КООРДИНАЦИОННАЯ ХИМИЯ, 2007, том 33, № 3, с. 231-238
УДК 541.49
APPLICATION OF ROTATE-BOMB CALORIMETER FOR DETERMINING THE STANDARD MOLAR ENTHALPY OF FORMATION OF Ln(Pdc)3(Phen) © 2007 S. P. Chen, S. L Gao, X. W. Yang, and Q. Z. Shi
Department of Chemistry, Shaanhi Key Laboratory of Physico-Inorganic Chemistry, Northwest University,
Xi'an, 710069 China Received January 12, 2006
Thirteen solid ternary complexes of Ln(Pdc)3(Phen) (Ln = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) have been synthesized in absolute ethanol by rare-earth element chloride low hydrate reacting with the mixed ligands of ammonium pyrrolidinedithiocarbamate (APdc) and 1,10-phenanthroline • H2O (o-Phen • H2O) in the ordinary laboratory atmosphere without any cautions against moisture or air sensitivity. IR spectra of the complexes showed that the Ln3+ coordinated with six sulfur atoms of three Pdc- and two nitrogen atoms of o-Phen • H2O. It is assumed that the coordination number of Ln3+ is eight. The constant-volume combustion energies of the complexes, AcU, were determined by a precise rotate-bomb calorimeter at 298.15 K. Their standard molar enthalpies of combustion, AcH^, and standard molar enthalpies of formation, AfHm were calculated.
INTRODUCTION
The chemistry of the complexes containing lan-thanide-sulfur bond has been of substantial interest because of their high performance of biological and friction properties [1]. In addition, they have been largely used because of their chemical and physical properties, such as vulcanization accelerator [2-4]. The vast investigations have been reported on preparations, characterizations, and structures of these compounds, which is of great importance for illuminating the bonding characterization of lanthanide series and enriching the application of these compounds [5-17]. Common to the preparation of the class of the complexes is observed that the experiments must be performed using anhydrous salts in dry inert gas just because of difficulty of preparation and stability of the complexes toward moisture [13]. There was the report on the preparation of the ternary complexes involving the variable-valence transition elements; 2,2'-bipyridyl (Bipy) or 1,10-phenanthroline ■ H2O (o-Phen • H2O, C12H8N2 ■ HgO) with n donor and dithiocarbamates (Dtc) were selected as ligands, which overcame the drawbacks of the preparation on the duality complexes [18]. In [19], the complexes of rare-earth elements with the mixed ligands of NaEt2Dtc with o-Phen ■ H2O were characterized. Eu(Et2Dtc)3(Phen) was structurally determined [20]. The complexes of rare-earth and the ligands of NaEt2Dtc with Bipy have been reported, and the crystal structure of Er(Et2Dtc)3 (Bipy) was described [21, 22].
In this paper, we describe the synthesis of the ternary complexes Ln(Pdc)3(Phen) (Ln = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu; Pdc- is pyrrolidinedithiocarbamate anion, C5H8N S2), which can be prepared and investigated using hydrated lanthanide
salts in the ordinary laboratory atmosphere without any cautions against moisture or air sensitivity. The title complexes were characterized by IR spectra. Their standard enthalpies of combustion and standard enthalpies of formation have been calculated on the basis of determination of the constant-volume energies of combustion of the complexes. The data provide thermodynamic insight into further understanding of these coordination compounds.
EXPERIMENTAL
Reagents. Lanthanide chloride hydrates, LnCl3 ■ nH2O (Ln = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu; n = 3, 4), were prepared in our experiment, for which Ln3+ was determined with Edta by complexono-metric titration. Ammonium pyrrolidinedithiocarbamate (APdc), o-Phen ■ H2O, absolute ethanol, and dichlo-romethane are of A. R. grade from Xi'an chemical reagent company.
Preparation and composition of the complexes. The complexes were synthesized as follows. LnCl3 ■ nH2O (8 mmol), APdc (24 mmol), and o-Phen ■ H2O (8 mmol) were dissolved in a minimal amount of anhydrous etha-nol. Then alcoholic solutions of o-Phen ■ H2O and APdc were mixed together. The solutions were dropped slowly to the salt alcoholic solution when keeping electromagnetic stirring. After the addition, the mixture was allowed to stand for 30 min and filtered. The crude product was rinsed by three a small amount of absolute ethanol portions, followed by purifying with dichlo-romethane. The final crystal was obtained and kept in vacuum over P4O10 to dryness for use.
