Tin(IV) and organotin(IV) derivatives of novel β-diketones Part IV. Triorganotin(IV) complexes of fluorinated 4-acyl-5-pyrazolones. Crystal structure of (1-(4-trifluoromethylphenyl)-3-methyl-4-acetylpyrazolon-5-ato)-triphenyltin(IV)

Article abstract of DOI:10.1016/S0022-328X(98)01173-5

The synthesis of three 1-(4-trifluoromethylphenyl)-3-methyl-4-R¹(C=O)-5-pyrazolone proligands LH (L¹H; R¹ = C₆H₅: L²H; R¹ = CH₃: L³H; R¹ = CF

Full text of DOI:10.1016/S0022-328X(98)01173-5

Journal of Organometallic Chemistry 580 (1999) 344–353
Tin(IV) and organotin(IV) derivatives of novel b-diketones
Part IV. Triorganotin(IV) complexes of fluorinated
4-acyl-5-pyrazolones. Crystal structure of
(1-(4-trifluoromethylphenyl)-3-methyl-4-acetylpyrazolon-5-ato)-
triphenyltin(IV)
Fabio Marchetti a,*, Claudio Pettinari a, Augusto Cingolani a, Lauro Brocanelli a,
Miriam Rossi b, Francesco Caruso c,1
a Dipartimento di Scienze Chimiche, Uni6ersita` degli Studi, 6ia S. Agostino 1, I-62032 Camerino, Macerata, Italy
b Vassar College, Department of Chemistry, Poughkeepsie, NY 12604, USA
c Istituto di Strutturistica Chimica G. Giacomello, CNR, CP 10, I-00016 Monterotondo Stazione, Roma, Italy
Received 2 November 1998
Abstract
The synthesis of three 1-(4-trifluoromethylphenyl)-3-methyl-4-R1(CꢀO)-5-pyrazolone proligands LH (L1H; R1=C6H5: L2H;
R1=CH3: L3H; R1=CF3) and their interaction with R3Sn(IV) acceptors (R=Me, Bun, Ph) are reported. When R=Me or Bun,
aquo (4-acylpyrazolonate)SnR3(H2O) derivatives are obtained and the anionic donors 4-acylpyrazolonate (L−) act in the
O–monodentate form. These triorganotin complexes are not stable in chlorohydrocarbon solvents and decompose to R4Sn and
bis(4-acyl-5-pyrazolonate)2SnR2. When R=Ph, stable (4-acyl-5-pyrazolonate)SnPh3 derivatives, both in solution and in the solid
state, are obtained. The crystal structure of (1-(4-trifluoromethylphenyl)-3-methyl-4-acetylpyrazolon-5-ato)triphenyltin(IV) shows
a five-coordinate tin atom in a strongly distorted cis-bipyramidal trigonal environment (axial angle=161.2(2)°) with the
˚
˚
acylpyrazolonate donor acting as an asymmetric O2–bidentate species (Sn–O(1)=2.081(6) A: Sn–O(2)=2.424(5) A). Electronic
effects are responsible for the different behavior shown by these trialkyl and triphenyl derivatives. © 1999 Elsevier Science S.A.
All rights reserved.
Keywords: 4-Acyl-5-pyrazolones; Crystal structure; IR; NMR; Triorganotin(IV) complex
1. Introduction
greatest use as boat bottom antifouling paints. Fouling
is caused by the growth of aquatic organisms on the
hull of vessels, which creates roughness and so reduces
speed per unit fuel and increases travel time. TBT-
based paints control fouling effectively by slow release
of the TBT moiety into the aqueous solution: TBT is
very toxic, even at small concentrations, to marine
organisms. Despite the effectiveness of these com-
pounds, this heavy tin use unfortunately leaves its mark
on the environment. As a consequence of organotin
sea-pollution, some countries [2,3] have severely re-
Triorganotin compounds are widely used as biocides.
For example, triphenyltin (TPT) derivatives are espe-
cially effective against two major plant diseases, late
blight on potatoes and leaf spot on sugar beet [1].
Tributyltin (TBT) compounds probably have their
* Corresponding author.
E-mail address: pettinar@camserv.unicam.it (F. Marchetti)
1 Also corresponding author.
E-mail address: car@isc.mlib.cnr.it (F. Caruso)
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(98)01173-5

F. Marchetti et al. / Journal of Organometallic Chemistry 580 (1999) 344–353
345
stricted their use with promising results; the concentra-
tion of organotins in sea water has decreased, although
in sediments the decrease is less pronounced [3]. Ulti-
mately, scientists are then faced with a two-fold re-
search problem; that of designing effective and
environmentally friendly organotin compounds and
that of developing specific extractants for tin to clean
organotins from harbor areas [3].
Tin toxicity to marine organisms usually occurs in
species such as marine bivalves that accumulate tri-
organotins since they cannot efficiently metabolize them
[4]. For example, a recent study showed mollusks on
the Spanish mediterranean coast have elevated amounts
of TBT derivatives [5]. In contrast, no organotins were
detected in fish muscle and the organotins found in fish
liver (red mullet) were TPTs [5]. Structure-activity stud-
ies on alkyltins have shown that increasing the alkyl
length induces stronger toxicity in aquatic life and
milder toxicity in mammals. In mammals, organotin
toxicity appears related to the liposolubility of these
compounds [6].
fashion through one carbonyl group. The other car-
bonyl is involved in an intermolecular H-bond network
with a nitrogen atom of another ligand. These com-
plexes are not stable and they easily disproportionate in
the solid phase and in solution Eq. (1).
2(L)SnR3(H2O) X 2(L)SnR3 X (L)2SnR2+SnR4
−2H O
2
(1)
On the other hand, the triaryltin(IV) complexes are
more stable to moisture as suggested by spectroscopic
methods [36].
The ligands reported here (Fig. 1) contain fluorine
substituents on the N1 phenyl and so resemble the aryl
moieties that proved effective in the antitumor study
mentioned above. We report the structural properties
and behavior in solution of triorganotin(IV) derivatives
of these ligands. The crystal structure of the title com-
pound provides an explanation for the different chemi-
cal behavior of TBT and TPT species.
2. Results and discussion
Recent studies performed on aquatic organisms show
that TPTs induce low enzymatic activity [7]. Unusual
enzymatic levels were also observed in mammals (rab-
bits and lambs), specifically in the liver and kidneys [8],
whereas the total prevention of implantation in the
early stages of pregnancy was observed in rats [9].
