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Synthesis and Structure of a 3D Porous Network Containing Aromatic 1D Chains of Li6 Rings: Experimental and Computational Studies Dibakar Deb,† Santanab Giri,‡ Pratim K. Chattaraj,*,‡ and Manish Bhattacharjee*,† Department of Chemistry and Center for Theoretical Studies, Indian Institute of Technology, Kharagpur 721 302, India ReceiVed: June 30, 2010; ReVised Manuscript ReceiVed: August 21, 2010
A bimetallic 3D network containing 1D chains of Li6 unit rings has been synthesized by using a molybdenum containing metalloligand and the DFT calculations reveal that the rings are aromatic in behavior and resemble the corresponding hydrocarbon analogues. Introduction In recent years syntheses of 3D polymeric materials are receiving more and more attention due to their potential use as small molecule storage materials.1 Similarly, all metal aromaticity has attracted a great deal of attention in these days.2 A few organometallic and all-metal aromatic compounds have been synthesized and structurally characterized.2e Boldyrev and coworkers reported gas phase synthesis and photoelectron spectroscopy of a series of bimetallic compounds of the type MAl4{M ) Li, Na, and Cu} and subsequently it was shown that the planar Al42- ion is aromatic in nature.3 This was followed by a host of reports on syntheses and theoretical investigations of all-metal aromatic compounds. Until recently, there was no report on the synthesis and structural characterization of aromatic compounds containing alkali metal ions. Two recent reports from this laboratory dealt with syntheses, structural characterizations, and theoretical investigations on [Na2MoO3L(H2O)2]n (1) {L ) iminodiacetate}4a and [K2MoO3L(H2O)3]n (2) containing 1D chains of A6 (A ) Na or K) aromatic rings, wherein it has been shown that Na6 rings are planar but K6 rings are not planar, but the geometry is similar to the chair form of cyclohexane.4 In the solid state, the compound [Na2MoO3L(H2O)2]n forms a porous 3D network through bridging carboxylate groups4 and [K2MoO3L(H2O)3]n forms a 2D polymeric potassium cluster sheet in the solid state. The NICS values show that the Na6 rings are more aromatic than the corresponding K6 rings.4 Thus, from these studies it is clear that the type of network and geometry, as well as the aromaticity, is highly dependent on the size of the alkali metal ions, as well as the type of metalloligand.4 We were also interested in the synthesis, structure, and aromaticity of the corresponding lithium compound. Herein we report the synthesis and structure of [Li2MoO3L(H2O)2]n (3) {LH2 ) iminodiacetic acid} and theoretical investigations on the aromaticity of the compound. Experimental Procedure Chemicals and solvents used were reagent grade products. The 1H and 7Li NMR spectra were recorded on a Bruker Avance II (1H frequency ) 400 MHz) spectrometer. Synthesis of Li2MoO4. H2MoO4 · H2O (0.180 g, 1 mmol; solid white powder) was added to an aqueous solution of lithium * To whom correspondence should be addressed. E-mail:
[email protected] and
[email protected]. † Department of Chemistry. ‡ Department of Chemistry and Center for Theoretical Studies.
