Energetic and structural properties of 4-nitro-2,1,3-benzothiadiazole

J. Chem. Thermodynamics 49 (2012) 146–153

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Energetic and structural properties of 4-nitro-2,1,3-benzothiadiazole M.D.M.C. Ribeiro da Silva a,⇑, V.L.S. Freitas a, M.A.A. Vieira a, M.J. Sottomayor a, W.E. Acree Jr. b a b

Centro de Investigação em Química, Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, 687, P-4169-007 Porto, Portugal Department of Chemistry, 1155 Union Circle Drive #305070, University of North Texas, Denton, TX 76203-5017, USA

a r t i c l e

i n f o

Article history: Received 26 December 2011 Accepted 21 January 2012 Available online 31 January 2012 Keywords: Nitroheterocyclic compounds Enthalpy of formation Enthalpy of sublimation Combustion calorimetry Calvet microcalorimetry Heat capacity G3(MP2)//B3LYP composite method

a b s t r a c t The energetic study of 4-nitro-2,1,3-benzothiadiazole has been developed using experimental techniques together with computational approaches. The standard (p° = 0.1 MPa) molar enthalpy of formation of crystalline 4-nitro-2,1,3-benzothiadiazole (181.9 ± 2.3 kJ  mol1) was determined from the experimental standard molar energy of combustion (3574.3 ± 1.3) kJ  mol1, in oxygen, measured by rotating-bomb combustion calorimetry at T = 298.15 K. The standard (p° = 0.1 MPa) molar enthalpy of sublimation, at T = 298.15 K, (101.8 ± 4.3) kJ  mol1, was determined by a direct method, using the vacuum drop microcalorimetric technique. From the latter value and from the enthalpy of formation of the solid, it was calculated the standard (p° = 0.1 MPa) enthalpy of formation of gaseous 4-nitro-2,1,3-benzothiadiazole as (283.7 ± 4.9) kJ  mol1. Standard ab initio molecular orbital calculations were performed using the G3(MP2)//B3LYP composite procedure and several working reactions in order to derive the standard molar enthalpy of formation 4-nitro-2,1,3-benzothiadiazole. The ab initio results are in good agreement with the experimental data. Ó 2012 Elsevier Ltd. All rights reserved.

1. Introduction In the context of a systematic study on the thermochemical properties of diazole derivatives (figure 1), we have performed experimental and theoretical studies on the alkyl or phenyl substituent effects through the nitrogen atoms in pyrazole and imidazole rings [1,2], which has been extended to include the effect of alkyl or aryl substituent in the carbon of the heterocycle of the bicyclic molecules derived from imidazole fused to an aromatic ring [3–7], in order to compare the effect of the substituent in the heterocycle of the bicyclic molecules with the corresponding monocyclic heteromolecules. On the other side, we have been also interested on the N–O dissociation bond in 2,1,3-benzoxadiazole-1-oxide (benzofuroxan) derivatives and this study requires the knowledge of data on the correspondent 2,1,3-benzoxadiazole (benzofurazan) derivatives, as it has been reported previously [8–10]. The purpose of this work is to study the 4-nitro-2,1,3-benzothiadiazole (figure 2), a molecule with two nitrogen atoms at 1 and 3 positions and one sulphur atom at 2 position in a di-unsaturated ring structure fused to a benzene ring that incorporates a nitro group on an adjacent position to the ‘‘junction’’ of the two cycles. The data reported for this compound affords the possibility to make comparisons with 4-nitro-benzofurazan [9] concerning the energetic effects on the presence of the sulphur instead an oxygen heteroatom on the benzodiazole ring. The nitro derivatives of ⇑ Corresponding author. Tel.: +351 220 402 538; fax: +351 220 402 522. E-mail address: [email protected] (M.D.M.C. Ribeiro da Silva). 0021-9614/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.jct.2012.01.018

benzazoles have found a wide range of applications, from medicine to agriculture to materials chemistry. Benzothiadiazole derivatives are well known for their biological activities such as inducers of systemic resistance to diseases rather than direct antifungal or antibacterial activities [11,12]. More recently, 2,1,3-benzothiadiazole derivatives were prepared and copolymerized with thiophene derivatives using cross-coupling reactions, resulting materials exhibiting a reduced band gap that were explored in polymer photovoltaic devices [13,14]. 2. Experimental details 2.1. Purification and purity control of 4-nitro-2,1,3-benzothiadiazole The 4-nitro-2,1,3-benzothiadiazole [CAS 6583-06-8] was purchased from Aldrich Chemical Company (99%) and re-crystallized three times from absolute ethanol. The melting point temperature of the re-crystallized sample, measured in a melting point apparatus, Stuart Scientific SMP2, was T = 383 K. Elemental analyses were in good agreement with expected values for C6H3N3O2S; found: C, 0.3971; H, 0.0173; N, 0.2315; calculated: C, 0.3979; H, 0.0167; and N, 0.2319 mass fractions. The compound has been submitted to additional purification by sublimation under reduced pressure, immediately before the calorimetric measurements. Purity details are given in table 1. The specific density for 4-nitro-2,1,3-benzothiadiazole is 1.5911 g  cm3 [15]. The relative atomic masses used were those recommended by the IUPAC commission in 2009 [16].

