide complexes present NiX and
NiP IR absorption bands in accordance with previous
work for similar complexes [11]. Complex IV, [Ni(dp-
pe)(NCS)2], shows IR absorptions in the ranges ex-
pected for N-bonded species [12], with an increase in
nCS, as compared to KNCS, and a lowering in dNCS. The
six complexes show a characteristic electronic transition
in the visible region, as well as strong CT bands in the
UV [13], as listed in Table 1. Table 1 also shows the
31P{1H} NMR chemical shifts in CDCl3 solution as well
as in the solid state for all the complexes and the free
diphosphines. The spectrum of I in the solid state gave
only one, somewhat broad absorption at d 60.7, which
in solution was shifted to d 57.7. Previous results had
shown [Ni(dppe)Cl2]CH2Cl2 to absorb at d 61.9 and
60.0 in the solid state, whereas in CDCl3 it absorbed at d
58.2 [8]. Interestingly, a sample of the complex obtained
from the reaction of (Et4N)2[NiCl4] and dppe produced
in the solid state NMR. absorptions at d 60.9, 55.0 and
53.0, respectively. The latter two values correspond to
the chemical shifts assigned to the unsolvated form,
FTIR spectra were obtained with an IR760 Nicolet-
Magna spectrophotometer, using CsI and polyethylene
pellets in the ranges 4000Á
/
200 and 600Á ,
50 cmꢂ1
/
respectively. Electronic spectra were recorded from a
Varian CARY 1E instrument, using 10ꢂ4 mol lꢂ1
solutions in CH2Cl2. Both solid state MAS 31P{1H}
and solution 31P{1H} NMR spectra were obtained from
a DRX300 MHz Bruker instrument. Spectroscopic data
are given in Table 1.
The molecular and crystal structures of the six
complexes were investigated using an automated
CAD4 diffractometer, with a graphite monochromator
˚
and Mo Ka radiation lꢀ/0.71073 A. The structures
were solved by SIR-92 [9] and the refinements were
carried out using SHELXL-97 [10]. All non-H atoms were
anisotropically refined. Tables 2 and 3 give the pertinent
data. Table 4 gives a summary of the most important
bond distances and bond angles.
Table 1
FTIR, electronic spectroscopy and 31P{1H} NMR data for the compounds under study
Compound
Selected IR absorptions (cmꢂ1
)
Electronic absorptionsa
l (nm) o, (l molꢂ1 cmꢂ1
31P{1H} NMR, d (ppm)
nCN
nCS
dNCS
nNiP nNiX
)
Solid state
60.7
CDCl3 solution
[Ni(dppe)Cl2]CH2Cl2 (I)
[Ni(dppen)]Cl2 (II)
390
337
314
475
336
240
(1112)
(13 896)
(13 042)
57.7
64.7
22.5
60.3
87.3
35.2
337
314
464
279
232
(2398)
(30 481)
(43 857)
69.4
[Ni(dppm)Br2]CH2Cl2 (III)
[Ni(dppe)(NCS)2] (IV)
[Ni(dppen)I2] (V)
284
275
493
271
230
(1811)
(16 037)
(29 170)
ꢂ
/
34.0
65.9
87.4
4.8
ꢂ/
2091
2092
842 462
822 454
330
304
436
257
234
(723)
(31 950)
(36 930)
355
280
522
287
239
(4030)
(42 170)
(45 600)
[Ni(dppp)Cl2]CH2Cl2 (VI)
365
347
322
464
287
229
(671)
(13 992)
(19 705)
dppe
ꢂ
/
12.6
31.6
25.5
21.9
ꢂ
/
12.1
22.7
21.8
16.6
dppen
dppm
dppp
KNCSb
ꢂ
/
ꢂ
/
ꢂ
/
ꢂ
/
ꢂ/
ꢂ/
2053
748 486
471
a
In CH2Cl2.
