Theoretical analysis of the terahertz spectrum of the high explosive PETN.

The experimental solid-state terahertz (THz) spectrum (3 to 120 cm(-1)) of the high explosive pentaerythritol tetranitrate (PETN, C(5)H(6)N(4)O(12)) has been modeled using solid-state density functional theory (DFT) calculations. Solid-state DFT, employing the BP density functional, is in best qualitative agreement with the features in the previously reported THz spectrum. The crystal environment of PETN includes numerous intermolecular hydrogen-bonding interactions that contribute to large (up to 80 cm(-1)) calculated shifts in molecular normal-mode positions in the solid state. Comparison of the isolated-molecule and solid-state normal-mode calculations for a series of density functionals reveals the extent to which the inclusion of crystal-packing interactions and the relative motions between molecules are required for correctly reproducing the vibrational structure of solid-state THz spectra. The THz structure below 120 cm(-1) is a combination of both intermolecular (relative rotations and translations) and intramolecular (torsions, large amplitude motions) vibrational motions. Vibrational-mode analyses indicate that the first major feature (67.2 cm(-1)) in the PETN THz spectrum contains all of the optical rotational and translational cell modes and no internal (molecular) vibrational modes.     

Ab initio and semiempirical computational studies on 1‐{(2E)‐2‐[(aminocarbonothioyl)hydrazono]‐2‐(3‐mesityl‐3‐methylcyclobutyl)ethyl}‐pyrrolidine‐2,5‐dione

The molecular geometry, vibrational frequencies, and gauge including atomic orbital (GIAO) ¹H‐ and ¹³C NMR chemical shift values of the title compound in the ground state have been calculated using the Hartree‐Fock (HF) and density functional theory (DFT) methods with 6‐31G(d) basis sets, and compared with the experimental data. The calculated results show that the optimized geometries can well reproduce the crystal structural parameters and the theoretical vibrational frequencies, and ¹H‐ and ¹³C NMR chemical shift values show good agreement with experimental data. To determine conformational flexibility, the molecular energy profile of the title compound was obtained by semiempirical (AM1) calculations with respect to the selected torsion angle, which was varied from ?180° to +180° in steps of 10°. The energetic behavior of the title compound in solvent media was examined using the B3LYP method with the 6‐31G(d) basis set by applying the Onsager and the polarizable continuum model (PCM). The results obtained with these methods reveal that the PCM method provided more stable structure than Qnsager's method. By using TD‐DFT method, electronic absorption spectra of the title compound have been predicted and a good agreement with the TD‐DFT method and the experimental one is determined. The predicted nonlinear optical properties of the title compound are much greater than ones of urea. In addition, the molecular electrostatic potential (MEP), frontier molecular orbitals (FMO) analysis, NBO analysis and thermodynamic properties of the title compound were investigated using theoretical calculations. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Quantum‐chemical,IR, NMR,and X‐ray diffraction studies on 2‐(4‐chlorophenyl)‐1‐methyl‐ 1H‐benzo[d]imidazole

The title molecule, 2‐(4‐chlorophenyl)‐1‐methyl‐1H‐benzo[d]imidazole (C₁₄H₁₁ClN₂), was prepared and characterized by ¹H NMR, ¹³C NMR, IR, and single‐crystal X‐ray diffraction. The molecular geometry, vibrational frequencies, and gauge including atomic orbital (GIAO) ¹H and ¹³C NMR chemical shift values of the title compound in the ground state have been calculated by using the Hartree‐Fock (HF) and density functional theory (DFT/B3LYP) method with 6‐31G(d) basis sets, and compared with the experimental data. The calculated results show that the optimized geometries can well reproduce the crystal structural parameters, and the theoretical vibrational frequencies and GIAO ¹H and ¹³C NMR chemical shifts show good agreement with experimental values. The energetic behavior of the title compound in solvent media has been examined using B3LYP method with the 6‐31G(d) basis set by applying the Onsager and the polarizable continuum model (PCM). Besides, molecular electrostatic potential (MEP), frontier molecular orbitals (FMO) analysis, and nonlinear optical (NLO) properties of the title compound were investigated by theoretical calculations. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

N,N‐Diethyl‐N′‐[(E)‐4‐pyridylmethylene]benzene‐1,4‐diamine: a combined X‐ray and density functional theory study

The crystal structure of the title compound, C₁₆H₁₉N₃, comprises neutral molecules of a dipolar Schiff base chromophore. A density functional theory (DFT) optimized structure at the B3LYP/6‐31G(d) level is compared with the molecular structure in the solid state. The compound crystallizes in the noncentrosymmetric space group Pna2₁ with a herring‐bone packing motif and is therefore a potential candidate for nonlinear optical effects in the bulk.     

