Reactivity of a binuclear nickel(II) sulfur bridged complex with alkylating agents: Crystal structure of [Ni(L)Br(μ-Br)]2, (L=2,6-bis[(benzyl)mercaptomethyl]pyridine)

Article abstract of DOI:10.1016/S0277-5387(99)00067-4

The reactivity of a binuclear nickel(II) sulfur bridged complex with benzyl bromide and methyl iodide has been studied. The preparation of a novel binuclear nickel(II) bromine bridged complex of 2,6-bis[(benzyl)mercaptomethyl)]pyridine has been carried out from the reaction involving bis[2,6-bis(mercaptomethyl)pyridino] dinickel(II) and benzyl bromide. The structure of [Ni(L)Br(μ-Br)]₂ was determined by single-crystal X-ray analysis. The coordination environment of the nickel atom can be described as a distorted octahedron. The octahedra from the two nickel atoms in the dinuclear complex share one edge. The midpoint is located in a center of symmetry. Elsevier Science Ltd.

Full text of DOI:10.1016/S0277-5387(99)00067-4

Polyhedron 18 (1999) 1903–1908
Reactivity of a binuclear nickel(II) sulfur bridged complex with alkylating
agents
Crystal structure of [Ni(L)Br(m-Br)]2,
(L52,6-bis[(benzyl)mercaptomethyl]pyridine)
a
b ,
b
c
c
*
´
´
V.E. Marquez , J.R. Anacona , R.J. Hurtado , G. Dıaz de Delgado , E.M. Roque
a
´
´
´
Departamento de Quımica Aplicada, Instituto Universitario de Tecnologıa, Apartado Postal 255, Cumana, Venezuela
b
´
´
Departamento de Quımica, Universidad de Oriente, Apartado Postal 208, Cumana, Venezuela
c
´
´
Laboratorio de Cristalografia, Departamento de Quımica, Facultad de Ciencias, Universidad de Los Andes, Merida 5101, Venezuela
Received 5 July 1998; accepted 2 March 1999
Abstract
The reactivity of a binuclear nickel(II) sulfur bridged complex with benzyl bromide and methyl iodide has been studied. The
preparation of a novel binuclear nickel(II) bromine bridged complex of 2,6-bis[(benzyl)mercaptomethyl)]pyridine has been carried out
from the reaction involving bis[2,6-bis(mercaptomethyl)pyridino] dinickel(II) and benzyl bromide. The structure of [Ni(L)Br(m-Br)]2 was
determined by single-crystal X-ray analysis. The coordination environment of the nickel atom can be described as a distorted octahedron.
The octahedra from the two nickel atoms in the dinuclear complex share one edge. The midpoint is located in a center of symmetry.
1999 Elsevier Science Ltd. All rights reserved.
Keywords: Nickel complexes; Polynuclear complexes; Crystal structure; Pyridine complexes
1. Introduction
reactions S-alkylation of the square-planar diamagnetic
nickel(II) complex is accompanied by an increase in the
coordination number resulting in paramagnetic octahedral
complexes. Furthermore, it was noted that under normal
conditions S-alkylation will only occur at sulfur atoms
which are terminal and therefore two coordinate. The
reaction of alkyl halides with bis(methyl-2,29-dimercap-
todiethylamine) dinickel(II) (1) which contains both termi-
nal and bridging (3-coordinate) sulfur atoms can be used as
an example to illustrate the different behaviour of sulfur
atoms. In this case, S-alkylation occurs only at the terminal
sulfur atoms. Kinetics studies have indicated that the sulfur
atom remains coordinated during the S-alkylation reaction
and Busch et al. have used this type of reaction with nickel
atom serving as a template for ring closure [2,3].
Recently [6], we have studied the reaction of 2,6-
bis(mercaptomethyl)pyridine with nickel(II), palladium(II)
and platinum(II) and based on physicochemical and
spectroscopic data a possible sulfur-bridged dimeric struc-
ture (2) was assumed for the divalent square-planar
complexes. In order to investigate the characteristics of the
mercaptide complexes further, particularly the bridging
The behaviour of the mercaptide ion as a donor in
transition metal complexes has not been subjected to such
detailed study as a number of other donor groups. This
arises, in part, because the mercapto group often gives
metal ion derivatives that are extremely insoluble, bridged,
or even polymeric. Further, these substances are easily
oxidized. These properties greatly complicate the charac-
terization of mercapto complexes. However, the theoretical
interest and biological importance of mercaptans cause the
elucidation of the manner of interaction of this function
with metal ions to be of great interest [1].
