Structures of [(CO2)n(CH3OH)m](-) (n = 1-4, m = 1, 2) cluster anions

The infrared photodissociation spectra of [(CO 2) n (CH 3OH) m ] (-) ( n = 1-4, m = 1, 2) are measured in the 2700-3700 cm (-1) range. The observed spectra consist of an intense broad band characteristic of hydrogen-bonded OH stretching vibrations at approximately 3300 cm (-1) and congested vibrational bands around 2900 cm (-1). No photofragment signal is observed for [(CO 2) 1,2(CH 3OH) 1] (-) in the spectral range studied. Ab initio calculations are performed at the MP2/6-311++G** level to obtain structural information such as optimized structures, stabilization energies, and vibrational frequencies of [(CO 2) n (CH 3OH) m ] (-). Comparison between the experimental and the theoretical results reveals the structural properties of [(CO 2) n (CH 3OH) m ] (-): (1) the incorporated CH 3OH interacts directly with either CO 2 (-) or C 2O 4 (-) core by forming an O-HO linkage; (2) the introduction of CH 3OH promotes charge localization in the clusters via the hydrogen-bond formation, resulting in the predominance of CO 2 (-).(CH 3OH) m (CO 2) n-1 isomeric forms over C 2O 4 (-).(CH 3OH) m (CO 2) n-2 ; (3) the hydroxyl group of CH 3OH provides an additional solvation cite for neutral CO 2 molecules.     

Structure and stability of (TiO2)n, (SiO2)n, and mixed Ti(m)Si(n-m)O(2n) [n = 2-5, m = 1 to (n - 1)] clusters

Structures, energetics, and vibrational spectra are investigated for small pure (TiO(2))(n), (SiO(2))(n), and mixed Ti(m)Si(n-m)O(2n) [n = 2-5, m = 1 to (n - 1)] oxide clusters by density functional theory (DFT). The BP86/ATZP level of theory is employed to obtain constitutional isomers of the oxide clusters. In accordance with previous studies, our calculations show three-dimensional compact structures are preferred for pure (TiO(2))(n) with oxo-stabilized higher hexavalent states, and linear chain structures are favored for pure (SiO(2))(n) with tetravalent states. However, the herein theoretically first reported mixed Ti(m)Si(n-m)O(2n) oxide clusters prefer either three-dimensional compact or linear chain structures depending upon the stoichiometry of the compound. Vibrational analysis of the important modes of some highly stable structures is provided. Coupled-cluster single and double excitation (with triples) [CCSD(T)] computed energy gaps for the TiO(2) dimers compare well with results from previous study. Excitation energies are computed by use of time-dependent (TD) DFT and equation-of-motion coupled-cluster calculations with singles and doubles (EOM-CCSD) for the most stable isomers.     

Flat-structural Motives in Small Alumino-Carbon Clusters C(n)Al(m) (n = 2-3, m = 2-8)

Small clusters consisting of a carbon diatom or triatom and several aluminum atoms are investigated ab initio, at an MP2 level of theory. The mainly ionic character of C-Al bonding predominantly leads to structures different from corresponding hydrocarbons (also if starting from analogous initial geometries), while still producing closed-shell ground states. It is found that in many cases stable geometries correspond to flat CAl(3) units. These include unique metal-framed dicarbon and tricarbon all-flat species with unusual planar tetra-coordination. Another frequent feature is a hyper-coordination of carbon atoms, supported by their high negative charges and critically examined via atom-in-molecule calculations. Also characterized are anionic states, electronic excitation and ionization, electron attachment and detachment, and charge distributions.     

Structures and stabilities of small lead oxide clusters PbmOn (m=1-4,n=1-2m)

The structures and stabilities of small lead oxide clusters PbmOn with m=1-4, n=1-2m are systematically studied using density functional theory. It is found that the lowest-energy structures of all these clusters can be obtained by the sequential oxidation of small "core" lead clusters. For Pb-rich clusters (oxygen-to-lead ratio<1), oxygen atoms favor bridge sites for Pb2On and Pb3On and surface sites for Pb4On. The lead-monoxide-like clusters (PbO)i (i=1-4) have great stability because of their significant dissociation energies and highest occupied molecular orbital-lowest unoccupied molecular orbital gaps. This suggests that they could be adopted as the building blocks of cluster-assembled materials. For O-rich clusters (oxygen-to-lead ratio>1), the grouping of oxygen atoms usually appears. It is found that the structures with a grouping of more than two oxygen atoms are unstable.     

