Miquel Solà (1964) obtained his PhD at the UAB in 1991 with academic honours. His doctoral research under the supervision of Profs. Juan Bertran and Agustí Lledós was awarded with the Saint Albert Prize. After several months in a consultant private company, in 1993 he moved to the University of Girona (UdG) as assistant researcher. In 1994 he did postdoctoral research in Amsterdam with Prof. Evert Jan Baerends and in 1995 in Calgary with Prof. Tom Ziegler. He was appointed assistant professor of the UdG in 1997. In 2001, he got the Distinction for the Promotion of University Research (young scientist category). Since 2003, he holds a permanent position as full professor in the UdG. He was awarded with the ICREA Academia Prize two times, in 2009 and 2014. In 2013 he got the Physical Chemistry prize awarded by the Spanish Royal Society of Chemistry. He is coauthor of about 325 scientific papers that have received about 10000 citations and he has an index h of 53. He has supervised 15 doctoral Theses. He serves in the Editorial Board of Front. Chem., Theor. Chem. Acc. and Sci. Rep. journals. At the UdG, he has served as director of the Institute of Computational Chemistry (2004-07), director of the Department of Chemistry (2007-10), and director of the School of Doctoral Studies (2010-14). He is now coordinator of the Scientific field in the AGAUR of the Generalitat de Catalunya and associate coordinator of Chemistry in the ANEP. Supervisors: Joan Bertran Rusca and Agustí Lledós Falcó
Abstract An ab initio 3-21G study of the direct addition of HF to C 2 H n F (4–n), with n= 0 to 4... more Abstract An ab initio 3-21G study of the direct addition of HF to C 2 H n F (4–n), with n= 0 to 4, has been performed to investigate the effect of the substituent on the reaction. Geometry optimization of all charge-transfer complexes and transition states has been done. Standard analysis of activation energies of addition reactions, vibrational and thermodynamical analysis, as well as Morokuma energy decomposition, BSSE correction, PMO analysis, and Pauling bond orders were used to explain the results. A subset of the reactions, including ...
The influence of the N-substituent on the aromaticity of azoles is a subject that has not yet bee... more The influence of the N-substituent on the aromaticity of azoles is a subject that has not yet been addressed in detail, in contrast to the good understanding of the corresponding C-substitution. In the present work, we analyze the aromaticities of a series of 1,2- and 1,3-azoles (pyrazoles and imidazoles, respectively) with the N-substituents NH(2), OH, Cl, SH, H, NO(2), CN, SO(2)F, SO(2)CF(3), and N(SO(2)CF(3))(2), which are also compared with the aromaticities of the corresponding substituted benzene series. The larger stabilitiy of the imidazole ring is due not to a higher aromaticity, but rather to the weakness of the N-N bond in the pyrazole series. The aromaticity of azoles was found to be significantly less robust to N-substitutions than that of their C-substituted benzene counterparts.
A series of eleven gas-phase chemical reactions have been examined to assess the dependence of tr... more A series of eleven gas-phase chemical reactions have been examined to assess the dependence of transition state geometries and energy barriers, as well as energy differences between reactants and products, on the a 0 B3LYP functional parameter. Throughout the study we have changed the a 0 parameter from 0.1 to 0.9 and for the ac and ax parameters we have followed the relationships ax= 1− a 0 and ac= a x. By comparing with the QCISD transition state geometries and energy barriers, our systematic study ...
Haptotropic rearrangement reaction mechanisms for a series of polycyclic aromatic hydrocarbons (P... more Haptotropic rearrangement reaction mechanisms for a series of polycyclic aromatic hydrocarbons (PAHs) with three and four fused six-membered rings attached to a tricarbonylchromium complex were investigated by DFT methods. We have explored all the possible ways by which haptomigrations can occur, as for the less asymmetric PAHs there are nonequivalent reaction pathways.
In this work, we study the reaction mechanism of the tricarbonylchromium complex haptotropic rear... more In this work, we study the reaction mechanism of the tricarbonylchromium complex haptotropic rearrangement between two six-membered rings arranged like in naphthalene of four polycyclic aromatic hydrocarbons (PAHs). It has been found that the reaction mechanism of this haptotropic migration can either occur in a single step or stepwise depending on the interaction between the orbitals of the Cr(CO) 3 and the PAH fragments. Our results show that the size of the cyclic system favors the metal migration whereas the curvature of the organic substrate tends to slow down the rearrangement. We discuss the key factors that help to explain this behavior through orbital and energy decomposition analysis.
