Showing papers on "Molecular geometry published in 2004"

Molecular Force Field for Ionic Liquids Composed of Triflate or Bistriflylimide Anions

Abstract: A set of force field parameters is proposed for the molecular simulation of ionic liquids containing the anions trifluoromethylsufate and bis(trifluoromethylsulfonyl)imide, also known as triflate and bistriflylimide, respectively. The new set can be combined with existing force fields for cations in order to simulate common room-temperature ionic liquids, such as those of the dialkylimidazolium family, and can be integrated with the OPLS-AA or similar force fields. Ab initio quantum chemical calculations were employed to obtain molecular geometry, torsional energy profiles, and partial charge distribution in the triflate and bistriflylimide anions. One of the torsions in bistriflylimide, corresponding to the dihedral angle S−N−S−C, has a complex energy profile which is precisely reproduced by the present parameter set. A new set of partial electrostatic charges is also proposed for the pyrrolidinium and tri- and tetra-alkylammonium cations. Again, these parameters can be combined with the OPLS-AA specific...

A stable compound containing a silicon-silicon triple bond.

Abstract: The reaction of 2,2,3,3-tetrabromo-1,1,4,4-tetrakis[bis(trimethylsilyl)methyl]-1,4-diisopropyltetrasilane with four equivalents of potassium graphite (KC 8 ) in tetrahydrofuran produces 1,1,4,4-tetrakis[bis(trimethylsilyl)methyl]-1,4-diisopropyl-2-tetrasilyne, a stable compound with a silicon-silicon triple bond, which can be isolated as emerald green crystals stable up to 100°C in the absence of air. The SiSi triple-bond length (and its estimated standard deviation) is 2.0622(9) angstroms, which shows half the magnitude of the bond shortening of alkynes compared with that of alkenes. Unlike alkynes, the substituents at the SiSi group are not arranged in a linear fashion, but are trans-bent with a bond angle of 137.44(4)°.

A semiempirical generalized gradient approximation exchange-correlation functional.

Abstract: We describe our attempts to improve upon the quality of the KT1 and KT2 generalized gradient approximation (GGA) exchange-correlation functionals [T. W. Keal and D. J. Tozer, J. Chem. Phys. 119, 3015 (2003)], through the introduction of additional gradient-corrected exchange and correlation terms. A GGA functional, denoted KT3, is presented, which maintains the high quality main-group nuclear magnetic resonance shielding constants obtained with KT1 and KT2; results are 2–3 times more accurate than conventional GGA and hybrid functionals. For the extensive range of systems considered in this study, KT3 also provides atomization energies, ionization potentials, electron affinities, proton affinities, bond angles, and electronic polarizabilities that are comparable to, or that surpass, those of the best present-day GGAs. Furthermore, it provides equilibrium molecular bond lengths and diatomic harmonic vibrational wave numbers that are as accurate as those from the best hybrid functionals. Further improvement...

Bonding Properties of the Water Dimer: A Comparative Study of Density Functional Theories

Abstract: For a variety of density functional theories, we examined the ground-state properties of the water monomer (geometry, vibrational frequencies, dipole moment, polarizability) and dimer (geometry, vibrational frequencies, bond energy, and barrier heights for the transition states for the interchange of hydrogen atoms within the dimer). Thus, we considered LDA (SVWN), seven pure GGA methods (BLYP, BP86, BPW91, PWPW, mPWPW, PBEPBE, and XLYP), and eight hybrid GGA methods (BH&HLYP, B3LYP, B3P86, B3PW91, PW1PW, mPW1PW, PBE1PBE and X3LYP). We find that the best overall performance is given by X3LYP, a hybrid method using a modified GGA constructed from a linear combination of the Becke and Perdew GGAs. Comparing with the exact values, the errors in X3LYP for the water dimer are 0.05 kcal/mol (bond energy), 0.004 A (bond distance), and 12 cm^(-1) (vibrational modes), and for the monomer, the errors are 0.002 A (bond distance), 0.6° (bond angle), 14 cm^(-1) (vibrational modes), 0.005 D (dipole moment), and 0.008 A^3 (polarizability). These data were not used in determining the parameters or form of X3LYP, suggesting that X3LYP should be generally useful for predicting accurate properties for systems dominated by hydrogen bonding, electrostatics, and van der Waals (dispersion) interactions, such as ligand/protein complexes.