hydroxide, LiOH · H2O (0.084 g, 2 mmol), and the mixture was stirred for 20 min. The solid powder was gradually dissolved and the resulting colorless solution was almost neutral (pH ∼7). The solution was filtered and the filtrate was allowed to stand in air at room temperature. After one week colorless needleshaped crystals of Li2MoO4 were obtained. Yield: 87% (0.15 g). Synthesis of Compound [Li2MoO3L(H2O)2]n {L ) Iminodiacetate}. An aqueous solution of Li2MoO4 (0.1738 g, 1 mmol) was added to an aqueous solution of iminodiacetic acid (0.133 g, 1 mmol). The mixture was refluxed for about 6 h, the resulting mixture was filtered, and the filtrate was allowed to stand in air at room temperature. After four weeks colorless block-shaped crystals of the compound, suitable for X-ray diffraction, were obtained. Yield: 82% (0.265 g). Anal. Calcd for C4H9Li2MoNO9 (mol wt ) 324.94): C; 14.79, H; 2.79, N; 4.31. Found: C; 14.34, H; 1.97, N; 4.07. IR (cm-1): 757, 838, 894, 1395, 1636. 1H NMR (D2O) in ppm: 3.16 (d, J ) 16 Hz, 1H), 3.81 (d, J ) 16 Hz, 1H). Single Crystal Data Collection and Refinements. Single crystal X-ray diffraction data of 3 were collected on a Bruker APEX SMART CCD system that uses graphite monochromated Mo KR radiation (λ ) 0.71073 Å). The structure was solved with the WinGX5 program embedded with SHELXS-976 and refined by least-squares methods on F2 using SHELXL-97.6 Non-hydrogen atoms were refined anisotropically and hydrogen atoms on C-atoms were fixed at calculated positions and refined using a riding model. Hydrogen atoms on the N atom and the O atom of water were located in difference Fourier maps and refined isotropically. ORTEP for windows,7 OLEX,8 and Mercurry softwares have been used for visualization of the structure. Crystal data for 3: C4H9NO9Li2Mo, 298(2) K, colorless block (0.2 × 0.2 × 0.1 mm3), monoclinic, C2/m, Z ) 4, a ) 13.0031(11) Å, b ) 14.4347(12) Å, c ) 5.1506(4) Å β ) 96.347(2)°, V ) 960.82(14) Å3, Fcalcd ) 2.246 Mg/m3, 2θmax ) 63.80, 7271 measured, 1573 unique (Rint ) 0.0247, Rσ ) 0.0253). R1 ) 0.0238, wR2 ) 0.0513 for 1480 reflections with I > 2σ(I) and R1 ) 0.0262, wR2 ) 0.0522 for all data; max/ min residual electron density ) 0.557/-0.937. Synthesis and Structure Elucidation. It has already been shown that iminodiacetic acid (LH2) on reaction with molybdate affords the metalloligand, [LMoO3]2- .4 Accordingly, a reaction of Li2MoO4 and iminodiacetic acid has been carried out in water and compound 3 has been isolated in high yield. The compound has been characterized by elemental analyses and spectroscopic
10.1021/jp106028y 2010 American Chemical Society Published on Web 09/21/2010
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Figure 2. Molecular structure of 3 (asymmetric unit is labeled) depicted by OLEX.8 Figure 1. ORTEP view of the asymmetric unit of 3. Hydrogen atoms have been omitted for clarity. Important bond distances [Å]: Li(1)-O(1), 2.347(4); Li(1)-O(1W), 2.0996(17); Li(1)-O(4), 2.121(4); Li(2)-O(2), 2.116(4); Li(2)-O(1), 2.1693(13); Li(1)-Li(2), 3.127(4); Mo(1)-N(1), 2.294(2); Mo(1)-O(1), 1.7359(13); Mo(1)-O(3), 2.2410(13).
