A structural and theoretical study of intermolecular interactions in nicotinohydrazide dihydrochloride

In the title compound [systematic name: 3‐(azaniumylcarbamoyl)pyridinium dichloride], C₆H₉N₃O²⁺·2Cl⁻, the ions are connected by N—H...Cl hydrogen bonds to form layers and C—H...Cl interactions expand the layers into a three‐dimensional net. The energies of the N—H...Cl interactions range from typical for very weak interactions (0.17 kcal mol⁻¹) to those observed for relatively strong interactions (29.1 kcal mol⁻¹). C—H...Cl interactions can be classified as weak and mildly strong (energies ranging from 2.2 to 8.2 kcal mol⁻¹). Despite the short contacts existing between the parallel aromatic rings of the cations, π–π interactions do not occur.     

A structural and theoretical study of the intermolecular interactions in 8‐hydroxyquinolinium‐7‐carboxylate monohydrate

In the title compound, C₁₀H₇NO₃·H₂O, the zwitterionic organic molecules and the water molecules are connected by N—H...O and O—H...O hydrogen bonds to form ribbons, and π–π stacking interactions expand these ribbons into a three‐dimensional net. The energies of these hydrogen bonds adopt values typical for mildly weak interactions (3.33–7.75 kcal mol⁻¹; 1 kcal mol⁻¹ = 4.184 kJ mol⁻¹). The total π–π stacking interactions between aromatic molecules can be classified as mildly strong (energies of 15.3 and 33.9 kcal mol⁻¹), and they are made up of multiple constituent π–π interactions between six‐membered rings. The short intermolecular C—H...O contact between two zwitterionic molecules is nonbonding in character.     

Energetic Ordering of Hydrogen Bond Strengths in Methanol-Water Clusters: Insights via Molecular Tailoring Approach

In this work, we examine the strength of various types of individual hydrogen bond (HB) in mixed methanol-water M_nW_m, (n+m=2 to 7) clusters, with an aim to understand the relative order of their strength, using our recently proposed molecular tailoring-based approach (MTA). Among all the types of HB, it is observed that the O_M−H…O_W HBs are the strongest (6.9 to 12.4 kcal mol⁻¹). The next ones are O_M−H…O_M HBs (6.5 to 11.6 kcal mol⁻¹). The O_W−H…O_W (0.2 to 10.9 kcal mol⁻¹) and O_W−H…O_M HBs (0.3 to 10.3 kcal mol⁻¹) are the weakest ones. This energetic ordering of HBs is seen to be different from the respective HB energies in the dimer i. e., O_M−H…O_M (5.0 to 6.0 kcal mol⁻¹)>O_W−H…O_M (1.5 to 6.0 kcal mol⁻¹)>O_M−H…O_W (3.8 to 5.6 kcal mol⁻¹)>O_W−H…O_W (1.2 to 5.0 kcal mol⁻¹). The plausible reason for the difference in the HB energy ordering may be attributed to the increase or decrease in HB strengths due to the formation of cooperative or anti-cooperative HB networks. For instance, the cooperativity contribution towards the different types of HB follows: O_M−H…O_W (2.4 to 8.6 kcal mol⁻¹)>O_M−H…O_M (1.3 to 6.3 kcal mol⁻¹)>O_W−H…O_W (−1.0 to 6.5 kcal mol⁻¹)>O_W−H…O_M (−1.2 to 5.3 kcal mol⁻¹). This ordering of cooperativity contribution is similar to the HB energy ordering obtained by the MTA-based method. It is emphasized here that, the interplay between the cooperative and anti-cooperative contributions are indispensable for the correct energetic ordering of these HBs.     

The thermodynamic stability of P8, A CBS‐Q study

The thermodynamic stabilities of P₂, P₄, and three P₈ cage structure were investigated through high‐precision CBS‐Q calculations. The CBS‐Q values for the bond energy of P₂ (ΔE_o: +115.7 kcal mol⁻¹) and the formation of P₄ from P₂ (Δ E_o:‐56.6 kcal mol⁻¹) were in excellent agreement with the experimental values (E_o: +117 and ‐56.4 kcal mol⁻¹ respectively). Among the P₈ cages, the cubane structure was the least stable (Δ E_o +37 kcal vs. 2×P₄). The most stable P₈ isomer adopts a cuneane structure resembling S₄N₄, and is more stable than white phosphorus at T = 0 K (Δ E_o −3.3 kcal mol⁻¹), but still unstable under standard conditions for entropic reasons (Δ G^o of +8.1 kcal mol⁻¹ vs. 2×P₄). The CBS‐Q energies represent significant revisions (6–20 kcal mol⁻¹) of previous computational predictions obtained by high‐level single method calculations. © 2005 Wiley Periodicals, Inc. Heteroatom Chem 16:453–457, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20119     