Vibrational Sum‐Frequency Generation Activity of a 2,4‐Dinitrophenyl Phospholipid Hybrid Bilayer: Retrieving Orientational Parameters from a DFT Analysis of Experimental Data

The vibrational nonlinear activity of films of 2,4‐dinitrophenyl phospholipid (DNP) at the solid interface is measured by sum‐frequency generation spectroscopy (SFG). Hybrid bilayers are formed by a Langmuir–Schaefer approach in which the lipid layer is physisorbed on top of a self‐assembled monolayer of dodecanethiol on Pt with the polar heads pointing out from the surface. The SFG response is investigated in two vibrational frequency domains, namely, 3050–2750 and 1375–1240 cm^?1. The first region probes the CH stretching modes of DNP films, and the latter explores the vibrational nonlinear activity of the 2,4‐dinitroaniline moiety of the polar head of the lipid. Analysis of the CH stretching vibrations suggests substantial conformational order of the aliphatic chains with only a few gauche defects. To reliably assign the detected SFG signals to specific molecular vibrations, DFT calculations of the IR and Raman activities of molecular models are performed and compared to experimental solid‐state spectra. This allows unambiguous assignment of the observed SFG vibrations to molecular modes localized on the 2,4‐dinitroaniline moiety of the polar head of DNP. Then, SFG spectra of DNP in the 1375–1240 cm^?1 frequency range are simulated and compared with experimental ones, and thus the 1,4‐axis of the 2,4‐dinitrophenyl head is estimated to have tilt and rotation angles of 45±5° and 0±30°, respectively.     

Theoretical Study on Hydrogen‐Bond Effects in IR Spectra of High‐ and Low‐Temperature Phases of Nitric Acid Dihydrate

The low‐ and high‐temperature phases (α and β, respectively) of solid nitric acid dihydrate (NAD) are studied in depth by DFT methods. Each phase contains two types of complex structures (H₃O⁺) ? (H₂O), designated A and B, with different hydrogen‐bonding (HB) characteristics. The theoretical study reveals that type A complexes are weakly bound and could be described as (H₃O)⁺ and H₂O aggregates, with decoupled vibrational modes, whereas in type B structures the proton is situated close to the centre of the O ??? O bond and induces strong vibrational coupling. The proton‐transfer mode is predicted at quite different wavenumbers in each complex, which provides an important differentiating spectral feature, together with splitting of some bands in β‐NAD. Theoretical spectra are estimated by using two GGA parameterizations, namely, PBE and BLYP. The potential‐energy surface for each type of HB in NAD is also studied, as is the spectral influence of displacement of the shared H atom along the O? O bond. The results are compared to literature infrared spectra recorded by different techniques, namely, transmission and reflection–absorption, with both normal and tilted incident radiation. This work provides a thorough assignment of the observed spectra, and predictions for some spectra not yet available. The usefulness of high‐level theoretical calculations as performed herein to discriminate between two phases of a solid crystal is thus evidenced.     