Bis (tricarbonylchromium) complexes of two-to four-fused benzenoid rings were investigated by mea... more Bis (tricarbonylchromium) complexes of two-to four-fused benzenoid rings were investigated by means of the B3LYP method. Our analysis was focused on both the molecular structure of the different isomers and their relative energies. For all the studied cases, the isomer with the lowest energy resulted to be the anti where both Cr (CO) 3 units are bonded to the most external rings. According to the calculated dissociation energies for the lowest energy isomers, stabilization due to metal bicomplexation is similar in angular and linear ...
A series of monocyclic planar inorganic compounds have been optimized at the B3LYP/6-311+G * leve... more A series of monocyclic planar inorganic compounds have been optimized at the B3LYP/6-311+G * level. GIAO-B3LYP nucleus-independent chemical shifts (NICS) profiles calculated in the perpendicular direction of each ring show that the series of analyzed compounds can be classified in three groups according to their aromatic, non-aromatic or antiaromatic character. Our results suggest exercising caution in the use of single-point NICS calculations as a quantitative measure of aromaticity for these species.
In this work, we analyze the geometry and electronic structure of the [X(n)M(3)](n-2) species (M ... more In this work, we analyze the geometry and electronic structure of the [X(n)M(3)](n-2) species (M = Be, Mg, and Ca; X = Li, Na, and K; n = 0, 1, and 2), with special emphasis on the electron delocalization properties and aromaticity of the cyclo-[M(3)](2-) unit. The cyclo-[M(3)](2-) ring is held together through a three-center two-electron bond of sigma-character. Interestingly, the interaction of these small clusters with alkali metals stabilizes the cyclo-[M(3)](2-) ring and leads to a change from sigma-aromaticity in the bound state of the cyclo-[M(3)](2-) to pi-aromaticity in the XM(3) (-) and X(2)M(3) metallic clusters. Our results also show that the aromaticity of the cyclo-[M(3)](2-) unit in the X(2)M(3) metallic clusters depends on the nature of X and M. Moreover, we explored the possibility for tuning the aromaticity by simply moving X perpendicularly to the center of the M(3) ring. The Na(2)Mg(3), Li(2)Mg(3), and X(2)Ca(3) clusters undergo drastic aromaticity alterations when changing the distance from X to the center of the M(3) ring, whereas X(2)Be(3) and K(2)Mg(3) keep its aromaticity relatively constant along this process.
In this work, we analyze the geometry and electronic structure of the [X(n)M(3)](n-2) species (M ... more In this work, we analyze the geometry and electronic structure of the [X(n)M(3)](n-2) species (M = Be, Mg, and Ca; X = Li, Na, and K; n = 0, 1, and 2), with special emphasis on the electron delocalization properties and aromaticity of the cyclo-[M(3)](2-) unit. The cyclo-[M(3)](2-) ring is held together through a three-center two-electron bond of sigma-character. Interestingly, the interaction of these small clusters with alkali metals stabilizes the cyclo-[M(3)](2-) ring and leads to a change from sigma-aromaticity in the bound state of the cyclo-[M(3)](2-) to pi-aromaticity in the XM(3) (-) and X(2)M(3) metallic clusters. Our results also show that the aromaticity of the cyclo-[M(3)](2-) unit in the X(2)M(3) metallic clusters depends on the nature of X and M. Moreover, we explored the possibility for tuning the aromaticity by simply moving X perpendicularly to the center of the M(3) ring. The Na(2)Mg(3), Li(2)Mg(3), and X(2)Ca(3) clusters undergo drastic aromaticity alterations when changing the distance from X to the center of the M(3) ring, whereas X(2)Be(3) and K(2)Mg(3) keep its aromaticity relatively constant along this process.