Chemistry of trifluorostyrenes and their dimmers: 3. Solvent effect on the kinetic parameters of the thermal cyclodimerization of α, β, β-trifluorostyrene1

Rate constants for the thermal cyclodimerization of α, β, β-trifluorostyrene (TFS) were determined in six solvents at 393°K. The products of this reaction were mixtures of roughly equal amounts of cis-trans isomers. The rate constants in 3 solvents, were calculated according to Arrhenius equation. In n-hexane, log A = 6.02±0.18, E_a= 19.5±0.3 kcal.mol^?1; in glyme, logA = 5.31 ± 0.19, E_a= 18.0±0.3 kcal.mol^?1; in methanol, IogA=4.93±0.13, E_a=17.1±0.3 kcal mol^?1. All data are consistent with a stepwise radical mechanism, and our reaction in this solvent series obeys an isokinetic relationship, with β = 478°K.     

Far-infrared spectra and barriers to internal rotation of ethyl nitrate

The far-infrared spectra of gaseous and solid ethyl nitrate, CH₃CH₂ONO₂, have been recorded from 500 to 50 cm⁻¹. The fundamental asymmetric torsion of the trans conformer which has a heavy atom plane has been observed at 112.50 cm⁻¹ with two excited states failing to lower frequencies, and the corresponding fundamental torsion of the gauche conformer was observed at 109.62 cm⁻¹ with two excited states also falling to lower frequencies. The results of a variable temperature Raman study indicate that the trans conformer is more stable than the gauche conformer by 328 ± 96 cm⁻¹ (938 ± 275 cal mol⁻¹). An asymmetric potential function governing the internal rotation about the CH₂O bond is reported which gives a trans to gauche barrier of 894 ± 15 cm⁻¹ (2.56 ± 0.04 kcal mol⁻¹) and a gauche to gauche barrier of 3063 ± 68 cm⁻¹ (8.76 ± 0.20 kcal mol⁻¹) with the trans conformer more stable by 220 ± 148 cm⁻¹ (0.63 ± 0.42 kcal mol⁻¹). Transitions arising from the symmetric CH₃ and NO₂ torsions are observed for both conformers, from which the threefold and twofold periodic barriers to internal rotation have been calculated. For the trans conformer the values are 1002 cm⁻¹ (2.87 kcal mol⁻¹) and 2355 ± 145 cm⁻¹ (6.73 ± 0.42 kcal mol⁻¹) and for the gauche conformer they are 981 cm⁻¹ (2.81 kcal mol⁻¹) and 2736 ± 632 cm⁻¹ (7.82 ± 1.81 kcal mol⁻¹) for the CH₃ and NO₂ rotors, respectively. These results are compared to the corresponding quantities for some similar molecules.     

Supramolecular Binding Thermodynamics by Dispersion‐Corrected Density Functional Theory

The equilibrium association free enthalpies ΔG_a for typical supramolecular complexes in solution are calculated by ab initio quantum chemical methods. Ten neutral and three positively charged complexes with experimental ΔG_a values in the range 0 to ?21 kcal mol^?1 (on average ?6 kcal mol^?1) are investigated. The theoretical approach employs a (nondynamic) single‐structure model, but computes the various energy terms accurately without any special empirical adjustments. Dispersion corrected density functional theory (DFT‐D3) with extended basis sets (triple‐ζ and quadruple‐ζ quality) is used to determine structures and gas‐phase interaction energies (ΔE), the COSMO‐RS continuum solvation model (based on DFT data) provides solvation free enthalpies and the remaining ro‐vibrational enthalpic/entropic contributions are obtained from harmonic frequency calculations. Low‐lying vibrational modes are treated by a free‐rotor approximation. The accurate account of London dispersion interactions is mandatory with contributions in the range ?5 to ?60 kcal mol^?1 (up to 200 % of ΔE). Inclusion of three‐body dispersion effects improves the results considerably. A semilocal (TPSS) and a hybrid density functional (PW6B95) have been tested. Although the ΔG_a values result as a sum of individually large terms with opposite sign (ΔE vs. solvation and entropy change), the approach provides unprecedented accuracy for ΔG_a values with errors of only 2 kcal mol^?1 on average. Relative affinities for different guests inside the same host are always obtained correctly. The procedure is suggested as a predictive tool in supramolecular chemistry and can be applied routinely to semirigid systems with 300–400 atoms. The various contributions to binding and enthalpy–entropy compensations are discussed.     