Theoretical Analysis of the Smallest Carbon Cluster Containing a Planar Tetracoordinate Carbon

Abstract: A series of molecules, based on the smallest carbon cluster with one planar tetracoordinate carbon atom, C52-, are presented. To gain a better understanding about which electronic factors contribute to their stabilization, several global reactivity indexes, molecular scalar fields, and magnetic responses were calculated. The optimized bond lengths and the topological analysis of the electron density show that the central carbon atom in the parent dianion C52- has a planar local environment, and it is coordinated to four other carbon atoms. The bonding of the parent dianion with the metal cations is highly ionic. The magnetic properties show that the C52- derivatives are strongly diatropic and have a remarkable transferability of structural and electronic features from the anion to the salts. The theoretical analysis suggests that the lithium salt, C5Li2, is the most plausible candidate for experimental detection.

Lock-and-key effect in the surface diffusion of large organic molecules probed by STM.

Abstract: A nanoscale understanding of the complex dynamics of large molecules at surfaces is essential for the bottom-up design of molecular nanostructures1,2,3,4,5,6,7,8. Here we show that we can change the diffusion coefficient of the complex organic molecule known as Violet Lander (VL, C108H104) on Cu(110) by two orders of magnitude by using the STM at low temperatures to switch between two adsorption configurations that differ only in the molecular orientation with respect to the substrate lattice. From an interplay with molecular dynamics simulations, we interpret the results within a lock-and-key model similar to the one driving the recognition between biomolecules: the molecule (key) is immobilized only when its orientation is such that the molecular shape fits the atomic lattice of the surface (lock); otherwise the molecule is highly mobile.

Ionization of N 2 , O 2 , and linear carbon clusters in a strong laser pulse

Abstract: Multiphoton ionization of linear molecules is studied using the strong-field S-matrix approach. Numerical calculations for the angular distribution and the energy spectrum of the photoelectron as well as the total ionization rates and yields in an intense linearly polarized laser pulse are performed. Results are obtained for molecules aligned along the polarization axis and for ensembles of molecules having a random orientation of the molecular axis with respect to the polarization direction. Signatures of the molecular geometry and the orbital symmetry are identified and discussed with reference to molecular imaging and alignment. It is found that these signatures are clearly marked for the diatomic molecules C-2, N-2, and O-2, but are much weaker for the group of linear carbon clusters due to the polyatomic character as well as to the competing contributions from different valence shells of these molecules. Finally, predictions of the present theory for the dependence of the total ionization rates and yields on the orientation of the molecule are compared with other theoretical models and recent experimental data.

Crystal Structure of Haloalkane Dehalogenase LinB from Sphingomonas paucimobilis UT26 at 0.95 Å Resolution: Dynamics of Catalytic Residues

Abstract: We present the structure of LinB, a 33-kDa haloalkane dehalogenase from Sphingomonas paucimobilis UT26, at 0.95 A resolution. The data have allowed us to directly observe the anisotropic motions of the catalytic residues. In particular, the side-chain of the catalytic nucleophile, Asp108, displays a high degree of disorder. It has been modeled in two conformations, one similar to that observed previously (conformation A) and one strained (conformation B) that approached the catalytic base (His272). The strain in conformation B was mainly in the CR-C‚-CA angle (126°) that deviated by 13.4° from the "ideal" bond angle of 112.6 °. On the basis of these observations, we propose a role for the charge state of the catalytic histidine in determining the geometry of the catalytic residues. We hypothesized that double-protonation of the catalytic base (His272) reduces the distance between the side-chain of this residue and that of the Asp108. The results of molecular dynamics simulations were consistent with the structural data showing that protonation of the His272 side-chain nitrogen atoms does indeed reduce the distance between the side-chains of the residues in question, although the simulations failed to demonstrate the same degree of strain in the Asp108 CR-C‚-CA angle. Instead, the changes in the molecular dynamics structures were distributed over several bond and dihedral angles. Quantum mechanics calculations on LinB with 1-chloro-2,2-dimethylpropane as a substrate were performed to determine which active site conformations and protonation states were most likely to result in catalysis. It was shown that His272 singly protonated at N‰1 and Asp108 in conformation A gave the most exothermic reaction (¢H )- 22 kcal/mol). With His272 doubly protonated at N‰1 and N2, the reactions were only slightly exothermic or were endothermic. In all calculations starting with Asp108 in conformation B, the Asp108 CR-C‚-CA angle changed during the reaction and the Asp108 moved to conformation A. The results presented here indicate that the positions of the catalytic residues and charge state of the catalytic base are important for determining reaction energetics in LinB.

