C2h Symmetry Research Articles

Pseudo-Jahn–Teller effect in Si4X4 (X = F, Cl, Br, I) molecules: a theoretical investigation

ABSTRACTThe variability of planar rings in Si4X4 (X = F, Cl, Br, I) molecules caused by the pseudo-Jahn–Teller impact (PJTE) was evaluated as an original PJTE work. Optimisation and the following frequency calculations in these molecules illustrated that in high-symmetry planar (with D4h symmetry) geometry, all of these compounds were unstable and their structures were puckered to lower C2h symmetry stable geometry. Furthermore, the vibronic coupling interaction between 1A1g ground and the first 1Eg excited states through (1A1g + 1Eg) ⊗ eg PJTE problem was the cause of non-planarity of the four-member ring and the symmetry breaking phenomenon in those series. The calculated gaps (Δ) between the ground state and the Eg excited state, the vibronic coupling (F) and ground state primary force constant values (k1) were obtained from the numerical fitting of the ground state adiabatic potential energy surface with the analytical expressions of these molecules. Finally, natural bond analysis (NBO) was used for the design of the strongest interaction and natural atomic charges of these structures.

The Second and Third Crystal Field Splitting Moments in Verification of the Trigonal and Hexagonal Crystal Field Parametrizations

The paper, as the third in a series, presents the complete formulas for the crystal field splitting third moment of free ion states as functions of the relevant crystal field parameters in the case of the trigonal and hexagonal crystal fields. The additive structure of the expressions consists of 21 independent components for the trigonal symmetry, 12 for the hexagonal one and only 4 components for the ideal hexagonal coordination. The two scalar characteristics of the crystal field Hamiltonian HCF – the crystal field splitting second and third moments – enable us to verify the HCF parametrizations solely in an algebraic way. Such verification concerns the multipolar structure of the parametrizations as well as the signs of the crystal field parameters. Both the crystal field splitting moments can ensure us in what degree the comprehensive HCF parametrizations are adequate with respect to the individual ionic states of the electron configuration. As an example two chosen HCF parametrizations, one for the hexagonal system Nd3+:LaCl3 of the C3h symmetry, and the second for the trigonal system Tb3+:Y2O2S of the C3v symmetry are subjected to in depth analysis. The presented approach provides a critical insight into the crystal field parametrizations from a different point of view, i.e., omitting the conventional fitting procedure. After the extended verification the studied classical HCF parametrizations withstand, in principle, the test of time.

Probing the Indigo Molecule in Maya Blue Simulants with Resonance Raman Spectroscopy

Maya blue (MB) simulants were prepared from mixtures of indigo and palygorskite (ind–paly) and investigated by resonance Raman and UV–vis absorption spectroscopies together with thermogravimetric analysis, aiming to enlarge the understanding of the dye–clay interaction, the relationship between color and chemical stability, and the alleged formation of dehydroindigo (DHI); for comparative purposes, other simulants were prepared using sepiolite, laponite, and montmorillonite. The results obtained here suggest that the greenish hue that develops when the ind–paly is heated seems to be linked with a decrease in the indigo molecular symmetry, which causes an increase in the oscillator strength of an absorption band at 500 nm (forbidden under the C2h symmetry) and a bathochromic shift and narrowing of the intense electronic transition at 657 nm (indigo). The DHI characteristic features are not observed in the resonance Raman spectrum (457.9 nm) of the ind–paly system, contrary to what happens with sepiolite, L...

Communication: Photoionization of degenerate orbitals for randomly oriented molecules: The effect of time-reversal symmetry on recoil-ion momentum angular distributions.

The photoelectron asymmetry parameter β, which characterizes the direction of electrons ejected from a randomly oriented molecular ensemble by linearly polarized light, is investigated for degenerate orbitals. We show that β is totally symmetric under the symmetry operation of the point group of a molecule, and it has mixed properties under time reversal. Therefore, all degenerate molecular orbitals, except for the case of degeneracy due to time reversal, have the same β (Wigner-Eckart theorem). The exceptions are e-type complex orbitals of the Cn, Sn, Cnh, T, and Th point groups, and calculations on boric acid (C3h symmetry) are performed as an example. However, including those point groups, all degenerate orbitals have the same β if those orbitals are real. We discuss the implications of this operator formalism for molecular alignment and photoelectron circular dichroism.