Benchmark Dynamics of Dipolar Molecular Rotors in Fluorinated Metal-Organic Frameworks

Fluorinated Metal-Organic Frameworks (MOFs), comprising a wheel-shaped ligand with geminal rotating fluorine atoms, produced benchmark mobility of correlated dipolar rotors at 2 K, with practically null activation energy (E_a=17 cal mol⁻¹). ¹H T₁ NMR revealed multiple relaxation phenomena due to the exchange among correlated dipole-rotor configurations. Synchrotron radiation X-ray diffraction at 4 K, Density Functional Theory, Molecular Dynamics and phonon calculations showed the fluid landscape and pointed out a cascade mechanism converting dipole configurations into each other. Gas accessibility, shown by hyperpolarized-Xe NMR, allowed for chemical stimuli intervention: CO₂ triggered dipole reorientation, reducing their collective dynamics and stimulating a dipole configuration change in the crystal. Dynamic materials under limited thermal noise and high responsiveness enable the fabrication of molecular machines with low energy dissipation and controllable dynamics.     

Mutual isomerization of cyclopentyl and 1-Penten-5-y1 radicals

Unimolecular reactions of mutual isomerization of cyclopentyl and 1-penten-5-yl radicals have been investigated by chemical activation. The radicals were generated by adding energized hydrogen atoms (E_H about 23 kcal mol⁻¹) to the double bond of either cyclopentane or 1,4-pentadiene. Based on the extensive steady-state RRKM calculations employing the experimental data from this work as well as from the literature, the threshold energies for the cyclopentyl ring opening and closure are 32 ± 0.3 and 16.2 ± 0.3 kcal mol⁻¹, respectively. The entropy of activation for the ring opening is close to zero.     

Solvent effects on the activation parameters of the reaction between an α‐tocopherol analogue and dpph•: The role of H‐bonded complexes

The analysis of the activation parameters for the formal H‐atom transfer reaction between 2,2,5,7,8‐pentamethyl‐6‐chromanol (ChrOH) and 2,2‐diphenyl‐1‐picrylhydrazyl (dpph^?) reveals that these parameters are effective probes of the actual reaction mechanism. Indeed, the A factors measured in various polar and apolar solvents are localized in three distinct domains according to whether the reaction occurs via outer‐sphere electron transfer (ET) from the anion ChrO^? or hydrogen atom transfer (HAT). For instance, A = 5.9 × 10⁵ M^?1 s^?1 and E_a = 2.5 kcal mol^?1 in cyclohexane where the reaction proceeds by HAT, whereas in methanol, ethanol, and their mixtures with water where there is a substantial ET contribution A > 10⁹ M^?1s^?1 and E_a > 7 kcal mol^?1. Interestingly, in nonhydroxylic polar solvents, A～ 10⁷ M^?1s^?1 and the E_a values reflect the H‐bond accepting ability of the solvent in agreement with the “standard” kinetic solvent effects on HAT reactions. Addition of small quantities of pyridine accelerates the reaction rates in these solvents. This suggests that the H‐bonded complex (ChrOH···Py) is able to react via intermolecular ET with dpph^?. It is known, in fact, that pyridine lowers the oxidation potential of phenols by ～0.5 V and the ΔG_ET of ChrOH + dpph^? consequently decreases by about 10 kcal mol^?1. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 524–531, 2012     

Stabilization of HHeF by Complexation: Is it a Really Viable Strategy?

