C2v Isomer Research Articles

Homoleptic Carbonyls of the Second-Row Transition Metals: Evaluation of Hartree-Fock and Density Functional Theory Methods.

The homoleptic mono- and multinuclear carbonyls for Mo, Tc, Ru, and Rh, namely, Mo(CO)6, Ru(CO)5, Tc2(CO)10, Ru3(CO)12, Rh4(CO)12, and Rh6(CO)16, are investigated theoretically by the Hartree-Fock method and three density functional theory (DFT) methods, i.e., BP86, B3LYP, and MPW1PW91, along with the SDD ECP basis sets. The results predicted by all the methods are basically in agreement with each other. The MPW1PW91 and BP86 methods predict geometric parameters and vibrational spectra, respectively, closest to the experimental values. For Ru3(CO)12 the relative energies of the D3h isomer with only terminal CO groups and the C2v isomer with two bridging CO groups are within 3 kcal/mol of each other with the lower energy isomer depending upon the computational method used. For Rh4(CO)12 the global minimum is predicted to have C3v symmetry, with three bridging and nine terminal carbonyls, in accord with experiment. The Rh6(CO)16 structure has Td symmetry and satisfies the Wade-Mingos rules for an octahedral cluster. Using the MPW1PW91 method the Rh-Rh distances in Rh4(CO)12 are found to be 2.692 Å and 2.750 Å and those in Rh6(CO)16 to be 2.785 Å.

Theoretical evidence of d‐orbital aromaticity in anionic metal X (X = Sc, Y, La) clusters

AbstractThe equilibrium geometries, total electronic energies, and vibrational frequencies for singlet, triplet, and quinted states of three all‐metal X (X = Sc, Y, and La) anions and nine relevant neutral singlet MX3 (M = Li, Na, K, X = Sc, Y, La) clusters are investigated with four density functional theory (DFT) and correlated ab initio methods B3LYP, B3PW91, MP2, and CCSD(T). To our knowledge, the theoretical study on these clusters composed of the transition metal Sc, Y, La is first reported here. The calculated results show that for the X clusters the singlet states with trigonal D3h structures are the lowest energetically, while the neutral singlet MX3 clusters each have two stable isomers: one trigonal pyramidal C3v and one bidentate C2v structures with the pyramidal C3v isomer being ground state. In addition, we calculate the resonance energies (RE) and nucleus‐independent chemical shift (NICS) for the singlet trigonal X rings and show that these singlet trigonal X rings exhibit higher degree of aromaticity. The detailed molecular orbital (MO) analyses reveal that the singlet trigonal X anions have one delocalized σ‐type and one delocalized π‐type MOs, which follow the 4n + 2 electron counting rule, respectively and play an important role in rendering these species two‐fold aromaticity. Here, an explicit theoretical evidence is given to prove that the contribution to the two‐fold aromaticity of the singlet trigonal X (X = Sc, Y, and La) rings originates primarily from the d‐orbital bonding interactions of these component transition metal X atoms. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007

Experimental and Computational Studies of Alkali-Metal Coinage-Metal Clusters

Coinage and alkali metal mixed clusters, M4Na- (M = Cu, Au) have been investigated experimentally using photoelectron spectroscopy and computationally at correlated ab initio levels. The related Cu4Li-, Ag4Li-, Ag4Na-, and Au4Li- clusters as well as the neutral Cu4Li2 and Cu4Na2 clusters have also been studied computationally. The calculations show that the two lowest isomers of the negatively charged clusters include a pyramidal C4v structure and a planar C2v species. For Cu4Li- and Cu4Na-, the C4v structure is calculated at correlated ab initio level to be 30.9 and 16.9 kJ/mol below the planar C2v isomer, whereas the planar isomers of Au4Li- and Au4Na- are found to be 29.7 and 49.4 kJ/mol below the pyramidal ones. For Ag4Li- and Ag4Na-, the pyramidal isomers are the lowest ones. Comparison of the calculated and measured photoelectron spectra of Cu4Na- and Au4Na- shows that the pyramidal Cu4Na- cluster of C4v symmetry and the planar Au4Na- of C2v symmetry are detected experimentally. Calculations of the magnetically induced current density in Cu4Li- and Cu4Li2 using the Gauge-Including Magnetically Induced Current (GIMIC) method show that strong ring currents are sustained mainly by the highest-occupied molecular orbital primarily derived from the Cu 4s. The GIMIC calculations thus show that the Cu4(2-) ring is -aromatic and that the d orbitals do not play any significant role for the electron delocalization effects. The present study does not support the notion that the square-planar Cu4(2-) is the first example of d-orbital aromatic molecules.

