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Synthesis, thermochemical and quantum chemical studies on antimony(III) and bismuth(III) complexes with 2,2′-bipyridine and 1,10-phenanthroline
Thermochimica Acta 676 (2019) 234–240
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Synthesis, thermochemical and quantum chemical studies on antimony(III) and bismuth(III) complexes with 2,2′-bipyridine and 1,10-phenanthroline
T
Evandro Paulo Soares Martinsa, , Gerd Bruno Rochab, José de Alencar Simonic, José Geraldo de Paiva Espínolab ⁎
a
Universidade Estadual do Piauí, 64260-000, Piripiri-PI, Brazil Departamento de Química, CCEN, Universidade Federal da Paraíba, Brasil, 58059-900 João Pessoa, Paraíba, Brazil c Instituto de Química, Universidade Estadual de Campinas, Brasil, Caixa Postal, Campinas, São Paulo, Brazil b
ARTICLE INFO
ABSTRACT
Keywords: Antimony(III) complex Bismuth(III) complex Thermochemical parameters Calorimetric study DFT calculations
A thermochemical study of [SbCl3(L)] and [BiBr3(L)] complexes, wherein L is 2,2′-bipyridine (bpy) or 1,10phenanthroline (phen), was performed by calorimetric measurements in solution. The complexes were synthesized and characterized by elemental analysis, FTIR spectroscopy and thermal analysis. From the enthalpies of dissolution of the complexes, salts and ligands in combination with auxiliary thermodynamic data, some thermochemical parameters of the complexes were determined by use of thermochemical cycles. Theoretical study on the complexes was performed using M06-2X/def2-TZVPP method. Donor-acceptor bond energies were obtained taking into account reorganization energies of the fragments. Our findings suggest that both the reorganization energy of the acceptor metal trihalide MX3 (113–136 kJ · mol−1) and the rigidity of the phen govern the dissociation energy of the complexes. The theoretical results indicated that the chemical stabilities of the complexes decreases in order [BiBr3(phen)] > [SbCl3(phen)] > [BiBr3(bpy)] > [SbCl3(bpy)], agreeing with the experimental enthalpies of coordination in solid state.
1. Introduction Antimony and bismuth trihalide compounds exhibit a variety of structural forms and have been used in several fields, including medicine [1–3], catalysis [4–6] and solid-state chemistry [7–9]. In recent years, these classes of compounds have been extensively studied in medicine as antimicrobial, anticancer and antiviral agents [10–12]. Recently, the antileishmanial activities of Sb(III) complexes with 2,2′bipiridine (bpy) and 1,10-phenantroline (phen) ligands were investigated [13]. These complexes showed very high activities against Leishmania infantum and Leishmania amanuensis and were significantly more actives than potassium antimony tartrate, which is the reference drug against such parasites. Bismuth compounds are considered biologically safe and nontoxic [14]. Due to these characteristics, these compounds have been extensively investigated in biomedical applications in the treatment of various gastrointestinal disorders and microbial infections, including syphilis, diarrhea and gastritis [14]. In addition, bismuth compounds play an important role in organic synthesis, acting as Lewis acid catalysts in aldolization, alkylation, arylation, amination, cycloaddition, cycloisomerization, epoxide ring opening, etherification, ⁎
hydroalkylation, hydroarylation and oxidation reactions [4,6]. Thermochemical studies of Sb(III) complexes with monodentate aromatic amines, pyridine and its derivatives, 2-methypyridine and 3methypyridine, were carried out in some papers [15–17]. Such studies are important to understand the forces involved in the coordination reaction, as well as the energy associated with the formation of Sb(III) complexes in the solid state. Reports on the synthesis, infrared and electronic spectra, and structural determination of Sb(III) and Bi(III) complexes with bpy and phen can be found in the literature [13,18,19]. Although the structures of [SbCl3(bpy)] and [SbCl3(phen)] complexes are already known [19,20], there is no information on the thermochemical data of theses complexes in condensed phase. In this paper, we have determined some thermochemical parameters of the Sb(III) and Bi(III) complexes with bpy and phen ligands. Additionally, the molecular geometries, thermochemical data of complexes in the gas phase and donor-acceptor bond energies were calculated by means of density functional theory (DFT). These thermochemical properties can be used in the interpretation of their chemical stabilities as well as in catalysis and solidstate chemistry applications.
Corresponding author. E-mail address: [email protected] (E.P.S. Martins).
https://doi.org/10.1016/j.tca.2019.05.005 Received 1 February 2019; Received in revised form 30 April 2019; Accepted 5 May 2019 Available online 06 May 2019 0040-6031/ © 2019 Elsevier B.V. All rights reserved.
Thermochimica Acta 676 (2019) 234–240
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2. Experimental
Table 1 Experimental elemental analysis data for the Sb(III) and Bi(III) complexes.
2.1. Synthesis of the complexes All the solvents were distilled through an efficient column and stored over Linde 4 Å molecular sieves. The salts of antimony trichloride (Sigma-Aldrich, 99%) and bismuth tribromide (JassenChimica, 98%) were sublimed and stored under vacuum. All preparations and manipulations were performed under dry conditions in nitrogen atmosphere. The 2,2′-bipiridine (bpy) and 1,10-phenantroline (phen) (Sigma-Aldrich, 99%) ligands were recrystallized from 2-propanone using the following procedure. In a 0.1 dm3 schlenk, the respective solid was dissolved to obtain a concentrated solution. Crystallization was achieved from slow evaporation of the solvent in a vacuum line at room temperature. The crystals formed were filtered off, dried in a vacuum and stored in a schlenk. The complexes were prepared by the mixing of an equimolar amount (≈ 6.3 mmol) of both reactants in propanone under stirring, i.e., the amine solution was added to the SbCl3 and BiBr3 solution under stirring, which was maintained this way for 3 h. After solvent has been removed by filtration, the solids were washed with propanone and dried under reduced pressure. The yields were about 80%. The halide contents were determined by the Volhard method with a standard 0.1 mol · dm−3 AgNO3 solution after dissolution of the complexes in a 6 mol · dm−3 HNO3 aqueous solution.
Compounds
%C
[SbCl3(bpy)] [SbCl3(phen)] [BiBr3(bpy)] [BiBr3(phen)]
Calc. 31.25 35.30 19.86 22.92
%H Found 31.21 35.34 19.90 23.01
Calc. 2.10 1.97 1.33 1.28
%N Found 2.20 1.51 1.20 1.24
Calc. 7.29 6.86 4.63 4.45
%X Found 6.78 6.85 4.53 4.51
Calc. 27.68 26.05 39.63 38.12
Found 27.45 26.52 39.01 39.02
Being Calc. = calculated; X = Cl or Br.
5.8 kJ · mol−1. Since counterpoise method generally overestimates BSSE, we computed the reactions energies without BSSE correction [28]. 3. Results and discussion The interaction of SbCl3 and BiBr3 with bpy and phen in propanone solution leads to the formation of yellow solids with a 1:1 stoichiometry. The experimental elemental analysis data are in good agreement with the expected values, as shown in Table 1. 3.1. FTIR spectral analysis The spectra of the ligands and metal complexes in the solid state were recorded in the range of 4000−400 cm−1 in KBr pellets in a Fourier transform infrared (FTIR) spectrometer. The vibrational frequencies of the free ligands and its complexes are listed in the Table 2. The experimental FTIR spectra of the complexes in the 1600−400 cm−1 region were consistent with coordinated bpy and phen [19,29]. The ring stretching vibrations are very important in the spectrum of heterocyclic amines since they are highly characteristic of the aromatic ring itself. The C⎯C and C⎯N stretching vibrational modes founds in the 1578−1415 cm−1 (bpy) and 1449–1505 cm−1 (phen) ranges showed relevant changes in FTIR spectra of complexes compared to the free ligands (see Table 2), confirming the coordination of two N atoms to Sb and Bi. Furthermore, the bands of bending in the plane for bpy at 652 and 618 cm−1 are displaced to 697 and 684 cm-1 in [SbCl3(bpy)], and to 646 and 639 cm−1 in [BiBr3(bpy)] complex, respectively. For Sb(III) and Bi(III) phen complexes, the bands of bending in plane of phen in the range of 736−621 cm−1 are displaced to 720−645 cm−1 in the complexes.