Ab initio calculations at the MP2 and CCSD(T) levels of theory have disclosed the conceivable existence of fluorine‐coordinated complexes of HHeF with alkali‐metal ions and molecules M⁺ (M⁺=Li⁺–Cs⁺), M⁺–OH₂, M⁺–NH₃ (M⁺=Li⁺, Na⁺), and MX (M=Li, Na; X=F, Cl, Br). All these ligands L induce a shortening of the H? He distance and a lengthening of the He? F distance accompanied by consistent blue‐ and redshifts, respectively, of the H? He and He? F stretching modes. These structural effects are qualitatively similar to those predicted for other investigated complexes of the noble gas hydrides HNgY, but are quantitatively more pronounced. For example, the blueshifts of the H? He stretching mode are exceptionally large, ranging between around 750 and 1000 cm^?1. The interactions of HHeF with the ligands investigated herein also enhance the (HHe)⁺F^? dipole character and produce large complexation energies of around 20–60 kcal mol^?1. Most of the HHeF–L complexes are indeed so stable that the three‐body dissociation of HHeF into H+He+F, exothermic by around 25–30 kcal mol^?1, becomes endothermic. This effect is, however, accompanied by a strong decrease in the H? He? F bending barrier. The complexation energies, ΔE, and the bending barriers, E*, are, in particular, related by the inverse relationship E*(kcal mol^?1)=6.9exp[?0.041ΔE(kcal mol^?1)]. Therefore the HHeF? L complexes, which are definitely stable with respect to H+He+F+L (ΔE≈25–30 kcal mol^?1), are predicted to have bending barriers of only 0.5–2 kcal mol^?1. Overall, our calculations cast doubt on the conceivable stabilization of HHeF by complexation.     

Stable Oxindolyl‐Based Analogues of Chichibabin's and Müller's Hydrocarbons

Chichibabin's and Müller's hydrocarbons are classical open‐shell singlet diradicaloids but they are highly reactive. Herein we report the successful synthesis of their respective stable analogues, OxR‐2 and OxR‐3 , based on the newly developed oxindolyl radical. X‐ray crystallographic analysis on OxR‐2 reveals a planar quinoidal backbone similar to Chichibabin's hydrocarbon, in accordance with its small diradical character (y₀=11.1 %) and large singlet–triplet gap (ΔE_S‐T=−10.8 kcal mol⁻¹). Variable‐temperature NMR studies on OxR‐2 disclose a slow cis/trans isomerization process in solution through a diradical transition state, with a moderate energy barrier (ΔG^≠_298K=15–16 kcal mol⁻¹). OxR‐3 exhibits a much larger diradical character (y₀=80.6 %) and a smaller singlet–triplet gap (ΔE_S‐T=−3.5 kcal mol⁻¹), and thus can be easily populated to paramagnetic triplet diradical. Our studies provide a new type of stable carbon‐centered monoradical and diradicaloid.     

Bonding Energetics of Palladium Amido/Aryloxide Complexes in DMSO: Implications for Palladium-Mediated Aniline Activation

Thermodynamic knowledge of the metal–ligand (M−L) σ-bond strength is crucial to understanding metal-mediated transformations. Here, we developed a method for determining the Pd−X (X=OR and NHAr) bond heterolysis energies (ΔG_het(Pd−X)) in DMSO taking [(tmeda)PdArX] (tmeda=N,N,N′,N′-tetramethylethylenediamine) as the model complexes. The ΔG_het(Pd−X) scales span a range of 2.6–9.0 kcal mol⁻¹ for ΔG_het(Pd−O) values and of 14.5–19.5 kcal mol⁻¹ for ΔG_het(Pd−N) values, respectively, implying a facile heterolytic detachment of the Pd ligands. Structure-reactivity analyses of a modeling Pd-mediated X−H bond activation reveal that the M−X bond metathesis is dominated by differences of the X−H and Pd−X bond strengths, the former being more influential. The ΔG_het(Pd−X) and pK_a(X−H) parameters enable regulation of reaction thermodynamics and chemoselectivity and diagnosing the probability of aniline activation with Pd−X complexes.     

Mechanisms of the hydrogen atom and the phenyl group migration in the molecule of heptaphenylcycloheptatriene

In terms of the density functional theory using the B3LYP functional, 1,2,3,4,5,6,7-heptaphenylcycloheptatriene was shown to be the most stable in the boat conformation of the cycloheptatriene ring with the H atom in the equatorial position. 1,5-Sigmatropic shifts of the H atom along the seven-membered ring perimeter take place when it is in the axial position through the asymmetric transition state with the barrier ΔE ^≠ _ZPE = 28.7 kcal mol^?1. The H atom can attain the axial position upon inversion of the seven-membered ring, which is accompanied by the orthogonal turn of the phenyl group at the sp³-hybridized C atom (ΔE ^≠ _ZPE = 22.6 kcal mol^?1). The energy barrier to the circular rearrangement of the H atom (ΔE ^≠ _ZPE = 32.2 kcal mol^?1) explains formation of isomers during the high-temperature synthesis of di(p-tolyl)pentaphenylcycloheptatriene. The barrier to the 1,5-sigmatropic shifts of the phenyl group is 19.7 kcal mol^?1 higher than that for the competing shifts of the H atom.     