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N N N H

N H

pyrazole

imidazole

H N

N

N

N

O

benzoimidazole

benzof urazan

FIGURE 1. Molecular structure of diazole compounds.

From each melting curve, the temperature and enthalpy of fusion were obtained. The fusion temperatures were taken as DSC onset temperatures. For each fusion peak six integrations were performed in order to compute the enthalpy of fusion. To detect the possible existence of phase transitions in the solid state, different scans were performed on heating, cooling and second heating over the temperature range from T = 283 K to the melting temperature at heating rates of (0.033 and 0.17) K  s1. Heat capacities as a function of temperature were determined by the step method, following the well-known three-step procedure, described in the literature [21] and using synthetic sapphire (a-aluminium oxide) as reference material [20]. The method consists in performing three runs with two crucibles, one measuring crucible and one reference crucible. The first run is performed with the two empty crucibles, the second run with a mass of sample in the measuring crucible and the third run with a reference material, with known heat capacity. Reference crucible is empty during all three runs. Each run consists in successive temperature increments (DT) performed at a given heating rate. For heat capacity determination, fresh samples weighing (20 to 25) mg were used. In a typical heat capacity experiment, the temperature was increased in steps of 10 K with a heating rate 0.17 K  s1. The average heat capacity for a given temperature step DT is assigned to the average temperature of the increment T = Ti + DT/2 (Ti is the initial temperature). 2.3. Rotating bomb calorimetry

FIGURE 2. Structure optimized at the B3LYP/6-31G(d) level of theory for the gaseous molecule of 4-nitro-2,1,3-benzothidiazole. Selected bond lengths (Å) and bond angles (°) are included, being the last parameter signaled at bold.

2.2. Differential scanning calorimetry DSC measurements were carried out with a Setaram, DSC 141 calorimeter, using standard aluminium pans in a nitrogen atmosphere. The temperature and power scales of the calorimeter were calibrated [17–19] at heating rates of 0.033 and 0.17 K  s1. The temperature scale was calibrated measuring the melting temperature of the recommended high-purity reference materials: naphthalene, benzoic acid, and indium [20]. The power scale was calibrated with high-purity indium (mass fraction > 0.99999) as reference material. To study the fusion process, thermograms of samples weighing (5 to 10) mg were recorded under a nitrogen atmosphere, using a heating rate 0.033 K  s1. All the pans were weighed before and after the experiments, to confirm that no product loss had occurred. A Mettler UMT2 microbalance, with a sensitivity of (1  107) g, has been used. DSC experiments were carried out from T = 298 K to around 20 K above the melting temperature. To verify the stability of the compound after melting, two scans were performed for each sample, to ensure that no decomposition occurred in the heating process.

The standard massic energy of combustion of 4-nitro-2,1,3-benzothiadiazole was measured using a rotating bomb calorimeter originally built in the National Physical Laboratory, Teddington, UK and installed in Porto University [22–24], where several changes in the auxiliary equipment were made. The bomb, with an internal volume 0.329 dm3, is internally lined with tantalum. Water was added to the calorimeter from a weighted Perspex vessel and for each experiment was made a correction to the energy equivalent for the deviation in the mass of water from 3965.0 g. The quantity of distilled water used as calorimetric liquid was weighed in a Mettler PC 8000 balance, sensitivity ±101 g, whereas a Mettler Toledo 245 balance, sensitivity ±105 g, was used to all the necessary weighing for the combustion experiments. The calorimetric system was calibrated using benzoic acid NIST Thermochemical Standard 39i [25], with a certified massic energy of combustion, under bomb conditions, of (26434 ± 3) J  g1. Calibration experiments were made in oxygen at 3.04 MPa, with 1.00 cm3 of water added to the bomb. One set of ten calibration experiments were performed leading to the following value for the energy equivalent, e = (20369.0 ± 2.3) J  K1 where the uncertainty corresponds to the standard deviation of the mean. The combustion experiments of crystalline 4-nitro-2,1,3-benzothiadiazole were burnt in pellet form, under a p = 3.04 MPa oxygen atmosphere, in the presence of 10.00 cm3 of deionised water added to the bomb. For each experiment, the ignition temperature was selected so that the final temperature would be as close as possible to 298.15 K. Calorimeter temperatures were measured using a Hewlett-Packard (HP-2804A) quartz thermometer interfaced to a microcomputer, programmed to compute the adiabatic temperature range. During each calorimetric experiment, the rotation of