studies as well as single crystal X-ray diffraction studies. The elemental analyses agree well with the composition. The 1H NMR (D2O) of the compound shows two doublets at 3.16 and 3.81 (J ) 16 Hz) ppm due to two diasterotopic -CH2 protons. The appearance of the two separate signals due to the -CH2 protons clearly reveals that in solution the iminodiacetate ligand remains coordinated to the molybdenum center. The 7Li NMR (D2O) of the compound shows a signal at 0.2 ppm and clearly shows that in solution the lithium ions remain coordinated to the metalloligand. The solid state structure of 3 was determined by single crystal X-ray diffraction. The asymmetric unit of 3 contains one molybdenum (Mo1) center coordinated to half of iminodiacetate and two oxo oxygens (O1 and O2), two lithium ions (Li1 and Li2), and one lithium coordinated water (O1W) where two independent Li centers lie on the 2-fold axes and molybdenum Mo(1), ligand nitrogen N(1), and oxo ligand O(1) lie on a mirror plane (Figure 1). The molybdenum center is in a distorted octahedral environment and is coordinated to three oxo oxygens (ModO) and two carboxylate oxygens and one nitrogen (Figure 2). The three oxo oxygens (MoO3) are coordinated to the Mo1 center in a facial arrangement. Each of the three ModO oxygens bridges two lithium ions in a µ3 fashion. In addition, the two lithium ions {Li1 and Li2} are bridged by one µ2-oxygen of water. Each carboxylate group bridges one molybdenum atom and two lithium ions, Li1 and Li1*. Thus, each Li ion is hexacoordinated and is in a distorted octahedral coordination environment. The coordination environments of the two lithium ions are slightly different. The Li1 center is coordinated to two symmetrically equivalent ModO oxygens, O(1), and two symmetrically equivalent carboxylate oxygens, O4, in cisfashion and two water oxygens, O1W, in trans-fashion, while the Li2 center is coordinated to two symmetrically equivalent ModO oxygen, O(2), and two water oxygens, O1W, in cisfashion and two symmetrically equivalent ModO oxygens, O1, in trans-fashion (Figure 3). In 3, six ModO oxygens from two metalloligands, two ModO oxygens (symmetrically equivalent O1) from two other metalloligands, and four bridging water, O1W, bind six lithium ions and form a hexagonal Li6 ring (Figure 4). One of the observed Li-Li distances {Li2-Li2a (a ) 1 - x, 2 - y, 1 - z) ) 2.851(5) Å} is distinctly shorter
Figure 3. Part of the polymeric structure showing formation of the Li6 ring viewed along a axes depicted by OLEX.8 Symmetry code: a ) 1 - x, 2 - y, 1 - z, b ) -x + 1, y, -z + 1, c ) -x + 1, -y, -z + 2, d ) -x + 1, y, -z + 2.
Figure 4. The 3D polymeric network in 3 along the c axis showing the 1D polymeric (Li4n+2) chain depicted by OLEX.8
compared to that in elemental lithium (3.04 Å). The Li1-Li2 distance {3.127 (17) Å} in the ring is slightly longer than that lithium. The short Li-Li distances clearly show the presence of Li · · · Li interaction in the solid state. It may be mentioned that similar short Li-Li distances were observed by Roesky and co-workers in the linear Li4 chain present in Li4[(MeGa)6(µ3O)2(t-BuPO3)6] · (THF)4.9 The most notable aspect of the solid state structure of the compound is the formation of a hexagonal 1D chain of (Li4n+2) rings (n ) 1 to ∞) (Figure 4). The infinite polymeric chain grows along the crystallographic c-axis. Another interesting feature
3D Network Containing 1D Chains of Li6 Unit Rings TABLE 1: Energy (E) and Energy (Ring)-1 Values of C4n+2H2n+4 and Li4n+2 [n ) 1-4] Molecules at the B3LYP/ 6-311+G(d) Level of Theory energy (E, au)
J. Phys. Chem. A, Vol. 114, No. 40, 2010 10873 TABLE 3: Polarizability (r, au) and Polarizability (Ring)-1 Values of C4n+2H2n+4 and Li4n+2 [n ) 1-4] Molecules at the B3LYP/6-311+G(d) Level of Theory
energy (ring)-1 (au)
polarizability (R, au)
polarizability (ring)-1 (au)
n
C4n+2H2n+4
Li4n+2
C4n+2H2n+4
Li4n+2
n
C4n+2H2n+4
Li4n+2
C4n+2H2n+4
Li4n+2
1 2 3 4
-232.30073 -385.97493 -539.64285 -693.30840
