Metal complexes with disubstituted oxamidic ligands

Article abstract of DOI:10.1016/S0020-1693(96)05520-X

Three oxamidic ligands have been prepared by reaction of oxalyldichloride with the appropriate amine H₂NC₆H₄P(C₆H₅) ₂ (H₂A), H₂NC₂H₄(NC₅H₄) (H₂B) and H₂NC₂H₄SC₆H₅ (H₂C). They have been characterized by elemental analyses, IR, NMR, mass spectrometry and for H₂B by X-ray diffractometry. The crystals, grown from a tetrahydrofuran/diethylether solution, are monoclinic, space group P2₁/c, cell dimensions a = 9.503(4), b = 6.278(4), c = 13.083(5) A and β = 100.24(4)^o with Z = 2. The asymmetric unit is half of the ligand molecule which shows an inversion centre between the C-C bond of the oxamidic group. The molecule is elongated in a three steps configuration. The reaction of H₂A with trans-Pd(C₆H₅CN)₂(Cl)₂ forms the white mononuclear cis-Pd(A) and the yellow homodinuclear trans-Pd₂(A) (Cl)₂ complexes as confirmed by scanning electron microscopy (SEM) and EDX analyses and by an X-ray structure of Pd₂(A) (Cl)₂. The yellow crystals, grown from alcoholic solution, are monoclinic, space group P2₁/c, cell dimensions a = 10.335(5), b = 10.246(5), c = 16.480(6) A and β = 100.81(5)^o with Z = 2; as for H₂B crystals, the asymmetric unit is half of the whole molecule. A distorted square planar coordination around each metal ion is reached by the coordination of a phosphorus, an oxygen and a nitrogen atom of the ligand and a chlorine atom. H₂B forms the homodinuclear nickel(II) and copper(II) complexes M(B)(X)₂ (X = C1^-, CH₃COO^-, ClO^-₄). Crystals of the dinuclear copper(II) complex Cu₂(B) (Cl)₂(dmso)₂, grown from dimethylsulphoxide, are triclinic, space group P1, cell dimensions a = 8.352(5), b = 8.361(5), c = 9.959(4) A, α = 83.39(4) β = 85.49(3), γ = 75.38(5)^o with Z = 1. Again the dinuclear entity shows a inversion centre between the two C-C bonds of the oxamide ligand. Each copper(II) ion has a distorted square pyramidal environment formed by two nitrogen atom and an oxygen atom of half oxamidic ligand, a chlorine atom and the oxygen atom of a dimethylsulphoxide molecule; the copper-copper distance is 5.28 A. An antiferromagnetic interaction was observed for the dinuclear copper(II) complexes. H₂C does not form complexes when reacted with transition metal ions.

Full text of DOI:10.1016/S0020-1693(96)05520-X

Inorganica Chimica Acta 260 (1997) 1–9
Metal complexes with disubstituted oxamidic ligands
U. Casellato, P. Guerriero, S. Tamburini, P.A. Vigato U
Istituto di Chimica e Tecnologie Inorganiche e dei Materiali Avanzati, CNR, C.so Stati Uniti 4, 35127 Padua, Italy
Received 1 February 1996; accepted 30 September 1996
Abstract
Three oxamidic ligands have been prepared by reaction of oxalyldichloride with the appropriate amine H2NC6H4P(C6H5)2 (H2A),
H2NC2H4(NC5H4)(H 2B) and H2NC2H4SC6H5 (H2C). They have been characterized by elemental analyses, IR, NMR, mass spectrometry
and for H2B by X-ray diffractometry. The crystals, grown from a tetrahydrofuran/diethylether solution, are monoclinic, space group P21/c,
˚
cell dimensions as9.503(4), bs6.278(4), cs13.083(5) A and bs100.24(4)8 with Zs2. The asymmetric unit is half of the ligand
molecule which shows an inversion centre between the C–C bond of the oxamidic group. The molecule is elongated in a three steps
configuration. The reaction of H2A with trans-Pd(C6H5CN)2(Cl)2 forms the white mononuclear cis-Pd(A) and the yellow homodinuclear
trans-Pd2(A)(Cl)2 complexes as confirmed by scanning electron microscopy (SEM) and EDX analyses and by an X-ray structure of
Pd2(A)(Cl)2. The yellow crystals, grown from alcoholic solution, are monoclinic, space group P21/c, cell dimensions as10.335(5),
˚
bs10.246(5), cs16.480(6) A and bs100.81(5)8 with Zs2; as for H2B crystals, the asymmetric unit is half of the whole molecule. A
distorted square planar coordination around each metal ion is reached by the coordination of a phosphorus, an oxygen and a nitrogen atom of
the ligand and a chlorine atom. H2B forms the homodinuclear nickel(II) and copper(II) complexes M(B)(X)2 (XsCly,CH 3COOy,
y
#
ClO4 ). Crystals of the dinuclear copper(II) complex Cu2(B)(Cl)2(dmso)2, grown from dimethylsulphoxide, are triclinic, space group P1,
˚
cell dimensions as8.352(5), bs8.361(5), cs9.959(4) A, as83.39(4) bs85.49(3), gs75.38(5)8 with Zs1. Again the dinuclear
entity shows a inversion centre between the two C–C bonds of the oxamide ligand. Each copper(II) ion has a distorted square pyramidal
environment formed by two nitrogen atom and an oxygen atom of half oxamidic ligand, a chlorine atom and the oxygen atom of a
˚
dimethylsulphoxide molecule; the copper–copper distance is 5.28 A. An antiferromagnetic interaction was observed for the dinuclear cop-
per(II) complexes. H2C does not form complexes when reacted with transition metal ions.
Keywords: Crystal structures; Transition metal complexes; Palladium complexes; Oxamidic acid complexes
1. Introduction
N,N9-disubstituted oxamides are versatile ligands for the
design and preparation of polynuclear systems [11–17].
Their cis™trans isomerization favours the formation of well
defined mononuclear, homo orheteropolynuclearcomplexes.
The ligands in the cis-configuration easy produce mononu-
clear complexes, which may be used as ‘ligands’ for subse-
quent heteronuclear complexation. On the contrary the
trans-configuration leads to the formation of homodinuclear
complexes, which may give rise to polynuclear species by
intermolecular aggregation [18–20].