TABLE 1 Purification details of the studied compounds. Chemical name

CAS

Provenance

Initial molar fraction purity

Purification method

Final mass fraction purity

Analysis method

4-Nitro-2,1,3-benzothiadiazole

6583-06-8

Aldrich Chemical Co.

0.99

Recrystallization and sublimation

0.9980

Gravimetric analysis

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the bomb started on the main period, when the temperature rise was about 63% of the total expected, so the frictional work due to bomb rotation could be included in the corrections for the heat leakage and work of stirring, in accordance with procedures of Good and Scott [26]. In all the experiments, the data acquisition and the control of the calorimeter have been performed by means of the LABTERMO program [27]. The electrical energy for the ignition was determined from the change in potential across a capacitor (1281 lF) when about 40 V were discharged through the platinum wire for the ignition. The massic energy of combustion of the cotton thread fuse, for which the empirical formula is CH1.686O0.843, is Dcu = 16,240 J  g1 [26], a value confirmed in our laboratory. The corrections to the formation of nitric acid formed, determined using the Devarda’s alloy method [28], were made using the value 59.7 kJ  mol1 for the standard molar energy of formation of 0.1 mol  dm3 of aqueous HNO3 from O2 (g), N2 (g), and H2O (l) [29]. The pressure coefficient of massic energy, (ou/op)T, at T = 298.15 K, was assumed as 0.2 J  g1  MPa1, a typical value for most organic compounds [30]. The corrections to the standard state, DUR, were calculated by the procedures given by Hubbard et al. [31] and by Good and Scott [32]. 2.4. Calvet microcalorimetry The measurement of the standard molar enthalpy of sublimation of 4-nitro-2,1,3-benzothiadiazole was performed by the vacuumsublimation drop microcalorimetric technique described by Skinner et al. [33], using a Calvet high-temperature microcalorimeter (Setaram HT1000) connected to a vacuum pump system. Crystalline samples of about (2 to 3) mg of 4-nitro-2,1,3-benzothiadiazole, contained in thin glass capillary tubes sealed at one end, were dropped from room temperature into the hot reaction vessel in the calorimeter held at a predefined temperature of 385.0 K and then removed from the hot zone by vacuum. The thermal corrections for the glass capillary tubes were determined in separate experiments, and were minimized by dropping tubes of nearly equal mass, to within 104 g, into each of the twin calorimetric cells. The microcalorimetry was calibrated in situ performing sublimation experiments with naphthalene, following the same procedure as the one described above for the compounds, using its reported standard molar enthalpy of sublimation, at T ¼ 298:15 K; 1 Dgcr Hm ¼ ð72:6  0:6Þ kJ  mol [20].

higher levels of theory, that include only valence electrons in the treatment of electron correlation (frozen core). The first higher level calculation is at the quadratic configuration interaction QCISD(T) [42] with the 6-31G(d) basis set, which is then followed by a second-order Møller–Plesset level (MP2) [43], frozen core (FC), single-point calculation with the GTMP2Large basis set. The G3(MP2)//B3LYP energy at T = 0 K considers the QCISD(T)/631G(d) energy which is corrected by the energetic difference on going from MP2(FULL)//6-31G(d) to MP2(FC)//GTMP2Large, with spin–orbit correction, DE(SO), that is included only for atomic species, higher level correction (HLC) for molecules and also the zero point energy correction E(ZPE), obtained from scaled B3LYP/631G(d) frequencies. The value of the total energy at T = 0 K is then corrected for T = 298.15 K by introducing the vibrational term computed also at the B3LYP/6-31G(d) and the translational, rotational and the pV terms. Finally, the harmonic vibrational frequencies, determined at the B3LYP/6-31G(d) level, are used to confirm that all of the structures considered correspond to real minima on the potential energy surface. In some reactions the bonds present in reactants and products are slightly different and thus are not compensated. In other cases, like reaction of atomization the bonds in the products of the reaction are not considered, therefore, in order to reduce the extension of those errors, we used the empirical correction procedure developed by Anantharaman and Melius [44], i.e., the bond additivity correction (BAC) scheme, where atomic, molecular and bond wise corrections are subtracted to the calculated enthalpy of formation of the compound derived from its reaction of atomization. All calculations were done with the Gaussian-03 computer program [45]. 4. Results and discussion 4.1. Experimental results 4.1.1. Enthalpy of formation in the crystalline phase Rotating bomb combustion calorimetry was used to measure the energy of combustion of crystalline 4-nitro-2,1,3-benzothidiazole compound, from which the standard molar enthalpy of formation was derived. In the experiments with the title compound (C6H3O2N3S), the products of its combustion consist of a gaseous phase and an aqueous mixture of sulphuric acid for which the thermodynamics properties are known. Its combustion reaction is represented by the following equation:

C6 H3 O2 N3 S ðcrÞ þ 7:25O2 ðgÞ þ 114:5H2 O ðlÞ 3. Computational details The computational study of the 4-nitro-2,1,3-benzothidiazole consisted on the design of several gas-phase work reactions [34– 37] (to cancel errors in the calculations) and calculation of the energies of the species there included using the G3(MP2)//B3LYP method [38]. For each work reaction, the value of the enthalpy of formation in the gas-phase of the 4-nitro-2,1,3-benzothiadiazole was calculated from the variation of the enthalpy of the work reaction (equal to the sum of the values of the enthalpies obtained computationally for the products and reagents) and the experimental standard molar gas-phase enthalpies of formation of each species available in the literature. In the G3(MP2)//B3LYP method (a variation of Gaussian-3 (G3) theory [39]) the total energy of a given molecular species is obtained by a sequence of well-defined molecular orbital calculations. The first step of this method consists in the optimization of the molecular geometry and calculation of the vibrational frequencies with the hybrid B3LYP method [40,41] with the 6-31G(d) basis set. Then, a series of single point energy calculations carried out at

! 6CO2 ðgÞ þ H2 SO4  115H2 O ðlÞ þ 1:5N2 ðgÞ:

ð1Þ

Table 2 lists the standard (p° = 0.1 MPa) massic energies of combustion, Dcu°, together with the results for the combustion experiments of 4-nitro-2,1,3-benzothidiazole. The energy associated to the isothermal bomb process DU(IBP), was calculated through:

DUðIBPÞ ¼ feðcalorÞ þ cp ðH2 O; lÞDmðH2 OÞgDT ad þ ðT i  298:15Þei þ ð298:15  T i  DT ad Þef þ DUðignÞ; ð2Þ where DTad is the calorimeter temperature corrected for the heat exchange, work of stirring and frictional work of bomb rotation, Dm(H2O) represents the deviation of the mass of water added to the calorimeter from 3965.0 g, the water assigned to e(calor), Ti and Tf are the initial and the final temperatures rise, respectively, ei and ef are the energies equivalent of the contents in the initial and final states, respectively, DU(ign) is the electric energy for the ignition and cp (H2O, l) is the massic heat capacity at constant pressure for liquid water. The standard state corrections, DUR

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M.D.M.C. Ribeiro da Silva et al. / J. Chem. Thermodynamics 49 (2012) 146–153 TABLE 2 Typical combustion results, at T = 298.15 K (p° = 0.1 MPa), for 4-nitro-2,1,3-benzothidiazole.a Experiment

1

m(cpd)/g 0.82710 m0 (fuse)/g 0.00213 Ti/K 297.4855 Tf/K 298.3083 DTad/K 0.79956 ei/(J  K1) 53.51 ef/(J  K1) 52.43 ecorr/(J  K1) 20479.88 Dm(H2O)/g 26.5 DU(IBP)b/J 16416.44 DU(fuse)/J 34.59 DU(HNO3)/J 44.12 DU(ign)/J 1.09 DUR/J 25.68 Dcu°/(J  g1) 19721.98 hDcu°i = (19728.9 ± 2.8)c J  g1

2

3

4

5

6

0.70367 0.00244 297.4177 298.1297 0.68335 53.39 52.28 20434.69 15.7 13999.50 39.63 50.33 1.09 22.88 19734.62

0.87046 0.00228 297.2565 298.1306 0.84482 53.55 52.46 20425.48 13.5 17300.06 37.03 59.40 1.09 26.47 19733.43

0.83662 0.00223 297.3005 298.1449 0.81212 53.52 52.42 20418.79 11.9 16624.92 36.22 63.40 1.09 25.70 19721.74

0.78219 0.00215 297.3382 298.1293 0.75995 53.46 52.36 20418.79 11.9 15556.86 34.92 59.46 1.08 24.55 19736.80

