Structures and bonding nature of small monoligated copper clusters (HCN-Cun, n = 1-3) through high-resolution infrared spectroscopy and theory

The structures, C-H stretching frequencies, and dipole moments of HCN-Cun (n = 1-3) clusters are determined through high-resolution infrared spectroscopy. The complexes are formed and probed within superfluid helium droplets, whereby the helium droplet beam is passed over a resistively heated crucible containing copper shot and then through a gas HCN pickup cell. All complexes are found to be bound to the nitrogen end of the HCN molecule and on the "atop site" of the copper cluster. Through the experimental C-H vibrational shifts of HCN-Cun and ab initio calculations, it was found that the HCN-metal interaction changes from a strong van der Waals bond in n = 1 to a partially covalent bond in HCN-Cu3. Comparisons with existing infrared data on copper surfaces show that the HCN-Cun bond must begin to weaken at very large copper cluster sizes, eventually returning to a van der Waals bond in the bulk copper surface case.     

Structures of HCN-Mgn (n=2-6) complexes from rotationally resolved vibrational spectroscopy and ab initio theory

High-resolution infrared laser spectroscopy has been used to determine the structures of HCN-Mgn complexes formed in helium nanodroplets. The magnesium atoms are first added to the droplets to ensure that the magnesium complexes are preformed before the HCN molecule is added. The vibrational frequencies, structures, and dipole moments of these complexes are found to vary dramatically with cluster size, illustrating the nonadditive nature of the HCN-magnesium interactions. All of the complexes discussed here have the nitrogen end of the HCN pointing towards the magnesium clusters. For Mg3, the HCN binds to the "threefold" site, yielding a symmetric top spectrum. Although the HCN-Mg4 complex also has C3v symmetry, the HCN sits "on-top" of a single magnesium atom. These structures are confirmed by both ab initio calculations and measurements of the dipole moments. Significant charge transfer is observed in the case of HCN-Mg4, indicative of charge donation from the lone pair on the nitrogen of HCN into the lowest unoccupied molecular orbital of the Mg4.     

Ab initio study of ternary radical–molecule complexes between HCN(HNC) and HO(HS) species

MP2 calculations with the cc-pVTZ basis set were used to analyze the intermolecular interactions in ternary radical–molecule complexes between HCN(HNC) and HO(HS) species, in gas phase and in water media. Particular attention was given to parameters such as the cooperative energies and many-body interaction energies. The results indicate that hydrogen bonding between two HCN(HNC) molecules gives more stability to triads than hydrogen bonding between HCN(HNC) and OH(SH) species. The electronic properties of the complexes were analyzed using the parameters derived from the atoms in molecules methodology. The water media has an enhancing influence on the stabilities of studied clusters versus the ones obtained in gas phase.     

Infrared spectroscopy of HCN-salt complexes formed in liquid-helium nanodroplets

Rotationally resolved infrared spectra are reported for the binary complexes of HCN and LiF, LiCl, NaF, and NaCl, formed in helium nanodroplets. Stark spectroscopy is used to determine the dipole moments for these complexes. Ab initio calculations are also reported for these complexes, revealing the existence of several different isomers of these binary systems. In the frequency region examined in this experimental study we only observe one of these, corresponding to the salt binding to the nitrogen end of the HCN molecule. The experimental rotational constants, dipole moments, and vibrational frequency shifts are all compared with the results from ab initio calculations for this isomer.     

Ab initio studies on hydrogen-bonded clusters. I. Linear and cyclic oligomers of hydrogen cyanide

Large-scale ab initio calculations have been performed on linear and cyclic oligomers of hydrogen cyanide molecules applying basis sets ranging from double-zeta to near-Hartree-Fock quality. Equilibrium geometries of linear (HCN)_n clusters with n = 1 to 5 and of cyclic clusters with n = 3, 4 are reported. For most of the complexes complete vibrational analysis has been carried out. In agreement with recent experimental data the linear HCN trimer was found to be more stable than the cyclic trimer. In case of the tetramer linear and cyclic structures are of comparable stability. The structural changes taking place upon polymerization of linear HCN clusters and the convergence of various stage properties to those of the infinite polymer (HCN)_∞ are discussed in detail. The evolution from vibrational spectra of small oligomers to phonon dispersion curves of the infinite polymer is illustrated too.     