It was found that in these polynuclear complexestheoxam-
idic group is an excellent bridging mediator of magnetic
exchange between neighbouring paramagnetic centres, the
type and magnitude of coupling depending on the metal ion
used and its coordination environment [11–32]. Thus the
aminoamides N,N9-bis(3-aminopropyl)oxamide or N,N9-
bis(2-amino-2,2-dimethylethyl)oxamide form, under suita-
ble experimental conditions, mononuclear or homodinuclear
copper(II) complexes and heterodinuclear or -trinuclear
Many studies have been devoted to the design and synthe-
sis of di- and poly-nucleating macrocyclic or macroacyclic
ligands and related homo and/or heteronuclear complexes
and to the interaction between metal ionsconnectedbyappro-
priate bridges [1–4]. These systems offer the possibility of
a knowledge of the magnetic pathway between paramagnetic
centres and more generally of the fundamental factors gov-
erning physico-chemical properties of the complexes con-
taining d- and/or f-metal ions [5]. An appropriate design of
these compounds makes them suitable building blocks to
obtain new materials. Moreover spin exchange, charge trans-
fer, etc., between metal ions in polymetallic systems are of
paramount relevance experimentally and theoretically in the
study of biological metallic sites and/or their chemical mod-
els [6–10].
U Corresponding author.
0020-1693/97/$17.00 q 1997 Elsevier Science S.A. All rights reserved
PII S0020-1693(96)05520-X

2
U. Casellato et al. / Inorganica Chimica Acta 260 (1997) 1–9
complexes containing d,d or d,f metal ions [11,12,14–
18,24,26]. Moreover an oligomerization or polymerization
of the dinuclear or trinuclear entities through the oxygen
atoms of the oxamidic ligands or the donor atoms of the
counter anions (i.e. Cly,CH 3COOy, NCOy, etc.) may
occur giving rise to zigzagging chains [19,21,26]. The X-
ray structural determinations of these complexes and an
appropriate study of their magnetic properties have given
essential information for a rationalization of the magnetic
coupling of paramagnetic species through the oxamide
bridge, allowing correct magneto-structural correlations also
in polymeric species.
2.1.1. Preparation of H2A, H2B and H2C
For the preparation of the three ligands, the following
experimental procedure was employed [36]: oxalyldichlor-
ide (10 mmol) in anhydroustetrahydrofuran(50 mmol)was
added dropwise and under nitrogen to an anhydrous tetra-
hydrofuran solution (100 ml) of the appropriate amine
(20 mmol) and triethylamine (2 mmol). The resulting sus-
pension was stirred at room temperature and under a nitrogen
flux for 24 h. The white precipitate was filtered and the tetra-
hydrofuran solution was partially evaporated under reduced
pressure. By the addition of diethylether to this reduced solu-
tion obtained, a pale yellow or white precipitatewasobtained.
It was filtered, washed with diethylether and dried in vacuo.
The melting points of the prepared compounds are H2Aat
215–2168C, H2B at 174–1758C and H2C at 199–2008C. H2A
and H2B are soluble in all the common organic solvents.
In the present paper we report the preparation and prop-
erties of the functionalized oxamide compounds H2A∆H2C
obtained by reaction of oxalyldichloride and the appropriate
amine H2N–R [RsC6H4P(C6H5)2,HC
2CH2(C5H4N),
CH2CH2S(C6H5)] in the presence of base, and related com-
plexes containing palladium(II), platinum(II), copper(II)
or nickel(II) together with the X-ray structure of H2B and of
the dinuclear complexes Pd2(A)(Cl)2 and Cu2(B)(Cl)2-
(dmso)2.
2.1.2. Preparation of cis-Pd(A) and trans-Pd2(A)(Cl)2
To a CHCl3 solution (50 ml) ofH2A(0.5 mmol, 304 mg),
trans-Pd(C6H5CN)2(Cl)2 (0.5 mmol, 191.5 mg) in MeOH
(50 ml) and triethylamine (1 mmol) were added at room
temperature. The solution was refluxed for 24 h. The yellow
precipitate formed was filtered. It contains cis-Pd(A) and
trans-Pd2(A)(Cl)2 which were separated by extraction in a
soxhlet with tetrahydrofuran. cis-Pd(A) is extracted and
obtained as white needles from the tetrahydrofuran solution,
while the residue is the trans-Pd2(A)(Cl)2 in a pure yellow
form. The yellow trans-Pd(A)(Cl)2 can be recrystallized
form an alcoholic solution and gives rise to yellow rhombi
suitable for an X-ray investigation.
During these investigations it was observed that it was
almost impossible to form heterodinuclear complexes: all the
attempts to synthesize these compounds, under different
experimental conditions, led to the formation of homodinu-
clear complexes.
2.1.3. Preparation of M2(B)(H2B)(X)2PnS (MsNi, XsCly,
CH3COOy, MsCu, XsClO4y, ns0–5, SsH2O, EtOH)
To a boiling ethanolic solution (50 ml) of H2B
(0.5 mmol), the appropriate metal(II) salt (0.5 mmol) dis-
solved in the minimum volume of H2O (5 ml) and triethyl-
amine (1 mmol) were added. The resulting solution was
refluxed for 3 h, then evaporated to dryness. The residue was
dissolved in ethanol and precipitated with diethyl ether. The
precipitate was collected by filtration, washed twice with a
1:1 ethanol/diethylether solution and dried in vacuo.
2. Experimental
2.1. Materials
Oxalyldichloride, 2-(2-aminoethyl)pyridine, 2-amino-
ethyl, phenyl-sulphide, triethylamine, the salts and the sol-
vents were commercial products used without further purifi-
cation, while tetrahydrofuran was anhydrified and purified
following literature methods [33]. Also 2-(diphenylphos-
phino)-aniline, trans-Pd(C6H5CN)2(Cl)2 and trans-Pt-
(CH3CN2)(Cl)2 were prepared according to literature [34].
Pyridine-2,6-dialdehyde was prepared by oxidation at
room temperature ofpyridine-2,6-dimethanol(Aldrich)with
activated MnO2 in CHCl3. The CHCl3 solution was stirred
for 4 days, then evaporated to dryness and the crude product
was purified by silica gel chromatography using CH2Cl2 as
eluant [35].
2.1.4. Preparation of M2(B)(X)2 (MsCu2q, Ni2q; XsCly,
CH3COOy)
To a boiling ethanolic solution (50 ml) of H2B
(0.5 mmol), the appropriate metal salt(0.5 mmol)dissolved
in the minimum volume of H2O (5 ml) and triethylamine
(1 mmol) were added. The resulting solution was refluxed
for 3 h, then evaporated to dryness. The residue was treated
with ethanol, collected by filtration, washed with ethanol and
dried in vacuo.
