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Metallacycles Capabilities in Host-Guest Chemistry.

Ponce-Vargas M - ChemistryOpen (2015)

View Article: PubMed Central - PubMed

Affiliation: Institut des Sciences Chimiques de Rennes UMR 6226, Université de Rennes 1 Campus de Beaulieu, 35042, Rennes, France.

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: Universidad Andrés Bello (Chile) : January 20th, 2015 : Dr. Alvaro Muñoz Castro, Universidad Autónoma de Chile, Carlos Antúnez 1920, Santiago (Chile) Host–guest chemistry encompasses the study of highly structured molecular complexes composed of at least two entities associated by noncovalent interactions, one possessing convergent binding sites, the host, and another possessing divergent binding sites, the guest... The metallacycle host interacts with the guest species via oxygen or nitrogen atoms located within the supporting ligands, while only to a minor extent, the metal centers play this role, giving rise to a more interesting scenario where the nature of the host–guest interactions is related to these uncommon binding sites... Two representative series of metallacycle systems have been selected for this research, the halide-centered hexanuclear copper(II) pyrazolate complexes [trans-Cu6(3,5-(CF3)2pz)6(OH)6X] (X=F, Cl, Br, I), synthesized by Mohamed and co-workers, and the di-halide cyclic pentameric perfluoroisopropylidenemercury complexes [(HgC(CF3)2)52X] (X=Cl, Br, I), synthesized by Antipin and co-workers, both with metal centers acting as binding sites and halide ions as guest species (Scheme 1)... In the halide-centered hexanuclear copper(II) pyrazolate complexes [trans-Cu6(3,5-(CF3)2pz)6(OH)6X] (X=F, Cl, Br, I), denoted as –X, the EDA reveals that the fluorine complex (–F) is the most favorable structure (−79.43 kcal mol of total interaction energy ΔEint), followed by the chloride (−73.00 kcal mol), bromide (−69.81 kcal mol) and iodide (−60.12 kcal mol) systems, suggesting that the copper metallacycle exhibit a preference for hard bases... These results are determined in a great extent by the magnitude of the destabilizing Pauli term (ΔEPauli), which decreases the total interaction energy as the guest size increases... This behavior can be attributed to the relevance of the ion–multipole interactions (ion–dipole, ion–quadrupole, quadrupole–dipole and quadrupole–quadrupole) between the binding sites of the host, namely the Cu centers, and the guest, resulting in the stabilization of the host–guest pair... To obtain a clear representation of the distortion from spherical symmetry experienced by the electronic density at the guest and host binding sites, we evaluated the corresponding quadrupole moment tensors, including their graphical representation as an isosurface, similarly to other second-rank tensor magnitudes... A set of principal axes can always be found such as the off-diagonal elements vanish leading to the principal axis representation, where the tensor is depicted in its own framework... We suggest that these electron-deficient regions are those that mainly interact with the negative axial distribution of the guest, leading to quadrupole–quadrupole forces... Interestingly, the guest axial component reaches its more negative value in –I, where a more effective match occurs with the metallacycle electron-deficient regions defined by the copper quadrupole positive lobes... The observed variation of the quadrupole moment of the host Cu centers reveals that metallacycles acting as hosts can offer clear advantages in comparison to their organic counterparts, prompted by the versatility of their metal centers capable to adjust their electron densities according to the incoming guest, leading to different ranges of electron-density anisotropies, associated to electron density fluctuations, and hence, to noncovalent interactions... The EDA also suggests the electrostatic character of the host–guest pair, which is ruled by the ion–multipole term by about 97 %, favoring the inclusion of the hardest ion... Interestingly, in this series, higher-order Coulombic terms do not arise in a great extent even in the iodide system... Additionally, by using the NPA, the importance of trifluoromethyl groups in promoting the electron-charge transfer is evidenced once again... As concluding remarks, we can mention that the methodologies here employed allowed us to determine the mainly electrostatic character of host–guest interactions in metallacycle-based complexes and to weigh the role of certain Coulombic terms, leading to a clear rationalization of the host–guest coupling.

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Graphical representation of the electric quadrupole tensors of the studied systems.
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fig02: Graphical representation of the electric quadrupole tensors of the studied systems.

Mentions: To obtain a clear representation of the distortion from spherical symmetry experienced by the electronic density at the guest and host binding sites, we evaluated the corresponding quadrupole moment tensors, including their graphical representation as an isosurface, similarly to other second-rank tensor magnitudes. A set of principal axes can always be found such as the off-diagonal elements vanish leading to the principal axis representation, where the tensor is depicted in its own framework. The graphical representation of the quadrupole tensors is given in Figure 2.


Metallacycles Capabilities in Host-Guest Chemistry.

