C2v Symmetry Research Articles

Photodynamic inactivation of Enterococcus faecalis by conjugates of zinc(II) phthalocyanines with thymol and carvacrol loaded into lipid vesicles

Terpene-macrocycle conjugates, consisting of thymol or carvacrol and phthalocyanine were synthesized, characterized, and subjected to detailed optical and biological studies. The macrocyclization reactions of terpene-substituted o-phthalonitrile derivatives were performed in a microwave reactor to give thymol- and carvacrol-phthalocyanine conjugates, which were carefully purified by column chromatography and subsequently analyzed using HPLC and characterized using UV–Vis, NMR and MS. Both isolated phthalocyanine derivatives represent isomers of C2v symmetry, which was confirmed by NMR study. The absorption UV–Vis spectra of studied thymol- and carvacrol-phthalocyanine conjugates with the Soret and the Q band possesses the same profile. Both molecules reveal emission in the red region of the spectrum with fluorescence quantum yields about two-fold lower in DMF and significantly lower in DMSO than that observed for zinc(II) phthalocyanine. The analyzed phthalocyanine derivatives generate singlet oxygen upon excitation with light at ca. three-fold lower level then that noticed for zinc(II) phthalocyanine. In comparison to zinc(II) phthalocyanine, both molecules also reveal two-fold lower photostability in DMF and similar stability in DMSO. Thymol- and carvacrol-phthalocyanine conjugates, zinc(II) phthalocyanine, thymol, and carvacrol were loaded into modified liposomes and subjected to biological activity study. Thymol-phthalocyanine conjugate at both 100 and 10 µM revealed high, ca. 5 log photoinactivation potential on the growth of Enterococcus faecalis, similarly to reference zinc(II) phthalocyanine. For carvacrol-phthalocyanine conjugate, an increase of photoinactivation activity was observed at only 100 µM in comparison to zinc(II) phthalocyanine, whereas a decrease at the concentration of 10 µM was noticed. It is crucial that both studied phthalocyanines cross the border of 3 log photoinactivation potential, which indicates their bactericidal potential. In the Microtox® bioassay both conjugates revealed significantly decreased dark toxicity in comparison to thymol and carvacrol only. Interestingly, the carvacrol-phthalocyanine conjugate was found to be more toxic in comparison to thymol-phthalocyanine conjugate and zinc(II) phthalocyanine.

Spectroscopic, vibrational and structural properties analysis of CaXen (n = 1–4) clusters

A systematic ab initio calculations based on a complete Configuration Interaction (CI) including the pseudo-potential model where the core valence correlation was presented by the Core Polarization Potential (CPP), were employed to determine the geometric structures of CaXen (n = 1–4) neutral clusters. For the diatomic (CaXe) and tri-atomic (CaXe2) systems, the potential energy curves for the ground and several excited states are determined and the different spectroscopic constants are illustrated. Interested structures were seen in the PECs which their effects in the vibrational levels' spacing and the electric dipole moments variations were shown. The agreement with the experimental and the theoretical constants for n = 1 was excellent. Accordingly, for the higher clusters the predicted geometries should be reliable. The bent geometry of CaXe2 ground state with (C2v) symmetry was performed and hence was concluded to be the most adaptable with a bond angle of 54.84° and bond distance dXe-Xe of 8.08 a0. As well as, the bent isomer for the excited states was also studied to illustrate the most compact geometry for each state. For the ground state of CaXe3, the most stable geometry was trigonal-pyramidal with (C3v) symmetry with dXe-Xe = 8.13 a0. And concerned n = 4, four configurations were treated; the tetrahedral structure, the square pyramid structure, the trigonal bipyramid structure with (C3v) symmetry and the trigonal bipyramid structure with (C2v) symmetry. The comparison between their minimal energies showed that the most compact geometry for CaXe4 is the trigonal bipyramid with (C3v) symmetry with dXe-Xe = 8.17 a0. Consequently, this work illustrates that the mechanism of cluster forming is consistent with the calcium location on the xenon clusters' surface model.