Exploring the Mechanism of a Chiral N-Alkyl Imine-Based Light-Driven Molecular Rotary Motor at MS-CASPT2//CASSCF and MS-CASPT2//(TD) DFT Levels

The working mechanism including the photoisomerization and thermal isomerization steps of a chiral N-alkyl imine-based motor synthesized by Lehn et al. are revealed by MS-CASPT2//CASSCF and MS-CASPT2//(TD-)DFT methods. For the photoisomerization process of the imine-based motor, it involves both the bright (π,π*) state and the dark (n,π*) state. In addition, the MECI has similar geometry and energy to the minimum of the S₁ state, which shows that the process is barrierless and keeps the unidirectionality of rotation well; the result confirms the imine-based motor is a good candidate for a light-driven molecular rotary motor. For the thermal isomerization process of the imine-based motor, there are two even isomerization paths: one with the mechanism of the in-plane N inversion, the energy barriers of which are 29.6 kcal mol⁻¹ at MS3-CASPT2//CAM-B3LYP level and 29.2 kcal mol⁻¹ at MS3-CASPT2//CASSCF level; the other with the mechanism of ring inversion of the cycloheptatriene moiety, with energy barriers of 28.1 kcal mol⁻¹ at MS3-CASPT2//CAM-B3LYP level and 18.1 kcal mol⁻¹ at MS3-CASPT2//CASSCF level. According to the structural feature of the stator moiety, the imine molecule can be used as a two-step or a four-step light-driven rotary motor.     

Theoretical prediction of Ni(I)-catalyst for hydrosilylation of pyridine and quinoline

Catalytic synthesis of dihydropyridine by transition-metal complex is one of the important research targets, recently. Density functional theory calculations here demonstrate that nickel(I) hydride complex (bpy)Ni^IH (bpy = 2,2′-bipyridine) 1 is a good catalyst for hydrosilylation of both quinoline and pyridine. Two pathways are possible; in path 1, substrate reacts with 1 to form stable intermediate Int1 . After that, N³─C¹ bond of substrate inserts into Ni─H bond of 1 via TS1 to afford N-coordinated 1,2-dihydroquinoline Int2 with the Gibbs activation energy (ΔG°^‡) of 21.8 kcal mol⁻¹. Then, Int2 reacts with hydrosilane to form hydrosilane σ-complex Int3 ; this is named path 1A. In the other route (path 1B), Int1 reacts with phenylsilane in a concerted manner via hydride-shuttle transition state TS2 to afford Int3 . In TS2 , Si atom takes hypervalent trigonal bipyramidal structure. Formation of hypervalent structure is crucial for stabilization of TS2 (ΔG°^‡ = 17.3 kcal mol⁻¹). The final step of path 1 is metathesis between Ni─N³ bond of Int3 and Si─H bond of PhSiH₃ to afford N-silylated 1,2-dihydroproduct and regenerate 1 (ΔG°^‡ = 4.5 kcal mol⁻¹). In path 2, 1 reacts with hydrosilane to form Int5 , which then forms adduct Int6 with substrate through Si–N interaction between substrate and PhSiH₃. Then, N-silylated 1,2-dihydroproduct is produced via hydride-shuttle transition state TS5 (ΔG°^‡ = 18.8 kcal mol⁻¹). The absence of N-coordination of substrate to Ni^I in TS5 is the reason why path 2 is less favorable than path 1B. Quinoline hydrosilylation occurs more easily than pyridine because quinoline has the lowest unoccupied molecular orbital at lower energy than that of pyridine. © 2019 Wiley Periodicals, Inc.     

Atomistic understanding of the C·T mismatched DNA base pair tautomerization via the DPT: QM and QTAIM computational approaches

