The interplay between attractive London dispersion forces and steric effects due to repulsive forces resulting from the Pauli principle often determines the geometry and stability of nanostructures. Aromatic polyimides (PI) and carbon nanotubes (CNT) were chosen as building blocks as two components in the hetero delocalized electron nanostructures. Two PIs, having the same diamine part and different linkage substituents between two phenyl rings of dianhydride part, one linked with ether bond (C-O-C) (OPI), the other with C-(CF3)2 (FPI), were investigated. Surprisingly, two CNT/PI nanocomposites show distinct failure mode from CNT yielding to CNT pull-out failure. Calculation of the interaction energy and chain conformations of each PI upon CNT was performed by accurate density functional theory (DFT) calculations and molecular dynamic simulation (MDS). OPI chain adopt helically wrapping conformation around CNT with relatively strong interaction energy. FPI chain take the one-side wavelike conformation upon CNT with relatively weak interaction energy.

Although CH…O hydrogen bonds are generally very weak, here investigated CH…O interactions of coordinated 1,10-phenanthroline (phen) are very frequent and quite strong. In the crystal structures from the Cambridge Structural Database, 8344 CH…O interactions between coordinated phen and water molecule in the second coordination sphere were found. We calculated all possible types of CH…O interaction energies at DLPNO-CCSDT/CBS level for non-coordinated and coordinated phen with a water molecule. The data for non-coordinated phen exhibited the weakest interactions, from −2.09 to −2.94 kcal/mol. Upon coordination of phen, interactions become stronger. In octahedral cobalt(II) complexes, interaction energies are from −3.37 to −4.35 kcal/mol. With the decrease in the complex coordination number, interaction energies become stronger, the strongest are for square planar palladium(II) complexes from −3.91 to −4.94 kcal/mol. There is a linear correlation between interaction energies and electrostatic potential values at the interacting hydrogen atom, with a correlation coefficient of 0.97. For all studied systems, the weakest is always a linear interaction, and the strongest is a bifurcated interaction. The strongest calculated CH…O interactions of coordinated phen with water in the second coordination sphere (−4.94 kcal/mol) are as strong as the hydrogen bond between two water molecules (−5.0 kcal/mol).

This study presents a quantum chemical investigation of halogen–π interactions involving halogen molecules (F₂, Cl₂, Br₂, and I₂) and a series of π-systems, including benzene, alkenes, and alkynes. Special emphasis is placed on the role of the position of the unsaturated bond (terminal vs. internal) in determining the strength and nature of these interactions. Geometry optimizations and interaction energies were calculated at the wB97X-D3/def2-TZVPP level of theory, with additional validation against CCSD(T)/CBS data. Energy decomposition analysis using SAPT0 and QTAIM analysis were also performed. The results show a clear increase in interaction strength from F₂ to I₂, with interaction energies ranging from −0.47 to −5.61 kcal/mol. The position of the double or triple bond and the local symmetry of the π-system significantly influence interaction energies, with internal and more substituted alkenes and alkynes forming stronger interactions than terminal analogs. SAPT analysis shows that halogen–π interactions are governed by a balance of electrostatic and dispersion contributions, with electrostatics representing the largest attractive term in most cases, whereas dispersion becomes increasingly important for heavier halogens and more extended π-systems and benzene. QTAIM analysis confirms the noncovalent nature of these interactions, with increasing electron density at bond critical points correlating with stronger binding.

Interaction energy of phthalimide (ph) with carbon nanotube (CNT) calculated at SAPT0 level with a mixed basis set (6-31G* for CNT and 6-311G* for ph) is -19.51 kcal/mol. Halo-substitution of the phthalimide generally strengthens its interaction with the CNT and interaction energies are in the range from -21.02 kcal/mol to -22.62 kcal/mol going from ph-Cl to ph-I. However, interaction energy for phthalimide substituted with F atom (ph-F) is weaker (-18.81 kcal/mol) than for non-substituted phthalimide. For ph-Cl, ph-Br, ph-I, the total interaction energy increases with the higher halogen atomic number, because of the significant dispersion term and, less pronounced, electrostatic term increase. The smallest dispersion is calculated for ph-F/CNT (-28.72 kcal/mol), while the remaining systems range from -31.51 kcal/mol for ph/CNT to -35.78 kcal/mol for ph-I/CNT. Apart from dispersion, the system with fluorine has a less pronounced electrostatic term than other substituted phthalimides and does not follow trends observed for other systems.

The interaction energy of phthalimide and carbon nanotube calculated at SAPT0/6-31G* level is -17.37 kcal/mol. After the substitution of phthalimide with a hydroxyl group interaction was stronger (-18.64 kcal/mol) because of the larger dispersion followed by an increase in the molecular planar surface and an increased electrostatic term due to the additional electronegative oxygen atom. When a hexafluoroisopropyl group is used as a substituent (ph-6F/CNT), the molecule loses planarity and the dispersion term only slightly increases, but not enough to compensate for the unfavorable shift in the exchange interaction contribution. Thus, the resulting interaction energy in the ph-6F/CNT system is weaker (16.63 kcal/mol) than in the original ph/CNT system. Electrostatic contributions are also significant, with the largest value calculated for ph-OH/CNT (11.32 kcal/mol), because of the additional electronegative oxygen atom in the hydroxyl group. The other two systems, ph/CNT and ph-6F/CNT have electrostatic interactions of 10.14 and 10.05 kcal/mol, respectively. Exchange interaction is more repulsive for ph-OH (+26.60 kcal/mol) and ph-6F (+26.29 kcal/mol) systems than the ph/CNT (+24.86 kcal/mol).