-45.06492 -75.11452 -105.16293 -135.21147
-232.30073 -192.98747 -179.88095 -173.32710
-45.06492 -37.55726 -35.05431 -33.80287
1 2 3 4
65.64300 115.79700 177.27170 250.20870
606.08067 1150.40233 1904.98933 2899.91133
65.64300 57.89850 59.09056 62.55217
606.08067 575.20117 634.99644 724.97783
TABLE 2: Hardness (η) and Hardness (Ring)-1 Values of C4n+2H2n+4 and Li4n+2 [n ) 1-4] Molecules at the B3LYP/ 6-311+G(d) Level of Theory hardness (η, eV)
TABLE 4: Electrophilicity (ω) and Electrophilicity (Ring)-1 Values of C4n+2H2n+4 and Li4n+2 [n ) 1-4] Molecules at the B3LYP/6-311+G(d) Level of Theory
hardness (ring)-1 (eV)
electrophilicity (ω, eV)
electrophilicity (ring)-1 (eV)
n
C4n+2H2n+4
Li4n+2
C4n+2H2n+4
Li4n+2
n
C4n+2H2n+4
Li4n+2
C4n+2H2n+4
Li4n+2
1 2 3 4
6.617 4.758 3.557 2.755
1.484 1.066 0.739 0.529
6.617 2.379 1.186 0.689
1.484 0.533 0.246 0.132
1 2 3 4
1.058 1.472 2.003 2.623
2.821 3.643 5.182 7.227
1.058 0.736 0.668 0.656
2.821 1.821 1.727 1.807
of the 1D chain is that the hexagonal rings are planar like benzene as evidenced by the observed three successive torsion angles (φ), which were found to be 0°. The polymeric chain is also planar like the corresponding polyacene analogue as the observed torsion angles (φ) between two adjacent ring lithiums are 180°. Interestingly, the carboxylate group in the metalloligand acts as a bridge between Mo and the Li center of the adjacent 1D polymeric units and forms a 3D polymeric network. The growth of the chain has been found to be along the crystallographic a and b axes in the solid state (Figure 4). In the 3D network there are two kinds of channels. The larger channel is of dimension 9.54 × 5.75 Å2 and the other type of channel is of dimension 8.51 × 4.35 Å2. Overall the solid state structure of the compound is similar to that of 1. Theoretical Investigations. The concept of “all-metal aromaticity”2 has seen an upsurge of interest in recent times and has been extended to analyze the structure and bonding of several all-metal compounds such as various cluster anions of Al, Ga, In, Hg, Sn, Si,2 polyacene analogues of inorganic ring compounds, and Na6 through photoelectron spectroscopy measurement and/or theoretical calculations.4 The interesting planar 1-D chain structure of the Li6 unit prompted us to investigate theoretically the properties and possible aromaticity of the cluster. Starting from the crystal structure of (Li4n+2), n ) 1-4, single point calculations have been carried out at the B3LYP/ 6-311+G(d) level of theory with the G03W program.10 It is expected to take care of the effect of the metalloligand in stabilizing the Li6 ring. For comparison the same basis set is employed for the optimization of the linear arenes, C4n+2H2n+4, n ) 1-4. Conceptual density functional theory11 (CDFT) based reactivity descriptors are quite successful in analyzing the stability, reactivity, and aromaticity of these clusters. Various electronic properties like energy (E), hardness12 (η), polarizability13 (R), and electrophilicity14 (ω ) χ2/2η, χ is the electronegativity15) have been calculated with standard techniques. These electronic properties and the same per unit ring of the arenes and Li6 are provided in Tables 1-4. It is observed that while the energy and hardness decrease, the polarizability and electrophilicity increase with an increase in the number of rings. Plots (Figure 5) of E, η, R, and ω per Li6 ring in Li4n+2, (n ) 1-4) clusters give a clear idea about stability and reactivity of the corresponding all-metal rings. It is further observed that for per ring quantity, with an increase in the number of rings