0.91223 0.00223 297.2113 298.1302 0.88800 53.59 52.49 20362.72 1.5 18128.66 36.22 71.76 1.09 27.23 19724.69

a

m(cpd) is the mass of the compound burnt in each experiment; m0 (fuse) is the mass of the fuse (cotton) used in each experiment; Ti is the initial temperature rise; Tf is the final temperature rise; DTad is the corrected temperature rise; ei is the energy equivalent of the contents in the initial state; ef is the energy equivalent of the contents in the final state; ecorr is the energy equivalent of the calorimeter corrected for the deviation of mass of water added to the calorimeter; Dm(H2O) is the deviation of mass of water added to the calorimeter from 3965.0 g; DU(IBP) is the energy change for the isothermal combustion reaction under actual bomb conditions; DU(fuse) is the energy of combustion of the fuse (cotton); DU(HNO3) is the energy correction for the nitric acid formation; DU(ign) is the electric energy for the ignition; DUR is the standard state correction; Dcu° is the standard massic energy of combustion. b DU(IBP) includes DU(ign). c Mean value of the standard massic energy of combustion and the standard deviation of the mean.

TABLE 3 Derived standard (p° = 0.1 MPa) molar values of 4-nitro-2,1,3-benzothidiazole in the crystalline phase, at T = 298.15 K.

Dc U m ðcrÞ=ðkJ  mol

1

Þ

3574.3 ± 1.3

Dc Hm ðcrÞ=ðkJ  mol 3573.7 ± 1.3

1

Þ

Df Hm ðcrÞ=ðkJ  mol

1

Þ

181.9 ± 2.3

(Washburn corrections) were calculated as recommended in the literature for organic sulphur compounds [31,32]. From the individual values of the Dcu° for each experiment, it has been calculated the mean standard massic energy of combustion and the corresponding standard deviation of the mean. Table 3 lists the derived values of standard molar energies and enthalpies of the reaction described by equation (1), respectively, Dc U m ðcrÞ and Dc Hm ðcrÞ, as well as the standard molar enthalpy of formation Df Hm ðcrÞ, of the crystalline compound. In accordance with the normal thermochemical practice, the uncertainties assigned to the standard molar enthalpies of combustion and formation are twice the overall standard deviation of the mean and include the uncertainties in calibration and the auxiliary quantities used. To derive Df Hm ðcrÞ from Dc Hm ðcrÞ, the standard molar enthalpies of formation of H2O (l), CO2 (g) and H2SO4 in 115H2O (l), at T = 298.15 K, respectively, (285.830 ± 0.042) kJ  mol1 [46], (393.51 ± 0.13) kJ  mol1 [46], and (887.81 ± 0.01) kJ  mol1 [29] were used. 4.1.2. Enthalpies of fusion and sublimation No solid–solid transitions were found in the temperature range from T = 283 K to the melting temperature of the compound. The values obtained from the DSC experiments for the temperature of fusion (Tfus) and the enthalpy of fusion at T = Tfus for 4-nitro-2,1,3-benzothiadiazole are, respectively, (381.4 ± 0.1) K and (22.6 ± 0.8) kJ  mol1. The reported values are the mean values of six independent experiments on fresh samples and the

uncertainties assigned are in each case twice the standard deviation of the mean. The molar heat capacities were measured from T = 283 K to near the melting temperature. The temperature dependence of heat capacity was close to linear. Therefore, the average heat capacity over each individual temperature step could be considered as the heat capacity at the mean temperature of the interval. The heat capacities of 4-nitro-2,1,3-benzothiadiazole, in the range from T = 283 K to T = 363 K, increase with temperature in a smooth way, without any thermal discontinuity, which means the compound is stable in this temperature range. A least square fitting of the experimental data yields equation (3) for the molar heat capacity curve as a function of temperature, in the temperature range 283 K to 363 K 1

C p;m ðcrÞ=ðJ  K1  mol Þ ¼ 15:6 þ 0:709ðT=KÞ  3:26  105 ðT=KÞ2 : ð3Þ Results of microcalorimetric determinations of the enthalpy of sublimation of 4-nitro-2,1,3-benzothidiazole are given in table 4. The observed enthalpy of sublimation, at experimental temperature g;385:0K T = 385.0 K, Dcr;298:15K Hm , correspond to the mean of five experiments with uncertainties given by their standard deviations. The enthalpy of sublimation was corrected to T = 298.15 K considering equation (4) and where the molar heat capacity of gaseous 4nitro-2,1,3-benzothidiazole, presented in equation (5), was derived from statistical thermodynamics using the vibrational frequencies from DFT calculations (B3LYP) with 6-31G(d) basis set [47], scaled by a factor of 0.9613 [48] to take into account known deficiencies at this level. The molar heat capacity in the gaseous phase for 4nitro-2,1,3-benzothidiazole between (200 and 600) K are given as supporting information (table S1).

