The geometric parameters of the perylene substructure in fullerenes were analyzed and found to lie within the range characteristic of stable fullerenes, indicating that this substructure does not induce significant molecular strain. However, the small energy difference (10 kcal/mol) between the singlet and triplet states of perylene may contribute to fullerene instability, as the transition to the higher-symmetry triplet state (C2v) becomes favorable compared to the singlet state (C2). The closed-shell nature of perylene ensures that its geometric and electronic properties remain largely unchanged upon incorporation into fullerene frameworks. Three distinct configurations of perylene in fullerenes were identified: separated (no shared bonds), adjacent (shared bonds), and intercrossed (shared hexagons). Separated perylene exhibits a closed electron shell, while adjacent and intercrossed structures predominantly display open-shell characteristics. This finding was checked for the C78 fullerene, in which the structural distortions are most pronounced in hexagons with delocalized π-bonds. Given the prevalence of perylene in numerous fullerenes, these findings provide valuable insights into the structural and electronic factors influencing fullerene stability.

Two series of bis-2,5-diphenyloxazolato cyclometalated iridium(III) complexes with substituted 2,2′-bipyridine or dipyridophenazine as the ancillary ligand have been prepared and characterized by X-ray structural analysis, 1 H NMR, and high resolution mass spectrometry. Bipyridine-based complexes exhibited bright emission in the yellow-orange region in solution, whereas their dipyridophenazine analogues demonstrated low quantum yields in the same spectral area. Varying the substituents in the ancillary ligand (CH 3 , H, COOH) caused noticeable shifts of the long-wavelength absorption bands retaining the redox potentials of the complexes practically unchanged. Crystallization of the complexes with iodine species gave interesting salts containing infinite polyiodide chains forming intermolecular contacts with the π-system of the ligands. Complexes bearing “anchoring” COOH-groups were used in sensitization of titania photoanodes followed by their study under the AM 1.5 G condition.

The IR spectra of calix[6]arenes with adamantylacetic acid (1) and adamantyl (2) substituents along the upper rim of the molecule were studied. It was shown that the formation of an intramolecular H-bond between carboxyl groups on the upper rim of the calix[6]arene molecules with adamantylacetic acid fragments does not weaken the cyclic cooperative H-bond at the lower rim of the macrocycle, which is confirmed by DFT calculations. The calculation has shown that molecules 1 and 2 take on the conformation of a compressed cone. The reactivity of adamantylcalix[6]arenes changes due to the association of carboxyl groups. The formation of dimeric complexes due to H-bonds of carboxyl groups along the upper rim of molecule 1 does not lead to a noticeable redistribution of the charges of hydroxyl groups on the lower rim. Heating a sample of 1 to a temperature of 180 degrees C destroys a small part of the H-bonds between neighboring carboxyl groups, as evidenced by the appearance of a weak band at 3535 cm(-1). However, after cooling to room temperature, the H-bonds between the carboxyl groups are restored. Heating up to 355 degrees C-leads to irreversible changes in the H-bonding system, but even at this temperature, structure destruction has not been observed. (C) 2021 Elsevier B.V. All rights reserved.

Abstract The IR and Raman spectra of 3-(3,3-Dimethylbutanoyl)-4-hydroxy-6-neopentyl-2H-pyran-2-one ( 1 ) in the crystalline state have been studied. The tautomerization of 1 was carried out by a quantum-chemical method at the DFT/B3LYP/6-311G** level. The experimental IR and Raman spectra of compound 1 are reproduced by calculations for the 4-hydroxy enol tautomer ( A ). The classification of the bands in the experimental vibrational spectra of 1 has been carried out. The intramolecular H-bond was characterized by IR spectroscopy. The free energies of the tautomers and their populations were calculated for two different solvents. HOMO and LUMO of molecule 1 are located on the pyran ring. During tautomeric transformations, there is a significant delocalization of charge and a change in the reactivity of the molecule. The reactivity of the pyrone 1 was characterized using descriptors. The enol form B was found to have higher ionization energy, electron affinity, chemical potential, and electrophilic index than the enol A form. The dipole moment is higher for form A , and the softness of the two molecules is the same.