Structure and bonding in cyclic isomers of B2AlH(n)(m) (n = 3-6, m = -2 to +1): a comparative study with B3H(n)(m), BAl2H(n)(m) and Al3H(n)(m)

The structure, bonding and energetics of B(2)AlH(n)(m) (n = 3-6, m = -2 to +1) are compared with corresponding homocyclic boron, aluminum analogues and BAl(2)H(n)(m) using density functional theory (DFT). Divalent to hexacoordinated boron and aluminum atoms are found in these species. The geometrical and bonding pattern in B(2)AlH(4)(-) is similar to that for B(2)SiH(4). Species with lone pairs on the divalent boron and aluminum atoms are found to be minima on the potential energy surface of B(2)AlH(3)(2-). A dramatic structural diversity is observed in going from B(3)H(n)(m) to B(2)AlH(n)(m), BAl(2)H(n)(m) and Al(3)H(n)(m) and this is attributable to the preference of lower coordination on aluminum, higher coordination on boron and the higher multicenter bonding capability of boron. The most stable structures of B(3)H(6)(+), B(2)AlH(5) and BAl(2)H(4)(-) and the trihydrogen bridged structure of Al(3)H(3)(2-) show an isostructural relationship, indicating the isolobal analogy between trivalent boron and divalent aluminum anion.     

Synthesis and characterization of novel monocarbollide exo-closo-(pi-arene)biruthenacarboranes [(PPh3)mClRu(eta6-C6H5R)Ru'CB10H11-n(OMe)n] (where R = H, m = 2, n = 1; R = mu-PPh2, m = 1, n = 0, 1)

The monocarbon carborane [Cs][nido-7-CB(10)H(13)] reacts with the 16-electron [RuCl(2)(PPh(3))(3)] in a solution of benzene/methanol in the presence of N,N,N',N'-tetramethylnaphthalene-1,8-diamine as the base to give a series of 12-vertex monocarbon arene-biruthenacarborane complexes of two types: [closo-2-[7,11-exo-RuClPPh(3)(mu,eta(6)-C(6)H(5)PPh(2))]-7,11-(mu-H)(2)-2,1-RuCB(10)H(8)R] (5, R = H; 6, R = 6-MeO; 7, R = 3-MeO) and [closo-2-(eta(6)-C(6)H(6))-10,11,12-[exo-RuCl(PPh(3))(2)]-10,11,12-(mu-H)(3)-2,1-RuCB(10)H(7)R(1)] (8a, R(1) = 6-MeO; 8b, R(1) = 3-MeO, inseparable mixture of isomers) along with trace amounts of 10-vertex mononuclear hypercloso/isocloso-type complexes [2,2-(PPh(3))(2)-2-H-3,9-(MeO)(2)-2,1-RuCB(8)H(7)] (9) and [2,5-(Ph(3)P)-2-Cl-2-H-3,9-(MeO)(2)-2,1-RuCB(8)H(6)] (10). Binuclear ruthenacarborane clusters of both series were characterized by a combination of analytical and multinuclear NMR spectroscopic data and by single-crystal X-ray diffraction studies of three selected complexes, 6-8. In solution, isomers 8a,b have been shown to undergo the isomerization process through the scrambling of the exo-[RuCl(PPh(3))(2)] fragment about two adjacent triangular cage boron faces B(7)B(11)B(12) and B(8)B(9)B(12).     

Ab Initio Study of the (DMF) m · (HCl) n (m,n = 0–2) Complexes

Based on the results of ab initio calculations (B3LYP, 6-31++G(d,p)), the structures and stability of the complexes DMFA · HCl, (DMF)₂ · HCl, DFF · (HCl)₂, and (DMF · HCl)₂ are compared. In the complex with a 1 : 1 composition, DMF and HCl form a hydrogen bond of the molecular type. In the heterotrimers with compositions 1 : 2 and 2 : 1, the hydrogen bond noticeably strengthens. In the tetramer (DMF · HCl)₂, the most pronounced proton transfer takes place and two quasi-symmetric hydrogen bridges O···H···Cl are formed and stabilize this complex. The results of calculations are compared with data on the structure of complexes between HCl and DMF obtained by crystal-structure XRD and vibrational spectroscopy in solutions.     

