102 research outputs found
10.術後逆流性食道炎の検討(第2報)(第526回千葉医学会例会・第9回佐藤外科例会)
Engineering
of novel systems capable of efficient energy capture and transfer
in a predesigned pathway could potentially boost applications varying
from organic photovoltaics to catalytic platforms and have implications
for energy sustainability and green chemistry. While light-harvesting
properties of different materials have been studied for decades, recently,
there has been great progress in the understanding and modeling of
short- and long-range energy transfer processes through utilization
of metal–organic frameworks (MOFs). In this Forum Article,
the recent advances in efficient multiple-chromophore coupling in
well-defined metal–organic materials through mimicking a protein
system possessing near 100% energy transfer are discussed. Utilization
of a MOF as an efficient replica of a protein β-barrel to maintain
chromophore emission was also demonstrated. Furthermore, we established
a novel dependence of a photophysical response on an electronic configuration
for chromophores with the benzylidene imidazolinone core. For that,
we prepared 16 chromophores, in which the benzylidene imidazolinone
core was modified with electron-donating and electron-withdrawing
substituents. To establish the structure-dependent photophysical properties
of the prepared chromophores, 11 novel molecular structures were determined
by single-crystal X-ray diffraction. These findings allow one to predict
the chromophore emission profile inside a rigid framework as a function
of the substituent, a key parameter for achieving the spectral overlap
necessary to study and increase resonance energy transfer efficiency
in MOF-based materials
Photoredox-Assisted Reductive Cross-Coupling: Mechanistic Insight into Catalytic Aryl–Alkyl Cross-Couplings
Here, we describe
a photoredox-assisted catalytic system for the
direct reductive coupling of two carbon electrophiles. Recent advances
have shown that nickel catalysts are active toward the coupling of
sp<sup>3</sup>-carbon electrophiles and that well-controlled, light-driven
coupling systems are possible. Our system, composed of a nickel catalyst,
an iridium photosensitizer, and an amine electron donor, is capable
of coupling halocarbons with high yields. Spectroscopic studies support
a mechanism where under visible light irradiation the Ir photosensitizer
in conjunction with triethanolamine are capable of reducing a nickel
catalyst and activating the catalyst toward cross-coupling of carbon
electrophiles. The synthetic methodology developed here operates at
low 1 mol % catalyst and photosensitizer loadings. The catalytic system
also operates without reaction additives such as inorganic salts or
bases. A general and effective sp<sup>2</sup>–sp<sup>3</sup> cross-coupling scheme has been achieved that exhibits tolerance
to a wide array of functional groups
Homochiral, Helical Coordination Complexes of Lanthanides(III) and Mixed-Metal Lanthanides(III): Impact of the 1,8-Naphthalimide Supramolecular Tecton on Structure, Magnetic Properties, and Luminescence
The reactions of the lithium salt
of (<i>S</i>)-2-(1,8-naphthalimido)-3-hydroxypropanoate
(<b>L</b><sub><b>ser</b></sub><sup>–</sup>), an
enantiopure carboxylate ligand containing a 1,8-naphthalimide
π···π stacking supramolecular tecton
and an alcohol functional group, with La(NO<sub>3</sub>)<sub>3</sub>, Ce(NO<sub>3</sub>)<sub>3</sub>, SmCl<sub>3</sub>, Eu(NO<sub>3</sub>)<sub>3</sub>, Gd(NO<sub>3</sub>)<sub>3</sub>, Tb(NO<sub>3</sub>)<sub>3</sub>, and Dy(NO<sub>3</sub>)<sub>3</sub> under solvothermal
conditions (water/ethanol) produced single crystals (characterized