2.2. Instrumental analysis The carbon, nitrogen and hydrogen contents were determined on a Perkin-Elmer model 2400 analyzer. The infrared spectra at room temperature were determined using KBr windows technique on a Bomem spectrometer MB series in the frequency range of 4000–400 cm−1 at a resolution of 4 cm−1 with 30 scans. TGA curves were obtained using a Shimadzu TG-50 thermo-balance in dynamic nitrogen atmosphere with a flow of 50 cm3 min−1 using sample masses of 5.0 ± 0.5 mg and a heating rate of 10 K · min−1. The calorimetric measurements were performed in a LKB 2225 precision isoperibol calorimeter. Ampoules containing 20–50 mg of reactant were prepared in a dry-box and broken in the glass reaction vessel charged using 25 cm3 of the calorimetric solvent at 298.15 ± 0.02 K. All reactants and complexes investigated in this study were soluble in dimethyl sulfoxide (DMSO) or dimethylacetamide (DMA), the chosen solvents. The accuracy of the calorimetric measurements was checked by measuring the dissolution enthalpy of tris-(hydroxymethyl) aminomethane in a 0.1 mol · dm-3 standard hydrochloric acid solution. The value obtained, agrees with the value of −29.7 ± 0.1 kJ · mol−1, -29.770 ± 0.032 kJ · mol−1 reported elsewhere [21].
3.2. Thermogravimetric analysis Thermogravimetric analysis of complexes were carried out at 30–900 °C under nitrogen atmosphere. The assignment of the decomposition stages of the complexes was carried out from the analysis of thermogravimetric curves (TGA) and their derivatives (DrTGA), Fig.1 and Fig. 2. The TGA curves of the Sb(III) complexes show the decomposition process in one step of mass loss. The decomposition of [SbCl3(bpy)] complex occurs in the range (177–278 °C), with mass loss of 95.8%, Fig.1(a), while the decomposition of the [SbCl3(phen)] occurs in the range (200–350 °C), with mass loss of 96.6%. The TGA/DrTGA curves of the Bi(III) complexes show the decomposition process in two steps of weight loss, Fig. 2. The TGA curve of the [BiBr3(bpy)] shows two overlapping decomposition stages, in the range (258–375 °C) with mass loss of 97.9%. The thermal analysis of [BiBr3(phen)], Fig. 2 (b), shows two stages of mass loss, associated with elimination of the complex in the range (301–847 °C), with weight loss of 99.9%. The thermal analysis indicate that the thermal stability of the complexes in solid phase decreases in the order: [BiBr3(phen)] > [BiBr3(bpy)] > [SbCl3(phen)] > [SbCl3(bpy)].
2.3. Computational methodology All DFT calculations were performed using the Gaussian 09 program, version c.01 [22]. The molecular structures of the all compounds were optimized in the gas phase, using density functional theory (DFT). The molecular structures of the compounds were attested to be minima on their respective potential energy surfaces using a vibrational frequency analysis, wherein the real minimum molecular structure must exhibit positive values for all frequencies. All the calculations were performed using a hybrid meta exchange-correlation density functional (DFT) M06-2X [23] with def2-TZVPP basis set [24] for C, N and H, and an effective core potential with relatively small core [25] was used for Sb and Bi. The choice of M06-2X method was based on its performance in predicting thermochemical data and geometric effects of sterically active lone electron pairs of the Sb(III) and Bi(III) compounds [26]. The dissociation energies of the complexes were corrected for zero point vibration energies (ZPVE). Basis set superposition errors (BSSE), estimated by counterpoise method [27], were found in the range 4.6235
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Table 2 Some infrared frequency dada (cm−1) for free 2,2′-bipyridine and 1,10-phenanthroline and its Sb(III) and Bi(III) complexes. Assignments
bpy
[SbCl3(bpy)]
[BiBr3(bpy)]
phen
[SbCl3(phen)]
[BiBr3(phen)]
νas(CH) νs(CH) ν(CC,CN) ν(CC,CN) ν(CC,CN) ν(CC,CN) β(CH) δ(NCC,CCC) δ(CCN, CCC)
3082w 3053w 1578s 1557m 1452s 1415m 758s 652w 618w
3090w 3061w 1600m 1585s 1527s 1430w 760s 697w 684w
3099w 3053w 3052w 1492m 1472w 1436s 766s 646w 639w
3058w 3030w 1503m 1492m 1419m 1340w 852s 736s 621w
3075w 3055w 1515m 1488w 1421m 1340w 854s 715m 645w
n.o. 3050w 1516m 1491w 1425m 1341w 851s 720m 643w
Abbreviation/symbols: ν, stretch; νas ; asymmetric stretch; νs ; symmetric stretch; δ, bending in plane; β, out-of-plane bending; Intensity of bands: s, strong; m, medium; w, weak, n.o.: not observed.
3.3. Computational studies In order to get more insight into the stabilities and geometries of the Sb(III) and Bi(III) complexes, quantum chemical computations were carried out. The ground state geometries and thermodynamic characteristics of the complexes in gas phase were calculated by means of M06-2X/def2-TZVPP method. Computed structural parameters of the Sb(III) complexes were compared with experimental data of singlecrystal X-ray [19,20]. Direct comparison between computed and experimental values for [BiBr3(L)] (L = bpy or phen) complexes was not possible due to the lack of experimental data. Optimized structures of complexes revealed a distorted square pyramidal geometry around metal center, (see Fig.3), consistent with the experimental geometries of the Sb(III) complexes in the solid state [19,20]. In these structures, the halogen atoms occupy equatorial position and nitrogen atoms occupy both equatorial and axial positions. The distortions from ideal square pyramidal geometry can be attributed to the influence of a stereochemically active lone pair of the antimony and crystal packaging. Selected theoretical and experimental geometric parameters such as bond lengths and bond angles are listed in Table 3. As observed in the solid state, calculated structures reveal equatorial Sb⎯N12 distances longer than the axial Sb⎯N6 distances by ca. 0.1 and 0.2 Å, for [SbCl3(bpy)] and [SbCl3(phen)] complexes, respectively. The differences comes from the repulsion of the sterically active lone electron pair of the antimony. The calculated Sb⎯N bond lengths by M06-
Fig. 1. TGA/DrTGA curves of (a) [SbCl3(bpy)] and (b) [SbCl3(phen)] complexes.
Fig. 3. Optimized structures of Sb(III) and Bi(III) complexes obtained by means of M06-2X/def2-TZPP theoretical level with effective core potential for Sb and Bi elements.
Fig. 2. TGA/DrTGA curves of the (a) [BiBr3(bpy)] and (b) [BiBr3(phen)] complexes. 236
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Table 3 Some experimental [19,20] and calculated (M06-2X/def2-TZVPP) geometric parameters of Sb(III) complexes. [SbCl3(bpy)] Parameters Bond length (Å) SbeN6 SbeN12 SbeCl2 SbeCl3 SbeCl4 Bond angles (°) Cl2eSbeCl3 Cl2eSbeCl4 Cl3eSbeCl4 Cl2eSbeN6 Cl2eSbeN12 Cl3eSbeN6 Cl3eSbeN12 Cl4eSbeN6 Cl4eSbeN12 N6eSbeN12
Table 5 Calculated (M06-2X/def2-TZVPP) standard dissociation enthalpies (kJ·mol−1) and entropies (J · mol−1 K−1) and values of the temperature, Tk=1(K), at which the equilibrium constant for the dissociation of the Sb(III) and Bi(III) complexes in gas phase is one.