(Invited) Structural Identification of 19 Purified Isomers of Opv Acceptor Material Bis[60]PCBM

The molecular structures of 19 purified isomers of bis-phenyl-C62-butyric acid methyl ester (“bis[60]PCBM”) were identified by a combination of 13C NMR and UV-Vis absorption spectroscopy, and HPLC retention time analysis. The 13C NMR spectra indicated the symmetry of each isomer. It also showed that all 19 isomers are dicyclopropa-fullerenes (none are homo-fullerenes). This is because the fullerene bridgehead for both addends are sp 3 hybridized; resonating between 75 and 85 ppm. According to UV-Vis spectroscopy, the 19 isomers were classified into 7 groups - each corresponding to one of the 7 bond types identified by Hirsch and co-workers (trans-1, trans-2, trans-3, trans-4, e, cis-3, cis-2). All 58 nominal molecular structures of Bis[60]PCBM were accounted for by isolating the first addend as bridging fullerenes carbon 1 and 9 by default, after which the 2nd addend may to one of the 29 remaining double bonds on C60 with two orientations relative to that of the 1st addend. However, symmetry reduced this number to 36 physically distinguishable isomers. Many of these isomers have enantiomers, and hence cannot be spectroscopically distinguished; which reduces the number of effective isomers to 22. If these, 3 are not expected to form owing to steric hindrance because each of these three isomers involve the cis-1 bond whereby the bulky addends would be attached to two adjacent double bonds on the same 6-membered ring on C60. There were 7 isomers with C1 molecular point group symmetry, 4 with CS, 6 with C2, 1 with C2v and 1 with C2h symmetry. The C2h, C2v, and all 5 non-equatorial C1 molecular structures were unambiguously assigned to their respective HPLC fractions. For the other 12 isomers, the 13C NMR and UV-Vis spectra placed them in 6 groups of two same-symmetry isomers. Based on the widely spaced HPLC retention times of the two isomers within each of these 6 groups, and the empirical inverse correlation between retention time and addend spacing, each molecular structure was assigned to its corresponding HPLC fraction. The information presented will enable those who follow and produce photovoltaic devices based purified isomers to know which specific isomer is being employed in their devices, develop a deeper understanding of morphological order/disorder within the acceptor phase, and thereby draw meaningful conclusions on why some isomers perform better than others.

A Cryptand-Type Aluminum Tris(salophen) Complex: Synthesis, Characterization, and Cell Imaging Application

Metal salen/salophen complexes have been used as fluorescent probes for cell imaging with various metal centers. Herein we synthesized cryptand-type aluminum salophen complexes LAl3 and the corresponding mononuclear compound LAl. X-ray crystal diffraction verifies the cryptand-type structure of LAl3 with C3h symmetry. Both LAl3 and LAl show moderate green fluorescence with quantum yields of 0.17 and 0.05, respectively. The hydrophilic and cationic nature of these aluminum salophen complexes renders them enhanced cellular uptake. Both complexes are internalized into cells by energy-dependent pathways and they distribute in lysosomal organelles.

Coordination Structure and Fragmentation Chemistry of the Tripositive Lanthanide-Thio-Diglycolamide Complexes.

Tripositive Ln(TMTDA)33+ complexes (Ln = La-Lu except Pm, TMTDA = tetramethyl 3-thio-diglycolamide) were observed in the gas phase by electrospray ionization of LnCl3 and TMTDA mixtures. Collision-induced dissociation (CID) was employed to investigate their fragmentation chemistry, which revealed the influence of metal center as well as ligand on the ligated complexes. Ln(TMTDA)2(TMTDA-45)3+ resulting from Ccarbonyl-N bond cleavage of TMTDA and hydrogen transfer was the major CID product for all Ln(TMTDA)33+ except Eu(TMTDA)33+, which predominantly formed charge-reducing product EuII(TMTDA)22+ via electron transfer from TMTDA to Eu3+. Density functional theory calculations on the structure of La(TMTDA)33+ and Lu(TMTDA)33+ revealed that Ln3+ was coordinated by six Ocarbonyl atoms from three neutral TMTDA ligands, and both complexes possessed C3h symmetry. The Sether atom deviating from the ligand plane was not coordinated to the metal center. On the basis of the CID results of Ln(TMTDA)33+, Ln(TMGA)33+, and Ln(TMOGA)33+, the fragmentation chemistry associated with the ligand depends on the coordination mode, while the redox chemistry of these tripositive ions is related to the nature of both metal centers and diamide ligands.