Atom-Bond Electronegativity Equalization Method Fused into Molecular Mechanics. II. A Seven-Site Fluctuating Charge and Flexible Body Water Potential Function for Liquid Water

Abstract: The ABEEM-7P model, which is a transferable, intermolecular-potential seven-points approach including fluctuating charges and flexible body, is based on the combination of the atom-bond electronegativity equalization (ABEEM) and molecular mechanics (MM). This model has been successfully explored in regard to the properties of gas-phase small water clusters in reasonable agreement with available experiments and other water models. This model is further tested by comparing the calculated energetic, structural, and dynamic properties of liquid water over a range of temperatures (260-348 K) with available experimental results and those from other water models. Molecular dynamics simulations of liquid water with ABEEM-7P were performed using the Tinker MM program. All simulations were conducted in the microcanonical NVE ensemble or canonical NVT ensemble, using 216 water molecules in a cubic simulation cell furnished with periodic boundary and minimum image conditions, and the density of the solvent was set to the experimental value for the temperature of interest. The ABEEM-7P potential gives a reasonable experimental reproduction of the intramolecular O-H bond length and H-O-H bond angle in the liquid at room temperature. The ABEEM-7P model presents the quantitative charges of O atoms, H atoms, O-H bonds, and lone-pair electrons per monomer water in the liquid and their changing in response to different ambient environment from 260 K to 348 K. Especially, ABEEM-7P applies the parameter k l p , H (R l p , H ) to explicitly describe short-range interaction of the hydrogen bond in the hydrogen-bond interaction region. The computed ABEEM-7P properties of the liquid-phase water at room temperature, such as average dipole moment, static dielectric constant, heats of vaporization, radial distribution function, and diffusion constant, are fairly consistent with the available experimental results. The ABEEM-7P model also performs well for the temperature dependence of liquid properties: the static dielectric constant and the heats of vaporization by ABEEM-7P decrease as the temperature increases, in good agreement with the experimental values.

Electronic structure and chain-length effects in diplatinum polyynediyl complexes trans,trans-[(X)(R3P)2Pt(C triple bond C)(n)Pt(PR3)2(X)]: a computational investigation.

Abstract: Structure and bonding in the title complexes are studied using model compounds trans,trans-[(C6H5)(H3P)2Pt(C triple bond C)(n)Pt(PH3)2(C6H5)] (PtCxPt; x = 2n = 4-26) at the B3LYP/LACVP* level of density functional theory. Conformations in which the platinum square planes are parallel are very slightly more stable than those in which they are perpendicular (DeltaE = 0.12 kcal mol(-1) for PtC8Pt). As the carbon-chain length increases, progressively longer C triple bond C triple bonds and shorter triple bond C-C triple bond single bonds are found. Whereas the triple bonds in HCxH become longer (and the single bonds shorter) as the interior of the chain is approached, the PtC triple bond C triple bonds in PtCxPt are longer than the neighboring triple bond. Also, the Pt-C bonds are shorter at longer chain lengths, but not the H-C bonds. Accordingly, natural bond orbital charge distributions show that the platinum atoms become more positively charged, and the carbon chain more negatively charged, as the chain is lengthened. Furthermore, the negative charge is localized at the two terminal C triple bond C atoms, elongating this triple bond. Charge decomposition analyses show no significant d-pi* backbonding. The HOMOs of PtCxPt can be viewed as antibonding combinations of the highest occupied pi orbital of the sp-carbon chain and filled in-plane platinum d orbitals. The platinum character is roughly proportional to the Pt/Cx/Pt composition (e.g., x = 4, 31 %; x = 20, 6 %). The HOMO and LUMO energies monotonically decrease with chain length, the latter somewhat more rapidly so that the HOMO-LUMO gap also decreases. In contrast, the HOMO energies of HCxH increase with chain length; the origin of this dichotomy is analyzed. The electronic spectra of PtC4Pt to PtC10Pt are simulated. These consist of two pi-pi* bands that redshift with increasing chain length and are closely paralleled by real systems. A finite HOMO-LUMO gap is predicted for PtCinfinityPt. The structures of PtCxPt are not strictly linear (average bond angles 179.7 degrees -178.8 degrees ), and the carbon chains give low-frequency fundamental vibrations (x = 4, 146 cm(-1); x = 26, 4 cm(-1)). When the bond angles in PtC12Pt are constrained to 174 degrees in a bow conformation, similar to a crystal structure, the energy increase is only 2 kcal mol(-1). The above conclusions should extrapolate to (C triple bond C)(n) systems with other metal endgroups.