[SbCl3(phen)]
Experimental
Calculated
Experimental
Calculated
Process
ΔdissH°
ΔdissS°
Tk=1
2.243 2.319 2.506 2.549 2.588
2.340 2.437 2.429 2.513 2.521
2.241 2.397 2.501 2.580 2.549
2.339 2.458 2.430 2.518 2.518
[SbCl3(bpy)] ⟶ SbCl3 + bpy [SbCl3(phen)] ⟶ SbCl3 + phen [BiBr3(bpy)] ⟶ BiBr3 + bpy [BiBr3(phen)] ⟶ BiBr3 + phen
36.3 65.0 59.8 91.1
159.6 158.7 150.5 160.5
228 410 398 568
93.2 90.1 162.0 88.1 158.9 80.1 85.6 82.4 85.0 70.9
93.2 92.6 152.1 88.6 156.2 76.4 83.7 76.5 80.1 67.7
86.9 95.6 161.4 86.0 155.1 81.8 80.7 80.0 89.8 71.0
93.5 93.3 151.6 87.7 156.3 76.4 81.5 76.4 81.2 68.6
energies of the Sb(III) complexes are lower than the analogous Bi(III) complexes, while bond energies values are almost the same. This difference is mainly attributed to the reorganization energy of the acceptor, about 136 kJ · mol−1 for SbCl3 and 113 kJ · mol−1 for BiBr3. Therefore, the reorganization energy of the group 15 halides plays a predominant role in the energetics of formation of their complexes with bpy and phen ligands. As expected, the reorganization energies of the donor fragment are lower than the acceptor one, computed in the range 1.6–4.1 kJ · mol−1. For trans-conformation of the nitrogen atoms in the free bpy, the value of reorganization energy is, on average, 34.6 kJ · mol−1. Upon coordination, the nitrogen atoms of the bpy take a cisconformation. Taking into account the trans-cis reorganization energy (32.5 kJ · mol−1), we obtain that the EDreorg of cis-bpy conformer are in range 1.6–2.6 kJ · mol−1. Comparison of the complexes with the same metal trihalide shows that donor-acceptor bond energy of the [MX3(phen)] complexes are, in average, 31.6 kJ · mol−1 higher. To assess the relative stabilities of the complexes in the gas phase, we have calculated the temperature in which the equilibrium constant for the complex dissociation process is equals to one [31] (see Table 5). It may be estimated using standard dissociation enthalpies and entropies: Tk=1≈ΔdissH°/ΔdissS°. The calculated thermodynamic parameters represent the dissociation from the ground-state reactant complexes to ground-state products. The ground-state trans-bpy conformer is planar, whereas the aromatic ring of the cis-bpy conformer are twisted by 36.9°, which lies 25.7 kJ · mol−1 higher in energy. According to Tk=1 values, phen complexes are most stable in gas phase, with Tk=1 values in range 410–568 K, this behavior is due to the enthalpy factor. Upon dissociation of the complexes, the free bpy takes on trans-conformation, more stable that cis-conformation in about 25.7 kJ · mol−1. Therefore, less energy is required for dissociation of the bpy complexes and it is the main source of the difference in the ΔdissH° of the [MX3(bpy)] and [MX3(phen)].
2X/def2-TZVPP theoretical level are in average 0.1 Å larger than experimental values. The experimental Sb⎯Cl bond lengths are longer than the calculated ones by ca. 0.1 Å, for both [SbCl3(bpy)] and [SbCl3(phen)] complexes. In general, calculated bond lengths are in good agreement with experimental values. The SbeNeC bond angles were calculated in the range 118.7–120.7° for [SbCl3(bpy)] and 116.1–123.8° for [SbCl3(phen)] complex. These angles differ from the experimental values in about 0.9 and 2.0°, respectively. The N6eSbeN12 bond angles calculated for Sb (III) complexes are smaller than experimental values, suggesting that steric effects of the antimony’s lone electron pair in the Sb(III) complexes in gas-phase is larger than in the solid-state. These findings were also observed in the study carried out by Haiges et al [26]. The Cl3eSbeN6 and Cl3eSbeN12 bond angles in the solid-state structure of the [SbCl3(phen)] complex are longer than the calculate ones in gas phase by ca. 5.4 and 8.5 Å. These structural deviation can be mainly attributed to the intermolecular interactions in the solid state structure which are absent in the gas phase. The energies of the donor-acceptor bond (EDA) for Sb(III) and Bi(III) complexes were estimated by using an approach proposed by Timoshkin et al [28,30]. In this approach, the energy of the donoracceptor bond can be estimated based on the dissociation energy (ΔEdiss) of the complexes and reorganization energies of the donor ligands (EDreorg) and acceptor metal trihalide (EAreorg) including basis set superposition error (BSSE) of the donor and acceptor fragments, respectively. The reorganization energies were calculated as the difference of the total energy of the free fragment and fragment within the complex. In the present study, we computed reorganization energies for the donor and acceptor fragments and calculated EDA without BSSE corrections:
EDA = Ediss + Ereorg + Ereorg D A
3.4. Calorimetric measurements The enthalpies of reaction in the solid-state (ΔrH°m(s)) were obtained from the enthalpies of dissolution of metal trihalides (Δ1H°m), the enthalpies of reaction for the formation of the complexes in solution (Δ2H°m) and the enthalpies of dissolution of the complexes (Δ3H°m) in dimethyl sulfoxide (DMSO) or dimethylacetamide (DMA). This information is detailed in Eqs. (2)–(5) and the corresponding data are presented in Table 6.
(1)
In the Table 4 are listed the dissociation, reorganization and bond energy for the Sb(III) and Bi(III) complexes. In general, the dissociation Table 4 Dissociation, reorganization and donor-acceptor bond energy (kJ · mol−1) for the Sb(III) and Bi(III) complexes calculated by M06-2X/def2-TZVPP method. Compounds
ΔEdiss
EDreorg
EAreorg
EDA
[SbCl3(bpy)] [SbCl3(phen)] [BiBr3(bpy)] [BiBr3(phen)]
44.2 73.5 67.6 99.5
2.6 4.1 1.6 2.8
136.5 136.4 113.2 112.7
183.3 214.0 182.5 215.0
MX3(s) + solvent ⟶ solution A Δ1H°m
(2)
L(s) + solution A ⟶ solution B Δ2H°m
(3)
[MX3(L)](s) + solvent ⟶ solution C Δ3H°m
(4)
Solution B ⟶ solution C Δ4H°m
(5)
The application of the of Hess’ law to the Eqs. (2)–(5) gives the standard enthalpies of coordination in solid-state (ΔrH°m(s)):
237
MX3(s) + L(s) ⟶ [MX3(L)](s) ΔrH°m(s)
(6)
ΔrH°m(s) = Δ1H°m + Δ2H°m − Δ3H°m
(7)
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Table 6 Standard molar enthalpies of dissolution and coordination reaction in dimethyl sulfoxide and dimethylacetamide at 298.15 K. Process
Nº of experiments
i
(ΔiH°m ± s )/kJ · mol−1
SbCl3(s) + (CH3)2SO(l) bpy(s) + SbCl3(sol) [SbCl3(bpy)](s) + (CH3)2SO(l) phen(s) + SbCl3(sol) [SbCl3(phen)](s) + (CH3)2SO(l) BiBr3(s) + (CH3)2SO(l) bpy(s) + BiBr3(sol) [BiBr3(bpy)](s) + (CH3)2SO(l) BiBr3(s) + (CH3)2NCOCH3(l) phen(s) + BiBr3(sol) [BiBr3(phen)](s) + (CH3)2NCOCH3(l)
5 5 5 4 4 5 4 5 4 4 4
2 3 4 3 4 2 3 4 2 3 4
−59.6 ± 1.5 15.4 ± 0.4 10.2 ± 0.2 2.6 ± 0.3 11.7 ± 0.3 −82.5 ± 2.2 20.6 ± 1.5 −9.97 ± 1.1 −76.4 ± 0.9 −5.5 ± 0.3 −11.6 ± 0.7
s=
n (X X¯ )2 i=1 i (n 1)
Table 8 Complementary enthalpies (kJ mol−1) of metal trihalides and ligands at 298.15 K. Compounds SbCl3 BiBr3 bpy phen a b c d e f
measurement; X¯ = mean value.
The enthalpy of dilution, Eq. 5, Δ4H°m, correspond to the infinite dilution state for each solute and under these conditions Δ4H°m ≈ 0. The ΔrH°m(s) values were calculated by using Eq. (7) and they are listed in Table 7. These enthalpies can be used to compare the basicity of the two ligands when the metal trihalide is kept the same. As expected, the basicity of phen is larger than the basicity of bpy, agreeing with the observed trend in the enthalpies of reactions in gas phase, calculated by M06-2X/def2-TZVPP method (Table 7). Compared to bpy, the phen ligand is characterized by two nitrogen donor atoms being held juxtaposed, and therefore, pre-organized for strong and entropically favored metal binding [32]. Consequently, the rigidity of the phen ligand should give its complexes greater thermodynamic stability as compared to its less pre-organized bpy. The standard enthalpies of formation of the complexes in the solid state (ΔfH°m(s)) were calculated from the enthalpies of coordination, ΔrH°m(s), and the enthalpies of formation of the ligands and metal trihalides in the solid state, using Eq.(8). The values of ΔfH°m(s) of complexes were obtained from the data in Table 8 and are shown in Table 7. For phen ligand, the ΔfH°m(s) was derived from of enthalpy of formation in gas phase (ΔfH°m(g)), calculated by quantum chemical composite method G4 [33] and experimental sublimation enthalpy (ΔsgH°m) using Eq.(9). The G4 method were used by Riou and Bouchoux [33] to determine accurate enthalpies of formation in gas phase for 2,2′-, 4,4′-and 2,4′-bipyridines and 1,10-phenantroline. For the set of reference compounds: ethane, benzene, toluene, biphenyl, pyridine, 2-methy pyridine and 4-methyl pyridine, the authors reported that the G4 methods provide enthalpies of formation in excellent agreement with experimental data (average deviation of 0.9 kJ · mol−1). ΔfH°m(s)(phen) = ΔfH°m(g) − Δs H°m
ΔsgH°m
−382.17b ± 0.06 −276.33c ± 2.09 186.1d ± 2.0 209e ± 1
68.2b 115.39c ± 0.17 81.8d ± 2.3 105.6f ± 0.8
Reference [33]. Reference [34]. Reference [35]. Reference [36]. Calculated according to Eq. (9). Reference [37].