Dinuclear Metal-Mediated Homo Base Pairs with Metallophilic Interactions: Theoretical Studies of G2M22+ (M\u2009=\u2009Cu, Ag, and Au) Ions

Dinuclear metal-mediated homo base pairs are interesting clusters with highly symmetric structures and significant stabilities. The geometric and electronic structures of G2M22+ (G = Guanine, M = Cu, Ag or Au) cluster ions were studied with quantum chemical calculations. The lowest-energy isomers of G2M22+ cluster ions have C2h symmetries with an approximately antiparallel alignment of two sets of N-M∙∙∙O groups being formed in the planar structures. The M-M distances are shorter than the sum of van der Waals radii of corresponding two homo coinage metal atoms, showing that metallophilic interactions significantly exist in these complexes. They have the large HOMO−LUMO gaps of about 5.80 eV at the DFT level and the bond dissociation energies of more than 5.60 eV at the DFT/B3LYP level, indicating that these cluster dications are highly stable. The second lowest-energy isomers stabilized by an approximately parallel alignment of one set of O-M-O group and one set of N-M-N group are found to be close to the lowest-energy isomers in energy. The barrier between the two isomers of G2M22+ cluster ions is significantly large, also showing that these lowest-energy isomers are very stable.

Theoretical Insights into the Electronic Structures and Stability of Dimetallofullerenes M2@Ih-C80

We present a theoretical study on the structural and electronic properties of a series of neutral and anionic species of M2@Ih-C80 (M = Sc, Y, La, Gd, Lu). Molecular orbital analysis suggests that the unpaired electron appears on the cage for neutral M2@Ih-C80 (M = Y, Gd, Lu), and is governed by the level of a metal-based (interstitial) orbital. We showed that anionization is an effective means to stabilize the neutral dimetallofullerenes because of the disappearance of the unpaired electron on the cage. Our theoretical studies on the paramagnetic di-EMF reveals that a strong ferromagnetic interaction is possible for [Gd2@Ih-C80]−. We have also investigated the absorption spectra and found that the anions [M2@Ih-C80]− with the D2h cage symmetry result in similar absorption spectra irrespective of the kinds of metals present (M = Y, La, Gd), while the absorption spectrum for [Sc2@Ih-C80]− with the strong interaction between the Sc metal and cage, which leads to the C2h symmetry, is different from those of D2h.

Improved assignments of the vibrational fundamental modes of ortho-, meta-, and para-xylene using gas- and liquid-phase infrared and Raman spectra combined with ab initio calculations: Quantitative gas-phase infrared spectra for detection

Xylenes contain a blend of the ortho-, meta-, and para- isomers, and all are abundant contaminants in the ground, surface waters, and air. To better characterize xylene and to better enable its detection, high quality quantitative vapor-phase infrared spectra of all three isomers over the 6500 – 540 cm−1 range are reported. All fundamental vibrational modes are assigned based on these vapor-phase infrared spectra, liquid-phase infrared and Raman spectra, along with density functional theory (DFT), ab initio MP2 and high energy-accuracy compound theoretical model (W1BD) calculations. Both MP2 and DFT predict a single conformer with C2v symmetry for ortho-xylene, and two conformers each for meta- and para-xylene, depending on the preferred orientations of the methyl groups. For meta-xylene the two conformers have Cs and C2 symmetry, and for para-xylene these conformers have C2v or C2h symmetry. Since the relative population of the two conformers is approximately 50% for both isomers and predicted frequencies and intensities are very similar for each conformer, an arbitrary choice to discuss the Cs conformer for meta-xylene and the C2v conformer for para-xylene is made. Integrated band intensities for all isomers are reported. Using the quantitative infrared data, the global warming potential values of each isomer are determined. Potential bands for atmospheric monitoring are also discussed.