Spin–phonon interactions in silicon carbide addressed by Gaussian acoustics

Hybrid spin-mechanical systems provide a platform for integrating quantum registers and transducers. Efficient creation and control of such systems require a comprehensive understanding of the individual spin and mechanical components as well as their mutual interactions. Point defects in silicon carbide (SiC) offer long-lived, optically addressable spin registers in a wafer-scale material with low acoustic losses, making them natural candidates for integration with high quality factor mechanical resonators. Here, we show Gaussian focusing of a surface acoustic wave in SiC, characterized by a novel stroboscopic X-ray diffraction imaging technique, which delivers direct, strain amplitude information at nanoscale spatial resolution. Using ab initio calculations, we provide a more complete picture of spin-strain coupling for various defects in SiC with C3v symmetry. This reveals the importance of shear for future device engineering and enhanced spin-mechanical coupling. We demonstrate all-optical detection of acoustic paramagnetic resonance without microwave magnetic fields, relevant to sensing applications. Finally, we show mechanically driven Autler-Townes splittings and magnetically forbidden Rabi oscillations. These results offer a basis for full strain control of three-level spin systems.

Thermally Induced Disorder-Order Phase Transition of Gd2Hf2O7:Eu3+ Nanoparticles and Its Implication on Photo- and Radioluminescence.

Crystal structure has a strong influence on the luminescence properties of lanthanide-doped materials. In this work, we have investigated the thermally induced structural transition in Gd2Hf2O7 (GHO) using Eu3+ ions as the spectroscopic probe. It was found that complete phase transition from the disordered fluorite phase (DFP) to the ordered pyrochlore phase (OPP) can be achieved in GHO with the increase of annealing temperature from 650 → 1100 → 1300 °C. OPP is the more stable structural form for the GHOE nanoparticles (NPs) annealed at a higher temperature based on the energy calculation by density functional theory (DFT). The asymmetry ratio of the GHOE-650 NPs was the highest, whereas the quantum yield, luminescence intensity, and lifetime values of the GHOE-1300 NPs were the highest. Emission intensity of Eu3+ ions increases significantly with the phase transition from the DFP to OPP phase and is attributed to the higher radiative transition rate (281 s–1) of the 5D0 level of the Eu3+ ion in the environment with relatively lower symmetry (C2v) because of the increase of crystal size. As the structure changes from DFP to OPP, radioluminescence showed tunable color change from red to orange. The Eu3+ local structure obtained from DFT calculation confirmed the absence of inversion symmetry in the DFP structure, which is consistent with the experimental emission spectra and Stark components. We also elucidated the host to dopant optical energy transfer through density of states calculations. Overall, our current studies present important observations for the GHOE NPs: (i) thermally induced order–disorder phase transition, (ii) change of point group symmetry around Eu3+ ions in the two phases, (iii) high thermal stability, and (iv) tunability of radioluminescent color. This work provides fundamental understanding of the relationship between the crystal structure and photophysical properties of lanthanide-doped materials and helps design a strategy for advanced optoelectronic materials.

Quantum anomalous Hall effects and various topological mechanisms in functionalized Sn monolayers

The topological behaviors of Sn monolayers partly passivated with H atoms are explored based on first-principles calculations. Obvious magnetism can be induced in the Sn monolayer due to the passivation. And the magnetism strength is found to be determined by the number difference of the H atoms bonding to the two sublattices of stanene. Quantum anomalous Hall (QAH) effects are found appearing easily in the systems with one of the sublattices fully passivated and the other not. The origin of the topological states can be ascribed to the coupling of the magnetism, the lattice symmetry (C3v), and the H-atom concentrations, which forms various mechanisms of the topological states. Particularly, band inversions are found playing completely different roles in forming the QAH effects for the different functionalized Sn monolayers.

Symmetry and thermodynamics of tellurium vacancies in cadmium telluride

The equilibrium geometries and thermodynamic properties of anion vacancies in cadmium telluride, as predicted by density functional theory, are revisited using semilocal and hybrid density functionals. We find that stable configurations in different charge states can only be found after a systematic search considering several starting geometries. The stable charge states, 0 and 2+, display closed-shell electronic configurations, without deep bandgap levels. The 2+ charge state has a Td symmetry with an outward relaxation, while the neutral state is a mixture of configurations with C2v and C3v symmetries, both with the same energy and a negligible energy barrier. Therefore, the neutral charge state presents an effective Td symmetry. Configurations with different symmetries, e.g., D2d, can exist as metastable states. We show that certain configurations may seem falsely stable due to several facts: the bandgap error of generalized gradient approximation, the k-point sampling used in small supercells, or the use of a restricted set of starting geometries. We believe that the HSE06 hybrid functional allows to obtain accurate formation energies and geometries. We analyze the effect of the spin-orbit coupling and GW quasiparticle corrections to the HSE06 results, and find no qualitative differences. The spin-orbit coupling and GW corrections to the HSE06 energies partially cancel each other. Finally, we investigate the divacancy VCdVTe. The obtained formation energies suggest that isolated tellurium vacancies in neutral charge state can be found only in Te-poor growth conditions, coexisting with divacancies.

