Preparation, crystal structure, thermal decomposition mechanism and thermodynamical properties of [Yb(NTO)3(H2O)4]·6H2O and [Sr(NTO)2(H2O)4]·2H2O

Article abstract of DOI:10.1016/S0040-6031(99)00015-5

[Yb(NTO)₃(H₂O)₄]·6H₂O was prepared by mixing the aqueous solution of lithium 3-nitro-1, 2, 4-triazol-5-onate and the dilute nitric acid solution of ytterbium oxide. The single crystal structure was determined by a four-circle X-ray diffractometer. The crystal is monoclinic, space group C2/c with crystal parameters of a = 3.6931 (5)nm, b = 0.6683(10) nm, c = 2.5656(3) nm, β = 130.974(5)°, V = 4.7811(11) nm³, Z = 8, μ = 40.17 cm^-1, F(000) = 2850, D_c = 2.013 g cm^-2, and λ(MoK_α) = 0.071073 nm. The final R is 0.0258. [Sr(NTO)₂(H₂O)₄]·2H₂O was prepared by mixing the aqueous solution of 3-nitro-1, 2, 4-triazol-5-one and the excessive strontium carbonate. The single crystal structure was determined by a four-circle X-ray diffractometer. The crystal is monoclinic, space group P2₁/c with crystal parameters of a = 1.1034(1) nm; b = 2.2742(2) nm, c = 0.63398(9) nm, β = 101.798(13)°, V = 1.5573(4) nm³, Z = 4, D_c = 1.936 g cm^-3, μ = 35.45 cm^-1, F(000) = 912, λ(MoK_α) = 0.071073 nm. The final R is 0.0347. Based on the results of thermal analysis, the thermal decomposition mechanism of [Yb(NTO)₃(H₂O)₄]·6H₂O and [Sr(NTO)₂(H₂O)₄]·2H₂O were derived. From measurements of the enthalpy of solution of [Yb(NTO)₃(H₂O)₄]·6H₂O and [Sr(NTO)₂(H₂O)₄]·2H₂O in water at 298.15 K, the standard enthalpy of formation, lattice energy, lattice enthalpy and standard enthalpy of dehydration have been determined as -(3853.3 ± 6.8) and -(2545.2 ± 4.7), -4596 and -2114, -4631 and -2136, 391 and 67.2 kJ mol^-1, respectively.

Full text of DOI:10.1016/S0040-6031(99)00015-5

Thermochimica Acta 331 (1999) 49±60
Preparation, crystal structure, thermal decomposition mechanism and thermo-
dynamical properties of [Yb(NTO) (H O) ]Á6H O and [Sr(NTO) (H O) ]Á2H O
3
2
4
2
2
2
4
2
a,*
b
b
Song Jirong , Hu Rongzu , Kang Bing , Li Fuping
b
a
Department of Chemical Engineering, Northwest University, Xian 710069, PR China
b
Xian Modern Chemistry Research Institute, Xian 710065, Shaanxi, PR China
Received 24 January 1998; received in revised form 24 January 1999; accepted 26 January 1999
Abstract
Yb(NTO)
dilute nitric acid solution of ytterbium oxide. The single crystal structure was determined by a four-circle X-ray diffractometer.
[
3
(H
2
4
O) ]Á6H
2
O was prepared by mixing the aqueous solution of lithium 3-nitro-1, 2, 4-triazol-5-onate and the
The crystal is monoclinic, space group C2/c with crystal parameters of a ˆ 3.6931 (5)nm, b ˆ 0.6683(10) nm, c ˆ 2.5656(3) nm,
3
� 1
� 2
ꢀ
nm. The ®nal R is 0.0258. [Sr(NTO)
ˆ 130.974(5)8, V ˆ 4.7811(11) nm , Z ˆ 8, ꢁ ˆ 40.17 cm , F(000) ˆ 2850, D
c
ˆ 2.013 g cm , and ꢂ(MoK
a
) ˆ 0.071073
2
(H O)
2
4
]Á2H
2
O was prepared by mixing the aqueous solution of 3-nitro-1, 2, 4-triazol-5-one
andtheexcessivestrontiumcarbonate. Thesinglecrystalstructurewasdeterminedbyafour-circleX-raydiffractometer. Thecrystal
is monoclinic, space group P2
1
/c with crystal parameters of a ˆ 1.1034(1) nm; b ˆ 2.2742(2) nm, c ˆ 0.63398(9) nm, ꢀ ˆ
3 � 3 � 1
c
1
01.798(13)8, V ˆ 1.5573(4) nm , Z ˆ 4, D
ˆ 1.936 g cm , ꢁ ˆ 35.45 cm , F(000) ˆ 912, ꢂ(MoK ) ˆ 0.071073 nm. The
3 2 4 2
a
®
nal R is 0.0347. Based on the results of thermal analysis, the thermal decomposition mechanism of [Yb(NTO) (H O) ]Á6H O and
[
Sr(NTO) (H O) ]Á2H O were derived. From measurements of the enthalpy of solution of [Yb(NTO) (H O) ]Á6H O and
2
2
4
2
3
2
4
2
[
Sr(NTO)
2
(H O)
2
4
]Á2H
2
O in water at 298.15 K, the standard enthalpy of formation, lattice energy, lattice enthalpy and standard
enthalpy of dehydration have been determined as � (3853.3 Æ 6.8) and � (2545.2 Æ 4.7), � 4596 and � 2114, � 4631 and � 2136,
�
1
3
91 and 67.2 kJ mol , respectively. # 1999 Elsevier Science B.V. All rights reserved.
Keywords: Crystal structure; Enthalpy of solution; NTO salt; Standard enthalpy of formation; Thermal decomposition mechanism
1
. Introduction
2. Experimental
Much attention has been paid to 3-nitro-1, 2, 4-
2.1. Materials
triazol-5-one (NTO) and its metal salts as a high
energy and low sensitivity energetic material [1±3].
Therefore the authors prepared the single crystal of
[Yb(NTO) (H O) ]Á6H O used in this research
3
2
4
2
work was prepared according to the following method:
an appropriate amount of NTO was put into the
distilled water, then stirred and titrated with an aqu-
eous solution of lithium hydroxide under 608C until
pH reached a value of 6±7. The resulting solution was
gradually dropped into a dilute nitric acid solution of
ytterbium oxide at 608C, then stirred and heated at
[
2
Yb(NTO) (H O) ]Á6H O and [Sr(NTO) (H O) ]Á
3
2
4
2
2
2
4
H O, determined their structure and studied their
2
thermal decomposition mechanism and thermody-
namic properties.
*
Corresponding author.
0040-6031/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved.
PII: S 0 0 4 0 - 6 0 3 1 ( 9 9 ) 0 0 0 1 5 - 5