Competitive retro-cycloaddition in [60]-and [70]fullerene homodimers (1a,1c) as well as [60]/[70]... more Competitive retro-cycloaddition in [60]-and [70]fullerene homodimers (1a,1c) as well as [60]/[70]heterodimer (1b), linked through 2-pyrazolinopyrrolidino bridges, has been studied by means of HPLC, mass spectrometry, and theoretical calculations at the density functional theory (DFT) level by using the two-layered ONIOM approach. The results of these investigations indicate that the retro-cycloaddition reaction of pyrrolidinofullerenes is favored compared to the retrocycloaddition reaction of 2-pyrazolinofullerenes in compounds 1a-c. Evidence of the occurrence of this process have been observed both by HPLC and MS-MALDI, these findings being in good agreement with those predicted by theoretical calculations. (1) Kroto, H. W.; Heath, J. R.; O'Brien, S. C.; Curl, R. F.; Smalley, R. E. Nature 1985, 318, 162. (2) (a) For a recent review, see: Delgado, J. L.; Herranz, M. A.; Martı´n, N. Altable, M.; Filippone, S.; Martı´n-Dom enech, A. Synlett 2007, 3077. (5) (a) Martı´n, N.; Altable, M.; Filippone, S.; Martı´n-Dom enech, A.; Echegoyen, L.; Cardona, C. M. Angew. Chem., Int. Ed. 2006, 45, 110. (b) Lukoyanova, O.; Cardona, C. M.; Echegoyen, L.; Altable, M.; Filippone, S.; Martı´n Dom enech, A.; Martı´n, N. Angew. Chem., Int. Ed. 2006, 45, 7430. (c) For a retro-cycloaddition on SWCNTs, see: Bruneti, F. G.; Herrero, M. A.; Muñoz, J. M.; Giordani, S.; Diaz-Ortiz, A.; Filippone, S.; Ruaro, G.; Meneghetti, M.; Prato, M.; V azquez, E.
The hydrogen-alkali metal bond is simple and archetypal, and thus an ideal model for studying the... more The hydrogen-alkali metal bond is simple and archetypal, and thus an ideal model for studying the nature of highly polar element-metal bonds. Thus, we have theoretically explored the alkali metal hydride monomers, HM, and (distorted) cubic tetramers, (HM) 4 , with M = Li, Na, K, and Rb, using density functional theory (DFT) at the BP86/TZ2P level. Our objective is to determine how the structure and thermochemistry (e.g., H-M bond lengths and strengths, oligomerization energies, etc.) of alkali metal hydrides depend on the metal atom, and to understand the emerging trends in terms of quantitative Kohn-Sham molecular orbital (KS-MO) theory. The H-M bond becomes longer and weaker, both in the monomers and tetramers, if one descends the periodic table from Li to Rb. Quantitative bonding analyses show that this trend is not determined by decreasing electrostatic attraction but, primarily, by the weakening in orbital interactions. The latter become less stabilizing along Li-Rb because the bond overlap between the singly occupied molecular orbitals (SOMOs) of H d and M d radicals decreases as the metal ns atomic orbital (AO) becomes larger and more diffuse. Thus, the H-M bond behaves as a text-book electron-pair bond and, in that respect, it is covalent, despite a high polarity. For the lithium and sodium hydride tetramers, the H 4 tetrahedron is larger than and surrounds the M 4 cluster (i.e., H-H 4 M-M). Interestingly, this is no longer the case in the potassium and rubidium hydride tetramers, in which the H 4 tetrahedron is smaller than and inside the M 4 cluster (i.e., H-H o M-M).
We have investigated the performance of a variety of density functional methods for weak intra-an... more We have investigated the performance of a variety of density functional methods for weak intra-and intermolecular dispersion interactions. Grimme's empirical dispersion correction method is shown to give a good description for these interactions and helps to improve the description of water-hexamer isomers, noble-gas dimers, hydrocarbon C 12 H 12 isomers, branching energy of linear versus branched octane, dissociation of the covalently bound anthracene dimer, and stacking within the adenine dimer. However, the dispersion correction does not correct all shortcomings of the different density functionals, which leads to sizeable differences compared to ab initio CCSD(T) and experimental reference data. The only exception is shown to be our recently presented SSB-D functional that works well for all systems studied here. q
The structures of alkali metal complexes of silyl-substituted ansa-tris(allyl) ligands [RSi(C 3 H... more The structures of alkali metal complexes of silyl-substituted ansa-tris(allyl) ligands [RSi(C 3 H 3 SiMe 3 ) 3 ] 3-(R = Me, L 1 ; or Ph, L 2 ) are discussed. Triple deprotonation of L 1 H 3 by nBuNa/tmeda affords [L 1 {Na(tmeda)} 3 ] (4) in which the sodium cations are complexed by η n -allyl ligands and the silyl substituents adopt [exo,exo][endo,exo] 2 stereochemistries in one crystallographically disordered form and [endo,exo] 3 in another. Triple deprotonation of L 2 H 3 with nBuLi/tmeda results in the formation of [L 2 {Li(tmeda)} 3 ] (5), the structure of which features silyl substituents with [exo,exo] 2 [endo,exo] stereochemistries. The trisodium complex [L 2 Na{Na-(tmeda)} 2 ] 2 (6) consists of a hexa(allylsodium) macrocycle that aggregates as a result of cation-π interactions between the phenyl substituents and the sodium cations. An attempt to prepare the tripotassium complex of L 1 resulted in the formation of the bimetallic potassium/lithium complex [a]