Selective Synthesis of the C3v Isomer of C60H18

[chemical structure: see text]. C60H18 has been produced by hydrogenation of C60 at 100 bar H2 pressure and 673 K for 10 h. We have investigated the crude material without any purification by use of 1H NMR, 13C NMR, and IR spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry. We show that the crude material consists of 95% of the C3v isomer of C60H18.

Theoretical study of hydrogenation of the doubly aromatic B 7 − cluster

We have studied the influence of hydrogenation on the relative stability of the low-lying isomers of the anionic B7- cluster, computationally. It is known that the pure-boron B7- cluster has a doubly (sigma- and pi-) aromatic C6v(3A1) quasi-planar wheel-type triplet global minimum (structure 1), a low-lying sigma-aromatic and pi-antiaromatic quasi-planar singlet C2v (1A1) isomer 2 (0.7 kcal mol(-1) above the global minimum), and a planar doubly (sigma- and pi-) antiaromatic C2v (1A1) isomer 3 (7.8 kcal mol(-1) above the global minimum). However, upon hydrogenation, an inversion in the stability of the species occurs. The planar B7H 2- (C2v, 1A1) isomer 4, originated from the addition of two hydrogen atoms to the doubly antiaromatic B7- isomer 3, becomes the global minimum structure. The second most stable B7H2- isomer 5, originated from the quasi-planar triplet wheel isomer 1 of B7- , was found to be 27 kcal mol(-1) higher in energy. The inversion in stability occurs due to the loss of the doubly aromatic character in the wheel-type global minimum isomer (C6v, 3A1) of B7- upon H2-addition. In contrast, the planar isomer of B7- (C2v, 1A1) gains aromatic character upon addition of two hydrogen atoms, which makes it more stable.

Ab initio study of structures and energies of Al2H4 and Al2H 4 −

The low-lying isomers of Al2H4 and their anions are investigated with the hybrid density functional B3LYP, the coupled-cluster CCSD and CCSD(T) methods, and the electron propagator theory. The positive adiabatic electron affinities 5,798 and 10,112 cm−1 are predicted for the neutral C2v and D2d symmetric isomers, respectively. The D2h symmetric anion is more stable by 852 cm−1 than the C2v symmetric anion. The photodetachment spectra for Al2H4− anions at the C2v and D2h symmetries are simulated on the basis of the Franck–Condon factor calculations, indicating a reasonable way to study the transition state of the intramolecular torsion process

Fabrication and characterization of field-effect transistor device with C2v isomer of Pr@C 82

A field-effect transistor (FET) device was fabricated with thin films of C 2v isomer of Pr@C 82. This device apparently showed n-channel normally on type FET properties, where non-zero current was observed at the gate–source voltage, V GS, of 0 V. Normally off FET properties were observed by subtraction of the non-zero current from the drain current. Thus the normally on properties are ascribed to the high bulk current caused by the small energy gap of ≈0.3 eV. The field-effect mobility for this FET was 1.5 × 10 −4 cm 2 V −1 s −1 at 320 K, being comparable to those of other endohedral metallofullerene FET devices.

The Perfluoroadamantyl Radicals C10F15 and Their Anions.