Additional interest in organotins arose recently as
some triorganotin containing O2–bidentate donors
(aryl acetates) showed strong antitumor activity, greater
than that of cisplatin and of the same order as that of
mitomycin C [10,11]. The same study showed that
triorganotin(IV) perfluorobenzoates are more active
than the non-fluorinated compounds against two breast
cancer cell lines (MCF-7, EVSA-T), a colon cancer
(WiDr), an ovarian cancer (IGROV), a melanoma
(M19 MEL) and a renal cancer (A498).
Because of the interest in organotin compounds,
some years ago, we started a systematic study on the
chemical, spectroscopic and structural properties of
diorganotin derivatives of 4-acyl-5-pyrazolone ligands.
These species provide the same framework of the classi-
cal b-diketones and are used as dyes [12] and metal
extractants [13–16]. The coordination chemistry of
these donors towards a variety of metal acceptors has
been studied recently. It is possible to find 4-acyl-5-
pyrazolonates in a quasi-symmetric O2–bidentate form
[17–22], in a strongly asymmetric O2–bidentate form
[23–33] and also in a O2,N–exotridentate form [34].
More recently a different coordination pattern was
found in aquotriorganotins, (H2O)SnR3(L), R=butyl,
L=1-phenyl-3-methyl-4-benzoylpyrazolon-5-ato [35]:
R=methyl, L=1-phenyl-3-methyl-4-methoxybenzoyl-
pyrazolon-5-ato [36]. In these trigonal bipyramidal
complexes a water molecule is bound to tin and the
acylpyrazolonato binds the tin center in a monodentate
2.1. Synthesis of the triorganotin(IV)deri6ati6es 1-9
The triorganotin(IV) derivatives have been obtained,
as anhydrous or aquo species, from the metathesis
reaction of LH, NaOCH3 and R3SnCl (R=Me, Bun or
Ph) in 1:1 molar ratio in benzene:
LH+NaOCH3+R3SnClbenzene/H O
“
(v)(L)SnR3(H2O)x
2
−CH OH
3
+NaCl
(2)
where LH=L1H, L2H or L3H; R=Me or Bun x=1;
R=Ph x=0.
The tributyl- and triphenyltin(IV) compounds can be
more readily obtained in higher yields by reacting
(R3Sn)2O with the neutral ligands LH in 1:2 molar ratio
in refluxing benzene:
2LH+(Ph3Sn)2Oben“zene2(L)SnR3
(3)
−H O
2
2LH+(Bu3nSn)2Oben“zene2(L)SnBu3n+2H O
“
2
(v)
−H O
2
2(L)SnBun3(H2O)
where LH=L1H, L2H or L3H.
(4)
Fig. 1. LH proligands used in this work.

346
F. Marchetti et al. / Journal of Organometallic Chemistry 580 (1999) 344–353
The tributyl and trimethyltin(IV) derivatives rapidly
absorb water on exposure to the atmosphere, whereas
the triphenyltin(IV) complexes are air and moisture
stable. All the compounds are generally low melting
solids, very soluble in acetone, acetonitrile, DMSO,
alcohol and chlorohydrocarbons, sparingly soluble in
diethyl ether and insoluble in hydrocarbons and water.
Conductivity values in dichloromethane are null.
This seems to indicate the existence in solution of
neutral species or of ion pairing effects. All the com-
plexes show conductivity in DMSO due to a partial
dissociation of about 30–50%. This suggest loss of an
anionic L− species, which is confirmed in Section 2.3.
Molecular-weight determinations carried out in chlo-
roform solution on selected triorganotin(IV) complexes
confirm a weak metal–donor interaction; the experi-
mental molecular-weight values are less than the theo-
retical ones. The ratio r (r=MW/FW) is on the order
of 0.7–0.9 and generally increases with the increase of
concentration: this seems to indicate partial dissociation
of the anionic (L−) donor and/or of H2O. We cannot
exclude the possibility of a decomposition process such
as (1), however, it could be accelerated at the experi-
mental temperature of 40°C. In the case of the
triphenyltin(IV) derivative 6 the ratio r is 0.93 in accor-
dance with a negligible dissociation.
Fig. 2. Isomers present in solution after dissolving (alkyl)3Sn(L)(H2O)
in chlorohydrocarbon solvents.
1
2.3. H- and 19F-NMR data
The donors L1H, L2H and L3H exist in chloroform in
the amino–diketo tautomeric form. In fact, in the
1H-NMR spectrum the acidic proton signal is found
between 2.50 and 4.50 ppm, a range typical of N–H
group: it has been observed that the 4-acylpyrazolones
previously investigated always showed a resonance up
to 10.0 ppm due to (O–H···O) systems [23–33]. Coordi-
nation of the donors in anionic form is confirmed by
the disappearance of the above signal. A slight shield-
ing of C3–CH3 (compounds 1–9) and of OꢀCCH3
signals (compounds 4–6) is generally observed, while
aromatics undergo a more complex pattern upon
chelation.
In the trimethyl and tri-n-butyltin(IV) derivatives we
have found two different sets of signals for the R group
bound to tin and the tin-proton coupling constant
2J(Sn–H) in the range 55–58 Hz, which is typical of
tetracoordinate species [45]. We have also observed that
these complexes are non electrolytes in chlorohydrocar-
bon solvents, even if they are largely dissociated. We
therefore suggest that in solution these compounds lose
the molecule of coordinated water and that they exist in
both of the isomeric non-fluxional forms shown in Fig.
2.
2.2. IR data
In the solid state, the donors L1H, L2H and L3H are
likely to exist in the amino–diketonic form, exhibiting a
broad band at ca. 3400 cm−1 due to intermolecular
(N–H···O) hydrogen bonds [37]. Upon coordination
these absorptions disappear and the w(CꢀO) at 1680–
1620 cm−1 undergoes a red shift (1630–1595 cm−1),
thus indicating loss of the acidic proton and involve-
ment of both the carbonyls in bonding with the metal
or, at least, in weak interactions with a neighbouring H
atom, as previously observed [35,36].
In the spectra of triphenyltin(IV) complexes it is not
possible to distinguish between signals due to aromatic
protons of the ligand and those linked to tin, but
integration takes their presence into account.
