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Molecular Spectroscopy and Molecular Structure: Commemorative Issue in Honor of Professor Austin J. Barnes on Occasion of his 75th Birthday

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A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Photochemistry".

Deadline for manuscript submissions: closed (30 September 2021) | Viewed by 33310

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Prof. Dr. Rui Fausto

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Department of Chemistry, Coimbra Chemistry Center (CQC-IMS), University of Coimbra, 3004-535 Coimbra, Portugal
Interests: photochemistry; molecular cryo- and biospectroscopy; quantum chemistry; molecular structure; photophysics; chemometrics
* ORCID: 0000-0002-8264-6854
Special Issues, Collections and Topics in MDPI journals

Prof. Dr. Sylvia Turrell

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Sylvia Turrell is Emeritus Professor of Chemistry of the University of Lille, France. Along her career, she has been a professor and researcher at several universities in Zaire, Canada (Montreal and Quebec) and France (Limoges, Lille). Her research focuses on the use of spectroscopic techniques for the characterization of the structure of materials and the elucidation of the mechanisms responsible for specific properties. Specifically, infrared and Raman spectroscopies and force-field calculations for crystalline systems, detection and characterization of Alzheimer's disease, development of sol–gel materials, fabrication and studies of planar wave guides, alteration processes in glasses, and fabrication and characterization of semiconductor nanoparticles for photonics and photovoltaics. She has a wide scientific curriculum and editorial experience. She is vice-president of the permanent Steering Committee of the EUCMOS (European Congress on Molecular Spectroscopy).
Department of Chemistry, Université des Sciences et Technologies de Lille 1, France
Interests: spectroscopy; characterization of materials; thin films; Alzheimer’s; glass structure and alteration; photonics; art and archeology; nanostructures
* ORCID: 0000-0003-0513-9450

Prof. Dr. Gulce Ogruc Ildiz

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1. Department of Chemistry, Coimbra Chemistry Center, University of Coimbra, Coimbra, Portugal
2. Faculty of Sciences & Letters, Department of Physics, Istanbul Kultur University, Istanbul, Turkey
Interests: photochemistry; molecular cryo- and biospectroscopy; quantum chemistry; molecular structure; photophysics; chemometrics
* ORCID: 0000-0002-7827-5050
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Molecules is very pleased to host this Special Issue in honor of Prof. Austin James Barnes, in acknowledgment of his influential scientific contributions in the fields of Molecular Spectroscopy and Molecular Structure., and we invite scientists to submit research article or review papers focusing on:

   • Molecular structure;
   • Molecular spectroscopy;
   • Hydrogen bonding;
   • Intermolecular interactions;
   • Chemical reactivity, kinetics, and mechanisms;
   • Transient species and reaction intermediates, weakly bound species and associates.

Austin James Barnes was born on 2 June 1945. He went to Gonville and Caius College, Cambridge, in 1963 and obtained his BA degree in 1966. He then moved to the University College of Swansea, where he was awarded his PhD degree in 1969 for research on infrared spectra of matrix-isolated species under the supervision of Dr. Harry Hallam, After a period of postdoctoral research in Swansea, he was appointed as a lecturer at the University of Salford in 1973, where he remained for the rest of his career. He was awarded a DSc degree by the University of Wales in 1986, and in 1991, was promoted to Reader. From 1996 to 1999, he served as Head of the Department of Chemistry and Applied Chemistry. He continued to teach on a part-time basis until 2005. He had a continued association with the University as an Honorary Visiting Professor until the end of 2015. Following on from his PhD work, Austin's principal research interests focused on infrared and Raman matrix isolation spectroscopy, particularly applied to the investigation of molecular interactions and conformational isomerism. Notable early work included the first reported use of a Fourier transform spectrometer to obtain far IR spectra of matrices, a critical review of the interpretation and prediction of matrix effects, and a study of experimental conditions for obtaining Raman spectra from matrices. Investigations of the conformational behavior of molecules trapped in matrices led to a proposed empirical relationship referred to by some authors as ‘the Barnes relation’. Austin's interests in strongly hydrogen-bonded systems have also extended to structural studies of ferroelectric crystals and nonlinear optical materials. He was one of the authors of an early report on the so-called ‘blue-shifting’ hydrogen bonds and has written a short review summarizing our knowledge of this phenomenon.

Austin has published about 125 research and review papers and edited many books and volumes of conference proceedings. He was awarded the Gold Medal of the University of Wroclaw, Poland, in 2008.

