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A novel crystallographic and improved computational study of three ligands of lead ion complex
Journal of Molecular Structure 892 (2008) 231–238
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A novel crystallographic and improved computational study of three ligands of lead ion complex Chia-Ching Su * Department of Applied Science, The ROC Naval Academy, 669, Jiun Shiaw Road, Kaohsiung, Taiwan 813, ROC
a r t i c l e
i n f o
Article history: Received 20 March 2008 Received in revised form 21 May 2008 Accepted 22 May 2008 Available online 7 June 2008 Keywords: Lariat crown ether SDD CEP-121G LanL2DZ Binding energies Binding enthalpies
a b s t r a c t The three novel lead(II) complexes, [Pb (L1) (NO3)2] (1), [Pb (L2) (NO3)2] (2), and [Pb (L3) (NO3)2] (3), were characterized by X-ray diffraction analysis. In order to understand the stereochemical structural nature and thermodynamic properties of these complex molecular systems, a theoretical study was conducted. The spatial coordinate positions of complex compounds 1–3 with lead were obtained from X-ray structural analysis and then used as initial coordinates to conduct density functional theory (DFT) theoretical calculations. This improved computational approach resulted in better accuracy when treating large, electron-rich species and better understanding of the complex compounds between the lariat crown ethers (LCEs) and lead ion. Through experimental data auxiliary of a quantum mechanical calculation approach, a DFT method was used to calculate the B3LYP/CEP-121G, B3LYP/SDD and B3LYP/LanL2DZ levels using the GAUSSIAN 03 package program. The calculations were conducted on the three novel LCEs complexed with lead ion. The theoretical calculation was to confirm the lowest energy, optimum geometric structure so as to receive more accurate thermodynamic properties and relative geometric stabilities of these three complex molecules. The atomic bond lengths, atomic torsion angles, binding energies and binding enthalpies of the three novel complex compounds were also calculated. The results of the DFT calculations show that these different complex compounds are cooperative participations of the oxygen on the C-pivot side arm with the ring oxygen molecules to form a six coordination number ligand of stable lead complex compound, which was also confirmed by the single crystal X-ray crystallography analysis. Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction It is known that lead has the highest atomic number of all stable elements. It is a soft, heavy, toxic, malleable poor metal. Lead is bluish white when freshly cut but tarnishes to dull gray when exposed to air. Lead is regarded as a serious environmental contaminant [1]. The knowledge of its environmental and health effects has led many authorities to forbid some of their uses in many developed countries that have contributed to a decrease in ambient lead levels in the environment. However, lead remains a high hazard to human health, and continues to be one of the most common pollutants. Lead was commonly used in building construction, lead storage batteries, pewter, and fusible alloys. Lead may result in a range of health effects, from behavioral problems and learning disabilities, to seizures and death. As a result, the development of medicines to counteract the effects of lead poisoning is especially
* Tel.: +886 7 583 4700x1213; fax: +886 7 347 2802. E-mail address: [email protected] 0022-2860/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2008.05.043
important. Therefore, the understanding of the preferred ligands of Pb(II) and the stereochemistry of those complexes are necessary. Coordination chemistry plays an essential role in chemical science [2]. Coordination bonding can be regarded as a kind of electrostatic force between the metal ion (Lewis acid) and ligand (Lewis base). Currently, we are interested in the coordination chemistry of lead(II) complexes supported by lariat crown ethers. The study of the interactions of ligand and metal ion, e.g. between lariat crown ethers and lead ions, is useful to establish the relationship between stereochemical structure and the stability of a complex. Ligands have many donor atoms that can form thermodynamically more stable complexes than their analogous containing unidentate ligands. In general, a crown ether has many neutral nitrogen or oxygen atoms which allows it to act as donor binding sites in multidentate ligands interacting with metal ions. Because of the highly favored complexation due to the chelate and macrocyclic effects, complex and macrocyclic ligands have been widely used for metal extractions or as chelating agents. The removal of toxic heavy metal contaminants from aqueous waste streams is one of the most important environmental issues. Predominantly, lariat crown ethers have been recognized as a very effective class of compounds to achieve
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selective separation of heavy metal ions from aqueous solutions. However, the chemistry of lead ions in natural systems is very complex and the exact form of lead in a sample depends on many circumstances [3]. Owing to significant progress in computer technology and algorithms of computational chemistry, molecular modeling has provided a powerful and reliable tool for exploring the complex molecular system. Accurate theoretical modeling has become an important tool to characterize coordination complex compounds. Over the last decade, the number of experimental and theoretical methods for stereochemical structural studies has grown markedly [4–16]. The application of quantum chemical calculation approaches to the interpretation of experimental data has became one of the most powerful tools for chemical investigation. However, no known theoretical investigations have been made on the lead–LCEs related complex compounds. To the best of our knowledge, the improved DFT calculation method is applied for the first time to the three novel complex molecules. In this research, we applied DFT theoretical calculation successfully through experimental data auxiliary to determine the optimal geometrical structure, binding energies, and binding enthalpies of the three novel complex compounds. DFT geometry optimization at the B3LYP/CEP-121G, B3LYP/SDD and B3LYP/ LanL2DZ level of theory was used for the three novel complex compounds. The spatial coordinate positions of the three novel complex compounds were obtained from X-ray structural analysis and used as initial coordinates for the theoretical calculations. The main goal of this research is to more accurately determine the lowest energy of the optimal complex molecular structure and to attain more accurate thermodynamic properties. This research showed that a more accurate theoretical method should be useful to those interested in modeling the three novel complex molecules. The research is also helpful for searching and determining the lowest energy of the optimal geometric structure and the influences of the different LCEs on the lead ion’s binding capability. 2. Experimental details 2.1. Reagents and chemicals All chemicals were obtained from commercial sources and used without further purification. Only analytical reagent grade chemicals were used in the preparation of these titled complex compounds. The hydroxy-sym-dibenzo-16-crown-5 ether was synthesized according to the literature method [17] and used after recrystallization from chloroform–hexane (1:5, V:V). 3-Phenylpropyl sym-dibenzo-16-crown-5 ether (L2) and 4-methoxybenzyl sym-dibenzo-16-crown-5 ether (L3) synthesized have been reported earlier [18,19]. 2.2. Synthesis of 20 -ethoxyethyl sym-dibenzo-16-crown-5-ether L1 Hydroxy-sym-dibenzo-16-crown-5-ether (1.73 g, 5 mmol) was dissolved in 50 mL anhydrous THF. NaH (0.8 g, 20 mmol) was added under nitrogen and the reaction mixture was heated under reflux for 30–40 min. After the addition of 2-bromoethyl ethyl ether (5 mmol), the mixture was refluxed for another 1 h. Deionized water was then added slowly to destroy the excess NaH and quench the reaction. The reaction mixture was then purified by column chromatography (silica gel, 70–230 mesh, CHCl3 eluent) to give the desired product in 70% (1.86 g) yield. m.p. 61.0–62.0 °C. MS (EI, 70 eV): m/z 418.0 (M+_, 100%), 175 (12%), 149 (16%), 136.0 (72%), 121.0 (44%), 109.0 (12%), 80 (17%), 73.0 (48%). Elemental analysis: Calc. (found) for C23H30O7; C, 66.01 (66.08); H, 7.23 (7.20). 1H NMR(CDCl3): d 1.24