DT298:15K Hm ðgÞ ¼

Z

T

298:15K

C p;m ðgÞdT;

ð4Þ

TABLE 4 Standard (p° = 0.1 MPa) molar enthalpy of sublimation for 4-nitro-2,1,3-benzothidiazole, at T = 298.15 K, determined by Calvet microcalorimetry. Number of experiments

T/K

1  Dg;385:0K Þ cr;298:15K Hm =ðkJ  mol

DT298:15K Hm ðgÞ=ðkJ  mol1 Þ

Dgcr Hm =ðkJ  mol1 Þ

5

385.0

116.5 ± 4.2

14.6803 ± 0.0004

101.8 ± 4.3

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FIGURE 3. Natural population charge (a) and electrostatic potential map (b) of 2,1,3-benzothiadiazole molecule (isovalue 0:05e  a3 0 , where a0 is the Bohr radius).

FIGURE 4. Natural population charge (a) and electrostatic potential map (b) of 4-nitro-2,1,3-benzothiadiazole molecule (isovalue 0:05e  a3 0 , where a0 is the Bohr radius).

4.1.3. Enthalpy of formation in the gaseous phase The standard (p° = 0.1 MPa) molar enthalpies of formation in the gaseous phase, at T = 298.15 K, Df Hm ðgÞ, of 4-nitro-2,1,3-benzothidiazole was derived from the experimental values of the enthalpies 1 of sublimation Dgcr Hm ¼ ð101:8  4:3Þ kJ  mol and of formation in 1  the crystalline phase Df Hm ðcrÞ ¼ ð181:9  2:3Þ kJ  mol , at the same temperature, yielding the value Df Hm ðgÞ ¼ ð283:7  4:9Þ 1 kJ  mol . 4.2. Computational results

FIGURE 5. Electron density contour of the (a) HOMO and (b) LUMO orbitals (isovalue 0:02e  a3 0 , where a0 is the Bohr radius).

1

C op;m ðgÞ=ðJ  K1  mol Þ ¼ 1:07340  107 ðT=KÞ3  2:35282  104 ðT=KÞ2 þ 5:90574  101 ðT=KÞ  7:48823  101 :

ð5Þ

4.2.1. Geometry, natural population analysis, electrostatic potential map and HOMO and LUMO orbitals Geometrical parameters of the isolated planar 4-nitro-benzothiadiazole structure optimized at the B3LYP/6-31G(d) level of theory are given in figure 2. In order to get a more detailed analysis of the effect of the introduction of the nitro group in the 4 position of the 2,1,3-benzothidiazole molecule, we present in figures 3 and 4 the natural population charge (a), from natural population analysis (NPA), and the electrostatic potential map (b) from total self consisting field density, of the 2,1,3-benzothidiazole and 4nitro-2,1,3-benzothidiazole molecules, respectively, determined

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TABLE 5 Working reactions for 4-nitro-2,1,3-benzothiadiazole and correspondent values for the enthalpies of reaction and formation in the gaseous-phase, at T = 298.15 K.

DRH(g)/(kJ  mol1)

Df Hm ðgÞ=ðkJ  mol1 Þ

Da/(kJ  mol1)

ð6Þ

6871.10

276.3b 278.4c

7.4 5.3

ð7Þ

109.27

287.0

3.3

ð8Þ

54.63

290.8

7.1

ð9Þ

51.53

287.8

4.1

ð10Þ

48.96

288.8

5.1

ð11Þ

28.34

289.7

6.0

ð12Þ

13.50

284.7

1.0

ð13Þ

13.07

292.4

8.7

ð14Þ

1.94

284.8

1.1

ð15Þ

29.66

285.4

1.7

ð16Þ

27.08

286.3

2.6

Working reactions NO2 N N

S

6 C + 3 H + 2 O + +3N + S

NO2 N N

O2 N S

+

S

+

N

+

N H

S

NO2 N N

O2 N

NO2 N N

N

+

N H

S

O2N S

+

S

+

N H

N

+

S

NO2 N N

O2 N

N H

N

+

S

NO2

NO2 N N

S

N

+

S

N

+

NO2

NO2 N N

S

N

+

N

S

+

NO2

NO2 N N

-

S

N

+ N

N

S

+

N

NO2

NO2 N N

S

N

+

N

N

N S

+

NO2 N N

S

+

S

+

N H

N

N N

O2 N S

+

S

+

N H

N

NO2 N N

N H

N

N N

O2 N

N H

N

(continued on next page)