Austin served as President of the International Committee of the European Congress on Molecular Spectroscopy (EUCMOS) during the period 1994–2016, and from 1979 to 1993, he served as Assistant Editor to Professor W.J. Orville-Thomas for both the Journal of Molecular Structure and the Journal of Molecular Structure (THEOCHEM). In January 1994, he was appointed to act as an Editor of the Journal of Molecular Structure and continued in this role until the end of 2009, during which period more than 300 volumes were published. A Special Issue of the Journal in his honor was published in 2010.

It is our great pleasure to invite you to submit an article for a high-profile Special Issue in honor of Prof. Austin James Barnes, in celebration of his 75th birthday, to be published in Molecules.

Prof. Austin J. Barnes has been one of the most influential scientists in the fields of molecular structure and molecular spectroscopy, and his long scientific career has been an example to follow. However, Austin is also an exceptional human being and his friendship is priceless to us. This Special Issue in an unpretentious attempt to show him our esteem, in the occasion of his 75th birthday. We are sure that these feelings are shared by many around the world who have had the opportunity to meet Austin somewhere in one of the many international congresses he has organized or supported, and who, same as we, want to thank him for his outstanding scientific contributions to the field of molecular structure and molecular spectroscopy and also for his friendship.

Research articles on both technical developments and applications on molecular structure and molecular spectroscopy (see the provided keywords) are welcome for publication in this Special Issue, as are review articles and perspectives from experts in the field.

Prof. Dr. Rui Fausto
Prof. Dr. Sylvia Turrell
Dr. Gulce Ogruc Ildiz
Guest Editors

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Molecules is an international peer-reviewed open access semimonthly journal published by MDPI.

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Keywords

Molecular structure
Molecular spectroscopy
Hydrogen bonding
Intermolecular interactions
Chemical reactivity, kinetics and mechanisms
Transient species and reaction intermediates, weakly bound species and associates

Published Papers (12 papers)

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Research

13 pages, 981 KiB

Open AccessArticle

Structure and IR Spectroscopic Properties of HNCO Complexes with SO₂ Isolated in Solid Argon

by Justyna Krupa, Maria Wierzejewska and Jan Lundell

Molecules 2021, 26(21), 6441; https://doi.org/10.3390/molecules26216441 - 25 Oct 2021

Cited by 2 | Viewed by 2425

Abstract

FTIR spectroscopy was combined with the matrix isolation technique and quantum chemical calculations with the aim of studying complexes of isocyanic acid with sulfur dioxide. The structures of the HNCO⋯SO₂ complexes of 1:1, 1:2 and 2:1 stoichiometry were optimized at the MP2, B3LYPD3, B2PLYPD3 levels of theory with the 6-311++G(3df,3pd) basis set. Five stable 1:1 HNCO⋯SO₂ complexes were found. Three of them contain a weak N-H⋯O hydrogen bond, whereas two other structures are stabilized by van der Waals interactions. The analysis of the HNCO/SO₂/Ar spectra after deposition indicates that mostly the 1:1 hydrogen-bonded complexes are present in argon matrices, with a small amount of the van der Waals structures. Upon annealing, complexes of the 1:2 stoichiometry were detected, as well. Full article

(This article belongs to the Special Issue Molecular Spectroscopy and Molecular Structure: Commemorative Issue in Honor of Professor Austin J. Barnes on Occasion of his 75th Birthday)

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15 pages, 2647 KiB

Open AccessArticle

Modeling of the Response of Hydrogen Bond Properties on an External Electric Field: Geometry, NMR Chemical Shift, Spin-Spin Scalar Coupling

by Ilya G. Shenderovich and Gleb S. Denisov

Molecules 2021, 26(16), 4967; https://doi.org/10.3390/molecules26164967 - 18 Aug 2021

Cited by 3 | Viewed by 2963

Abstract

The response of the geometric and NMR properties of molecular systems to an external electric field has been studied theoretically in a wide field range. It has been shown that this adduct under field approach can be used to model the geometric and spectral changes experienced by molecular systems in polar media if the system in question has one and only one bond, the polarizability of which significantly exceeds the polarizability of other bonds. If this requirement is met, then it becomes possible to model even extreme cases, for example, proton dissociation in hydrogen halides. This requirement is fulfilled for many complexes with one hydrogen bond. For such complexes, this approach can be used to facilitate a detailed analysis of spectral changes associated with geometric changes in the hydrogen bond. For example, in hydrogen-bonded complexes of isocyanide C≡¹⁵N-¹H⋯X, ¹J(¹⁵N¹H) depends exclusively on the N-H distance, while δ(¹⁵N) is also slightly influenced by the nature of X. Full article

