Thermochemistry of adducts of tin(IV) chloride with heterocyclic bases

Article abstract of DOI:10.1016/S0040-6031(02)00326-X

The compounds [SnCl₄(L)_n] (where L is pyridine (py), 4-methylpyridine (γ-pico), 3-methylpyridine (β-methylpyridine (β-pico), piperidine (pipd), morpholine (morph), piperazine (pipz), 3-cyanopyridine (3-cyanopy), 4-cyanopyridine (4-cy

Full text of DOI:10.1016/S0040-6031(02)00326-X

Thermochimica Acta 398 (2003) 1–7
Thermochemistry of adducts of tin(IV) chloride
with heterocyclic bases
Pedro Oliver Dunstan∗
Instituto de Qu´ımica, Universidade Estadual de Campinas, C.P. 6154, CEP 13083-970, Campinas, São Paulo, Brazil
Received 31 January 2002; received in revised form 29 April 2002; accepted 8 May 2002
Abstract
The compounds [SnCl4(L)n] (where L is pyridine (py), 4-methylpyridine (␥-pico), 3-methylpyridine (␤-pico), piperidine
(pipd), morpholine (morph), piperazine (pipz), 3-cyanopyridine (3-cyanopy), 4-cyanopyridine (4-cyanopy), quinoline (quin)
or 2,2ꢀ-bipyridine (bipy) and n = 2, 1 or 3/2) were synthesized and characterized by elemental analysis, melting points, thermal
studies and IR spectroscopy. The enthalpies of dissolution of adducts, tin(IV) chloride and ligands in 1,2-dichloroethane or
25% (v/v) aqueous HCl 1.2 M in methanol were measured and, by using thermochemical cycles, the following thermochemical
parameters for the adducts have been determined: the standard enthalpies for the Lewis acid/base reaction (ꢀrH◦), the standard
enthalpies of formation (ꢀf H◦), the standard enthalpies of decomposition (ꢀDH◦), the lattice standard enthalpies (ꢀMH◦)
and the standard enthalpies for the Lewis acid/base reaction in the gaseous phase (ꢀrH◦). The mean standard enthalpies of the
¯
tin–nitrogen bonds (D(Sn–N)) have been estimated. Based on these last values, the basicity orders: pipd > morph > ␥-pico =
␤-pico > py > 4-cyanopy > 3-cyanopy and pipz > quin are obtained.
© 2002 Elsevier Science B.V. All rights reserved.
Keywords: Sn–N bonds; Tin(IV) chloride; Thermochemical parameters; Heterocyclic bases; Thermochemistry
1. Introduction
cal data for these compounds. No information about
the enthalpies of dissociation of the tin(IV)–nitrogen
bonds is available.
The acceptor properties of tin(IV) chloride are
well established in the literature and the synthesis of
numerous adducts have been reported. The main em-
phasis of the studies made on this kind of compounds
has been on searching for a physical approach to the
stereochemistry and thermodynamic stability of them
[1]. Among the adducts studied, it is found adducts
of tin(IV) chloride with ligands containing nitrogen
as the donor atom [1–4]. However, little have been
done for determining the energies evolved in the
adduct formation. There is a lack of thermodynami-
In this paper, we described the synthesis of adducts
of tin(IV) chloride with heterocyclic amines with
the purpose of obtaining the enthalpies involved
in the formation of the adducts. Correlations bet-
ween the bond dissociation enthalpies and other ther-
mochemical parameters are also established. Inductive
effects on the energy of the Sn–N bonds due to the
substitution of one hydrogen atom of the pyridine
ring by the electronic donator methyl group, or by
the electronic withdrawing cyano group, as well as,
the effect of the substitution of one carbon atom
in the piperidine ring by the more electronegative
nitrogen or oxygen atoms, were also studied.
∗
Tel.: +55-197883088; fax: +55-197883023.
E-mail address: dunstan@iqm.unicamp.br (P.O. Dunstan).
0040-6031/03/$ – see front matter © 2002 Elsevier Science B.V. All rights reserved.
PII: S0040-6031(02)00326-X

2
P.O. Dunstan / Thermochimica Acta 398 (2003) 1–7
2. Experimental
by distillation and stored over Linde 4 Å molecular
sieves.
Due to the moisture sensitivity and toxic nature
of the compounds, all preparations and manipulations
were made under a dry nitrogen atmosphere.