by single-crystal X-ray crystallography) of [La<sub>3</sub>(<b>L</b><sub><b>ser</b></sub>)<sub>8</sub>(OH)(H<sub>2</sub>O)]·(H<sub>2</sub>O,EtOH)<sub><i>x</i></sub> (<b>1</b>), [Ce<sub>3</sub>(<b>L</b><sub><b>ser</b></sub>)<sub>8</sub>(OH)(H<sub>2</sub>O)]·(H<sub>2</sub>O,EtOH)<sub><i>x</i></sub> (<b>2</b>), [Sm<sub>3</sub>(<b>L</b><sub><b>ser</b></sub>)<sub>8</sub>(OEt)]·(H<sub>2</sub>O,EtOH)<sub><i>x</i></sub> (<b>3</b>), [Eu<sub>3</sub>(<b>L</b><sub><b>ser</b></sub>)<sub>8</sub>(OEt)]·(H<sub>2</sub>O,EtOH)<sub><i>x</i></sub> (<b>4</b>), [Gd<sub>3</sub>(<b>L</b><sub><b>ser</b></sub>)<sub>8</sub>(OEt)]·(H<sub>2</sub>O,EtOH)<sub><i>x</i></sub> (<b>5</b>), [Tb<sub>3</sub>(<b>L</b><sub><b>ser</b></sub>)<sub>8</sub>(OEt)]·(H<sub>2</sub>O,EtOH)<sub><i>x</i></sub> (<b>6</b>), and [Dy<sub>3</sub>(<b>L</b><sub><b>ser</b></sub>)<sub>8</sub>(OEt)]·(H<sub>2</sub>O,EtOH)<sub><i>x</i></sub> (<b>7</b>), respectively. Mixed-metal complexes [Ce<sub>2.3</sub>Tb<sub>0.7</sub>(<b>L</b><sub><b>ser</b></sub>)<sub>8</sub>(OH)]·(H<sub>2</sub>O,EtOH)<sub><i>x</i></sub> (<b>8</b>), [Gd<sub>0.4</sub>Tb<sub>2.6</sub>(<b>L</b><sub><b>ser</b></sub>)<sub>8</sub>(OEt)]·(H<sub>2</sub>O,EtOH)<sub><i>x</i></sub> (<b>9</b>), and
[Ce<sub>1.4</sub>Gd<sub>0.3</sub>Tb<sub>1.3</sub>(<b>L</b><sub><b>ser</b></sub>)<sub>8</sub>(OH)]·(H<sub>2</sub>O,EtOH)<sub><i>x</i></sub> (<b>10</b>) were prepared by using two or more types of lanthanides in the
solvothermal reactions (additional mixed-metal complexes were
prepared and characterized by ICP-MS). Single crystals of compounds <b>1</b>–<b>10</b> are isostructural: trinuclear, carboxylate-bonded
helicates organized by the non-covalent, π···π
stacking interactions of the 1,8-naphthalimide groups into <i>intertwined M</i> helices, with a pitch of 56 Å,
that are further arranged into a three-dimensional supramolecular
framework by additional π···π stacking
interactions. Magnetic measurements of several compounds were as expected
for the metal(s) present, indicating no significant interactions between
metals within the helicates. The Ce complex <b>2</b> showed
weak antiferromagnetic ordering below 50 K. All of the
complexes, with the exception of <b>2</b>, showed luminescence
based on the 1,8-naphthalimide group. Complex <b>2</b> has no emission, and complexes with mixed Ce/Tb ratios showed significant
quenching of the naphthalimide-based luminescence, as quantitated
with solid-state, absolute quantum yield measurements of these mixed-metal
and the pure metal complexes. Lanthanide-based luminescence was only
observed for the Eu complex <b>4</b>
Zinc Paddlewheel Dimers Containing a Strong π···π Stacking Supramolecular Synthon: Designed Single-Crystal to Single-Crystal Phase Changes and Gas/Solid Guest Exchange
The ligand 4-(1,8-naphthalimido)benzoate, <b>L</b><sub><b>C4</b></sub><sup><b>–</b></sup>, containing a linear link between the strong π···π stacking 1,8-naphthalimide supramolecular synthon and the carboxylate donor group, reacts with Zn(O<sub>2</sub>CCH<sub>3</sub>)<sub>2</sub>(H<sub>2</sub>O)<sub>2</sub> in the presence of dimethylsulfoxide (DMSO) to yield [Zn<sub>2</sub>(<b>L</b><sub><b>C4</b></sub>)<sub>4</sub>(DMSO)<sub>2</sub>]·2(CH<sub>2</sub>Cl<sub>2</sub>). This compound contains the “paddlewheel” Zn<sub>2</sub>(O<sub>2</sub>CR)<sub>4</sub> secondary building unit (SBU) that organizes the rigid phenylene and naphthalimide rings of the carboxylate ligands in a square arrangement. The supramolecular architecture is dominated by π···π stacking interactions between naphthalimide rings of one dimer with four adjacent dimers, essentially at right angles, forming an open three-dimensional network structure. Two symmetry equivalent networks of this type interpenetrate generating overall a densely packed three-dimensional, 2-fold interpenetrated