(s, 3H, OCH2CH2OCH2CH3), 3.56 (q, 2H, OCH2CH2OCH2CH2CH3), 3.64 (t, 2H, OCH2CH2OCH2CH3), 3.92 (t, 2H, OCH2CH2OCH2CH3), 3.97 (m, 4H, OCH2CH2O CH2CH2O), 4.15 (m, 3H, OCHH0 CHCHH0 O; 4H, OCH2CH2O CH2CH2O), 4.33 (m, 2H, OCHH0 CHCHH0 O), 6.84-7.01 (m, 8H, benzo group). 2.3. Synthesis of lead and lariat crown complex 1–3 and X-ray structure determination The complex of lariat 16-crown-5 ether with Pb (NO3)2 was prepared by having [Pb (NO3)2] (0.0662 g, 0.2 mmol) dissolved in methanol–water (4:1, V:V) and lariat crown ether (0.1 mmol) in chloroform (1 mL). The mixture was filtered and then put into a crystal-growing bottle, and ethanol vapor was diffused into the product until a perfect crystal was produced. The structure of the resulting single crystals was then analyzed by X-ray crystallography. Data was then collected using a Nonius CAD-4 diffractometer with graphite-monochromated Mo-Ka radiation at 25 °C. Then, atomic scattering factors were taken from the International Tables for X-ray Crystallography, and data reduction and structural refinement were performed using NRCVAX packages. Cell parameters were then obtained from 25 reflections with 2h at 20.70–27.12°, 18.74–26.44°, and 16.94–26.22°, respectively. 3. Computational approaches All computations were conducted using the GAUSSIAN 03 program package, and the standard CEP-121G, SDD and LanL2DZ different basis sets. Electron correlation was partially taken into account by means of density function theory (DFT) using the GAUSSIAN 03 version of the hybrid three-parameter function developed by Becke and denoted as B3LYP. The B3LYP method has been proved to be the best compromise between computational cost and accuracy. From experimental data auxiliary, we conducted the theoretical calculation studies of 16-crown-5 (16c5) ether and its lead ion complexes. The improved DFT calculations were performed to analyze the complex molecular system with more accuracy. The large total number of atoms and the precise lead ion with 16c5 complex of three-dimensional spatial positions in the complex compounds of molecular system resulted in computational convergence difficulty. All calculated structures were completely optimized by GAUSSIAN 03 program package. For each optimized structure, a frequency calculation was also performed using these basis sets. Zero point energies obtained from these frequency calculations were used to correct free energy values for each structure. All calculated frequencies were positive. Therefore, we are confident that a definite absolute minimum in the potential energy surface was found. 3.1. Free ligands The spatial positions of uncomplexed lariat crown ether 1–3, obtained from X-ray structural analysis with no lead, were used as initial coordinates for DFT theoretical calculations. The geometry of all ligands was fully optimized and the minima with all real harmonic frequencies were obtained. 3.2. Ligands complexes of Pb2+ The theoretical study of the conformational and electronic properties of the three novel complex compounds was carried out using crystallographic data. The initial three-dimensional coordinates of the complex compounds 1–3 obtained from the X-ray structural analysis were used in the DFT calculation. The calculated structure of the six coordinate LCEs reproduced almost the same
C.-C. Su / Journal of Molecular Structure 892 (2008) 231–238
general features as the observed values in distorted octahedral, six coordinate lead complex compounds. Furthermore, binding energies (DE) between 16-crown-5 ether (16c5) and lead ion were calculated. The binding affinities of the 16-crown-5 ethers for the lead ion were evaluated by computing the energies of the association reactions 2þ
Pb
2þ
þ 16c5 ! Pb =16c5
ð1Þ
where the free ligands is corrected to the lowest energy of optimal geometric structure. Basis set superposition error was accounted for in an approximate manner by the full counterpoise correction of Boys and Bernardi [20]. The binding enthalpies, DH, for the reaction of lead ion with ligands [Pb2+ + L ? PbL] are given by the following equation: 2þ
2þ
DH ¼ DHðPb ::ligandÞ fDHðPb Þ þ DHðligandÞg
ð2Þ
2+
where DH (Pb ) and DH (ligand) are the enthalpy of the lead ion and ligand molecules, respectively, and DH (Pb2+..ligand) is the enthalpy of the complex. The binding energies (DE) and binding enthalpies (DH) could be estimated in detail according to the literature [21,22].
4. Results and discussions In all three independent complex molecules, lead ion forms six strong Pb–O bonds. The ligand molecule provides lead ion with the correct number and types of binding sites to form stable complex molecules. Thus, six oxygen atoms occupy four equatorial and two axial positions to form six coordination numbers of complex compounds. A distorted octahedral geometrical structure is therefore predicted. The optimal geometric structures of the three novel complex compounds show that the lead ion was coordinated with the six donor atoms of the LCEs. The results of the study indicate that the theoretical calculation can result in more accurate determination of the optimal complex molecular structure and thermodynamic properties between lead ion and lariat 16-crown-5 ether.
233
4.1. Molecular parameters The DFT theoretical calculation was conducted through experimental data auxiliary to search for the minimal energy and optimal stereochemical structures of the three novel complex compounds. With the improved DFT calculation, the input coordinate data has more accuracy. It was also found that the DFT calculations could achieve convergence more rapidly. The converged calculations can then result in the optimal geometric bond lengths, bond angles and dihedral angles of the three novel complex compounds. The results of X-Ray diffraction studies upon single crystals of the three novel complex compounds between lead and LCEs are shown in Figs. 1–3. The geometric optimization was then conducted using the B3LYP method with SDD, CEP-121G and LanL2DZ basis set. We analyzed the available experimental data and DFT calculation positions of the six oxygen atoms relative to the three novel complex compounds. The bridge oxygen atom and the parent group of five oxygen atoms in the 16-crown-5 ether with lead ion form a six coordination number of a stable complex compound. In the three novel complex compounds 1– 3, lead ion shows a positive charge and all six oxygen atoms are negatively charged. As a result, distortions to geometric structures are expected to have a significant impact on the Lewis basicity of the six oxygen donor atoms. According to the DFT theoretical calculations, the three novel complex compounds 1–3 all shown no symmetric geometrical structure of C1 point group. Table 1 provides the resulting Pb–O bond lengths of the complex compounds 1–3 from the X-ray crystallography structural analysis and DFT theoretical calculations. The observed X-ray crystal structures of the three novel complex compounds were compared to the optimized geometries obtained from the DFT calculations. The DFT calculation of the asymmetric complex molecular system showed that the six lead–oxygen coordinate atoms have bond distances in the range of 2.410–2.679 Å. In all three complex compounds the calculated PbO distance is shorter than that in the
Fig. 1. X-ray crystal structure of ORTEP diagram of lead ion in complex compound 1 with atom labeling; hydrogen atoms omitted for simplicity.
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C.-C. Su / Journal of Molecular Structure 892 (2008) 231–238
Fig. 2. X-ray crystal structure of ORTEP diagram of lead ion in complex compound 2 with atom labeling; hydrogen atoms omitted for simplicity.
crystal. The average lengths of the Pb–O bond predicted by the B3LYP calculations are ca. 0.1–0.4 Å shorter than the corresponding experimental X-ray data. It is therefore indicated that the three complex compounds can formed a more stable geometric structure of complex molecules than from X-ray crystallographic analysis. As from my previous research result [22], the improved DFT calculation can gain more optimal and accurate complex geometric molecular structure. Table 2 provides the resulting Pb-connected torsion angles of the complex compounds 1–3 from the X-ray crystallographic structural analysis and the DFT theoretical calculations. The two tables show that both the bond lengths and torsion angles of complex compounds 1–3 obtained from the theoretical calculations are in good agreement with those from experimental investigations using X-ray crystallography. The crystallographic data collected are listed in Table 3.
As a result, the structures of complex 1 and 3 molecules show the same crystal systems and space groups. However, complex compound 2 has a different crystal system and space group. Table 4 shows the binding energies and enthalpies of the three complex compounds of lariat 16-crown-5 ether–Pb2+. 4.2. Molecular first ionization potentials, HOMO and LUMO energies, and energy gaps Table 5 lists the calculated values of the first ionization potentials, HOMO, LUMO, and energy gap (DeHOMOLUMO) of the three novel complex compounds. All DFT calculation results show that the first ionization potential of complex compound 3 was the lowest. On the other hand, the energy gap of complex compound 1 was found to be the highest, indicating the lowest conductivity, reactivity and formation a more stable complex compound. It also shows
Fig. 3. X-ray crystal structure of ORTEP diagram of lead ion in complex compound 3 with atom labeling; hydrogen atoms omitted for simplicity.