Between 1500 and 1600 cm−1 the vibrations of the
azomethine bond in the pyrazole and those of Ph rings
are observed. In the range 400–500 cm−1 some bands
due to w(Sn–O) have been found [23,33]. In the
Bun3Sn(IV) and Me3Sn(IV) derivatives the absorptions
assignable to was(Sn–C) and ws(Sn–C) are observed
[38–40] in the range 500–620 cm−1 whereas in the
Ph3Sn(IV) complexes the was(Sn–C) and ws(Sn–C) are in
the 200–300 cm−1 region [41–44]. The presence of
ws(Sn–C) in the spectra of aquo derivatives suggests
(for a TBP trans-O–SnR3–O system) a deviation from
planarity of the SnR3 moiety which lowers the local
symmetry from D3h to C36. In the spectra of aquo
derivatives the band at 3100–3200 cm−1 is attributed
to intermolecular H-bonded water [35,36].
1
We have also carried out H-NMR spectroscopy of
compound 4 in DMSO; two sets of signals have been
found, of which the more intense is likely due to a
tetracoordinate triorganotin species, whereas the other
is assigned to a bis(acylpyrazolonate)diorganotin(IV)
complex which arises from the decomposition reaction
(1).
2
In a coordinating solvent such as DMSO the J(Sn–
H) coupling constants due to triorganotin(IV)-acylpyra-
zolonates, as well as those for the starting
triorganotin(IV) halide, are of the same order (60–70
Hz). This suggests that DMSO can displace the anionic
ligand (L−) from the coordination sphere.

F. Marchetti et al. / Journal of Organometallic Chemistry 580 (1999) 344–353
347
Derivatives 1–9 were also studied with 19F-NMR
spectroscopy. The donors L1H and L2H absorb at
+62.3 ppm whereas L3H shows two resonances; at
+63.0 ppm, which is due to CF3 at the same position
in L1H and L2H, and at +75.3 ppm that belongs to the
CF3 in R1 position. The latter is similar to the signal
shown by another 4-acylpyrazolone donor previously
used [25]. Only very small shifts have been detected
among the free neutral ligands (L1H, L2H and L3H)
and their triorganotin derivatives. In the spectra of 3, 4
and 5 several signals appeared in accordance with iso-
mers and/or species arising from the reaction (1).
2.4. 119Sn-NMR data
The alkyl complexes generally show two resonance
bands in the range (+80)–(+155) ppm typical of
R3SnO tetrahedral species [46,47], and in agreement
with breaking of the Sn–OH2 bond and formation in
solution of both the isomers shown in Fig. 2. Instead,
the triphenyltin(IV) derivatives give a unique resonance
between −132 and −181 ppm implying a five-coordi-
nate cis-O2SnR3 TBP geometry [48].
Fig. 3. An ORTEP diagram of compound 6. Displacement ellipsoids
are shown at the 30% probability level.
As previously observed [35,36] the aquo derivatives
undergo a decomposition reaction; in two days, R4Sn
and (L)2SnR2 compounds are always recovered from
the solutions. The stability of the complexes has been
monitored by using 119Sn-NMR spectroscopy. We have
recorded the spectra with a different number of cycles
acquired and have found that (L)SnPh3 are always
more stable than the (L)SnMe3 and (L)SnBun3, however
they are somewhat less stable than all the previously
reported (4-acyl-5-pyrazolonate)triphenyltin(IV) species
[36].
bond angle (O2–Sn–C16) is 161.2(2)° and is similar for
the bzbz species (163.7(2)°) showing that both com-
pounds have large distortion from a regular TBP ge-
ometry of 180°. The equatorial angles (O1–Sn–C22,
O1–Sn–C28 and C22–Sn–C28) add to 353.3° (355° for
the bzbz complex) confirming the departure from the
TBP configuration that is characterized by a value of
˚
360°. In addition, the metal appears 0.32 A out of the
trigonal plane (defined by O1, C22 and C28) towards
C16 and resembles a system approaching tetrahedral
geometry.
2.5. X-ray crystallography
Table 1
˚
Selected bond distances (A) of 6
The crystal structure of (1-(4-trifluoromethylphenyl)-
3-methyl-4-acetylpyrazolon-5-ato)triphenyltin(IV), 6, is
made up of discrete molecules and no crystallographic
imposed symmetry is found. A view of the molecular
structure is shown in Fig. 3. Table 1 and Table 2 show
relevant geometrical parameters. The metal coordina-
tion number is five as three C atoms, from the phenyl
groups, and two O atoms, from the chelating ligand,
are coordinated to the tin. This species resembles
Ph3Sn(bzbz), (bzbz =1,3-diphenylpropane-1,3-dionato
or benzoylbenzoate), which has a TBP configuration
[49], with the chelating b-diketonate ligand bzbz form-
ing a 6-membered ring C–C–O–Sn–O–C as in our
case. In the bzbz complex one oxygen occupies an axial
˚
Bond
Distance (A)
Sn–O1
Sn–O2
2.081(6)
2.424(5)
2.169(7)
2.137(6)
2.121(7)
1.283(9)
1.24(1)
1.403(9)
1.36(1)
1.42(1)
1.32(1)
1.43(1)
1.50(1)
1.41(1)
1.42(1)
1.18(1)
1.28(2)
1.18(2)
Sn–C16
Sn–C22
Sn–C28
O1–C5
O2–C13
N1–N2
N1–C5
N1–C6
N2–C3
C3–C4
C3–C12
C4–C5
C4–C13
F1–C15
F2–C15
F3–C15
˚
position (Sn–O2=2.267(6) A) and the other an equa-
˚
torial site (Sn–O1=2.094(7) A); two phenyls are in the
trigonal plane and the third is apical. Both Sn–O bonds
differ more in our complex (Sn–O2=2.424(5) and
˚
Sn–O1=2.081(6)A) than in the bzbz species. Our axial

348
F. Marchetti et al. / Journal of Organometallic Chemistry 580 (1999) 344–353
Table 2
Selected bond angles (°) of 6
In ‘SnO2C3’ TBP species, the apical positions are
occupied by either two oxygens or one oxygen and one
C atom. Interestingly, the literature shows that when
both apical positions are occupied by O atoms, the two
Sn–O bonds differ, even in some cases with the exis-
tence of equivalent environments above and below the
trigonal plane. Thus, it is not surprising that a symmet-
ric ligand such as bzbz also shows (as mentioned above)
two different Sn–O bonds in a more distorted geome-
try. Therefore the greater difference between the two
Sn–O bonds of our complex can be ascribed to the
asymmetry of our ligand.