Ref. [12].
b

J.A.S. Bomfim et al. / Polyhedron 22 (2003) 1567Á
/1573
1569
Table 2
Crystal data and structure refinement for I, II and III
Complex
I
II
III
Crystal system
Space group
Unit cell
monoclinic
P21/c
monoclinic
C2
monoclinic
P21/n
˚
a (A)
12.258(1)
15.403(3)
15.299(2)
104.804(8)
2792.7(6)
4/1.458
15.524(3)
8.005(1)
12.455(1)
124.628(9)
1273.6(3)
2/1.372
10.762(1)
20.468(1)
12.597(1)
93.86(1)
2768.5(4)
4/1.650
˚
b (A)
˚
c (A)
b (8)
3
V (A )
˚
Z, Dcalc (Mg mꢂ3
)
m (mmꢂ1
)
1.207
1.108
3.910
Crystal size (mm)
Theta range for data collection
Temperature (K)
0.40ꢃ
2.32/27.4
293(2)
/
0.35ꢃ
/
0.20
0.38ꢃ
3.0/30.0
293(2)
/
0.23ꢃ/0.20
0.23ꢃ
2.4/28.1
293(2)
/
0.40ꢃ0.57
/
Index ranges
ꢂ
/
155
05k 5
05l 519
/
h 5
/15
ꢂ
ꢂ/
/
215
115
05l 5
/
h 5
k 5
17
/
17
05
05
165
/
h 5
k 5
l 5
/
14
/
/19
/
/
0
/
/
27
/
/
/
/
ꢂ
/
/
/
16
Reflections collected
Reflections unique
6581
6344
3322
0.055
304
2061
1980
1620
0.018
141
7038
6692
3180
0.055
298
Reflections I ꢀ/2s(I)
Rint
Refined parameters
Goodness-of-fit
1.008
1.055
1.059
R [I ꢀ
/
2s(I)]
R1ꢀ
wR2ꢀ
R1ꢀ0.160
wR2ꢀ0.155
0.086/ꢂ0.713
/
0.053
R1ꢀ
wR2ꢀ
R1ꢀ0.058
wR2ꢀ0.105
0.584/ꢂ0.406
/
0.038
R1ꢀ
wR2ꢀ
R1ꢀ0.179
wR2ꢀ0.178
0.556/ꢂ0.594
/
0.055
/0.123
/
0.095
/0.146
R (all data)
/
/
/
/
/
/
Dr (e Aꢂ3
)
/
/
/
Table 3
Crystal data and structure refinement for IV, V and VI
Complex
IV
V
VI
Crystal system
Space group
Unit cell
trigonal
P3121
monoclinic
P21/n
orthorhombic
Pnma
˚
a (A)
8.662(2)
8.7624(8)
14.630(1)
20.278(1)
92.895(9)
2596.2(1)
4/1.814
12.238(1)
15.239(1)
15.620(2)
˚
b (A)
˚
c (A)
31.800(2)
b (8)
3
V (A )
˚
2066.30(7)
3/1382
0.992
2913.1(5)
4/1.430
1.159
Z, Dcalc (Mg mꢂ3
)
m (mmꢂ1
)
3.26
Crystal size (mm)
Theta range for data collection
Temperature (K)
0.25ꢃ
2.7/29.4
273(2)
/
0.25ꢃ/0.30
0.075ꢃ
2.5/30.0
293(2)
/0.125ꢃ/0.50
0.20ꢃ
2.5/26.3
293(2)
/
0.35ꢃ
/
0.50
Index ranges
05
05
435
/
h 5
k 5
l 5
/
10
ꢂ
/
125
215
285
/
h 5
k 5
l 528
/
0
ꢂ
/
145
185
195
/
h 5
k 5
l 518
/
15
/
/
10
ꢂ
/
/
/
0
ꢂ
/
/
/
18
ꢂ
/
/
/43
ꢂ/
/
/
ꢂ/
/
/
Reflections collected
Reflections unique
2520
2237
1235
0.098
159
8000
7552
4948
0.025
281
5483
3073
2160
0.076
164
Reflections I ꢀ/2s(I)
Rint
Refined parameters
Goodness-of-fit
1.026
1.012
1.012
R [I ꢀ
R (all data)
Dr (e Aꢂ3
/
2s(I)]
R1ꢀ
wR2ꢀ
R1ꢀ0.121
wR2ꢀ0.124
0.362/ꢂ0.220
/
0.046
R1ꢀ
wR2ꢀ
R1ꢀ0.085
wR2ꢀ0.087
1.223/ꢂ0.794
/
0.034
R1ꢀ
wR2ꢀ
R1ꢀ0.062
wR2ꢀ0.110
0.485/ꢂ0.675
/
0.038
/0.103
/
0.075
/0.103
/
/
/
/
/
/
)
/
/
/

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J.A.S. Bomfim et al. / Polyhedron 22 (2003) 1567Á1573
/
By far the most interesting results are those dealing
with the structural data, given by the X-ray diffraction.