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C.-C. Su / Journal of Molecular Structure 892 (2008) 231–238 Table 1 Crystallographic data and selected optimal Pb–O bond lengths (Å) of complex compound 1–3 obtained using improved DFT calculations
Table 2 Crystallographic data and optimal structure Pb-connected atomic torsion angle (°) of complex compound 1–3 obtained improved DFT calculations
Complex compound
Atomic bond lengths (Å)
Crystallographic B3LYP/CEPdata 121G
B3LYP/ SDD
B3LYP/ LanL2DZ
Complex compound
Atomic torsion angle (°)
Crystallographic data
B3LYP/ CEP-121G
B3LYP/ SDD
B3LYP/ LanL2DZ
1
Pb–O2 Pb–O3 Pb–O4 Pb–O5 Pb–O6 Pb–O7
2.681(7) 2.800(7) 2.803(7) 2.728(6) 2.879(7) 2.864(6)
2.487 2.410 2.481 2.526 2.503 2.411
2.640 2.524 2.609 2.663 2.650 2.527
2.546 2.441 2.530 2.598 2.575 2.446
1
2
Pb–O1 Pb–O2 Pb–O3 Pb–O4 Pb–O5 Pb–O6
2.712(3) 2.750(3) 2.878(3) 2.715(4) 2.851(3) 2.867(3)
2.473 2.432 2.487 2.523 2.496 2.421
2.618 2.546 2.610 2.654 2.651 2.538
2.528 2.461 2.531 2.586 2.572 2.457
3
Pb–O2 Pb–O3 Pb–O4 Pb–O5 Pb–O6 Pb–O7
2.708(19) 2.907(18) 2.882(23) 2.709(21) 2.765(23) 2.796(19)
2.466 2.415 2.511 2.540 2.492 2.413
2.604 2.536 2.665 2.679 2.621 2.525
2.509 2.454 2.587 2.611 2.546 2.440
O2–Pb–O3 O2–Pb–O4 O2–Pb–O5 O2–Pb–O6 O2–Pb–O7 O3–Pb–O4 O3–Pb–O5 O3–Pb–O6 O3–Pb–O7 O4–Pb–O5 O4–Pb–O6 O4–Pb–O7 O5–Pb–O6 O5–Pb–O7 O6–Pb–O7 C4–O2–Pb C5–O2–Pb C6–O3–Pb C12–O4–Pb C13–O4–Pb C14–O5–Pb C15–O5–Pb C16–O6–Pb C17–O6–Pb C22–O7–Pb C23–O7–Pb
61.5 (2) 116.0(2) 167.2 (2) 110.6(2) 59.9(2) 54.6(2) 112.4(2) 102.6(2) 63.2(2) 59.8(2) 86.9 (2) 92.8(2) 58.4(2) 107.5(2) 54.1(2) 132.2(7) 110.6(6) 116.5(5) 120.0(6) 115.1(6) 117.7(6) 108.5(6) 119.1(6) 126.5(6) 127.2(5) 115.2(6)
69.0 132.0 152.9 118.6 69.0 65.6 131.9 128.4 73.3 66.4 101.6 110.7 65.4 128.4 65.2 138.7 103.7 117.3 119.8 117.8 115.8 108.7 121.2 120.0 123.0 117.0
65.9 126.5 167.6 118.7 65.4 62.5 125.0 122.4 72.8 63.0 100.7 110.4 62.4 121.4 62.4 139.8 103.2 117.9 119.1 120.0 115.5 109.8 121.6 120.1 124.3 117.9
67.4 129.4 160.6 118.6 66.9 64.3 128.7 126.3 73.8 64.4 101.9 111.7 63.5 124.5 63.9 139.1 103.8 118.1 119.2 120.2 115.2 109.7 121.9 119.8 124.0 117.9
2
O1–Pb–O2 O1–Pb–O3 O1–Pb–O4 O1–Pb–O5 O1–Pb–O6 O2–Pb–O3 O2–Pb–O4 O2–Pb–O5 O2–Pb–O6 O3–Pb–O4 O3–Pb–O5 O3–Pb–O6 O4–Pb–O5 O4–Pb–O6 O5–Pb–O6 Pb–O1–C1 Pb–O1–C2 Pb–O2–C11 Pb–O2–C12 Pb–O3–C17 Pb–O3–C18 Pb–O4–C19 Pb–O4–C20 Pb–O5–C21 Pb–O5–C22 Pb–O6–C27 Pb–O6–C28
63.2(1) 115.9(1) 158.5(1) 101.9(1) 56.8(1) 53.8(1) 112.2(1) 111.5(1) 63.9(1) 59.3(1) 91.3 (1) 84.8(1) 59.0(1) 101.8(1) 55.1(1) 109.2(3) 134.5(3) 114.0(3) 114.3(3) 110.9(3) 114.1(3) 116.9(3) 108.6(3) 118.4(3) 125.1(3) 124.7(3) 116.2(3)
67.9 129.7 153.6 120.6 68.6 65.3 131.8 126.5 73.0 66.5 101.8 112.7 65.6 129.1 65.1 105.1 133.2 117.6 122.3 120.1 117.7 115.7 108.6 121.1 120.4 122.9 117.8
65.4 125.9 168.4 118.4 65.1 62.3 121.8 121.8 72.2 63.2 100.4 109.5 62.5 121.1 62.3 104.6 137.4 117.9 121.8 119.4 119.6 115.5 109.7 121.4 120.3 124.1 118.3
66.9 128.2 160.9 119.7 66.7 64.1 128.6 124.6 73.3 64.6 101.4 112.3 63.6 125.0 63.7 105.0 136.7 118.0 122.2 119.6 119.5 115.6 109.8 121.7 120.1 123.9 118.3
3
O2–Pb–O3 O2–Pb–O4 O2–Pb–O5 O2–Pb–O6 O2–Pb–O7 O3–Pb–O4 O3–Pb–O5 O3–Pb–O6 O3–Pb–O7 O4–Pb–O5 O4–Pb–O6 O4–Pb–O7 O5–Pb–O6 O5–Pb–O7 O6–Pb–O7 C8–O2–Pb C10–O3–Pb C11–O3–Pb C16–O4–Pb C17–O4–Pb C18–O5–Pb C19–O5–Pb C20–O6–Pb C21–O6–Pb C26–O7–Pb C27–O7–Pb
59.4(6) 110.2(6) 166.8 (6) 114.5(6) 60.5(7) 54.0(6) 107.6(6) 92.8(6) 63.8(6) 58.7(7) 88.0 (7) 103.4(7) 60.9(7) 113.1(7) 54.1(6) 132.6(15) 115.8(17) 126.0(17) 126.7(19) 119.1(20) 109.0(18) 116.2(17) 115.7(20) 121.0(21) 120.0(18) 118.7(18)
68.9 118.1 154.0 131.7 68.9 65.0 127.6 110.6 73.5 65.2 102.3 128.9 66.0 131.3 65.4 133.0 117.1 123.2 120.0 121.3 108.6 115.1 118.5 119.4 122.6 116.9
65.6 118.6 168.3 126.4 65.9 62.1 120.6 109.5 72.9 62.2 100.1 122.3 62.7 124.5 62.2 132.9 117.6 124.6 120.2 121.5 109.4 115.1 120.1 119.0 122.5 117.3
67.2 119.2 161.0 129.2 67.5 63.6 124.1 111.7 74.0 63.3 101.2 125.6 64.1 128.1 64.1 132.7 117.7 124.3 119.8 121.9 109.7 115.4 119.9 119.1 122.9 117.4
that 2 and 3 have almost the same energy gap that is lower indicating higher conductivity. 4.3. Complex of binding energies and binding enthalpies The B3LYP/CEP-121G theoretical calculation shows that the binding energies (DE) for the three novel complex compounds are between 288.74 and 297.81 kcal mol1. However, the calculated binding enthalpies (DH) are between 288.32 and 296.70 kcal mol1 for the three novel complex compounds. Additionally, the B3LYP/SDD theoretical calculation shows that the are between 230.95 and binding energies (DE) 241.45 kcal mol1 and the binding enthalpies (DH) are between 230.45 and 240.37 kcal mol1. On the other hand, the B3LYP/ LanL2DZ theoretical calculation shows that the binding energies (DE) are between 255.30 and 265.84 kcal mol1 and the binding enthalpies (DH) are between 254.75 and 264.69 kcal mol1. As a result, complex compound 1 has the largest binding energy (DE) and binding enthalpy (DH) followed by complex compound 3 and complex compound 2. Overall, the formation of the three novel complex compounds 1–3 is exothermic (DH < 0) and therefore the complex molecules are more rigid. This is probably the reason why the entropy change for the reaction is slightly negative. Thus, the DFT calculation results also indicate that the three complex compounds are formed most readily and are also the most stable ones. 5. Summary Three novel complex compounds 1–3 were synthesized and the optimal geometric structures were determined through experimental data auxiliary together with DFT theoretical calculations. We have performed a combined theoretical and experimental study of the three novel complex compounds. The result obtained from the improved DFT calculation was found to be more accurate, based on which the X-ray crystallography analysis. As a result the more optimal stereochemical structures of three novel complex compounds 1–3 were obtained (see Figs. 4–6). In addition, molecular structural conformation optimized using the B3LYP/CEP-121G, B3LYP/SDD and B3LYP/LanL2DZ methods indicated that there were a considerable differences in the energies of the three novel complex compounds. Moreover, comparison of
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employed DFT methodologies with respect to the structural and vibrational properties of the three novel complex compounds were compared. The experimental results and the DFT calculations (B3LYP) also complementarily established the electronic structures of these complex molecular species and provided insight into the more accurate molecular mechanics. From the DFT theoretical calculations using the CEP-121G, SDD and LanL2DZ basis sets, data of the three complex compounds of conformational analysis was successfully obtained. Based on the results of the DFT study, we introduced a novel molecular model for the complexation of LCEs and lead ion. The DFT calculated bond lengths and torsion angles of the three novel complex compounds are very close to the experimental values and are quite reasonable. As a result, the improved DFT calculation has been shown to be essential for obtaining accurate results. The DFT theoretical calculations of binding energies and binding enthalpies show that the three novel complex compounds are all located at the stable, minimum points of the potential energy surfaces. The DFT calculation results support the fact that lead ion with bridge oxygen and five oxygen atoms of the parent group of LCE form six coordination number of complex compound. The results presented here support the hypothesis that, in complexes containing high density ligands, twisted geometries might be favored by the presence of donor atoms with special affinity to-