2.2. Analytical
Carbon, hydrogen and nitrogen contents were de-
termined by microanalytical procedures. Tin was
determined by gravimetry as stannic oxide following
precipitation of hydrated stannic oxide by ammonia
solution from the nitric acid solution of the adducts.
The precipitate was ignited to stannic oxide. The fil-
trate was used for the determination of chloride as
silver chloride, using 0.1 M AgNO3 solution.
2.1. Chemicals
Tin(IV) chloride (99%, Aldrich) was purified
by the method of Hildebrand and Caster [5].
Pyridine (A.C.S. Reagent), 3-methylpyridine (p.a.
Baker), 4-methylpyridine (p.a. Baker), piperidine
(99% RPE Analyticals, Carlo Erba), morpho-
line (99%, A.C.S. Aldrich) and quinoline (98%,
Aldrich) were purified by distillation using an
efficient column and stored over 4 Å molecular
sieves (bp obtained: 111–112, 139–140, 140–141,
103–104, 123–124 and 111–112/120 mm Hg, re-
spectively). Piperazine (99%, Aldrich) was pu-
rified by recrystallization from methanol (m.p.:
107–108 ◦C). 3-Cyanopyridine (98%, Aldrich) and
4-methylpyridine (98%, Aldrich) were purified
by recrystallization from methanol (m.p.: 48–50
and 78–80 ◦C, respectively). 2,2ꢀ-Bipyridine (99%,
Aldrich) was purified by recrystallization from ethanol
according to the method described by Gallagher et al.
[6] (m.p.: 193–194 ◦C). Solvents used in the syn-
thesis and calorimetric measurements were purified
2.3. Synthesis of the adducts
The adducts were obtained from the reaction of
tin(IV) chloride and ligands in solution. A typical pro-
cedure is given bellow.
2.3.1. SnCl4–py
On mixing a solution of 1.00 ml (8.55 mmol) of
SnCl4 in 10 ml of carbon tetrachloride with 1.40 ml
(17.38 mmol) of pyridine, under a dry nitrogen atmo-
sphere current, a white solid appeared. The stirring
was kept during several hours. The solid was fil-
tered, washed with three portions of petroleum ether
and dried in vacuum and stored in a desiccator over
Table 1
Yields on preparation, melting points, appearance and analytical data of the adducts
Compound
Yield/% Melting
pointa/◦C
Appearanceb
C
H
N
Sn
Cl
Calc. Found Calc. Found Calc. Found Calc. Found Calc. Found
[SnCl4(py)2]
100
97
100
100
100
100
338–340c
316–318
335–337
216–218
203–205
270–272
262–264
267–268
225–227
360d
wh. pw.
wh. pw.
wh. pw.
wh. pw.
wh. pw.
wh. pw.
wh. pw.
wh. pw.
wh. crs.
wh. pw.
28.69 28.77 2.41 2.45
32.26 32.62 3.16 3.17
32.26 31.94 3.16 3.19
27.88 27.60 5.15 5.28
22.10 21.89 4.17 4.22
18.49 18.28 4.36 4.50
30.75 30.45 1.72 1.80
30.75 30.63 1.72 1.93
35.70 36.04 2.33 2.55
28.83 28.89 1.94 2.10
6.69 6.76 28.35 28.45 33.87 33.30
6.27 6.24 26.57 26.56 31.74 32.01
6.27 6.30 26.57 26.54 31.74 32.04
6.50 6.48 27.55 27.65 32.92 32.99
6.44 6.20 27.30 27.28 32.62 32.80
10.78 10.55 30.46 30.50 36.39 36.66
11.95 11.88 25.32 25.35 30.25 30.40
11.95 11.80 25.32 25.36 30.25 30.43
4.63 4.74 26.13 26.05 31.22 31.01
6.72 6.88 28.48 28.49 34.03 33.81
[SnCl4(␤-pico)2]
[SnCl4(␥-pico)2]
[SnCl4(pipd)2]
[SnCl4(morph)2]
[SnCl4(pipz)3/2
[SnCl4(3-cyanopy)2] 92
[SnCl4(4-cyanopy)2] 92
]
[SnCl4(quin)3/2
[SnCl4(bipy)]
]
100
100
a Melting point with decomposition.
b wh., white; pw., powder; crs., crystals.
c Partial sublimation.
d Without melting till 360 ◦C.

P.O. Dunstan / Thermochimica Acta 398 (2003) 1–7
3
calcium chloride. All the adducts were prepared with
2.6. Calorimetric measurements
a molar ratio tin(IV)/ligand of 1/2.