2.2. X-ray crystallography
The elemental analyses of the prepared ligands and related
complexes are reported in Table 1.
The cell parameters and intensity data were collected on a
Philips PW1100 (FEBO System) automatic diffractometer

U. Casellato et al. / Inorganica Chimica Acta 260 (1997) 1–9
3
Table 1
Elemental analyses of the prepared ligands and related complexes
Complex
Found (%)
Calc. (%)
CHNCHN
H2A
H2B
H2C
74.99
64.42
59.97
61.28
50.85
43.92
48.17
43.49
39.04
44.00
27.10
45.00
39.25
4.60
18.78
7.77
3.76
2.95
5.00
4.94
4.49
3.48
4.09
3.05
3.95
2.95
4.97
6.08
5.59
3.17
3.00
11.64
12.44
11.15
10.86
9.84
8.20
11.05
11.40
75.00
63.87
59.99
60.94
51.27
44.43
47.93
42.78
38.88
44.36
27.68
45.17
39.65
4.33
18.80
7.85
4.31
3.17
5.48
5.36
4.39
3.26
4.10
3.48
4.17
3.33
5.16
6.43
5.79
3.74
3.15
12.19
12.42
11.09
11.33
10.35
8.07
[Pd(A)]P2(H2O)
Pd2(A)(Cl)2
Ni2(B)(H2B)(Cl)2P5(H2O)PEtOH
Ni2(B)(H2B)](Ac)2P4H2O
Cu2(B)(H2B)(ClO4)2(EtOH)2
Cu2(B)(Cl)2
Cu2(B)(Ac)2
Cu2(B)(ClO4)2P4H2O
Ni2(B)(Ac)2
10.53
11.65
Ni2(B)(Cl)2
˚
using Mo Ka radiation (ls0.71069 A) and v–2u scan
method. Owing to its instability in air, the copper complex
was sealed into a quartz capillary with its mother liquor. No
appreciable decomposition was observed during data
collections.
assigned by the spin decoupling technique. All the samples
examined were dissolved in hot dmso-d6 or CDCl3 used also
as internal references.
The homogeneity of the heteropolynuclear samples was
checked by using a Philips XL40 model scanning electron
microscopy equipped with an EDAX PV99 X-ray energy
dispersive spectrometer. Metal ratios were determined by
energy dispersive X-ray spectrometry (EDX) [39].
The solvent content (H2O or MeOH) was evaluated by
thermal analysis curves using a Netzsch STA 429 thermo-
analytical equipment. The tests were performed in a nitro-
gen atmosphere (flux rate 250 ml miny1; heating rate
58C miny1) and in air under the same conditions. Neutral
alumina (Carlo Erba product) wasusedasreferencematerial.
All mass spectrometric measurements were performed on
a VG ZAB 2F instrument (VG analytical Ltd.) operating in
electron impact (EI) (70 eV, 200 mA, ion source tempera-
ture 2008C) and fast atom bombardment (FAB) (8 keV Xe
atom bombarding a thioglicerol/acetic solution of the sam-
ple) conditions [40,41].
All intensity data were corrected for Lorentz and polari-
zation effects. Because of the relatively high absorption coef-
ficients of the palladium and copper complexes, absorption
corrections were applied based on c-scans of three strong
reflections [37].
The three structures were solved by direct methods/Pat-
terson and Fourier methods and subsequent refinement by
full-matrix least-squares; a unit weighting scheme was
applied.
In all three data sets, reflections with IG3s(I) were con-
sidered observed and used in the structural analyses. Anisot-
ropy was introduced for all non-hydrogen atoms.
Hydrogen bonded to carbon atoms were introduced in cal-
culated positions with fixed C–H distances and isotropictem-
2
˚
˚
perature factors (C–Hs1.08 A, Uisos0.08 A ).
Crystal and intensity data for the compounds are reported
in Table 2; atomic positional parameters with estimated stan-
dard deviations are listed in Tables 3–5; selected bond dis-
tances and angles in Tables 6 and 7 Table 8.
Magnetic susceptibilities were determined by the Faraday
method at room temperature, the apparatus (Oxford Instru-
ments) being calibrated with HgCo(NCS)4 [42]. Diamag-
netic corrections were performed [43].
The thermal and hydrogen atom positional parameters and
observed/calculated structural factors have been deposited
as Supplementary Material.
3. Results and discussion
All calculations were carried out on a DIGITAL ALPHA-
AXP 300 computer and using SHELX-76 and SHELX-86
[38] programs.
The phosphino-oxamidic ligand H2A was prepared by
reaction of oxalyldichloride and 2-(diphenyl-phosphino)-
aniline in anhydrous tetrahydrofuran in the presence of tri-
ethylamine. It is a white solid, very stable in air; as expected
the phosphinic group is not oxidized to the corresponding
phosphine oxide. It is very soluble in tetrahydrofuran and
CHCl3, but shows a low solubility in other organic solvents
(i.e. MeOH, EtOH, CH3CN, Et2O). The IR spectrum shows
a band at 3325 cmy1 due to nN–H and a strong absorption at
1696 cmy1 attributed to nC_O of the amidic groups. The 1H
2.3. Physico-chemical measurements
IR spectra were recorded as KBr pellets on a MattsonFTIR
3000 spectrometer.
1H and 13C NMR spectra were recorded at 200.132 MHz
on a Bruker AC200 spectrometer equipped with an Aspect
3000 computer at room temperature. Some ofthesignalswere

4
U. Casellato et al. / Inorganica Chimica Acta 260 (1997) 1–9
Table 2
Crystal and intensity data for H2B, Pd2(A)(Cl)2, and Cu2(B)(Cl)2(dmso)2
Compound
Formula
d
H2BP
C16H18N4O2
299.8
colourless, irregular blocks
0.32=0.24=0.18
monoclinic
2(A)(Cl)2
C38H28N2O2Cl2P2Pd2
892.3
yellow prisms
0.25=0.20=0.33
monoclinic
Cu2(B)(Cl)2(dmso)2
C20H28N4O4S2Cl2Cu2
650.6
Formula weight
Colour and habit
Crystal size (mm)
Crystal system
Space group
green prisms
0.19=0.38=0.23
triclinic
#
P21/c (No. 14)
P21/c (No. 14)
P1 (No. 2)
Cell parameters
˚
a (A)
9.503(4)
6.278(4)
13.083(5)
10.335(5)
10.246(5)
16.480(6)
8.352(5)
8.361(5)
9.959(4)
83.39(4)
85.49(3)
73.38(5)
667.6
˚
b (A)
˚
c (A)
a (8)
b (8)
g (8)
100.24(4)
100.81(5)
3
˚
Cell volume (A )
Z
768.1
2 a
1.29
1714
2 a
1 a
Calc. density (g cmy3
T (K)
)
1.72
295
1.62
295
295
F(000) (elec.)