The most polar bond in chemistry is that between a fluorine and an alkalimetal atom. Inspired by ... more The most polar bond in chemistry is that between a fluorine and an alkalimetal atom. Inspired by our recent finding that other polar bonds (CÀ ÀM and HÀ ÀM) have important covalent contributions (i.e., stabilization due to bond overlap), we herein address the question if covalency is also essential in the FÀ ÀM bond. Thus, we have theoretically studied the alkalimetal fluoride monomers, FM, and (distorted) cubic tetramers, (FM) 4 , with M ¼ Li, Na, K, and Rb, using density functional theory at the BP86/TZ2P level. Our objective is to determine how the structure and thermochemistry (e.g., FÀ ÀM bond lengths and strengths, oligomerization energies, etc.) of alkalimetal fluorides depend on the metal atom, and to understand the emerging trends in terms of quantitative Kohn-Sham molecular orbital theory. The analyses confirm the extreme polarity of the FÀ ÀM bond (dipole moment, Voronoi deformation density and Hirshfeld atomic charges), and they reveal that bond overlap-derived stabilization (ca. À6, À6, and À2 kcal/mol) contributes only little to the bond strength (À136, À112, and À114 kcal/mol) and the trend therein along Li, Na, and K. According to this and other criteria, the FÀ ÀM bond is not only strongly polar, but also has a truly ionic bonding mechanism. Interestingly, the polarity is reduced on tetramerization. For the lithium and sodium fluoride tetramers, the F 4 tetrahedron is larger than and surrounds the M 4 cluster (i.e., FÀ ÀF > MÀ ÀM). But in the potassium and rubidium fluoride tetramers, the F 4 tetrahedron is smaller than and inside the M 4 cluster (i.e., FÀ ÀF < MÀ ÀM).
International Conference of Computational Methods in Sciences and Engineering 2009 (Iccmse 2009), 2012
ABSTRACT We recently reported a study into what causes the dramatic differences between OPBE and ... more ABSTRACT We recently reported a study into what causes the dramatic differences between OPBE and PBE for reaction barriers, spin-state energies, hydrogen-bonding and π-π stacking energies.1 It was achieved by smoothly switching from OPBE to PBE at a predefined point P of the reduced density gradient s. By letting the point P run as function of the reduced density gradient s, with values from s=0.1 to s=10, we could determine which part of the exchange functional determines its behavior for the different interactions. Based on the thus obtained results, we created a new exchange functional that showed the good results of OPBE for reaction barriers and spin-state energies, and combined it with the good (H-bonds) and reasonable (π-stacking) results of PBE for weak interactions. In other words, it combined the best of OPBE with the best of PBE. Encouraged by these good results, we have further improved the new exchange functional and fine-tuned its parameters.2 Similar to the switched functional from ref. 1, our new SSB functional2 works well for SN2 barriers (see e.g. ref. 3), spin states and H-bonding interactions. Moreover, by including Grimme&#39;s dispersion corrections4,5 (to give our final SSB-D functional) it also works well for π-π stacking interactions.2 In summary, we have constructed a new GGA exchange functional that when combined with the sPBE correlation functional6 gives the correct spin ground-state of iron complexes, and small deviations for SN2 barriers (2.7 kcal.mol-1), geometries (0.005 A˚), Hbond distances (0.012 A˚), weak interactions (S22 set, 0.5 kcal.mol-1), and transition-metal ligand distances (0.008 A˚).
An expansion of the energy functional in terms of the total number of electrons and the normal co... more An expansion of the energy functional in terms of the total number of electrons and the normal coordinates within the canonical ensemble is presented. A comparison of this expansion with the expansion of the energy in terms of the total number of electrons and the external potential leads to new relations among common density functional reactivity descriptors. The formulas obtained provide explicit links between important quantities related to the chemical reactivity of a system. In particular, the relation between the nuclear and the electronic Fukui functions is recovered. The connection between the derivatives of the electronic energy and the nuclear repulsion energy with respect to the external potential offers a proof for the ''Quantum Chemical le Chatelier Principle.'' Finally, the nuclear linear response function is defined and the relation of this function with the electronic linear response function is given.