Table 3 Crystallographic data Complex compound
1
2
3
Empirical formula Formula weight Crystal system Space group
C23H30N2O13Pb 749.69 Monoclinic P2(1)/a
C28H32N2O12Pb 795.76 Triclinic P 1
C27H30N2O13Pb 797.73 Monoclinic P2(1)/a
Unit cell dimensions a (Å) b (Å) c (Å) a (°) b (°) c (°) Volume (Å3) Z (atoms/unit cell) Dcalc (Mg m3) l (mm1) F(0 0 0) Range of 2h (°) Crystal size (mm)
17.124(3) 8.443(2) 19.388(4) 90 103.62 90 2724(1) 4 1.828 6.27 1472 49.8 0.45 .35 0.10
9.186(4) 11.541(3) 14.501(4) 94.20 103.47 14.50 1462(1) 2 1.808 5.85 784 49.8 0.40 0.25 0.20
18.285(2) 8.340(3) 19.341(2) 90 102.37 90 2881(1) 4 1.839 5.94 1568 51.8 0.30 0.15 0.08
20 to 19 0 to 10 0 to 23 4912
10 to 10 0 to 13 17 to 17 5353
22 to 22 0 to 10 0 to 23 5831
4763
5130
5657
3649
4597
3504
353 0.057–0.273 0.038 0.047 2.616
389 0.211–0.294 0.024 0.027 2.2346
389 0.06–0.295 0.108 0.131 3.876
Octants measured h k l Number of reflections measured Number of unique reflection Number of reflections with I > 2.5 or 2.0r(I) Number of variables Absorption correction Rf Rw GoF
Table 5 Comparison of HOMO, LUMO, energy gaps (DeHOMOLUMO), and first ionization potentials of three novel complex compounds (eV)
the calculated geometry of the complex compounds 1–3 with the structure obtained from X-ray diffraction indicates a more stable geometric structure of complex molecules. Vibrational frequency analyses performed at the B3LYP/CEP121G, B3LYP/SDD and B3LYP/LanL2DZ theoretical levels yielded zero imaginary frequency and confirmed that all optimized structures were in the ground state. The performances of various
Complex compound
DFT methods
eHOMO
eLUMO
I1st
DeHOMOLUMO
1
B3LYP/CEP-121G B3LYP/SDD B3LYP/LanL2DZ
11.9759 11.8587 11.9191
7.1829 7.4784 7.3045
11.9759 11.8587 11.9191
4.7930 4.3803 4.6145
2
B3LYP/CEP-121G B3LYP/SDD B3LYP/LanL2DZ
10.9422 10.5978 10.6296
7.1502 7.5578 7.3750
10.9422 10.5978 10.6296
3.7920 3.0399 3.2546
3
B3LYP/CEP-121G B3LYP/SDD B3LYP/LanL2DZ
10.6758 10.5847 10.6010
7.1209 7.4123 7.2319
10.6758 10.5847 10.6010
3.5550 3.1724 3.3691
Table 4 Binding energies and binding enthalpies of lariat crown ether–Pb2+
Complex compound
R
B3LYP/CEP-121G 1
1 2 3
CH2CH2OCH2CH3 CH2CH2CH2Ph
B3LYP/SDD 1
B3LYP/LanL2DZ 1
1
DE (kcal mol )
DH (kcal mol )
DE (kcal mol )
DH (kcal mol )
DE(kcal mol1)
DH (kcal mol1)
297.81 288.74
296.70 288.32
241.45 230.95
240.37 230.45
265.84 255.30
264.69 254.75
296.18
295.40
239.17
238.35
263.51
262.66
C.-C. Su / Journal of Molecular Structure 892 (2008) 231–238
237
Fig. 5. Improved DFT calculation diagram of complex compound 2.
Fig. 4. Improved DFT calculation diagram of complex compound 1.
ward Pb(II). In the final geometry found in the corresponding lead(II) complex, it is found that not only the nature of the donor atom present in the ligand molecule but also its charge has a main influence in the lead(II)-lone pair activity. The three novel complex compounds have the same parent macrocycle but contain different sidearms. The sidearm effect of
the lariat 16-crown-5 ethers can also result in higher differences in the relative binding energy and binding enthalpy. Therefore, with different sidearms resulting in conformational change, different complex ability between lariat crown ethers and lead ion can be shown. Thus, the sidearm effect appears to be a strong influence on lead ion’s binding capability. The estimated binding energies and binding enthalpies values obtained this way can be used as the substitutes for unavailable experimental values, especially for those complex compounds for which the experimental determination is very difficult. In sum, the DFT method, through experimental auxiliary, appears to provide results that were trustworthy and reasonable. The calculated method also provided a framework for searching
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C.-C. Su / Journal of Molecular Structure 892 (2008) 231–238
the lowest energy and optimal geometric structure of this class of complex compounds. The obtained information should be highly transferable to other theoretical studies on lead ion complexes and biological systems, as will be demonstrated in forthcoming application studies. Acknowledgements The author thanks the National Science Council of the Republic of China (Taiwan) for its financial support (NSC 96-2113-M-012001). The helpful suggestions from Professor L. Liu-Kao and Operator T.S. Kuo of National Taiwan Normal University, Department of Chemistry, are greatly appreciated. Dr. Y.C. Su, P.E., of Houston, TX, USA, is also greatly appreciated for providing a critical reading review of this manuscript prior to completion. References [1] D. Esteban-Gómez, C. Platas-Iglesia, F. Avecilla, A. de Blas, T. Rodríguez-Blas, Eur. J. Inorg. Chem. (2007) 1635. [2] J.Z. Ramìrez, R. Vargas, J. Garza, B.P. Hay, J. Chem. Theory Comput. 2 (2006) 1510. [3] M. Breza, A. Manová, J. Mol. Struct. (THEOCHEM) 765 (2006) 121. [4] A.R. Katritzky, N.G. Akhmedov, J. Doskocz, P.P. Mohapatra, C. Dennis-Hall, A. Güven, Magn. Reson. Chem. 45 (2007) 532. [5] E. Regulska, M. Samsonowicz, R. S´wisłocka, W. Lewandowski, J. Phys. Org. Chem. 20 (2007) 93. [6] T. Delaine, V. Bernardes-Génisson, J.L. Stigliani, H. Gornitzka, B. Meunier, J. Bernadou, Eur. J. Org. Chem. (2007) 1624. [7] I. Kostova, N. Peica, W. Kiefer, J. Raman Spectrosc. 38 (2007) 205. [8] M. Samsonowicz, R. S´wislocka, E. Regulska, W. Lewandowski, Int. J. Quantum Chem. 107 (2007) 480. [9] M.H. Palmer, J. Mol. Struct. 834–836 (2007) 13. [10] M.B. Williams, P. Campuzano-Jost, B.M. Cossairt, A.J. Hynes, A.J. Pounds, J. Phys. Chem. A 111 (2007) 89. [11] M. Shiotani, A. Lund, S. Lunell, F. Williams, J. Phys. Chem. A 111 (2007) 321. [12] F.A. Villamena, E.J. Locigno, A. Rockenbauer, C.M. Hadad, J.L. Zweier, J. Phys. Chem. A 111 (2007) 384. [13] L. Calucci, C. Forte, K. Fodor-Csorba, B. Mennucci, S. Pizzanelli, J. Phys. Chem. B 111 (2007) 53. [14] M. Baasandorj, P.S. Stevens, J. Phys. Chem. A 111 (2007) 640–649. [15] K.E. Gutowski, V.A. Cocalia, S.T. Griffin, N.J. Bridges, D.A. Dixon, R.D. Rogers, J. Am. Chem. Soc. 129 (2007) 526. [16] I.V. Glukhov, K.A. Lyssenko, A.A. Korlyukov, M.Y. Antipin, Faraday Discuss. 135 (2007) 203. [17] (a) E.P. Kyba, R.C. Helegeson, K. Madan, G.W. Gokel, T.L. Tarnowski, S.S. Moore, D.J. Cram, J. Am. Chem. Soc. 99 (1977) 2564; (b) G.S. Heo, R.A. Bartsch, L.L. Schobohm, J.G. Lee, J. Org. Chem. 46 (1981) 3574. [18] C.C. Su, L.H. Lu, J. Mol. Struct. 702 (2004) 23–31. [19] L.H. Lu, C.C. Su, T.J. Hsieh, J. Mol. Struct. 831 (2007) 151. [20] S.F. Boys, F. Bernardi, Mol. Phys. 19 (1970) 553. [21] A.L. Sargent, B.J. Mosley, J.W. Sibert, J. Phys. Chem. A 110 (2006) 3826. [22] C.C. Su, J. Mol. Struct. 888 (2008) 33.