Synthesis and characterisation of the vibrational and electrical properties of antiferromagnetic 6L-Ba2CoTeO6 ceramics.

Optimal processing conditions for fabrication of dense single-phase 6L-Ba2CoTeO6 ceramics via the solid-state reaction method were determined. These ceramics possess a room-temperature crystal structure described by the centrosymmetric P3[combining macron]m1 space group. Polarized Raman spectroscopy enabled the observation of all the 25 predicted Raman modes and assignment of their symmetries. On cooling, BCTO ceramics exhibit two antiferromagnetic transitions at 3 K and 12.5 K, in broad agreement with a recent single-crystal study [P. Chanlert, N. Kurita, H. Tanaka, D. Goto, A. Matsuo and K. Kindo, Phys. Rev. B: Condens. Matter Mater. Phys., 2016, 93, 094420]. Low temperature Fourier-transform infrared reflectivity analyses suggest the antiferromagnetic phase transitions to be driven by small distortions of the CoO6 octahedra, lowering locally their C3v symmetry. This causes splitting of the associated vibrational modes, but without a long-range structural change. AC impedance spectroscopy revealed BCTO ceramics to be leaky insulators with an activation energy for conduction of ∼0.15-0.25 eV, which suggests electron hopping between mixed oxidation states of Co.

A stable bis(methylene)-λ4-selane with a >C[double bond, length as m-dash]Se[double bond, length as m-dash]C< bond containing Se(iv).

Bis(methylene)-λ4-selane 1, which represents a new class of heteroallenes, was synthesized and isolated as a stable purple crystalline solid. X-ray crystallographic analysis revealed a bent allene-type structure with pseudo C2v symmetry and a bent C[double bond, length as m-dash]Se[double bond, length as m-dash]C moiety that contains a 3-center-4-electron π-bond. The NMR spectrum of 1 shows compelling evidence for a slow rotation of the Se[double bond, length as m-dash]C moieties at room temperature. The 77Se NMR spectrum of 1 contains one signal in the region characteristic for Se(iv) compounds.

Accurate calculation of electron affinity for S3**Project supported by the National Natural Science Foundation of China (Grant Nos. 11874179, 11447194,11574114, and 11874177) and the Natural Science Foundation of Jilin Province, China (Grant No. 20180101289JC).

The accurate equilibrium structures of S3 and are determined by the coupled-cluster method with single, double excitation and perturbative triple excitation (CCSD(T)) with basis sets of aug-cc-pV(n + d)Z (n = T, Q, 5, or 6), complete basis set extrapolation functions with two-parameters and three-parameters, together with considering the contributions due to the core-valence electron correlation, scalar relativistic effects, spin–orbit coupling, and zero-point vibrational corrections. Our calculations show that both the neutral S3 and anion have open forms with C2v symmetry. On the basis of the stable geometries, the adiabatic electron affinity of S3 is determined to be 19041(11) cm−1, which is in excellent agreement with the experimental data (19059(7) cm−1). The dependence of geometries and electron affinity on the computation level and physical corrections is discussed. The present computational results are helpful to the experimental molecular spectroscopy and bonding of S3.