architecture in which the CH<sub>2</sub>Cl<sub>2</sub> solvate molecules are trapped in isolated pockets. Upon cooling, single crystals of [Zn<sub>2</sub>(<b>L</b><sub><b>C4</b></sub>)<sub>4</sub>(DMSO)<sub>2</sub>]·2(CH<sub>2</sub>Cl<sub>2</sub>) undergo two distinct crystallographic phase transitions, as characterized by X-ray diffraction at different temperatures, without loss of crystallinity. These two new phases have supramolecular structures very similar to the room temperature structure, but changes in the ordering of the CH<sub>2</sub>Cl<sub>2</sub> solvate cause shifting of the naphthalimide rings and a lowering of the symmetry. Crystals of [Zn<sub>2</sub>(<b>L</b><sub><b>C4</b></sub>)<sub>4</sub>(DMSO)<sub>2</sub>]·2(CH<sub>2</sub>Cl<sub>2</sub>) undergo a single-crystal to single-crystal gas/solid guest exchange upon exposure to atmospheric moisture, or faster if placed under vacuum or heated under dry gas to 100 °C, followed by atmospheric moisture, to yield [Zn<sub>2</sub>(<b>L</b><sub><b>C4</b></sub>)<sub>4</sub>(DMSO)<sub>2</sub>]·3.9(H<sub>2</sub>O). The molecular and supramolecular structures of this new compound are very similar to the dichloromethane adduct, with now the water molecules encapsulated into the framework. The remarkable feature of both the phase changes and exchange of solvates is that this robust network is not porous; local distortions (ring slippage and tilting changes) of the π···π stacking interactions of the naphthalimide rings that organize these structures allow these changes to take place without the loss of crystallinity. The complexes [Zn<sub>2</sub>(<b>L</b><sub><b>C4</b></sub>)<sub>4</sub>(DMSO)<sub>2</sub>]·2(CH<sub>2</sub>Cl<sub>2</sub>) and [Zn<sub>2</sub>(<b>L</b><sub><b>C4</b></sub>)<sub>4</sub>(DMSO)<sub>2</sub>]·3.9(H<sub>2</sub>O) show green emission in the solid state
Zinc Paddlewheel Dimers Containing a Strong π···π Stacking Supramolecular Synthon: Designed Single-Crystal to Single-Crystal Phase Changes and Gas/Solid Guest Exchange
The ligand 4-(1,8-naphthalimido)benzoate, <b>L</b><sub><b>C4</b></sub><sup><b>–</b></sup>, containing a linear link between the strong π···π stacking 1,8-naphthalimide supramolecular synthon and the carboxylate donor group, reacts with Zn(O<sub>2</sub>CCH<sub>3</sub>)<sub>2</sub>(H<sub>2</sub>O)<sub>2</sub> in the presence of dimethylsulfoxide (DMSO) to yield [Zn<sub>2</sub>(<b>L</b><sub><b>C4</b></sub>)<sub>4</sub>(DMSO)<sub>2</sub>]·2(CH<sub>2</sub>Cl<sub>2</sub>). This compound contains the “paddlewheel” Zn<sub>2</sub>(O<sub>2</sub>CR)<sub>4</sub> secondary building unit (SBU) that organizes the rigid phenylene and naphthalimide rings of the carboxylate ligands in a square arrangement. The supramolecular architecture is dominated by π···π stacking interactions between naphthalimide rings of one dimer with four adjacent dimers, essentially at right angles, forming an open three-dimensional network structure. Two symmetry equivalent networks of this type interpenetrate generating overall a densely packed three-dimensional, 2-fold interpenetrated architecture in which the CH<sub>2</sub>Cl<sub>2</sub> solvate molecules are trapped in isolated pockets. Upon cooling, single crystals of [Zn<sub>2</sub>(<b>L</b><sub><b>C4</b></sub>)<sub>4</sub>(DMSO)<sub>2</sub>]·2(CH<sub>2</sub>Cl<sub>2</sub>) undergo two distinct crystallographic phase transitions, as characterized by X-ray diffraction at different temperatures, without loss of crystallinity. These two new phases have supramolecular structures very similar to the room temperature structure, but changes in the ordering of the CH<sub>2</sub>Cl<sub>2</sub> solvate cause shifting of the naphthalimide rings and a lowering of the symmetry. Crystals of [Zn<sub>2</sub>(<b>L</b><sub><b>C4</b></sub>)<sub>4</sub>(DMSO)<sub>2</sub>]·2(CH<sub>2</sub>Cl<sub>2</sub>) undergo a single-crystal to single-crystal gas/solid guest exchange upon exposure to atmospheric moisture, or faster if placed under vacuum or heated under dry gas to 100 °C, followed by atmospheric moisture, to yield [Zn<sub>2</sub>(<b>L</b><sub><b>C4</b></sub>)<sub>4</sub>(DMSO)<sub>2</sub>]·3.9(H<sub>2</sub>O). The molecular and supramolecular structures of this new compound are very similar to the dichloromethane adduct, with now the water molecules encapsulated into the framework. The remarkable feature of both the phase changes and exchange of solvates is that this robust network is not porous; local distortions (ring slippage and tilting changes) of the π···π stacking interactions of the naphthalimide rings that organize these structures allow these changes to take place without the loss of crystallinity. The complexes [Zn<sub>2</sub>(<b>L</b><sub><b>C4</b></sub>)<sub>4</sub>(DMSO)<sub>2</sub>]·2(CH<sub>2</sub>Cl<sub>2</sub>) and [Zn<sub>2</sub>(<b>L</b><sub><b>C4</b></sub>)<sub>4</sub>(DMSO)<sub>2</sub>]·3.9(H<sub>2</sub>O) show green emission in the solid state
Homochiral, Helical Coordination Complexes of Lanthanides(III) and Mixed-Metal Lanthanides(III): Impact of the 1,8-Naphthalimide Supramolecular Tecton on Structure, Magnetic Properties, and Luminescence
The reactions of the lithium salt
of (<i>S</i>)-2-(1,8-naphthalimido)-3-hydroxypropanoate
(<b>L</b><sub><b>ser</b></sub><sup>–</sup>), an
enantiopure carboxylate ligand containing a 1,8-naphthalimide
π···π stacking supramolecular tecton
and an alcohol functional group, with La(NO<sub>3</sub>)<sub>3</sub>, Ce(NO<sub>3</sub>)<sub>3</sub>, SmCl<sub>3</sub>, Eu(NO<sub>3</sub>)<sub>3</sub>, Gd(NO<sub>3</sub>)<sub>3</sub>, Tb(NO<sub>3</sub>)<sub>3</sub>, and Dy(NO<sub>3</sub>)<sub>3</sub> under solvothermal
conditions (water/ethanol) produced single crystals (characterized
by single-crystal X-ray crystallography) of [La<sub>3</sub>(<b>L</b><sub><b>ser</b></sub>)<sub>8</sub>(OH)(H<sub>2</sub>O)]·(H<sub>2</sub>O,EtOH)<sub><i>x</i></sub> (<b>1</b>), [Ce<sub>3</sub>(<b>L</b><sub><b>ser</b></sub>)<sub>8</sub>(OH)(H<sub>2</sub>O)]·(H<sub>2</sub>O,EtOH)<sub><i>x</i></sub> (<b>2</b>), [Sm<sub>3</sub>(<b>L</b><sub><b>ser</b></sub>)<sub>8</sub>(OEt)]·(H<sub>2</sub>O,EtOH)<sub><i>x</i></sub> (<b>3</b>), [Eu<sub>3</sub>(<b>L</b><sub><b>ser</b></sub>)<sub>8</sub>(OEt)]·(H<sub>2</sub>O,EtOH)<sub><i>x</i></sub> (<b>4</b>), [Gd<sub>3</sub>(<b>L</b><sub><b>ser</b></sub>)<sub>8</sub>(OEt)]·(H<sub>2</sub>O,EtOH)<sub><i>x</i></sub> (<b>5</b>), [Tb<sub>3</sub>(<b>L</b><sub><b>ser</b></sub>)<sub>8</sub>(OEt)]·(H<sub>2</sub>O,EtOH)<sub><i>x</i></sub> (<b>6</b>), and [Dy<sub>3</sub>(<b>L</b><sub><b>ser</b></sub>)<sub>8</sub>(OEt)]·(H<sub>2</sub>O,EtOH)<sub><i>x</i></sub> (<b>7</b>), respectively. Mixed-metal complexes [Ce<sub>2.3</sub>Tb<sub>0.7</sub>(<b>L</b><sub><b>ser</b></sub>)<sub>8</sub>(OH)]·(H<sub>2</sub>O,EtOH)<sub><i>x</i></sub> (<b>8</b>), [Gd<sub>0.4</sub>Tb<sub>2.6</sub>(<b>L</b><sub><b>ser</b></sub>)<sub>8</sub>(OEt)]·(H<sub>2</sub>O,EtOH)<sub><i>x</i></sub> (<b>9</b>), and
[Ce<sub>1.4</sub>Gd<sub>0.3</sub>Tb<sub>1.3</sub>(<b>L</b><sub><b>ser</b></sub>)<sub>8</sub>(OH)]·(H<sub>2</sub>O,EtOH)<sub><i>x</i></sub> (<b>10</b>) were prepared by using two or more types of lanthanides in the
solvothermal reactions (additional mixed-metal complexes were
prepared and characterized by ICP-MS). Single crystals of compounds <b>1</b>–<b>10</b> are isostructural: trinuclear, carboxylate-bonded
helicates organized by the non-covalent, π···π
stacking interactions of the 1,8-naphthalimide groups into <i>intertwined M</i> helices, with a pitch of 56 Å,