Fig. 6. Improved DFT calculation diagram of complex compound 3.
Contents lists available at ScienceDirect
Journal of Molecular Structure journal homepage: www.elsevier.com/locate/molstruc
A novel crystallographic and improved computational study of three ligands of lead ion complex Chia-Ching Su * Department of Applied Science, The ROC Naval Academy, 669, Jiun Shiaw Road, Kaohsiung, Taiwan 813, ROC
a r t i c l e
i n f o
Article history: Received 20 March 2008 Received in revised form 21 May 2008 Accepted 22 May 2008 Available online 7 June 2008 Keywords: Lariat crown ether SDD CEP-121G LanL2DZ Binding energies Binding enthalpies
a b s t r a c t The three novel lead(II) complexes, [Pb (L1) (NO3)2] (1), [Pb (L2) (NO3)2] (2), and [Pb (L3) (NO3)2] (3), were characterized by X-ray diffraction analysis. In order to understand the stereochemical structural nature and thermodynamic properties of these complex molecular systems, a theoretical study was conducted. The spatial coordinate positions of complex compounds 1–3 with lead were obtained from X-ray structural analysis and then used as initial coordinates to conduct density functional theory (DFT) theoretical calculations. This improved computational approach resulted in better accuracy when treating large, electron-rich species and better understanding of the complex compounds between the lariat crown ethers (LCEs) and lead ion. Through experimental data auxiliary of a quantum mechanical calculation approach, a DFT method was used to calculate the B3LYP/CEP-121G, B3LYP/SDD and B3LYP/LanL2DZ levels using the GAUSSIAN 03 package program. The calculations were conducted on the three novel LCEs complexed with lead ion. The theoretical calculation was to confirm the lowest energy, optimum geometric structure so as to receive more accurate thermodynamic properties and relative geometric stabilities of these three complex molecules. The atomic bond lengths, atomic torsion angles, binding energies and binding enthalpies of the three novel complex compounds were also calculated. The results of the DFT calculations show that these different complex compounds are cooperative participations of the oxygen on the C-pivot side arm with the ring oxygen molecules to form a six coordination number ligand of stable lead complex compound, which was also confirmed by the single crystal X-ray crystallography analysis. Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction It is known that lead has the highest atomic number of all stable elements. It is a soft, heavy, toxic, malleable poor metal. Lead is bluish white when freshly cut but tarnishes to dull gray when exposed to air. Lead is regarded as a serious environmental contaminant [1]. The knowledge of its environmental and health effects has led many authorities to forbid some of their uses in many developed countries that have contributed to a decrease in ambient lead levels in the environment. However, lead remains a high hazard to human health, and continues to be one of the most common pollutants. Lead was commonly used in building construction, lead storage batteries, pewter, and fusible alloys. Lead may result in a range of health effects, from behavioral problems and learning disabilities, to seizures and death. As a result, the development of medicines to counteract the effects of lead poisoning is especially
* Tel.: +886 7 583 4700x1213; fax: +886 7 347 2802. E-mail address: [email protected] 0022-2860/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2008.05.043
important. Therefore, the understanding of the preferred ligands of Pb(II) and the stereochemistry of those complexes are necessary. Coordination chemistry plays an essential role in chemical science [2]. Coordination bonding can be regarded as a kind of electrostatic force between the metal ion (Lewis acid) and ligand (Lewis base). Currently, we are interested in the coordination chemistry of lead(II) complexes supported by lariat crown ethers. The study of the interactions of ligand and metal ion, e.g. between lariat crown ethers and lead ions, is useful to establish the relationship between stereochemical structure and the stability of a complex. Ligands have many donor atoms that can form thermodynamically more stable complexes than their analogous containing unidentate ligands. In general, a crown ether has many neutral nitrogen or oxygen atoms which allows it to act as donor binding sites in multidentate ligands interacting with metal ions. Because of the highly favored complexation due to the chelate and macrocyclic effects, complex and macrocyclic ligands have been widely used for metal extractions or as chelating agents. The removal of toxic heavy metal contaminants from aqueous waste streams is one of the most important environmental issues. Predominantly, lariat crown ethers have been recognized as a very effective class of compounds to achieve
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selective separation of heavy metal ions from aqueous solutions. However, the chemistry of lead ions in natural systems is very complex and the exact form of lead in a sample depends on many circumstances [3]. Owing to significant progress in computer technology and algorithms of computational chemistry, molecular modeling has provided a powerful and reliable tool for exploring the complex molecular system. Accurate theoretical modeling has become an important tool to characterize coordination complex compounds. Over the last decade, the number of experimental and theoretical methods for stereochemical structural studies has grown markedly [4–16]. The application of quantum chemical calculation approaches to the interpretation of experimental data has became one of the most powerful tools for chemical investigation. However, no known theoretical investigations have been made on the lead–LCEs related complex compounds. To the best of our knowledge, the improved DFT calculation method is applied for the first time to the three novel complex molecules. In this research, we applied DFT theoretical calculation successfully through experimental data auxiliary to determine the optimal geometrical structure, binding energies, and binding enthalpies of the three novel complex compounds. DFT geometry optimization at the B3LYP/CEP-121G, B3LYP/SDD and B3LYP/ LanL2DZ level of theory was used for the three novel complex compounds. The spatial coordinate positions of the three novel complex compounds were obtained from X-ray structural analysis and used as initial coordinates for the theoretical calculations. The main goal of this research is to more accurately determine the lowest energy of the optimal complex molecular structure and to attain more accurate thermodynamic properties. This research showed that a more accurate theoretical method should be useful to those interested in modeling the three novel complex molecules. The research is also helpful for searching and determining the lowest energy of the optimal geometric structure and the influences of the different LCEs on the lead ion’s binding capability. 2. Experimental details 2.1. Reagents and chemicals All chemicals were obtained from commercial sources and used without further purification. Only analytical reagent grade chemicals were used in the preparation of these titled complex compounds. The hydroxy-sym-dibenzo-16-crown-5 ether was synthesized according to the literature method [17] and used after recrystallization from chloroform–hexane (1:5, V:V). 3-Phenylpropyl sym-dibenzo-16-crown-5 ether (L2) and 4-methoxybenzyl sym-dibenzo-16-crown-5 ether (L3) synthesized have been reported earlier [18,19]. 2.2. Synthesis of 20 -ethoxyethyl sym-dibenzo-16-crown-5-ether L1 Hydroxy-sym-dibenzo-16-crown-5-ether (1.73 g, 5 mmol) was dissolved in 50 mL anhydrous THF. NaH (0.8 g, 20 mmol) was added under nitrogen and the reaction mixture was heated under reflux for 30–40 min. After the addition of 2-bromoethyl ethyl ether (5 mmol), the mixture was refluxed for another 1 h. Deionized water was then added slowly to destroy the excess NaH and quench the reaction. The reaction mixture was then purified by column chromatography (silica gel, 70–230 mesh, CHCl3 eluent) to give the desired product in 70% (1.86 g) yield. m.p. 61.0–62.0 °C. MS (EI, 70 eV): m/z 418.0 (M+_, 100%), 175 (12%), 149 (16%), 136.0 (72%), 121.0 (44%), 109.0 (12%), 80 (17%), 73.0 (48%). Elemental analysis: Calc. (found) for C23H30O7; C, 66.01 (66.08); H, 7.23 (7.20). 1H NMR(CDCl3): d 1.24