Probing the global potential energy minimum of (CH2O)2: THz absorption spectrum of (CH2O)2 in solid neon and para-hydrogen.

The true global potential energy minimum configuration of the formaldehyde dimer (CH2O)2, including the presence of a single or a double weak intermolecular CH⋯O hydrogen bond motif, has been a long-standing subject among both experimentalists and theoreticians as two different energy minima conformations of Cs and C2h symmetry have almost identical energies. The present work demonstrates how the class of large-amplitude hydrogen bond vibrational motion probed in the THz region provides excellent direct spectroscopic observables for these weak intermolecular CH⋯O hydrogen bond motifs. The combination of concentration dependency measurements, observed isotopic spectral shifts associated with H/D substitutions and dedicated annealing procedures, enables the unambiguous assignment of three large-amplitude infrared active hydrogen bond vibrational modes for the non-planar Cs configuration of (CH2O)2 embedded in cryogenic neon and enriched para-hydrogen matrices. A (semi)-empirical value for the change of vibrational zero-point energy of 5.5 ± 0.3 kJ mol-1 is proposed for the dimerization process. These THz spectroscopic observations are complemented by CCSD(T)-F12/aug-cc-pV5Z (electronic energies) and MP2/aug-cc-pVQZ (force fields) electronic structure calculations yielding a (semi)-empirical value of 13.7 ± 0.3 kJ mol-1 for the dissociation energy D0 of this global potential energy minimum.

Ab Initio Investigating the Bonding and Electronic Structure in Bismuth Calixarene Complexes

The geometric and electronic structures of calixarene bismuth(III) complexes have been investigated by ab initio method in this study. Three conformations (cone shape conformation with C2v symmetry, 1,2-alternative conformation with C2h symmetry and 1,3-alternative conformation) are investigated as possible binding modes between bismuth fragment and calixarene fragment. The optimized geometries are then compared with the recent reported crystal structure. Two bis-muth(III) fragments are needed to bind with calixarene ligand due to the inert-pair effect. Co-crystalized LiCl-DMSO fragment plays a crucial role in stabilizing the bismuth calixarene crystal, where the binding energy ΔH is estimated to be 55.3 kcal/mol or 56.1 kcal/mol with zero-point energy correction. The estimated ΔG is -28.2 kcal/mol for the complex, which is consistent with the strong HC4Bi-ClLi interactions. The trans effect is evidenced by two slight longer Bi-O bond lengths.

Critical Role of Molecular Symmetry for Charge Transport Properties: A Paradigm Learned from Quinoidal Bithieno[3,4-b]thiophenes

High molecular symmetry is always observed in high-performance organic semiconductors. However, whether it is an essential factor for molecular design is unclear. In this work, we designed and synthesized three quinoidal isomers, QBTT-o, QBTT-i, and QBTT-s, with different sulfur orientations and a stable E configuration to investigate the relationship between the structure symmetry and organic thin-film transistor performance. We found that QBTT-o and QBTT-i with high C2h symmetry exhibit electron mobilities of 0.02 and 0.15 cm2 V–1 s–1, respectively, while QBTT-s exhibits an unexpectedly high electron mobility of 0.32 cm2 V–1 s–1 with Ion/Ioff ratios of ≤106. The enhanced electron mobilities from QBTT-o and QBTT-i to QBTT-s can be attributed to the different sulfur orientations, especially, molecular symmetry. The thin-film microstructures of three QBTTs were systematically investigated by grazing incidence wide-angle X-ray scattering, near-edge X-ray absorption fine structure spectroscopy, atomic force ...