Complexes more closely related to 6 include some
recently described trialkyltin pyrazolonates [Bun3Sn(Q%)-
(H2O)], (Q%=1-phenyl-3-methyl-4-benzoylpyrazolon-5-
ato) [35] and [Me3Sn(QA)(H2O) (QA=1-phenyl-3-
methyl-4-methoxybenzoyl-pyrazolon-5-ato) [36]: they
show the second O of the pyrazolone ligand out of the
coordination sphere of the TBP geometry and replaced
by a water molecule. However these complexes dispro-
portionate Eq. (1). Instead, the presence of Ph groups
in our complex confers more stability to the system and
such a reaction is not allowed. Therefore the ligand
chelating effect preserves the triphenyl complex since no
water enters the coordination sphere.
Bond
Angle (°)
O2–Sn–O1
C5–N1–N2
C16–Sn–O1
C6–N1–N2
C16–Sn–O2
C6–N1–C5
C22–Sn–O1
C3–N2–N1
C22–Sn–O2
C4–C3–N2
C22–Sn–C16
C12–C3–N2
C28–Sn–O1
C12–C3–C4
C28–Sn1–O2
C5–C4–C3
C28–Sn–C16
C13–C4–C3
C28–Sn–C22
C13–C4–C5
N1–C5–O1
C4–C5–O1
C4–C5–N1
76.8(2)
111.8(6)
84.6(2)
118.7(6)
161.2(2)
129.3(6)
121.7(2)
104.8(7)
83.2(2)
112.2(7)
105.3(2)
118.1(8)
107.3(2)
129.7(8)
83.8(2)
104.4(7)
104.3(2)
133.6(7)
124.3(3)
121.9(7)
120.9(6)
132.3(7)
106.7(6)
The different behavior is due to the electron with-
drawing effect of the phenyl group which removes
electron density from the metal, making it more acidic.
This induces an increased donation from an O2 lone-
pair such that a balance of charge on the metal is
reached. Similar behavior by the Ph group was ob-
Such a trend away from TBP geometry can also be
observed by examining the bond angles subtended by
O2 on the equatorial plane. The angles O2–Sn–O1,
O2–Sn–C22 and O2–Sn–C28 are 76.8(2), 83.2(2) and
83.8(2)°, respectively, are all much lower than the ex-
pected 90° for a regular TBP geometry. However, at the
other apex of the bipyramid, C16 subtends much larger
angles; the angles C16–Sn–O1, C16–Sn–C22 and
C16–Sn–C28 are 84.6(2), 105.0(3) and 104.3(2)°, re-
spectively. This is coherent with an approximate tetra-
hedral system. We conclude that the metal coordination
geometry can be described as intermediate between a
TBP and a tetrahedron: a pure tetrahedral scheme
would exclude O2 from the coordination sphere.
A search in the literature [50] on the geometry of
‘SnO2C3’ species shows an overwhelming number (81/
94=86%) being TBP, as seen in the sum of the equato-
rial angles being 360°. The trans axial angle of the
bipyramid is in the range of 167–180°. Many of these
species are polymeric with the second oxygen atom, O2,
belonging to a different anion. The remaining 13 spe-
cies are monomeric and represent cases in between TBP
and tetrahedral geometries where O2 is not strongly
coordinated, as in compound 6. The trans axial angle
range is 147.2–163.7° for this second group.
served in
a
bis(pyrazolonato)diphenyltin species,
Ph2Sn(QBr)2, (QBr)=1-phenyl-3-methyl-4-(4-bromoben-
zoyl)pyrazolon-5-ato [18] and results in the shortest
Sn–O2 bond distance for the entire family of bis(4-
˚
acyl-5-pyrazolonato)diorganotins (Sn–O1=2.13 A,
˚
Sn–O2=2.24 A: average values on the two ligands).
Comparison with the antitumor compound
Ph3Sn(benzoate) [11] (Sn–O1=2.073(3), Sn–O2=
˚
2.674(3) A) shows the same type of structure and equal
covalent (primary) bonds (Sn–O1), whereas in 6, the
coordinative (secondary) bond (Sn–O2) is somewhat
shorter.
The bite angle of the chelating ligand ranges from 79
to 85° in bis(4–acyl-5-pyrazolonato)diorganotins
[18,23–26,28,29,31–33]. The present study shows that
such angle bite can be further reduced, as O1–Sn–O2 is
76.8(2)°. Together with a small bite angle, two different
Sn–O bonds are found [18,23–26,28,29,31–33] and for
˚
6 this is confirmed as Sn–O1=2.081(6) A and Sn–
˚
O2=2.424(5) A. These lengths compare well with
For chelating ligands having lower bite angle such as
carboxylates, three geometric categories; TBP (poly-
meric), pure tetrahedral and intermediate cases are
allowed. The factors affecting the structure of triorgan-
otin carboxylates were previously discussed [51,52] and
recently reviewed [53].
˚
2.094(9) and 2.42(1) A, respectively, found in
Cy2Sn(QD)2 (QD)=1,3-dimethyl-4-acetylpyrazolon-5-
ato [32]. All of the other pairs of related Sn–O bonds
found in the literature [18,23–26,28,29,31,33] show less
difference between them than that seen in 6, according

F. Marchetti et al. / Journal of Organometallic Chemistry 580 (1999) 344–353
349
to the rule: the smaller the bite, the greater the differ-
ence between Sn–OP and Sn–OS (OP/OS refers to pri-
mary/secondary bond).
All chelating 4-acyl-5-pyrazolone-organotins show
O1 (the oxygen closer to the N moiety) associated to
the primary bond [18,23–29,31–33] and this feature is
also confirmed for 6. Since in a TBP geometry an axial
bond is longer than an equatorial bond, O2 is logically
found at the apex of the bipyramid.
ing its work. Interesting examples are some tri- and
di-phenyltin-trichloroacetates [54] which degrade to di-
and mono-organotins. Since mono-organotins and in-
organic tin species are non-toxic, such a finding should
be desirable for organotin biocides. Commercial TBT
paints do not provide such a feature as toxic derivatives
are accumulated in the environment. In the title com-
pounds, the presence of a 4-trifluoromethyl-phenyl
linked to N1 position of the pyrazole ring lowers the
b-diketonate donor ability, making the tin derivatives
less stable to hydrolysis and also increasing decomposi-
tion in solution, mainly in the case of alkyltin(IV)
derivatives.