5
0
S. Jirong et al. / Thermochimica Acta 331 (1999) 49±60
6
08C for 30 min. This solution was allowed to stand
ratus (TA, USA), and the thermal decomposition
process of [Sr(NTO) (H O) ]Á2H O was studied on
for 10 h until yellow precipitate formed. The precipi-
tate was recrystallized with distilled water at room
temperature to obtain the yellow single crystal for X-
ray measurement. Its purity was >99.6%. Dimensions
2
2
4
2
a Delta Series TGA 7 (Perkin±Elmer, USA). The
conditions of TG and DTA were as follows: sample
�
1
mass ca. 1 mg; heating rate 108C min ; atmosphere,
3
of the single crystal were 0.46 Â 0.37 Â 0.32 mm .
a ¯owing N /O mixture (with the same ratio as in air).
2
2
The conductivity of deionized water used in the
.
The DSC experiments were carried out with a model
CDR-1 differential scanning calorimeter with an alu-
minium cell (diameter 5 mm, length 3 mm), whose
side was rolled up. The conditions of DSC measure-
ment were as follows: sample mass ca. 1 mg; heating
�
8
� 1
experiment was 5.48 Â 10 Scm
[
Sr(NTO) (H O) ]Á2H O used in this research work
2
2
4
2
was prepared according to the following method: an
appropriate amount of NTO was put into the distilled
water, then stirred and strontium carbonate added in
excess at 608C. When carbon dioxide evolution
ceased, the resulting solution was stirred and heated
at 608C for 30 min, then ®ltered off while still hot. The
precipitate was then dissolved in ethyl alcohol, and the
�
1
rate 108C min ; atmosphere static air; reference
sample, a-Al O ; thermocouple plate, Ni/Cr±Ni/Si.
The infrared spectra of the decomposition residues
2
3
were recorded in KBr discs on a 60 SXR FT-IR
�
1
spectrometer (Nicolet, USA) at 4 cm resolution.
All measurements of the enthalpy of solution in
deionized water were made using a Calvet microca-
lorimeter, type BT215 from Setaram, France, and
operated at 298.15 Æ 0.005 K.
undissolved SrCO was separated. This solution was
3
allowed to stand for 8 h, until a yellow precipitate
formed. The precipitate was recrystallized from dis-
tilled water in a Petri dish at 258C to obtain the yellow
single crystal for X-ray measurement. Its purity was
The experimental precision and accuracy of enthal-
>
99.6%. Dimensions of the single crystal were 0.56
3
pies of solution were frequently checked by measuring
0
 0.32  0.14 mm . The conductivity of deionized
the enthalpies of solution (Á H ) of crystalline KC1
sol
1
�
8
� 1
.
water used in the experiment was 5.48 Â 10 Scm
.2. Experimental equipment and conditions
in deionized water at 298.15 K. The experimental
value of Á H0 ˆ (17.217 Æ 0.053) kJ mol is in
� 1
sol
1
0
1
2
excellent agreement with that of Á H
ˆ
sol
�
1
7.234 kJ mol , reported in the literature [4].
1
In the determination of the structure of the single
crystal, X-ray intensities were recorded by a Siemens
P4 automatic diffractometer with graphite, monochro-
3. Results and discussion
3.1. Crystal structure of [Yb(NTO) (H O) ]Á6H O
matized MoK radiation, ꢂ ˆ 0.071073 nm. The 5756
a
independent re¯ections were obtained in the range of
3
2
4
2
3 ꢀ 2ꢃ ꢀ 568, out of which 4570 with I > 2ꢄ(I) were
used for the determination and re®nement of the
The crystal structure of [Yb(NTO) (H O) ]Á6H O
3
2
4
2
crystal structure of [Yb(NTO) (H O) ]Á6H O. The
was found to be monoclinic, which belongs to space
group C2/c with crystallographic parameters of a ˆ
3.6931(5) nm, b ˆ 0.6683(10) nm, c ˆ 2.5656(3) nm,
3
2
4
2
3
202 independent re¯ections were obtained in the
range of 4.18 ꢀ 2ꢃ ꢀ 52.988, out of which 1915 with
I > 2ꢄ(I) were used for the determination and re®ne-
ment of crystal structure of [Sr(NTO) (H O) ]Á2H O.
3
ꢀ ˆ 130.974(5)8, V ˆ 4.7811(11) nm , Z ˆ 8, ꢁ ˆ
�
1
40.17 cm
,
F(000) ˆ 2850, and D ˆ 2.013 g
2
2
4
2
c
�
3
The coordinates of Yb and Sr atoms were obtained by
a direct method and those of the other atoms by
difference Fourier synthesis. Re®nement was per-
formed by block-diagonal least-square methods using
anisotropic thermal parameters for non-hydrogen
atoms and isotropic thermal parameters for hydrogen
atoms.
cm . The ®nal R ˆ 0.0258, WR ˆ 0.0815.
The atomic coordinates, thermal parameters, bond
lengths and bond angles are summarized in Tables 1±
3. The molecular structure and atom labelling are
shown in Fig. 1, the packing of the molecule in the
crystal lattice and the coordination polyhedron of
3
‡
Yb are illustrated in Figs. 2 and 3.
The results indicate that four water molecules and
the three carbonyls of three NTO anions are coordi-
The thermal decomposition process of [Yb(N-
TO) (H O) ]Á6H O was studied on a TGA-DTA appa-
3
2
4
2