All the solution calorimetric determinations were
carried out in an LKB 8700-1 precision calorimeter
as described elsewhere [7]. The solution calorimetric
measurements were performed by dissolving sam-
ples from 0.9 to 129.7 mg of the adducts or tin(IV)
chloride in 100 ml of methanol or 1,2-dichloroethane
and the ligand in this last solution maintaining a mo-
lar relation equal to the stoichiometry of the adduct.
The accuracy of the calorimeter was carried out
by determining the heat of dissolution of tris [(hy-
droxymethyl)amino]methane in 0.1 mol dm−3 HCl.
2.4. Infrared (IR) spectra
Spectra were obtained with samples in KBr matrix
for adducts and solid ligands. For liquid ligands, a film
of the ligand sandwiched between NaCl plates was
used. A Perkin Elmer 1600 series FTIR spectropho-
tometer in the 4000–400 cm−1 region was used.
2.5. Thermal studies
The result (−29.78
0.03 kJ mol−1) is in agree-
TG/DTG and DSC measurements were obtained
in argon atmosphere using a Du Pont 951 TG an-
alyzer with samples varying in mass from 5.07 to
11.02 mg (TG/DTG) and from 4.72 to 4.83 mg (DSC)
and a heating rate of 10 K min−1 in the 298–1173 K
(TG/DTG) and 298–673 K (DSC) temperature ranges.
TG calibration for temperature was made using metal-
lic aluminum as a standard (m.p.: 660.37 ◦C) and the
calibration for mass was carried out automatically.
The DSC calibration was made using metallic indium
as a standard (m.p.: 165.73 ◦C, ꢀsl H◦: 28.4 J g−1).
ment with the value recommended by IUPAC [8]
(−29.763 0.000 kJ mol−1).
3. Results and discussion
All the adducts obtained were solids. For the
adduct of pyridine, it was observed when the capillary
melting point was determined, its partial sublimation
with the decomposition of the residue. For the other
Table 2
a
Main IR absorption bands (cm−1
)
of complexes and free ligands
Compound
ν(N–H)
ν(C–C)
ν(C–N)
Ring
ν(C–O–C)
δ(H–N–C)
α(C–C–C)
φ(C–C)
New bands
py
1573sh
1609s
1585s, 1545s
1627s
1572sh, 1558s
1579m
1467s
1455s
1452s
1450s
1461s
584s
n.o.
n.o.
557m
652sh
659m
431m
433m
439w
n.o.
[SnCl4(py)2]
␥-pico
[SnCl4(␥-pico)2]
␤-pico
[SnCl4(␤-pico)2]
pipd
[SnCl4(pipd)2]
morph
[SnCl4(morph)2]
pipz
[SnCl4(pipz)3/2
3-cyanopy
[SnCl4(3-cyanopy)2]
4-cyanopy
[SnCl4(4-cyanopy)2]
quin
1249w
1234w
1206s
1214s
1206m
1188s
n.o.
3276m
3178s
3320m
3120m
3275s
3244s
860s, 825m
871s, 855m
889m, 835s
899m, 872s
861m, 815s
868m
1097s
1114s
]
1440s
2231s
2247m
2236s
2243m
1219s
1195s
1216s
1224m
1031m
952m
1596s
1596m
1579s
1599s
n.o.
[SnCl4(quin)3/2
bipy
[SnCl4(bipy)]
]
1228m
759vs
n.o.
994m
1031m
1320m, 724s
a α, ring deformation in plane; φ, ring deformation out of plane; ν, stretching; δ, angular deformation; ring, ring breathing; n.o., not
observed. Intensity of bands: vs, very strong; s, strong; m, medium; w, weak; sh, shoulder.

4
P.O. Dunstan / Thermochimica Acta 398 (2003) 1–7
adducts, the determination of their capillary melting
points leaded to the decomposition of the adducts.