[MX3(L)](s) ⟶ MX3(s) + L(g) ΔDH°m
(10)
[MX3(L)](s) ⟶ MX3(g) + L(g) ΔMH°m
(11)
The values of ΔDH°m and ΔMH°m, present in Table 7, were calculated from the standard enthalpies of sublimation of the ligands [34,35], metal trihalides [32,33] and the enthalpies of formation of the complexes in the solid-state: ΔDH°m = ΔrH°m(s) + ΔsgH°m(L)
(12)
g
ΔMH°m = ΔDH°m + Δs H°m(MX3)
(13)
As the complexes decomposed on heating, their enthalpies of sublimation (ΔsgH°m) were estimated by using a combination of experimental lattice enthalpies and the computed (M06-2X/def2-TZVPP) enthalpies of the coordination reactions in gas phase ΔsgH°m = ΔrH°m(g) − ΔMH°m
(14)
The values of standard enthalpies of sublimation, (see Table 7), indicate that the thermal stabilities of the complexes in solid phase decrease in the order: [BiBr3(phen)] > [BiBr3(bpy)] > [SbCl3(phen)] > [SbCl3(bpy)], agreeing with the order of stabilities determined from thermogravimetric analysis. 4. Conclusions Sb(III) and Bi(III) complexes were synthesized by the interaction of the bpy and phen ligands with antimony trichloride and bismuth tribromide in propanone. The dissolution enthalpies of the complexes, salts and reaction enthalpies in solution were obtained by calorimetric experiments, leading to the determination of the enthalpies coordination reaction and formation of complexes in the solid-state. The elemental analysis demonstrated that the compounds were
(8)
g
315a
ΔfH°m(s)
The standard enthalpies of decomposition (ΔDH°m) and the lattice (ΔMH°m) of the complexes were calculated from Eqs. (12) and (13), respectively. These enthalpies correspond to the following processes:
. in which n is the experiment number; Xi = experimental
ΔfH°m(s) = ΔrH°m(s) + ΔfH°m(MX3)(s) + ΔfH°m(L)(s)
ΔfH°m(g)
(9)
Table 7 Thermochemical parameters of Sb(III) and Bi(III) complexes (kJ·mol−1). Compounds
ΔrH°m(s)a
[SbCl3(bpy)] [SbCl3(phen)] [BiBr3(bpy)] [BiBr3(phen)]
−52.3 −66.8 −51.5 −70.3
a b c d e f
± ± ± ±
ΔfH°m(s)b 1.6 1.5 2.9 1.2
−248.4 −239.5 −141.8 −138.0
ΔDH°mc ± ± ± ±
2.6 1.7 4.1 2.5
134.1 172.4 133.3 175.9
Calculated according to Eq. (7). Calculated according to Eq. (8). Calculated according to Eq. (12). Calculated according to Eq. (13). Calculated by M06-2X/def2-TZVPP method. Calculated according to Eq. (14). 238
± ± ± ±
ΔMH°md 2.8 1.7 3.7 1.4
−202.3 −240.6 −248.7 −291.3
± ± ± ±
2.8 1.7 3.7 1.5
ΔrH°m(g)e
Δsg H°mf
−36.3 −65.0 −59.8 −91.1
166 176 189 199
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obtained with 1:1 stoichiometry (metal trihalide/ligand). Based on the ΔrH°m(s) values, basicity of the ligand decrease in order phen > bpy, a result that agrees to the measurements of pKa of the corresponding conjugate acids in water. From the ΔsgH°m values, it is possible to suggest that the intermolecular forces in the solid state are larger for the BiBr3 complexes. Theoretical studies at the M06-2X/def2-TZVPP level of theory revealed that chemical stabilities of complexes decrease in order [BiBr3(phen)] > [SbCl3(phen)] > [BiBr3(bpy)] > [SbCl3(bpy)], in line with experimental values of the enthalpies of coordination in solid state. Comparison of the Sb(III) complexes to the analogous Bi(III) complexes showed that reorganization energy of the metal trihalides is the main contributing factor to the differences in dissociation energy of these complexes. Comparison between the [MX3(phen)] and [MX3(bpy)] indicates that phen complexes exhibit greater ΔdissH° than bpy complexes, where the rigidity of the phen ligand plays a significant role on the stability of its complexes.
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Funding sources This study was in part financed by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior-Brasil (CAPES) through the research project Bioinformática Estrutural de Proteínas: Modelos, Algoritmos e Aplicações Biotecnológicas (Edital Biologia Computacional 51/2013, processo AUXPE1375/2014 da CAPES). G.B.R. acknowledges support from the Brazilian National Council for Scientific and Technological Development (CNPq grant no. 309761/ 2017-4). Acknowledgments The authors gratefully acknowledge the financial support from the Brazilian agencies, Institutes and networks: Instituto Nacional de Ciência e Tecnologia de Nanotecnologia para Marcadores Integrados (INCT-INAMI), Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Coordenação de Aperfeiçoamento de Pessoal de Nível Superior-Brasil (CAPES), Programa de Apoio a Núcleos de Excelência (PRONEX-FACEPE), Financiadora de Estudos e Projetos (FINEP) and Fundação de Apoio à Pesquisa do Estado de São Paulo (FAPESP). The authors also acknowledge the physical structure and computational support provided by Universidade Federal da Paraíba (UFPB) and the computer resources of Centro Nacional de Processamento de Alto Desempenho em São Paulo (CENAPAD-SP) and Chemistry Institute of Campinas State University (UNICAMP). References [1] E.H. Lizarazo-Jaimes, R.L. Monte-Neto, P.G. Reis, N.G. Fernandes, N.L. Speziali, M.N. Melo, F. Frézard, C. Demicheli, Improved antileishmanial activity of dppz through complexation with antimony(III) and bismuth(III): investigation of the role of the metal, Molecules. 17 (2012) 12622–12635. [2] P. Baiocco, G. Colotti, S. Franceschini, A. Ilari, Molecular basis of antimony treatment in leishmaniasis, J. Med. Chem. 52 (2009) 2603–2612. [3] I.I. Ozturk, C.N. Banti, M.J. Manos, A.J. Tasiopoulos, N. Kourkoumelis, K. Charalabopoulos, S.K. Hadjikakou, Synthesis, characterization and biological studies of new antimony(III) halide complexes with ω-thiocaprolactam, J. Inorg. Biochem. 109 (2012) 57–65. [4] J.M. Bothwell, S.W. Krabbe, R.S. Mohan, Applications of bismuth(III) compounds in organic synthesis, Chem. Soc. Rev. 40 (2011) 4649–4707. [5] R. Hua, Recent advances in bismuth-catalyzed organic synthesis, Curr. Org. Synth. 5 (2008) 1–27. [6] T. Ollevier, New trends in bismuth-catalyzed synthetic transformations, Org. Biomol. Chem. 11 (2013) 2740–2755. [7] J. Rodriguez-Castro, P. Dale, M.F. Mahon, K.C. Molloy, L.M. Peter, Deposition of antimony sulfide thin films from single-source antimony thiolate precursors, Chem. Mater. 19 (2007) 3219–3226. [8] Z.M. Handong, Wang Li, Bismuth- Containing Compounds, Springer, New York, 2013.