(s, 3H, OCH2CH2OCH2CH3), 3.56 (q, 2H, OCH2CH2OCH2CH2CH3), 3.64 (t, 2H, OCH2CH2OCH2CH3), 3.92 (t, 2H, OCH2CH2OCH2CH3), 3.97 (m, 4H, OCH2CH2O CH2CH2O), 4.15 (m, 3H, OCHH0 CHCHH0 O; 4H, OCH2CH2O CH2CH2O), 4.33 (m, 2H, OCHH0 CHCHH0 O), 6.84-7.01 (m, 8H, benzo group). 2.3. Synthesis of lead and lariat crown complex 1–3 and X-ray structure determination The complex of lariat 16-crown-5 ether with Pb (NO3)2 was prepared by having [Pb (NO3)2] (0.0662 g, 0.2 mmol) dissolved in methanol–water (4:1, V:V) and lariat crown ether (0.1 mmol) in chloroform (1 mL). The mixture was filtered and then put into a crystal-growing bottle, and ethanol vapor was diffused into the product until a perfect crystal was produced. The structure of the resulting single crystals was then analyzed by X-ray crystallography. Data was then collected using a Nonius CAD-4 diffractometer with graphite-monochromated Mo-Ka radiation at 25 °C. Then, atomic scattering factors were taken from the International Tables for X-ray Crystallography, and data reduction and structural refinement were performed using NRCVAX packages. Cell parameters were then obtained from 25 reflections with 2h at 20.70–27.12°, 18.74–26.44°, and 16.94–26.22°, respectively. 3. Computational approaches All computations were conducted using the GAUSSIAN 03 program package, and the standard CEP-121G, SDD and LanL2DZ different basis sets. Electron correlation was partially taken into account by means of density function theory (DFT) using the GAUSSIAN 03 version of the hybrid three-parameter function developed by Becke and denoted as B3LYP. The B3LYP method has been proved to be the best compromise between computational cost and accuracy. From experimental data auxiliary, we conducted the theoretical calculation studies of 16-crown-5 (16c5) ether and its lead ion complexes. The improved DFT calculations were performed to analyze the complex molecular system with more accuracy. The large total number of atoms and the precise lead ion with 16c5 complex of three-dimensional spatial positions in the complex compounds of molecular system resulted in computational convergence difficulty. All calculated structures were completely optimized by GAUSSIAN 03 program package. For each optimized structure, a frequency calculation was also performed using these basis sets. Zero point energies obtained from these frequency calculations were used to correct free energy values for each structure. All calculated frequencies were positive. Therefore, we are confident that a definite absolute minimum in the potential energy surface was found. 3.1. Free ligands The spatial positions of uncomplexed lariat crown ether 1–3, obtained from X-ray structural analysis with no lead, were used as initial coordinates for DFT theoretical calculations. The geometry of all ligands was fully optimized and the minima with all real harmonic frequencies were obtained. 3.2. Ligands complexes of Pb2+ The theoretical study of the conformational and electronic properties of the three novel complex compounds was carried out using crystallographic data. The initial three-dimensional coordinates of the complex compounds 1–3 obtained from the X-ray structural analysis were used in the DFT calculation. The calculated structure of the six coordinate LCEs reproduced almost the same
C.-C. Su / Journal of Molecular Structure 892 (2008) 231–238
general features as the observed values in distorted octahedral, six coordinate lead complex compounds. Furthermore, binding energies (DE) between 16-crown-5 ether (16c5) and lead ion were calculated. The binding affinities of the 16-crown-5 ethers for the lead ion were evaluated by computing the energies of the association reactions 2þ
Pb
2þ
þ 16c5 ! Pb =16c5
ð1Þ
where the free ligands is corrected to the lowest energy of optimal geometric structure. Basis set superposition error was accounted for in an approximate manner by the full counterpoise correction of Boys and Bernardi [20]. The binding enthalpies, DH, for the reaction of lead ion with ligands [Pb2+ + L ? PbL] are given by the following equation: 2þ
2þ
DH ¼ DHðPb ::ligandÞ fDHðPb Þ þ DHðligandÞg
ð2Þ
2+
where DH (Pb ) and DH (ligand) are the enthalpy of the lead ion and ligand molecules, respectively, and DH (Pb2+..ligand) is the enthalpy of the complex. The binding energies (DE) and binding enthalpies (DH) could be estimated in detail according to the literature [21,22].
4. Results and discussions In all three independent complex molecules, lead ion forms six strong Pb–O bonds. The ligand molecule provides lead ion with the correct number and types of binding sites to form stable complex molecules. Thus, six oxygen atoms occupy four equatorial and two axial positions to form six coordination numbers of complex compounds. A distorted octahedral geometrical structure is therefore predicted. The optimal geometric structures of the three novel complex compounds show that the lead ion was coordinated with the six donor atoms of the LCEs. The results of the study indicate that the theoretical calculation can result in more accurate determination of the optimal complex molecular structure and thermodynamic properties between lead ion and lariat 16-crown-5 ether.
233
4.1. Molecular parameters The DFT theoretical calculation was conducted through experimental data auxiliary to search for the minimal energy and optimal stereochemical structures of the three novel complex compounds. With the improved DFT calculation, the input coordinate data has more accuracy. It was also found that the DFT calculations could achieve convergence more rapidly. The converged calculations can then result in the optimal geometric bond lengths, bond angles and dihedral angles of the three novel complex compounds. The results of X-Ray diffraction studies upon single crystals of the three novel complex compounds between lead and LCEs are shown in Figs. 1–3. The geometric optimization was then conducted using the B3LYP method with SDD, CEP-121G and LanL2DZ basis set. We analyzed the available experimental data and DFT calculation positions of the six oxygen atoms relative to the three novel complex compounds. The bridge oxygen atom and the parent group of five oxygen atoms in the 16-crown-5 ether with lead ion form a six coordination number of a stable complex compound. In the three novel complex compounds 1– 3, lead ion shows a positive charge and all six oxygen atoms are negatively charged. As a result, distortions to geometric structures are expected to have a significant impact on the Lewis basicity of the six oxygen donor atoms. According to the DFT theoretical calculations, the three novel complex compounds 1–3 all shown no symmetric geometrical structure of C1 point group. Table 1 provides the resulting Pb–O bond lengths of the complex compounds 1–3 from the X-ray crystallography structural analysis and DFT theoretical calculations. The observed X-ray crystal structures of the three novel complex compounds were compared to the optimized geometries obtained from the DFT calculations. The DFT calculation of the asymmetric complex molecular system showed that the six lead–oxygen coordinate atoms have bond distances in the range of 2.410–2.679 Å. In all three complex compounds the calculated PbO distance is shorter than that in the
Fig. 1. X-ray crystal structure of ORTEP diagram of lead ion in complex compound 1 with atom labeling; hydrogen atoms omitted for simplicity.
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C.-C. Su / Journal of Molecular Structure 892 (2008) 231–238
Fig. 2. X-ray crystal structure of ORTEP diagram of lead ion in complex compound 2 with atom labeling; hydrogen atoms omitted for simplicity.
crystal. The average lengths of the Pb–O bond predicted by the B3LYP calculations are ca. 0.1–0.4 Å shorter than the corresponding experimental X-ray data. It is therefore indicated that the three complex compounds can formed a more stable geometric structure of complex molecules than from X-ray crystallographic analysis. As from my previous research result [22], the improved DFT calculation can gain more optimal and accurate complex geometric molecular structure. Table 2 provides the resulting Pb-connected torsion angles of the complex compounds 1–3 from the X-ray crystallographic structural analysis and the DFT theoretical calculations. The two tables show that both the bond lengths and torsion angles of complex compounds 1–3 obtained from the theoretical calculations are in good agreement with those from experimental investigations using X-ray crystallography. The crystallographic data collected are listed in Table 3.
As a result, the structures of complex 1 and 3 molecules show the same crystal systems and space groups. However, complex compound 2 has a different crystal system and space group. Table 4 shows the binding energies and enthalpies of the three complex compounds of lariat 16-crown-5 ether–Pb2+. 4.2. Molecular first ionization potentials, HOMO and LUMO energies, and energy gaps Table 5 lists the calculated values of the first ionization potentials, HOMO, LUMO, and energy gap (DeHOMOLUMO) of the three novel complex compounds. All DFT calculation results show that the first ionization potential of complex compound 3 was the lowest. On the other hand, the energy gap of complex compound 1 was found to be the highest, indicating the lowest conductivity, reactivity and formation a more stable complex compound. It also shows
Fig. 3. X-ray crystal structure of ORTEP diagram of lead ion in complex compound 3 with atom labeling; hydrogen atoms omitted for simplicity.