Ponce-Vargas M - ChemistryOpen (2015)

Graphical representation of the electric quadrupole tensors of the studied systems.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4608535&req=5

fig02: Graphical representation of the electric quadrupole tensors of the studied systems.
Mentions: To obtain a clear representation of the distortion from spherical symmetry experienced by the electronic density at the guest and host binding sites, we evaluated the corresponding quadrupole moment tensors, including their graphical representation as an isosurface, similarly to other second-rank tensor magnitudes. A set of principal axes can always be found such as the off-diagonal elements vanish leading to the principal axis representation, where the tensor is depicted in its own framework. The graphical representation of the quadrupole tensors is given in Figure 2.

View Article: PubMed Central - PubMed

Affiliation: Institut des Sciences Chimiques de Rennes UMR 6226, Université de Rennes 1 Campus de Beaulieu, 35042, Rennes, France.

AUTOMATICALLY GENERATED EXCERPT
Please rate it.

: Universidad Andrés Bello (Chile) : January 20th, 2015 : Dr. Alvaro Muñoz Castro, Universidad Autónoma de Chile, Carlos Antúnez 1920, Santiago (Chile) Host–guest chemistry encompasses the study of highly structured molecular complexes composed of at least two entities associated by noncovalent interactions, one possessing convergent binding sites, the host, and another possessing divergent binding sites, the guest... The metallacycle host interacts with the guest species via oxygen or nitrogen atoms located within the supporting ligands, while only to a minor extent, the metal centers play this role, giving rise to a more interesting scenario where the nature of the host–guest interactions is related to these uncommon binding sites... Two representative series of metallacycle systems have been selected for this research, the halide-centered hexanuclear copper(II) pyrazolate complexes [trans-Cu6(3,5-(CF3)2pz)6(OH)6X] (X=F, Cl, Br, I), synthesized by Mohamed and co-workers, and the di-halide cyclic pentameric perfluoroisopropylidenemercury complexes [(HgC(CF3)2)52X] (X=Cl, Br, I), synthesized by Antipin and co-workers, both with metal centers acting as binding sites and halide ions as guest species (Scheme 1)... In the halide-centered hexanuclear copper(II) pyrazolate complexes [trans-Cu6(3,5-(CF3)2pz)6(OH)6X] (X=F, Cl, Br, I), denoted as –X, the EDA reveals that the fluorine complex (–F) is the most favorable structure (−79.43 kcal mol of total interaction energy ΔEint), followed by the chloride (−73.00 kcal mol), bromide (−69.81 kcal mol) and iodide (−60.12 kcal mol) systems, suggesting that the copper metallacycle exhibit a preference for hard bases... These results are determined in a great extent by the magnitude of the destabilizing Pauli term (ΔEPauli), which decreases the total interaction energy as the guest size increases... This behavior can be attributed to the relevance of the ion–multipole interactions (ion–dipole, ion–quadrupole, quadrupole–dipole and quadrupole–quadrupole) between the binding sites of the host, namely the Cu centers, and the guest, resulting in the stabilization of the host–guest pair... To obtain a clear representation of the distortion from spherical symmetry experienced by the electronic density at the guest and host binding sites, we evaluated the corresponding quadrupole moment tensors, including their graphical representation as an isosurface, similarly to other second-rank tensor magnitudes... A set of principal axes can always be found such as the off-diagonal elements vanish leading to the principal axis representation, where the tensor is depicted in its own framework... We suggest that these electron-deficient regions are those that mainly interact with the negative axial distribution of the guest, leading to quadrupole–quadrupole forces... Interestingly, the guest axial component reaches its more negative value in –I, where a more effective match occurs with the metallacycle electron-deficient regions defined by the copper quadrupole positive lobes... The observed variation of the quadrupole moment of the host Cu centers reveals that metallacycles acting as hosts can offer clear advantages in comparison to their organic counterparts, prompted by the versatility of their metal centers capable to adjust their electron densities according to the incoming guest, leading to different ranges of electron-density anisotropies, associated to electron density fluctuations, and hence, to noncovalent interactions... The EDA also suggests the electrostatic character of the host–guest pair, which is ruled by the ion–multipole term by about 97 %, favoring the inclusion of the hardest ion... Interestingly, in this series, higher-order Coulombic terms do not arise in a great extent even in the iodide system... Additionally, by using the NPA, the importance of trifluoromethyl groups in promoting the electron-charge transfer is evidenced once again... As concluding remarks, we can mention that the methodologies here employed allowed us to determine the mainly electrostatic character of host–guest interactions in metallacycle-based complexes and to weigh the role of certain Coulombic terms, leading to a clear rationalization of the host–guest coupling.

No MeSH data available.