Raman studies of solid hydrogen cyanide (HCN,DCN) and of HCN argon matrices

Raman spectra of single crystal-like oriented solid HCN and DCN, as well as of HCN molecules and clusters in argon matrices, have been recorded and analysed with respect to both so far uninterpreted spectral features reported in the literature and to the applicability of Raman experiments for studying molecular clusters in inert gas matrices. The main results obtained are: (i) splitting of both the intramolecular bending modes and librations of solid HCN has to be interpreted in terms of TO/LO splitting rather than site group splitting; (ii) the nature of the phase transition at 170 K reported as tI6 to oI6 must be doubted; and (iii) the previous results of HCN(DCN)/Ar matrices obtained by IR studies are confirmed.     

A computational study of 1:1 and 1:2 complexes of nitryl halides (O2NX) with HCN and HNC

Quantum calculations at the MP2/cc-pVTZ have been used to examine 1:1 and 1:2 complexes between O₂NX (X = Cl, Br) with HCN and HNC moieties. The interaction of the lone pair of the HCN(HNC) with the σ-hole and π-hole of O₂NX molecules and hydrogen bonding between lone pairs of X and O of O₂NX with H of HCN and HNC have been considered in 1:1 complexes. The 1:1 complexes can easily be differentiated using the stretching frequency of the N–X bond. Thus, those complexes with σ-hole and H···O₂NX interactions show a blue shift of the N-X bond stretching while a red shift is observed in the complexes along the π-hole and H···XNO₂ interactions. In the 1:2 complexes, the cooperative and diminutive energetic effects have been analyzed using the many-body interaction energies. The nature of the interactions has been characterized with the Atoms in Molecules (AIM) and Natural Bond Orbital (NBO) methodologies. Stabilization energies of 1:1 and 1:2 complexes including the variation of the zero-point vibrational energy (ΔZPVE) are in the range 3–9 kJ mol^?1 and 21–40 kJ mol^?1, respectively.     

The isomers of HF-HCN formed in helium nanodroplets: Infrared spectroscopy and ab initio calculations

Binary complexes containing hydrogen cyanide and hydrogen fluoride are formed in helium nanodroplets, and studied using high-resolution infrared laser spectroscopy. Rotationally resolved spectra are reported for the H-F and C-H stretches of the linear HCN-HF complex, a system that has been thoroughly studied in the gas phase. We report the high-resolution spectra of the higher energy, bent HF-HCN isomer, which is also formed in helium. Stark spectra are reported for both isomers, providing dipole moments of these complexes. The experimental results are compared with ab initio calculations, also reported here. Spectra are reported for several ternary complexes, including (HCN)2-HF, HCN-(HF)2, HF-(HCN)2, and HF-HCN-HF.     

Theoretical study of hydrogen bonded clusters of water and fulminic acid

Ab initio and density functional calculations are used to analyze the interaction between a molecule of fulminic acid with 1, 2, 3, and 4 molecules of water along with a 2:2 complex at B3LYP/6-31+G(d,p) and MP2/6-311++G(d,p) computational levels. Cooperative effect (CE) in terms of stabilization energy of clusters are calculated and discussed as well. CE is increased with increasing cluster size of studied clusters. Red shifts of H–C stretching frequency for complexes involving HCNO as H-donor are predicted.     

Theoretical study of aromaticity in inorganic tetramer clusters

Ground state geometry and electronic structure of M ₄ ^2- cluster (M = B, Al, Ga) have been investigated to evaluate their aromatic properties. The calculations are performed by employing the Density Functional Theory (DFT) method. It is found that all these three clusters adopt square planar configuration. Results reveal that square planar M ₄ ^2- dianion exhibits characteristics of multifold aromaticity with two delocalised π-electrons. In spite of the unstable nature of these dianionic clusters in the gas phase, their interaction with the sodium atoms forms very stable dipyramidal M₄Na₂ complexes while maintaining their square planar structure and aromaticity.     

High-resolution infrared spectroscopy of HCN-Znn (n = 1-4) clusters: structure determination and comparisons with theory

High-resolution infrared laser spectroscopy has been used to obtain rotationally resolved spectra of HCN-Zn(n) (n = 1-4) complexes formed in helium nanodroplets. In the present study the droplets passed through a metal oven, where the zinc vapor pressure was adjusted until one or more atoms were captured by the droplets. A second pickup cell was then used to dope the droplets with a single HCN molecule. Rotationally resolved infrared spectra are obtained for all of these complexes, providing valuable information concerning their structures. Stark spectra are reported and used to determine the corresponding permanent electric dipole moments. Ab initio calculations are also reported for these complexes for comparison with the experimental results.     

