Synthesis and characterization of sulfonamides containing 8-aminoquinoline and their Ni(II) complexes. Crystalline structures of the Ni complexes

Article abstract of DOI:10.1016/S0277-5387(02)00997-X

Reaction between 8-aminoquinoline and benzenesulfonyl, toluene-4-sulfonyl and naphthalene-2-sulfonyl chlorides in a basic medium leads to the formation of the corresponding sulfonamides. Reaction of these sulfonamides with Ni(II) salts leads to the formation of the corresponding complexes, with a NiL₂ stoichiometry. Determination of the crystalline structure by X-ray diffraction shows an octahedral environment for the Ni(II) ions, sulfonamides acting as bidentate ligands and two solvent molecules completing the octahedral coordination. The spectroscopic and magnetic properties of these compounds are also discussed.

Full text of DOI:10.1016/S0277-5387(02)00997-X

Polyhedron 21 (2002) 1229Á1234
/
www.elsevier.com/locate/poly
Synthesis and characterization of sulfonamides containing
8-aminoquinoline and their Ni(II) complexes.
Crystalline structures of the Ni complexes
Benigno Mac´ıas a,*, Isabel Garc´ıa a, Mar´ıa V. Villa a, Joaqu´ın Borra´s b,
Alfonso Castineiras c, Francisca Sanz d
˜
a Departamento de Qu´ımica Inorga´nica, Facultad de Farmacia, Universidad de Salamanca, Campus Unamuno,
Avda. Campo Charro, s.n., E-37007 Salamanca, Spain
b Departamento de Qu´ımica Inorga´nica, Facultad de Farmacia, Universidad de Valencia, Valencia, Spain
c Departamento de Qu´ımica Inorga´nica, Facultad de Farmacia, Universidad de Santiago de Compostela, Santiago de Compostela, Spain
d Servicio de Rayos X, Universidad de Salamanca, Salamanca, Spain
Received 13 December 2001; accepted 27 March 2002
Abstract
Reaction between 8-aminoquinoline and benzenesulfonyl, toluene-4-sulfonyl and naphthalene-2-sulfonyl chlorides in a basic
medium leads to the formation of the corresponding sulfonamides. Reaction of these sulfonamides with Ni(II) salts leads to the
formation of the corresponding complexes, with a NiL2 stoichiometry. Determination of the crystalline structure by X-ray
diffraction shows an octahedral environment for the Ni(II) ions, sulfonamides acting as bidentate ligands and two solvent molecules
completing the octahedral coordination. The spectroscopic and magnetic properties of these compounds are also discussed. # 2002
Elsevier Science Ltd. All rights reserved.
Keywords: Nickel complexes; Sulfonamide complexes; 8-Aminoquinoline; X-ray crystal structures
1. Introduction
especially copper, have been studied, probably because
they may act as chemical nucleases [6Á9].
/
Coordination chemistry of nickel with ligands con-
taining N-donor atoms has been widely studied in the
literature and in recent years such studies have been
mostly addressed to ligands with a biological interest,
such as peptides [1,2]; the Ni(II)-promoted hydrolysis of
these peptides has been one of the aims of these sorts of
studies [3]. Recent findings showing the role of Ni(II)
ions in several processes taking place in living organisms
(where it is coordinated by N-donor ligands) have been
probably the origin of these studies [4]. However,
complexes of this ion with sulfonamides are not well
known, and only a few examples have been described in
the literature [5], despite the fact that complexes formed
by sulfonamides and other transition metal cations,
In the present paper, we describe the synthesis of three
new sulfonamides derived from 8-aminoquinoline and
benzenesulfonyl, toluene-4-sulfonyl and naphthalene-2-
sulfonyl chlorides, which have then been used as ligands
to coordinate Ni(II) ions.
2. Experimental
2.1. Materials and methods
8-Aminoquinoline and the sulfonyl chlorides were
provided by Aldrich and Fluka, respectively, and all
reagents were of analytical grade.
Chemical analyses for carbon, hydrogen and nitrogen
were performed on a 2400 elemental analyzer from
* Corresponding author. Tel.: ꢀ
514.
E-mail address: bmacias@usal.es (B. Mac´ıas).
/
34-923-294-524; fax: 34-923-294-
PerkinÁ
/
Elmer. Nickel was determined on an ICP
Elmer model 2380 Plasma 2).
spectrometer (PerkinÁ
/
0277-5387/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved.