The optimized geometries, electron affinities, and harmonic vibrational frequencies of perfluoroadamantyl radicals (C10F15) have been obtained using four carefully calibrated density functional theory methods in conjunction with diffuse function augmented double-ζ plus polarization (DZP++) basis sets. There are two C10F15 isomers with close energies. With the DZP++ B3LYP method, the C3v isomer (1-C10F15) lies energetically above the Cs isomer (2-C10F15) by 0.086 eV (2.0 kcal/mol), while the anionic 1-C10F15(-) isomer is predicted to lie below 2-C10F15(-) anion by 1.00 eV (23.0 kcal/mol). The DZP++ B3LYP method predicts the ZPVE-corrected adiabatic electron affinity for the C3v isomer (1-C10F15) to be 4.16 eV, and that for the Cs isomer (2-C10F15) is 3.10 eV. These EAad values are significantly larger than that (1.31 eV) of the parent molecule perfluoroadamantane (C10F16). For the 1-C10F15 radical, the C*-C bond length is shortened by 0.043 Å upon removal of F from the C10F16 molecule. The C*-C bond distance for the 1-C10F15(-) anion is 0.068 Å shorter than that for C10F16. Similarly, for 2-C10F15 the C*-C distance is 0.053 Å shorter than for C10F16, while re(C*-C) for the anion is 0.061 Å shorter than for C10F16.

The First Crystal Structure of a Halogenated Higher Fullerene, C78Br18, Obtained by Bromination of a Fullerene Mixture.

Simple bromination of a fullerene mixture allowed the separation of C78 from other fullerenes in form of crystalline C78Br18. The first X-ray single-crystal structure of a halogenated higher fullerene, C78Br18, revealed that the addition pattern of 18 bromine atoms on the C78 cage corresponds to a partial retention of the conjugated double bond systems and the formation of isolated C−C double bonds. Evidently, even a separation of the C2v and D3 isomers of C78 occurred in the course of bromination and precipitation. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

The First Crystal Structure of a Halogenated Higher Fullerene, C78Br18, Obtained by Bromination of a Fullerene Mixture

AbstractSimple bromination of a fullerene mixture allowed the separation of C78 from other fullerenes in form of crystalline C78Br18. The first X‐ray single‐crystal structure of a halogenated higher fullerene, C78Br18, revealed that the addition pattern of 18 bromine atoms on the C78 cage corresponds to a partial retention of the conjugated double bond systems and the formation of isolated C−C double bonds. Evidently, even a separation of the C2v and D3 isomers of C78 occurred in the course of bromination and precipitation. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Structures and stabilities of small silicon clusters: Ab initio molecular-orbital calculations of Si7–Si11

Ab initio all-electron molecular-orbital calculations have been carried out to study the structure and relative stability of small silicon clusters (Sin, n=7–11). A number of low-energy geometric isomers are optimized at the second-order Møller–Plesset (MP2) MP2/6-31G(d) level. Harmonic vibrational analysis has been performed to assure that the optimized geometries are stable. The total energies of stable isomers are computed at the coupled-cluster single and double substitutions (including triple excitations) [CCSD(T)] CCSD(T)/6-31G(d) level. The calculated binding energies per atom at both the MP2/6-31G(d) and CCSD(T)/6-31G(d) levels agree with the experiments. For Si7, Si8, and Si10, the lowest-energy structures are the same as those predicted previously from the all-electron optimization at the Hartree–Fock (HF) HF/6-31G(d) level [Raghavachari and Rohlfing, J. Chem. Phys. 89, 2219 (1988)]. For Si9, the lowest-energy isomer is same as that predicted based on density-functional plane-wave pseudopotential method [Vasiliev, Ogut, and Chelikowsky, Phys. Rev. Lett. 78, 4805 (1997)]. Particular attention has been given to Si11 because several low-energy geometric isomers were found nearly isoenergetic. On the basis of MP2/6-311G(2d)//CCSD(T)/6-311G(2d) calculation, we identified that the C2v isomer, a tricapped trigonal prism with two additional caps on side trigonal faces, is most likely the global-minimum structure. However, another competitive geometric isomer for the global minimum is also found on basis of the MP2/6-311G(2d)//CCSD(T)/6-311G(2d) calculation. Additionally, calculations of the binding energy and the cluster polarizability offer more insights into relatively strong stability of two magic-number clusters Si6 and Si10.