316
0.52
1032 (6–618)
973 b
937
884
12.11
332
19.89
2147 (5.0–508)
1971
1901
0.884–1.00
172 (11.1)
0.025
Absorption m (cmy1) (Mo Ka)
Data collected (2u limits)
Unique data
2030 (6.4–59.88)
1959 b
1924
0.787–0.988
181 (10.6)
0.028
Data with I)3s(I)
Transmission coeff.
Number of param. (observ. per param.)
R c
127 (7.4)
0.036
0.34
GOF
1.58
0.55
Highest shift/e.s.d.
Highest map residual (e A
0.865
0.16
0.001
0.382
0.004
0.372
y3
˚
)
a The asymmetric unit is half of the whole molecule.
b Owing to the poor quality of the crystals, a low number of reflections has been collected.
c Rs8(NFocNyNF N)/8(F ).
o
Table 3
SEM investigationsshow whiteneedlesandyellowrhombi
for the palladium(II) complexes, which are attributable to
the cis and trans form, respectively, on the basis of EDX
analyses. A careful investigation, carried out on both samples
by means of the microprobe, evidences a Pd:P ratio of 1:2 in
the white needles and a Pd:P:Cl ratio of 1:1:1 in the yellow
rhombi, confirming the presence of both compounds.
Fractional coordinates with equivalent isotropic thermal parameters for H2B
a
2
˚
Atom
x
y
z
Ueq (A )
N(1)
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
C(7)
C(8)
N(2)
O(1)
0.7861(2)
0.6857(3)
0.5533(3)
0.5217(2)
0.6238(2)
0.7550(2)
0.8669(2)
0.8560(2)
0.9372(2)
0.9605(2)
0.8272(1)
0.7544(3)
0.8747(4)
0.9116(4)
0.8251(4)
0.7054(4)
0.6704(3)
0.5319(4)
0.3017(3)
0.0689(3)
0.1634(3)
0.0849(3)
0.7295(1)
0.7615(2)
0.7035(2)
0.6068(2)
0.5715(2)
0.6346(1)
0.6008(2)
0.6370(2)
0.5103(1)
0.6026(1)
0.4456(1)
0.0523(6)
0.0667(9)
0.066(1)
0.0639(8)
0.0559(7)
0.0415(6)
0.0527(8)
0.0480(7)
0.0446(6)
0.0469(5)
0.0647(6)
A subsequent soxhlet extraction of the mixture of cis- and
trans-palladium(II) complexes by tetrahydrofuran, allows a
separation of the more soluble cis from the trans complex.
The two compounds show very similar IR spectra. In partic-
ulara strong bandat1647 cmy1, duetothenC_O oftheamidic
group, is clearly detectable; trans-Pd2(A)(Cl)2 shows an
additional IR band at 322 cmy1 due to nPd–Cl
.
a Ueq is defined as one third of the trace of the orthogonalized Uij tensor.
By recrystallization of trans-Pd2(A)(Cl)2 from an alco-
holic solution, yellow crystals suitable for an X-ray investi-
gation were obtained. A perspective view of the complex
with atom labelling is shown in Fig. 1. Selected bond lengths
and angles are given in Table 7. The asymmetric unit is
formed by half a molecule of the complex which shows an
inversion centre between the carbon atoms C(1)–C(19)of
the oxamidic group. The centre of the molecule is almost
planar, except for the benzene rings of the phosphine groups.
Each palladium(II) atom is in a distorted square planar envi-
ronment, being coordinated by a phosphorus, an oxygen and
NMR spectrum in CDCl3 shows a peak at 10.06 ppm due to
the amidic NH protons while the peaks at 8.02, 7.07, 6.86
and 6.73 ppm are due to the aromatic protons. No signals due
to the presence of phosphine-oxide groups are present in the
IR and NMR spectra.
H2A reacts with trans-Pd(C6H5)2(Cl)2 in CHCl3 and in
the presence of base (NEt3), giving rise to the mononuclear
cis-Pd(A) and the homodinuclear, trans-Pd(A)(Cl)2
according to the Scheme 1.