PII: S 0 2 7 7 - 5 3 8 7 ( 0 2 ) 0 0 9 9 7 - X

1230
B. Mac´ıas et al. / Polyhedron 21 (2002) 1229Á1234
/
FT-IR spectra were recorded using KBr mulls and a
PerkinÁElmer FT-IR 1730 instrument. Electronic spec-
tra were recorded on a Shimadzu 8452A diode spectro-
Analytical data: [Ni(qbsa)2(H2O)(MeOH)]: Found: C,
55.31; H, 4.21; N, 8.43; Ni, 8.92%. Calculated for
NiC31H28N4O6S2: C, 55.13; H, 4.18; N, 8.29; Ni,
/
photometer.
8.69%. MS: m/zꢂ
625 [M]ꢀ
[Ni(qtsa)2(H2O)2]: Found: C, 56.01; H, 4.47; N, 8.33;
Ni, 8.39%. Calculated for NiC32H30N4O6S2: C, 55.75;
/
Molecular masses were measured by Servicio de
Masas (Universidad Auto´noma de Madrid, Spain) by
the FAB method with samples held on a nitrobenzyl
alcohol (NBA) matrix.
Magnetic susceptibility measurements at room tem-
perature (r.t.) were taken with a fully automatized
AZTEC DSM8 pendulum-type susceptometer. Mercury
tetrakis(thiocyanate)cobaltate(II) was used as a suscept-
ibility standard. Corrections for diamagnetism were
estimated from Pascal’s constants.
H, 4.39; N, 8.13; Ni, 8.52%. MS: m/zꢂ
652.1 [M]ꢀ
[Ni(qnsa)2(H2O)2].2DMF: Found: C, 57.91; H, 4.91;
N, 9.06; Ni, 6.55%. Calculated for NiC44H44N6O8S2: C,
/
58.22; H, 4.89; N, 9.26; Ni, 6.47%. MS: m/zꢂ
725 [M]ꢀ.
The most significant IR bands are listed in Table 3.
/
l
max nm (o, Mꢁ1 cmꢁ1): 266 (18 000), 370 (12 000), 585
(20), 785 (30).
2.4. X-ray data collection and processing
2.2. Synthesis of the ligands
A green needle crystal of [Ni(qtsa)2(H2O)2] was
mounted on an Enraf Nonius CAD4 automatic drif-
fractometer to be used for the structure determination.
X-ray diffraction data for [Ni(qbsa)2(H2O)(MeOH)] and
The sulfonamides were prepared by direct synthesis
between 8-amino quinoline with the corresponding
sulfonyl chloride, using pyridine as solvent. The proce-
dure is as follows: 5 mmol 8-amino quinoline and 5
mmol sulfonyl chloride are dissolved in 10 ml pyridine
[Ni(qnsa)2(H2O)2]×/2DMF were collected on a four circle
Seifert XRD 3003 SC diffractometer. Data of these
Ni(II) complexes were collected at r.t. using Cu Ka
and the mixture is heated under reflux at 110Á120 8C
/
radiation and the v Á2u scan technique. The unit cell
/
for 30 min. The solution is then left to cool down to
70 8C and is added to a beaker containing 10 ml water.
A brown precipitated is formed; this is filtered and
washed with distilled water until all pyridine has been
parameters were determined by least-squares refinement
on the 2u values of 25 strong well centered reflections in
the range 13.58B
88Bu B208 for
[Ni(qnsa)2(H2O)2]×2DMF compounds. Scattering fac-
/
u B
/
278 for [Ni(qtsa)2(H2O)2] and
/
/
[Ni(qbsa)2(H2O)(MeOH)]
and
removed. Yield is 85Á90%.
/
/
Analytical data: For N-quinolin-8-yl-benzenesulfona-
mide, Hqbsa: Found: C, 63.30; H, 4.04; N, 10.25%.
Calculated for C15H12N2O2S: C, 63.37; H, 4.25; N,
9.85%. For N-quinolin-8-yl-p-toluenesulfonamide,
Hqtsa: Found: C, 64.38; H, 4.69; N, 9.47%. Calculated
for C16H14N2O2S: C, 64.44; H, 4.73; N, 9.43%. For N-
tors for neutral atoms and anomalous dispersion
correction for Ni, C, N, O and S were taken from
‘International Tables for X Ray Crystallography’ [10].