The S-alkylation of coordinated thiolo groups has been
observed to occur when certain metal complexes of thiols
are treated with alkyl halides. In the course of a detailed
study of this type of reaction, Busch and his coworkers
[2–5] have investigated the S-alkylation of the nickel(II)
complex of 2-aminoethanethiol with alkyl halides. In these
*Corresponding author.
0277-5387/99/$ – see front matter
PII: S0277-5387(99)00067-4
1999 Elsevier Science Ltd. All rights reserved.

´
V.E. Marquez et al. / Polyhedron 18 (1999) 1903–1908
1904
and reactivity of coordinated sulfur atoms, the present
work was undertaken.
diamagnetism of the complex were estimated from Pasc-
al’s constants. Microanalyses were performed by the
Cambridge University Microanalytical Department.
2.3. Preparation of bis[2,6-
bis(mercaptomethyl)pyridino]dinickel(II) (2)
2.3.1. Method I
Nickel sulfate hexahydrate (6 g, 22.8 mmol) was
dissolved in concentrated ammonia solution (d50.88 g/
cm3, 20 cm3) and water (75 cm3). To this solution was
added, with stirring, 2,6-bis(mercaptomethyl)pyridine
(1.98 g, 11.6 mmol) dissolved in methanol (15 cm3). A
light brown precipitate was formed immediately. The solid
was separated by filtration and dried in vacuo over
sulphuric acid. Yield 2.23 g, 85.5%.
2.3.2. Method II
Nickel chloride hexahydrate (1.19 g, 5 mmol) was
dissolved in absolute ethanol (50 cm3). To this solution
was added slowly, with stirring, 2,6-bis(mercap-
tomethyl)pyridine (0.86 g, 5 mmol) in absolute ethanol (13
cm3). A light brown precipitate was formed immediately
and separated by filtration, washed with absolute ethanol
and ether, and then dried in vacuo over sulphuric acid.
Yield 0.95 g, 82.6%.
2. Experimental
2.4. Reaction of nickel(II) complex (2) with benzyl
bromide
2.1. Materials
The bis[2,6-bis(mercaptomethyl)pyridino] dinickel(II)
(0.3 g, 0.7 mmol) was suspended in 250 cm3 of chloro-
form and then 1.2 g, 7 mmol of benzyl bromide were
added. The mixture was stoppered and stirred for 24 h at
room temperature. During this time the solid dissolved,
giving a red–brown solution which was reduced in volume
to about 100 cm3 and then diethyl ether was added,
whereupon a light precipitate formed. The precipitate was
collected by filtration, washed with chloroform and ether,
and dried in vacuo over sulphuric acid. Yield 90%. Found:
C, 44.5; H, 3.9; N, 2.2%. Calcd. for Ni2(C21H21NS2)2Br4:
C, 44.2; H, 3.7; N, 2.5%.
Published methods were used to prepare 2,6-bis(mercap-
tomethyl)pyridine [7–9]. Solvents used for synthetic and
spectroscopic work were distilled over appropriate drying
agents prior to use. All other chemicals for synthetic
experiments were of analytical grade, available commer-
cially. Unless otherwise stated the reactions were carried
out under inert atmosphere of dry dinitrogen, but the final
work-up was performed in air.
2.2. Physical measurements
The infrared spectra were recorded on a Perkin-Elmer
Model 983 spectrophotometer and obtained by the KBr or
CsBr pellet method. The spectra were calibrated against
the 1603 cm21 band of polystyrene. Measurements of d–d
transitions in the visible and near infrared region were
taken with a Cary recording spectrophotometer Model
17D, while a Pye Unicam PU8800 spectrophotometer was
used for recording the visible and ultraviolet spectra.