U. Casellato et al. / Inorganica Chimica Acta 260 (1997) 1–9
5
Table 4
Table 6
˚
Fractional coordinates with equivalent isotropic thermal parameters for
Selected bond distances (A) and angles (8) for H2B
Pd2(A)(Cl)2
N(1)–C(1)
C(1)–C(2)
C(3)–C(4)
C(5)–C(6)
C(7)–N(2)
C(8)–O(1)
1.341(3)
1.368(3)
1.370(3)
1.500(3)
1.450(3)
1.227(2)
N(1)–C(5)
C(2)–C(3)
C(4)–C(5)
C(6)–C(7)
C(8)–N(2)
1.333(2)
a
2
˚
Atom
x
y
z
Ueq (A )
1.361(4)
1.385(3)
1.530(3)
1.328(3)
Pd(1)
Cl(1)
O(1)
C(1)
N(1)
P(1)
C(3)
C(4)
C(5)
C(6)
0.19311(4)
0.4150(1)
0.1702(3)
0.0524(5)
0.10516(4)
0.0861(2)
0.11646(2) 0.0280(1)
0.16042(9) 0.0462(5)
y0.0371(4)
y0.0417(5)
0.1109(4)
0.2655(1)
0.1835(3)
0.2534(3)
0.3274(3)
0.3314(3)
0.2615(3)
0.1875(3)
0.4540(3)
0.5714(3)
0.6549(3)
0.6210(3)
0.5036(3)
0.4201(3)
0.1395(3)
0.1226(3)
0.2212(3)
0.3367(3)
0.3537(3)
0.2550(3)
0.0214(2)
0.038(1)
0.032(2)
0.030(1)
y0.0159(3)
0.0818(2)
N(1)∆N(2a)
3.012(2)
y0.0039(4)
0.1694(1)
y0.2164(3)
y0.2801(3)
y0.2067(3)
y0.0698(3)
y0.0061(3)
y0.0794(3)
0.3451(3)
0.3799(3)
0.2822(3)
0.1498(3)
0.1150(3)
0.2127(3)
0.2209(4)
0.2758(4)
0.3527(4)
0.3746(4)
0.3197(4)
0.2429(4)
0.19880(8) 0.0302(4)
C(1)–N(1)–C(5)
C(1)–C(2)–C(3)
C(3)–C(4)–C(5)
C(4)–C(5)–C(6)
C(5)–C(6)–C(7)
N(2)–C(8)–
117.5(2)
118.4(2)
120.2(2)
121.8(2)
111.5(2)
125.1(2)
N(1)–C(1)–C(2)
C(2)–C(3)–C(4)
N(1)–C(5)–C(4)
N(1)–C(5)–C(6)
C(6)–C(7)–N(2)
C(7)–N(2)–C(8)
123.9(2)
118.7(2)
121.3(2)
116.9(2)
112.4(2)
122.5(2)
0.1180(2)
0.1716(2)
0.2351(2)
0.2450(2)
0.1913(2)
0.1278(2)
0.1665(2)
0.1334(2)
0.0928(2)
0.0853(2)
0.1183(2)
0.1589(2)
0.3463(2)
0.4297(2)
0.4729(2)
0.4327(2)
0.3494(2)
0.3062(2)
0.040(2)
0.048(2)
0.053(2)
0.043(2)
0.033(2)
0.031(2)
0.044(2)
0.055(2)
0.064(3)
0.064(3)
0.051(2)
0.031(2)
0.058(2)
0.069(3)
0.059(3)
0.059(2)
0.051(2)
0.035(2)
C(7)
C(2)
C(9)
O(1)
a Symmetry codes2yx, 0.5qy, 1.5yz.
C(10)
C(11)
C(12)
C(13)
C(8)
C(15)
C(16)
C(17)
C(18)
C(19)
C(14)
Table 7
˚
Selected bond distances (A) and angles (8) for Pd2(A)(Cl)2
Pd(1)–Cl(1)
Pd(1)–N(1)
O(1)–C(1)
P(1)–C(7)
P(1)–C(14)
2.280(2)
2.010(4)
1.258(6)
1.795(3)
1.793(4)
Pd(1)–O(1)
Pd(1)–P(1)
N(1)–C(2)
P(1)–C(8)
C(3)–C(4)
2.121(4)
2.173(2)
1.422(5)
1.803(4)
1.395(5)
N(1)–Pd(1)–P(1)
O(1)–Pd(1)–N(1)
Cl(1)–Pd(1)–N(1)
Pd(1)–O(1)–C(1)
Pd(1)–P(1)–C(14)
Pd(1)–P(1)–C(7)
C(7)–P(1)–C(14)
P(1)–C(7)–C(6)
N(1)–C(2)–C(7)
P(1)–C(8)–C(13)
P(1)–C(14)–C(19)
85.9(1)
81.0(2)
176.2(1)
110.5(3)
119.7(1)
99.8(1)
107.6(2)
122.4(3)
115.1(3)
120.5(3)
123.8(3)
O(1)–Pd(1)–P(1)
Cl(1)–Pd(1)–P(1)
Cl(1)–Pd(1)–O(1)
Pd(1)–N(1)–C(2)
Pd(1)–P(1)–C(8)
C(8)–P(1)–C(14)
C(7)–P(1)–C(8)
P(1)–C(7)–C(2)
N(1)–C(2)–C(3)
P(1)–C(8)–C(9)
P(1)–C(14)–C(15)
166.1(1)
95.20(8)
98.2(1)
a Ueq is defined as one third of the trace of the orthogonalized Uij tensor.
Table 5
119.5(3)
111.8(1)
108.9(2)
108.1(2)
117.6(3)
124.6(3)
119.5(3)
116.2(3)
Fractional coordinates with equivalent isotropic thermal parameters for
Cu2(B)(Cl)2(dmso)2
a
2
˚
Atom
x
y
z
Ueq (A )
Cu(1)
Cl(1)
O(1)
O(2)
N(1)
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
C(7)
N(2)
C(8)
S(1)
C(9)
C(10)
0.22377(4)
0.1893(1)
0.29439(4)
0.09950(8)
0.4021(2)
0.5054(2)
0.2049(2)
0.1669(3)
0.1183(4)
0.1097(4)
0.1467(4)
0.1941(3)
0.2337(3)
0.4070(3)
0.4130(3)
0.5046(3)
0.54333(8)
0.6295(5)
0.7315(4)
0.15255(3)
0.32323(7)
0.1645(2)
0.2693(2)
0.1301(2)
0.2444(3)
0.2424(4)
0.1218(4)
0.0045(4)
0.0102(3)
y0.1181(3)
y0.1295(3)
y0.0296(2)
y0.0565(2)
0.38591(7)
0.5040(4)
0.0323(1)
0.0463(2)
0.0363(7)
0.0478(7)
0.0343(8)
0.044(1)
0.051(1)
0.052(1)
0.050(1)
0.0355(9)
0.0397(9)
0.038(1)
0.0330(7)
0.0304(9)
0.0432(3)
0.071(2)
0.056(1)
y0.0199(2)
0.2720(3)
0.4715(3)
0.5562(4)
0.7266(4)
0.8144(4)
0.7297(4)
0.5584(3)
0.4653(3)
0.3477(3)
0.2108(3)
0.0641(3)
0.1481(1)
0.2453(5)
y0.0003(4)
˚
˚
2.010(4) A and Pd–P 2.173(1) A. The metalionliesapprox-
imately in the mean plane of the coordinating atoms O(1),
˚
P(1) and Cl(1) (0.003 A above). The Pd«Pd distance is
˚
5.44 A; the other bond distances and angles are normal. There
are no significant intermolecular interactions, thus the binu-
clear entities are isolated in the crystal packing.
Attempts to obtain heterodinuclear complexes, using cis-
Pd(A) as ‘ligand’ and copper(II), nickel(II) or lantha-
num(III) salts, failed: in each case the final compound
recovered and characterized is the homodinuclear trans-Pd2-
(A)(X)2.
0.3354(3)
By using an experimental procedure similar to that
employed for H2A we have prepared the ligands H2B and
H2C, containing respectively pyridinic or thioether groups.