Ab initio quantum chemical studies of the electronic properties of the hydrogen bonded N2HF,N2HCl, (HCN)2 and NH3HCN complexes

The results of ab initio self-consistent field (SCF) and configuration interaction (CI) calculations on the hydrogen bonded N₂HF, N₂HCl, (HCN)₂ and NH₃HCN complexes, using basis sets that range from double-zeta plus polarization to triple-zeta plus double polarization, are reported. The primary objective of this work has been to calculate the changes in the dipole moments and the electric field gradients (EFGs) at the quadrupolar ¹⁴N, ²H and ³⁵Cl nuclei that are induced by H-bonding. Since the interpretation of the H-bond induced shifts requires a knowledge of the molecular dynamics in weakly H-bonded molecular complexes such as those studied in the present work, we have taken into account the effects of vibrational averaging on both the EFGs and dipole moments utilizing harmonic intermolecular force fields that were generated using ab initio SCF methods. The results of these calculations are compared with the corresponding experimental quantities that are obtained from the microwave spectra of these complexes.     

Theoretical investigation of the large nonlinear optical properties of (HCN)n clusters with Li atom

Two new classes of (HCN)(n)...Li and Li...(HCN)(n) (n = 1, 2, 3) clusters with the electride characteristic are formed in theory by the metal Li atom attaching to the (HCN)(n) (n = 1, 2, 3) clusters. Because of the interaction between the Li atom and the (HCN)(n) part, the 2s valence electron of the Li atom becomes a loosely bound excess electron. Our high-level ab initio calculations show that these new clusters with the excess electron have large first hyperpolarizabilities, for example, beta(0) = -15,258 au for (HCN)...Li and beta(0) = -3401 au for Li...(HCN) at the QCISD/6-311++G(3df,3pd) level (only beta(0) = -2.8 au for HCN monomer(26)). Obviously, the excess electron from the Li atom plays a crucial role in the large first hyperpolarizabilities of these clusters. The beta(0) value of (HCN)(n)...Li (beta(0) > 10(4) au, from sigma --> pi* transition) is larger than that of Li...(HCN)(n) (beta(0) > 10(3) au, from sigma --> sigma* transition) for n = 1, 2, or 3. In addition, two interesting rules have been observed. They are that |beta(0)| decreases with lengthening of the HCN chain for (HCN)(n)...Li clusters and that |beta(0)| increases as n increases for Li...(HCN)(n) clusters. In this paper, we discuss two classes of clusters that are highly similar to the electride structure model, of which the structural characteristics are that alkali metal atoms ionize to form cations and trapped electrons under the action of other polar molecules. Thus, the investigation on the large first hyperpolarizabilities of (HCN)(n)...Li and Li...(HCN)(n) (n = 1, 2, 3) may prompt one to study the unusual nonlinear optical responses of some electrides.     

Homonuclear chalcogen–chalcogen bond interactions in complexes pairing YO3 and YHX molecules (Y = S,Se; X = H,Cl, Br,CCH, NC,OH, OCH3): Influence of substitution and cooperativity

MP2/aug‐cc‐pVTZ calculations are performed on complexes of YO₃ (Y = S, Se) with a series of electron‐donating chalcogen bases YHX (X = H, Cl, Br, CCH, NC, OH, OCH₃). These complexes are formed through the interaction of a positive electrostatic potential region (π‐hole) on the YO₃ molecule with the negative region in YHX. Interaction energies of the binary O₃Y???YHX complexes are in the range of ?4.37 to ?12.09 kcal/mol. The quantum theory of atoms in molecules and the natural bond orbital analysis were applied to characterize the nature of interactions. It was found that the formation and stability of these binary complexes are ruled mainly by electrostatic effects, although the electron charge transfer from YHX to YO₃ unit also seems to play an important role. In addition, mutual influence between the Y???N and Y???Y interactions is studied in the ternary HCN???O₃Y???YHX complexes. The results indicate that the formation of a Y???N interaction tends to weaken Y???Y bond in the ternary systems. Although the Y???Y interaction is weaker than the Y???N one, however, both types of interactions seem to compete with each other in the HCN???O₃Y???YHX complexes. © 2016 Wiley Periodicals, Inc.     