S. Jirong et al. / Thermochimica Acta 331 (1999) 49±60
51
Table 1
Atomic coordinates and thermal parameters (Â10 , in nm )
Table 2
3
2
Bond distances (in nm)
Atoms
x
y
z
U
eq
Yb±O(4)
Yb±O(7)
0.2207(3)
Yb±O(1)
0.2223(4)
0.2235(4)
0.2289(5)
0.2351(4)
0.1225(7)
0.1274(6)
0.1215(6)
0.1218(6)
Yb±O(12)
Yb±O(10)
O(1)±C(1)
O(3)±N(4)
O(5)±N(8)
O(7)±C(5)
O(9)±N(12)
0.2235(4)
0.2315(4)
0.1269(6)
0.1222(6)
0.1218(6)
0.1273(6)
0.1221(6)
Yb
O(1)
0.1637(1)
0.0854(1)
0.0125(2)
0.4254(1)
0.3630(7)
0.1743(12)
0.1222(9)
0.3141(6)
0.4386(8)
0.3422(9)
0.3211(7)
0.3375(9)
0.3560(9)
0.6830(7)
0.6924(7)
0.5612(7)
0.0959(7)
0.3259(13)
0.8897(12)
1.1053(9)
0.1896(8)
0.8982(7)
0.5333(34)
0.2043(1)
0.1316(2)
0.20(1)
0.40(1)
0.79(2)
0.57(1)
0.30(1)
0.47(1)
0.58(1)
0.35(1)
0.53(1)
0.54(1)
0.36(1)
0.43(1)
0.39(1)
0.53(1)
0.93(2)
0.79(2)
0.55(1)
0.41(1)
0.34(1)
1.33(23)
Yb±O(13)
Yb±O(11)
O(2)±N(4)
O(4)±C(3)
O(6)±N(8)
O(8)±N(12)
O(2)
� 0.1122(3)
� 0.1456(2)
0.1482(2)
0.0047(2)
� 0.0895(2)
0.3035(2)
0.5137(2)
0.5855(2)
0.1245(2)
0.2462(2)
0.2687(2)
0.2172(2)
0.1529(3)
0.6700(3)
0.7208(2)
0.3879(2)
0.3340(2)
0.7500
O(3)
� 0.0579(2)
0.1861(1)
0.2333(2)
0.1643(2)
0.2334(1)
0.4093(1)
0.3973(2)
0.1297(1)
0.2179(1)
0.1493(2)
0.1540(2)
� 0.0037(2)
0.4480(2)
0.4127(2)
0.1761(2)
0.1953(1)
0.5000
O(4)
O(5)
O(6)
O(7)
O(8)
N(1)±C(1)
N(2)±C(2)
N(3)±c(1)
N(5)±C(3)
N(6)±C(4)
N(7)±C(3)
N(9)±N(10)
N(10)±C(6)
N(11)±C(5)
0.1374(6)
0.1305(7)
0.1342(7)
0.1345(6)
0.1317(6)
0.1354(6)
0.1354(6)
0.1305(6)
0.1343(6)
N(1)±N(2)
N(3)±C(2)
N(4)±C(2)
N(5)±N(6)
N(7)±C(4)
N(8)±C(4)
N(9)±C(5)
N(11)±C(6)
N(12)±C(6)
0.1377(6)
0.1342(6)
0.1464(7)
0.1363(6)
0.1326(6)
0.1454(6)
0.1366(6)
0.1336(6)
0.1457(6)
O(9)
O(10)
O(11)
O(12)
O(13)
O(14)
O(15)
O(16)
O(17)
O(18)
O(19)
Table 3
N(1)
N(2)
N(3)
N(4)
N(5)
N(6)
N(7)
N(8)
N(9)
N(10)
N(11)
N(12)
0.0045(1)
� 0.0269(1)
0.0490(2)
� 0.0158(2)
0.1298(2)
0.1295(2)
0.2055(2)
0.1923(2)
0.2598(2)
0.3022(2)
0.3141(1)
0.3822(2)
0.2896(7)
0.2348(7)
0.2680(7)
0.1711(8)
0.3183(8)
0.3349(8)
0.3495(7)
0.3802(8)
0.3493(7)
0.3563(8)
0.3338(7)
0.3463(8)
0.0467(2)
� 0.0218(2)
0.0180(2)
� 0.1024(3)
0.0282(2)
� 0.0251(2)
0.0780(2)
� 0.0282(2)
0.4147(2)
0.4803(2)
0.4040(2)
0.5273(2)
0.31(1)
0.29(1)
0.31(1)
0.41(1)
0.29(1)
0.31(1)
0.25(1)
0.33(1)
0.29(1)
0.30(1)
0.22(1)
0.33(1)
Bond angles (8)
O(4)±YbO(1)
103.1(2)
142.2(2)
83.5(2)
O(4)±Yb±O(7)
O(4)±Yb±O(12)
O(7)±Yb±O(12)
O(1)±Yb±O(13)
O(12)±Yb±O(13)
O(1)±Yb±O(10)
O(12)±Yb±O(10)
O(4)±Yb±O(11)
O(7)±Yb±O(11)
O(13)±Yb±O(11)
C(1)±O(1)±Yb
C(5)±O(7)±Yb
C(2)±N(2)±N(1)
O(3)±N(4)±O(2)
O(2)±N(4)±C(2)
C(4)±N(6)±N(5)
O(6)±N(8)±O(5)
O(5)±N(8)±C(4)
89.61(14)
172.9(2)
86.5(2)
O(1)±Yb±O(7)
O(1)±Yb±O(12)
O(4)±Yb±O(13)
O(7)±Yb±O(13)
O(4)±Yb±O(10)
O(7)±Yb±O(10)
O(13)±Yb±O(10)
O(1)±Yb±O(11)
O(12)±Yb±O(11)
O(10)±Yb±O(11)
C(3)±O(4)±Yb
C(1)±N(1)±N(2)
C(2)±N(3)±C(1)
O(3)±N(4)±C(2)
C(3)±N(5)±N(6)
C(4)±N(7)±C(3)
O(6)±N(8)±C(4)
86.1(2)
73.0(2)
72.5(2)
98.5(2)
83.8(2)
75.2(2)
142.2(2)
142.9(2)
140.8(2)
84.1(2)
95.6(2)
89.0(2)
73.5(2)
146.2(2)
143.6(4)
151.1(4)
100.1(4)
124.5(6)
117.5(5)
100.1(4)
125.3(5)
116.8(4)
69.3(2)
140.7(3)
110.5(5)
102.1(4)
117.9(5)
111.3(4)
101.9(4)
117.9(5)
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
0.0502(2)
0.0025(2)
0.1748(2)
0.1758(2)
0.2667(2)
0.3319(2)
0.3095(8)
0.2252(9)
0.3273(8)
0.3531(8)
0.3336(8)
0.3462(8)
0.0703(3)
� 0.0335(3)
0.0895(2)
0.0097(3)
0.3687(2)
0.4690(2)
0.30(1)
0.30(1)
0.24(1)
0.25(1)
0.24(1)
0.24(1)
N(10)±N(9)±C(5) 110.9(4)
C(6)±N(11)±C(5) 101.5(4)
O(8)±N(12)±C(6) 116.6(4)
C(6)±N(10)±N(9) 100.2(4)
O(8)±N(12)±O(9) 125.0(5)
O(9)±N(12)±C(6) 118.4(5)
3
‡
nated with Yb . The coordinated bond lengths are
between 0.2207 and 0.2351 nm and the pentagonal
bipyramid is formed. The bond length from Yb to O11
O(1)±C(1)±N(3)
N(3)±C(1)±N(1)
N(2)±C(2)±N(4)
O(4)±C(3)±N(5)
N(5)±C(3)±N(7)
N(6)±C(4)±N(8)
129.2(5)
108.3(5)
119.6(5)
125.2(5)
108.5(4)
119.0(4)
O(1)±C(1)±N(1)
N(2)±C(2)±N(3)
N(3)±C(2)±N(4)
O(4)±C(3)±N(7)
N(6)±C(4)±N(7)
N(7)±C(4)±N(8)
O(7)±C(5)±N(9)
122.5(6)
118.9(5)
121.5(5)
126.3(4)
118.3(4)
122.8(5)
124.9(4)
(
the water molecule) is the longest one (0.2351 nm),
and the shortest bond length is the Yb±O4 distance in
the NTO (0.2207 nm). The others are Yb±O7 (0.2235
nm), Yb±O13 (0.2289 nm), Yb±O1 (0.2223 nm), Yb±
O12 (0.2235 nm) and Yb±O10 (0.2315 nm). All of
these are typical coordinated bond lengths.
O(7)±C(5)±N(11) 126.7(5)
N(11)±C(5)±N(9) 108.4(4)
N(10)±C(6)±N(12) 119.5(4)
N(10)±C(6)±N(11) 118.9(4)
N(11)±C(6)±N(12) 121.6(4)

5
2
S. Jirong et al. / Thermochimica Acta 331 (1999) 49±60
Fig. 1. Molecular structure of [Yb(NTO)
3
(H
2
O)
4
2
]Á6H O.
3
‡
in [Yb(NTO)
Fig. 3. Coordination polyhedron of Yb
O) O.
]Á6H
3
-
(
H
2
4
2
Fig. 2. Packing of the molecule [Yb(NTO)
3
(H
2
O)
4
2
]Á6H O in the crystal lattice.