Short- and intermediate-range structural correlations in amorphous silicon carbide: a molecular dynamics study

Abstract: Short- and intermediate-range structural correlations in amorphous silicon carbide $(\mathrm{a}\text{\ensuremath{-}}\mathrm{SiC})$ are studied in terms of partial pair distributions, bond angle distribution functions, and shortest-path ring statistics. A well relaxed sample is prepared following a slow annealing schedule of the simulation at the experimental density of the amorphous phase. The short-range correlation functions indicate a locally ordered amorphous structure with heteronuclear bonds, $\mathrm{Si}--\mathrm{C}$, with no phase separation, and no graphitic or diamond structures present. The bond distances and coordination numbers are similar to those in the crystalline phase. The rings statistics indicate an intermediate-range topology formed by the rearrangement of tetrahedra with the occurrence of corner and edge sharing units connecting two- ($\ensuremath{\sim}5%$ of total), three-, four-, and five-fold rings. The presence of large size rings indicates the existence of nano-voids in the structure, which explains the low density compared with the crystal phase while keeping the same coordination number and bond distance. These simulation results agree well with experimental results.

Modulation of the Absorption, Fluorescence, and Liquid-Crystal Properties of Functionalised Diarylethene Derivatives

Abstract: Systematic variation of the molecular symmetry in a photochromic system based on a 1,2-bis(2-methylbenzo[b]thiophen-3-yl)hexafluorocyclopentene group, connected by decyl spacers to two cyanobiphenyl groups as mesogens, allows for a systematic investigation of the correlations between molecular shape and symmetry, electronic effects, photochromic conversion and liquid-crystalline properties.

Molecular structure and vibrational spectra of 3-chloro-4-methyl aniline by density functional theory and ab initio Hartree-Fock calculations

Abstract: The molecular geometry and vibrational frequencies of 3-chloro-4-methyl aniline (3-Cl-4ma) in the ground state have been calculated by using the Hartree-Fock and density functional methods (B3LYP and BLYP) with 6-31G (d) as the basis set. The optimized geometric bond lengths obtained by using B3LYP and bond angles obtained by BLYP were given corresponding experimental values of aniline molecule. Comparison of the observed fundamental vibrational frequencies of 3-Cl-4ma and calculated results by density functional B3LYP, BLYP and Hartree-Fock methods indicates that B3LYP is superior to the scaled Hartree-Fock and BLYP approach for molecular vibrational problems.

Structural variation and crystal chemistry of LiMe3+Si2O6 clinopyroxenes Me3+ = Al, Ga, Cr, V, Fe, Sc and In

Abstract: Li-clinopyroxenes / Crystal chemistry / Single crystal structure analysis / X-ray diffraction Abstract A total of 32 synthetic end-member and solid- solution compounds of the LiM3+Sh06 (Li = M2 site, M3+ = Ml site = AI, Ga, V, Fe, Sc and In) clinopyroxene series have been investigated by single-crystal X-ray dif- fraction Except LiCrSh06, all compounds show C2Ic symmetry at 295 K LiCrSh06 has space group P21/c but transforms to the high temperature C2/c structure at 335 K The variations of structural parameters in the LiMe3+Sh06 clinopyroxenes are dominated by the Me3+ site The average Ml-O bond length is linearly correlated with the ionic radius of the M 1 cation Octahedra reflect the increasing size of the Ml cations by steadily increas- ing bond and edge lengths, the variations however are not uniform With increasing size of the Ml cation, octahedra deviate from ideal octahedral geometry Octahedral edges, shared with other structural units, are distinctly hampered in expansion with increasing size of the Ml cation The increasing size of the Ml octahedral chain is compensated by changing the kinking of the tetrahedral chain and by alterations of bond and edge lengths as well as the bond angles within the tetrahedron Three different mechanisms of adapting of the structural building units with increasing M3+ cationic radius can be identified: (i) expansion of the tetrahedral chain by stretching (ii) transition form "0" to "s" chain conformation after full expansion and (iii) final- ly a limit of expansion in a direction We stress that ca- tions larger than In3+ cannot be substituted at the Ml site because of too large geometrical differences between octa- hedral and tetrahedral chains