Conductance measurements were made using a Wayne
Kerr Universal Bridge. The conductivity cell was cali-
brated with aqueous KCl. Magnetic moments were re-
corded on a John Matthey Magnetic Susceptibility Balance
MSB1 Model. Mercury tetrakis(thiocyanate) cobaltate(II)
was used as a susceptibility standard. Corrections for
2.5. Reaction of nickel(II) complex (2) with methyl
iodide
The bis[2,6-bis(mercaptomethyl)pyridino] dinickel(II)
(0.3 g, 0.7 mmol) was suspended in 250 cm3 of chloro-
form and then 1.2 g, 8.5 mmol of methyl iodide were
slowly added by means of a syringe. The flask was
stoppered and the suspension was stirred at room tempera-
ture for a period of approximately 3 h. During this time the
solid dissolved forming a deep red solution which upon
continued stirring changed to a dark yellow color. The
solution was reduced in volume to about 100 cm3 and then
diethyl ether was added, whereupon a dark yellow precipi-

´
V.E. Marquez et al. / Polyhedron 18 (1999) 1903–1908
1905
tate formed. This precipitate was collected by filtration,
washed with chloroform, methanol and ether and dried in
vacuo over sulphuric acid. Yield 73%. Found: C, 21.4; H,
2.8; N, 3.0%. Calcd. for Ni2(C9H13NS2)2I4: C, 21.1; H,
2.5; N, 2.7%.
hydrogen atoms were obtained in successive difference
Fourier maps with SHELXL-97 [11]. The refinement of
atomic coordinates and anisotropic thermal parameters was
carried out by full-matrix least-squares techniques on F2
with SHELXL-97. The hydrogen atoms of the ligand were
included in geometrically calculated positions and refined
using a riding model maintaining the C–H distances at
˚
2.6. Crystal structure determination of [Ni(L)Br(m-Br)]2
0.93 and 0.97 A for the aromatic and secondary –CH2
groups, respectively. They were assigned isotropic thermal
parameters equal to 1.5 times the Ueq of the carbon atom to
which they are attached. The details of the data collection
procedure and the structure refinement results are summa-
rized in Table 1. Selected bond lengths and angles are
summarized in Table 2.
For structural investigations
a single crystal of
[Ni2(C21H21NS2)2Br4] with approximate dimensions 0.23
0.330.4 mm was selected. Preliminary oscillation and
Weissenberg photographs allowed to determine approxi-
mate cell parameters and possible space group. The
intensities of 3982 reflections were collected at 293(2) K
in the u22u mode on a Nicolet P3/F diffractometer
automated by Crystal Logic, Inc., using monochromated
˚
3. Results and discussion
Mo Ka radiation (l50.7107 A). Unit-cell parameters
were calculated from the least-squares fitting of the angular
settings of 30 reflections with 208#2u #308. Three check
reflections were measured at intervals of 97 reflections in
order to monitor crystal stability and alignment. No
significant variation was detected in the intensities of the
standards.
Starting positions for the heavy atoms were obtained by
interpretation of the Patterson map calculated with
SHELXS-97 [10]. The positions for the rest of the non-
The reaction of an excess of methyl iodide or benzyl
bromide with the dimeric nickel complex (2) proceeds at a
fairly rapid rate in chloroform. The color change is usually
found to be complete within 20 to 30 min. To ensure
complete reaction both processes were allowed to proceed
for approximately 3 h. In the benzylated case a single light
green crystalline product [Ni2(C21H21NS2)2Br4] formed
and in the methylated case a single brown crystalline
product [Ni2(C9H13NS2)2I4] formed. The expected com-
positions of these products were confirmed by elemental
analysis.
Table 1
Crystal data and structure refinement for [Ni2(C21H21NS2)2Br4]
The infrared spectra of the products show the absorp-
tions expected for alkylated ligands. They are observed in
the following regions: 3000–3100 cm21 phenyl and
pyridine nCH vibrations, 2900–3000 cm21 aliphatic nCH
stretchings and four bands between 1420–1600 cm21
region attributed to the pyridine ring. In addition, the
spectra show characteristic bands for Ni–pyridine and
Ni–S bond stretching frequencies at 314 and 241 cm21 for
benzyl bromide, respectively. Methyl iodide also presents
these bands at 317 and 247 cm21, respectively. Bands in
both complexes for Ni–X vibrations appear at 218 cm21
for X5bromide and 186 cm21 for X5iodide.
Magnetic susceptibilities were measured in the solid
state. The benzylated and methylated complexes exhibit
magnetic moments of 3.30 and 3.08 BM, respectively,
corresponding to typical values of two unpaired electrons
in structures involving high-spin octahedral nickel(II).
The electronic spectra of these nickel(II) complexes
were recorded in dichloromethane as solvent in the range
8000–40 000 cm21 and the interpretation of spectral data
for the methylated complex was made based on a tetragon-
al model. Its low energy band presents a smooth splitting
and the positions of the two, almost equal intensity,
components are at 10 100 and 10 750 cm21. These two
components may represent a tetragonal component [12].