S. Jirong et al. / Thermochimica Acta 331 (1999) 49±60
53
According to the calculation, the equations of the
planes of three NTO anions are as follows:
3.2. Crystal structure of [Sr(NTO) (H O) ]Á2H O
2
2
4
2
The crystal structure was found to be monoclinic,
which belongs to space group P2 /c with crystallo-
�
�
1:069x ‡ 6:420y � 4:861z ˆ � 1:6074
6:454x ‡ 6:570y ‡ 1:898z ˆ � 1:2099
(1)
(2)
(3)
1
graphicparametersofa ˆ 1.1034(1)nm,b ˆ 2.2742(2)
nm, c ˆ 0.63398(9) nm, ꢀ ˆ 101.798(13)8, V ˆ
1
:706x ‡ 6:666y � 1:809z ˆ 2:0134
The dihedral angles between planes (1) and (2), (1)
and (3), (2) and (3) are 15.38, 13.78 and 12.78.
3
� 3
1
.5573(4)nm , Z ˆ 4, D ˆ 1.936 g cm , ꢁ ˆ 35.45
c
� 1
cm , and F(000) ˆ 912. The ®nal R ˆ 0.0347.
The atom coordinates, thermal parameters, bond
lengths and bond angles are summarized in Tables 4±
6. The molecular structure and atom labelling are
shown in Fig. 4, the packing of the molecule in the
2
‡
Table 4
crystal lattice and the coordination polyhedron of Sr
are illustrated in Figs. 5 and 6.
3
2
Atomic coordinated and thermal parameters (Â10 , in nm )
The results indicate that there is a symmetry centre
in the molecular structure. The oxygen atoms [O(7),
O(7A), O(8), O(9), O(10)] of the ®ve water molecules,
the N(7) and O(5) atoms in the NTO(2) ring, the
O(4A) atom in the NTO(2A) ring and the O(1) atom
in the NTO(1) ring are coordinated to the centre Sr.
The oxygen atoms [O(7), O(7A), O(8A) O(9A),
O(10A)] of ®ve water molecules, the N(7A) and
O(5A) atoms in the NTO (2A) ring, the O(4) atom
in the NTO(2) ring and the O(1A) atom in the NTO
(1A) ring are coordinated to another centre SrA. The
coordinated bond lengths are in the 0.2535±0.2867 nm
range and all of these are typical coordinated bond
lengths. The O(7), O(7A), NTO(2A) and NTO(2)
formed bridges between Sr and SrA. The distance
Atoms
x
y
z
U
eq
Sr
0.1467(1)
0.5539(1)
0.6825(1)
0.23(1)
C(1)
C(2)
C(3)
C(4)
� 0.0475(4)
� 0.2291(4)
0.1405(4)
0.3205(4)
0.6350(2)
0.6676(2)
0.3873(2)
0.4213(2)
0.9654(7)
0.9072(7)
0.5559(6)
0.6408(7)
0.27(1)
0.24(1)
0.23(1)
0.25(1)
O(1)
O(2)
O(3)
O(4)
O(5)
O(6)
O(7)
O(8)
O(9)
O(10)
O(11)
O(12)
0.0487(3)
� 0.4189(3)
� 0.4129(3)
0.0262(2)
0.3941(3)
0.5264(3)
0.0393(2)
0.3094(3)
0.2417(3)
0.2258(3)
0.4072(3)
0.1502(4)
0.6036(1)
0.6227(1)
0.7177(1)
0.3789(1)
0.5149(1)
0.4439(1)
0.5126(1)
0.6332(2)
0.4995(1)
0.6120(2)
0.6865(2)
0.7711(2)
0.9930(5)
0.8301(6)
0.8541(7)
0.5016(5)
0.6853(6)
0.7440(6)
0.2789(4)
0.8574(7)
1.0440(5)
0.3840(6)
0.2764(7)
1.0488(8)
0.32(1)
0.53(1)
0.69(1)
0.30(1)
0.49(1)
0.56(1)
0.27(1)
0.53(1)
0.34(1)
0.55(1)
0.74(1)
1.13(2)
Table 5
Bond distances (in nm)
N(1)
N(2)
N(3)
N(4)
N(5)
N(6)
N(7)
N(8)
0.0472(3)
� 0.1659(3)
� 0.1671(3)
� 0.3631(3)
0.2272(3)
0.3455(3)
0.2033(3)
0.4215(3)
0.6954(2)
0.7167(1)
0.6167(1)
0.6698(2)
0.3429(1)
0.3646(1)
0.4392(1)
0.4627(1)
0.9706(6)
0.9325(6)
0.9242(5)
0.8596(6)
0.5908(6)
0.6457(6)
0.5900(5)
0.6938(6)
0.33(1)
0.34(1)
0.26(1)
0.38(1)
0.26(1)
0.28(1)
0.23(1)
0.34(1)
Sr±O(4A)
Sr±O(7A)
Sr±O(9)
Sr±O(7)
Sr±O(5)
0.2535(3)
0.2602(2)
0.2627(3)
0.2756(3)
0.2867(3)
Sr±O(10)
Sr±O(8)
Sr±O(1)
Sr±N(7)
Sr±SrA
0.2601(3)
0.2625(3)
0.2682(3)
0.2774(3)
0.43349(9)
C(1)±O(1)
C(1)±N(1)
C(2)±N(3)
C(3)±O(4)
C(3)±N(5)
C(4)±N(7)
0.1260(4)
0.1375(5)
0.1337(5)
0.1252(4)
0.1377(5)
0.1330(5)
C(1)±N(3)
C(2)±N(2)
C(2)±N(4)
C(3)±N(7)
C(4)±N(6)
C(4)±N(8)
0.1357(5)
0.1309(5)
0.1448(5)
0.1363(5)
0.1317(4)
0.1446(5)
H(7A)
H(7B)
H(8A)
H(8B)
H(9A)
H(9B)
H(10A)
H(10B)
H(N5)
0.0109(2)
0.0991(2)
0.5453(1)
0.4902(1)
0.1830(4)
0.2192(4)
0.32
0.32
0.3110(79) 0.6684(35)
0.3743(31) 0.6265(20)
0.3140(31) 0.5076(16)
0.2266(33) 0.4618(13)
0.2866(40) 0.6410(2)
0.0329(57) 0.7230(34)
0.2110(33) 0.3052(12)
0.9524(164) 3.78(79)
0.8302(71)
1.1293(67)
1.0372(65)
0.3742(89)
0.42(17)
0.56(16)
0.44(14)
1.24(26)
O(2)±N(4)
O(4)±SrA
O(6)±N(8)
0.1232(4)
0.2535(3)
0.1214(4)
O(3)±N(4)
O(5)±N(8)
O(7)±SrA
0.1216(4)
0.1223(4)
0.2602(2)
1.0135(167) 2.71(47)
0.5856(61) 0.28(12)
N(1)±N(2)
0.1371(5)
N(5)±N(6)
0.1371(4)