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C.-C. Su / Journal of Molecular Structure 892 (2008) 231–238 Table 1 Crystallographic data and selected optimal Pb–O bond lengths (Å) of complex compound 1–3 obtained using improved DFT calculations
Table 2 Crystallographic data and optimal structure Pb-connected atomic torsion angle (°) of complex compound 1–3 obtained improved DFT calculations
Complex compound
Atomic bond lengths (Å)
Crystallographic B3LYP/CEPdata 121G
B3LYP/ SDD
B3LYP/ LanL2DZ
Complex compound
Atomic torsion angle (°)
Crystallographic data
B3LYP/ CEP-121G
B3LYP/ SDD
B3LYP/ LanL2DZ
1
Pb–O2 Pb–O3 Pb–O4 Pb–O5 Pb–O6 Pb–O7
2.681(7) 2.800(7) 2.803(7) 2.728(6) 2.879(7) 2.864(6)
2.487 2.410 2.481 2.526 2.503 2.411
2.640 2.524 2.609 2.663 2.650 2.527
2.546 2.441 2.530 2.598 2.575 2.446
1
2
Pb–O1 Pb–O2 Pb–O3 Pb–O4 Pb–O5 Pb–O6
2.712(3) 2.750(3) 2.878(3) 2.715(4) 2.851(3) 2.867(3)
2.473 2.432 2.487 2.523 2.496 2.421
2.618 2.546 2.610 2.654 2.651 2.538
2.528 2.461 2.531 2.586 2.572 2.457
3
Pb–O2 Pb–O3 Pb–O4 Pb–O5 Pb–O6 Pb–O7
2.708(19) 2.907(18) 2.882(23) 2.709(21) 2.765(23) 2.796(19)
2.466 2.415 2.511 2.540 2.492 2.413
2.604 2.536 2.665 2.679 2.621 2.525
2.509 2.454 2.587 2.611 2.546 2.440
O2–Pb–O3 O2–Pb–O4 O2–Pb–O5 O2–Pb–O6 O2–Pb–O7 O3–Pb–O4 O3–Pb–O5 O3–Pb–O6 O3–Pb–O7 O4–Pb–O5 O4–Pb–O6 O4–Pb–O7 O5–Pb–O6 O5–Pb–O7 O6–Pb–O7 C4–O2–Pb C5–O2–Pb C6–O3–Pb C12–O4–Pb C13–O4–Pb C14–O5–Pb C15–O5–Pb C16–O6–Pb C17–O6–Pb C22–O7–Pb C23–O7–Pb
61.5 (2) 116.0(2) 167.2 (2) 110.6(2) 59.9(2) 54.6(2) 112.4(2) 102.6(2) 63.2(2) 59.8(2) 86.9 (2) 92.8(2) 58.4(2) 107.5(2) 54.1(2) 132.2(7) 110.6(6) 116.5(5) 120.0(6) 115.1(6) 117.7(6) 108.5(6) 119.1(6) 126.5(6) 127.2(5) 115.2(6)
69.0 132.0 152.9 118.6 69.0 65.6 131.9 128.4 73.3 66.4 101.6 110.7 65.4 128.4 65.2 138.7 103.7 117.3 119.8 117.8 115.8 108.7 121.2 120.0 123.0 117.0
65.9 126.5 167.6 118.7 65.4 62.5 125.0 122.4 72.8 63.0 100.7 110.4 62.4 121.4 62.4 139.8 103.2 117.9 119.1 120.0 115.5 109.8 121.6 120.1 124.3 117.9
67.4 129.4 160.6 118.6 66.9 64.3 128.7 126.3 73.8 64.4 101.9 111.7 63.5 124.5 63.9 139.1 103.8 118.1 119.2 120.2 115.2 109.7 121.9 119.8 124.0 117.9
2
O1–Pb–O2 O1–Pb–O3 O1–Pb–O4 O1–Pb–O5 O1–Pb–O6 O2–Pb–O3 O2–Pb–O4 O2–Pb–O5 O2–Pb–O6 O3–Pb–O4 O3–Pb–O5 O3–Pb–O6 O4–Pb–O5 O4–Pb–O6 O5–Pb–O6 Pb–O1–C1 Pb–O1–C2 Pb–O2–C11 Pb–O2–C12 Pb–O3–C17 Pb–O3–C18 Pb–O4–C19 Pb–O4–C20 Pb–O5–C21 Pb–O5–C22 Pb–O6–C27 Pb–O6–C28
63.2(1) 115.9(1) 158.5(1) 101.9(1) 56.8(1) 53.8(1) 112.2(1) 111.5(1) 63.9(1) 59.3(1) 91.3 (1) 84.8(1) 59.0(1) 101.8(1) 55.1(1) 109.2(3) 134.5(3) 114.0(3) 114.3(3) 110.9(3) 114.1(3) 116.9(3) 108.6(3) 118.4(3) 125.1(3) 124.7(3) 116.2(3)
67.9 129.7 153.6 120.6 68.6 65.3 131.8 126.5 73.0 66.5 101.8 112.7 65.6 129.1 65.1 105.1 133.2 117.6 122.3 120.1 117.7 115.7 108.6 121.1 120.4 122.9 117.8
65.4 125.9 168.4 118.4 65.1 62.3 121.8 121.8 72.2 63.2 100.4 109.5 62.5 121.1 62.3 104.6 137.4 117.9 121.8 119.4 119.6 115.5 109.7 121.4 120.3 124.1 118.3
66.9 128.2 160.9 119.7 66.7 64.1 128.6 124.6 73.3 64.6 101.4 112.3 63.6 125.0 63.7 105.0 136.7 118.0 122.2 119.6 119.5 115.6 109.8 121.7 120.1 123.9 118.3
3
O2–Pb–O3 O2–Pb–O4 O2–Pb–O5 O2–Pb–O6 O2–Pb–O7 O3–Pb–O4 O3–Pb–O5 O3–Pb–O6 O3–Pb–O7 O4–Pb–O5 O4–Pb–O6 O4–Pb–O7 O5–Pb–O6 O5–Pb–O7 O6–Pb–O7 C8–O2–Pb C10–O3–Pb C11–O3–Pb C16–O4–Pb C17–O4–Pb C18–O5–Pb C19–O5–Pb C20–O6–Pb C21–O6–Pb C26–O7–Pb C27–O7–Pb
59.4(6) 110.2(6) 166.8 (6) 114.5(6) 60.5(7) 54.0(6) 107.6(6) 92.8(6) 63.8(6) 58.7(7) 88.0 (7) 103.4(7) 60.9(7) 113.1(7) 54.1(6) 132.6(15) 115.8(17) 126.0(17) 126.7(19) 119.1(20) 109.0(18) 116.2(17) 115.7(20) 121.0(21) 120.0(18) 118.7(18)
68.9 118.1 154.0 131.7 68.9 65.0 127.6 110.6 73.5 65.2 102.3 128.9 66.0 131.3 65.4 133.0 117.1 123.2 120.0 121.3 108.6 115.1 118.5 119.4 122.6 116.9
65.6 118.6 168.3 126.4 65.9 62.1 120.6 109.5 72.9 62.2 100.1 122.3 62.7 124.5 62.2 132.9 117.6 124.6 120.2 121.5 109.4 115.1 120.1 119.0 122.5 117.3
67.2 119.2 161.0 129.2 67.5 63.6 124.1 111.7 74.0 63.3 101.2 125.6 64.1 128.1 64.1 132.7 117.7 124.3 119.8 121.9 109.7 115.4 119.9 119.1 122.9 117.4
that 2 and 3 have almost the same energy gap that is lower indicating higher conductivity. 4.3. Complex of binding energies and binding enthalpies The B3LYP/CEP-121G theoretical calculation shows that the binding energies (DE) for the three novel complex compounds are between 288.74 and 297.81 kcal mol1. However, the calculated binding enthalpies (DH) are between 288.32 and 296.70 kcal mol1 for the three novel complex compounds. Additionally, the B3LYP/SDD theoretical calculation shows that the are between 230.95 and binding energies (DE) 241.45 kcal mol1 and the binding enthalpies (DH) are between 230.45 and 240.37 kcal mol1. On the other hand, the B3LYP/ LanL2DZ theoretical calculation shows that the binding energies (DE) are between 255.30 and 265.84 kcal mol1 and the binding enthalpies (DH) are between 254.75 and 264.69 kcal mol1. As a result, complex compound 1 has the largest binding energy (DE) and binding enthalpy (DH) followed by complex compound 3 and complex compound 2. Overall, the formation of the three novel complex compounds 1–3 is exothermic (DH < 0) and therefore the complex molecules are more rigid. This is probably the reason why the entropy change for the reaction is slightly negative. Thus, the DFT calculation results also indicate that the three complex compounds are formed most readily and are also the most stable ones. 5. Summary Three novel complex compounds 1–3 were synthesized and the optimal geometric structures were determined through experimental data auxiliary together with DFT theoretical calculations. We have performed a combined theoretical and experimental study of the three novel complex compounds. The result obtained from the improved DFT calculation was found to be more accurate, based on which the X-ray crystallography analysis. As a result the more optimal stereochemical structures of three novel complex compounds 1–3 were obtained (see Figs. 4–6). In addition, molecular structural conformation optimized using the B3LYP/CEP-121G, B3LYP/SDD and B3LYP/LanL2DZ methods indicated that there were a considerable differences in the energies of the three novel complex compounds. Moreover, comparison of
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employed DFT methodologies with respect to the structural and vibrational properties of the three novel complex compounds were compared. The experimental results and the DFT calculations (B3LYP) also complementarily established the electronic structures of these complex molecular species and provided insight into the more accurate molecular mechanics. From the DFT theoretical calculations using the CEP-121G, SDD and LanL2DZ basis sets, data of the three complex compounds of conformational analysis was successfully obtained. Based on the results of the DFT study, we introduced a novel molecular model for the complexation of LCEs and lead ion. The DFT calculated bond lengths and torsion angles of the three novel complex compounds are very close to the experimental values and are quite reasonable. As a result, the improved DFT calculation has been shown to be essential for obtaining accurate results. The DFT theoretical calculations of binding energies and binding enthalpies show that the three novel complex compounds are all located at the stable, minimum points of the potential energy surfaces. The DFT calculation results support the fact that lead ion with bridge oxygen and five oxygen atoms of the parent group of LCE form six coordination number of complex compound. The results presented here support the hypothesis that, in complexes containing high density ligands, twisted geometries might be favored by the presence of donor atoms with special affinity to-