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[35] A.S. Groups, C. Butler, The thermodynamic properties of bismuth(I) bromide and bismuth(III) bromide, Inorg. Chem. 7 (1968) 208–2011. [36] M.A.V. Ribeiro da Silva, V.M.F. Morais, M.A.R. Matos, C.M.A. Rio, Thermochemical and theoretical studies of some bipyridines, J. Org. Chem. 60 (1995) 5291–5294. [37] B. Brunetti, A. Lapi, S. Vecchio Ciprioti, Thermodynamic study on six tricyclic nitrogen heterocyclic compounds by thermal analysis and effusion techniques, Thermochim. Acta. 636 (2016) 71–84.
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Synthesis, thermochemical and quantum chemical studies on antimony(III) and bismuth(III) complexes with 2,2′-bipyridine and 1,10-phenanthroline
T
Evandro Paulo Soares Martinsa, , Gerd Bruno Rochab, José de Alencar Simonic, José Geraldo de Paiva Espínolab ⁎
a
Universidade Estadual do Piauí, 64260-000, Piripiri-PI, Brazil Departamento de Química, CCEN, Universidade Federal da Paraíba, Brasil, 58059-900 João Pessoa, Paraíba, Brazil c Instituto de Química, Universidade Estadual de Campinas, Brasil, Caixa Postal, Campinas, São Paulo, Brazil b
ARTICLE INFO
ABSTRACT
Keywords: Antimony(III) complex Bismuth(III) complex Thermochemical parameters Calorimetric study DFT calculations
A thermochemical study of [SbCl3(L)] and [BiBr3(L)] complexes, wherein L is 2,2′-bipyridine (bpy) or 1,10phenanthroline (phen), was performed by calorimetric measurements in solution. The complexes were synthesized and characterized by elemental analysis, FTIR spectroscopy and thermal analysis. From the enthalpies of dissolution of the complexes, salts and ligands in combination with auxiliary thermodynamic data, some thermochemical parameters of the complexes were determined by use of thermochemical cycles. Theoretical study on the complexes was performed using M06-2X/def2-TZVPP method. Donor-acceptor bond energies were obtained taking into account reorganization energies of the fragments. Our findings suggest that both the reorganization energy of the acceptor metal trihalide MX3 (113–136 kJ · mol−1) and the rigidity of the phen govern the dissociation energy of the complexes. The theoretical results indicated that the chemical stabilities of the complexes decreases in order [BiBr3(phen)] > [SbCl3(phen)] > [BiBr3(bpy)] > [SbCl3(bpy)], agreeing with the experimental enthalpies of coordination in solid state.
1. Introduction Antimony and bismuth trihalide compounds exhibit a variety of structural forms and have been used in several fields, including medicine [1–3], catalysis [4–6] and solid-state chemistry [7–9]. In recent years, these classes of compounds have been extensively studied in medicine as antimicrobial, anticancer and antiviral agents [10–12]. Recently, the antileishmanial activities of Sb(III) complexes with 2,2′bipiridine (bpy) and 1,10-phenantroline (phen) ligands were investigated [13]. These complexes showed very high activities against Leishmania infantum and Leishmania amanuensis and were significantly more actives than potassium antimony tartrate, which is the reference drug against such parasites. Bismuth compounds are considered biologically safe and nontoxic [14]. Due to these characteristics, these compounds have been extensively investigated in biomedical applications in the treatment of various gastrointestinal disorders and microbial infections, including syphilis, diarrhea and gastritis [14]. In addition, bismuth compounds play an important role in organic synthesis, acting as Lewis acid catalysts in aldolization, alkylation, arylation, amination, cycloaddition, cycloisomerization, epoxide ring opening, etherification, ⁎
hydroalkylation, hydroarylation and oxidation reactions [4,6]. Thermochemical studies of Sb(III) complexes with monodentate aromatic amines, pyridine and its derivatives, 2-methypyridine and 3methypyridine, were carried out in some papers [15–17]. Such studies are important to understand the forces involved in the coordination reaction, as well as the energy associated with the formation of Sb(III) complexes in the solid state. Reports on the synthesis, infrared and electronic spectra, and structural determination of Sb(III) and Bi(III) complexes with bpy and phen can be found in the literature [13,18,19]. Although the structures of [SbCl3(bpy)] and [SbCl3(phen)] complexes are already known [19,20], there is no information on the thermochemical data of theses complexes in condensed phase. In this paper, we have determined some thermochemical parameters of the Sb(III) and Bi(III) complexes with bpy and phen ligands. Additionally, the molecular geometries, thermochemical data of complexes in the gas phase and donor-acceptor bond energies were calculated by means of density functional theory (DFT). These thermochemical properties can be used in the interpretation of their chemical stabilities as well as in catalysis and solidstate chemistry applications.
Corresponding author. E-mail address: [email protected] (E.P.S. Martins).
https://doi.org/10.1016/j.tca.2019.05.005 Received 1 February 2019; Received in revised form 30 April 2019; Accepted 5 May 2019 Available online 06 May 2019 0040-6031/ © 2019 Elsevier B.V. All rights reserved.
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2. Experimental
Table 1 Experimental elemental analysis data for the Sb(III) and Bi(III) complexes.
2.1. Synthesis of the complexes All the solvents were distilled through an efficient column and stored over Linde 4 Å molecular sieves. The salts of antimony trichloride (Sigma-Aldrich, 99%) and bismuth tribromide (JassenChimica, 98%) were sublimed and stored under vacuum. All preparations and manipulations were performed under dry conditions in nitrogen atmosphere. The 2,2′-bipiridine (bpy) and 1,10-phenantroline (phen) (Sigma-Aldrich, 99%) ligands were recrystallized from 2-propanone using the following procedure. In a 0.1 dm3 schlenk, the respective solid was dissolved to obtain a concentrated solution. Crystallization was achieved from slow evaporation of the solvent in a vacuum line at room temperature. The crystals formed were filtered off, dried in a vacuum and stored in a schlenk. The complexes were prepared by the mixing of an equimolar amount (≈ 6.3 mmol) of both reactants in propanone under stirring, i.e., the amine solution was added to the SbCl3 and BiBr3 solution under stirring, which was maintained this way for 3 h. After solvent has been removed by filtration, the solids were washed with propanone and dried under reduced pressure. The yields were about 80%. The halide contents were determined by the Volhard method with a standard 0.1 mol · dm−3 AgNO3 solution after dissolution of the complexes in a 6 mol · dm−3 HNO3 aqueous solution.
Compounds
%C
[SbCl3(bpy)] [SbCl3(phen)] [BiBr3(bpy)] [BiBr3(phen)]
Calc. 31.25 35.30 19.86 22.92
%H Found 31.21 35.34 19.90 23.01
Calc. 2.10 1.97 1.33 1.28
%N Found 2.20 1.51 1.20 1.24
Calc. 7.29 6.86 4.63 4.45
%X Found 6.78 6.85 4.53 4.51
Calc. 27.68 26.05 39.63 38.12
Found 27.45 26.52 39.01 39.02
Being Calc. = calculated; X = Cl or Br.
5.8 kJ · mol−1. Since counterpoise method generally overestimates BSSE, we computed the reactions energies without BSSE correction [28]. 3. Results and discussion The interaction of SbCl3 and BiBr3 with bpy and phen in propanone solution leads to the formation of yellow solids with a 1:1 stoichiometry. The experimental elemental analysis data are in good agreement with the expected values, as shown in Table 1. 3.1. FTIR spectral analysis The spectra of the ligands and metal complexes in the solid state were recorded in the range of 4000−400 cm−1 in KBr pellets in a Fourier transform infrared (FTIR) spectrometer. The vibrational frequencies of the free ligands and its complexes are listed in the Table 2. The experimental FTIR spectra of the complexes in the 1600−400 cm−1 region were consistent with coordinated bpy and phen [19,29]. The ring stretching vibrations are very important in the spectrum of heterocyclic amines since they are highly characteristic of the aromatic ring itself. The C⎯C and C⎯N stretching vibrational modes founds in the 1578−1415 cm−1 (bpy) and 1449–1505 cm−1 (phen) ranges showed relevant changes in FTIR spectra of complexes compared to the free ligands (see Table 2), confirming the coordination of two N atoms to Sb and Bi. Furthermore, the bands of bending in the plane for bpy at 652 and 618 cm−1 are displaced to 697 and 684 cm-1 in [SbCl3(bpy)], and to 646 and 639 cm−1 in [BiBr3(bpy)] complex, respectively. For Sb(III) and Bi(III) phen complexes, the bands of bending in plane of phen in the range of 736−621 cm−1 are displaced to 720−645 cm−1 in the complexes.