The structures of [Ni(qtsa)2(H2O)2] and [Ni(qb-
sa)2(H2O)(MeOH)] were resolved by direct methods
and refined in the monoclinic space groups P21/c and
quinolin-8-yl-naphthalene-2-sulfonamide,
Hqnsa:
C2/c, respectively. The structure of [Ni(qnsa)2(H2O)2]×
/
Found: C, 68.08; H, 4.07; N, 8.32%. Calculated for
C19H14N2O2S: C, 68.24; H, 4.22; N, 8.38%. The most
significant IR bands are listed in Table 3. lmax nm (o,
Mꢁ1 cmꢁ1): 250 (16 000), 320 (7000).
2DMF was resolved by Patterson methods and refined
in the monoclinic space group P2(1)/n. Full-matrix
least-squares refinement with anisotropic thermal para-
meters for non-H atoms was carried out by minimizing
v(Fo ꢁ
Fc ) . Refinement on F2 for all reflections,
/
2
2 2
2.3. Synthesis of the nickel complexes
weighted R factors (Rv), and all goodness-of-fit S are
based on F2, while conventional R factors (R) are based
on F; R factors based on F2 are statistically about twice
as large as those based on F, and R factors based on all
data will be even larger.
Most of the calculations for [Ni(qtsa)2(H2O)2] were
carried out using CAD4-EXPRESS [11] software for data
collection, GENHKL [12] program for data reduction,
SHELX-97 [13] to refine the structure and PLATON [14]
for molecular graphics. All calculations for [Ni(qb-
Although direct synthesis between the sulfonamide
and the metallic salt is possible with the copper
complexes [6], addition of a base is required in the
case of the Ni derivatives in order to deprotonate the
sulfonamidate nitrogen atom. So 1.5 mmol sulfonamide
are dissolved in 75 ml DMF and 2 ml NH3 2 M are
added. Then a solution containing 0.75 mmol Ni(II)
chloride dissolved in 25 ml methanol is slowly added
dropwise to the former solution. Once the addition has
been completed, the original green color of the solution
becomes enhanced. Upon very slow evaporation of the
solvent, green crystals (suitable for structural determi-
nation by X-ray diffraction) were obtained.
sa)2(H2O)(MeOH)] and [Ni(qnsa)2(H2O)2]×
/
2DMF were
performed using CRYSOM [15] software for data collec-
TM
tion, X-ray8O [16] for data reduction, SHELXTL
to resolve and refine the structure and to prepare
[17]
material for publication.

B. Mac´ıas et al. / Polyhedron 21 (2002) 1229Á
/1234
1231
Table 1
Summary of crystal parameters, data collection and refinement for the three crystal structures
[Ni(qbsa)2(H2O)(MeOH)]
[Ni(qtsa)2(H2O)2]
[Ni(qnsa)2(H2O)2]2DMF
Empirical formula
Formula weight
Temperature (K)
NiC31H28N4O6S2
675.40
293(2)
NiC32H30N4O6S2
689.43
213(2)
NiC44H40N6O8S2
903.65
293(2)
˚
Wavelength (A)
1.54180
monoclinic
C2/c
1.54184
monoclinic
P21/c (No.14)
1.54180
monoclinic
P21/n
Crystal system
Space group
Unit cell dimensions
˚
a (A)
11.868(2)
16.161(3)
31.417(6)
90
13.361(12)
10.238(4)
24.056(16)
90
10.554(2)
30.480(6)
14.004(3)
90
˚
b (A)
˚
c (A)
a (8)
b (8)
g (8)
100.06(3)
90
101.06(7)
90
109.58
90
3
˚
Volume (A )
Z
Dcalc (g cmꢁ3
5932.8(21)
8
1.441
3229.4(4)
4
1.482
4244.4(15)
4
1.414
)
Absorption coefficient (mmꢁ1
F(000)
Crystal size (mm)
)
0.838
2672
2.491
1432
0.617
1880
0.04ꢃ0.04ꢃ0.06
0.20ꢃ0.10ꢃ0.05
0.30ꢃ0.04ꢃ0.06
u Range for data collection (8)
Index ranges
4.88Á
ꢁ14Bh B14
0Bk B19
/
67.26
5.48Á
ꢁ15Bh B1
0Bk B12
/
65.01
1.45Á64.34
ꢁ12Bh B11
0Bk B36
/
0BlB31
5249, 5147, 0.0219
ꢁ28BlB28
6243, 5476, 0.0509
0BlB14
5096, 4780, 0.0709
Reflections collected, unique, Rint
Refined method
full-matrix least-squares on F2 full-matrix least-squares on F2 full-matrix least-squares on F2
Data, restraints, parameters
Goodness-of-fit on F2
5125, 0, 510
1.160
5476, 0, 410
1.039
4764, 0, 654
1.216
Final R indices [I ꢀ2s(I)]
R indices (all data)
Largest differential peak and hole (e A
R1ꢂ0.0765, wR2ꢂ0.1556
R1ꢂ0.1130, wR2ꢂ0.2030
0.481 and ꢁ0.875
R1ꢂ0.0595, wR2ꢂ0.1184
R1ꢂ0.1551, wR2ꢂ0.1434
0.335 and ꢁ0.366
R1ꢂ0.0997, wR2ꢂ0.1730
R1ꢂ0.1724, wR2ꢂ0.2290
0.380 and ꢁ0.664
ꢁ3
˚
)
Crystal data and some details of the structural
determination are given in Table 1. Table 2 shows
some selected geometrical information.