A Quantum Chemistry Based Force Field for Poly(dimethylsiloxane)

Abstract: A classical force field for poly(dimethylsiloxane) (PDMS) and its oligomers has been derived on the basis of intermolecular binding energies, molecular geometries, molecular electrostatic potentials, and conformational energies obtained from quantum chemistry calculations on model compounds. The force field accurately reproduces the molecular properties of the model compounds obtained from quantum chemistry, including the Si−O−Si bond linearization energy. Molecular dynamics simulations performed on PDMS of various molecular weights between 310 and 1571 using the quantum chemistry based force field yielded good agreement with experiment for their densities, enthalpies of vaporization, and X-ray structure factors. The characteristic ratio of PDMS was also found to be in good agreement with experimental values. Molecular dynamics as represented by the melt self-diffusion coefficient and viscosity at 298 K as a function of molecular weight were also found to be in reasonable agreement with experimental value...

Superionic behavior of lithium oxide Li 2 O : A lattice dynamics and molecular dynamics study

Abstract: We report a cumulative study of lithium oxide in its normal as well as superionic phase using both lattice dynamical and molecular dynamical calculations. Molecular dynamics simulations have been carried out to study the fast ion phase and the diffusion behavior of lithium and oxygen ions. The results obtained for the diffusion constant and the thermal amplitude of lithium are in very good agreement with experimental observations. The pair correlation functions, $\mathrm{Li}\mathrm{O}\mathrm{Li}$ bond angle distribution and snapshots of the positions of lithium atoms over a range of time steps, provide a microscopic picture of the local structure indicating that as in other fluorites, the lithium ions diffuse via an interstitial mechanism but the distortions due to this movement are small. Lattice dynamical calculations have been done using a shell model in the quasiharmonic approximation. We have calculated the equilibrium structure, phonon frequencies, the elastic constants and the specific heat, which are in excellent agreement with the available experimental data. We also predict the pressure variation of the phonon dispersion and the equation of state.

Structural and electronic evolution of the As(OH)3 molecule in high temperature aqueous solutions: an x-ray absorption investigation.

Abstract: The geometrical and electronic structure of the arsenious acid molecule As(OH)3 in aqueous solutions has been investigated by x-ray absorption spectroscopy (XAS) within extended x-ray absorption spectroscopy (EXAFS) and x-ray absorption near edge structure (XANES), using realistic first-principle calculations in the latter case. This investigation was performed on aqueous solutions of arsenious acid from ambient to supercritical conditions (P=250 and 600 bars, T⩽500 °C) using a new optical cell. The analysis of the XAS spectra is consistent with (1) a constant As-O distance, (2) an opening of the O-As-O angles within the C3V pyramidal structure in the range 30–200 °C. This structural evolution comes along with a small decrease of the partial charges of the atoms in the As(OH)3 molecule. The explanation invoked for both structural and electronic modifications observed is the weakening of the interactions, through hydrogen bonds, between the As(OH)3 complex and water molecules. This is a fingerprint of the ...

Theoretical Investigation of the 3,4-Ethylenedioxythiophene Dimer and Unsubstituted Heterocyclic Derivatives

Abstract: The molecular geometry, torsional potential, and selected electronic properties (ionization potential and band gap) of the 3,4-ethylenedioxythiophene dimer in both neutral and doped (radical cation) states were investigated using quantum mechanical methods. Calculations were performed using the HF, B3LYP, B3PW91, MPW1PW91, and MP2 methods and the 6-31G(d), 6-31+G(d,p), and 6-311++G(d,p) basis sets. In all cases, calculations on the neutral and radical states were carried out considering the restricted and unrestricted formalisms, respectively. Results have been compared with experimental data when available. Furthermore, five derivatives of the 3,4-ethylenedioxythiophene dimer were built by changing the heteroatoms at both the five- and six-membered rings. Their conformational and electronic properties were studied using B3PW91/6-31+G(d,p) calculations. Results indicated that the material generated by interchanging the positions of the oxygen and sulfur atoms with respect to the parent compound presents v...