(This article belongs to the Special Issue Molecular Spectroscopy and Molecular Structure: Commemorative Issue in Honor of Professor Austin J. Barnes on Occasion of his 75th Birthday)

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17 pages, 4479 KiB

Open AccessArticle

Spectroscopic and Structural Study of a New Conducting Pyrazolium Salt

by Sylwia Zięba, Agata Piotrowska, Adam Mizera, Paweł Ławniczak, Karolina H. Markiewicz, Andrzej Gzella, Alina T. Dubis and Andrzej Łapiński

Molecules 2021, 26(15), 4657; https://doi.org/10.3390/molecules26154657 - 31 Jul 2021

Cited by 4 | Viewed by 2661

Abstract

The increase in conductivity with temperature in 1H-pyrazol-2-ium 2,6-dicarboxybenzoate monohydrate was analyzed, and the influence of the mobility of the water was discussed in this study. The electric properties of the salt were studied using the impedance spectroscopy method. WB97XD/6-311++G(d,p) calculations were performed, and the quantum theory of atoms in molecules (QTAiM) approach and the Hirshfeld surface method were applied to analyze the hydrogen bond interaction. It was found that temperature influences the spectroscopic properties of pyrazolium salt, particularly the carbonyl and hydroxyl frequencies. The influence of water molecules, connected by three-center hydrogen bonds with co-planar tetrameters, on the formation of structural defects is also discussed in this report. Full article

(This article belongs to the Special Issue Molecular Spectroscopy and Molecular Structure: Commemorative Issue in Honor of Professor Austin J. Barnes on Occasion of his 75th Birthday)

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16 pages, 5905 KiB

Open AccessArticle

Solvatochromic Study of Two Carbanion Monosubstituted 4-Tolyl-1,2,4-triazol-1-ium Phenacylids in Binary Hydroxyl Solvent Mixtures

by Dana Ortansa Dorohoi, Dan-Gheorghe Dimitriu, Mihaela Maria Dulcescu-Oprea, Ana Cezarina Morosanu, Nicoleta Puica-Melniciuc, Elena Ardelean, Antonina Gritco-Todirascu and Corina Cheptea

Molecules 2021, 26(13), 3910; https://doi.org/10.3390/molecules26133910 - 26 Jun 2021

Cited by 3 | Viewed by 1799

Abstract

Two 4-tolyl-1,2,4-triazol-1-ium methylids, namely 4-tolyl-1,2,4-triazol-1-ium-phenacylid and 4-tolyl-1,2,4-triazol-1-ium-4′-nitro-phenacylid, are studied from solvatochromic point of view in binary solvent mixtures of water with ethanol and water with methanol. The contributions (expressed in percent) of the universal and specific interactions are separated from the spectral shifts recorded in the visible range for each composition of the binary solvent mixture. The essential role of the orientation and induction interactions in the studied solutions was demonstrated. Based on the statistic cell model of the binary solvent mixture solutions, the difference between the formation energies of ylid-water and ylid-alcohol complexes is estimated. The composition of the ylid’s first solvation shell was also established using the model of the binary solvent mixture solutions. The results obtained from the statistical cell model were compared with those obtained by using the Suppan’s model, resulting a good agreement. Full article

(This article belongs to the Special Issue Molecular Spectroscopy and Molecular Structure: Commemorative Issue in Honor of Professor Austin J. Barnes on Occasion of his 75th Birthday)

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12 pages, 2376 KiB

Open AccessArticle

PLS-DA Model for the Evaluation of Attention Deficit and Hyperactivity Disorder in Children and Adolescents through Blood Serum FTIR Spectra

by Gulce Ogruc Ildiz, Ahmet Karadag, Ersin Kaygisiz and Rui Fausto

Molecules 2021, 26(11), 3400; https://doi.org/10.3390/molecules26113400 - 03 Jun 2021