quinoline group), which act as bidentate ligands,
together with two oxygen atoms from two water
molecules. The sulfonamide molecule forms a stable
five-member ring with the metal cation. It should be
noticed that the hydrogen atoms from the water
molecules are not shown in the structural formula of
3. Results and discussion
the complex, [Ni(qnsa)2(H2O)2]×
/
2DMF, as they were
The synthetic route used to prepare the sulfonamides
can be depicted as in Scheme 1 for N-quinolin-8-yl-
naphthalene-2-sulfonamide, Hqnsa.
Deprotonation of the sulfonamide takes place in an
ammonia medium to yield the sulfonamidate anion,
qnsaꢁ, which readily reacts with Ni(II) ions to form
complexes with a NiL2 stoichiometry, although solvent
molecules also exist completing the coordination around
the Ni(II) cations.
not located by X-ray diffraction.
Selected bond distances and angles are summarized in
Table 2. Only minor differences can be seen in the local
environment of the nickel ions among the three com-
plexes prepared, as expected bearing in mind that the
organic chains differentiating the three ligands studied
are rather far away from the coordinating (donor) sites
of these molecules. From the bond angles given, it can
be also concluded that the distortion is not too severe,
the angle between trans atoms being close to 1808, and
that between cis atoms close to 908.
3.1. Description of the crystal structures
The most significant distortions are observed for the
complex [Ni(qsba)2(H2O)(MeOH)], where two different
molecules (water and methanol) complete the octahedral
coordination around the Ni(II) cation, opposite to the
findings for the other complexes, where two water
As it could be readily expected, the local environment
around the Ni(II) cations is very similar in all three
cases, with a distorted octahedral structure (Figs. 1Á3).
/
The coordination polyhedron is formed by four N
atoms from both sulfonamide molecules (one nitrogen
atom from the sulfonamide group, and another from the
molecules exist. Consequently, the O1ꢀ
/
Niꢀ/O2 angle
decreases to 85.38, with respect to the values determined

1232
B. Mac´ıas et al. / Polyhedron 21 (2002) 1229Á1234
/
Table 2
˚
Selected bond lengths (A) and angles (8) for nickel complexes
[Ni(qbsa)2(H2O)(MeOH)]
[Ni(qtsa)2(H2O)2]
[Ni(qnsa)2(H2O)2]2DMF
Bond lengths
NiꢀN(21)
NiꢀN(11)
NiꢀO(1)
NiꢀN(12)
NiꢀN(22)
NiꢀO(2)
2.077(5)
2.048(5)
2.122(7)
2.139(5)
2.101(5)
2.068(7)
2.049(4)
2.060(5)
2.098(4)
2.119(4)
2.136(4)
2.152(4)
2.063(10)
2.067(9)
2.087(8)
2.127(10)
2.117(10)
2.097(7)
Bond angles
N(21)ꢀNiꢀN(11)
N(21)ꢀNiꢀO(1)
N(11)ꢀNiꢀO(1)
N(21)ꢀNi-N(12)
N(11)ꢀNiꢀN(12)
O(1)ꢀNiꢀN(12)
N(21)ꢀNiꢀN(22)
N(11)ꢀNiꢀN(22)
O(1)ꢀNiꢀN(22)
N(12)ꢀNiꢀN(22)
N(21)ꢀNiꢀO(2)
N(11)ꢀNiꢀO(2)
O(1)ꢀNiꢀO(2)
N(12)ꢀNiꢀO(2)
N(22)ꢀNiꢀO(2)
95.0(2)
176.9(2)
86.5(3)
91.1(2)
79.2(2)
91.9(3)
78.8(2)
92.3(2)
98.4(2)
166.2(2)
93.2(3)
171.7(3)
85.3(3)
99.9(3)
90.1(3)
91.7(19)
175.8(17)
92.3(17)
94.1(17)
79.4(17)
88.2 (16)
79.6(17)
91.5(18)
98.7(15)
168.8(18)
88.1(17)
177.4(18)
88.0(16)
98.1(17)
91.0(17)
91.7(4)
176.4(4)
90.5(3)
94.0(4)
79.6(4)
89.2(3)
78.4(4)
94.0(4)
98.6(3)
170.0(3)
90.8(3)
176.6(4)
87.0(3)
97.9(3)
88.7(3)
for the other two complexes (88.08 and 87.08); similarly,
the N11ꢀNiꢀO2 angle also decreases (171.78 vs. 177.438
and 176.68), while angle N21ꢀNiꢀO2 is slightly larger
(93.28 instead of 88.18 and 90.88).