The observed bands (triplet–triplet transitions) and the
Formula
[Ni2(C21H21NS2)2Br4]
1140.08
Formula weight
Temperature
Radiation
293(2) K
˚
Mo Ka (l50.71069 A),
graphite monochromator
Crystal system
Space group
Triclinic
¯
P1
Crystal size, mm
Color, shape
0.230.330.4
Olive-green, parallelepiped
˚
Unit cell dimensions
a511.306(3) A a594.820(10)8
˚
b511.694(3) A b5102.730(10)8
˚
c58.572(2) A g5101.970(10)8
3
˚
Volume, A
1071.4(5)
Z
1
Dc, g cm23
1.767
m, cm21
48.36
F(000)
568
Absorption correction
Normalized transmission factors
2u range for data collection
Index ranges
Semi-empirical, from c-scan data
0.787–1.00
1.90 to 25.008
2 13 # h # 13
0 # k # 13
2 10 # l # 10
Reflections collected/unique
Refinement method
3982/3776 [Rint 50.0341, Rs 50.0621]
Full-matrix least-squares on F2
3776/0/244
Data/restraints/parameters
Goodness-of-fit on F2
1.043
Final R indices (I . 2s(I))
R
R
1 5 0.0517, wR2 5 0.1233
1 5 0.0858, wR2 5 0.1427
R indices (all data)
3
˚
Largest diff. peak and hole, e A
1.353 and 20.882

´
V.E. Marquez et al. / Polyhedron 18 (1999) 1903–1908
1906
Table 2
Selected bond lengths [A] and angles [8] for [Ni2(C21H21NS2)2Br4]a
˚
Ni–N(1)
Ni–S(1)
Ni–S(2)
Ni–Br(2)
2.057(5)
2.4271(19)
2.4592(19)
2.5291(11)
2.5405(11)
2.6101(11)
2.6101(11)
1.801(7)
1.829(7)
1.792(7)
1.821(7)
1.344(8)
1.355(8)
1.381(10)
1.514(9)
1.367(11)
1.364(12)
83.41(15)
82.01(15)
165.42(7)
94.60(14)
86.04(5)
C(4)–C(5)
C(5)–C(14)
C(5)–C(14)
C(7)–C(8)
C(8)–C(9)
C(8)–C(13)
C(9)–C(10)
1.378(10)
1.516(10)
1.516(10)
1.505(9)
Ni–Br(1)
1.371(10)
1.379(10)
1.384(11)
1.368(13)
1.329(13)
1.390(11)
1.492(10)
1.390(11)
1.396(10)
1.386(12)
1.363(14)
1.358(14)
1.400(12)
99.79(5)
Ni–Br(1)[1
Br(1)–Ni[1
S(1)–C(6)
C(10)–C(11)
C(11)–C(12)
C(12)–C(13)
C(15)–C(16)
C(16)–C(21)
C(16)–C(17)
C(17)–C(18)
C(18)–C(19)
C(19)–C(20)
C(20)–C(21)
S(2)–Ni–Br(1)
Br(2)–Ni–Br(1)
N(1)–Ni–Br(1)[1
S(1)–Ni–Br(1)[1
S(2)–Ni–Br(1)[1
Br(2)–Ni–Br(1)[1
Br(1)–Ni–Br(1)[1
Ni–Br(1)–Ni[1
S(1)–C(7)
S(2)–C(14)
S(2)–C(15)
N(1)–C(5)
N(1)–C(1)
C(1)–C(2)
C(1)–C(6)
C(2)–C(3)
C(3)–C(4)
N(1)–Ni–S(1)
N(1)–Ni–S(2)
S(1)–Ni–S(2)
N(1)–Ni–Br(2)
S(1)–Ni–Br(2)
S(2)–Ni–Br(2)
N(1)–Ni–Br(1)
S(1)–Ni–Br(1)
90.85(4)
90.12(13)
95.69(5)
84.28(5)
95.20(5)
174.09(14)
94.71(5)
175.13(4)
184.48(4)
95.52(4)
a Symmetry transformations used to generate equivalent atoms: [1: 2 x 1 2, 2 y 1 1, 2 z 1 1.
assignments for the methylated complex considering a
weak tetragonal field (D4h) are: 10 100 cm21 (3B1g →3Ega ),
10 750 cm21 (3B1g →3B2g), 12 900 cm21 (3B1g →3Aa2g)
and 17 240 cm21 (3B1g →3Ebg). In addition, there is a
further intense band at 27 400 cm21 attributable to a
charge transfer absorption.
used successfully in other cases [14]. The conductivity
measurement on dichloromethane solutions (4.4 cm2 /ohm/
mol) provide a molar conductance value that is within the
range usually expected of non-electrolytes, suggesting that
the bromine atoms is still coordinated to the metal.