Anion Photoelectron Spectroscopy and Theoretical Investigation on Nb2Sin–/0 (n = 2–12) Clusters

We measured the photoelectron spectra of Nb2Sin– (n = 2–12) anions and investigated the geometric structures and electronic properties of Nb2Sin– anions and their neutral counterparts with ab initio calculations. The most stable structures of Nb2Sin–/0 (n = 2–12) clusters can be regarded as a central axis of Nb2 surrounded by the Si atoms. The most stable isomers of Nb2Sin– anions are in spin doublet states, while those of the neutral clusters are in spin singlet states. The results showed that the two Nb atoms in Nb2Sin–/0 clusters incline to form a strong Nb–Nb bond and also prefer to occupy the high coordination sites to form more Nb–Si bonds. The most stable isomers of anionic and neutral Nb2Si3 are D3h-symmetric trigonal bipyramid structures, and that of Nb2Si6– has C2h symmetry with the six Si atoms forming a chair-shaped structure. The ground state structure of the Nb2Si12– anion is a C6v-symmetric capped hexagonal antiprism in which one Nb atom is encapsulated inside the Si12 cage and the second N...

Structural Identification of 11 of the 19 Isomers of the Opv Acceptor Bispcbm Via 13c NMR and UV-Vis Absorption Spectroscopy, and Cyclic Voltammetry, Coupled with DFT Simulations

The as-produced isomer mixture of the organic photovoltaic acceptor material bisPCBM has recently been purified into 19 components by peak-recycling HPLC and their frontier orbitals have been characterised by UV-Vis absorption spectroscopy and cyclic voltammetry. OPV devices based on the purified isomers may now be made, but before meaningful conclusions can be made about why some isomers are better that others in these devices, we mush first know which particular isomer is used in which OPV device. Here we present the structural identification of more than half (11) of the 19 isomers by 13C NMR and UV-Vis spectroscopy. Via UV-Vis spectroscopy the 19 isomers of bisPCBM were classified into 7 different groups, with each group containing 2 or 3 members. Each of the 7 groups corresponds to 1 of the 7 bond types identified by Hirsch (trans-1, trans-2, trans-3, trans-4, e, cis-3, cis-2). By examining the molecular structure of each of the 19 isomers, we conclude that 11 isomers have C1 symmetry, 3 isomers have Cs symmetry, 3 have C2 symmetry, 1 has C2h symmetry and 1 has C2v symmetry; and we have confirmed this prediction experimentally by 13C NMR spectroscopy. The two high-symmetry isomers, C2h and C2v, which correspond to the two polar isomers (where the two addends bridge the 1,9 and 52,60 bond of C60with the two addends having opposing relative orientations) correspond to the first and third HPLC fractions by retention time, respectively. Unfortunately, the other isomers cannot be identified from the NMR spectra alone. However, as the UV-Vis spectra and 7 groups identified above reduce the uncertainty to no more than 3 isomers, when coupled with the symmetry identified from NMR spectra, some of the isomers may be confidently identified. For example, the 13th HPLC fraction belongs to the cis-2 group which contains one C s and two C 1 isomers. The NMR spectra shows that this 13th fraction is the C s isomer, which involves the 32,33 bond of C60. By this method, the other C s and C 2isomers were also unambiguously confirmed. The remaining unidentified isomers all have C 1 symmetry and cannot be further identified by this method. For these isomers, the HOMOs and HOMO-LUMO gaps were calculated by DFT and TD-DFT methods. By comparing the experimental and calculated results, some, but not all, the C 1 isomers were tentatively identified with reasonable confidence. For the remaining 8 C1 isomers the DFT calculations were not able to adequately distinguish, so the identification of these isomers will have to wait for single crystal analysis. A full description of the identification of the isomers will be presented in the meeting.

Promotion of CO oxidation on the Fe/N X clusters embedded graphene

CO catalytic oxidation on the two-dimensional (2D) Fe/N X clusters embedded graphene (G) (X = 4, 3, 2, 1) with D 4h, C 2v, C 2h, and C S symmetries is investigated using the first-principle method. Fe/N2-G system with C 2h symmetry facilitates the O2 adsorption. The strong interaction between the Fe atom and O2 in Fe/N2-G system can be contributed from the high energy of Fe’s $$d_z^2$$ orbit. The CO oxidation reaction on Fe/N2-G system has a small energy barrier (0.43 eV) by the Langmuir–Hinshelwood (LH) mechanism (CO + O2 → OOCO → CO2 + Oads), which would be useful in evaluating the reactivity of Fe catalyst and serving as a good candidate for efficient non-noble metal catalyst. The results provide valuable guidance on selecting catalysts of low cost and superior activity to fabricate graphene-based materials.