5
4
S. Jirong et al. / Thermochimica Acta 331 (1999) 49±60
Table 6
The dihedral angles between planes (4) and (5), (4)
and (6), (5) and (6) are 4.18, 93.18 and 90.28.
Bond angles (8)
O(4A)±Sr±O(10) 72.06(11)
O(10)±Sr±O(7A) 138.80(11)
O(4A)±Sr±O(7A) 81.93(8)
O(4A)±Sr±O(8)
O(7A)±Sr±O(8)
O(10)±Sr±O(0)
O(8)±Sr±O(9)
O(10)±Sr±O(1)
O(8)±Sr±O(1)
O(4A)±Sr±O(7)
O(7A)±Sr±O(7)
O(9)±Sr±O(7)
O(4A)±Sr±N(7)
O(7A)±Sr±N(7)
O(9)±Sr±N(7)
O(7)±Sr±N(7)
O(10)±Sr±O(5)
O(8)±Sr±O(5)
O(1)±Sr±O(5)
N(7)±Sr±O(5)
O(10)±Sr±SrA
O(8)±Sr±SrA
O(1)±Sr±SrA
N(7)±Sr±SrA
99.56(11)
147.63(11)
137.78(11)
80.72(11)
124.46(11)
75.17(12)
68.75(8)
O(10)±Sr±O(8)
O(4A)±Sr±O(9)
O(7A)±Sr±O(9)
O(4A)±Sr±O(1)
O(7A)±Sr±O(1)
O(9)±Sr±O(1)
O(10)±Sr±O(7)
O(8)±Sr±O(7)
O(1)±Sr±O(7)
O(10)±Sr±N(7)
O(8)±Sr±N(7)
O(1)±Sr±N(7)
O(4A)±Sr±O(5)
O(7A)±Sr±O(5)
O(9)±Sr±O(5)
O(7)±Sr±O(5)
O(4A)±Sr±SrA
O(7A)±Sr±SrA
O(9)±Sr±SrA
69.89(13)
144.52(10)
79.97(9)
3
.3. Mechanism of thermal decomposition of
Yb(NTO) (H O) ]Á6H O
[
3
2
4
2
72.86(9)
The DTA and TG curves for [Yb(NTO) (H O) ]Á
74.45(8)
3
2
4
72.99(9)
6H O are shown in Fig. 7. The DTA curve shows
2
69.02(10)
138.89(11)
131.58(8)
101.55(11)
124.85(11)
133.93(9)
144.64(9)
125.99(8)
68.83(10)
97.37(9)
72.01(9)
that there are two endothermic and two exothermic
processes at temperatures >54.08C.
The TG curve shows that the ®rst mass loss is 14.7%
between 54.08 and 104.88C, which coincides with the
calculated value (14.6%) of losing six water molecules
from the complex. At the higher temperature, between
131.96(99)
130.57(9)
71.86(8)
70.98(9)
63.62(8)
72.60(11)
69.03(11)
130.73(10)
56.95(8)
1
04.88 and 147.58C, the mass loss is 24.2% which
coincides with the calculated value (24.3%) of losing
ten water molecules from the complex. Therefore, it
was estimated that 10 water molecules were lost in two
71.66(6)
102.95(9)
170.37(9)
105.13(6)
62.01(6)
37.20(6)
108.69(7)
34.81(5)
processes. The IR spectrum of the residue shows the
� 1
O(7)±Sr±SrA
absence of absorption peaks at 3407 cm
�
and
56 cm , which denotes that the complex has been
O(5)±Sr±SrA
115.74(6)
O(1)±C(1)±N(3) 127.7(4)
N(3)±C(1)±N(1) 108.0(4)
N(2)±C(2)±N(4) 119.4(4)
O(4)±C(3)±N(7) 128.8(4)
N(7)±C(3)±N(5) 107.1(3)
N(6)±C(4)±N(8) 119.0(4)
1
6
dehydrated.
O(1)±C(1)±N(1) 124.4(4)
N(2)±C(2)±N(3) 118.6(4)
N(3)±C(2)±N(4) 122.0(4)
O(4)±C(3)±N(5) 124.1(4)
N(6)±C(4)±N(7) 119.6(3)
N(7)±C(4)±N(8) 121.5(3)
Between 147.58 and 311.68C, there is a rather
severe mass loss. The IR spectrum of the residue at
3
NO ) at 1513 cm and 1301 cm , and the charac-
208C shows the absence of absorption peaks (for
C(1)±O(1)±Sr
N(8)±O(5)±Sr
126.2(3)
121.9(2)
�
1
� 1
2
C(3)±O(4)±SrA
SrA±O(7)±Sr
131.0(3)
teristic absorption peaks of Yb (CO ) and a polymer
2
107.99(9)
N(2)±N(1)±C(1) 110.5(3)
C(2)±N(3)±C(1) 102.2(3)
O(3)±N(4)±C(2) 118.2(4)
N(6)±N(5)±C(3) 111.8(3)
C(4)±N(7)±C(3) 102.2(3)
3 3
C(2)±N(2)±N(1) 100.7(3)
O(3)±N(4)±O(2) 124.4(4)
O(2)±N(4)±C(2) 117.3(4)
containing the ±CO±NH-group being formed at 1525
�
1
and 835, 3394, 1533 and 1384 cm , respectively.
These observations show that the decomposition resi-
due for this stage is a mixture. The amount of each
component cannot be determined from the present
experiments and it is impossible to determine the
decomposition change stoichiometrically. The IR
spectrum of the residue at 5208C shows that a strong
C(4)±N(6)±N(5)
C(4)±N(7)±Sr
99.3(3)
119.1(2)
C(3)±N(7)±Sr
135.9(2)
O(6)±N(8)±O(5) 124.6(4)
O(5)±N(8)±C(4) 116.7(3)
O(6)±N(8)±C(4) 118.7(3)
from Sr to SrA is 0.4335 nm, and the angle of Sr±
O(7)±SrA is 108.08.
According to the calculation, the equations of the
planes of NTO rings and Sr SrA O(7) O(7A) are as
follows:
� 1
absorption peak of Yb O is formed at 572 cm . At
2
3
the end of this stage, the residue amounted to 26.0%.
This value is in good agreement with the calculated
loss of 26.6%.
On the basis of experimental and calculated
results, the thermal decomposition mechanism of
[Yb(NTO) (H O) ]Á6H O is postulated to be as
NTOꢁ1† : 2:185x � 0:892y ‡ 6:335z ˆ 5:6461
(4 )
3
2
4
2
follows:
NTOꢁ2† : 2:948x � 0:670y ‡ 6:324z ˆ 2:8355
(
5)
‰YbꢁNTO† ꢁH O† Š Á 6H O
3
2
4
2
SrSrAOꢁ7†Oꢁ7A† : 6:497x ‡ 18:092y � 0:123z
! ‰YbꢁNTO† ꢁH2O† Š ! YbꢁNTO†
3
4
3
ˆ
8:9846
(6)
! Yb2ꢁCO3† ‡ polymer ! Yb2O3
3

S. Jirong et al. / Thermochimica Acta 331 (1999) 49±60
55
Fig. 4. Molecular structure of [Sr(NTO)
2
(H
2
O)
4
2
]Á2H O.
3
.4. Mechanism of thermal decomposition of
Sr(NTO) (H O) ]Á2H O
The second stage of the decomposition process of
[
[Sr(NTO) (H O) ]Á2H O appears as a relatively sharp
2
2
4
2
2
2
4
2
peak between 258 and 3558C on the DSC curve, and
the mass loss corresponding to the temperature
range is 35.8%, as obtained from TG-DTG analyses.
The IR spectrum of the residue at 3608C shows
The DSC and TG-DTG curves for [Sr(NTO)2-
H O) ]Á2H O are shown in Fig. 8. The ®rst stage
(
2
4
2
of the decomposition process of [Sr(NTO) (H O) ]Á
2
2
4
�
1
2
H O appears as an endothermic peak between 758
2
absorption bands at 2184 and 1178 cm , which
may be assigned to the compound Sr(OCN) , and at
and 1588C on the DSC curve. Otherwise, the TG-DTG
curves show two mass loss processes. The ®rst mass
loss is 8.1% between 708 and 988C, which coincides
with the calculated value (7.9%) of losing two water
molecules from the complex. The second mass loss is
2
�
1
1466 and 866 cm which may be assigned to SrCO .
3
�
1
The absorption bands at 3406, 1634 and 1554 cm
show that some kind of a polyamide exists in the
residue, and the residue from decomposition is, there-
fore, a mixture.
2
4.2% between 988 and 1628C, which coincides with
the calculated value (23.8%) of losing six water
molecules from the complex. Therefore, it was esti-
mated that the six water molecules were lost in two
processes, the ®rst involving loss of two water mole-
cules and the second corresponding to the loss of the
remaining four water. The IR spectrum of the residue
The third stage of decomposition of [Sr(NTO)2-
(H O) ]Á2H O shows a gradual exothermic peak
2
4
2
between 4298 and 5108C. The IR spectrum of the
residue shows absorption bands only at 1457, 859 and
�
1
701 cm , which coincide well with those in the
standard spectrum of SrCO . The TG-DTG curves
3
�
1
shows the absence of absorption peaks at 3406 cm
1
indicate that the mass loss corresponding to this
temperature range is 10.8% and the residue comprises
32.2%, which agrees well with the theoretical value of
�
and 656 cm , which denotes that the complex have
been dehydrated.