The nature of the chemical bonding in the D3h and C2v isomers of Fe3(CO)12

The bonding in the D3h and C2v isomers of Fe3(CO)12 has been studied with two complementary topological approaches, namely the atoms-in-molecules (AIM) theory and the analysis of the electron localization function (ELF). Both methods indicate that the stabilization of the C2v isomer is mostly due to the presence of two ligands in bridging positions, which take advantage of a rather large electron transfer from the iron atoms. Within the ELF framework, each of these latter ligands is involved in three-center (3c–4e) bonds with the two adjacent iron atoms.

Structure and stability of B6, B, and B clusters

AbstractWe investigated various isomers of B6, B, and B clusters with ab initio [Hartree–Fock (HF), MP2)] and density functional theory (DFT) methods. Ten B6 isomers, 6 B isomers, and 6 B isomers are determined to be local minima on their potential energy hypersurfaces by the HF, B3LYP, B3PW91, and MP2 methods. Fourteen of these structures are first reported. The most stable neutral B6 cluster is the capped pentagonal pyramid (C5v), in agreement with the results reported previously. Hexagon B (C2h) isomer and fan‐shaped B (C2v) isomer are found to be the most stable on the cationic and anionic energy hypersurfaces, respectively. Natural bond orbital analysis suggests that there are three‐centered bonds in the most stable B6 neutral and ionic clusters. The multicentered bonds are responsible for the special stability of the lowest‐energy isomer. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 94: 269–278, 2003

Crystallographic characterization of Isomer 2 of Er2@C82 and comparison with Isomer 1 of Er2@C82

The X-ray crystal structure of (Isomer 2 of Er2@C82). NiII(OEP).2(benzene) shows that the fullerene cage in Isomer 2 of Er2@C82 is the C3v isomer (82:8) and that the erbium ions are distributed over 23 interior sites with occupancies ranging from 0.25 to 0.03.

Probing the Electronic Structure and Aromaticity of Pentapnictogen Cluster Anions Pn5-(Pn = P, As, Sb, and Bi) Using Photoelectron Spectroscopy and ab Initio Calculations

The electronic structure and chemical bonding of the pentapnictogen cluster anions, Pn5- (Pn = P, As, Sb, and Bi), were investigated using both photoelectron spectroscopy and ab initio calculations. Well-resolved photoelectron spectra were obtained for the anions at several photon energies and were analyzed according to the theoretical calculations. The ground state of all the Pn5- species was found to be the aromatic cyclic D5h structure with a C2v low-lying isomer. We found that the C2v isomer gains stability from P5- to Sb5-, consistent with the experimental observation of the coexistence of both isomers in the spectra of Sb5-. The valence molecular orbitals (MOs) of the D5h Pn5- were analyzed and compared to those of the aromatic C5H5- hydrocarbon. The same set of π-MOs is shown to be occupied in the D5h Pn5- and C5H5- species, except that the MO ordering is slightly different. Whereas the three π-MOs in C5H5- all lie above the σ-MOs, the third π orbital (1a2‘ ‘ in Pn5-) lies below the σ-MOs. The stab...