3. Conclusions
A series of triorganotin(IV) species has been obtained
with new functionalized 4-acyl-5-pyrazolonates. In the
solid state the alkylorganotins exist in a trans-TBP
geometry with the donor as a monodentate ligand and
a molecule of water in an apical position. Instead,
triphenyltin complexes adopt a cis-TBP configuration,
with the ligand acting in the bidentate form. The elec-
tron withdrawing effect of the phenyl groups on tin is
responsible for the inclusion of the second O atom of
the ligand in the metal coordination sphere. A large
distortion is present in the structure, however, which
can be interpreted as an intermediate stage between a
TBP and a tetrahedral configuration. The alkyl deriva-
tives undergo a change from the solid state (trans-TBP
five-coordinate) to a four-coordinate species in solution,
whereas for the phenyl species the cis-TBP solid state
geometry is retained in solution.
This study also shows that:
1. DMSO easily displaces the anionic ligand in the title
compounds, a useful feature as a potential additive
to organotin antifouling paints.
2. Since the fluorinated beta-diketonate ligands used in
this study result in less stable organotin complexes,
their potential use as organotin extractants is not as
effective as the ones previously described [24–33].
3. The structure of compound 6 is similar to that of a
related potent antitumor species [11]; they have
equal Sn–O covalent bonds while the secondary
bond (Sn–O2) is somewhat shorter than in the
antitumor complex.
4. Experimental
In the literature, there are examples of structural
changes upon dissolving triorganotins (R=Ph [51c,52],
R=alkyl [51d]). Although available IR and 119Sn-
NMR data that can help in describing definite trends
are limited, it seems that, in solution, triaryltin(IV)
complexes are more stable than trialkyltin(IV) species.
In particular, trans-TBP species tend to disassociate in
solution [51,52]. Since this geometry is more common
for alkyl than aryl derivatives, this may explain the
greater efficiency of TBT species over triaryltins in
antifouling paints. Thus, the chelating effect operating
in the cis-TBP configuration, commonly found in tri-
aryltin species, provides more stability. These properties
are probably related to degradation of organotins and
studies of such features are underway by our group.
As mentioned in the Introduction, the effectiveness of
TBT antifouling paints is due to slow release of the
organotin moiety. Therefore, organotins with tunable
half-lives can help in regulating levels of acceptable
pollution while still providing excellent properties as
biocides. Tin has the unique property that, as an inor-
ganic species, it is harmless. (This feature is not shared
by other toxic organometals, Pb, Hg, etc. since the
metals themselves are toxic.) The ideal metal biocide
should be an organotin that undergoes a fast degrada-
tion to mono-organotin or inorganic tin after perform-
4.1. General comments
The reactions were carried out under N2 stream using
Schlenk techniques. Solvents were dried by standard
techniques. The samples were dried in vacuo to con-
stant weight (20°C, ca 0.1 Torr). H-, 19F- and 119Sn-
1
NMR spectra were recorded operating at room
1
temperature (300 for H, 282.2 MHz for 19F and 111.9
MHz for 119Sn). H, F and Sn chemical shifts are
reported in ppm versus Me4Si, CFCl3 and Me4Sn,
respectively. The tin spectra were run with a spectral
width of 1000 ppm, and the chemical shifts were
checked for aliasing by varying the center of the win-
dow. Each tin spectrum was acquired in ca 30 min (ca
300 transients). All the chemicals were analytical
reagent grade from Aldrich.
4.2. Syntheses of the ligands
4.2.1. 1-(4-Trifluoromethylphenyl)-3-
methylpyrazol-5-one
Ethyl acetylacetate (0.027 mol, 3.47 g) was added
dropwise to
a
solution (30 cm3) of 1-(4-trifl-
uoromethylphenyl)hydrazine (0.027 mol, 4.7 g). KOH
(1.8 mmol, 0.1 g) was subsequently added. The mixture
was heated to reflux and stirred for 1 h, then the solvent

350
F. Marchetti et al. / Journal of Organometallic Chemistry 580 (1999) 344–353
was removed on a rotary evaporator and the crude
product washed with diethyl ether (50 ml) and light
petroleum (50 ml). After filtration the brown powder
was dried in vacuo and shown to be 1-(4-trifl-
uoromethyl-phenyl)-3-methylpyrazol-5-one. Yield 46%.
M.p.: 183–185°C. Anal. Calc. for C11H9F3N2O: C,
54.5; H, 3.7; N, 11.6. Found: C, 54.4; H, 3.8; N, 11.4%.
IR data: 2700 br, w(O–H···O), 1629 s, w(CꢀO). 1H-
NMR data (CDCl3): 2.22 s (3C–CH3), 3.47 s (4CH2),
7.64 d, 8.06 d (4-C6H4CF3). MS: m/z 242 (M+).
mmol) was added to a methanolic solution (10 cm3) of
sodium methoxide (1.0 mmol) and refluxed for 1 h. A
benzene solution (20 cm3) of Me3SnCl (1.0 mmol) was
then added to the above solution dropwise and the
reaction mixture was stirred at room temperature for
about 3 h. Sodium chloride was filtered off and the
solvent removed under reduced pressure on a rotary
evaporator until a thick oil was obtained. This was
treated with diethyl ether and light petroleum, and a
brown solid afforded. This was recrystallized from ben-
zene/petroleum ether mixture and shown to be com-
pound 1.
If the synthesis is carried out without the base a
dark-red powder is recovered from the solution which
1
has been identified by H-NMR as a mixture of 1-(4-
Yield 42%. M.p.:137–138°C. Anal. Calc. for
C21H23F3N2O3Sn: C, 47.85; H, 4.40; N, 5.31%. Found:
C, 47.60; H, 4.54; N, 5.16%. LM (CH2Cl2): 0.5 V−1 cm2
mol−1, 0.9.10−3 M: LM (DMSO): 17.9 V−1 cm2
mol−1, 0.8.10−3 M. FW Calc.: 527; MW Found
(CHCl3): 365, r: 0.69, 0.9×10−2 m; 378, r: 0.72, 1.8×
trifluoromethylphenyl)-3-methylpyrazol-5-one and of
the condensation intermediate ethyl 3-[2-(4-trifl-
uoromethylphenyl) hydrazono]butanoate, which shows
the following signals: 1.95 s (NꢀC–CH3), 1.27 t,4.18 q
(OCH2CH3), 3.36 s (4CH2), 7.08 d, 7.45 d (4-C6H4CF3),
8.42 s br (N–H).