5
6
S. Jirong et al. / Thermochimica Acta 331 (1999) 49±60
Fig. 5. Packing of the molecule [Sr(NTO)
2
(H
2
O)
4
2
]Á2H O in the crystal lattice.
3
2.5%. It could be concluded that the ®nal decom-
position residue of [Sr(NTO) (H O) ]Á2H O is stron-
2
2
4
2
tium carbonate.
The experimental results con®rm that the thermal
decomposition mechanisms of [Sr(NTO) (H O) ]Á
2
2
4
2
H O can be expressed as:
2
‰
SrꢁNTO† ꢁH2O† Š Á 2H2O
2
4
!
!
‰SrꢁNTO† ꢁH O† Š ! SrꢁNTO†
2
2
4
2
SrCO3 ‡ SrꢁOCN† ‡ polyamides
2
‡
volatile substances ! SrCO3
3
.5. Enthalpy of an aqueous solution of
Yb(NTO) (H O) ]Á6H O
[
3
2
4
2
Results for the enthalpy of a solution of [Yb(N-
TO) (H O) ]Á6H O in deionized water at 298.15 K are
3
2
4
2
reported in Table 7, where ÁsolHꢃ denotes the
m
2
‡
in [Sr(NTO)
enthalpy of an aqueous solution of [Yb(NTO)3-
Fig. 6. Coordination polyhedron of Sr
O) O.
]Á2H
2
-
(
H
2
4
2
(H O) ]Á 6H O, m the mass of [Yb(NTO) (H O) ]Á
2
4
2
3
2
4

S. Jirong et al. / Thermochimica Acta 331 (1999) 49±60
57
�
1
Fig. 7. DTA and TG curves for [Yb(NTO)
3
(H
2
O)
4
]Á6H
2
O at a heating rate of 108C min .
Table 7
Enthalpy of aqueous solution of [Yb(NTO)
98.15 K
6
H O, and r the molar ratio n(H O)/n{[Yb(NTO) -
2
2
3
3
(H
2
O)
4
]Á6H
2
O(cr) at
(
H O) ]Á6H O}.
2
4
2
2
Since [Yb(NTO) (H O) ]Á6H O is completely
3
2
4
2
ꢃ
m
� 1
m/mg
r
ÁsolH /kJ mol
ionized in aqueous solution, its ionization process
can be represented as
3
5
5
7
8
9
.01
.10
.11
.10
.11
.01
109 212
64 747
63 329
46 613
40 625
45 683
29 746
37.44
ÁsolHꢃ
37.64
YbꢁNTO† ꢁH2O† Š Á 6H2O ! Yb3‡ꢁaq; 1†
m
‰
37.92
3
4
37.11
�
‡
In process (7), the greater values of r were used.
3NTO ꢁaq; 1† ‡ 10H2Oꢁl†
(7)
37.77
37.82
1
1.10
38.10
Mean 37.68 Æ 0.46
Therefore, the mean of ÁsolHꢃ in Table 7 can be
considered at in®nite dilution.
m
�
1
Fig. 8. DSC and TG-DTG curves for [Sr(NTO)
2
(H
2
O)
4
]Á2H
2
O at a heating rate of 108C min .