The yields ranged from 92 to 100 %. The yields,
melting points, colors, appearance and analytical data
are summarized in Table 1.
mation region (889-815 cm−1) also affords evidence
of coordination of the nitrogen atom of the ligands
[11]. The coordinated pyridine is distinguished from
free pyridine by the presence in the adducts of a weak
band at 1250 cm−1 and by the splitting of bands at
584 and 431 cm−1 in free pyridine, to higher frequen-
cies [12]. The IR spectra of ␤- and ␥-picoline adducts
show appreciable splitting towards higher frequencies
of the bands at 1585–1545 and 1206 cm−1 in the free
ligands [13,14]. For 3- and 4-cyanopyridine adducts,
3.1. IR spectra
The more important IR bands are reported in
Table 2. Considerable shifts to lower frequencies of
the ν(N–H) bands of the ligands pipd, morph and pipz
after coordination are observed. This is indicative of
coordination of them through the nitrogen atom of
their NH group [9,10]. In the morpholine adduct, the
positive shift of the band attributed to the C–O–C
stretching vibration, with respect to free morpholine,
excludes the possibility of oxygen-to-tin(IV) coordi-
nation [9]. The change observed in the H–N–C defor-
this last band is observed at 1195 and 1224 cm−1
,
respectively (1219 and 1216 cm−1 in free ligands).
As the band attributed to the stretching of the nitrile
group in the free ligands (2236–2231 cm−1) increases
its frequency very little and its intensity decreases
after coordination, these exclude the coordination of
the ligands trough the nitrogen atom of the nitrile
group [15].
Table 3
Thermochemical data of the compounds
Compound
% Mass lost
TG temperature range/K
Species lost
DSC peak temperature/K
ꢀH◦/kJ mol−1
Calcd.
Obs.
100
[SnCl4(py)2]
[SnCl4(␤-pico)2]
100
100
495–555
504–548
−2py–SnCl4
n.o.a
388
98.6
Pyrolysis
1.74
1.4b
98.1
1.9b
[SnCl4(␥-pico)2]
100
502–541
Pyrolysis
n.o.
[SnCl4(pipd)2]
11.9
88.1
11.6c
77.3c
3.7b
422–464
464–681
−0.6pipd
374
428
453
451
471
0.12
0.34
2.46
2.00
1.36
−1.4pipd–SnCl4
[SnCl4(morph)2]
100
100
80.3c
6.9
12.8b
98.6
1.4b
500–619
872–937
Pyrolysis
Pyrolysis
[SnCl4(pipz)3/2
]
458–494
386
31.35
[SnCl4(3-cyanopy)2]
[SnCl4(4-cyanopy)2]
4.4
95.6
4.4
324–346
489–676
−0.2SnCl4
317
344
0.32
2.98
88.2d
9.2b
Pyrolysis
100
100
97.9
2.1b
97.5d
2.5b
452–491
379–507
Pyrolysis
Pyrolysis
545
128.38
[SnCl4(quin)3/2
[SnCl4(bipy)]
]
345
402
504
n.o.
5.45
8.94
0.81
100
95.4
4.6b
597–642
Pyrolysis
a Not observed.
b Residue at 1173 K.
c Two overlapping steps.
d Three overlapping steps.

P.O. Dunstan / Thermochimica Acta 398 (2003) 1–7
5
Then, the IR data for these adducts, can be in-
IV. [SnCl4(L)2] → [(SnCl4)0.8(L)2] + 0.2SnCl4
[(SnCl4)0.8(L)2] → pyrolysis
terpreted in terms of coordination through the hete-
rocyclic nitrogen atom of the ligands to the tin(IV)
atom [12–15]. The IR spectra of the bipyridine adduct
shows the appearance of new bands after coordina-
The adduct of py followed process I. Those of ␤-pico,
␥-pico, morph, pipz, 4-cyanopy, quin and bipy fol-
lowed process II. The adduct of pipd followed process
III and the adduct of 3-cyanopy followed process IV.
The DSC curves of the adducts are consistent with
TG/DTG data. They present several endothermic
peaks due to pyrolysis, partial elimination of ligand or
tin(IV) chloride or partial elimination of both ligand
and tin(IV) chloride. Table 3 lists the thermoanalytical
data of the adducts.
tion. Two new bands appear at 1320 and 724 cm−1
,
both of which are absent in free bipy and are due to
the adduct formation [16]. The IR spectra of the quin
adduct shows the splitting of several bands with re-
spect to the free ligand [17]. A new band is observed at
1228 cm−1 after coordination. The IR data of the bipy
and quin adducts can be interpreted in terms of coor-
dination of these ligands through the nitrogen atom to
the tin(IV) atom [16,17].