The selectivity between inner C-cyanation and alkylation in cobalt(II) complexes of N-confused porphyrin with an axial NCS− ligand

Some inner C-cyanation and C-alkylation complexes have been described. Reactions of 2-N-substituted N-confused tetraphenylporphyrin (2-NCH2YNCTPPH) with Co(SCN)2 afford C-alkylation (14) and C-cyanation (15–17) complexes. The crystal structures for the inner C-alkylation product of thiocyanato(2-aza-2-[p-methylbenzyl]-5,10,15,20-tetraphenyl-21-benzyl-21-carbaporphyrinato-N,N′,N″)cobalt(II)·0.5 octane solvate [Co(2-NCH2-p-CH3C6H4-21-CH2C6H5NCTPP)(NCS)·0.5C8H18; 14·0.5C8H18] and the inner C-cyanation products of thiocyanato(2-aza-2-ethoxycarbonylmethyl-5,10,15,20-tetraphenyl-21-cyano-21-carbaporphyrinato-N,N′,N″)cobalt(II) [Co(2-NCH2COOCH2CH3-21-CN NCTPP) (NCS); 15], thiocyanato(2-aza-2-methyl-5,10,15,20-tetraphenyl-21-cyano-21-carbaporphyrinato-N,N′,N″)cobalt(II)[Co(2-NCH3-21-CNNCTPP) (NCS); 16], and thiocyanato(2-aza-2-benzyl-5,10,15,20-tetraphenyl-21-cyano-21-carbaporphyrinato-N,N′,N″)cobalt(II) [Co(2-NCH2C6H5-21-CNNCTPP) (NCS); 17] have been reported. The geometry around Co2+ ion in these four complexes is a distorted tetrahedron with a C2v symmetry. Two possible mechanisms were proposed to explain the formation of inner C-alkylation (14·0.5C8H18) versus C-cyanation (15–17) products in these complexes with an axial *NCS− ligand.

Density-functional-theory calculations of structural and electronic properties of vacancies in monolayer hexagonal boron nitride (h-BN)

We have carried out the density functional theory calculations of vacancies in monolayer h-BN. We model five configurations, two configurations of monovacancies (VB and VN) and three configurations (VBB, VNN, and VBN) of divacancies. In the case of monovacancies, we find that VB and VN form a C3V symmetry. In the divacancy case, we find that VNN produces a heart-like configuration having two pentagons and leaving two dangling bonds, while VBB leaves four dangling bonds. As for VBN, it produces two pentagons and has no dangling bond. The calculated formation energies of VB,VN,VBB,VNN, and VBN are 11.65 eV, 12.05 eV, 17.59 eV, 22.32 eV, and 16.89 eV, respectively. These energies show that VB is more stable than VN, while VBB is more stable than VNN. We conclude that the N-rich h-BN sheet is energetically more favorable to be formed rather than the B-rich one. However, the most stable configuration of the divacancies belongs to VBN compensating from the absence of the dangling bond, which obeys the dangling-bond-counting-model. Furthermore, we calculate band structures of the most stable mono- and divacancies. We find that monovacancy somewhat changes the electronic structure, shown by localized states near the Fermi level, while the divacancy produces two new states above the Fermi level.

The Imino Stannylene SnNH Incorporated in a Molecular Tin‐Nitrogen Cage and other Tin(II)‐Nitrogen Derivatives

The iminostannylene HNSn was successfully incorporated in a molecular cage of composition (Me2RSi–NSn)3(HNSn) with group R either being a methyl (1) or vinyl (2) substituent. An X‐ray structure analysis reveals that 2 consists of a distorted Sn4N4 cube. The Sn–N(H) bond lengths [2.189(2) Å] are in the range for Sn4N4 hetero cubanes. When stored in a toluene solution the clusters 1 and 2 decompose slowly into the symmetric cubanes (Me2RSi–NSn)4 [R = Me (3), CHCH2 (4)] and an amorphous and insoluble powder of composition HNSn. The decomposition follows a first order rate law as established for 2 with a half life time t1/2 = 320 d at 20 °C. The compounds 1 and 2 can thus be regarded as a result of interaction between three entities {Me2RSi–NSn} and one entity {HNSn}. We also isolated the twistane‐like Me2Si(NtBu)2Sn2NtBu (5) in a crystalline form. The central structure of this molecule, which has almost C2v symmetry, has a trigonal bipyramid Sn2N3 unit with the nitrogen atoms occupying the equatorial plane. Each nitrogen atom has a tert‐butyl ligand and two of the N atoms are further connected by the dimethylsilyl group. There is one nitrogen atom in an almost planar environment (only bonding to tert‐butyl and two tin atoms) with a remarkable short Sn–N bond length of 2.048(5) Å. Both tin atoms in cage 5 can bond to Cr(CO)5 to form [Me2Si(NtBu)2Sn2NtBu][Cr(CO)5]2 (6) with an almost linear Cr–Sn···Sn–Cr arrangement and Sn–Cr bond lengths of 2.581(1) Å (X‐ray diffraction).