that are further arranged into a three-dimensional supramolecular
framework by additional π···π stacking
interactions. Magnetic measurements of several compounds were as expected
for the metal(s) present, indicating no significant interactions between
metals within the helicates. The Ce complex <b>2</b> showed
weak antiferromagnetic ordering below 50 K. All of the
complexes, with the exception of <b>2</b>, showed luminescence
based on the 1,8-naphthalimide group. Complex <b>2</b> has no emission, and complexes with mixed Ce/Tb ratios showed significant
quenching of the naphthalimide-based luminescence, as quantitated
with solid-state, absolute quantum yield measurements of these mixed-metal
and the pure metal complexes. Lanthanide-based luminescence was only
observed for the Eu complex <b>4</b>
Understanding the Formation of Salt-Inclusion Phases: An Enhanced Flux Growth Method for the Targeted Synthesis of Salt-Inclusion Cesium Halide Uranyl Silicates
Salt-inclusion
compounds (SICs) are known for their structural
diversity and their potential applications, including luminescence
and radioactive waste storage forms. Currently, the majority of salt-inclusion
phases are grown serendipitously and the targeted growth of SICs has
met with only moderate success. We report an enhanced flux growth
method for the targeted growth of SICs. Specifically, the use of (1)
metal halide reagents and (2) reactions with small surface area to
volume ratios are found to favor the growth of salt-inclusion compounds
over pure oxides and thus enable a more targeted synthetic route for
their preparation. The Cs–X–U–Si–O (X
= F, Cl) pentanary phase space is used as a model system to demonstrate
the generality of this enhanced flux method approach. Single crystals
of four new salt-inclusion uranyl silicates, [Cs<sub>3</sub>F][(UO<sub>2</sub>)(Si<sub>4</sub>O<sub>10</sub>)], [Cs<sub>2</sub>Cs<sub>5</sub>F][(UO<sub>2</sub>)<sub>2</sub>(Si<sub>6</sub>O<sub>17</sub>)], [Cs<sub>9</sub>Cs<sub>6</sub>Cl][(UO<sub>2</sub>)<sub>7</sub>(Si<sub>6</sub>O<sub>17</sub>)<sub>2</sub>(Si<sub>4</sub>O<sub>12</sub>)], and [Cs<sub>2</sub>Cs<sub>5</sub>F][(UO<sub>2</sub>)<sub>3</sub>(Si<sub>2</sub>O<sub>7</sub>)<sub>2</sub>], were grown using this enhanced flux
growth method. A detailed discussion of the factors that favor salt-inclusion
phases during synthesis and why specifically uranyl silicates make
excellent frameworks for salt-inclusion phases is given
A Family of A‑Site Cation-Deficient Double-Perovskite-Related Iridates: Ln<sub>9</sub>Sr<sub>2</sub>Ir<sub>4</sub>O<sub>24</sub> (Ln = La, Pr, Nd, Sm)
The
compositions of the general formula Ln<sub>11–<i>x</i></sub>Sr<sub><i>x</i></sub>Ir<sub>4</sub>O<sub>24</sub> (Ln = La, Pr, Nd, Sm; 1.37 ≥ <i>x</i> ≥
2) belonging to a family of A-site cation-deficient double-perovskite-related
oxide iridates were grown as highly faceted single crystals from a
molten strontium chloride flux. Their structures were determined by
single-crystal X-ray diffraction. On the basis of the single-crystal
results, additional compositions, Ln<sub>9</sub>Sr<sub>2</sub>Ir<sub>4</sub>O<sub>24</sub> (Ln = La, Pr, Nd, Sm), were prepared as polycrystalline
powders via solid-state reactions and structurally characterized by
Rietveld refinement. The compositions Ln<sub>9</sub>Sr<sub>2</sub>Ir<sub>4</sub>O<sub>24</sub> (Ln = La, Pr, Nd, Sm) contain Ir(V)
and Ir(IV) in a 1:3 ratio with an average iridium oxidation state
of 4.25. The single-crystal compositions La<sub>9.15</sub>Sr<sub>1.85</sub>Ir<sub>4</sub>O<sub>24</sub> and Pr<sub>9.63</sub>Sr<sub>1.37</sub>Ir<sub>4</sub>O<sub>24</sub> contain relatively less Ir(V), with
the average iridium oxidation states being 4.21 and 4.09, respectively.