The recently reported SSB-D functional [J. Chem. Phys. 2009, 131, 094103] is used to check the pe... more The recently reported SSB-D functional [J. Chem. Phys. 2009, 131, 094103] is used to check the performance for obtaining nuclear magnetic resonance (NMR) shielding constants. Four different databases were studied, which contain a diversity of molecules and nuclear shielding constants. The SSB-D functional is compared with its &amp;amp;amp;amp;amp;amp;amp;amp;quot;parent&amp;amp;amp;amp;amp;amp;amp;amp;quot; functionals (PBE, OPBE), the KT2 functional that was designed specially for NMR applications and the coupled cluster CCSD(T) method. The best performance for the experimentally most-used elements ((1)H, (13)C) is obtained for the SSB-D and KT2 functionals.
Abstract An ab initio 3-21G study of the direct addition of HF to C 2 H n F (4–n), with n= 0 to 4... more Abstract An ab initio 3-21G study of the direct addition of HF to C 2 H n F (4–n), with n= 0 to 4, has been performed to investigate the effect of the substituent on the reaction. Geometry optimization of all charge-transfer complexes and transition states has been done. Standard analysis of activation energies of addition reactions, vibrational and thermodynamical analysis, as well as Morokuma energy decomposition, BSSE correction, PMO analysis, and Pauling bond orders were used to explain the results. A subset of the reactions, including ...
The influence of the N-substituent on the aromaticity of azoles is a subject that has not yet bee... more The influence of the N-substituent on the aromaticity of azoles is a subject that has not yet been addressed in detail, in contrast to the good understanding of the corresponding C-substitution. In the present work, we analyze the aromaticities of a series of 1,2- and 1,3-azoles (pyrazoles and imidazoles, respectively) with the N-substituents NH(2), OH, Cl, SH, H, NO(2), CN, SO(2)F, SO(2)CF(3), and N(SO(2)CF(3))(2), which are also compared with the aromaticities of the corresponding substituted benzene series. The larger stabilitiy of the imidazole ring is due not to a higher aromaticity, but rather to the weakness of the N-N bond in the pyrazole series. The aromaticity of azoles was found to be significantly less robust to N-substitutions than that of their C-substituted benzene counterparts.
A series of eleven gas-phase chemical reactions have been examined to assess the dependence of tr... more A series of eleven gas-phase chemical reactions have been examined to assess the dependence of transition state geometries and energy barriers, as well as energy differences between reactants and products, on the a 0 B3LYP functional parameter. Throughout the study we have changed the a 0 parameter from 0.1 to 0.9 and for the ac and ax parameters we have followed the relationships ax= 1− a 0 and ac= a x. By comparing with the QCISD transition state geometries and energy barriers, our systematic study ...
Haptotropic rearrangement reaction mechanisms for a series of polycyclic aromatic hydrocarbons (P... more Haptotropic rearrangement reaction mechanisms for a series of polycyclic aromatic hydrocarbons (PAHs) with three and four fused six-membered rings attached to a tricarbonylchromium complex were investigated by DFT methods. We have explored all the possible ways by which haptomigrations can occur, as for the less asymmetric PAHs there are nonequivalent reaction pathways.
In this work, we study the reaction mechanism of the tricarbonylchromium complex haptotropic rear... more In this work, we study the reaction mechanism of the tricarbonylchromium complex haptotropic rearrangement between two six-membered rings arranged like in naphthalene of four polycyclic aromatic hydrocarbons (PAHs). It has been found that the reaction mechanism of this haptotropic migration can either occur in a single step or stepwise depending on the interaction between the orbitals of the Cr(CO) 3 and the PAH fragments. Our results show that the size of the cyclic system favors the metal migration whereas the curvature of the organic substrate tends to slow down the rearrangement. We discuss the key factors that help to explain this behavior through orbital and energy decomposition analysis.
Bis (tricarbonylchromium) complexes of two-to four-fused benzenoid rings were investigated by mea... more Bis (tricarbonylchromium) complexes of two-to four-fused benzenoid rings were investigated by means of the B3LYP method. Our analysis was focused on both the molecular structure of the different isomers and their relative energies. For all the studied cases, the isomer with the lowest energy resulted to be the anti where both Cr (CO) 3 units are bonded to the most external rings. According to the calculated dissociation energies for the lowest energy isomers, stabilization due to metal bicomplexation is similar in angular and linear ...