C, H, N, and S analyses were carried out by a Vario EL ffl CHNOS instrument (Germany). The final results
Table 1. The elemental analysis data of the complexes Ln(Pdc)3(Phen) (Ln = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu)
Complex Content (found/calcd), %
Ln S C N H
La(Pdc)3(Phen) 18.10/18.33 25.30/25.39 42.60/42.79 9.17/9.24 4.20/4.26
Pr(Pdc)3(Phen) 18.57/18.54 25.23/25.32 42.45/42.68 9.11/9.22 4.17/4.24
Nd(Pdc)3(Phen) 19.06/18.90 25.19/25.21 42.24/42.49 9.10/9.18 4.20/4.23
Sm(Pdc)3(Phen)P 19.50/19.54 25.00/25.01 42.09/42.15 9.09/9.10 4.08/4.19
Eu(Pdc)3(Phen) 19.97/19.71 25.01/24.96 41.98/42.06 8.99/9.08 3.99/4.18
Gd(Pdc)3(Phen) 20.31/20.26 24.63/24.79 41.81/41.78 8.98/9.02 4.01/4.16
Tb(Pdc)3(Phen) 20.38/20.43 24.61/24.73 41.58/41.69 8.98/9.02 4.00/4.15
Dy(Pdc)3(Phen) 20.79/20.79 24.54/24.62 41.37/41.50 8.77/8.96 4.01/4.13
Ho(Pdc)3(Phen) 21.24/21.04 24.42/24.54 41.42/41.37 8.81/8.93 4.25/4.11
Er(Pdc)3(Phen) 20.30/20.27 24.40/24.47 41.29/41.25 8.79/8.91 4.00/4.10
Tm(Pdc)3(Phen) 21.23/21.44 24.21/24.42 41.17/41.16 8.78/8.89 3.86/4.09
Yb(Pdc)3(Phen) 21.67/21.85 24.11/24.29 40.71/40.95 8.55/8.84 3.81/4.07
Lu(Pdc)3(Phen) 21.89/22.04 24.09/24.23 40.65/40.85 8.44/8.82 3.77/4.06
are showed in Table 1, which are identified as the general formula Ln(Pdc)3(Phen).
Apparatus and experimental condition. The constant-volume combustion energies of the complexes were determined by a precise rotate-bomb calorimeter (RBC-type II) [23]. The main experimental procedures were described previously. The bicyclic structure of the crucible support in the oxygen bomb, as showed in Fig. 1, was constructed, so that the bomb can make a compound rotation about an axis perpendicular to the bomb axis (i.e., end-over-end rotation) and about the bomb axis (axial rotation) at the same time, assuring that the combustion reaction is proceeding completely.
The initial temperature was regulated to (25.0000 ± ± 0.0005)°, and the initial oxygen pressure was 2.5 MPa. The digital indicator for temperature measurement was used to promote the precision and accuracy of the experiment. The correct value of the heat exchange was calcu-
Fig. 1. Bicyclic structure of the crucible support in the oxygen bomb.
lated according to the Linio-Pyfengdelel-Wsava formula [24]:
À(À T ) = nVo + ^J! V
T„ - Tn
T 0 + Tn
X T nTo
i =i /
(1)
where A(AT) denotes the correct value of the heat exchange; n is the number of readings for the main (or reaction) period; V0 and Vn are the rate of temperature change at the initial and final stages, respectively (V is
positive when the temperature decreased); T 0 and Tn are the average temperatures of calorimeter at the initial and final stages, respectively (average temperature for the first and last reading); T0 is the last reading of the initial stage; Tn is the first reading of the final stage;
Xn- \ Ti is the sum of all the readings, except for the
Vn - V
last one of the main period; =—n0 is the constant.
Tn - T o
The energy equivalent of the RBC-type II calorimeter was determined from 6 combustion experiments using about 0.8 g of NIST 39i benzoic acid with a certified massic energy of combustion AcU = (-26434 ± 3) J g-1 under the same experimental conditions to be (17775.09 ± 7.43) J K-1 by formula (2). The calibrated experimental results with an uncertainty of 4.68 x 10-4 are summarized in Table 2.
W = 0a.
Gb + 5.97c
ÀT
(2)
where W is the energy equivalent of the rotate-bomb calorimeter (in J K-1), Q is the combustion enthalpy of
benzoic acid (in J g-1), a is the mass of determined benzoic acid (in g), G is the combustion enthalpy of Ni-Cr wire for ignition (0.9 J cm-1), b is the length of the actual Ni-Cr wire consumed (in cm), 5.97 is the formation enthalpy and solution enthalpy of acid corresponding to 1 ml of 0.1000 mol l-1 solution of NaOH (in J ml-1), c the volume (in ml) of consumed 0.1000 mol l-1 solution of NaOH, and AT is the correct value of the temperature rise.
After the experiment ended, the final products of the combustion reaction were analyzed [23]. The gaseous sulfurous anhydride produced during the process of the combustion reaction was converted catalytically to sulfur trioxide, where the platinum lining of the interior surfaces of the bomb was thought as catalyst. The bomb solution then absorbed the gaseous sulfur trioxide, generating aqueous sulfuric acid. The amount of sulfuric acid was determined by the BaSO4 gravimetric method. The remains of the gases formed in the combustion were collected in a gas-collecting bag. The volume was measured by a gas meter, which was fitted between the bag and bomb. The gaseous carbon dioxide produced in the combustion was absorbed by a weighted absorption tube containing alkali asbestos. The amount of CO2 was determined through the weight increment of the tube after absorbing carbon dioxide. The amount of CO2 dissolved in the final solution was neglected. Four absorption tubes were connected in series with each other for the vapor measurement. The first was filled with P4O10 and CaCl2 (anhydrous) to absorb the water vapor contained in the gas, the second was filled with active MnO2 in order to absorb nitrogen oxides, the third was filled with alkali asbestos to absorb CO2, and the fourth was full of solid P4O10 and CaCl2 (anhydrous) to absorb the water vapor formed in the determination. Nitrogen oxides (NO*) produced from oxidation of a trace of nitrogen contained in the bomb main
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