The benzylated material is very soluble in dichlorome-
thane and when dissolved in it, an orange solution is
obtained. Crystals were grown from dichloromethane by
slow diffusion of acetone. After several days, green
crystals appeared in the orange solution corresponding to
the dimeric adduct [Ni2(C21H21NS2)2Br4]. In order to
elucidate the structure of this product a crystal structure
determination was undertaken.
The molecular structure of [Ni2(C21H21NS2)2Br4] (3)
and the atom labelling scheme, are shown in Fig. 1
(ORTEP-III) [15]. The compound is dinuclear, with the
two Ni atoms sharing two bridging bromines. In contrast
with Busch results, the linkage of the benzyl group has
occurred on the four sulfur atoms. A structural search in
the Cambridge Structural Database indicates that a similar
molecular structure is adopted by the cadmium complex of
2,6-bis(ethylthiomethyl)pyridine [16]. In this case, chlorine
atoms provide a bridge between the cadmium atoms.
The coordination environment of each Ni atom is
composed of one nitrogen, two sulfurs, and three bromine
atoms. The coordination polyhedron around Ni can be
approximated by a distorted octahedron. The Ni, S(1),
S(2), and N atoms lie in a plane and the Br(2) atom and a
Br(1)9 atom with symmetry operation 2 x 1 2, 2 y 1 1,
2 z 1 1, occupy the apical positions at distances of
The benzylated complex displays a well-resolved split-
ting of the low energy band with two weak components at
10 200 and 13 000 cm21. The observed triplet–triplet
absorptions and the assignments for the benzylated com-
plex considering distorted octahedron are: 10 200 and
13 000 cm21 (3A2g →3T2g, n1), 18 000 cm21 (3A2g →3T1g
(F), n2), 22 400 cm21 which may have charge transfer
character, 30 300 and 37 600 cm21 assigned to the n→p*
and p→p*, respectively, within the organic molecule.
Conductivity measurements in different solvents provide
molar conductance values that suggest different conclu-
sions. In dimethylsulphoxide solutions the values are
within the range usually expected of four-univalent elec-
trolyte (155 and 130 cm2 /ohm/mol for benzyl bromide
and methyl iodide, respectively). They showed to be three-
univalent electrolytes in dimethylformamide (206 and 152
cm2 /ohm/mol for benzyl bromide and methyl iodide,
respectively) and di-univalent in methanol. The molar
conductance of the benzylated complex was made in
dichloromethane giving very low molar conductivities, less
than 10 cm2 /ohm/mol for 1023 M solution. Drago and
Rosenthal [13] have criticized the use of dichloromethane
for conductivity studies due to its extensive ion pairing and
poor solvating properties, but dichloromethane has been

´
V.E. Marquez et al. / Polyhedron 18 (1999) 1903–1908
1907
Fig. 2. Projection of the structure of bis[Ni2(C21H21NS2)2Br4] down the
c-axis (ORTEP-III, ellipsoids drawn at the 50% level of probability).
1/2, 1/2. The dinuclear units repeat in three dimensions,
maintaining the axes of the phenyl rings approximately
parallel to h010j and the axes of the pyridine rings parallel
to h102j. Fig. 2 shows a projection of the structure down
the c-axis.
Attempts to characterize further the nickel(II)
methylated complex were unsuccessful. Despite the crys-
talline nature of the product, none of the crystals proved
suitable for X-ray structure determination. In the absence
of X-ray structural data for this complex, it is difficult to
assign its solid state structure, but it may well involve
coordination as the benzylated product.
Fig. 1. Structure of bis[Ni2(C21H21NS2)2Br4] indicating the atom label-
ling scheme (ORTEP-III, ellipsoids drawn at the 50% level of probabili-
ty).
˚
2.514(2) and 2.596(4) A below and above the plane,
respectively. The Ni–Br bond lengths are 2.529(1),
˚
2.541(1), and 2.610(1) A for Br(2), Br(1), and Br(1)9. The
˚
Ni–S distances differ by 0.032 A (2.427(2) and 2.459(2)
˚
A for S(1) and S(2), respectively). These distances are
longer than in the related ethylthiolato- and phenylthiolato-
(pyridine-2,6-dimethylthiolato-S,S9,N)nickel(II) (4 and 5)
[17], where the Ni–S distances are 2.183(1) and 2.165(1)
Supplementary data
˚
A for the ethylthiolato complex, and 2.171(2) and 2.167(1)
Listings of atomic position and anisotropic thermal
parameters for the crystal structure have been deposited at
the Cambridge Crystallographic Data Centre under the
deposition number CCDC 114173.