3.3. Calorimetric measurements
3.2. Thermal studies
The standard enthalpies of dissolution of tin(IV)
chloride, ligands and adducts were obtained as previ-
ously reported [7]. Table 4 gives the values obtained
for the enthalpies of dissolution of SnCl4 (ꢀ1H◦),
ligand into the solution of SnCl4 (ꢀ2H◦) and of the
adduct (ꢀ3H◦). Uncertainty intervals given in this ta-
ble are twice the standard deviation of the means of
3–6 replicate measurements on each compound. Com-
bined errors were calculated from the square root of
Thermogravimetry and derivative thermogravime-
try of the adducts show that the thermal dissociation
process of the adducts are of different types:
I. [SnCl4(L)2] → SnCl4 + 2L
II. [SnCl4(L)2] → pyrolysis
III. [SnCl4(L)2] → [SnCl4(L)1.4] + 0.6L
[SnCl4(L)1.4] → pyrolysis
Table 4
Enthalpies of dissolution at 298.15 Ka
Compound
Calorimetric solvent
Number of experiments
ꢀiH◦/kJ mol−1
SnCl4(l)
py(l)
[SnCl4(py)2](s)
␥-pico(l)
[SnCl4(␥-pico)2](s)
quin(l)
[SnCl4(quin)3/2
SnCl4(l)
␤-pico(l)
[SnCl4(␤-pico)2](s)
pipd(l)
[SnCl4(pipd)2](s)
morph(l)
[SnCl4(morph)2](s)
SnCl4(l)
pipz(s)
[SnCl4(pipz)1.5
3-cyanopy(s)
[SnCl4(3-cyanopy)2](s)
4-cyanopy(s)
A
11
5
4
6
5
5
3
6
4
4
5
3
6
3
11
3
3
5
3
4
5
(i = 1) −137.69
(i = 2) −34.82
(i = 3) 14.58
(i = 2) −35.88
(i = 3) 16.27
(i = 2) −36.27
(i = 3) 24.82
(i = 1) −78.26
(i = 2) −65.20
(i = 3) 46.09
(i = 2) −205.10
(i = 3) 22.63
(i = 2) −142.12
(i = 3) 27.00
(i = 1) −121.07
(i = 2) −60.63
(i = 3) 36.96
(i = 2) 41.23
(i = 3) 24.56
(i = 2) 50.94
(i = 3) 58.06
2.09
1.15
0.21
0.53
1.11
0.79
2.03
2:1 SnCl4–A
A
2:1 SnCl4–A
A
1.5:1 SnCl4–A
A
B
2:1 SnCl4–B
B
2:1 SnCl4–B
B
2:1 SnCl4–B
B
C
1.5:1 SnCl4–C
C
2:1 SnCl4–C
C
2:1 SnCl4–C
C
]
(s)
2.28
1.86
1.67
2.30
0.62
3.21
1.47
0.78
1.83
1.15
2.20
0.66
0.96
2.91
]
(s)
[SnCl4(4-cyanopy)2](s)
a A: 1–2% water in 1,2-dichloroethane; B: dry 1,2-dichloroethane; C: methanol.

P.O. Dunstan / Thermochimica Acta 398 (2003) 1–7
7
the sum of the squares of the component errors. The
adduct of bipyrine is extremely insolved in most sol-
vents and it was not possibly determined its enthalpy
of dissolution.
erwise, the basicity order observed is the expected
order.
The expected basicity order for saturated hetero-
cyclic amines would be pipd > morph due to an in-
ductive effect of substitution of one carbon atom in
the ring of pipd by the more electronegative atom of
oxygen, leading to the decrease of the electronic den-
sity available for bonding on the nitrogen atom of the
ring. The order observed matches the expected order.
As a whole it is observed that the mean tin–nitrogen
coordinate bond dissociation energies for the adducts
here studied, are higher than the mean dissociation
energies of the tin(IV)–oxygen or tin(IV)–sulfur bonds
in comparable adducts of tin(IV) chloride with amides
or thioamides [25,26].
From the values obtained for the standard en-
thalpies of dissolution and by using appropriate
thermochemical cycles [7,18], the following thermo-
chemical parameters were determined: the standard
enthalpies of the acid/base reactions (ꢀrH◦), the stan-
dard enthalpies of formation (ꢀfH◦), the standard
enthalpies of decomposition (ꢀDH◦), the standard
lattice enthalpies (ꢀMH◦) and the standard enthalpies
of the Lewis acid/base reactions in the gaseous phase
(ꢀrH◦(g)). The ꢀrH◦(g) values can be used to calcu-
late the standard enthalpies of the Sn–N bonds [18],
being equal to D(Sn–N) = ꢀrH◦(g)/n (where n = 2
¯
or 3/2). Table 5 lists the values obtained for all these
thermochemical parameters for the adducts. For the
determination of ꢀrH◦(g), it was necessary to assume
that the molar standard enthalpies of sublimation of
the adducts were equal to the enthalpies of sublima-
tion or vaporization of 1 mol of the respective ligand
[23,24], as melting points and thermal studies showed
that the adducts decomposed on heating and were not
found in the liquid phase and probably, not in the
gaseous phase.