5
8
S. Jirong et al. / Thermochimica Acta 331 (1999) 49±60
�
� 1
ꢃ
3
.6. Standard enthalpy of information of [Yb(NTO) -
3
(NTO , g) ˆ � 374.3 kJ mol [7], Á H (H O, g) ˆ
f
m
2
ꢃ
� 1
� 1
.
(
H O) ]Á6H O(cr) Áf H {[Yb(NTO) (H O) ]
� 241.82 kJ mol [5],Án ˆ � 14;RT ˆ 2.5 kJ mol
2
4
2
m
3
2
4
Á6H O, cr, 298.15 K}
By substituting the above-mentioned data into
Eqs. (10) and (11), the following values are obtained:
2
ꢃ
By substituting the mean of ÁsolH listed in Table 7
m
ꢃ
ꢃ
m
3‡
�
0
m
ÁH f‰YbꢁNTO† ꢁH2O† Š Á 6H2O; crg
L
3
4
and the reported values of Áf H (Yb , aq, 1) ˆ
�
1
ꢃ
m
� 1
�
�
�
674.4 kJ mol
[5], Á H (NTO , aq, 1) ˆ
ˆ � 4631 kJ mol
f
�
1
(94.3 Æ 2.1) kJ mol [6], and Á H (H O, l) ˆ
f
2
ꢃ
�
1
285.83 kJ mol [5], into Eq. (2), we obtain
ÁULf‰YbꢁNTO†3ꢁH2O†4Š Á 6H2O; crg
1
ˆ
� 4596 kJ mol�
ꢃ
Áf H f‰YbꢁNTO† ꢁH2O† Š Á 6H2O; cr; 298:15 Kg
m
3
4
ꢃ
m
3‡
1
�
ˆ
‡
Á H ꢁYb ; aq; 1† ‡ 3Á H ꢁNTO ; aq; 1†
3.8. Standard enthalpy of dehydration of [Yb(NTO) -
3
f
f
m
ꢃ
d
ꢃ
ꢃ
(H O) ]Á6H O(cr) ÁH {[Yb(NTO) (H O) ]
2
4
2
3
2
4
10Á H ꢁH O; l† � Á H
(8)
f
m
2
sol
m
Á6H O, cr}
2
the following values was obtained:
ꢃ
m
According to process (12) and Eq. (13), namely
Áf H f‰YbꢁNTO† ꢁH2O† ŠÁ6H2O; cr; 298:15 Kg
3
4
�
1
‰YbꢁNTO† ꢁH O† Š Á 6H O
3
2
4
2
ˆ
� ꢁ3853:3 Æ 6:8† kJ mol
ꢃ
d
ÁH f‰YbꢁNTO† ꢁH2O† ŠÁ6H2O;crg
3
4
!
YbꢁNTO† ꢁcr†
3
3
.7. Lattice enthalpy and energy of [Yb(NTO) -
3
ꢃ
L
‡ 10H2Oꢁl†
(12)
(
H O) ]Á6H OÁH {[Yb(NTO) (H O) ]Á6H O,
ꢃ
3 2 4 2
2
4
2
3
2
4
2
cr}, Á {[Yb(NTO) (H O) ]Á6H O,cr}
L
and
ꢃ
d
ꢃ
L
ÁH f‰YbꢁNTO† ꢁH O† Š Á 6H O; crg
3
2
4
2
Setting ÁH {[Yb(NTO) (H O) ]Á6H O,cr} as the
3
2
4
2
ꢃ
Â
lattice enthalpy in forming the crystal [Yb(NTO) -
3
ˆ Áf H ‰YbꢁNTO† ; crŠ ‡ 10Áf H ꢁH2O; l†
m
3
m
3
‡
�
(
H O) ]Á6H O from Yb (g), NTO (g) and H O (g) at
2
4
2
2
ꢃ
�
Áf H f‰YbꢁNTO† ꢁH2O† Š
ꢃ
L
m
3
4
2
the crystal lattice energy.
98.15 K, and ÁU {[Yb(NTO) (H O) ]Á6H O,cr} as
3
2
4
2
Á 6H2O; cr; 298:15 Kg
(13)
ꢃ
3‡
�
the value of Á H {[Yb(NTO) (H O) ]Á6H O,cr,
Yb ꢁg† ‡ 3NTO ꢁg† ‡ 10H2Oꢁg†
f
d
3
2
4
2
�
1
2
98.15 K} ˆ 391 kJ mol
may be obtained from
(H O) O,cr,
ꢃ
ÁH
L
ꢃ
m
!
‰YbꢁNTO† ꢁH2O† Š Á 6H2Oꢁcr† (9)
the value of Áf H {[Yb(NTO)
3
2
4
]Á6H
2
3
4
�
1
2
98.15 K} ˆ -3853.3kJ mol , obtained in this work,
ꢃ
m
We have
and the reported values ÁfH [Yb(NTO) ,cr,198.15 K]
3
�
1
ꢃ
m
ˆ
� 604.0 kJ mol [7], Áf H (H O,l) ˆ � 285.83 kJ
ꢃ
2
ÁH f‰YbꢁNTO† ꢁH2O† Š Á 6H2O; crg
L
3
4
� 1
mol [5].
ꢃ
m
ˆ
Áf H f‰YbꢁNTO† ꢁH2O† Š
3
4
Á 6H O; cr; 298:15 Kg � Á H ꢁYb3‡; g†
ꢃ
3.9. Enthalpy of solution in water of
[Sr(NTO) (H O)
]Á2H
2
f
m
ꢃ
m
�
Â
m
2
2
4
O
2
ˆ
3Áf H ꢁNTO ; g† � 10Áf H ꢁH2O; g†
(10)
The mean of the enthalpy of solution of [Sr(NTO)2-
H O) ]Á2H O in deionized water at 298.15 K is
(
9
and
2
4
2
�
1
5.81 Æ 0.53 kJ mol . The molar ratio n(H O)/n-
2
ꢃ
ÁU f‰YbꢁNTO† ꢁH2O† Š Á 6H2O; crg
L
ˆ
�
3
4
{Sr(NTO) (H O) ]Á2H O} lies in the 65 701±92 829
2 2 4 2
ꢃ
ꢃ
m
range. Therefore, the mean of ÁsolH can be consid-
ered at in®nite dilution.
ÁH f‰YbꢁNTO† ꢁH2O† Š Á 6H2O; crg
L
3
4
ÁnRT
(11)
Since [Sr(NTO) (H O) ]Á2H O is completely
2
2
4
2
where Áf H (Yb3‡, g) ˆ 4318.9 kJ mol� 1 [5], Áf Hꢃ
0
ionized in aqueous solution, its ionization process
m
m

S. Jirong et al. / Thermochimica Acta 331 (1999) 49±60
59
0
m
2‡
� 1
ꢃ
can be represented as
where Á H (Sr , g) ˆ 1790.6 kJ mol [5]; Á Hꢃ
f
f
m
�
� 1
ÁsolHꢃ
(NTO , g) ˆ � 374.3 kJ mol [7]; Áf Hm (H
2
O,g) ˆ
‰
SrꢁNTO† ꢁH2O† Š Á 2H2O ! Sr2‡ꢁaq; 1†
m
� 241.82 kJ mol [5]; Án ˆ � 9; RT ˆ 2.5 kJ mol
�
1
� 1
.
2
4
By substituting the above-mentioned data into
Eqs. (17) and (18), the following values are obtained:
�
‡
2NTO ꢁaq; 1† ‡ 6H Oꢁl†
(14)
2
ꢃ
L
3
.10. Standard enthalpy of formation of [Sr(NTO) -
2
ÁH f‰SrꢁNTO† ꢁH O† Š Á 2H O; crg
2
2
4
2
ꢃ
(
cr, 298.15 K}
H O) ]Á2H OÁ H {[Sr(NTO) (H O) ]Á2H O,
� 1
2
4
2
f
m
2
2
4
2
ˆ
� 2136 kJ mol
;
ꢃ
ÁU f‰SrꢁNTO† ꢁH2O† Š Á 2H2O; crg
L
2
4
ꢃ
By substituting the mean of ÁsolH and the reported
� 1
;
m
ˆ � 2114 kJ mol
ꢃ
m
2‡
� 1
values of Áf H (Sr ,aq,1) ˆ � 545.8 kJ mol [5],
ꢃ
m
� 1
ꢃ
m
Áf H (H O, l) ˆ � 285.83 kJ mol
[5], and Áf H
2
3.12. Lattice energy and enthalpy of Sr (NTO) (cr),
2
�
� 1
(
Eq. (15),
NTO ,aq,1) ˆ � (94.3 Æ 2.1) kJ mol
[6], into
ꢃ
L
ꢃ
L
ÁU [Sr(NTO) ,cr], ÁH [Sr(NTO) ,cr]
2
2
ꢃ
ꢃ
m
Values of ÁU [Sr(NTO) , cr] are calculated using
L
2
Á H f‰SrꢁNTO† ꢁH O† Š Á 2H O; cr; 298:15 Kg
f
2
2
4
2
Kapustinskii's equation [8]:
P
ꢃ
2‡
ꢃ
�
ˆ
Á H ꢁSr ; aq; 1† ‡ 2Á H ꢁNTO ; aq; 1†
f
m
f
m
ꢀ
ꢁ
0
ꢅ1ꢅ2
n
0:345
ꢃ ꢃ
ꢃ
L
� 1
kJ mol
‡ 6Áf H ꢁH2O; l† � ÁsolH
the following value was obtained:
(15)
ÁU ˆ 1201:6
1 �
m
m
ꢆ1 ‡ ꢆ2
ꢆ1 ‡ ꢆ2
(
19)
ꢃ
m
� 1
Áf H ˆ � ꢁ2545:2 Æ 4:7† kJ mol
where ꢅ and ꢅ are the moduli of the anion and cation
1 2
charges, n the number of ions in the molecule, ꢆ and
1
0
3
.11. Lattice enthalpy and energy of [Sr(NTO) -
2
Ê
0
ꢆ the radii of anion and cation, respectively, in A. For
2
ꢃ
(
H O) ]Á2H OÁH {[Sr(NTO) (H O) Á2H O,
ꢃ
2 2 4 2
2
4
2
L
2
2
4
2
Sr(NTO) (cr), ꢅ ˆ ꢅ
ˆ 1, ꢅ ˆ ꢅ 2‡ ˆ 2, n ˆ 3,
2
1
NTO
Ê
2
Sr
2‡
�
cr}, ÁU {[Sr(NTO) (H O) ]Á2H O, cr}
Ê
L
ꢆ
1
ˆ ꢆ(NTO ,g) ˆ 2.5 A[9],ꢆ
10].
The result of the calculation are obtained as follows:
2
ˆ ꢆ(Sr ,g) ˆ 1.13 A
[
ꢃ
L
Setting ÁH {[Sr(NTO) (H O) Á2H O,cr} as the
2
2
4
2
lattice enthalpy in forming the crystal [Sr(NTO) -
2
ꢃ
L
� 1
2
‡
�
ÁU ‰SrꢁNTO† ; crŠ ˆ � 1797 kJ mol
(
H O) ]Á2H O from Sr (g), NTO (g) and H O(g)
2
2
4
2
2
ꢃ
L
at 298.15 K, and ÁU {[Sr(NTO) (H O) ]Á2H O,cr}
ꢃ
2
2
4
2
The ÁH [Sr(NTO) ,cr] are calculated according to
L
2
as the crystal lattice energy
Eq. (20):
2
‡
�
Sr ꢁg† ‡ 2NTO ꢁg† ‡ 6H2Oꢁg†
ꢃ
L
ꢃ
L
ÁH ‰SrꢁNTO† ; crŠ ˆ ÁU ‰SrꢁNTO† ; crŠ ‡ ÁnRT
2
2
ꢃ
Á‰SrH
L
(
20)
!
ꢁNTO† ꢁH2O† Š Á 2H2Oꢁcr†
(16)
2
4
�
1
where Án ˆ � 3, RT ˆ 2.5 kJ mol .
The result of the calculation is obtained as follows:
we have
ꢃ
l
ÁH fSrꢁNTO† ꢁH2O† Š Á 2H2O; crg
ꢃ
L
� 1
2
4
ÁH ‰SrꢁNTO† ; crŠ ˆ � 1805 kJ mol
2
ꢃ
ˆ
Áf H f‰SrꢁNTO† ꢁH2O† Š Á 2H2O; cr; 298:15 Kg
�
�
m
2
4
ꢃ
m
2‡
ꢃ
m
�
3
.13. Standard enthalpy of formation of
ꢃ
Áf H ꢁSr ; g† � 2Áf H ꢁNTO ; g†
6Áf H ꢁH2O; g†
Sr(NTO) (cr) Á H [Sr(NTO) , cr, 298.15 K]
ꢃ
2
f
m
2
(17)
m
ꢃ
m
The value of Áf H [Sr(NTO) ,cr,298.15 K] are cal-
and
2
culated according to the process (21) and Eq. (22):
ꢃ
ꢃ
L
Á‰U fSrꢁNTO† ꢁH O† Š Á 2H O; crg
2
2
4
2
ÁH ‰SrꢁNTO† ;crŠ
L
2
2
‡
�
ꢃ
Sr ꢁg† ‡ 2NTO ꢁg†
!
SrꢁNTO† ꢁcr†
ˆ
ÁH f‰SrꢁNTO† ꢁH2O† Š Á 2H2O; crg
ÁnRT
2
L
2
4
�
(18)
(21)