(MN)nHm(M=Ga,In; n=1-4; m=1, 2)团簇的结构与稳定性

采用密度泛函理论(DFT)的B3LYP方法, 在6-31G**和Lanl2dz水平上分别对(MN)nHm(M=Ga, In; n=1-4; m=1, 2)进行了优化和振动频率计算. 得到了上述团簇的最稳定构型、H原子的结合能以及它们的能隙. 结果表明, (MN)nH(M=Ga, In; n=1-4)的基态构型均为双重态, (MN)nH2(M=Ga, In; n=1-4)的基态构型均为单重态; 当氢的个数为1时, 加在N原子上比加在M(M=Ga, In)原子上稳定, 如有N3单元, 那么加在N3单元两侧的构型是相同的, 且它是最稳定的; 当氢的个数为2时, 除n=1外, 分别加在两个N原子上的构型是最稳定的, 如有N3单元, 那么分别加在N3单元分离最远的两个N原子的构型是最稳定的. GaNH、(GaN)3H 和InNH的结合能和能隙都很大, 说明这些团簇都有很高的稳定性.     

Structures of [(CO2)n(H2O)m]- (n=1-4, m=1,2) cluster anions. I. Infrared photodissociation spectroscopy

The infrared photodissociation spectra of [(CO(2))(n)(H(2)O)(m)](-) (n=1-4, m=1, 2) are measured in the 3000-3800 cm(-1) range. The [(CO(2))(n)(H(2)O)(1)](-) spectra are characterized by a sharp band around 3570 cm(-1) except for n=1; [(CO(2))(1)(H(2)O)(1)](-) does not photodissociate in the spectral range studied. The [(CO(2))(n)(H(2)O)(2)](-) (n=1, 2) species have similar spectral features with a broadband at approximately 3340 cm(-1). A drastic change in the spectral features is observed for [(CO(2))(3)(H(2)O)(2)](-), where sharp bands appear at 3224, 3321, 3364, 3438, and 3572 cm(-1). Ab initio calculations are performed at the MP2/6-311++G(**) level to provide structural information such as optimized structures, stabilization energies, and vibrational frequencies of the [(CO(2))(n)(H(2)O)(m)](-) species. Comparison between the experimental and theoretical results reveals rather size- and composition-specific hydration manner in [(CO(2))(n)(H(2)O)(m)](-): (1) the incorporated H(2)O is bonded to either CO(2) (-) or C(2)O(4) (-) through two equivalent OH...O hydrogen bonds to form a ring structure in [(CO(2))(n)(H(2)O)(1)](-); (2) two H(2)O molecules are independently bound to the O atoms of CO(2) (-) in [(CO(2))(n)(H(2)O)(2)](-) (n=1, 2); (3) a cyclic structure composed of CO(2) (-) and two H(2)O molecules is formed in [(CO(2))(3)(H(2)O)(2)](-).     

The structures and electronic states of zinc-water clusters Zn(n)(H2O)(m) (n = 1-32 and m = 1-3)

Ab initio and Density Functional Theory (DFT) calculations have been carried out for zinc-water clusters Zn(n)-(H2O)(m) (n = 1-32 and m = 1-3, where n and m are the numbers of zinc atoms and water molecules, respectively) to elucidate the structure and electronic states of the clusters and the interaction of zinc cluster with water molecules. The binding energies of H2O to zinc clusters were small at n = 2-3 (2.3-4.2 kcal mol(-1)), whereas the energy increased significantly in n = 4 (9.0 kcal mol(-1)). Also, the binding nature of H2O was changed at n = 4. The cluster size dependency of the binding energy of H2O accorded well with that of the natural population of electrons in the 4p orbital of the zinc atom. In the larger clusters (n > 20), it was found that the zinc atoms in surface regions of the zinc cluster have a positive charge, whereas those in the interior region have a negative charge with the large electron population in the 4p orbital. The interaction of H2O with the zinc clusters were discussed on the basis of the theoretical results.     

Theoretical studies on structures of neptunyl carbonates: NpO2(CO3)m(H2O)n(q-) (m = 1-3, n = 0-3) in aqueous solution

Extensive ab inito computations have been carried out to study the equilibrium structure, infrared spectra, and bonding characteristics of a variety of hydrated NpO2(CO3)m(q-) complexes by considering the solvent as a polarizable dielectric continuum as well as the corresponding anhydrate complexes in the gas phase. The computed structural parameters and vibrational results at the MP2 level in aqueous solution are in good agreement with Clark et al.'s experiments and provide realistic pictures of the neptunyl complexes in an aqueous environment. Our computed hydration energies reveal that the complex with water molecules directly bound to it yields the best results. Our analysis of the nature of the bonding of neptunyl complexes provides insight into the nature of 6d and 5f bonding in actinide complexes.     