Fundamental Intrinsic Lifetimes in Semiconductor Self-Assembled Quantum Dots

The self-assembled quantum dots (QDs) provide an ideal platform for realization of quantum information technology because it provides on demand single photons, entangled photon pairs from biexciton cascade pro- cess, single spin qubits, and so on. The fine structure splitting (FSS) of exciton is a fundamental property of QDs for thees applications. From the symmetry point of view, since the two bright exciton states belong to two different representations for QDs with C2v symmetry, they should not only have different energies, but also have different lifetimes, which is termed exciton lifetime asymmetry. In contrast to extensively studied FSS, the investigation of the exciton lifetime asymmetry is still missed in literature. In this work, we carried out the first investigation of the exciton lifetime asymmetry in self-assembled QDs and presented a theory to deduce lifetime asymmetry indirectly from measurable qualities of QDs. We further revealed that intrinsic lifetimes and their asymmetry are fundamental quantities of QDs, which determine the bound of the extrinsic lifetime asymmetries, polarization angles, FSSs, and their evolution under uniaxial external forces. Our findings provide an important basis to deeply understanding properties of QDs.

Parent bending effects on nonadiabatic transition dynamics: Isotopomer-resolved imaging of photodissociation of CF3Br at two source temperatures.

Nonadiabatic transition between electronic states plays a critical role in the photodissociation of the CX3Y (X = H and F; Y = Cl, Br, and I) system, and the transition probability was considered to be closely related to the X-C-Y bending motion. Hereby the effect of F-C-Br bending vibration on the nonadiabatic transition dynamics is studied by time-sliced ion velocity imaging of Br(2P1/2,3/2) isotopomers produced from the photodissociation of title molecules at two source temperatures, 298 K and 473 K, respectively. At the photolysis wavelength 234 nm, the anisotropy parameter (β) of the Br(2P3/2) products decreases from 1.3 at 298 K to 0.9 at 473 K, while the β of Br(2P1/2) remains at almost 2 at two temperatures, indicating the significant effect of bending excitation on the ground channel. Two nonadiabatic dissociation pathways are suggested in the Br(2P3/2) channel. One of them is the parallel excitation from the ground state to the 3 Q 0 state in C3V symmetry, and then transition to the 1 Q 1 state via conical intersection, and the other is the perpendicular excitation to the 3A' state in Cs symmetry and then decomposition along this state in the presence of the avoided crossing between 3A' and 4A' states. Closely related to the F-C-Br bending vibration of CF3Br is the latter transition.

Syntheses and crystal structures of neodymium(III) and europium(III) complexes bearing dimethyl-, pyrrolidine-, or S-prolinol- dithiocarbamato ligands and their natural and magnetic circular dichroism spectra

A series of NdIII and EuIII complexes containing achiral or chiral dithiocarbamato (dtc) ligands, [Ln(Xdtc)3(NN)] {Ln = Nd or Eu; X = dimethyl- (Me2), pyrrolidine- (pyr), or (S)-prolinol- (S-proOH); NN = 1,10-phenanthroline (phen) or 2,2′-bipyridine (bpy)}, were prepared and their crystal structures and spectroscopic properties, in particular the natural circular dichroism (CD) and magnetic circular dichroism (MCD), were investigated. The crystal structures of the complexes analyzed by the X-ray diffraction method showed an 8-coordinate geometry around the LnIII center with comparable structural parameters to one another and to the related complexes reported previously. These complexes exhibited similar spectral patterns in their absorption, natural CD and MCD spectra in solution. Weak but characteristic sharp f–f transition bands were observed in the absorption and MCD spectra, but no CD signals associated with these transitions were observed even in the S-proOHdtc complexes. The MCD spectral pattern of the EuIII complexes revealed a local C2v symmetry around the LnIII center in solution, in contrast to the aqua and the analogous β-diketonato EuIII complexes.

Revisit of large-gap Si16 clusters encapsulating group-IV metal atoms (Ti, Zr, Hf).