2.2. Instrumental analysis The carbon, nitrogen and hydrogen contents were determined on a Perkin-Elmer model 2400 analyzer. The infrared spectra at room temperature were determined using KBr windows technique on a Bomem spectrometer MB series in the frequency range of 4000–400 cm−1 at a resolution of 4 cm−1 with 30 scans. TGA curves were obtained using a Shimadzu TG-50 thermo-balance in dynamic nitrogen atmosphere with a flow of 50 cm3 min−1 using sample masses of 5.0 ± 0.5 mg and a heating rate of 10 K · min−1. The calorimetric measurements were performed in a LKB 2225 precision isoperibol calorimeter. Ampoules containing 20–50 mg of reactant were prepared in a dry-box and broken in the glass reaction vessel charged using 25 cm3 of the calorimetric solvent at 298.15 ± 0.02 K. All reactants and complexes investigated in this study were soluble in dimethyl sulfoxide (DMSO) or dimethylacetamide (DMA), the chosen solvents. The accuracy of the calorimetric measurements was checked by measuring the dissolution enthalpy of tris-(hydroxymethyl) aminomethane in a 0.1 mol · dm-3 standard hydrochloric acid solution. The value obtained, agrees with the value of −29.7 ± 0.1 kJ · mol−1, -29.770 ± 0.032 kJ · mol−1 reported elsewhere [21].
3.2. Thermogravimetric analysis Thermogravimetric analysis of complexes were carried out at 30–900 °C under nitrogen atmosphere. The assignment of the decomposition stages of the complexes was carried out from the analysis of thermogravimetric curves (TGA) and their derivatives (DrTGA), Fig.1 and Fig. 2. The TGA curves of the Sb(III) complexes show the decomposition process in one step of mass loss. The decomposition of [SbCl3(bpy)] complex occurs in the range (177–278 °C), with mass loss of 95.8%, Fig.1(a), while the decomposition of the [SbCl3(phen)] occurs in the range (200–350 °C), with mass loss of 96.6%. The TGA/DrTGA curves of the Bi(III) complexes show the decomposition process in two steps of weight loss, Fig. 2. The TGA curve of the [BiBr3(bpy)] shows two overlapping decomposition stages, in the range (258–375 °C) with mass loss of 97.9%. The thermal analysis of [BiBr3(phen)], Fig. 2 (b), shows two stages of mass loss, associated with elimination of the complex in the range (301–847 °C), with weight loss of 99.9%. The thermal analysis indicate that the thermal stability of the complexes in solid phase decreases in the order: [BiBr3(phen)] > [BiBr3(bpy)] > [SbCl3(phen)] > [SbCl3(bpy)].
2.3. Computational methodology All DFT calculations were performed using the Gaussian 09 program, version c.01 [22]. The molecular structures of the all compounds were optimized in the gas phase, using density functional theory (DFT). The molecular structures of the compounds were attested to be minima on their respective potential energy surfaces using a vibrational frequency analysis, wherein the real minimum molecular structure must exhibit positive values for all frequencies. All the calculations were performed using a hybrid meta exchange-correlation density functional (DFT) M06-2X [23] with def2-TZVPP basis set [24] for C, N and H, and an effective core potential with relatively small core [25] was used for Sb and Bi. The choice of M06-2X method was based on its performance in predicting thermochemical data and geometric effects of sterically active lone electron pairs of the Sb(III) and Bi(III) compounds [26]. The dissociation energies of the complexes were corrected for zero point vibration energies (ZPVE). Basis set superposition errors (BSSE), estimated by counterpoise method [27], were found in the range 4.6235
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Table 2 Some infrared frequency dada (cm−1) for free 2,2′-bipyridine and 1,10-phenanthroline and its Sb(III) and Bi(III) complexes. Assignments
bpy
[SbCl3(bpy)]
[BiBr3(bpy)]
phen
[SbCl3(phen)]
[BiBr3(phen)]
νas(CH) νs(CH) ν(CC,CN) ν(CC,CN) ν(CC,CN) ν(CC,CN) β(CH) δ(NCC,CCC) δ(CCN, CCC)
3082w 3053w 1578s 1557m 1452s 1415m 758s 652w 618w
3090w 3061w 1600m 1585s 1527s 1430w 760s 697w 684w
3099w 3053w 3052w 1492m 1472w 1436s 766s 646w 639w
3058w 3030w 1503m 1492m 1419m 1340w 852s 736s 621w
3075w 3055w 1515m 1488w 1421m 1340w 854s 715m 645w
n.o. 3050w 1516m 1491w 1425m 1341w 851s 720m 643w
Abbreviation/symbols: ν, stretch; νas ; asymmetric stretch; νs ; symmetric stretch; δ, bending in plane; β, out-of-plane bending; Intensity of bands: s, strong; m, medium; w, weak, n.o.: not observed.
3.3. Computational studies In order to get more insight into the stabilities and geometries of the Sb(III) and Bi(III) complexes, quantum chemical computations were carried out. The ground state geometries and thermodynamic characteristics of the complexes in gas phase were calculated by means of M06-2X/def2-TZVPP method. Computed structural parameters of the Sb(III) complexes were compared with experimental data of singlecrystal X-ray [19,20]. Direct comparison between computed and experimental values for [BiBr3(L)] (L = bpy or phen) complexes was not possible due to the lack of experimental data. Optimized structures of complexes revealed a distorted square pyramidal geometry around metal center, (see Fig.3), consistent with the experimental geometries of the Sb(III) complexes in the solid state [19,20]. In these structures, the halogen atoms occupy equatorial position and nitrogen atoms occupy both equatorial and axial positions. The distortions from ideal square pyramidal geometry can be attributed to the influence of a stereochemically active lone pair of the antimony and crystal packaging. Selected theoretical and experimental geometric parameters such as bond lengths and bond angles are listed in Table 3. As observed in the solid state, calculated structures reveal equatorial Sb⎯N12 distances longer than the axial Sb⎯N6 distances by ca. 0.1 and 0.2 Å, for [SbCl3(bpy)] and [SbCl3(phen)] complexes, respectively. The differences comes from the repulsion of the sterically active lone electron pair of the antimony. The calculated Sb⎯N bond lengths by M06-
Fig. 1. TGA/DrTGA curves of (a) [SbCl3(bpy)] and (b) [SbCl3(phen)] complexes.
Fig. 3. Optimized structures of Sb(III) and Bi(III) complexes obtained by means of M06-2X/def2-TZPP theoretical level with effective core potential for Sb and Bi elements.
Fig. 2. TGA/DrTGA curves of the (a) [BiBr3(bpy)] and (b) [BiBr3(phen)] complexes. 236
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Table 3 Some experimental [19,20] and calculated (M06-2X/def2-TZVPP) geometric parameters of Sb(III) complexes. [SbCl3(bpy)] Parameters Bond length (Å) SbeN6 SbeN12 SbeCl2 SbeCl3 SbeCl4 Bond angles (°) Cl2eSbeCl3 Cl2eSbeCl4 Cl3eSbeCl4 Cl2eSbeN6 Cl2eSbeN12 Cl3eSbeN6 Cl3eSbeN12 Cl4eSbeN6 Cl4eSbeN12 N6eSbeN12
Table 5 Calculated (M06-2X/def2-TZVPP) standard dissociation enthalpies (kJ·mol−1) and entropies (J · mol−1 K−1) and values of the temperature, Tk=1(K), at which the equilibrium constant for the dissociation of the Sb(III) and Bi(III) complexes in gas phase is one.