Ge9{M(CO)5}3]4-: electrophilic addition of M(CO)5 and [E9]4- Zintl anions (M = Cr, Mo, W).

Nucleophilic substitution reactions of K4Ge9 and M(CO)6 produced [Ge9{M(CO)5}3]4- (M = Cr, 1a; Mo, 2a; W, 3a). The electrophilic addition of M(CO)5 and [Ge9]4- occurred at the three capping sites to form almost perfect tricapped trigonal prismatic 1a-3a with crystallographic C3h symmetry.

Anion photoelectron imaging spectroscopy of glyoxal

We report a photoelectron imaging study of the radical-anion of glyoxal. The 532nm photoelectron spectrum provides the first direct spectroscopic determination of the adiabatic electron affinity of glyoxal, EA=1.10±0.02eV. This assignment is supported by a Franck-Condon simulation of the experimental spectrum that successfully reproduces the observed spectral features. The vertical detachment energy of the radical-anion is determined as VDE=1.30±0.04eV. The reported EA and VDE values are attributed to the most stable (C2h symmetry) isomers of the neutral and the anion.

Effect of phase modifiers TBP and iso-decanol on the extraction and complexation of Eu3+ with CMPO

ABSTRACTThe effect of tri-n-butyl phosphate (TBP) and iso-decanol as phase modifiers on the complexation of Eu3+ with octyl-phenyl N,N-diisobutyl carbamoyl methyl phosphine oxide (CMPO) was studied. On an increase of iso-decanol the extraction efficiency of Eu3+ decreases. The metal–ligand stoichiometry was found to be 1:3. The Eu complex of CMPO–TBP was more symmetric compared to CMPO–iso-decanol. The Eu3+ complex exhibited D3h and C3h symmetry for 30% and 5% iso-decanol, while that for TBP was C6v. The radiative, non-radiative life time, electric and magnetic dipole transition probabilities, branching ratio, quantum efficiency etc. were evaluated. The covalency between Eu3+ and CMPO is as follows: CMPO–TBP < CMPO-5% iso-decanol < CMPO-30% iso-decanol.

Understanding the complexation of the Eu3+ ion with TODGA, CMPO, TOPO and DMDBTDMA: Extraction, luminescence and theoretical investigation

A comparative study was carried out to understand the complexation behavior of the Eu3+ ion with important reagents, namely TODGA (N,N,N′,N′ tetraoctyl diglycolamide), CMPO (octyl (phenyl)-N, N-diisobutyl carbamoyl methyl phosphine oxide), DMDBTDMA (dimethyl dibutyl tetradecyl malonamide) and TOPO (tri-n-octyl phosphine oxide) in dodecane, used for the separation of actinides and lanthanides from lab and nuclear high-level wastes, by experimental (extraction and luminescent) and theoretical means. A solvent extraction study revealed the metal–ligand stoichiometry as 1:3 for all the systems with the extraction efficiency TOPO>CMPO>TODGA>DMDBTDMA at 1M HNO3, while TODGA>CMPO>DMDBTDMA>TOPO at 3M HNO3. A luminescence investigation revealed the presence of single species in the extracted complex for all the systems, with no inner sphere water molecules for all the systems except for DMDBTDMA which had one inner sphere water molecule. The high intensity of the 5D0–7F2 transition revealed the presence of Eu3+ ions in an asymmetric environment with the local point group symmetry C3v for the TODGA and DMDBTDMA complexes, compared to C3h symmetry for the CMPO and TOPO complexes. Judd–Offelt parameters, radiative, non-radiative lifetimes, branching ratio, transition probabilities and quantum efficiencies for all the complexes were estimated and compared. Three O-donor atoms from each TODGA molecule coordinated to the Eu3+ ion in the first coordination sphere, while three CMPO units were found to be coordinated in a monodentate fashion. For the Eu-TOPO complex, three O donor atoms from each of the three TOPO molecules and six O donor atoms from three nitrate ions were coordinated. Out of three DMDBTDMA ligands, one was found to be coordinated in a bidentate mode, whereas two were in a monodentate mode, along with three nitrate ligands bonding in a monodentate fashion.