The vibrational spectra of calix[4]arene (p-CAC) and thiacalix[4]arenes with azobenzene units having carboxylate groups in the para (p-CATC) and meta position (m-CATC) were recorded and analyzed.The calculated structures of molecules p-CAC, p-CATC, and m-CATC are consistent with experimental X-ray data. The most stable and polar is the cone conformation with four intramolecular cooperative hydrogen bonds. In classical calixarenes, the hydrogen bonds are shorter and, therefore, more durable than in thiacalixarenes. The cone conformation retains for all the studied calixarene molecules. The energy differences between E- and Z-forms of azobenzene groups in p-CAC, p-CATC, and m-CATC are 254.4, 260.2, and 249.4 kJ/mol, respectively. The shape of the molecules changes noticeably upon isomerization of azobenzene groups.Upon passing from thiacalixarenes to classical calixarenes, the dipole moment of the molecule increases. The polarity of calixarene molecules changes upon isomerization of azobenzene units. Ionization energy electron affinity and electrophilicity are higher in classical calixarenes compared to thiacalixarenes. There are active sites of reaction and interaction in the narrow and wide rims of the calixarene molecules. Carboxylate groups are most active in the formation of complexes with metals.

The vibrational spectra of the p-tetrasulfonatothiacalix[4]arene pentasodium salt (TCAS) and tert-butylthiacalix[4]arene (BuTCA) were studied. Comparison of the TCAS and BuTCA IR spectra allows us to isolate the bands of tert-butyl and sulfonate groups. Geometry, IR and Raman spectra were calculated for conformation cone, partial cone, 1,2-, and 1,3-alternate. The most stable conformation of the TCAS is the cone. Characteristic bands were determined for each of the possible conformations. In the case of the TCAS molecule, four ions of sodium are coordinated with the oxygen atoms of sulfonate groups, and the fifth ion interacts with the oxygen and sulfur atoms of the macrocycle. Under the influence of sodium ions, the distribution of electron density in the TCAS molecule and its ability to supramolecular interactions change.

Abstract Using a theoretical approach supported by DFT calculations, the features of molecular structure of isomer 17418 (C1) of fullerene C76 with the distribution of single, double and delocalized π-bonds has been determined for the first time. It is shown the radical nature together with the well-known overstrain due to pentalene fragment are the reasons for the instability of this fullerene as empty molecule. The synthesis of endohedral metallofulerenes is accompanied by the formation of an ion pair: the fullerene anion and a metal cation inside the molecule. It`s leading to the closure of the electron shell of the fullerene molecule and the removal of excess local strains. The previously experimentally determined cations sites inside the fullerene, which stabilize the molecule as a whole, are close to the disclosed radical clusters.

A substructural approach has been applied to study the peculiarities of molecular structures for selected isomers of fullerene C96 obtained previously as exohedral derivatives and characterized by X-ray analysis in the group of Tamm N.B. with colleagues. Their bond distributions are presented as structural formulas. The instability of the studied isomers is caused by a sizeable local overstrain due to substructures containing a significant number of condensed (fused) hexagons. The hexagons with delocalized π-bonds in the initial isomers have demonstrated the most advantageous position for addition of addends. We believe the analysis of the structural features of fullerene molecules is especially important for predicting the possibility of their synthesis in the form of derivatives and assessing their reactivity.

The IR spectra of p-(3-carboxy-1-adamantyl)thiacalix[4]arene (1-AdCOOHTC4A) have been studied. IR spectra of crystalline 1-AdCOOHTC4A obtained at room temperature or upon heating to 250 °C or its dilute solutions lack bands of free hydroxyl groups. The frequency of hydroxyl groups at 3377 cm−1 indicates the formation of an intramolecular H-bond along the lower rim of the 1-AdCOOHTC4A molecule. On the top edge of thiacalixarene, the carboxyl groups form dimeric or cyclic tetrameric complexes via intermolecular H-bonds. The conformation of the cone persists, but there is a mutual influence of H-bonds along the upper and lower rims of the thiacalix[4]arene molecule. The structure with dimer H-bonds between carboxyl groups is 31.9 KJ/mol less preferable than the conformation with tetramer cyclic H-bonds for 1-AdCOOHTC4A. Comparison of the absorption band of νOH alcohol hydroxyl groups in the IR spectra of 1-AdCOOHTC4A at 3377 cm−1, with the corresponding band of 1-AdTC4A at 3372 cm−1, suggests that the presence of the second system of H-bonds of carboxyl groups in the first molecule does not affect the H-bond of alcohol hydroxyl groups.