Synthesis,crystal structure,spectral characterization,and DFT studies on 4‐((1‐phenyl‐1H‐tetrazol‐5‐ylthio)methyl)benzoic acid

A new thiotetrazole compound, 4‐((1‐phenyl‐1H‐tetrazol‐5‐ylthio)methyl) benzoic acid ( 1 ), has been synthesized and characterized by elemental analysis, ¹H and ¹³C NMR, ESI‐MS, FT‐IR, UV–vis, fluorescence spectra, and single‐crystal X‐ray diffraction analysis. The structural analysis reveals that compound 1 adopts a nonplanar geometric structure and exhibits an extensive but not uniform π delocalization with all members of the tetrazolyl ring and the exocyclic sulfur atom. A density functional theory (DFT) calculation at B3LYP/6‐31G** level of theory was performed to elucidate the structure of this thiotetrazole system. And the time‐dependent DFT (TD‐DFT) calculations of absorption spectra reveal two electron‐transition bands derived from the contribution of π → π* transitions, which are in agreement with experimental results. Moreover, compound 1 exhibits a blue‐light emission (λ_em = 441 nm) in the solid state at room temperature. © 2012 Wiley Periodicals, Inc. Heteroatom Chem 23:435–443, 2012; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.21034     

1,3,5‐Tris(bromomethyl)benzene

The asymmetric unit of the title compound, C₉H₉Br₃, is composed of a single molecule. Two bromo substituents are located on one side of the plane of the aromatic ring and the third is on the opposite side, with the molecular unit exhibiting an approximate noncrystallographic C_s point group. The crystal structure is rich in Br...Br, CH₂...Br and CH...π weak intermolecular contacts which mediate the crystal packing of individual molecules. These interactions promote a red‐shift of a handful of vibrational modes (associated with the pendant –CH₂Br groups) compared with values from theoretical density functional theory (DFT) calculations.     

Solid-state modeling of the terahertz spectrum of the high explosive HMX

The experimental solid-state terahertz (THz) spectrum (3-120 cm(-1)) of the beta-crystal form of the high explosive octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) has been analyzed using solid-state density functional theory calculations. Various density functionals (both generalized gradient approximation and local density approximation) are compared in terms of their abilities to reproduce the experimentally observed solid-state structure and low-frequency vibrational motions. Good-to-excellent agreement between solid-state theory and experiment can be achieved in the THz region where isolated-molecule calculations fail to reproduce the observed spectral features, demonstrating a clear limitation of using isolated-molecule calculations for the assignment of THz frequency motions in molecular solids. The deficiency of isolated-molecule calculations is traced to modification of the molecular structure in the solid state through crystal packing effects and the formation of weak C-H...O hydrogen bonds.     

Oxadiazole‐2‐thiol Adsorption on Gold Nanorods: A Joint Theoretical and Experimental Study by Using SERS,XPS, and DFT

The chemisorption of 1,3,4‐oxadiazole‐2‐thiol (ODT) on gold nanorods has been investigated by using surface‐enhanced Raman spectroscopy (SERS) and density functional theory (DFT). Although most of the SERS spectra have remarkable similarity to the normal Raman spectra of the pure analyte, the adsorption of ODT on a gold surface leads to a drastic change in its Raman spectrum and distinct vibrational features are obtained with gold nanorods and spherical nanoparticles. Simulated Raman spectra for hybrid systems that consist of an oxadiazole moiety coordinated to a Au₂₀ gold cluster provided valuable information about the coordination mode and enabled us to assign vibration modes.     

An experimental and theoretical approach to the molecular structure of 3‐{[4‐(3‐Methyl‐3‐phenyl‐cyclobutyl)‐thiazol‐2‐yl]‐hydrazono}‐1,3‐dihydro‐ indol‐2‐one

The title molecule, 3‐{[4‐(3‐methyl‐3‐phenyl‐cyclobutyl)‐thiazol‐2‐yl]‐hydrazono}‐1,3‐dihydro‐indol‐2‐one (C₂₂H₂₀N₄O₁S₁), was prepared and characterized by ¹H NMR, ¹³C NMR, IR, UV–visible, and single‐crystal X‐ray diffraction. The compound crystallizes in the monoclinic space group P21 with a = 8.3401(5), b = 5.6976(3), c = 20.8155(14) Å, and β = 95.144(5)°. Molecular geometry from X‐ray experiment and vibrational frequencies of the title compound in the ground state has been calculated using the Hartree–Fock with 6‐31G(d, p) and density functional method (B3LYP) with 6‐31G(d, p) and 6‐311G(d, p) basis sets, and compared with the experimental data. The calculated results show that optimized geometries can well reproduce the crystal structural parameters, and the theoretical vibrational frequencies values show good agreement with experimental data. Density functional theory calculations of the title compound and thermodynamic properties were performed at B3LYP/6‐31G(d, p) level of theory. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Combined experimental and computational modeling studies on 3,5‐dimethyl‐pyrazole‐1‐carbodithioic acid benzyl ester