Thus, by reaction of oxalyldichloride and 2-(2-aminoethyl)-
pyridine or 2-aminoethyl, phenylsulphide in anhydrous
tetrahydrofuran and in the presence of NEt3, white solids of
the two functionalized amides have been obtained in good
yields. H2B is very soluble in the common organic solvents
and insoluble in diethylether while H2C is soluble only in
a Ueq is defined as one third of the trace of the orthogonalized Uij tensor.
a nitrogen atom of the ligand, which behavesasadinucleating
hexadentate chelate. A chlorine atom fills the fourth coordi-
nation site. Thus the organic ligand forms with the central
metal ion two five-membered rings with bond angles of
81.0(2)8 for O(1)–Pd(1)–N(1) and 85.9(1)8 for N(1)–
Pd(1)–P(1). The bond distances related to the coor-
˚
˚
dination are: Pd–Cl 2.280(1) A, Pd–O 2.121(3) A, Pd–N

6
U. Casellato et al. / Inorganica Chimica Acta 260 (1997) 1–9
Table 8
dimethylsulphoxide or dimethylformamide. The IR spectrum
of H2B shows bands at 3311 cmy1 (nN–H) and at 1655 cmy1
(nC_O) while the 1H NMR spectrum in CDCl3 shows three
peaks at 8.15, 7.59 and 7.16 ppm due to the protons of the
pyridine rings and a peak at 8.10 ppm attributed to the amidic
protons and two peaks at 3.00 and 3.74 ppm due to the meth-
ylenic protons, the peaks at 3.74 ppm showing a coupling
with the aminic proton.
The IR spectrum of H2C parallels that of H2B; the nN–H
and nC_O lie respectively at 3276 cmy1 and 1657 cmy1. The
1H NMR in dmso-d5 shows the amidic protons at 8.99 ppm,
the aromatic protons at 7.80 ppm and the protons of the two
methylenic groups at 3.31 and 3.07 ppm.
The proposed structures of H2C and H2B were also cor-
roborated by FAB mass spectrometry (the parent peak at the
appropriate m/z value was detected) and was confirmed by
an X-ray difractometric investigation on H2B. Crystals of
H2B, grown from a tetrahydrofuran diethylether solution,
show the asymmetric unit is formed by half a molecule of the
ligand which has an inversion centre in between the carbon
atoms C(8)–C(89) of the oxamidic group. A perspective
view of the molecule with atom labelling is shown in Fig. 2.
Selected bond lengths and angles are given in Table 6. In the
cell the molecule is elongated (Fig. 3) and can be described
as a three-step system, where the two lateral (or external)
steps are formed by the planes of the pyridinic rings and the
˚
Selected bond distances (A) and angles (8) for Cu2(B)(Cl)2(dmso)2
Cu(1)–Cl(1)
Cu(1)–N(2)
N(1)–C(1)
C(1)–C(2)
C(3)–C(4)
C(5)–C(6)
C(7)–N(2)
Cu(1)–O(2)
S(1)–C(9)
2.269(1)
1.962(2)
1.351(4)
1.377(5)
1.377(5)
1.508(4)
1.450(3)
2.352(3)
1.789(5)
Cu(1)–O(1)
Cu(1)–N(1)
N(1)–C(5)
C(2)–C(3)
C(4)–C(5)
C(6)–C(7)
N(2)–C(8)
O(2)–S(1)
S(1)–C(10)
2.007(2)
2.019(2)
1.348(3)
1.357(5)
1.383(4)
1.529(3)
1.300(3)
1.500(2)
1.788(3)
N(1)–Cu(1)–N(2)
O(2)–Cu(1)–N(1)
O(1)–Cu(1)–N(1)
Cl(1)–Cu(1)–N(2)
Cl(1)–Cu(1)–O(2)
Cu(1)–O(2)–S(1)
Cu(1)–N(1)–C(1)
N(1)–C(1)–C(2)
C(2)–C(3)–C(4)
N(1)–C(5)–C(4)
N(1)–C(5)–C(6)
C(6)–C(7)–N(2)
C(7)–N(2)–C(8)
O(2)–S(1)–C(10)
C(9)–S(1)–C(10)
92.7(1)
88.4(1)
O(2)–Cu(1)–N(2)
O(1)–Cu(1)–N(2)
O(1)–Cu(1)–O(2)
Cl(1)–Cu(1)–N(1)
Cl(1)–Cu(1)–O(1)
Cu(1)–N(1)–C(5)
C(1)–N(1)–C(5)
C(1)–C(2)–C(3)
C(3)–C(4)–C(5)
C(4)–C(5)–C(6)
C(5)–C(6)–C(7)
Cu(1)–N(2)–C(7)
Cu(1)–N(2)–C(8)
O(2)–S(1)–C(9)
98.1(1)
83.0(1)
89.3(1)
174.8(1)
158.3(1)
102.48(7)
111.4(2)
116.8(2)
122.6(3)
118.8(4)
120.8(3)
118.7(3)
109.8(2)
120.3(2)
107.5(2)
96.2(2)
94.7(1)
90.36(9)
124.7(2)
118.2(3)
119.3(4)
120.3(3)
120.5(3)
113.3(2)
125.7(2)
114.0(2)
106.2(2)
Fig. 2. Perspective view of H2B.
Scheme 1.
Fig. 1. The crystal structure of trans-Pd2(A)(Cl)2.
Fig. 3. The crystal packing of H2B.

U. Casellato et al. / Inorganica Chimica Acta 260 (1997) 1–9
7
third inside step formed by the plane containing the atoms
C(7), N(2), C(8), O(1) and the corresponding atoms
C(79), N(29), C(89), O(19) related by a symmetryinversion
centre. The bond distance and angles of the pyridine rings are
acetate groups may act as a unidentate or a highly un-
symmetrical bidentate. In the perchlorate complex
Cu2(B)(ClO4)2PnS strong absorptions at 1145 1091 and
1035 cmy1 are indicative of perchlorate groups possibly
interacting with the central metal ion. Finally in the complex
˚
normal, the mean C–C and C–N distance being 1.39 A and
1.34 A and the angles ranging from 118 to 1238. The bond
Ni2(B)(Cl)2 nNi–Cl lies at 323–325 cmy1
.
˚
distances, containing the amidic nitrogen, are different:
In the related complexes Ni2(B)(H2B)(CH3COO)2 a
strong absorption at 1600 cmy1 (nsymm COO) and less
intense band at 1330 cmy1 also suggest the acetate groups
act as monodentate or as largely asymmetric chelates. In the
Cu2(B)(H2B)(ClO4)2(EtOH)2 a strong band centred at
1091 cmy1, due to an almost ionic ClOy4 group, is clearly
detectable.