HCN(HNC)与NH3, H2O和HF分子间相互作用的理论研究

在MP2/aug-cc-pVTZ水平上, 对HCN(HNC)与NH3, H2O和HF分子间可能存在的氢键型复合物进行了全自由度能量梯度优化, 通过在相同水平上的频率验证分析发现了稳定的分子间相互作用形式是HCN(HNC)作为质子供体或作为质子受体形成的复合物. 基组重叠误差对总相互作用能的影响均小于3.34 kJ/mol. 通过自然键轨道(NBO)分析, 研究了单体和复合物中的原子电荷和电荷转移对分子间相互作用的影响. 对称性匹配微扰理论(SAPT, Symmetry Adapted Perturbation Theory)能量分解结果表明, 在分子间相互作用中, 静电作用与诱导作用占主导地位, 而诱导作用与复合物的电荷转移之间具有良好的正相关性.     

Hydrogen-bonded clusters of hydroperoxyl radical with ammonia: a theoretical study

Ab initio calculations at MP2/6-311++G(d,p) computational level were used to analyze the interaction between a molecule of the hydroperoxyl radical with 1 up to 4 molecules of ammonia. Three minima were found for 1:2 and 1:4 complexes of HOO and NH₃. Two complexes were located as minima on the potential energy surface of 1:3 complexes. Red shifts of the OH stretching frequency upon complex formation in the range between 560 and 1,116 cm⁻¹ are predicted. Cooperative effect in terms of stabilization energy is calculated for the studied clusters. The cooperative effect is increased with the increasing size of studied clusters. The Quantum Theory Atoms in Molecules (QTAIM) theory was also applied to explain the nature of the complexes.     

Glucose interaction with Au,Ag, and Cu clusters: Theoretical investigation

Interactions of α‐D ‐glucose with gold, silver, and copper metal clusters are studied theoretically at the density functional theory (CAM‐B3LYP) and MP2 levels of theory, using trimer clusters as simple catalytic models for metal particles as well as investigating the effect of cluster charge by studying the interactions of cationic and anionic gold clusters with glucose. The bonding between α‐D ‐glucose and metal clusters occurs by two major bonding factors; the anchoring of M atoms (M = Cu, Ag, and Au) to the O atoms, and the unconventional M…H? O hydrogen bond. Depending on the charge of metal clusters, each of these bonds contributes significantly to the complexation. Binding energy calculations indicate that the silver cluster has the lowest and gold cluster has the highest affinity to interact with glucose. Natural bond orbital analysis is performed to calculate natural population analysis and charge transfers in the complexes. Quantum theory of atoms in molecules was also applied to interpret the nature of bonds. © 2012 Wiley Periodicals, Inc.     

Unusual hydrogen bonding behavior in binary complexes of coinage metal anions with water

We have studied the interaction of atomic coinage metal anions with water molecules by infrared photodissociation spectroscopy of M-.H2O.Ar(n) clusters (M=Cu, Ag, Au; n=1, 2). We compare our observations with calculations on density-functional and coupled cluster levels of theory. The gold anion is bound to the water molecule by a single ionic hydrogen bond, similar to the halide-water complexes. In contrast, zero-point motion in the silver and copper complexes leads to a deviation from this motif.     

Catalytic activation of nitrobenzene on PVP passivated silver cluster: A DFT investigation

Poly(N‐vinyl‐2‐pyrrolidone) (PVP) has been used extensively to stabilize the surface of noble metal nanoparticles against aggregation and also to produce anisotropic nanostructures. Naturally, it is very important to understand the effect of such surface stabilization by PVP on the catalytic activity of these nanoparticles. This communication investigates through DFT calculations the electronic properties of PVP stabilized 13‐atom Ag cluster for catalytic activation of nitrobenzene (NB). These computations suggest that poly(N‐vinyl‐2‐pyrrolidone) (PVP) interact with silver (Ag) cluster mainly through oxygen atom and acts not only as a stabilizer to prevent the aggregation of Ag clusters but also as an electron donor to activate the Ag clusters for further reaction. Natural Bonding Orbital (NBO) calculations show that catalytic activation of NB by PVP passivated Ag cluster occurs due to interaction of the oxygen of the nitro group with the Ag cluster. Weak back donation of electrons from M(dπ) orbital of Ag to antibonding σ* of one of the N O bond, facilitates the formation of the nitroso intermediate. To understand the extent and the nature of this interaction better, vibrational frequency calculation of nitrobenzene association with Ag13‐2PVP cluster is carried out. Red shift in the frequencies is consequence of strong interaction with that of silver cluster present in Ag13‐2PVP‐NB model.