A series of monocyclic planar inorganic compounds have been optimized at the B3LYP/6-311+G * leve... more A series of monocyclic planar inorganic compounds have been optimized at the B3LYP/6-311+G * level. GIAO-B3LYP nucleus-independent chemical shifts (NICS) profiles calculated in the perpendicular direction of each ring show that the series of analyzed compounds can be classified in three groups according to their aromatic, non-aromatic or antiaromatic character. Our results suggest exercising caution in the use of single-point NICS calculations as a quantitative measure of aromaticity for these species.
In this work, we analyze the geometry and electronic structure of the [X(n)M(3)](n-2) species (M ... more In this work, we analyze the geometry and electronic structure of the [X(n)M(3)](n-2) species (M = Be, Mg, and Ca; X = Li, Na, and K; n = 0, 1, and 2), with special emphasis on the electron delocalization properties and aromaticity of the cyclo-[M(3)](2-) unit. The cyclo-[M(3)](2-) ring is held together through a three-center two-electron bond of sigma-character. Interestingly, the interaction of these small clusters with alkali metals stabilizes the cyclo-[M(3)](2-) ring and leads to a change from sigma-aromaticity in the bound state of the cyclo-[M(3)](2-) to pi-aromaticity in the XM(3) (-) and X(2)M(3) metallic clusters. Our results also show that the aromaticity of the cyclo-[M(3)](2-) unit in the X(2)M(3) metallic clusters depends on the nature of X and M. Moreover, we explored the possibility for tuning the aromaticity by simply moving X perpendicularly to the center of the M(3) ring. The Na(2)Mg(3), Li(2)Mg(3), and X(2)Ca(3) clusters undergo drastic aromaticity alterations when changing the distance from X to the center of the M(3) ring, whereas X(2)Be(3) and K(2)Mg(3) keep its aromaticity relatively constant along this process.
In this work, we analyze the geometry and electronic structure of the [X(n)M(3)](n-2) species (M ... more In this work, we analyze the geometry and electronic structure of the [X(n)M(3)](n-2) species (M = Be, Mg, and Ca; X = Li, Na, and K; n = 0, 1, and 2), with special emphasis on the electron delocalization properties and aromaticity of the cyclo-[M(3)](2-) unit. The cyclo-[M(3)](2-) ring is held together through a three-center two-electron bond of sigma-character. Interestingly, the interaction of these small clusters with alkali metals stabilizes the cyclo-[M(3)](2-) ring and leads to a change from sigma-aromaticity in the bound state of the cyclo-[M(3)](2-) to pi-aromaticity in the XM(3) (-) and X(2)M(3) metallic clusters. Our results also show that the aromaticity of the cyclo-[M(3)](2-) unit in the X(2)M(3) metallic clusters depends on the nature of X and M. Moreover, we explored the possibility for tuning the aromaticity by simply moving X perpendicularly to the center of the M(3) ring. The Na(2)Mg(3), Li(2)Mg(3), and X(2)Ca(3) clusters undergo drastic aromaticity alterations when changing the distance from X to the center of the M(3) ring, whereas X(2)Be(3) and K(2)Mg(3) keep its aromaticity relatively constant along this process.
Competitive retro-cycloaddition in [60]-and [70]fullerene homodimers (1a,1c) as well as [60]/[70]... more Competitive retro-cycloaddition in [60]-and [70]fullerene homodimers (1a,1c) as well as [60]/[70]heterodimer (1b), linked through 2-pyrazolinopyrrolidino bridges, has been studied by means of HPLC, mass spectrometry, and theoretical calculations at the density functional theory (DFT) level by using the two-layered ONIOM approach. The results of these investigations indicate that the retro-cycloaddition reaction of pyrrolidinofullerenes is favored compared to the retrocycloaddition reaction of 2-pyrazolinofullerenes in compounds 1a-c. Evidence of the occurrence of this process have been observed both by HPLC and MS-MALDI, these findings being in good agreement with those predicted by theoretical calculations. (1) Kroto, H. W.; Heath, J. R.; O'Brien, S. C.; Curl, R. F.; Smalley, R. E. Nature 1985, 318, 162. (2) (a) For a recent review, see: Delgado, J. L.; Herranz, M. A.; Martı´n, N. Altable, M.; Filippone, S.; Martı´n-Dom enech, A. Synlett 2007, 3077. (5) (a) Martı´n, N.; Altable, M.; Filippone, S.; Martı´n-Dom enech, A.; Echegoyen, L.; Cardona, C. M. Angew. Chem., Int. Ed. 2006, 45, 110. (b) Lukoyanova, O.; Cardona, C. M.; Echegoyen, L.; Altable, M.; Filippone, S.; Martı´n Dom enech, A.; Martı´n, N. Angew. Chem., Int. Ed. 2006, 45, 7430. (c) For a retro-cycloaddition on SWCNTs, see: Bruneti, F. G.; Herrero, M. A.; Muñoz, J. M.; Giordani, S.; Diaz-Ortiz, A.; Filippone, S.; Ruaro, G.; Meneghetti, M.; Prato, M.; V azquez, E.