Cited by 8 | Viewed by 2410

Abstract

Attention deficit and hyperactivity disorder (ADHD) is one of the most common neurodevelopmental disorders of childhood. It affects ~10% of the world’s population of children, and about 30–50% of those diagnosed in childhood continue to show ADHD symptoms later, with 2–5% of adults having the condition. Current diagnosis of ADHD is based on the clinical evaluation of the patient, and on interviews performed by clinicians with parents and teachers of the children, which, together with the fact that it shares common symptoms and frequent comorbidities with other neurodevelopmental disorders, makes the accurate and timely diagnosis of the disorder a difficult task. Despite the large effort to identify reliable biomarkers that can be used in a clinical environment to support clinical diagnosis, this goal has never been achieved hitherto. In the present study, infrared spectroscopy was used together with multivariate statistical methods (hierarchical clustering and partial least-squares discriminant analysis) to develop a model based on the spectra of blood serum samples that is able to distinguish ADHD patients from healthy individuals. The developed model used an approach where the whole infrared spectrum (in the 3700–900 cm⁻¹ range) was taken as a holistic imprint of the biochemical blood serum environment (spectroscopic biomarker), overcoming the need for the search of any particular chemical substance associated with the disorder (molecular biomarker). The developed model is based on a sensitive and reliable technique, which is cheap and fast, thus appearing promising to use as a complementary diagnostic tool in the clinical environment. Full article

(This article belongs to the Special Issue Molecular Spectroscopy and Molecular Structure: Commemorative Issue in Honor of Professor Austin J. Barnes on Occasion of his 75th Birthday)

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16 pages, 5912 KiB

Open AccessArticle

Structural Insights of Three 2,4-Disubstituted Dihydropyrimidine-5-carbonitriles as Potential Dihydrofolate Reductase Inhibitors

by Lamya H. Al-Wahaibi, Althaf Shaik, Mohammed A. Elmorsy, Mohammed S. M. Abdelbaky, Santiago Garcia-Granda, Subbiah Thamotharan, Vijay Thiruvenkatam and Ali A. El-Emam

Molecules 2021, 26(11), 3286; https://doi.org/10.3390/molecules26113286 - 29 May 2021

Cited by 2 | Viewed by 2492

Abstract

In this report, we describe the structural characterization of three 2,4-disubstituted-dihydropyrimidine-5-carbonitrile derivatives, namely 2-{[(4-nitrophenyl)methyl]sulfanyl}-6-oxo-4-propyl-1,6-dihydropyrimidine-5-carbonitrile 1, 4-(2-methylpropyl)-2-{[(4-nitrophenyl)methyl]sulfanyl}-6-oxo-1,6-dihydropyrimidine-5-carbonitrile 2, and 2-[(2-ethoxyethyl)sulfanyl]-6-oxo-4-phenyl-1,6-dihydropyrimidine-5-carbonitrile monohydrate 3. An X-ray diffraction analysis revealed that these compounds were crystallized in the centrosymmetric space groups and adopt an L-shaped conformation. One of the compounds (3) crystallized with a water molecule. A cyclic motif (R₂²(8)) mediated by N–H···O hydrogen bond was formed in compounds 1 and 2, whereas the corresponding motif was not favorable, due to the water molecule, in compound 3. The crystal packing of these compounds was analyzed based on energy frameworks performed at the B3LYP/6-31G(d,p) level of theory. Various inter-contacts were characterized using the Hirshfeld surface and its associated 2D-fingerprint plots. Furthermore, a molecular docking simulation was carried out to assess the inhibitory potential of the title compounds against the human dihydrofolate reductase (DHFR) enzyme. Full article

(This article belongs to the Special Issue Molecular Spectroscopy and Molecular Structure: Commemorative Issue in Honor of Professor Austin J. Barnes on Occasion of his 75th Birthday)

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16 pages, 3977 KiB

Open AccessArticle

Spectroscopic Study of the Molecular Structure of the New Hybrid with a Potential Two-Way Antibacterial Effect

by Dorota Kowalczuk, Agata Gładysz, Monika Pitucha, Daniel M. Kamiński, Agnieszka Barańska and Bartłomiej Drop

Molecules 2021, 26(5), 1442; https://doi.org/10.3390/molecules26051442 - 07 Mar 2021