Table 4 gives the most important bond lengths and bond
angles of the complexes, and Figs. 1 and 2 show the
molecular structures of complexes IÁVI. The structures
/
of complexes I [7,8,15] and II [7] are known and will be
given here for comparison. All other structures are being
reported for the first time.
All six complexes present an approximately square
planar environment around the Ni atom. Complex VI is
the only one to show Pꢀ
/
Niꢀ
/
P and Xꢀ
/
Niꢀ/X angles close
to 908, as expected. The ligand dppp has a longer chain
and can be accommodated in the chelate structure
without causing any great strain. All other complexes
present an Xꢀ
/
Niꢀ
/
X angle considerably greater than
908, and a PꢀNiꢀ
/
/
P angle below 908, which in the case of
complex III is dramatically lowered to only 75.628. This
reflects the considerable strain posed by the four-
membered ring which the Ni atom is constrained to
form by dppm. The bond distance data also show a
marked difference between VI, on the one hand, and the
other complexes, on the other. If one compares the
complexes with the Clꢂ ligand, the Niꢀ
show only slight variations. Now if we take the Niꢀ
distances, those found for VI, 2.1791 A, are higher than
those for all other complexes. The longer carbon chain
in dppp is likely to make this ligand to accept less p
backbonding from the Ni atom than the other dipho-
/
Cl distances
/P
˚
sphines, hence the longer Niꢀ
/
P distances in VI. In
complex IV, the NꢀC and CꢀS distances are quite in
/
/
accordance with expected values for the N-bonded
isothiocyanate ligand, and also in agreement with the
results shown by the IR results given in Table 1.
It is quite interesting to look at the crystal arrange-
Fig. 1. Molecular structures of complexes I (top) and II (bottom).
ments of complexes IÁVI. In spite of a certain regularity
/
namely [Ni(dppe)Cl2] [8]. Table 1 shows that when one
goes from the free ligands to the complexes the chemical
shifts undergo a notable increase. Complexation de-
shields the phosphorus atoms considerably, due to a
shift in the electron cloud to the region between
phosphorus and the metal. It is interesting to note that
the phosphorus nuclei in complex VI show a lesser
chemical shift variation compared to the free ligand
than the situation prevailing in the other complexes.
This is likely to be related to the decreased strain and
less p backbonding present in this complex, as the
discussion of the molecular structures will show. The
dppm complex, III, on the other hand, is the only one in
which a decrease in d was observed in solution as well as
in the solid state on going from the free ligand to the
complex. Our NMR data follow a trend similar to what
has been observed in diphosphine organo-platinum
complexes, in which the ring formed by the metal and
the diphosphine greatly affects the phosphorus chemical
in their molecular structures, their packing in the
crystalline state varies considerably, and is given in
Figs. 3 and 4. These figures show the dppe and dppen
complexes, i.e. I, II, IV and V, to form layered
structures, whereas III forms lump-like clusters. The
most interesting structure is that of VI, in which the
layers present tubular arrangements for the phenyl rings.
The molecular structure of the monoclinic complex
[Ni(dppe)Cl2], I, shows that the dihedral angle between
rings a and b is 70.428, whereas that between rings c and
d is 63.538. The presence of a solvent molecule is likely
to contribute to this asymmetry, which is absent in the
analogous [Ni(dppe)(NCS)2] complex, IV. In the latter,
the angles between the phenyl rings on each phosphorus
is 59.468. The crystal structure of the two complexes
shows this difference markedly. Whereas I forms
monoclinic crystals, the crystals of IV are trigonal.