˚
˚
1.450(3) A for N(2)–C(7) and 1.328(3) A for N(2)–
C(8);thisdifferenceisduetopartialelectronicdelocalization
on N(2)–C(8) caused by the presence of a double bond in
˚
C(8)–O(1), (1.227(2) A). An intermolecular hydrogen
bond network is present (Fig. 3) involving N(1)(pyridinic)
and N(2)(amidic) atoms (Table 6).
H2B reacts with copper(II) and nickel(II) salts in alco-
holic solution to produce the homodinuclear complexes
M2(B)(X)2PnSX( sCH3COOy,Cl y, ClO4y ns1–2.5,
SsH2O, EtOH).
The nickel(II) complexes, when used as ‘ligands’ in the
formation of heteropolynuclear complexes, undergo a trans-
metallation reaction; thus when the light-brown complex
Ni2(B)(H2B)(Cl)2 is reacted, in alcoholic solution, with
copper(II) salts (i.e. CuCl2PnH2O), the green homodinu-
clear complex Cu2(B)(Cl)2 is formed. In contrast, when
Cu2(B)(H2B)(ClO4)2 is reacted with NiCl2P6H2O, no
transmetallation occurs and the dinuclear Cu2(B)(Cl)2 com-
plex is obtained. These reactions can conveniently be fol-
lowed by SEM and EDX analyses. The final green
dicopper(II) product shows a very high homogeneity with a
Cu:Cl ratio of 1:1, while signals due to nickel(II), detected
in the starting complex by EDX in a 1:1 nickel:chlorine ratio,
are completely absent.
These results also indicate the difficulty in obtaining
heterodinuclear complexes containing copper(II) and
nickel(II). All the reactions produce completely or predom-
inantly the homodinuclear copper(II) complexes. Thususing
only mild conditions and Ni(ClO4) a small amount of the
heterodinuclear complex CuNi(B)(ClO4)2(H2O)2EtOH
has been obtained and characterized; the major product
remains the unreacted starting complex Cu2(B)(H2B)-
(ClO4)2. In particular when reacted with Ni(ClO4)2 in ace-
tonitrile at room temperature, Cu2(B)(H2B)(ClO4)2 reacts
partially to form the heterodinuclear complex CuNi-
(B)(ClO4)2(H2O)2EtOH; theresidueobtainedfromtheace-
tonitrile solution, evaporated to dryness, contains the starting
mononuclear complex, the heterodinuclear copper(II)–
nickel(II) complex, Ni(ClO4)2 and other unidentified prod-
ucts. The dissolution of the mixture in ethanol andsubsequent
addition of diethyl ether precipitates Cu2(B)(H2B)(ClO4)2,
as ascertained by elemental analyses and IR spectroscopy.
SEM and EDX investigations reveal that the copper:chlorine
ratio is 1:1 with a negligible presence of nickel(II). From the
mother liquor a pale blue complex was recovered. It appears
to be a true heterodinuclear copper(II)–nickel(II) complex
formulable as CuNi(B)(ClO4)2(H2O)2EtOH. The SEMand
EDX analyses indicate the compound is homogeneous with
a Cu:Ni:Cl ratio of 1:1:2.
The preparation of mononuclear complexes was also car-
ried out. When H2B is reacted with copper(II) or nickel(II)
salts in ethanol in a 1:1 molar ratio and in the presence of
triethylamine, compounds formulable as M(HB)(X)PnS
(MsCu2q,Ni 2q;X sCly,CH 3COOy, ClOy4 ; ns1–2,5;
SsH2O, EtOH) have been obtained. These complexescould
correspond to complexes of the type M2(B)(H2B)(X)2.nS,
in agreement with the structurally characterized [Cu2(B)-
(H2B)(H2O)2](NO3)2.8H2O, where dinuclear entities
[Cu2(B)(H2O)2]2q are held together in infinite zig-zag
chains by the pyridyl nitrogens of neutral H2B molecules
[44]. Thus we can relate to this complex structure also our
prepared compounds; in fact without an X-ray structural
determination the proposal of monomeric compounds of the
type M(HB)X is highly questionable. For Ni2(B)(H2B)-
(Cl)2 and Cu2(B)(H2B)(ClO4)2PnS the correct 1:1
metal:chlorine ratio and the homogeneity of the sampleswere
ascertained by SEM and EDX analyses. It must be noted that
nickel(II) forms these complexes more easily than cop-
per(II). Thus nickel(II) chlorideandacetateformcomplexes
formulable as Ni2(B)(H2B)(X)2 while, under similar con-
ditions, copper(II) chloride and acetate give rise to Cu2(B)-
(X)2; only Cu(ClO4)2 can produce Cu2(B)(H2B)-
(ClO4)2PnS. The dinuclear complexes M2(B)(X)2 show a
strong and sharp IR absorption at f1620–1630 cmy1 due to
the amide I band (1654 cmy1 in H2B). Similar IR spectra
occur also for M2(B)(H2B)(X)2 where a peak (or a shoul-
der) at f3190–3150 cmy1 due to nNH (3310 cmy1 in the
free ligand) can be detected. Moreover there is a broadening
of the absorption at f1530–1525 cmy1, which may be diag-
nostic of the presence of H2B [44,45]. These data seem to
corroborate the formulation proposed, but it must be empha-
sized that the IR spectra do not show the clear evidencefound
in the recent literature [44,45].
In the complexes Ni2(B)(CH3COO)2 and Cu2(B)-
(CH3COO)2 intense absorptions around 1606–1600 cmy1
and at 1340–1310 cmy1 due respectively to the antisymme-
tric and symmetric stretching of the COO group are detecta-
ble. The relative intensities of the two bands suggest that the
The dinuclear entity of the homodinuclear copper(II)
complexes was ascertained by single crystal X-ray diffrac-
tometry on green crystals of Cu2(B)(Cl)2(dmso)2, obtained
by slow crystallization of Cu2B(Cl)2 from a dimethylsul-

8
U. Casellato et al. / Inorganica Chimica Acta 260 (1997) 1–9
indicating that an antiferromagnetic interaction takes place
between the two copper(II) ions. Very likely an antiferrom-
agnetic interaction is operating also in Cu2(B)(CH3COO)2
where a mBs1.34 BM for copper atom was found. The mag-
netic behaviour proposed for the prepared complexes must
be considered with great caution. We can anticipate that for
Cu2(B)(Cl)2(dmso)2, according to its X-ray structure, only
an intradimer interaction is operating. This conclusioncannot
be extended to the other copper(II) complexesCu2(B)(Cl)2
and Cu2(B)(Ac)2 where Cly and Acy may serve as binding
ligands between dimers giving risetopolynuclearcomplexes.