The hydrogen-alkali metal bond is simple and archetypal, and thus an ideal model for studying the... more The hydrogen-alkali metal bond is simple and archetypal, and thus an ideal model for studying the nature of highly polar element-metal bonds. Thus, we have theoretically explored the alkali metal hydride monomers, HM, and (distorted) cubic tetramers, (HM) 4 , with M = Li, Na, K, and Rb, using density functional theory (DFT) at the BP86/TZ2P level. Our objective is to determine how the structure and thermochemistry (e.g., H-M bond lengths and strengths, oligomerization energies, etc.) of alkali metal hydrides depend on the metal atom, and to understand the emerging trends in terms of quantitative Kohn-Sham molecular orbital (KS-MO) theory. The H-M bond becomes longer and weaker, both in the monomers and tetramers, if one descends the periodic table from Li to Rb. Quantitative bonding analyses show that this trend is not determined by decreasing electrostatic attraction but, primarily, by the weakening in orbital interactions. The latter become less stabilizing along Li-Rb because the bond overlap between the singly occupied molecular orbitals (SOMOs) of H d and M d radicals decreases as the metal ns atomic orbital (AO) becomes larger and more diffuse. Thus, the H-M bond behaves as a text-book electron-pair bond and, in that respect, it is covalent, despite a high polarity. For the lithium and sodium hydride tetramers, the H 4 tetrahedron is larger than and surrounds the M 4 cluster (i.e., H-H 4 M-M). Interestingly, this is no longer the case in the potassium and rubidium hydride tetramers, in which the H 4 tetrahedron is smaller than and inside the M 4 cluster (i.e., H-H o M-M).
We have investigated the performance of a variety of density functional methods for weak intra-an... more We have investigated the performance of a variety of density functional methods for weak intra-and intermolecular dispersion interactions. Grimme's empirical dispersion correction method is shown to give a good description for these interactions and helps to improve the description of water-hexamer isomers, noble-gas dimers, hydrocarbon C 12 H 12 isomers, branching energy of linear versus branched octane, dissociation of the covalently bound anthracene dimer, and stacking within the adenine dimer. However, the dispersion correction does not correct all shortcomings of the different density functionals, which leads to sizeable differences compared to ab initio CCSD(T) and experimental reference data. The only exception is shown to be our recently presented SSB-D functional that works well for all systems studied here. q
The structures of alkali metal complexes of silyl-substituted ansa-tris(allyl) ligands [RSi(C 3 H... more The structures of alkali metal complexes of silyl-substituted ansa-tris(allyl) ligands [RSi(C 3 H 3 SiMe 3 ) 3 ] 3-(R = Me, L 1 ; or Ph, L 2 ) are discussed. Triple deprotonation of L 1 H 3 by nBuNa/tmeda affords [L 1 {Na(tmeda)} 3 ] (4) in which the sodium cations are complexed by η n -allyl ligands and the silyl substituents adopt [exo,exo][endo,exo] 2 stereochemistries in one crystallographically disordered form and [endo,exo] 3 in another. Triple deprotonation of L 2 H 3 with nBuLi/tmeda results in the formation of [L 2 {Li(tmeda)} 3 ] (5), the structure of which features silyl substituents with [exo,exo] 2 [endo,exo] stereochemistries. The trisodium complex [L 2 Na{Na-(tmeda)} 2 ] 2 (6) consists of a hexa(allylsodium) macrocycle that aggregates as a result of cation-π interactions between the phenyl substituents and the sodium cations. An attempt to prepare the tripotassium complex of L 1 resulted in the formation of the bimetallic potassium/lithium complex [a]
The most polar bond in chemistry is that between a fluorine and an alkalimetal atom. Inspired by ... more The most polar bond in chemistry is that between a fluorine and an alkalimetal atom. Inspired by our recent finding that other polar bonds (CÀ ÀM and HÀ ÀM) have important covalent contributions (i.e., stabilization due to bond overlap), we herein address the question if covalency is also essential in the FÀ ÀM bond. Thus, we have theoretically studied the alkalimetal fluoride monomers, FM, and (distorted) cubic tetramers, (FM) 4 , with M ¼ Li, Na, K, and Rb, using density functional theory at the BP86/TZ2P level. Our objective is to determine how the structure and thermochemistry (e.g., FÀ ÀM bond lengths and strengths, oligomerization energies, etc.) of alkalimetal fluorides depend on the metal atom, and to understand the emerging trends in terms of quantitative Kohn-Sham molecular orbital theory. The analyses confirm the extreme polarity of the FÀ ÀM bond (dipole moment, Voronoi deformation density and Hirshfeld atomic charges), and they reveal that bond overlap-derived stabilization (ca. À6, À6, and À2 kcal/mol) contributes only little to the bond strength (À136, À112, and À114 kcal/mol) and the trend therein along Li, Na, and K. According to this and other criteria, the FÀ ÀM bond is not only strongly polar, but also has a truly ionic bonding mechanism. Interestingly, the polarity is reduced on tetramerization. For the lithium and sodium fluoride tetramers, the F 4 tetrahedron is larger than and surrounds the M 4 cluster (i.e., FÀ ÀF > MÀ ÀM). But in the potassium and rubidium fluoride tetramers, the F 4 tetrahedron is smaller than and inside the M 4 cluster (i.e., FÀ ÀF < MÀ ÀM).