Table 3 Crystallographic data Complex compound
1
2
3
Empirical formula Formula weight Crystal system Space group
C23H30N2O13Pb 749.69 Monoclinic P2(1)/a
C28H32N2O12Pb 795.76 Triclinic P 1
C27H30N2O13Pb 797.73 Monoclinic P2(1)/a
Unit cell dimensions a (Å) b (Å) c (Å) a (°) b (°) c (°) Volume (Å3) Z (atoms/unit cell) Dcalc (Mg m3) l (mm1) F(0 0 0) Range of 2h (°) Crystal size (mm)
17.124(3) 8.443(2) 19.388(4) 90 103.62 90 2724(1) 4 1.828 6.27 1472 49.8 0.45 .35 0.10
9.186(4) 11.541(3) 14.501(4) 94.20 103.47 14.50 1462(1) 2 1.808 5.85 784 49.8 0.40 0.25 0.20
18.285(2) 8.340(3) 19.341(2) 90 102.37 90 2881(1) 4 1.839 5.94 1568 51.8 0.30 0.15 0.08
20 to 19 0 to 10 0 to 23 4912
10 to 10 0 to 13 17 to 17 5353
22 to 22 0 to 10 0 to 23 5831
4763
5130
5657
3649
4597
3504
353 0.057–0.273 0.038 0.047 2.616
389 0.211–0.294 0.024 0.027 2.2346
389 0.06–0.295 0.108 0.131 3.876
Octants measured h k l Number of reflections measured Number of unique reflection Number of reflections with I > 2.5 or 2.0r(I) Number of variables Absorption correction Rf Rw GoF
Table 5 Comparison of HOMO, LUMO, energy gaps (DeHOMOLUMO), and first ionization potentials of three novel complex compounds (eV)
the calculated geometry of the complex compounds 1–3 with the structure obtained from X-ray diffraction indicates a more stable geometric structure of complex molecules. Vibrational frequency analyses performed at the B3LYP/CEP121G, B3LYP/SDD and B3LYP/LanL2DZ theoretical levels yielded zero imaginary frequency and confirmed that all optimized structures were in the ground state. The performances of various
Complex compound
DFT methods
eHOMO
eLUMO
I1st
DeHOMOLUMO
1
B3LYP/CEP-121G B3LYP/SDD B3LYP/LanL2DZ
11.9759 11.8587 11.9191
7.1829 7.4784 7.3045
11.9759 11.8587 11.9191
4.7930 4.3803 4.6145
2
B3LYP/CEP-121G B3LYP/SDD B3LYP/LanL2DZ
10.9422 10.5978 10.6296
7.1502 7.5578 7.3750
10.9422 10.5978 10.6296
3.7920 3.0399 3.2546
3
B3LYP/CEP-121G B3LYP/SDD B3LYP/LanL2DZ
10.6758 10.5847 10.6010
7.1209 7.4123 7.2319
10.6758 10.5847 10.6010
3.5550 3.1724 3.3691
Table 4 Binding energies and binding enthalpies of lariat crown ether–Pb2+
Complex compound
R
B3LYP/CEP-121G 1
1 2 3
CH2CH2OCH2CH3 CH2CH2CH2Ph
B3LYP/SDD 1
B3LYP/LanL2DZ 1
1
DE (kcal mol )
DH (kcal mol )
DE (kcal mol )
DH (kcal mol )
DE(kcal mol1)
DH (kcal mol1)
297.81 288.74
296.70 288.32
241.45 230.95
240.37 230.45
265.84 255.30
264.69 254.75
296.18
295.40
239.17
238.35
263.51
262.66
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Fig. 5. Improved DFT calculation diagram of complex compound 2.
Fig. 4. Improved DFT calculation diagram of complex compound 1.
ward Pb(II). In the final geometry found in the corresponding lead(II) complex, it is found that not only the nature of the donor atom present in the ligand molecule but also its charge has a main influence in the lead(II)-lone pair activity. The three novel complex compounds have the same parent macrocycle but contain different sidearms. The sidearm effect of
the lariat 16-crown-5 ethers can also result in higher differences in the relative binding energy and binding enthalpy. Therefore, with different sidearms resulting in conformational change, different complex ability between lariat crown ethers and lead ion can be shown. Thus, the sidearm effect appears to be a strong influence on lead ion’s binding capability. The estimated binding energies and binding enthalpies values obtained this way can be used as the substitutes for unavailable experimental values, especially for those complex compounds for which the experimental determination is very difficult. In sum, the DFT method, through experimental auxiliary, appears to provide results that were trustworthy and reasonable. The calculated method also provided a framework for searching
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the lowest energy and optimal geometric structure of this class of complex compounds. The obtained information should be highly transferable to other theoretical studies on lead ion complexes and biological systems, as will be demonstrated in forthcoming application studies. Acknowledgements The author thanks the National Science Council of the Republic of China (Taiwan) for its financial support (NSC 96-2113-M-012001). The helpful suggestions from Professor L. Liu-Kao and Operator T.S. Kuo of National Taiwan Normal University, Department of Chemistry, are greatly appreciated. Dr. Y.C. Su, P.E., of Houston, TX, USA, is also greatly appreciated for providing a critical reading review of this manuscript prior to completion. References [1] D. Esteban-Gómez, C. Platas-Iglesia, F. Avecilla, A. de Blas, T. Rodríguez-Blas, Eur. J. Inorg. Chem. (2007) 1635. [2] J.Z. Ramìrez, R. Vargas, J. Garza, B.P. Hay, J. Chem. Theory Comput. 2 (2006) 1510. [3] M. Breza, A. Manová, J. Mol. Struct. (THEOCHEM) 765 (2006) 121. [4] A.R. Katritzky, N.G. Akhmedov, J. Doskocz, P.P. Mohapatra, C. Dennis-Hall, A. Güven, Magn. Reson. Chem. 45 (2007) 532. [5] E. Regulska, M. Samsonowicz, R. S´wisłocka, W. Lewandowski, J. Phys. Org. Chem. 20 (2007) 93. [6] T. Delaine, V. Bernardes-Génisson, J.L. Stigliani, H. Gornitzka, B. Meunier, J. Bernadou, Eur. J. Org. Chem. (2007) 1624. [7] I. Kostova, N. Peica, W. Kiefer, J. Raman Spectrosc. 38 (2007) 205. [8] M. Samsonowicz, R. S´wislocka, E. Regulska, W. Lewandowski, Int. J. Quantum Chem. 107 (2007) 480. [9] M.H. Palmer, J. Mol. Struct. 834–836 (2007) 13. [10] M.B. Williams, P. Campuzano-Jost, B.M. Cossairt, A.J. Hynes, A.J. Pounds, J. Phys. Chem. A 111 (2007) 89. [11] M. Shiotani, A. Lund, S. Lunell, F. Williams, J. Phys. Chem. A 111 (2007) 321. [12] F.A. Villamena, E.J. Locigno, A. Rockenbauer, C.M. Hadad, J.L. Zweier, J. Phys. Chem. A 111 (2007) 384. [13] L. Calucci, C. Forte, K. Fodor-Csorba, B. Mennucci, S. Pizzanelli, J. Phys. Chem. B 111 (2007) 53. [14] M. Baasandorj, P.S. Stevens, J. Phys. Chem. A 111 (2007) 640–649. [15] K.E. Gutowski, V.A. Cocalia, S.T. Griffin, N.J. Bridges, D.A. Dixon, R.D. Rogers, J. Am. Chem. Soc. 129 (2007) 526. [16] I.V. Glukhov, K.A. Lyssenko, A.A. Korlyukov, M.Y. Antipin, Faraday Discuss. 135 (2007) 203. [17] (a) E.P. Kyba, R.C. Helegeson, K. Madan, G.W. Gokel, T.L. Tarnowski, S.S. Moore, D.J. Cram, J. Am. Chem. Soc. 99 (1977) 2564; (b) G.S. Heo, R.A. Bartsch, L.L. Schobohm, J.G. Lee, J. Org. Chem. 46 (1981) 3574. [18] C.C. Su, L.H. Lu, J. Mol. Struct. 702 (2004) 23–31. [19] L.H. Lu, C.C. Su, T.J. Hsieh, J. Mol. Struct. 831 (2007) 151. [20] S.F. Boys, F. Bernardi, Mol. Phys. 19 (1970) 553. [21] A.L. Sargent, B.J. Mosley, J.W. Sibert, J. Phys. Chem. A 110 (2006) 3826. [22] C.C. Su, J. Mol. Struct. 888 (2008) 33.
Fig. 6. Improved DFT calculation diagram of complex compound 3.