Cited by 7 | Viewed by 2123

Abstract

Bacterial strains become resistant to almost all classes of antibiotics, which makes it necessary to look for new substitutes. The non-absorbable ciprofloxacin–biguanide bismuth complex, used locally, may be a good alternative to a conventional therapy. The purpose of this study was to study the structure of the proposed ciprofloxacin (CIP) -bismuth(III)—chlorhexidine (CHX) composite (CIP-Bi-CHX). The spectroscopic techniques such as UV-VIS (ultraviolet-visible) spectroscopy, FTIR (Fourier-transform infrared) spectroscopy and NMR (Nuclear Magnetic Resonance) spectroscopy were used for structure characterization of the hybrid compound. The performed analysis confirmed the presence of the two active components—CIP and CHX and revealed the possible coordination sites of the ligands with bismuth ion in the metallo-organic structure. Spectroscopic study showed that the complexation between Bi(III) and CIP occurs through the carboxylate and ketone groups of the quinolone ring, while CHX combines with the central ion via the biguanide moieties. Full article

(This article belongs to the Special Issue Molecular Spectroscopy and Molecular Structure: Commemorative Issue in Honor of Professor Austin J. Barnes on Occasion of his 75th Birthday)

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19 pages, 2915 KiB

Open AccessArticle

Complexes of Formaldehyde and α-Dicarbonyls with Hydroxylamine: FTIR Matrix Isolation and Theoretical Study

by Barbara Golec, Magdalena Sałdyka and Zofia Mielke

Molecules 2021, 26(4), 1144; https://doi.org/10.3390/molecules26041144 - 20 Feb 2021

Cited by 3 | Viewed by 2718

Abstract

The interactions of formaldehyde (FA), glyoxal (Gly) and methylglyoxal (MGly) with hydroxylamine (HA) isolated in solid argon and nitrogen were studied using FTIR spectroscopy and ab initio methods. The spectra analysis indicates the formation of two types of hydrogen-bonded complexes between carbonyl and hydroxylamine in the studied matrices. The cyclic planar complexes are stabilized by O–H⋯O(C), and C–H⋯N interactions and the nonplanar complexes are stabilized by O–H⋯O(C) bond. Formaldehyde was found to form with hydroxylamine, the cyclic planar complex and methylglyoxal, the nonplanar one in both argon and nitrogen matrices. In turn, glyoxal forms with hydroxylamine the most stable nonplanar complex in solid argon, whereas in solid nitrogen, both types of the complex are formed. Full article

(This article belongs to the Special Issue Molecular Spectroscopy and Molecular Structure: Commemorative Issue in Honor of Professor Austin J. Barnes on Occasion of his 75th Birthday)

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10 pages, 18408 KiB

Open AccessFeature PaperArticle

Spectroscopic and Theoretical Study of the Intramolecular π-Type Hydrogen Bonding and Conformations of 2-Cyclopenten-1-ol

by Esther J. Ocola and Jaan Laane

Molecules 2021, 26(4), 1106; https://doi.org/10.3390/molecules26041106 - 19 Feb 2021

Cited by 1 | Viewed by 2105

Abstract

The conformations of 2-cyclopenten-1-ol (2CPOL) have been investigated by high-level theoretical computations and infrared spectroscopy. The six conformational minima correspond to specific values of the ring-puckering and OH internal rotation coordinates. The conformation with the lowest energy possesses intramolecular π-type hydrogen bonding. A second conformer with weaker hydrogen bonding has somewhat higher energy. Ab initio coupled-cluster theory with single and double excitations (CCSD) was used with the cc-pVTZ (triple-ζ) basis set to calculate the two-dimensional potential energy surface (PES) governing the conformational dynamics along the ring-puckering and internal rotation coordinates. The two conformers with the hydrogen bonding lie about 300 cm⁻¹ (0.8 kcal/mole) lower in energy than the other four conformers. The lowest energy conformation has a calculated distance of 2.68 Å from the hydrogen atom on the OH group to the middle of the C=C double bond. For the other conformers, this distance is at least 0.3 Å longer. The infrared spectrum in the O-H stretching region agrees well with the predicted frequency differences between the conformers and shows the conformers with the hydrogen bonding to have the lowest values. The infrared spectra in other regions arise mostly from the two hydrogen-bonded species. Full article

(This article belongs to the Special Issue Molecular Spectroscopy and Molecular Structure: Commemorative Issue in Honor of Professor Austin J. Barnes on Occasion of his 75th Birthday)

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10 pages, 3626 KiB

Open AccessArticle

Luminescent Ink Based on Upconversion of NaYF₄:Er,Yb@MA Nanoparticles: Environmental Friendly Synthesis and Structural and Spectroscopic Assessment

by T. M. Dung Cao, T. T. Giang Le, Sylvia Turrell, Maurizio Ferrari, Quang Vinh Lam and T. T. Van Tran