6
0
S. Jirong et al. / Thermochimica Acta 331 (1999) 49±60
Á H ‰SrꢁNTO† ; crŠ ˆ Á H ꢁSr2‡; g†
ꢃ
m
ꢃ
m
the value of Á H {[Sr(NTO) (H O) ]Á2H O,cr} of
ꢃ
f
2
f
f
d
2
2
4
2
�
1
ꢃ
�
ꢃ
67.2 kJ mol
ꢃ
may be obtained from the values
of Áf H {[Sr(NTO) (H O) ]Á2H O,cr,298.15 K} as
‡
2Áf H ꢁNTO ; g† ‡ ÁH ‰SrꢁNTO† ; crŠ
m
L
2
m
2
2
4
ꢃ
m
2
(
22)
� 1
2
kJ mol , obtained in this work, and the reported
545.2 kJ mol and Áf H [Sr(NTO) , cr] as � 763
2
�
1
where Áf H (Sr , g) ˆ 1790.6 kJ mol ; Áf Hꢃ
ꢃ
m
2‡
� 1
m
0
m
� 1
�
� 1
ꢃ
L
values Áf H (H O, l) as � 285.83 kJ mol
.
(
NTO ,g) ˆ � 374.3 kJ mol ; ÁH [Sr(NTO) ,
2
2
�
1
cr] ˆ � 1805 kJ mol
.
By substituting the above-mentioned data into
Eq. (22), the following value is obtained:
References
ꢃ
m
� 1
Á H ‰SrꢁNTO† ; crŠ ˆ � 763 kJ mol
f
2
[1] Hu Rongzu, Song Jirong, Li Fuping, Thermochim. Acta 299
1997) 87±93.
(
[
2] Song Jirong, Chen Zhaoxu, Xiao Heming, Hu Rongzu, Acta
Chimica 56(3) (1998) 270±277.
3
.14. Standard enthalpy of dehydration of
ꢃ
[
Sr(NTO) (H O) ]Á2H O(cr)ÁH
[3] Song Jirong, Hu Rongzu, Li Fuping, Chinese Science Bulletin
1(21) (1996) 1806±1810.
2
2
4
2
d
4
{
[Sr(NTO) (H O) ]Á2H O,cr}
2
2
4
2
[
4] R.C. Weast, CRC Handbook of Chemistry and Physics, 70th
edn. CRC Press Inc., Boca Raton, FL, 1989, p. D122.
According to process (23) and Eq. (24)
[
5] R.C. Weast, CRC Handbook of Chemistry and Physics, 63rd
edn. CRC Press Inc., Boca Raton, FL, 1982±1983, pp. D52±
‰
SrꢁNTO† ꢁH O† Š Á 2H O
2
2
4
2
95.
ꢃ
d
ÁH f‰SrꢁNTO† ꢁH2O† ŠÁ2H2O;cr
[6] A. Finch, P.J. Gardner, A.J. Head, H.S. Majdi, J. Chem.
Thermodyn. 23(12) (1991) 1169±1173.
2
4
!
SrꢁNTO† ꢁcr†
2
[
7] Hu Rongzu, Meng Zihui, Kang Bing, Thermochim. Acta 275
1996) 159±172.
[8] A.F. Kapustinskii, Quart. Rev. 10 (1956) 283.
‡
6H2Oꢁl†
(23)
(
ꢃ
ÁH f‰SrꢁNTO† ꢁH O† Š Á 2H O; crg
d
2
2
4
2
[
9] A. Finch, P.J. Gardner, A.J. Head, H.S. Majdi, Thermochim.
Acta 213 (1993) 17±22.
ꢃ
m
q
m
ˆ
�
Áf H ‰SrꢁNTO† ; crŠ ‡ 6ÁfH ꢁH2O; l†
2
[
10] Gao Shengli, Zhao Rui, Lang Huiyun, A Periodic Table of the
Chemical Elements, Northwest University Press, Xian, P.R.
China.
ꢃ
m
Áf H f‰SrꢁNTO† ꢁH2O† Š
2
4
Á 2H O; cr; 298:15 Kg
(24)
2