It was established that the cytosine·thymine (C·T) mismatched DNA base pair with cis‐oriented N1H glycosidic bonds has propeller‐like structure (|N3C4C4N3| = 38.4°), which is stabilized by three specific intermolecular interactions–two antiparallel N4H…O4 (5.19 kcal mol^?1) and N3H…N3 (6.33 kcal mol^?1) H‐bonds and a van der Waals (vdW) contact O2…O2 (0.32 kcal mol^?1). The C·T base mispair is thermodynamically stable structure (ΔG_int = ?1.54 kcal mol^?1) and even slightly more stable than the A·T Watson–Crick DNA base pair (ΔG_int = ?1.43 kcal mol^?1) at the room temperature. It was shown that the C·T ? C*·T* tautomerization via the double proton transfer (DPT) is assisted by the O2…O2 vdW contact along the entire range of the intrinsic reaction coordinate (IRC). The positive value of the Grunenberg's compliance constants (31.186, 30.265, and 22.166 Å/mdyn for the C·T, C*·T*, and TS_{C·T ? C*·T*}, respectively) proves that the O2…O2 vdW contact is a stabilizing interaction. Based on the sweeps of the H‐bond energies, it was found that the N4H…O4/O4H…N4, and N3H…N3 H‐bonds in the C·T and C*·T* base pairs are anticooperative and weaken each other, whereas the middle N3H…N3 H‐bond and the O2…O2 vdW contact are cooperative and mutually reinforce each other. It was found that the tautomerization of the C·T base mispair through the DPT is concerted and asynchronous reaction that proceeds via the TS_{C·T ? C*·T*} stabilized by the loosened N4? H? O4 covalent bridge, N3H…N3 H‐bond (9.67 kcal mol^?1) and O2…O2 vdW contact (0.41 kcal mol^?1). The nine key points, describing the evolution of the C·T ? C*·T* tautomerization via the DPT, were detected and completely investigated along the IRC. The C*·T* mispair was revealed to be the dynamically unstable structure with a lifetime 2.13·× 10^?13 s. In this case, as for the A·T Watson–Crick DNA base pair, activates the mechanism of the quantum protection of the C·T DNA base mispair from its spontaneous mutagenic tautomerization through the DPT. © 2013 Wiley Periodicals, Inc.     

Theoretical Investigations on the Agostic Interactions of the Molybdenum and Manganese Complexes

The essential participation of agostic interactions in C−H bond activation, cyclometallation and other catalytic processes has been widely observed. To quantitatively evaluate the Mo−H−C agostic interaction in the Mo β/γ- agostomers [CpMo(CO)₂(PiPr₃)]⁺ ( Mo , 1 and Mo , 2 ) and the Mn−H−C agostic interaction in the Mn α/ϵ-agostomers [(C₆H₉]Mo(CO)₃] ( Mn , 1 and Mn , 2 ), the comprehensive density functional theory (DFT) theoretical investigations were performed. Results indicated that the Mo β-agostomer 1 is only favorable by 0.5 kcal mol⁻¹ than Mo γ-agostomer 2 , and the Gibbs barrier for their interconversion was 9.1 kcal mol⁻¹. A slightly higher Gibbs barrier of 12.7 kcal mol⁻¹ for the isomerization between the Mn α/ϵ-agostomers was also obtained. The relatively strong agostic interactions in Mo β-agostomer 1 and Mn α-agostomer 1 were further verified by the AIM (Atoms-In-Molecules) analyses and the NAdOs (natural adaptive orbitals) analyses. The findings on the agostic interaction presented in this study are believed to benefit the understandings of the agostic interaction involved catalytic processes and to promote the development of new organometallic complexes.     

Tailoring the cavities of hydrogen-bonded amphidynamic crystals using weak contacts: towards faster molecular machines

This work describes the use of C–H⋯F–C contacts in the solid-state from the stator towards the rotator to fine-tune their internal motion, by constructing a set of interactions that generate close-fitting cavities in three supramolecular rotors 1–3I. The crystal structures of these rotors, determined by synchrotron radiation experiments at different temperatures, show the presence of such C–H⋯F–C contacts between extended carbazole stators featuring fluorinated phenyl rings and the 1,4-diazabicyclo[2.2.2]octane (DABCO) rotator. According to the ²H NMR results, using deuterated samples, and periodic density functional theory computations, the rotators experience fast angular displacements (preferentially 120° jumps) due to their low rotational activation energies (E_a = 0.8–2.0 kcal mol⁻¹). The higher rotational barrier for 1 (2.0 kcal mol⁻¹) is associated with a larger number of weak C–H⋯F–C contacts generated by the stators. This strategy offers the possibility to explore the correlation among weak intermolecular forces, cavity shape, and internal dynamics, which has strong implications in the design of future fine-tuned amphidynamic crystals.

This work describes the use of C–H⋯F–C contacts in the solid-state from the stator towards the rotator to fine-tune their internal motion, by constructing a set of interactions that generate close-fitting cavities in three supramolecular rotors 1–3I.