References
[1] I.R. Beattil, Quart. Rev. Chem. Soc. 17 (1963) 382.
[2] S.S. Sing, C.B.S. Sengar, Israel J. Chem. 7 (1969) 471.
[3] W.R. Trost, Can. J. Chem. 30 (1952) 842.
[4] M.F. Lappert, G. Srivastava, Inorg. Nucl. Chem. Lett. 1 (1965)
53.
[5] J.H. Hildebrand, J.M. Caster, J. Am. Chem. Soc. 54 (9) (1932)
3592.
[6] M.J. Gallagher, D.P. Graddon, A.R. Sheikh, Thermochim.
Acta 27 (1978) 269.
[7] P.O. Dunstan, Thermochim. Acta 197 (1992) 201.
[8] E.F. Herrington, Pure Appl. Chem. 40 (1974) 391.
[9] I.S. Ahuja, Inorg. Chim. Acta 3 (1969) 110.
[10] I.S. Ahuja, A. Garg, Inorg. Nucl. Chem. Lett. 7 (1971) 937.
[11] R. Sariego, J.A. Costamagna, J. Inorg. Nucl. Chem. 33 (1971)
1528.
Based on the ꢀrH◦ values for the adducts, we ob-
tain the basicity order: pipd > morph > ␤-pico >
␥-pico > py > 4-cyanopy > 3-cyanopy and pipz >
¯
quin. Using the D(Sn–N) values, we obtain the ba-
sicity order: pipd > morph > ␥-pico = ␤-pico >
py > 4-cyanopy > 3-cyanopy and pipz > quin. The
expected order for pyridine and derivatives would be
␥-pico > β-pico > py > 3-cyanopy > 4-cyanopy
due to an inductive effect of substitution of one hy-
drogen atom in the pyridine ring, by the electron
donator methyl group in ␤- or ␥-pico or by the elec-
tron withdrawing cyano group in 3- or 4-cyanopy.
This causes the increase or the decrease, respectively,
of the electronic density available for bonding on the
nitrogen atom of the ring, relative to unsubstituted
pyridine. The effect is stronger in p-substitution than
in m-substitution. The inversion observed between
4- and 3-cyanopy could be due to the contribution
of another kind of interaction like hydrogen bonding
between the nitrogen atom of the cyano groups and
the carbon atoms from pyridine rings [22], being this
effect stronger for 4- than for 3-cyanopyrine. Oth-
[12] N.S. Gill, R.H. Nutall, D.E. Scaife, D.W.A. Sharp, J. Inorg.
Nucl. Chem. 18 (1981) 79.
[13] D.P. Graddon, E.C. Watton, Aust. J. Chem. 18 (1965) 507.
[14] N.S. Gill, H.J. Kingdon, Aust. J. Chem. 19 (1966) 2197.
[15] T.L. Brown, M. Kubota, J. Am. Chem. Soc. 83 (1966) 4175.
[16] S.P. Sinha, Spectrochim. Acta 20 (1964) 879.
[17] B.K. Mohapatra, D.V. Romana Rao, Inorg. Chim. Acta 4
(1970) 404.
[18] P.O. Dunstan, L.C.R. dos Santos, Thermochim. Acta 156
(1989) 163.
[19] D.D. Wagman, W.H. Evans, V.P. Parker, R.H. Schumn, I.
Halow, S.M. Churney, R.L. Nuttall, J. Phys. Chem. Ref. Data
II (1982) 2–116.
[20] J.B. Pedley, J. Rylance, Sussex-NPL Computer Analysed
Thermochemical Data: Organic and Organo-metallic
Compounds, Sussex University, Brighton, England, 1970.
[21] P.O. Dunstan, J. Chem. Eng. Data 41 (1996) 1450.
[22] P.O. Dunstan, Thermochim. Acta 303 (1997) 209.
[23] P.O. Dunstan, Thermochim. Acta 240 (1994) 91.
[24] A.P. Chagas, C. Airoldi, Polyhedron 8 (1989) 1093.
[25] P.O. Dunstan, Thermochim. Acta 345 (2000) 117.
[26] P.O. Dunstan, Thermochim. Acta 376 (2001) 17.