Geometry and stability of BenCm (n=1-10; m=1, 2, ..., to 11-n) clusters

Density functional theory B3PW91/6-31+G* calculations on BenCm (n=1-10; m=1, 2, ..., to 11-n) clusters have been carried out to examine the effect of cluster size, relative composition, binding energy per atom, HOMO-LUMO gap, vertical ionization potential, and electron affinity on their relative stabilities. The most stable planar cyclic conformations of these clusters always show at least a set of two carbon atoms between two beryllium atoms, while structures where beryllium atoms cluster together, or allow the intercalation of one carbon atom between two of them, generally seem to be the least stable ones. Clusters containing 1, 2, and 3 beryllium atoms (Be2C8, Be3C6, Be2C6, BeC6, Be2C4, BeC4, Be2C2, and BeC2) are identified as clusters of "magic numbers" in terms of their high binding energy per atom, high HOMO-LUMO gap, vertical ionization potential, and second difference in energy per beryllium atom.     

IR spectroscopy on isolated Co(n)(alcohol)m cluster anions (n=1-4, m=1-3): structures and spin states

Isolated cobalt-alcohol cluster anions containing n=1-4 cobalt and m=1-3 alcohol molecules (alcohol=methanol, ethanol, propanol) are produced in a supersonic beam by using a laser ablation source. By applying IR photodissociation spectroscopy vibrational spectra in the OH stretching region are obtained. Several structures in different spin states are discussed for the (n,m) clusters. In comparison with density functional theory calculations applied to both the Co/alcohol clusters and the naked Co cluster anions, an unambiguous structural assignment is achieved. It turns out that structures are preferred with a maximum number of hydrogen bonds between the OH groups and the Co···Co units. These hydrogen bonds are typical for anionic species leading to an activation of the OH groups which is indicated by large red-shifts of the OH stretching frequencies compared to the naked alcohols. For each (n,m) cluster, the frequency shifts systematically with respect to the different alcohols, but the type of structure is identical for all alcohol ligands. The application of IR spectroscopy turns out to be an ideal tool not only as a probe for structures but also for spin states which significantly influence the predicted OH stretching frequencies.     

LaC4^n（n=—2,—1,0,＋1,＋2）分子簇的结构与稳定性

本文用密度泛函方法研究了ＬａＣ４ｎ（ｎ＝－２,－１,０,＋１,＋２）分子簇的结构与稳定性。振动频率分析表明,在所提出的九个构型中,当ｎ＝－２,０,＋１,＋２时,稀土位于碳环上最稳定,而当ｎ＝－１时,尽管稀土位于碳环上能量最低,但没有找到稳定的构型,我们的结果还指出,稀土元素是分子簇中对外部环境最敏感的部位,即最具有反应活性     

Structures and photoelectron spectroscopy of Cu(n)(BO2)m-(n, m=1, 2) clusters: observation of hyperhalogen behavior

The electronic structures of CuBO(2)(-), Cu(BO(2))(2)(-), Cu(2)(BO(2))(-), and Cu(2)(BO(2))(2)(-) clusters were investigated using photoelectron spectroscopy. The measured vertical and adiabatic detachment energies of these clusters revealed unusual properties of Cu(BO(2))(2) cluster. With an electron affinity of 5.07 eV which is larger than that of its BO(2) superhalogen (4.46 eV) building-block, Cu(BO(2))(2) can be classified as a hyperhalogen. Density functional theory based calculations were carried out to identify the ground state geometries and study the electronic structures of these clusters. Cu(BO(2)) and Cu(BO(2))(2) clusters were found to form chainlike structures in both neutral and anionic forms. Cu(2)(BO(2)) and Cu(2)(BO(2))(2) clusters, on the other hand, preferred a chainlike structure in the anionic form but a closed ringlike structure in the neutral form. Equally important, substantial differences between adiabatic detachment energies and electron affinities were found, demonstrating that correct interpretation of the experimental photoelectron spectroscopy data requires theoretical support not only in determining the ground state geometry of neutral and anionic clusters, but also in identifying their low lying isomers.     