1
10−2 m. H-NMR (CDCl3): l(H2O), 1.85 s br; l(Sn–
The donors L1H, L2H and L3H were then synthesized
following the procedure reported by Jensen [55].
CH3), 0.59 s (2J(Sn–H)=56.3 Hz): l(L1), 1.98 s br
(C3–CH3), 7.45–7.65m, 7.70 d, 8.10 d (OꢀCC6H5, N1–
C6H4CF3). 19F-NMR (CDCl3): −62.3. 119Sn-NMR
(CDCl3): +152.2, +148.7. IR (nujol) cm−1: 3180 br,
w(H2O): 1658 m, l(H2O): 1606 m, w(CꢀO): 565 m, 552
vs, w(Sn–C): 440 s, 419 m, 403 w, w(Sn–O).
4.2.2. 1-(4-Trifluoromethylphenyl)-3-methyl-4-
benzoyl-pyrazol-5-one (L1H)
Yield 92%. M.p.: 150–152°C. Anal. Calc. for
C18H13F3N2O2: C, 62.4; H, 3.8; N, 8.1. Found: C, 62.2;
H, 3.9; N, 8.3%. IR data: 3340 br, w(N–H···O), 1635 m,
w(CꢀO). 1H-NMR data (CDCl3): 2.10 s (C3–CH3)
7.50–7.70 m, 7.75 d, 8.12 d (OꢀCC6H5, N1-4-C6H4CF3),
3.70 s br (N–H···O). 19F-NMR data (CDCl3): −62.4.
Compounds 2–9 were obtained in a similar fashion.
For derivatives 2, 3, 5, 6, 8 and 9, the following
alternative synthesis can also be used: a benzene solu-
tion (30 cm3) of (R3Sn)2O (R=Bun or Ph) (1.0 mmol)
was added to a benzene solution (30 cm3) of the ligand
LH (2.0 mmol), and the reaction mixture was refluxed
for about 2 h. After removing the solvent under re-
duced pressure on a rotary evaporator, a thick oil was
obtained. This was treated with diethyl ether and
petroleum ether, and a solid formed, which was recrys-
tallized from benzene/petroleum ether mixture.
4.2.3. 1-(4-Trifluoromethylphenyl)-3-
methyl-4-acetyl-pyrazol-5-one (L2H)
Yield 68%. M.p.: 112–114°C. Anal. Calc. for
C13H11F3N2O2: C, 54.9; H, 3.9; N, 9.9. Found: C, 54.7;
H, 4.0; N, 9.6%. IR data: 3420 br, w(N–H···O), 1645 m,
w(CꢀO). 1H-NMR data (CDCl3): 2.18 s, 247 s (C3–
CH3, OꢀCCH3), 7.70 d, 8.08 d (N1-4-C6H4CF3), 4.50 s
br (N–H···O). 19F-NMR data (CDCl3): −62.4.
4.3.2. [Aquotri-n-butyl(1-(4-trifluoromethylphenyl)-
4-benzoyl-pyrazolon-5-ato) tin(IV)],
[(L1)Sn(C4H9)3(H2O)], 2
Yield 38%. M.p.:249–251°C. Anal. Calc. for
C30H41F3N2O3Sn: C, 55.15; H, 6.33; N, 4.29%. Found:
C, 54.96; H, 6.38; N, 4.12%. LM (CH2Cl2): 0.7 V−1 cm2
mol−1, 0.8×10−3 M. LM (DMSO): 21.6 V−1 cm2
mol−1, 0.5×10−3 M. 1H-NMR (CDCl3): l(H2O),
1.80s br: l(Sn–C4H9), 0.93 t, 1.25–1.47 m, 1.58–1.72
m; l(L1), 2.11 s (C3–CH3), 7.48–7.75 m, 8.05–8.15 m
(OꢀCC6H5, N1–C6H4CF3). 19F-NMR (CDCl3): −62.3.
119Sn-NMR (CDCl3): +128.2. IR (nujol) cm−1: 3120
br, w(H2O); 1656 m, l(H2O); 1616 m, w(CꢀO); 592 m,
504 s, w(Sn–C): 440 m, 420 m, 409 w, w(Sn–O).
4.2.4. 1-(4-Trifluoromethylphenyl)-3-
methyl-4-trifluoroacetyl-pyrazol-5-one (L3H)
Yield 75%. M.p.: 123–124°C. Anal. Calc. for
C13H8F6N2O2: C, 46.17; H, 2.38; N, 8.28. Found: C,
45.96; H, 2.53; N, 8.12%. IR data; 3420 br, w(N–
H···O), 1645 m, w(CꢀO). 1H-NMR data (CDCl3): 2.48 q
(C3–CH3), 7.74 d, 8.01 d (N1-4-C6H4CF3), 4.10s br
(N–H···O). 19F-NMR data (CDCl3): −63.0, −75.3.
4.3. Syntheses of the complexes
4.3.1. [Aquotrimethyl(1-(4-trifluoromethylphenyl)-
4-benzoyl-pyrazolon-5-ato)tin(IV)],
4.3.3. [Triphenyl(1-(4-trifluoromethylphenyl)-
4-benzoyl-pyrazolon-5-ato) tin(IV)], [(L1)Sn(C6H5)3], 3
Yield 56%. M.p.:252–254°C. Anal. Calc. for
C36H27F3N2O2Sn: C, 62.19; H, 3.91; N, 4.03%. Found:
[(L1)Sn(CH3)3(H2O)], 1
A benzene solution (30 cm3) of the ligand L1H (1.0

F. Marchetti et al. / Journal of Organometallic Chemistry 580 (1999) 344–353
351
C, 62.05; H, 3.78; N, 4.20%. LM (CH2Cl2): 0.9 V−1 cm2
mol−1, 0.6×10−3 M. LM (DMSO): 22.1 V−1 cm2
mol−1, 0.3×10−3 M. 1H-NMR (CDCl3): l(Sn–C6H5),
not distinguishable from aromatics of the ligand: l(L1),
1.95 s (C3–CH3), 7.40–7.80 m, 8.00–8.16 m (OꢀCC6H5,
N1–C6H4CF3). 19F-NMR (CDCl3): −62.5 [1], −62.4
[3], −62.3 [1]. 119Sn-NMR (CDCl3): −168.2. IR (nu-
jol) cm−1: 1610 s, w(CꢀO); 251 vs, 233 m, w(Sn–C); 440
vs, 422 m, 408 m, w(Sn–O).
ligand; l(L2), 2.40 s br (C3–CH3), 7.40–7.60 m, 7.65–
7.90 m, 8.04 d (OꢀCC6H5, N1–C6H4CF3). 19F-NMR
(CDCl3): −62.3. 119Sn-NMR (CDCl3): −179.8. IR
(nujol) cm−1: 1622 s, w(CꢀO); 238 s, w(Sn–C); 455 sh,
450 vs 442 sh, w(Sn–O).