Molecules 2021, 26(4), 1041; https://doi.org/10.3390/molecules26041041 - 17 Feb 2021

Cited by 7 | Viewed by 2830

Abstract

NaYF₄:Er,Yb upconversion luminescent nanoparticles (UCNPs) were prepared by hydrothermal methods at 180 °C for 24 h. The X-ray diffraction (XRD) and TEM (transmission electron microscopy) images show that the resulting 60 nm UCNPs possess a hexagonal structure. In this work, maleic anhydride (MA) was grafted on the surface of UCNPs to induce hydrophilic properties. The photoluminescence spectra (PL) show upconversion emissions centered around 545 nm and 660 nm under excitation at 980 nm. The luminescent inks, including UCNPs@MA, polyvinyl alcohol (PVA), deionized water (DI), and ethylene glycol (EG), exhibit suitable properties for screen printing, such as high stability, emission intensity, and tunable dynamic viscosity. The printed patterns with a height of 5 mm and a width of 1.5 mm were clearly observed under the irradiation of a 980 nm laser. Our strategy provides a new route for the controlled synthesis of hydrophilic UCNPs, and shows that the UCNPs@MAs have great potential in applications of anti-counterfeiting packing. Full article

(This article belongs to the Special Issue Molecular Spectroscopy and Molecular Structure: Commemorative Issue in Honor of Professor Austin J. Barnes on Occasion of his 75th Birthday)

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20 pages, 2429 KiB

Open AccessArticle

The Structures, Molecular Orbital Properties and Vibrational Spectra of the Homo- and Heterodimers of Sulphur Dioxide and Ozone. An Ab Initio Study

by Thomas A. Ford

Molecules 2021, 26(3), 626; https://doi.org/10.3390/molecules26030626 - 25 Jan 2021

Cited by 1 | Viewed by 3309

Abstract

The structures of a number of dimers of sulphur dioxide and ozone were optimized by means of a series of ab initio calculations. The dimer species were classified as either genuine energy minima or transition states of first or higher order, and the most probable structures consistent with the experimental data were confirmed. The molecular orbitals engaged in the interactions resulting in adduct formation were identified and relations between the orbitals of the dimers of the valence isoelectronic monomer species were examined. The vibrational spectra of the most probable structures were computed and compared with those reported in the literature, particularly with spectra observed in cryogenic matrices. The calculations were extended to predict the properties of a number of possible heterodimers formed between sulphur dioxide and ozone. Full article

(This article belongs to the Special Issue Molecular Spectroscopy and Molecular Structure: Commemorative Issue in Honor of Professor Austin J. Barnes on Occasion of his 75th Birthday)

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50 pages, 10786 KiB

Open AccessFeature PaperArticle

Structural Aspects of the Ortho Chloro- and Fluoro- Substituted Benzoic Acids: Implications on Chemical Properties

by Gulce Ogruc Ildiz and Rui Fausto

Molecules 2020, 25(21), 4908; https://doi.org/10.3390/molecules25214908 - 23 Oct 2020

Cited by 13 | Viewed by 3321

Abstract

This article presents a detailed comprehensive investigation of the ortho fluoro- and chloro- substituted benzoic acids both, as isolated molecules and in the crystalline phase. Quantum chemical calculations performed within the density functional theory (DFT) formalism are used to investigate the potential energy landscapes of the molecules, taking into special consideration the effects of the interactions between the carboxylic group and the ortho halogen substituents, as well as the nature of these later on the structure and properties of the investigated systems. The structures of the relevant conformers of the molecules are discussed in comparative terms, and used to rationalize experimental data obtained for the compounds in the gas phase and isolated in low-temperature inert matrices. The UV-induced photofragmentation reactions of two of the compounds isolated in cryogenic inert matrices were studied as illustrative cases. The structures of the crystals reported previously in the literature are revisited and discussed also in a comparative basis. Particular emphasis is given to the analysis of the intermolecular interactions in the different crystals, using Hirshfeld surface analysis, the CE-B3LYP energy decomposition model and the HOMA index, and to their correlation with thermodynamic data. Full article

(This article belongs to the Special Issue Molecular Spectroscopy and Molecular Structure: Commemorative Issue in Honor of Professor Austin J. Barnes on Occasion of his 75th Birthday)

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Molecular Spectroscopy and Molecular Structure: Commemorative Issue in Honor of Professor Austin J. Barnes on Occasion of his 75th Birthday

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