[SbCl3(phen)]
Experimental
Calculated
Experimental
Calculated
Process
ΔdissH°
ΔdissS°
Tk=1
2.243 2.319 2.506 2.549 2.588
2.340 2.437 2.429 2.513 2.521
2.241 2.397 2.501 2.580 2.549
2.339 2.458 2.430 2.518 2.518
[SbCl3(bpy)] ⟶ SbCl3 + bpy [SbCl3(phen)] ⟶ SbCl3 + phen [BiBr3(bpy)] ⟶ BiBr3 + bpy [BiBr3(phen)] ⟶ BiBr3 + phen
36.3 65.0 59.8 91.1
159.6 158.7 150.5 160.5
228 410 398 568
93.2 90.1 162.0 88.1 158.9 80.1 85.6 82.4 85.0 70.9
93.2 92.6 152.1 88.6 156.2 76.4 83.7 76.5 80.1 67.7
86.9 95.6 161.4 86.0 155.1 81.8 80.7 80.0 89.8 71.0
93.5 93.3 151.6 87.7 156.3 76.4 81.5 76.4 81.2 68.6
energies of the Sb(III) complexes are lower than the analogous Bi(III) complexes, while bond energies values are almost the same. This difference is mainly attributed to the reorganization energy of the acceptor, about 136 kJ · mol−1 for SbCl3 and 113 kJ · mol−1 for BiBr3. Therefore, the reorganization energy of the group 15 halides plays a predominant role in the energetics of formation of their complexes with bpy and phen ligands. As expected, the reorganization energies of the donor fragment are lower than the acceptor one, computed in the range 1.6–4.1 kJ · mol−1. For trans-conformation of the nitrogen atoms in the free bpy, the value of reorganization energy is, on average, 34.6 kJ · mol−1. Upon coordination, the nitrogen atoms of the bpy take a cisconformation. Taking into account the trans-cis reorganization energy (32.5 kJ · mol−1), we obtain that the EDreorg of cis-bpy conformer are in range 1.6–2.6 kJ · mol−1. Comparison of the complexes with the same metal trihalide shows that donor-acceptor bond energy of the [MX3(phen)] complexes are, in average, 31.6 kJ · mol−1 higher. To assess the relative stabilities of the complexes in the gas phase, we have calculated the temperature in which the equilibrium constant for the complex dissociation process is equals to one [31] (see Table 5). It may be estimated using standard dissociation enthalpies and entropies: Tk=1≈ΔdissH°/ΔdissS°. The calculated thermodynamic parameters represent the dissociation from the ground-state reactant complexes to ground-state products. The ground-state trans-bpy conformer is planar, whereas the aromatic ring of the cis-bpy conformer are twisted by 36.9°, which lies 25.7 kJ · mol−1 higher in energy. According to Tk=1 values, phen complexes are most stable in gas phase, with Tk=1 values in range 410–568 K, this behavior is due to the enthalpy factor. Upon dissociation of the complexes, the free bpy takes on trans-conformation, more stable that cis-conformation in about 25.7 kJ · mol−1. Therefore, less energy is required for dissociation of the bpy complexes and it is the main source of the difference in the ΔdissH° of the [MX3(bpy)] and [MX3(phen)].
2X/def2-TZVPP theoretical level are in average 0.1 Å larger than experimental values. The experimental Sb⎯Cl bond lengths are longer than the calculated ones by ca. 0.1 Å, for both [SbCl3(bpy)] and [SbCl3(phen)] complexes. In general, calculated bond lengths are in good agreement with experimental values. The SbeNeC bond angles were calculated in the range 118.7–120.7° for [SbCl3(bpy)] and 116.1–123.8° for [SbCl3(phen)] complex. These angles differ from the experimental values in about 0.9 and 2.0°, respectively. The N6eSbeN12 bond angles calculated for Sb (III) complexes are smaller than experimental values, suggesting that steric effects of the antimony’s lone electron pair in the Sb(III) complexes in gas-phase is larger than in the solid-state. These findings were also observed in the study carried out by Haiges et al [26]. The Cl3eSbeN6 and Cl3eSbeN12 bond angles in the solid-state structure of the [SbCl3(phen)] complex are longer than the calculate ones in gas phase by ca. 5.4 and 8.5 Å. These structural deviation can be mainly attributed to the intermolecular interactions in the solid state structure which are absent in the gas phase. The energies of the donor-acceptor bond (EDA) for Sb(III) and Bi(III) complexes were estimated by using an approach proposed by Timoshkin et al [28,30]. In this approach, the energy of the donoracceptor bond can be estimated based on the dissociation energy (ΔEdiss) of the complexes and reorganization energies of the donor ligands (EDreorg) and acceptor metal trihalide (EAreorg) including basis set superposition error (BSSE) of the donor and acceptor fragments, respectively. The reorganization energies were calculated as the difference of the total energy of the free fragment and fragment within the complex. In the present study, we computed reorganization energies for the donor and acceptor fragments and calculated EDA without BSSE corrections:
EDA = Ediss + Ereorg + Ereorg D A
3.4. Calorimetric measurements The enthalpies of reaction in the solid-state (ΔrH°m(s)) were obtained from the enthalpies of dissolution of metal trihalides (Δ1H°m), the enthalpies of reaction for the formation of the complexes in solution (Δ2H°m) and the enthalpies of dissolution of the complexes (Δ3H°m) in dimethyl sulfoxide (DMSO) or dimethylacetamide (DMA). This information is detailed in Eqs. (2)–(5) and the corresponding data are presented in Table 6.
(1)
In the Table 4 are listed the dissociation, reorganization and bond energy for the Sb(III) and Bi(III) complexes. In general, the dissociation Table 4 Dissociation, reorganization and donor-acceptor bond energy (kJ · mol−1) for the Sb(III) and Bi(III) complexes calculated by M06-2X/def2-TZVPP method. Compounds
ΔEdiss
EDreorg
EAreorg
EDA
[SbCl3(bpy)] [SbCl3(phen)] [BiBr3(bpy)] [BiBr3(phen)]
44.2 73.5 67.6 99.5
2.6 4.1 1.6 2.8
136.5 136.4 113.2 112.7
183.3 214.0 182.5 215.0
MX3(s) + solvent ⟶ solution A Δ1H°m
(2)
L(s) + solution A ⟶ solution B Δ2H°m
(3)
[MX3(L)](s) + solvent ⟶ solution C Δ3H°m
(4)
Solution B ⟶ solution C Δ4H°m
(5)
The application of the of Hess’ law to the Eqs. (2)–(5) gives the standard enthalpies of coordination in solid-state (ΔrH°m(s)):
237
MX3(s) + L(s) ⟶ [MX3(L)](s) ΔrH°m(s)
(6)
ΔrH°m(s) = Δ1H°m + Δ2H°m − Δ3H°m
(7)
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Table 6 Standard molar enthalpies of dissolution and coordination reaction in dimethyl sulfoxide and dimethylacetamide at 298.15 K. Process
Nº of experiments
i
(ΔiH°m ± s )/kJ · mol−1
SbCl3(s) + (CH3)2SO(l) bpy(s) + SbCl3(sol) [SbCl3(bpy)](s) + (CH3)2SO(l) phen(s) + SbCl3(sol) [SbCl3(phen)](s) + (CH3)2SO(l) BiBr3(s) + (CH3)2SO(l) bpy(s) + BiBr3(sol) [BiBr3(bpy)](s) + (CH3)2SO(l) BiBr3(s) + (CH3)2NCOCH3(l) phen(s) + BiBr3(sol) [BiBr3(phen)](s) + (CH3)2NCOCH3(l)
5 5 5 4 4 5 4 5 4 4 4
2 3 4 3 4 2 3 4 2 3 4
−59.6 ± 1.5 15.4 ± 0.4 10.2 ± 0.2 2.6 ± 0.3 11.7 ± 0.3 −82.5 ± 2.2 20.6 ± 1.5 −9.97 ± 1.1 −76.4 ± 0.9 −5.5 ± 0.3 −11.6 ± 0.7
s=
n (X X¯ )2 i=1 i (n 1)
Table 8 Complementary enthalpies (kJ mol−1) of metal trihalides and ligands at 298.15 K. Compounds SbCl3 BiBr3 bpy phen a b c d e f
measurement; X¯ = mean value.