˚
A for the phenylthiolato complex. The corresponding Ni–S
bond lengths in cis-dichloroh2,11-dithiah[3,3](2,6)-
pyridinophanejnickel(II) (6) [18] are also shorter than in
the compound under investigation (2.407(1) and 2.385(1)
˚
A).
With regard to the Ni–N distance, the value obtained
˚
(2.057(5) A) is longer than the Ni–N bond lengths in
Acknowledgements
˚
compounds 4 and 5, (1.910(3) and 1.901(4) A) but shorter
˚
than the Ni–N bond in compound 6 (2.084 A). The planes
The financial support from Programa de Nuevas Tec-
´
of the phenyl rings form an angle of 3.4(5)8 between each
other, and angles of 28.9(3) and 25.7(3)8 with respect to
the plane of the pyridine ring.
The structure can be described in terms of pairs of
edge-sharing octahedra with the midpoint of the shared
edge coincident with the center of symmetry located at 0,
nologıas of CONICIT, through Grant NM-18 for the
establishment of the Centro Nacional de Difraccion de
Rayos-X, is gratefully acknowledged. V.E.M thanks Prof.
Lord Lewis and Prof. E. Constable for many useful
suggestions and encouragement. We are grateful to Lic.
Erasto Bastardo for his computational help.

´
1908
V.E. Marquez et al. / Polyhedron 18 (1999) 1903–1908
[11] G.M. Sheldrick, SHELXL-97, A program for the refinement of
References
¨
crystal structures from diffractometric data, University of Gottingen,
Germany, 1997.
[1] S.E. Livingstone, J. Chem. Soc. (1956) 437.
[2] D.H. Busch, J.A. Burke, D.C. Jicha, M.C. Thompson, M.L. Morris,
Adv. Chem. Ser. 37 (1967) 125.
[3] E.L. Blinn, D.H. Busch, J. Am. Chem. Soc. 90 (1968) 4280.
[4] D.H. Busch, D.C. Jicha, M.C. Thompsom, J.W. Wrathall, E.L. Blinn,
J. Am. Chem. Soc. 86 (1964) 3642.
[12] L.Y. Martin, C.R. Sperati, D.H. Busch, J. Am. Chem. Soc. 99 (1977)
2968.
[13] M.R. Rosenthal, R.S. Drago, Inorg. Chem. 4 (1965) 840.
[14] F. Uguagliati, D. Daganello, L. Busetto, V. Belluco, Inorg. Chem. 8
(1969) 1625.
[15] M.N. Burnett, C.K. Johnson, ORTEP-III Oak Ridge Thermal
Ellipsoid Plot Program for Crystal Structure Illustrations, ORNL-
6895, Oak Ridge National Laboratory, Tennessee, 1996.
[16] F.H. Allen, J.E. Davies, J.J. Galloy, O. Johnson, O. Kennard, C.F.
Macrae, B.M. Mitchell, G.F. Mitchell, J.M. Smith, D.G. Watson, J.
Chem. Inf. Comp. Sci. 31 (1991) 187.
[5] N.J. Rose, C.A. Root, D.H. Busch, Inorg. Chem. 6 (1967) 1431.
´
[6] V.E. Marquez, J.R. Anacona, Polyhedron 16 (1997) 1931.
[7] Brystol-Myers Co., US Patent 3290319/1966; Chem. Abstr. 66
(1967) 115609K
[8] Banyu Pharmaceutical Co., Ltd., Japanese Patent 7217778/1972;
Chem. Abstr. 77 (1972) 151979S.
¨
[17] H.-J. Kruger, R.H. Holm, Inorg. Chem. 28 (1989) 1148.
´
[9] V.E. Marquez, Ph.D. Thesis, University of Cambridge, Cambridge,
´
[18] E.C. Constable, J. Lewis,V.E. Marquez, P.R. Raithby, J. Chem. Soc.,
1988.
Dalton Trans. (1986) 1747.
[10] G.M. Sheldrick, SHELXS-97, A program for the solution of crystal
structures from diffractometric data, University of Gottingen, Ger-
many, 1997.