The IR and Raman spectra of p-(3-carboxymethyl-1-adamantyl)calix[4]arene (1) and tetrapropoxy-p-(3carboxymethyl-1-adamantyl)calix[4]arene (2) were studied. In the IR spectra of crystals and solutions of calixarenes, there is no band of stretching vibrations of free OH groups. In the IR spectrum of compound 1 in the crystalline state, an intense wide band is observed at 3187 cm & minus;1. In the IR spectrum of a dilute solution in CCl4, this band shifts to 3118 cm & minus;1. The carboxyl groups form cyclic dimer or tetramer complexes.& nbsp; The formation of dimers of carboxyl groups is more favorable than for cyclic tetramers. The energy difference is 33.8 and 53.0 kJ/mol in compounds 1 and 2, respectively. The calculation showed that molecules 1 and 2 of dimeric and tetrameric complexes assume the cone conformation. The molecules of compound 2 are in the cone conformation even in the absence of hydrogen bonds along the lower rim.& nbsp; (c) 2021 Elsevier B.V. All rights reserved.

The molecular structure of the 28324 isomer (C1) of C80 fullerene was analyzed based on the concept of substructures in fullerene molecules and with allowance for results of relevant quantum chemical calculations. The distribution of single, double, and delocalized π-bonds is presented for the first time. It is shown that the instability of the fullerene studied is due to its open-shell structure and high local strain. It was found that positions of endohedral metal atoms inside the fullerene cage are in the region of the radical cluster discovered.

This review describes the most significant published results devoted to the study of the nature of the higher fullerenes stability, revealing of correlations between the structural features of higher fullerene molecules and the possibility of their producing. A formalization of the substructure approach to assessing the stability of higher fullerenes is proposed, which is based on a detailed analysis of the main structural features of fullerene molecules. The developed substructure approach, together with the stability of the substructures constituting the fullerene molecule, helps to understand deeper the features of the electronic structure of fullerenes.

The vibrational spectra of p-hexasulfonatocalix[6]arene hexasodium salt (SC6) and p -tert- butylcalix[6]arene (TB6) were studied. The comparison of the IR spectra SC6 and TB6 allows to distinguish bands of tert -butyl and sulfonate groups. The structure and the vibrational spectra of the SC6 molecule were calculated for the conformations of the compressed cone and the double partial cone . For the molecule SC6, the conformation of a compressed cone is the most stable, and the conformation of a double partial cone is 43.6 Kcal/mol less stable. When replacing tert -butyl groups with sulfonatel groups, the cavity size of calixarene molecules increases from 5.22 (TB6) to 7.80 A (SC6). In the sodium salt of the SC6 molecule, six sodium ions are coordinated with the oxygen atoms of the sulfonate groups. Under the influence of sodium ions, the electron density is redistributed in the SC6 molecule, and its supramolecular properties change. The transition from TB6 to SC6 increases the ionization energy, electronic affinity, chemical potential and dipole moment. In the SC6 molecule, the frontal orbitals are located on aromatic and sulfonate groups. Due to these orbitals, calixarenes interact with biological objects. (c) 2021 Elsevier B.V. All rights reserved.

Based on our approach of theoretical modeling of the fullerene molecule electronic structures, an analysis of the molecular structures of isolated pentagon rule (IPR) isomer 450 (D5) of fullerene C100 and IPR isomer 1771 (D2) of fullerene C108 has been carried out. For the first time, the data about the distributions of single, double, and delocalized π-bonds in studied isomer molecules as well as their molecular formulas are presented. It is revealed that isomer 450 (D5) of fullerene C100 contains two substructures from condensed phenalenyl-radicals at the poles of the molecule (i.e., has an open electronic shell), whereas isomer 1771 (D2) of fullerene C108 has a closed electronic shell and contains substructure from condensed coronenes at the equator of the molecule. Their stabilities are evaluated in accordance with local strains in the molecules and/or the presence of radical substructures.