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TABLE 5 (continued)

DRH(g)/(kJ  mol1)

Working reactions NO2 N N

N S

+

S

+

N

N H

N

O2 N S

+

S

+

NO2 N N

N N H

N

N H

N

O2 N

Df Hm ðgÞ=ðkJ  mol

b c d

Þ

Da/(kJ  mol1)

ð17Þ

33.76

294.4

10.7

ð18Þ

35.76

284.9

1.2

N H

h286.2 ± 6.6di a

1

2.5

D corresponds to Df Hm ðcalc; gÞ  Df Hm ðexp; gÞ. Uncorrected gas-phase enthalpy of formation. BAC-corrected gas-phase enthalpy of formation. Mean value from the enthalpies of formation calculated with reactions (6) to (12), (14) to (16) and (18).

N

N S

N O

N

N

A - (276.5 ± 2.5) [51]

C - (300.2 ± 2.1) [8]

(7.2 ± 5.5)

(6.4 ± 6.4)

O

N

O

N

O

O

N

N

O

E – (298.5 ± 2.2) [8] (1.4 ± 3.4)

O

O

O

N

N S

N

O

O

N

N

N

O

B - (283.7 ± 4.9)

a

D – [306.6 ± 6.2] [9] b

F – (299.9 ± 2.6) [9]

SCHEME 1. Enthalpic increments (values in kJ  mol1) for the substitution of hydrogen atom (–H) by a nitro (–NO2) group in benzene ring of the diazole derivatives: A – 2,1,3-benzothiadiazole; B – 4-nitro-2,1,3-benzothiadiazole; C – benzofurazan; D – 4-nitrobenzofurazan; E – benzofuroxan; F – 4-nitrobenzofurazan-1-oxide. aThis work and b estimated value.

by computational studies based on Natural Bond Orbital (NBO) theory [49]. A colour spectrum is presented in the electrostatic potential map, with red as the lowest electrostatic potential energy value (higher charge density) and blue as the highest (lower charge density), to convey the varying intensities of the electrostatic potential energy values. Analyzing the natural population charge and the electrostatic potential map for 2,1,3-benzothidiazole molecule, it is possible to verify a symmetry in the atomic charges, but with the nitro group in the position 4 it is evidenced that there is an electronic delocalization into this group. This behaviour is reasonable given the nitro substituent characteristic, a strong p acceptor and also a strong r acceptor since the point of attachment to the ring is at the nitrogen atom. From the electrostatic potential map of 4-nitro-2,1,3-benzothidiazole molecule, it is possible to identify a particular electronic concentration on nitro group (low potential energy) which reveals its strong affinity for interacting with charged particles nearby. In figure 5 are presented the HOMO (a) and LUMO (b) orbitals of the 4-nitro-2,1,3-benzothidiazole, where LUMO map provides an indicatory for nucleophilicity.

4.2.2. Enthalpy The numerical values calculated for the enthalpies of reaction and of formation, at T = 298.15 K, of the isolated 4-nitro-2,1,3-benzothiadiazole compound, considering different gas-phase working reactions appear in table 5, respectively, together with deviations from the calculated and experimental Df Hm ðgÞ. The G3(MP2)// B3LYP absolute enthalpies and the experimental gas-phase enthalpies of formation, at the T = 298.15 K, for all the species considered in this work (title compound and auxiliary species appearing in the equations in table 5) are given as supporting information (table S2). In the calculation of the enthalpy of formation of the 4-nitro-2,1,3benzothiadiazole, thirteen working reactions (equations (6) to (18)) were considered, yielding values ranging from (276.3 to 294.4) kJ  mol1. Upon the introduction of BAC corrections on equation (6), the calculated enthalpy of formation of 4-nitro2,1,3-benzothidiazole becomes 278.4 kJ  mol1, which is near from the experimental result (D = 5.3 kJ  mol1). Considering the estimated values of the molar enthalpy of formation for 4-nitro-2,1,3benzothiadiazole, in the gaseous phase, from equations (6) to (12),