Crystal structures of dicarboxy-2,2′-bipyridyl complexes: The role of hydrogen bonding and stacking interactions

Abstract: The crystal structures of three complexes of dicarboxy-2,2′-bipyridyl ligands, 5,5′-dicarboxy-2,2′-bipyridyl (1) and 4,4′-dicarboxy-2,2′-bipyridyl (2) are reported. [Rh(1H)3] shows two interpenetrating, homochiral rhombohedral networks linked by short carboxylate–carboxylic acid hydrogen bonds, in which each complex acts as a node for six hydrogen bonds. [Ru(1H2)(1H)2] forms only four such hydrogen bonds, leading to the formation of heterochiral chains held together by stacking between bipyridyls. [Co(2H)3] can in principle form six hydrogen bonds, but in practice forms only four in a layer structure where stacking interactions are important. This is attributed to differences in molecular shape.

Ab initio structure determination of the hygroscopic anhydrous form of α-lactose by powder X-ray diffraction

Abstract: Annealing of α-lactose monohydrate at 408 K yielded a mixture of this compound with hygroscopic anhydrous α-lactose. A powder X-ray diffraction pattern of this mixture was recorded at room temperature. The starting structural model of hygroscopic α-lactose was found by a Monte Carlo simulated-annealing method. The final structure was obtained through Rietveld refinements, with soft restraints on inter­atomic bond lengths and bond angles, and crystalline energy minimization to locate the H atoms of the hydroxy groups. The crystalline cohesion is achieved by networks of O—H⋯O hydrogen bonds that differ from those of the monohydrate phase. The width of the Bragg peaks is interpreted by a phenomenological microstructural approach in terms of isotropic size effects and anisotropic strain effects.

Multicenter bonding in organic chemistry. Geometry-sensitive 3c-2e bonding in (C...H...C) fragments of organic cations.

Abstract: This paper reports the application of a new general tool for the study of multicenter bonding, namely the so-called generalized population analysis, to the investigation of interesting geometry dependent variation of 3c-2e bonding in the (C...H...C) fragments of ingeniously designed organic cations I and II. This phenomenon was previously characterized by the correlation between experimental (1)H NMR chemical shifts of the central hydrogen in the (C...H...C) fragment and the changes in the corresponding C-H-C bond angle. The observed values of both chemical shifts and C-H-C angles are shown herein to correlate with the calculated 3-center bond indices but the dependence displays splitting into two separate lines according to the type of corresponding cation.

Linear carbon dioxide in the high-pressure high-temperature crystalline phase IV.

Abstract: High-temperature IR absorption spectra of solid CO2 in phases II and IV were measured in a resistive heated diamond anvil cell up to 30 GPa. The spectral structures of the bending mode, observed in high quality thin crystalline samples, and of the IR lattice phonons, measured for the first time between 80 and 640 K, are discussed using group theory arguments. According to this analysis the claimed bent molecular geometry of CO2 in phase IV can be unambiguously ruled out. Furthermore, the structures of both phases II and IV have been identified, among those so far proposed, as orthorhombic.

The gas-phase hydrogen bond complexes between formic acid with hydroxyl radical: a theoretical study.

Abstract: We report a theoretical study on seven radical hydrogen bond complexes between syn-HCOOH and OH and eight radical hydrogen bond complexes between anti-HCOOH and OH, that have been carried out by using the B3 LYP, MP2, QCISD, and CCSD(T) theoretical approaches with the 6-311 G(2df,2p) basis set. In all cases, the bonding features were analysed using the atoms in molecules (AIM) theory by Bader and the natural bond orbital (NBO) partition scheme by Weinhold et al. We have found twelve complexes having a single hydrogen bond and three complexes presenting a cyclic structure with multiple bonds, pointing out the existence of a cooperative effect. One of them presents a bound O ¥¥¥ O interaction producing a stabilisation effect. The stability of these complexes has been calculated to be in the 0.81 and 5.96 kcal mol 1 range and their possible implication in the HCOOH plus OH reaction is also discussed. Finally, we also report the computed harmonic vibrational frequencies of the two OH stretching modes and the HOC outof-plane wagging mode, along with the frequency red-shifts originated by the complex formation and the corresponding computed intensity ratio relative to the monomers.