the Li4n+2, (n ) 1-4) clusters obey the basic electronic structure principles like maximum hardness principle16 (MHP), minimum polarizability principle17 (MPP), and minimum electrophilicity principle18 (MEP) in most cases. Although electrophilicity is not an extensive property, as χ and η are not so, a hand waving rationale toward the use of the corresponding quantity may be envisaged as follows: ω ) χ2. S and the softness (S ) 1/2η) is additive over individual atoms/groups, and the constancy of χ over the whole molecule (Sanderson15) allows us to obtain ω from the corresponding atom/group resolved quantities. This analysis implies that with an increase in chain length the average reactivity increases. Corresponding linear arenes19 also behave like Li4n+2 clusters with respect to their stability and reactivity patterns. To check whether these clusters (Li4n+2) are aromatic we have calculated the nucleus independent chemical shift20 at the center {NICS(0)} and 1 Å above the ring {NICS(1)} using the gauge-independent atomic orbital (GIAO) method.21 Table 5 presents the generic template and the NICS(0,1) values of the C4n+2H2n+4 and Li4n+2 systems. A comparison of per ring {NICS(0)} quantities of C4n+2H2n+4 and Li4n+2 is given in Figure 6. It is interesting to note that the aromaticity of Li4n+2 clusters is similar to that of their polyacene analogues. Their NICS(0) values are comparable. As reported22 the inner rings are more reactive and more aromatic than the outer rings, which are less reactive and are more aromatic than benzene, and the same has been found to be valid for (Li4n+2) clusters. However the NICS(0,1) values for the inner rings of Li14 and Li18 clusters show some differences from their corresponding polyacene counterparts. To compare the aromaticity patterns between polyacene and the all-metal systems, a NICS scan (Figure 7) for anthracene and its corresponding Li4n+2 analogue, Li14, has been performed. From Figure 7 it is observed that the NICS(1) value of anthracene becomes more negative due to the existence of current density generated from the π-electron cloud situated above the aromatic ring. The corresponding NICS values become less negative with increasing distance from the ring center, which is quite expected. However, like the Na14 system4 for the Li14, the NICS(1) and the other corresponding NICS values become less negative as we move outward from the ring. This may be attributed to the presence of σ- aromaticity in the Li4n+2 system. To analyze the bonding pattern of Li4n+2 clusters, some important frontier orbitals of both linear arenes and Li4n+2, n ) 1-4, have been generated at the B3LYP/6-311+G(d) level of
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Figure 5. (a) Energy (E, hartree), (b) hardness (η, eV), (c) polarizability (R, au), and (d) electrophilicity (ω, eV) profiles per unit C6 ring/Li6 ring.
TABLE 5: NICS(0) and NICS(1) Values at Different Ring Centers of C4n+2H2n+4 and Li4n+2 (n ) 1-4)
Figure 6. NICS(0) profiles per unit C6 ring/Li6 ring.
theory with use of the GV03 program package.10 The corresponding MO pictures are provided in Figure 8. A close look at Figure 8 reveals that the electron-density distributions in the frontier orbitals of the Li4n+2 clusters and the respective polyacene analogues almost mimic each other. It is important
to mention that the aromaticity in the former system is essentially of σ-type whereas that of the latter is of π-type. Figure 9 provides the charges (both using natural (NPA) and Mulliken population (MPA) analyses schemes) on Li atoms in the Li6 and Li10 systems. Single point calculations at the B3LYP/6-311+G(d) level have been performed on the neutral molecular fragments (cf. Figure 2) to generate the MPA and NPA charges. Another set of single point calculations have been done on Li6 and Li10 units with the total
3D Network Containing 1D Chains of Li6 Unit Rings
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Figure 7. Variation of NICS values against the distance, r, from the ring center of (a) anthracene and (b) Li-anthracene ring.
Figure 8. Frontier molecular orbitals of Li4n+2 and C4n+2H2n+4 rings.
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Figure 9. Calculated NPA (MPA) charges on Li atoms in Li6 and Li10 systems.
Figure 10. Calculated NBO charges on Li atoms through the single point calculation on the neutral molecular fragment (Figure 2) at the B3LYP/ LANL2DZ level of theory.