The title compound, 3,5‐Dimethyl‐pyrazole‐1‐carbodithioic acid benzyl ester, has been synthesized and structurally characterized by X‐ray single crystal diffraction, elemental analysis, IR spectra, and UV‐Vis spectrum. The crystal belongs to orthorhombic, space group P212121, with a = 5.3829(15), b = 11.193(3), c = 21.824(6) Å, V = 1315.0(6) ų, and Z = 4. The molecules are connected via intermolecular C–H···N hydrogen bonds into 1D infinite chains. The crystal structure is consolidated by the intramolecular C–H···S hydrogen bonds. Furthermore, Density functional theory (DFT) calculations of the structure, stabilities, orbital energies, composition characteristics of some frontier molecular orbitals and Mulliken charge distributions of the title compound were performed by means of Gaussian 03W package and taking B3LYP/6‐31G(d) basis set. The time‐dependent DFT (TD‐DFT) calculations have been employed to calculate the electronic spectrum of the title compound, and the UV‐Vis spectra has been discussed on this basis. The results show that DFT method at B3LYP/6‐31G(d) level can well reproduce the structure of the title compound. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Experimental and theoretical investigation of the molecular and electronic structure of N′‐benzylidene‐N‐[4‐(3‐methyl‐3‐phenyl‐cyclobutyl)‐thiazol‐2‐yl]‐chloro‐acetic acid hydrazide

The title compound, N′‐benzylidene‐N‐[4‐(3‐methyl‐3‐phenyl‐cyclobutyl)‐thiazol‐2‐yl]‐chloro‐acetic acid hydrazide, has been synthesized and characterized by elemental analysis, IR, ¹H and ¹³C NMR, and X‐ray single crystal diffraction. The compound crystallizes in the orthorhombic space group P 21 21 21 with a = 5.8671 (3) Å, b = 17.7182 (9) Å, and c = 20.6373 (8) Å. Moreover, the molecular geometry from X‐ray experiment, the molecular geometry, vibrational frequencies, and gauge‐including atomic orbital ¹H and ¹³C chemical shift values of the title compound in the ground state have been calculated by using the Hartree–Fock and density functional methods (B3LYP) with 6‐31G(d) and 6‐31G(d,p) basis sets. The results of the optimized molecular structure are exhibited and compared with the experimental X‐ray diffraction. Besides, molecular electrostatic potential, Frontier molecular orbitals, and thermodynamic properties of the title compound were determined at B3LYP/6‐31G(d) levels of theory. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

1‐[2‐(2,6‐Diisopropylanilino)‐1‐naphthyl]isoquinoline

The molecule of the title compound, C₃₁H₃₀N₂, contains a single intramolecular hydrogen bond, in contrast with the related N‐methyl compound which exists as hydrogen‐bonded dimers in the solid state [Cortright, Huffman, Yoder, Coalter & Johnston (2004). Organometallics, 23 , 2238–2250]. Application of the density functional theory programs CASTEP and DMol³ allows accurate assignment of the location of the H atoms in the structure.     

N,N′‐Dicyclohexyl‐N‐[4‐(1H‐indol‐3‐yl)butanoyl]urea

The title compound, C₂₅H₃₅N₃O₂, is a novel urea derivative. Pairs of intermolecular N—H...O hydrogen bonds join the molecules into centrosymmetric R₂²(12) and R₂²(18) dimeric rings, which are alternately linked into one‐dimensional polymeric chains along the [010] direction. The parallel chains are connected via C—H...O hydrogen bonds to generate a two‐dimensional framework structure parallel to the (001) plane. The title compound was also modelled by solid‐state density functional theory (DFT) calculations. A comparison of the molecular conformation and hydrogen‐bond geometry obtained from the X‐ray structure analysis and the theoretical study clearly indicates that the DFT calculation agrees closely with the X‐ray structure.     