/
/
/
/
As expected, the angle formed by the Ni(II) cation
with the two N atoms belonging to the same ligand
molecule (N11ꢀ
/
Niꢀ
/
N12 and N21ꢀ
/
Niꢀ
/
N22) remain
constant in all three complexes, although small differ-
ences are seen for angles formed between N atoms from
both ligands (e. g. N11ꢀ
consequence of the changes in other angles commented
above. The NiꢀN(sulfonamidate) distances are also
slightly larger than the NiꢀN(quinoline) ones. In any
/
Niꢀ
/
N21), probably as a
/
Fig. 1. Molecular structure of [Ni(qbsa)2(H2O)(MeOH)] showing the
atom numbering scheme.
/
case, the bond and angle distances measured for these
complexes are very similar to those previously reported
[5,18] for complexes similar to those prepared here.
the deprotonation of the N(sulfonamide) atom. It
should also be mentioned that the splitting of bands
due to the symmetric and antisymmetric stretching
modes of the SO2 group, probably because of the
3.2. FT-IR spectroscopy
different spatial orientation of the Sꢁ
/
O bonds upon
Data are summarized in Table 3. It should be noticed
that the removal of the band at 3260 cmꢁ1, due to the
coordination of the sulfonamide to the metal cation.
Both bands shift approximately 30 cmꢁ1 downwards
when passing from the ligands to the complexes,
Nꢀ
/
H stretching mode, in the complexes demonstrates
Scheme 1. Formation of N-quinolin-8-yl-naphthalene-2-sulfonamide.

B. Mac´ıas et al. / Polyhedron 21 (2002) 1229Á
/1234
1233
Table 3
similar to those previously reported for similar com-
pounds [19].
3.3. Magnetic susceptibility and electronic spectra
The effective magnetic moments at room temperature
of the complexes are in the range 2.95Á3.13 BM, in
/
agreement with the octahedral environment around the
Ni(II) cations. These values are only slightly larger than
that corresponding to the spin-only value (2.83 BM),
thus suggesting an orbital contribution by mixing of the
ground state with low energy excited states, or because
the ground state is orbitally degenerated.
The two intense bands recorded in the electronic
spectra of the complexes at 266 and 370 nm are
probably due to charge transfer processes. The two
Fig. 2. Molecular structure of [Ni(qtsa)2(H2O)2] showing the atom
numbering scheme.
bands at 785 and 585 nm are recorded in the ranges
3
usually expected for transitions A2g0
/
3T1g and
3A2g0
complexes [20].
/
3T1g(P), respectively, of octahedral Ni(II) (d8)
4. Supplementary material
Complete lists with atomic coordinates, anisotropic
displacement parameters, bond lengths and angles have
been deposited at the Cambridge Crystallographic Data
Center, 912 Union Road, Cambridge CB2 1EZ, UK
Fig. 3. Molecular structure of [Ni(qnsa)2(H2O)2]×
/2DMF showing the
atom numbering scheme.
probably due to a charge transfer from the deproto-
nated, negatively-charge N atom to the oxygen atom of
the sulfonyl group [7]; consequently, the double bond
(fax: ꢀ44-1223-336033; e-mail: deposit@ccdc.cam.ac.uk
or www: http://www.ccdc.cam.ac.uk) [CCDC 173676,
173677, 173866].