International Conference of Computational Methods in Sciences and Engineering 2009 (Iccmse 2009), 2012
ABSTRACT We recently reported a study into what causes the dramatic differences between OPBE and ... more ABSTRACT We recently reported a study into what causes the dramatic differences between OPBE and PBE for reaction barriers, spin-state energies, hydrogen-bonding and π-π stacking energies.1 It was achieved by smoothly switching from OPBE to PBE at a predefined point P of the reduced density gradient s. By letting the point P run as function of the reduced density gradient s, with values from s=0.1 to s=10, we could determine which part of the exchange functional determines its behavior for the different interactions. Based on the thus obtained results, we created a new exchange functional that showed the good results of OPBE for reaction barriers and spin-state energies, and combined it with the good (H-bonds) and reasonable (π-stacking) results of PBE for weak interactions. In other words, it combined the best of OPBE with the best of PBE. Encouraged by these good results, we have further improved the new exchange functional and fine-tuned its parameters.2 Similar to the switched functional from ref. 1, our new SSB functional2 works well for SN2 barriers (see e.g. ref. 3), spin states and H-bonding interactions. Moreover, by including Grimme&#39;s dispersion corrections4,5 (to give our final SSB-D functional) it also works well for π-π stacking interactions.2 In summary, we have constructed a new GGA exchange functional that when combined with the sPBE correlation functional6 gives the correct spin ground-state of iron complexes, and small deviations for SN2 barriers (2.7 kcal.mol-1), geometries (0.005 A˚), Hbond distances (0.012 A˚), weak interactions (S22 set, 0.5 kcal.mol-1), and transition-metal ligand distances (0.008 A˚).
An expansion of the energy functional in terms of the total number of electrons and the normal co... more An expansion of the energy functional in terms of the total number of electrons and the normal coordinates within the canonical ensemble is presented. A comparison of this expansion with the expansion of the energy in terms of the total number of electrons and the external potential leads to new relations among common density functional reactivity descriptors. The formulas obtained provide explicit links between important quantities related to the chemical reactivity of a system. In particular, the relation between the nuclear and the electronic Fukui functions is recovered. The connection between the derivatives of the electronic energy and the nuclear repulsion energy with respect to the external potential offers a proof for the ''Quantum Chemical le Chatelier Principle.'' Finally, the nuclear linear response function is defined and the relation of this function with the electronic linear response function is given.
The recently reported SSB-D functional [J. Chem. Phys. 2009, 131, 094103] is used to check the pe... more The recently reported SSB-D functional [J. Chem. Phys. 2009, 131, 094103] is used to check the performance for obtaining nuclear magnetic resonance (NMR) shielding constants. Four different databases were studied, which contain a diversity of molecules and nuclear shielding constants. The SSB-D functional is compared with its &amp;amp;amp;amp;amp;amp;amp;amp;quot;parent&amp;amp;amp;amp;amp;amp;amp;amp;quot; functionals (PBE, OPBE), the KT2 functional that was designed specially for NMR applications and the coupled cluster CCSD(T) method. The best performance for the experimentally most-used elements ((1)H, (13)C) is obtained for the SSB-D and KT2 functionals.
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Papers by Miquel Solà