Exploring the Vibrational Side of Spin‐Phonon Coupling in Single‐Molecule Magnets via 161Dy Nuclear Resonance Vibrational Spectroscopy

Synchrotron‐based nuclear resonance vibrational spectroscopy (NRVS) using the Mössbauer isotope ¹⁶¹Dy has been employed for the first time to study the vibrational properties of a single‐molecule magnet (SMM) incorporating Dy^III, namely [Dy(Cy₃PO)₂(H₂O)₅]Br₃?2 (Cy₃PO)?2 H₂O ?2 EtOH. The experimental partial phonon density of states (pDOS), which includes all vibrational modes involving a displacement of the Dy^III ion, was reproduced by means of simulations using density functional theory (DFT), enabling the assignment of all intramolecular vibrational modes. This study proves that ¹⁶¹Dy NRVS is a powerful experimental tool with significant potential to help to clarify the role of phonons in SMMs.     

Theoretical study of molecular and electronic structure of 2‐Se‐(2‐methyl‐2‐propenyl)‐1‐benzoic acid

A theoretical study of 2‐Se‐(2‐methyl‐2‐propenyl)‐1‐benzoic acid was carried out to investigate the molecular and electronic structure of this molecule, using the B3LYP density functional theory (DFT) method with the 6‐311+G** basis set. The optimized geometry of the molecule was obtained for the ortho, meta, and para isomers of the complex. In addition, the theoretical vibrational spectrum is presented, and thermal corrections in the limit of 100–1,000 K are discussed using the Shomate thermodynamic equations. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Experimental and quantum chemical calculational studies on N‐[4‐(3‐Methyl‐3‐phenyl‐cyclobutyl)‐thiazol‐2‐yl]‐N′‐pyridin‐3ylmethylene‐hydrazine

The title molecule, N‐[4‐(3‐Methyl‐3‐phenyl‐cyclobutyl)‐thiazol‐2‐yl]‐N′‐pyridin‐3ylmethylene‐ hydrazine (C₂₀ H₂₀ N₄ S₁), was characterized by ¹H‐NMR, ¹³C‐NMR, IR, UV‐visible, and X‐ray determination. In addition to the molecular geometry from X‐ray experiment, the molecular geometry, vibrational frequencies and gauge including atomic orbital ¹H‐ and ¹³C‐NMR chemical shift values of the title compound in the ground state have been calculated using the Hartree‐Fock and density functional method (B3LYP) with 6‐31G(d, p) basis set. The calculated results show that optimized geometries can well reproduce the crystal structural parameters. By using time‐dependent density functional theory method, electronic absorption spectrum of the title compound has been predicted. © 2011 Wiley Periodicals, Inc.     

Molecular analysis of water clusters: Calculation of the cluster structures and vibrational spectrum using density functional theory

Density functional theory (DFT) is applied to obtain absorption spectra at THz frequencies for molecular clusters of H₂O. The vibrational modes of the clusters are calculated. Coupling among molecular vibrational modes explains their spectral features associated with THz excitation. THz excitation is associated with vibrational frequencies which are here calculated within the DFT approximation of electronic states. This is done for both isolated molecules and collections of molecules in a cluster. The principal result of the paper is that a crystal-like cluster of 38 water molecules together with a continuum solvent background is sufficient to replicate well the experimental vibrational frequencies.     

Incorporating two different chromophores onto a silicon atom: the crystal structure and photophysical properties of 9‐{4‐[(9,9‐dimethyl‐9H‐fluoren‐2‐yl)dimethylsilyl]phenyl}‐9H‐carbazole

The crystal structure of the title bifunctional silicon‐bridged compound, C₃₅H₃₁NSi, (I), has been determined. The compound crystallizes in the centrosymmetric space group P2₁/c. In the crystal structure, the pairs of aryl rings in the two different chromophores, i.e. 9‐phenyl‐9H‐carbazole and 9,9‐dimethyl‐9H‐fluorene, are positioned orthogonally. In the crystal packing, no classical hydrogen bonding is observed. UV–Vis absorption and fluorescence emission spectra show that the central Si atom successfully breaks the electronic conjugation between the two different chromophores, and this was further analysed by density functional theory (DFT) calculations.