/
character of the Sꢁ/O group results larger in the free
ligands than in the complexes.
The remaining bands are recorded in close positions
both for the ligands and for the complexes, except the
Acknowledgements
band due to the Sꢀ
/
N stretching mode, which shifts
approximately 30 cmꢁ1 upwards, thus confirming the
donor role of the N atom. Overall, the positions are
The authors thank CICYT (grant PM97-0105-C02-
02) for financial support. Critical reading of the manu-
script by Professor V. Rives is also acknowledged.

1234
B. Mac´ıas et al. / Polyhedron 21 (2002) 1229Á
/1234
[12] M. Kretschmar, GENHKL Program for the reduction of
References
CAD4 Diffractometer data, University of Tubingen, Germany,
¨
1997.
[13] G.M. Sheldrick, SHELXL-97. Program for the Refinement of
[1] H. Sigel, R.B. Martin, Chem. Rev. 82 (1982) 385.
[2] R.B. Martin, in: H. Sigel, A. Sigel (Eds.), Metal Ions in Biological
Systems, vol. 23, 1988, p. 123.
Crystal Structures, University of Gottingen, Germany, 1997.
¨
[14] A.L. Spek, PLATON. A Multipurpose Crystallographic Tool,
Utrecht University, Utrecht, The Netherlands, 2000.
[15] M. Mart´ınez-Ripoll, F.H. Cano, An Interactive Program for
Operating Rich. Seifert Single-Crystal Four-Circle Diffract-
ometers, Institute of Physical Chemistry Rocasolano, CSIC,
Madrid, Spain, 1996.
[3] G.M. Polzin, J.N. Burstyn, in: H. Sigel, A. Sigel (Eds.), Metal
Ions in Biological Systems, vol. 38, 2001, p. 103.
[4] W. Kaim, B. Schwederski, Bioinorganic Chemistry: Inorganic
Elements in the Chemistry of Life. An Introduction and guide,
Wiley, Chichester, 1994, pp. 172Á184.
/
[5] S. Cabaleiro, J. Castro, E. Vazquez-Lopez, J.A. Garcia-Vazquez,
J. Romero, A. Sousa, Polyhedron 18 (1999) 1669.
[6] B. Macias, M.V. Villa, E. Fiz, I. Garcia, A. Castineiras, M.
˜
[16] J.M. Stewart, F.A. Kundell, J.C. Baldwin, The X-ray80 System,
Computer Science Center, University of Maryland, College Park,
MD, USA, 1990.
Gonzalez-Alvarez, J. Borras, J. Inorg. Biochem. 88 (2002) 101.
[7] C.A. Otter, S.M. Couchman, J.C. Jeffery, K.L.V. Mann, E.
Psillakis, M.D. Ward, Inorg. Chim. Acta 278 (1998) 178.
[8] N.P. Farrel (Ed.),Use of Inorganic Chemistry in Medicine, The
Royal Society of Chemistry, Cambridge, 1999.
[17] Siemens SHELTXTLTM, Version 5.0, Siemens Analytical X-ray
Instruments Inc., Madison, WI 53719, 1995.
[18] A.D. Garnovskii, A.S. Burlov, D.A. Garnovskii, I.S. Vasilchenco,
A.S. Antsichkina, G.G. Sadikov, A. Sousa, J.A. Garcia-Va´zquez,
J. Romero, M.L. Duran, A. Sousa-Pedrares, C. Gomez, Poly-
hedron 18 (1999) 863.
[9] J. Casanova, G. Alzuet, J. Borras, O. Carugo, J. Chem. Soc.,
Dalton Trans. (1996) 2239.
[19] G. Alzuet, S. Ferrer-Llusar, J. Borra´s, J. Server-Carrio, R.
[10] International Tables for X-ray Crystallography, vol. C, Kluwer
Academic Publishers, Dordrecht, The Netherlands, 1995.
[11] B.V. Nonius, CAD4-Express Software, Ver. 5.1/1.2, Enraf Nonius,
Delft, The Netherlands, 1994.
Martinez-Manez, J. Inorg. Biochem. 75 (1999) 189.
˜
[20] A.B.P. Lever, Inorganic Electronic Spectroscopy, second ed.,
Elsevier, New York, 1984.