金属串配合物(n,m)[Cr3(PhPyF)4Cl2](n=2, 3, 4; m=2, 1, 0)的配位结构及其与电场的关系

应用密度泛函理论BP86 方法研究具有分子导线潜在应用的金属串配合物(n, m)[Cr₃(PhPyF)₄Cl₂](HPhPyF=N, N'-苯基吡啶基甲脒; n=2, 3, 4; m=2, 1, 0)的配位结构及其受电场作用的影响, n、m分别表示PhPyF-的苯环在左侧和在右侧的配体个数. 结果表明: (1) 零电场下, 四个PhPyF-的(2, 2)、(3, 1)和(4, 0)三种配位方式能量差别很小, 为竞争态, (2, 2)最稳定. (4, 0)结构中两端轴向配体Cl 均可与Cr 配位, 且Cl₄―Cr1 键比Cl5―Cr3键更强, 若作为分子器件可与电极结合, 这与(4, 0)[CuCuM(npa)₄Cl][PF₆](M=Pd, Pt; Hnpa=2-萘啶苯胺)靠近苯环一端的轴向配体无法与M配位不同. (2) 在(2, 2)、(3, 1)和(4, 0)中, Cr₃⁶⁺链均具有三中心三电子离域σ键, 但离域性逐渐减弱. 随四个PhPyF-配位方式趋于一致, 分子极性逐渐增大, 由Cl₄指向Cl5(Z)方向, Cr1的α自旋密度增大, Cr2 的β和Cr3 的α自旋密度减小. (3) 分子的几何结构和电子结构在电场下发生规律性变化, 在-Z方向电场作用下, (3, 1)、(4, 0)电子移动方向与极性方向相同, 使分子的键长、自旋密度、电荷和能隙变化显著性均大于Z方向电场, 且极性越大变化越显著, 有利于提高分子导电性.     

Geometrical and electronic structures of Au(m)Ag(n) (2 < or = m + n < or = 8)

The structural and electronic properties of Au(m)Ag(n) binary clusters (2 < or = m + n < or = 8) have been investigated by density functional theory with relativistic effective core potentials. The results indicate that Au atoms tend to occupy the surface of Au(m)Ag(n) clusters (n > or = 2 and m > or = 2). As a result, segregation of small or big bimetallic clusters can be explained according to the atomic mass. The binding energies of the most stable Au(m)Ag(n) clusters increase with increasing m+n. The vertical ionization potentials of the most stable Au(m)Ag(n) clusters show odd-even oscillations with changing m+n. The possible dissociation channels of the clusters considered are also discussed.     

Association patterns in (HF)(m)(H2O)(n) (m + n = 2-8) clusters

In an attempt to understand the phase behavior of aqueous hydrogen fluoride, the clustering in the mixture is investigated at the molecular level. The study is performed at the mPW1B95/6-31+G(d,p) level of theory. Several previous studies attempted to describe the dissociation of HF in water, but in this investigation, the focus is only on the association patterns that are present in this binary mixture. A total of 214 optimized geometries of (HF)n(H2O)m clusters, with m + n as high as 8, were investigated. For each cluster combination, several different conformations are investigated, and the preferred conformations are presented. Using multiple linear regressions, the average strengths of the four possible H-bonding interactions are obtained. The strongest H-bond interaction is reported to be the H2O...H-F interaction. The most probable distributions of mixed clusters as a function of composition are also deduced. It is found that the larger (HF)n(H2O)m clusters are favored both energetically and entropically compared to the ones that are of size m + n < or = 3. Also, the clusters with equimolar contributions of HF and H2O are found to have the strongest interactions.     

Silver-halogen cluster compounds Ag n X m (n≥2; 0≤m≤n;X=F,Br)

Nonstoichiometric silver-halogen cluster compounds Ag _n X _m (0≤m≤n;X=F, Br) are generated by cocondensation of Ag atoms and AgX species using a slightly modified gas aggregation technique. The AgX molecules are produced by partial decomposition of SF₆ and Br₂ respectively at the surface of the hot silver containing crucible, followed by the reaction of halogen atoms with silver, giving rise to the formation of AgX molecules. In a heterogeneous nucleation between these molecules and evaporated Ag atoms the afore mentioned cluster compounds are formed. The degree of halogenation can either be controlled by the adjustment of the silver evaporation rate, or even more easily by controlling the partial pressure of the halogenating agent. The mass spectra of singly charged halogenated clusters, which are generated by electron impact ionization, reflect the stability of ions. These mass spectra demonstrate that there is an alternation in the intensity pattern up to a relatively high degree of halogenation (m) for each of the investigated compound series Ag _n X _m ,n≤8. This behavior is similar to the well-known odd-even effect for pure metal clusters, allowing us to postulate the existence of a “metallic” core which governs the stability of the cluster ion (at least for not too high degree of halogenation).