The two dppen complexes, [Ni(dppen)Cl2], II, and
[Ni(dppen)I2], V, are both monoclinic, but whereas II
presents a higher molecular symmetry, with an angle of
59.468 between both sets of phenyl rings, V, possibly
shift values: [Me2Pt(dppm)], d ꢂ
/
40.0; [Me2Pt(dppe)], d
54.5; [Me2Pt(dppp)], d 3.3 [14].

J.A.S. Bomfim et al. / Polyhedron 22 (2003) 1567Á
/1573
1571
Fig. 2. Molecular structures of complexes IIIÁVI.
/
Table 4
Selected bond distances (A) and angles (8) for complexes IÁ
˚
/VI
[Ni
(dppe)Cl2]CH2Cl2
(I)
[Ni(dppen)Cl2]
(II)
[Ni(dppm)Br2]CH2Cl2
(III)
[Ni(dppe)(NCS)2] [Ni(dppen)I2]
(IV) (V)
[Ni(dppp)Cl2]CH2Cl2
(VI)
Bond distances
Niꢀ
Niꢀ
Niꢀ
Niꢀ
/
P(1)
P(2)
X(1)
X(2)
2.145(1)
2.160(1)
2.208(1)
2.200(1)
1.841(4)
1.826(4)
1.505(6)
2.144(1)
2.144(1)
2.189(1)
2.189(1)
1.799(4)
1.799(4)
1.314(3)
2.143(2)
2.152(2)
2.335(1)
2.324(1)
1.847(8)
1.852(2)
2.151(1)
2.1569(9)
2.1791(8)
/
2.151(1)
1.880(4)
1.880(4)
1.831(5)
1.831(5)
1.47(1)
2.1632(10)
2.5353(5)
2.5184(5)
1.808(3)
1.808(4)
1.320(5)
2.1791(8)
2.1991(9)
2.1991(9)
1.827(3)
1.827(3)
1.515(4)
/
/
P(1)ꢀ
P(2)ꢀ
C(1)ꢀ
Nꢀ
Cꢀ
/
C(1)
/
C(2)
/C(2)
Á/
Á/
Á/
/C
Á/
Á/
Á/
Á/
1.149(6)
1.609(6)
Á/
Á/
Á/
Á/
/S
Bond angles
P(1)ꢀ
P(1)ꢀ
P(1)ꢀ
P(2)ꢀ
P(2)ꢀ
X(1)ꢀ
P(1)ꢀC(1)ꢀ
CꢀNꢀ
NꢀCꢀ
/
Niꢀ
Niꢀ
Niꢀ
Niꢀ
Niꢀ
Niꢀ
/
P(2)
X(1)
X(2)
X(1)
X(2)
86.99(5)
88.78(5)
175.11(5)
175.29(5)
88.92(5)
95.41(5)
86.71(7)
86.71(7)
174.52(5)
174.52(5)
87.82(4)
97.65(6)
75.62(8)
91.90(7)
169.98(8)
165.76(7)
95.59(6)
97.37(5)
90.8(3)
86.99(7)
89.2(1)
87.81(4)
89.69(3)
91.77(4)
88.705(6)
175.28(4)
175.28(4)
88.705(6)
90.82(5)
/
/
/
/
176.1(1)
176.1(1)
89.2(1)
174.60(3)
176.76(3)
88.29(3)
/
/
/
/
/
/X(2)
94.6(3)
94.341(16)
/
/
P(2)
Á/
Á/
Á/
Á/
Á/
Á/
Á/
Á/
Á/
Á/
Á/
Á/
Á/
/
/Ni
Á/
Á/
167.1(5)
178.2(5)
/
/S

1572
J.A.S. Bomfim et al. / Polyhedron 22 (2003) 1567Á1573
/
Fig. 3. Crystal packing of complexes I, II, IV and V.
because of distortion due to the larger iodide ligands,
shows angles of 70.148 between rings a and b and 56.358
between rings c and d. They also pack quite distinctly in
the crystals: while the more symmetric complex II shows
all the Cl atoms sticking towards the same direction, V
shows an alternation amongst the Cl atoms.