Obviously dmso in Cu2(B)(Cl)2(dmso)2 does not act as
bridging ligand and favours a discrete dinuclear entity as
already found for similar compounds. Attempts to grow crys-
tals suitable for X-ray determinations were unsuccessful, and
the magnetic behaviour of these complexes over a tempera-
ture range (from liquid helium to room temperature) is cur-
rently under investigation.
The magnetic moments of the nickel(II) complexes
(mBs2.5 BM for Ni2(B)(H2B)(Cl)2 and mBs2.8 BM for
Ni2(B)(H2B)(CH3COO)2 are lower than expected and may
be due to an antiferromagnetic interaction between the two
nickel(II) ions in the dinuclear entity. The corresponding
homodinuclear Ni2(B)(Cl)2 and Ni2(B)(CH3COO)2 com-
plexes show magnetic moments of mBs2.8 BM and
mBs4.2 BM, respectively. An antiferromagnetic interaction
may be proposed for Ni2(B)(Cl)2; a more complicatedstruc-
ture, possibly involving bridging acetate groups between dif-
ferent dinuclear entities, may exist for Ni2(B)(CH3COO)2.
Again a correct explanation of the magnetic behaviour of
these nickel(II) complexes is precluded by the lack of struc-
tural information.
Fig. 4. The crystal structure of Cu2(B)(Cl)2(dmso)2.
phoxide solution saturated with diethylether. The crystals are
not stable in air but do not suffer appreciate decomposition
when kept in their mother liquor. Thus the X-ray data collec-
tion was carried out by introducing the crystal and its mother
liquor into a sealed quarz capillary. A perspective view of the
complex with atom labelling is shown in Fig. 4;selectedbond
lengths and angles are given in Table 7. As found for the
ligand H2B, and the Pd complex, the asymmetric unit is
formed by half of the complex, owing to the presence of an
inversion centre between the carbon atoms C(8)–C(89)of
the oxamidic group. The ligand in the trans configuration
behaves as a hexadentate dinegative compartmental dinu-
cleating agent: each copper(II) ion is bound by a pyridine
nitrogen, an oxygen and a nitrogen atom of the oxamidic
group of one compartment of the ligand. A chlorine atom and
an oxygen atom of a dimethylsulphoxide molecule complete
the coordination polyhedron around the central metal ion.
Thus each copper(II) atom is pentacoordinated and the coor-
dination polyhedron may be best described as a distorted
square planar pyramid, with the oxygen of the dimethylsul-
phoxide occupying the axial position.
Susceptibility measurements over a temperature range
together with attempts to grow good crystals for further X-
ray investigations are currently under way in ordertoevaluate
more conveniently the magneto-structural correlations in
these systems.
The Cu–N(1) (pyridine) bond distance is longer
Surprisingly H2C does not react with transition metal salts:
when reacted with copper(II) and nickel(II) acetate or chlo-
ride or with trans-Pd(C6H5CN)2(Cl)2, the starting ligand
can be recovered in an almost quantitatively yield. Owing to
the low solubility of H2C in the common organic solvents,
the reactions were carried out in hot dimethylformamide;
probably these experimental conditions do not favour the
formation of complexes, neither when soft metal ions such
as palladium(II) are used.
In conclusion, the data obtained show that it is easy to
obtain homodinuclear complexes. The formation of trans-
homodinuclear species is governed mainly by the configu-
ration of the ligands which are very probably trans, this
suggestion being confirmed for H2B by an X-ray structural
investigation.
˚
(2.019(2) A) than that of Cu–N(2) (amidic)
˚
(1.962(2) A); this is because the amidic nitrogen is nega-
˚
tively charged. The Cu–Cl distance is 2.269(1) A while the
˚
Cu–O(1) distance is 2.007(2) A and the Cu–O(2)(dmso)
˚
˚
is 2.352(3) A. The copper atom is 0.169 A above the mean
plane formed by basal plane O(1), Cl(1), N(1) and N(2)
towards the apical O(2) oxygen of the dimethylsulphoxide.
The ligand gives rise with the metal ion to a six-membered
ring (N(1), C(5), C(6), C(7), N(2), Cu) forming an
N(1)–Cu–N(2) angle of 92.7(1)8 and a five-memberedring
(N(2), C(8), C(89), O(1), Cu) forming a N(2)–Cu–O(1)
angle of 83.0(1)8. The otherbond distancesandangleswithin
the ligand are normal.
The magnetic moment at room temperatureprovidesuseful
information about the magnetic exchange between paramag-
netic centres in the prepared complexes. Thus for
Cu2(B)(H2B)(ClO4)2 a mBs1.69 BM was found while
Cu2(B)(Cl)2 shows a mBs1.19 BM for the copper atom,
As expected, the oxamidic group is a good mediator of
magnetic exchange, consequently these systems can conven-
iently be proposed for studies of magnetically interacting
systems. In these complexes the presence of a solvent mole-

U. Casellato et al. / Inorganica Chimica Acta 260 (1997) 1–9
[15] Y. Journaux, J. Sletten and O. Kahn, Inorg. Chem., 25 (1986) 439.
9
cule directly bonded to the copper(II) ion, filling the fifth
coordination site of the square-pyramidal geometry about the
central metal ion, prevents the formation of polymeric zig-
zagging chains and favours the formation of discrete dinu-
clear entities. If this solvent molecule is removed (for
instance by heating), a polymeric complex is very probably
synthesized which, in turn, may give rise to the dinuclear
species by treatment with coordinating solvents. Thusaneasy
dinuclear–polynuclear process may be obtained and the var-
iation of the physico-chemical properties associated with
these reactions investigated in detail. Studies on these reac-
tions are currently in progress.
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Acknowledgements
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We thank Mrs O. Biolo, Mr A. Aguiari and E. Bullita for
experimental assistance in the preparation of the ligands and
complexes and in their characterization. We are indebted to
Progetto Strategico, CNR ‘Tecnologie Chimiche Innovative’
for financial support.
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