Photodissociation and theoretical studies of the Au+–(C5H5N) complex

Laser vaporization combined with a supersonic molecular beam was employed to generate and study the Au(C5H5N)+ complex for the first time. On the basis of the ionization energies (IE) between gold and pyridine, the Au(C5H5N)+ species is viewed as being a Au+–C5H5N species. Photodissociative charge transfer was observed with exclusive C5H5N+ (pyridine) formation. The photofragmentation spectrum of Au+–(C5H5N) was scanned by monitoring the pyridine fragments. A structureless continuum spectrum was observed and the onset of C5H5N+ appearance indicates the upper limit on the Au+–C5H5N bond strength to be 59.6 kcal mol−1. Ab initio calculations at the MP2 level were employed to optimize the geometries of the gold complexes and binding energies were obtained using CCSD(T) single point calculations. Besides from the C2v structure observed in Cu+ and Ag+ complexes, the theoretical results yielded a second isomer with C1 symmetry which is 24 kcal mol−1 less stable in energy than the C2v isomer.

Valence bond and molecular orbital studies of three N2O isomers, and valence bond representations for some azide decompositions

The results of STO-6G valence bond calculations with Lewis-type valence bond structures are reported for the S=0 spin ground states of the linear NNO (C∞v) and NON (D∞h) isomers of N2O. It is calculated that the singlet diradical character of the NON isomer is substantially larger than for the NNO isomer. The results of B3LYP/6-31G(d) density functional calculations are also reported for the C∞v and D∞h ground states, the single-determinant approximations to the lowest-energy S=1 spin excited states of these two isomers, and for the triangular C2v isomer. The calculated bond lengths are in accord with qualitative valence bond considerations.

Fullerene C80: Are there still more isomers?

A theoretical investigation of fullerene C80 using density functional theory is presented. Following the isolated pentagon rule (IPR), seven different topologies are considered. Calculated energy differences are less than 30 kJ/mol except for Ih topology which is more unstable. Isomers of D5d, C2v(I), and D2 topology are found to have singlet ground states. Calculated nuclear magnetic resonance and electronic absorption spectra allow to identify the two known isomers as D2 and D5d, in agreement with previous assignments. The absolute configuration of the chiral D2 isomer is predicted by means of the calculated electronic circular dichroism spectrum. The results further suggest that the C2v(I) isomer might be accessible from soots. All other IPR isomers are either diradicals or have nearly zero singlet–triplet splittings. These species are expected to polymerize, forming insoluble solids. The classification of fullerenes according to their gap is analyzed, and computational methods for treating small gap cases are discussed.

Isolation and Structural and Optical Characterization of the C2v 1,2-Naphthalocyanine Isomer

Abstract The C2v isomer of Co(1,2-Nc-C2v) (1,2-Nc = 1,2-naphthalocyaninato) has been isolated by fractional crystallization of the crude mixture of four isomers (C4h, Cs, C2v, D2h), and its crystal structure, electronic absorption, and magnetic circular dichromism have been discussed.

The performance of density-functional theory in challenging cases: Halogen oxides

Halogen dioxides (FOO, ClOO, BrOO, OClO, OBrO), their cationic and anionic derivatives and two isomers of ClO3 have been studied by means of density-functional theory (DFT) and the results compared with those from high level ab initio molecular orbital calculations. Three different density functionals (SVWN, B3LYP, and G96LYP) combined with a 6-311+G(2df ) basis set were used to obtain geometries and vibrational frequencies, which were then compared with MP2 (second-order Moller–Plesset), QCISD, and CCSD(T) (coupled-cluster single double triple) results. The B3LYP/6-311+G(2df ) calculations generally give geometries and frequencies in excellent agreement with those calculated from high level ab initio calculations such as CCSD(T). Exceptions, such as ClOO and BrOO, arise when high spin contamination at B3LYP level produces spurious results. Atomisation enthalpies evaluated at B3LYP/6-311+G(3df ) level of theory are observed to be in good agreement with the experimental values. In some particular cases this agreement is better than that obtained at CCSD(T)/6-311+G(3df ) level. For ionization enthalpies the CCSD(T) calculations seem to be superior to the DFT ones. Wave function instabilities [with respect to the UHF (unrestricted Hartree–Fock) transformation in the case of the cations and internal symmetry breaking in the case of the OXO (X=Cl, Br) compounds and the C3v isomer of ClO3] are observed less frequently when DFT methods are used.