charge as obtained in the previous step. The qualitative nature of the charge distribution is similar in the two schemes. The slight positive charge on each Li atom except for the bridge Li-atoms in the naphthalene analogue, Li10, is stabilized as expected by the metalloligand. Moreover, these sites will facilitate attacks by anions or hard nucleophiles. The NBO charges on the neutral molecular fragment in Figure 2 have been calculated through a single point calculation at the B3LYP/LANL2DZ level. The NBO charges on the Li6 units are depicted in Figure 10. It may not be inappropriate to compare the σ-aromaticity proposed here with that in a related system Li3+. We have calculated the
NICS values for Li3+ at the B3LYP/LANL2DZ level and have seen that NICS(0) ) -11.08 ppm and NICS(1) ) -6.78 ppm. The charge on each Li unit is +1/3, as expected from the symmetry. Although the electron count and the NICS values suggest that the Li3+ molecule is σ-aromatic in nature, the current density maps do not support23 that. However, a quantum theory of atoms-in-a-molecule (QTAIM) study delineates that the charge on each Li atom is 0.820 au whereas the basin of a pseudoatom at the center of the ring (“NonNuclear Maxima”) possesses24 an electronic charge of -1.450 au, which is verified in our calculation as well. This fact deserves careful scrutiny.
3D Network Containing 1D Chains of Li6 Unit Rings Conclusion A 1-D chain of hexagonal Li6 rings has been successfully synthesized and structurally characterized. Through conceptual density functional theory calculations it has been shown that the stability and reactivity patterns of Li6 rings go hand-in-hand with the corresponding organic polyacene analogues. The high aromatic nature of the all-metal rings with negative NICS(0,1) values is also closely mimicked by that of the related polyacene systems. Acknowledgment. We thank CSIR, New Delhi for financial assistance and the Department of Science and Technology (DST), Govt. of India, for NMR and single crystal X-ray diffraction facilities. We are grateful to the referees for constructive criticism. One of the authors (P.K.C.) would like to thank the DST, New Delhi for a J. C. Bose Fellowship. Supporting Information Available: Tables containing important bond distances and bond angles. CIF file of crystallographic data. This material is available free of charge via the Internet at http://pubs.acs.org. References and Notes (1) (a) Liu, X.; Park, M.; Hongh, S.; Oh, M.; Yoon, J. W.; Chang, J.-S.; Lah, M. S. Inorg. Chem. 2009, 48, 11507. (b) Ren, H.; Ben, T.; Wang, E.; Jing, X.; Xue, M.; Liu, B.; Cui, Y.; Qiu, X.; Zhu, G. Chem. Commun. 2010, 291. (c) Zou, R.-Q.; Jiang, L.; Senoh, H.; Takeichi, N.; Xu, Q. Chem. Commun. 2005, 3526. (2) (a) Huang, X.; Zhai, H. J.; Kiran, B.; Wang, L. S. Angew. Chem., Int. Ed. 2005, 44, 7251. (b) Erhardt, S.; Frenking, G.; Chen, Z.; Schleyer, P. v. R. Angew. Chem., Int. Ed. 2005, 44, 1078. (c) Alexandrova, A. N.; Boldyrev, A. I. J. Phys. Chem. A 2003, 107, 554. (d) Boldyrev, A. I.; Kuznetsov, A. E. Inorg. Chem. 2002, 41, 532. (e) Boldyrev, A. I.; Wang, L.-S. Chem. ReV. 2005, 105, 3716. (f) Datta, A.; Pati, S. K. Chem. Commun. 2005, 5032. (3) Li, X.; Kuznetsov, A. E.; Zhang, H. F.; Boldyrev, A. I. Science 2001, 291, 859. Alexandrova, A. N.; Bodyrev, A. I.; Zhai, H.-J.; Wang, L.-S. Coord. Chem. ReV. 2006, 250, 2811. (4) (a) Khatua, S.; Roy, D. R.; Chattaraj, P. K.; Bhattacharjee, M. Chem. Commun. 2007, 135. (b) Khatua, S.; Roy, D. R.; Bultinck, P.; Bhattacharjee, M.; Chattaraj, P. K. Phys. Chem. Chem. Phys. 2008, 10, 2461.