4.3.7. [Aquotrimethyl(1-(4-trifluoromethylphenyl)-
4-trifluoroacetyl-pyrazolon-5-ato)tin(IV)],
[(L3)Sn(CH3)3(H2O),] 7
Yield 42%. M.p.:173–175°C. Anal. Calc. for
C16H18F6N2O3Sn: C, 37.03; H, 3.50; N, 5.40%. Found:
C, 36.82; H, 3.62; N, 5.27%. LM (CH2Cl2): 0.9 V−1 cm2
mol−1, 0.7×10−3 M. LM (DMSO): 23.5 V−1 cm2
mol−1, 0.6×10−3 M. 1H-NMR (CDCl3): l(H2O), 1.75
br: l(Sn–CH3), 0.62 s (2J(Sn–H)=58.4, 56.0 Hz); l(L3),
2.45 q (C3–CH3), 7.46 d, 8.11 d (N1–C6H4CF3). 19F-
NMR (CDCl3): −63.1, −72.2. 119Sn-NMR (CDCl3):
+142.7. IR (nujol) cm−1: 3120 br, w(H2O); 1645 sh,
l(H2O); 1614 s br, w(CꢀO): 553 vs, 530 m, w(Sn–C);
463 m, 441 s, 416 s, 402 m w(Sn–O).
4.3.4. [Aquotrimethyl(1-(4-trifluoromethylphenyl)-
4-acetyl-pyrazolon-5-ato) tin(IV)],
[(L2)Sn(CH3)3(H2O)], 4
Yield 63%. M.p.:194–195°C. Anal. Calc. for
C16H21F3N2O3Sn: C, 41.32; H, 4.55; N, 6.02%. Found:
C, 41.28; H, 4.68; N, 5.87%. LM (CH2Cl2): 0.8 V−1 cm2
mol−1, 0.8×10−3 M. LM (DMSO): 13.6 V−1 cm2
mol−1, 0.9×10−3 M. 1H-NMR (CDCl3): l(H2O), 1.90
s br; l(Sn–CH3), 0.66 s br (2J(Sn–H)=56.8 Hz); l(L2),
2.21 s, 2.30 s, 2.55 s, 2.70 s (C3–CH3, OꢀCCH3), 7.70 d
br, 8.08 d br (N1–C6H4CF3). 1H-NMR (DMSO):
4.3.8. [Aquotri-n-butyl(1-(4-trifluoromethylphenyl)-
4-trifluoroacetyl-pyrazolon-5-ato)tin(IV)],
l(H2O), 2.98 s br; l(Sn–CH3), 0.81 s [1] (2J(Sn–H)
=
128.6, 123.8 Hz), 0.54 s [3] (2J(Sn–H)=69.0, 66.4 Hz);
l(L3), 2.33 s [3], 2.29 s [3], 2.13 s [1], 2.08 s [1]
(C3–CH3, OꢀCCH3), 7.68 d, 7.79 m, 8.08 m, 8.32 d
(N1–C6H4CF3). 19F-NMR (CDCl3): −62.6 [6], −62.5
[1], −62.3 [1]. 119Sn-NMR (CDCl3): +155.2, +152.0.
IR (nujol) cm−1: 3180 br, w(H2O); 1657 m, l(H2O);
1612 s, w(CꢀO); 553 s, 527 m, w(Sn–C): 443 s, 402 m,
w(Sn–O).
[(L3)Sn(C4H9)3(H2O)], 8
Yield 64%. M.p.:95–100°C. Anal. Calc. for
C25H36F6N2O3Sn: C, 46.54; H, 5.62; N, 4.34%. Found:
C, 46.17; H, 5.75; N, 4.40%. LM (CH2Cl2): 0.4 V−1 cm2
mol−1, 1.0×10−3 M. LM (DMSO): 25.1 V−1 cm2
mol−1, 1.0×10−3 M. 1H-NMR (CDCl3): l(H2O), 1.80
s br; l(Sn–C4H9), 0.85 t, 1.25–1.45 m, 1.60–1.75 m;
l(L3), 2.36 q (C3–CH3), 7.55 d br, 7.80 d br (OꢀCC6H5,
N1–C6H4CF3). 19F-NMR (CDCl3): −62.8, −73.2.
119Sn-NMR (CDCl3): +148.7, +128.2. IR (nujol)
cm−1: 3370 br, w(H2O): 1706 m, l(H2O); 1659 s,
w(CꢀO); 619 s, 528 m, w(Sn–C); 455 vs, 407 m, w(Sn–
O).
4.3.5. [Aquotri-n-butyl(1-(4-trifluoromethylphenyl)-
4-acetyl-pyrazolon-5-ato) tin(IV)],
[(L2)Sn(C4H9)3(H2O)], 5
Yield 42%. M.p.:208–209°C. Anal. Calc. for
C25H39F3N2O3Sn: C, 50.78; H, 6.65; N, 4.74%. Found:
C, 50.55; H, 6.71; N, 4.48%. LM (CH2Cl2): 0.6 V−1 cm2
mol−1, 0.9×10−3 M. LM (DMSO): 19.3 V−1 cm2
mol−1, 0.6×10−3 M. 1H-NMR (CDCl3): l(H2O), 1.95
s br; l(Sn–C4H9), 0.96 t, 1.20–1.54 m, 1.62–1.80 m;
l(L2), 2.15 s, 2.22 s (C3–CH3), 7.38–7.64 m, 8.00–8.12
m (OꢀCC6H5, N1–C6H4CF3). 19F-NMR (CDCl3): −
62.6 [1], −62.5 [1], −62.4 [1], −62.3 [4]. 119Sn-NMR
(CDCl3): +152.0, +83.8. IR (nujol) cm−1: 3210 br,
w(H2O); 1645 m, l(H2O): 1618 s, w(CꢀO); 615 s, 542 m,
w(Sn–C); 443 s, 412 m, w(Sn–O).