It is well-known that the small non-IPR fullerenes Cn (n < 60) are highly unstable and that is why they cannot be obtained as empty cages. However, they become stable as exohedral or endohedral derivatives. In this report, the molecular structures of non-IPR isomers 29 (C2) and 40 (Td) of fullerene C40 are investigated using a semiempirical approach developed earlier for higher fullerenes. Quantum-chemical calculations (DFT) show that isomers 29 (C2) and 40 (Td) have open-shell structures. The distributions of single, double, and delocalized π-bonds in the isomer molecules in question are presented for the first time as well as their molecular formulas. It is found unusual for higher fullerenes chain of π-bonds passing through some cycles. Identified features in the structures of small fullerene molecules can be predictive of the ability to their synthesis as derivatives and will assist in their structure determination.

The molecular structures of non-IPR C40 fullerene isomers 31 (Cs), 38 (D2) and 39 (D5d) were studied using a semiempirical approach developed earlier for higher fullerenes. Quantumchemical calculations (DFT) showed that they have closed shells. The distributions of single, double and delocalized π bonds in the test isomer molecules and their molecular formulas are presented for the first time.

It is well-known that non-IPR fullerenes are highly unstable. For this reason, they cannot be obtained as pristine fullerenes; however, some of them become stable as derivatives (exohedral or endohedral). In this article, we attempted to elucidate in detail molecular structure for such a non-IPR fullerene. Using theoretical approach supported by DFT calculations, the features of molecular structure of isomer 17894 (C1) of fullerene C76 with data about distribution of single, double and delocalized π-bonds as well its structural formula has been determined for the first time. The instability of the studied fullerene molecule caused by its open-shell structure and significant local overstrains related to the high folding angle value of pentagons in pentalene fragment. The supposed synthesis of the endohedral molecule starts with the ionic pair formation, i.e. anionic fragment of fullerene cage and metal cation electrostatically bound with it. It would lead to closing of open electron shell of fullerene and local overstrain release at pentalene fragment. As to the exohedral derivatives the probable positions of addends are discussed. Both methods in their own demonstrate the possibilities to stabilize the molecule of the C76 isomer 17894. The elucidation and analysis of structural features along with electronic characteristics of non-IPR fullerene molecules appear to be useful for predicting the possibility of their synthesis as derivatives and will assist in determination of their reactivity. This will ensure the targeted production of fullerenes and their derivatives for the needs of medicine, electronics and other industries. The fundamental knowledge of the properties of nanoobjects, namely fullerenes, is actually developing as the independent direction with a long-term perspective.

Here for the first time, we applied approach developed earlier for higher fullerenes to investigate the features of molecular structures of non-IPR isomers 270 (D3) and 271 (D5h) of small fullerene C50. The bond distributions are presented as structural formulas. The instability of the studied isomers is caused by a significant local overstrain due to the excessive folding of pentagons in pentalene fragments, which typically are planar molecules. It is found that the chains of π-bonds are passing through some cycles like in the previously studied higher non-IPR fullerenes C66 and C68. Chemical shifts of the centers of the pentagons and hexagons (NICS(0)) are reported. It is shown that chlorine atoms in the exohedral derivative C50Cl10 of isomer 271 (D5h) are attached to the indacene-like substructures confirming the preference of addition to π-delocalized hexagons in radical reactions. The identified features in the structures of smaller fullerene molecules can be predictive of the ability to be synthesized as derivatives and will assist in determination of their reactivity.

The IR spectra of p-(3-carboxy-1-adamantyl)-calix[4]arene (AdC4A) were studied. Using IR spectroscopy, it has been shown that in calixarene in dilute solution in CCl4, there was no free hydroxyl absorption band. The hydroxyl group band was characterized by a very low frequency, which indicates a strong intramolecular hydrogen bond on the lower rim of the calixarene molecules. On the upper rim of the calixarene, the carboxyl groups form cyclic dimer or tetramer complexes via intermolecular hydrogen bonds. The cone conformation persists, but there is a mutual influence of the hydrogen bonds along the top and bottom rims of the calixarene molecule. The structure with dimeric hydrogen bonds between the carboxyl groups is 16.5 KJ/mol more preferable than the structure with tetrameric cyclic hydrogen bonds for AdC4A. The reactivity depends on the type of association on the upper rim, whether these are hydrogen-bonded dimers or cyclic tetrameric association.