Complexes III, [Ni(dppm)Br2]CH2Cl2, and VI,
[Ni(dppp)Cl2] CH2Cl2, form monoclinic and orthor-
hombic crystals, respectively. The former shows an
asymmetry in the molecular arrangement due to the
position of the solvate molecule. As a consequence, the
phenyl rings in III have angles of 70.148 (rings a and b)
and 56.358 (rings c and d). Complex VI, on the other
hand, is very symmetric regarding both the molecular as
well as the crystal structure. The position occupied by
the CH2Cl2 solvate molecule is such that the angles
between the two sets of phenyl rings are the same
(86.548).
ties in the solid state. This was shown especially in
complexes III and VI, for which the solid state arrange-
ments deviate considerably from those of their counter-
parts (I, II, IV and V), as given by the crystallographic
data and the solid state 31P NMR results. Therefore
caution should be exerted when comparing data ob-
tained for a series of apparently similar complexes. In
addition to solution data and molecular structures, a
knowledge of the packing of individual molecules, as
this study showed, can lead to important differences
which may be reflected in the chemistry of the com-
pounds.
5. Supplementary data
Crystallographic data for the complexes have been
deposited at the Cambridge Crystallographic Data
Centre. The CCDC numbers are 188923 for complex I,
188924 for complex II, 189328 for complex III, 188926
for complex IV, 188925 for complex V and 189327 for
complex VI. The copies of this information may be
obtained free of charge from The Director, CCDC, 12
4. Conclusion
This work showed that homologous Ni(II) dipho-
sphine complexes, in spite of their similarities, differ in
several aspects of their molecular geometry, and that
differences in their crystalline arrangement are even
more marked, possibly leading to quite different proper-
Union Road, Cambridge, CB2 1EZ, UK (fax: ꢁ44-
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1223-336033; e-mail: deposit@ccdc.cam.ac.uk or www:
http://www.ccdc.cam.ac.uk).

J.A.S. Bomfim et al. / Polyhedron 22 (2003) 1567Á
/1573
1573
Acknowledgements
The authors would like to thank the agencies CNPq,
Faperj, FUJB and Fapesp for financial support.
References
[1] L. Sacconi, J. Gelsomini, Inorg. Chem. 7 (1968) 291.
[2] J.T. Wang, C. Udovich, K. Nakamoto, A. Quattrochi, J.R.
Ferraro, Inorg. Chem. 9 (1970) 12.
[3] A.F. Williams, Acta Crystallogr. Sect. C 45 (1989) 1002.
[4] J.A. Rahn, A. Delian, J.H. Nelson, Inorg. Chem. 28 (1989) 215.
[5] A. Del Zotto, A. Mezzetti, V. Novelli, P. Rigo, M. Lanfranchi, A.
Tiripicchio, J. Chem. Soc., Dalton Trans. (1990) 1035.
[6] L. Manojlovic-Muir, H. Mirza, N. Sadiq, R. Puddephatt, Inorg.
Chem. 3 (1993) 117.
[7] W. Oberhauser, C. Bachmann, T. Stampfl, R. Haid, P. Bruggeller,
¨
Polyhedron 16 (1997) 2827.
[8] R. Busby, M. Hursthouse, P. Jarrett, C.W. Lehmann, K.M.
Abdul Malik, C. Phillips, J. Chem. Soc., Dalton Trans. (1993)
3767.
[9] A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi, J.
Appl. Crystallogr. 26 (1993) 343.
[10] G.M. Sheldrick, SHELXL-97, Program for Refinement of Crystal
Structures, University of Gottingen, Germany, 1997.
¨
[11] C. Udovich, J. Takemoto, K. Nakamoto, J. Coord. Chem. 1
(1971) 89.
[12] K. Nakamoto, Infrared and Raman Spectra of Inorganic and
Coordination Compounds, 4th ed., Wiley, New York, 1986, p.
284.
[13] A.B.P. Lever, Inorganic Electronic Spectroscopy, 2nd ed., Else-
vier, Amsterdam, 1984, p. 535.
[14] P.E. Garrou, Chem. Rev. 81 (1981) 229.
[15] A.L. Spek, B.P. van Eijck, R.J.F. Jans, G. van Koten, Acta
Crystallogr. Sect. C 43 (1987) 1878.
Fig. 4. Crystal packing of complexes III and VI.