4.3.9. [Triphenyl(1-(4-trifluoromethylphenyl)-
4-trifluoroacetyl-pyrazolon-5-ato) tin(IV)],
[(L3)Sn(C6H5)3], 9
Yield 85%. M.p.:120–121°C. Anal. Calc. for
C31H22F6N2O2Sn: C, 54.18; H, 3.23; N, 4.08%. Found:
C, 54.25; H, 3.45; N, 4.26%. LM (CH2Cl2): 0.2 V−1 cm2
mol−1, 0.5×10−3 M. LM (DMSO): 16.1 V−1 cm2
mol−1, 1.3×10−3 M. 1H-NMR (CDCl3): l(Sn–C6H5),
not distinguishable from aromatics of the ligand; l(L3),
2.35 q (C3–CH3), 7.26–7.44 m, 7.57 d, 7.69 m, 7.87 d
(OꢀCC6H5, N1–C6H4CF3). 19F-NMR (CDCl3): −62.8,
−74.2. 119Sn-NMR (CDCl3): −119.9. IR (nujol)
cm−1: 1636 s, w(CꢀO); 278 s, 263 s, 234 vs w(Sn–C);
453 vs, 444 vs, 403 m, w(Sn–O).
4.3.6. [Triphenyl(1-(4-trifluoromethylphenyl)-
4-acetyl-pyrazolon-5-ato)tin(IV)], [(L2)Sn(C6H5)3], 6
Yield 72%. M.p.:115–118°C. Anal. Calc. for
C31H25F3N2O2Sn: C, 58.80; H, 3.98; N, 4.42%. Found:
C, 58.58; H, 3.75; N, 4.23%. LM (CH2Cl2): 0.7 V−1 cm2
mol−1, 0.8×10−3 M: LM (DMSO): 20.1 V−1 cm2
mol−1, 0.8×10−3 M. FW Calc.: 633; MW found
4.4. Crystallographic study of [(L2)SnPh3]
A P21 Syntex diffractometer was used for the mea-
surements of the cell constants and for the data collec-
tion. A summary of crystal data together with details of
1
(CHCl3): 590, r: 0.93, 1.0.10−2 m. H-NMR (CDCl3):
l(Sn–C6H5), not distinguishable from aromatics of the

352
F. Marchetti et al. / Journal of Organometallic Chemistry 580 (1999) 344–353
expected
F atoms. These peaks have acceptable
data collection and computer resolution is given in
Table 3. Monitoring of three check reflections (taken
every 100 reflections) indicated no decay. No
absorption phenomena were found after a psi-scan on
reflection [0, 0, −4]. Data were corrected for Lorentz
and polarization. The molecular structure was solved
using the heavy atom method in CAOS [56]. A
Patterson map showed the position of the tin atom
which gave an R value of 0.27. A Fourier map revealed
the remaining non-H atoms, although the F atoms
showed disorder and their positions were determined
later.
F–C(15)–F bond angles. As the real occupational
factor could not be estimated, they were assigned a
factor of 1. Fig. 3 indicates clearly the rotational
disorder for the CF3 group, and must be considered
cautiously because the real displacement parameters for
these three atoms are smaller than those shown (shrunk
ellipsoids should correspond to these F atoms). At this
point, H atoms were introduced at fixed positions with
˚
a C–H distance of 0.96 A. H isotropic displacement
parameters were kept fixed until refinement
convergence. Atomic scattering factors and anomalous
dispersion terms were taken from the literature [58].
Subsequent calculations were performed as follows;
refinement, on F, based on the minimization of
S w(ꢀFoꢀ−ꢀFcꢀ)2
with
the
weighting
scheme
5. Supplementary material available
w=1/(a+Fo+cF2o), where a and c are of the order of
2Fo(min) and 2/Fo(max) [57], respectively: anisotropic
displacement parameters were refined for non-H atoms.
After refinement convergence, an atomic list (C(15)
excluded) provided a Fourier analysis which showed 5
peaks of similar intensity corresponding to F atoms and
additional areas of diffuse intensity were observed in
the map. The 5 peaks were at expected C–F distances
Crystallographic data for the structural analysis has
been deposited with the Cambridge Crystallographic
Data Centre, CCDC No. 110211 for 6. Copies of the
information can be obtained free of charge from The
Director, CCDC, 12 Union Road, Cambridge, CB2
1EZ, UK (Fax: +44-1223-336-033; e-mail: de-
posit@ccdc.cam.ac.uk
www.ccdc.cam.ac.uk. Fo/Fc listing is available from
F.C.
or
www:
http://
˚
from C(15) (they are in the range 1.18–1.35 A). As a
good model for this system was not found, three
rational peaks were chosen and assigned to the 3
Table 3
Acknowledgements
Summary of crystal data and computer resolution
Emperical formula
Formula weight
Temperature (K)
Crystal system
Space group
C31H25N2O2F3Sn
633.24
298
Financial support by Universita` degli Studi di
Camerino, Consiglio Nazionale delle Ricerche C.N.R.
Rome, The Camille and Henry Dreyfus Foundation
(M.R.) and the Vassar College Research Committee
(M.R.).
Triclinic
(
P1
˚
a (A)
10.202(2)
11.960(2)
13.315(3)
68.14(1)
73.14(1)
75.46(2)
1424.2(5)
2
˚
b (A)
˚
c (A)
h (°)
i (°)
k (°)
References
3
˚
V (A )
[1] (a) W.T. Piver, Environ. Health Perspect. 4 (1973) 61. (b) G.J.M.
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Toxicol. 32 (1997) 198.
Z
v (Mo–Ka (mm−1))
Crystal color
Crystal habit
Crystal size (mm)
Reflections collected
Reflections refined
Reflections unique
2qmax (°)
9.57
Colorless
Block
0.40×0.20×0.15
7532
3502
6886
54.1
Scan speed (° min−1
Scan range (°)
Parameters refined
R(F, F\4|(F))a
Rw
)
2
0.85
352
0.041
0.053
0.999
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Sb
a R(F)=S ꢀ(Fo−Fc)ꢀ/S Fo.
b S=[S{w(Fo2−Fc2)2}/(n−p)]0.5, n=no. of data and p=no. of
refined parameters.

F. Marchetti et al. / Journal of Organometallic Chemistry 580 (1999) 344–353
353
[11] R. Willem, A. Bouhdid, B. Mahieu, L. Ghys, M. Biesemans,
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