M.D.M.C. Ribeiro da Silva et al. / J. Chem. Thermodynamics 49 (2012) 146–153

(14) to (16) and (18) the mean value obtained is from (286.2 ± 6.6) kJ  mol1, (being the uncertainty assigned equal to twice the standard deviation of the mean) which is in good agreement with 1 the experimental result, Df Hm ðgÞ ¼ ð283:7  4:9Þ kJ  mol . 5. Final remarks Good agreement is found between experimental (283.7 ± 4.9) kJ  mol1 and computational (286.2 ± 6.6) kJ  mol1 standard molar enthalpies of formation, at T = 298.15 K, of 4-nitro-2,1, 3-benzothiadiazole in the gas-phase, which supports previous evidences that the computational approach considered in this work is an excellent choice when dealing with sulphur-containing compounds [50]. The Df Hm ðgÞ obtained in this work for 4-nitro-2,1,3-benzothiadiazole together with the values of 2,1,3-benzothiadiazole [51], benzofuran [8], 4-nitrobenzofurazan [9], benzofuroxan [8], and 4-nitrobenzofurazan-1-oxide [9] were employed to calculate the enthalpic increments, which appear in scheme 1, concerning the substitution of the hydrogen atom (–H) in benzene ring of the diazole derivatives by a nitro (–NO2) group. To the formerly referred to substitutions are associated enthalpic increments of 2,1,3-benzothiadiazole ? 4-nitro-2,1,3-benzothiadiazole (7.2 ± 5.5) kJ  mol1, benzofurazan ? 4-nitro-benzofurazan (6.4 ± 6.5) kJ  mol1 and benzofuroxan ? 4-nitrobenzofurazan-1-oxide (1.4 ± 3.4) kJ  mol1. From these enthalpic increments, it is possible to conclude that the substitution of the hydrogen atom by a nitro group in the 4th position (adjacent position to the ‘‘junction’’ of the two cycles) of these diazole derivatives is enthalpically not favourable. Acknowledgements Thanks to Fundação para a Ciência e a Tecnologia, Lisbon, Portugal, for financial support to Centro de Investigação em Química of the University of Porto (CIQ – UP) and to FEDER for financial support to the research project POCTI/44471/QUI/2002. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.jct.2012.01.018. References [1] M.A.V. Ribeiro da Silva, M.D.M.C. Ribeiro da Silva, M. Agostinha, R. Matos, P. Jimenez, M.V. Roux, J. Elguero, R. Claramunt, P. Cabildo, A. Sanchez-Migallón, J. Chem. Thermodyn. 31 (1999) 129. [2] O. Mó, M. Yáñez, M.V. Roux, P. Jimenez, J.Z. Dávalos, M.A.V. Ribeiro da Silva, M.D.M.C. Ribeiro da Silva, M.A.R. Matos, L.M.P.F. Amaral, A. Sánchez-Migallon, P. Cabildo, R. Claramunt, J. Elguero, J.F. Liebman, J. Phys. Chem. A 103 (1999) 9336. [3] P. Jimenez, M.V. Roux, J.Z. Dávalos, M. Temprado, M.A.V. Ribeiro da Silva, M.D.M.C. Ribeiro da Silva, L.M.P.F. Amaral, P. Cabildo, R.M. Claramunt, O. Mó, M. Yáñez, J. Elguero, Mol. Phys. 102 (2004) 711. [4] M.A.V. Ribeiro da Silva, M.D.M.C. Ribeiro da Silva, L.M.P.F. Amaral, J. Elguero, P. Jimenez, M.V. Roux, J.Z. Dávalos, M. Temprado, P. Cabildo, R. Claramunt, O. Mó, M. Yáñez, J. Chem. Thermodyn. 37 (2005) 1168. [5] M.D.M.C. Ribeiro da Silva, S.C.C. Ferreira, I.A.P. Rodrigues, L.C.M. Silva, W.E. Acree Jr., S. Pandey, L.E. Roy, J. Chem. Thermodyn. 33 (2001) 1227. [6] M.A.V. Ribeiro da Silva, M.D.M.C. Ribeiro da Silva, L.M.P.F. Amaral, P. Jimenez, M.V. Roux, J.Z. Dávalos, M. Temprado, P. Cabildo, R.M. Claramunt, J. Elguero, O. Mó, M. Yáñez, J. Chem. Thermodyn. 36 (2004) 533. [7] L. Infantes, O. Mó, M. Yáñez, M.V. Roux, P. Jimenez, J.Z. Dávalos, M. Temprado, M.A.V. Ribeiro da Silva, M.D.M.C. Ribeiro da Silva, L.M.P.F. Amaral, P. Cabildo, R. Claramunt, J. Elguero, J. Phys. Chem. A 110 (2006) 2535. [8] M.L.P. Leitão, G. Pilcher, W.E. Acree Jr., A.I. Zvaigzne, S.A. Tucker, M.D.M.C. Ribeiro da Silva, J. Chem. Thermodyn. 22 (1990) 923. [9] W.E. Acree Jr., S.G. Bott, S.A. Tucker, M.D.M.C. Ribeiro da Silva, M.A.R. Matos, G. Pilcher, J. Chem. Thermodyn. 28 (1996) 673.

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JCT-11-594