The magnetic properties of Ln<sub>9</sub>Sr<sub>2</sub>Ir<sub>4</sub>O<sub>24</sub> (Ln = La, Pr, Nd, Sm) were measured, and complex magnetic
behavior was observed in all cases at temperatures below 30 K
Metal- and Ligand-Centered Reactivity of <i>meta</i>-Carboranyl-Backbone Pincer Complexes of Rhodium
We
report the synthesis of the chelating phosphinite-arm carboranyl
POBOP-H (POBOP = 1,7-OP(<i>i</i>-Pr)<sub>2</sub>-<i>m</i>-carboranyl) ligand precursor, preparation of its rhodium
complexes, and their reactivity in oxidative addition/reductive elimination
reactions. The oxidative addition of iodobenzene to the low-valent
(POBOP)Rh(PPh<sub>3</sub>) resulted in the selective formation of
the 16-electron complex (POBOP)Rh(Ph)(I), featuring a highly strained
exohedral rhodium–boron bond. The complex (POBOP)Rh(Ph)(I)
is the first example of a B-carboranyl aryl metal complex, which is
a proposed intermediate in metal-promoted B–C coupling reactions.
The complex (POBOP)Rh(Ph)(I) was selectively and directly converted,
in the presence of acetonitrile, to (POB(BPh)OP)Rh(H)(I)(CH<sub>3</sub>CN) (POB(BPh)OP = 1,7-OP(<i>i</i>-Pr)<sub>2</sub>-2-Ph-<i>m</i>-carboranyl) through unprecedented cascade reductive elimination
of the phenyl-<i>B</i>-carboranyl and the oxidative addition
of a vicinal B–H bond of the boron cluster to the metal center,
exhibiting both metal- and cluster-centered reactivity
Comprehensive Experimental Study of N<i>-</i>Heterocyclic π‑Stacking Interactions of Neutral and Cationic Pyridines
A comprehensive experimental study
was carried out by measuring the relative strengths of parallel π-stacking
interactions of N<i>-</i>heterocycles with nonheterocycles.
A versatile and rigid model system was developed, which was in equilibrium
between a “closed” conformation that forms an intramolecular
π-stacking interaction and an “open” conformation
that cannot form the interaction. First, the formation and geometries
of the intramolecular N<i>-</i>heterocyclic π-stacking
interactions were verified by X-ray crystallography. Next, the closed/open
ratios were measured in solution via integration of the <sup>1</sup>H NMR spectra, providing an accurate comparison of the N-heterocyclic
π-stacking interactions. The synthetic versatility of this model
system enabled the systematic and comprehensive comparison of the
influences of position, charge, and substituent effects of the nitrogen
atom of the N-heterocycles within a single model system. The π-stacking
interactions of the neutral N-heterocyclic rings were slightly stronger
than that of nonheterocyclic rings. Cationic N-heterocycles formed
significantly stronger π-stacking interactions than neutral
N-heterocycles. The position of the nitrogen atom also had a strong
influence on the stability of N-heterocyclic π-stacking complexes.
Interestingly, opposite stability trends were observed for neutral
and cationic N-heterocycles. For neural N-heterocycles, geometries
with the nitrogen away from the π-face of the opposing ring
were the more stable. For cationic N-heterocycles, geometries with
the nitrogen close to the π-face of the opposing ring were the
more stable. Finally, N-methylated heterocycles consistently formed
stronger π-stacking interactions than N-protonated heterocycles
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