The enthalpy of dilution, Eq. 5, Δ4H°m, correspond to the infinite dilution state for each solute and under these conditions Δ4H°m ≈ 0. The ΔrH°m(s) values were calculated by using Eq. (7) and they are listed in Table 7. These enthalpies can be used to compare the basicity of the two ligands when the metal trihalide is kept the same. As expected, the basicity of phen is larger than the basicity of bpy, agreeing with the observed trend in the enthalpies of reactions in gas phase, calculated by M06-2X/def2-TZVPP method (Table 7). Compared to bpy, the phen ligand is characterized by two nitrogen donor atoms being held juxtaposed, and therefore, pre-organized for strong and entropically favored metal binding [32]. Consequently, the rigidity of the phen ligand should give its complexes greater thermodynamic stability as compared to its less pre-organized bpy. The standard enthalpies of formation of the complexes in the solid state (ΔfH°m(s)) were calculated from the enthalpies of coordination, ΔrH°m(s), and the enthalpies of formation of the ligands and metal trihalides in the solid state, using Eq.(8). The values of ΔfH°m(s) of complexes were obtained from the data in Table 8 and are shown in Table 7. For phen ligand, the ΔfH°m(s) was derived from of enthalpy of formation in gas phase (ΔfH°m(g)), calculated by quantum chemical composite method G4 [33] and experimental sublimation enthalpy (ΔsgH°m) using Eq.(9). The G4 method were used by Riou and Bouchoux [33] to determine accurate enthalpies of formation in gas phase for 2,2′-, 4,4′-and 2,4′-bipyridines and 1,10-phenantroline. For the set of reference compounds: ethane, benzene, toluene, biphenyl, pyridine, 2-methy pyridine and 4-methyl pyridine, the authors reported that the G4 methods provide enthalpies of formation in excellent agreement with experimental data (average deviation of 0.9 kJ · mol−1). ΔfH°m(s)(phen) = ΔfH°m(g) − Δs H°m
ΔsgH°m
−382.17b ± 0.06 −276.33c ± 2.09 186.1d ± 2.0 209e ± 1
68.2b 115.39c ± 0.17 81.8d ± 2.3 105.6f ± 0.8
Reference [33]. Reference [34]. Reference [35]. Reference [36]. Calculated according to Eq. (9). Reference [37].
[MX3(L)](s) ⟶ MX3(s) + L(g) ΔDH°m
(10)
[MX3(L)](s) ⟶ MX3(g) + L(g) ΔMH°m
(11)
The values of ΔDH°m and ΔMH°m, present in Table 7, were calculated from the standard enthalpies of sublimation of the ligands [34,35], metal trihalides [32,33] and the enthalpies of formation of the complexes in the solid-state: ΔDH°m = ΔrH°m(s) + ΔsgH°m(L)
(12)
g
ΔMH°m = ΔDH°m + Δs H°m(MX3)
(13)
As the complexes decomposed on heating, their enthalpies of sublimation (ΔsgH°m) were estimated by using a combination of experimental lattice enthalpies and the computed (M06-2X/def2-TZVPP) enthalpies of the coordination reactions in gas phase ΔsgH°m = ΔrH°m(g) − ΔMH°m
(14)
The values of standard enthalpies of sublimation, (see Table 7), indicate that the thermal stabilities of the complexes in solid phase decrease in the order: [BiBr3(phen)] > [BiBr3(bpy)] > [SbCl3(phen)] > [SbCl3(bpy)], agreeing with the order of stabilities determined from thermogravimetric analysis. 4. Conclusions Sb(III) and Bi(III) complexes were synthesized by the interaction of the bpy and phen ligands with antimony trichloride and bismuth tribromide in propanone. The dissolution enthalpies of the complexes, salts and reaction enthalpies in solution were obtained by calorimetric experiments, leading to the determination of the enthalpies coordination reaction and formation of complexes in the solid-state. The elemental analysis demonstrated that the compounds were
(8)
g
315a
ΔfH°m(s)
The standard enthalpies of decomposition (ΔDH°m) and the lattice (ΔMH°m) of the complexes were calculated from Eqs. (12) and (13), respectively. These enthalpies correspond to the following processes:
. in which n is the experiment number; Xi = experimental
ΔfH°m(s) = ΔrH°m(s) + ΔfH°m(MX3)(s) + ΔfH°m(L)(s)
ΔfH°m(g)
(9)
Table 7 Thermochemical parameters of Sb(III) and Bi(III) complexes (kJ·mol−1). Compounds
ΔrH°m(s)a
[SbCl3(bpy)] [SbCl3(phen)] [BiBr3(bpy)] [BiBr3(phen)]
−52.3 −66.8 −51.5 −70.3
a b c d e f
± ± ± ±
ΔfH°m(s)b 1.6 1.5 2.9 1.2
−248.4 −239.5 −141.8 −138.0
ΔDH°mc ± ± ± ±
2.6 1.7 4.1 2.5
134.1 172.4 133.3 175.9
Calculated according to Eq. (7). Calculated according to Eq. (8). Calculated according to Eq. (12). Calculated according to Eq. (13). Calculated by M06-2X/def2-TZVPP method. Calculated according to Eq. (14). 238
± ± ± ±
ΔMH°md 2.8 1.7 3.7 1.4
−202.3 −240.6 −248.7 −291.3
± ± ± ±
2.8 1.7 3.7 1.5
ΔrH°m(g)e
Δsg H°mf
−36.3 −65.0 −59.8 −91.1
166 176 189 199
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obtained with 1:1 stoichiometry (metal trihalide/ligand). Based on the ΔrH°m(s) values, basicity of the ligand decrease in order phen > bpy, a result that agrees to the measurements of pKa of the corresponding conjugate acids in water. From the ΔsgH°m values, it is possible to suggest that the intermolecular forces in the solid state are larger for the BiBr3 complexes. Theoretical studies at the M06-2X/def2-TZVPP level of theory revealed that chemical stabilities of complexes decrease in order [BiBr3(phen)] > [SbCl3(phen)] > [BiBr3(bpy)] > [SbCl3(bpy)], in line with experimental values of the enthalpies of coordination in solid state. Comparison of the Sb(III) complexes to the analogous Bi(III) complexes showed that reorganization energy of the metal trihalides is the main contributing factor to the differences in dissociation energy of these complexes. Comparison between the [MX3(phen)] and [MX3(bpy)] indicates that phen complexes exhibit greater ΔdissH° than bpy complexes, where the rigidity of the phen ligand plays a significant role on the stability of its complexes.
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Funding sources This study was in part financed by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior-Brasil (CAPES) through the research project Bioinformática Estrutural de Proteínas: Modelos, Algoritmos e Aplicações Biotecnológicas (Edital Biologia Computacional 51/2013, processo AUXPE1375/2014 da CAPES). G.B.R. acknowledges support from the Brazilian National Council for Scientific and Technological Development (CNPq grant no. 309761/ 2017-4). Acknowledgments The authors gratefully acknowledge the financial support from the Brazilian agencies, Institutes and networks: Instituto Nacional de Ciência e Tecnologia de Nanotecnologia para Marcadores Integrados (INCT-INAMI), Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Coordenação de Aperfeiçoamento de Pessoal de Nível Superior-Brasil (CAPES), Programa de Apoio a Núcleos de Excelência (PRONEX-FACEPE), Financiadora de Estudos e Projetos (FINEP) and Fundação de Apoio à Pesquisa do Estado de São Paulo (FAPESP). The authors also acknowledge the physical structure and computational support provided by Universidade Federal da Paraíba (UFPB) and the computer resources of Centro Nacional de Processamento de Alto Desempenho em São Paulo (CENAPAD-SP) and Chemistry Institute of Campinas State University (UNICAMP). References [1] E.H. Lizarazo-Jaimes, R.L. Monte-Neto, P.G. Reis, N.G. Fernandes, N.L. Speziali, M.N. Melo, F. Frézard, C. Demicheli, Improved antileishmanial activity of dppz through complexation with antimony(III) and bismuth(III): investigation of the role of the metal, Molecules. 17 (2012) 12622–12635. [2] P. Baiocco, G. Colotti, S. Franceschini, A. Ilari, Molecular basis of antimony treatment in leishmaniasis, J. Med. Chem. 52 (2009) 2603–2612. [3] I.I. Ozturk, C.N. Banti, M.J. Manos, A.J. Tasiopoulos, N. Kourkoumelis, K. Charalabopoulos, S.K. Hadjikakou, Synthesis, characterization and biological studies of new antimony(III) halide complexes with ω-thiocaprolactam, J. Inorg. Biochem. 109 (2012) 57–65. [4] J.M. Bothwell, S.W. Krabbe, R.S. Mohan, Applications of bismuth(III) compounds in organic synthesis, Chem. Soc. Rev. 40 (2011) 4649–4707. [5] R. Hua, Recent advances in bismuth-catalyzed organic synthesis, Curr. Org. Synth. 5 (2008) 1–27. [6] T. Ollevier, New trends in bismuth-catalyzed synthetic transformations, Org. Biomol. Chem. 11 (2013) 2740–2755. [7] J. Rodriguez-Castro, P. Dale, M.F. Mahon, K.C. Molloy, L.M. Peter, Deposition of antimony sulfide thin films from single-source antimony thiolate precursors, Chem. Mater. 19 (2007) 3219–3226. [8] Z.M. Handong, Wang Li, Bismuth- Containing Compounds, Springer, New York, 2013.
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