J. Phys. Chem. A, Vol. 114, No. 40, 2010 10877 (5) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837. (6) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112. (7) Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565. (8) Dolomanov, O. V.; Blake, A. J.; Champness, N. R.; Schroder, V. J. Appl. Crystallogr. 2003, 36, 1283. (9) Walawalkar, M. G.; Murugavel, R.; Voigt, A.; Roesky, H. W.; Schmidt, H. G. J. Am. Chem. Soc. 1997, 119, 4656. (10) Gaussian 03, Revision B.03; Gaussian Inc., Pittsburgh, PA. (11) (a) Parr, R. G.; Yang, W. Density Functional Theory of Atoms and Molecules; Oxford University Press: Oxford, UK, 1989. (b) Geerlings, P.; De Proft, F.; Langenaeker, W. Chem. ReV. 2003, 103, 1793. (c) Chattaraj, P. K. Ed. Chemical ReactiVity Theory: A Density Functional View; Taylor & Francis/CRC Press: Boca Raton, FL, 2009. (d) Chattaraj, P. K.; Giri, S. Annu. Rep. Prog. Chem., Sect. C: Phys. Chem. 2009, 105, 13. (e) Deb, B. M.; Chattaraj, P. K.; Mishra, S. Phys. ReV. A 1991, 43, 1248. (f) Chattaraj, P. K.; Cedillo, A.; Parr, R. G.; Arnett, E. M. J. Org. Chem. 1995, 60, 4707. (g) Sengupta, S.; Chattaraj, P. K. Phys. Lett. A 1996, 215, 119. (h) Fuentealba, P.; Simon-Manso, Y.; Chattaraj, P. K. J. Phys. Chem. A 2000, 104, 3185. (i) Padmanabhan, J.; Parthasarathi, R.; Subramanian, V.; Chattaraj, P. K. Bioorg. Med. Chem. 2006, 14, 1021. (12) (a) Parr, R. G.; Pearson, R. G. J. Am. Chem. Soc. 1983, 105, 7512. (b) Pearson, R. G. Chemical Hardness: Applications from Molecules to Solids; Wiley-VCH: Weinheim, Germany, 1997. (13) Ghanty, T. K.; Ghosh, S. K. J. Phys. Chem. 1993, 97, 4951. (14) (a) Parr, R. G.; Szentpaly, L. v.; Liu, S. J. Am. Chem. Soc. 1999, 121, 1922. (b) Chattaraj, P. K.; Sarkar, U.; Roy, D. R. Chem. ReV. 2006, 106, 2065. (c) Chattaraj, P. K.; Roy, D. R. Chem. ReV. 2007, 107, PR46. (15) (a) Parr, R. G.; Donnelly, R. A.; Levy, M.; Palke, W. E. J. Chem. Phys. 1978, 68, 3801. (b) Chattaraj, P. K. J. Indian Chem. Soc. 1992, 69, 173. (16) Parr, R. G.; Chattaraj, P. K. J. Am. Chem. Soc. 1991, 113, 1854. (17) Chattaraj, P. K.; Sengupta, S. J. Phys. Chem. 1996, 100, 16126. (18) (a) Parthasarathi, R.; Elango, M.; Subramanian, V.; Chattaraj, P. K. Theor. Chem. Acc. 2005, 113, 257–266. (b) Chamorro, E.; Chattaraj, P. K.; Fuentealba, P. J. Phys. Chem. A 2003, 107, 7068. (19) Phukan, A. K.; Kalagi, R. P.; Gadre, S. R.; Jemmis, E. D. Inorg. Chem. 2004, 43, 5824. (20) Schleyer, P. v. R.; Maerker, C.; Dransfeld, A.; Jiao, H.; Hommes, N. J. R. v. E. J. Am. Chem. Soc. 1996, 118, 6317. (21) Iijima, S. Nature 1991, 354, 56. (22) Chen, Z.; Wannere, C. S.; Corminboeuf, C.; Puchta, R.; Schleyer, P. v. R. Chem. ReV. 2005, 105, 3842. (23) Havenith, R. W. A.; De Proft, F.; Fowler, P. W.; Geerlings, P. Chem. Phys. Lett. 2005, 407, 391. (24) Foroutan-Najed, C.; Rashidi-Ranjbar, P. THEOCHEM 2009, 901, 243.
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