Doped clusters by Si16 cage encapsulating group-IV metal atoms (M@Si16 , M = Ti, Zr and Hf) are computationally investigated by both density functional theory (DFT) and high-level CCSD(T) method. Their low-energy structures are globally searched using a genetic algorithm based on DFT. The ground state structures of neutral and anionic M@Si16 are determined by calculating the vertical and adiabatic detachment energies and comparing them with the experimental data. For neutral Ti@Si16 , the Frank-Kasper (FK) deltahedron with T d symmetry and distorted FK isomer with C3v symmetry are nearly degenerate as the ground state and may coexist in laboratory, while the distorted FK isomer is the most probable structure for Ti@Si16 - anion. For neutral and anionic Zr@Si16 and Hf@Si16 clusters, the ground states at finite temperatures up to 300 K are the fullerene-like D 4d bitruncated square trapezohedron. These theoretical results establish a more complete picture for the most stable structures of M@Si16 clusters, which possess large gaps and may serve as building blocks for electronic and optoelectronic applications.

Synthesis, Structure and Spectroscopic Properties of Oxovanadium Tris(3,5-dimethylpyrazolyl)borate Aroylthiourea Complexes

Aroylthiourea ligands, 1-aroyl-3-cyclohexyl-3-methylthiourea (HL1), 1-(2-chloroaroyl)-3-cyclohexyl-3-methylthiourea (HL2), 1-(3-chloroaroyl)-3-cyclohexyl-3-methylthiourea (HL3) and 1-(4-chloroaroyl)-3-cyclohexyl-3-methylthiourea (HL4) were synthesized through a condensation reaction of methylcyclohexylamine and aroylisothiocyanate with a general formula (X-Ph)(CO)NH(CS)N(C6H5)(CH3) where X = H, o-Cl, m-Cl and p-Cl, fully characterized by CHNS micro elemental analysis, infrared spectroscopy, UV-visible, nuclear magnetic resonance (1H, 13C) and X-ray crystallography. 1-(3-chloroaroyl)-3-cyclohexyl-3-methylthiourea (HL3) crystallized in the monoclinic system, a=14.504(3), b=4.9599(11), c=22.325(5) A, β=98.461(7)°, Z= 4 and V=1588.5(6) A with space group P21/c. The IR spectra of the ligands exhibits the characteristic v(CO) and v(N-H) at range 1701-1640 cm-1 and 3317-3144 cm-1, respectively. Whereas the 1H and 13C NMR spectra shows the resonances for N-H and -CO groups at range 8.3-8.5 and 160-163 ppm, respectively. A one-pot reaction involving the aroylthiourea ligand, oxovanadium(IV) ion and potassium hydrotris(3,5-dimethylpyrazolyl)borate (KTp*) complex gave the desired [oxovanadium(IV)(tris(pyrazolyl)borate)(aroylthiourea)] complexes namely Tp*VOL1, Tp*VOL2, Tp*VOL3 and Tp*VOL4 and all complexes were characterized accordingly. X-ray study showed that Tp*VOL1 adopted a monoclinic crystal, a=3.415(2), b=19.463(3), c=14.22(3) A, β=107.411(4)°, Z= 4 and V=3542.7(11) A with P21/c space group. The VO2+ center adopted a pseudo-octahedral geometry O2N3S, with the oxovanadium(IV) coordinated to the bidentate ligand (X-Ph)(CO)NH(CS)N(C6H5)(CH3) and tridentate Tp* ligands. The results showed that aroylthiourea ligands behave as bidentate chelate through O and S atom and the Tp* C3v symmetry adds stabilization to the VO2+ through its protective tripodal geometry.

Impact of tetrahedral and square planar geometry of Ni(II) complexes with (pseudo)halide ligands to magnetic properties

Four tetracoordinate Ni(II) complexes have been prepared, structurally characterized, and subjected to magnetometric studies. The complexes [Ni(PPh3)2(NCS)2], [Ni(dppp)(NCS)2], and [Ni(dppm)Br2] are planar and thus diamagnetic. The complex [Ni(biqu)Br2] is quasi-tetrahedral, with the geometry close to C2v symmetry, and paramagnetic. While on one side it resembles a prolate bisphenoid (the angle N-Ni-N = 83 deg), on the second side it mimics an oblate bisphenoid (Br-Ni-Br = 126 deg). It exhibits a zero-field splitting of the ground term 3A2 into three crystal-field multiplets that can be described by D and E parameters within the spin Hamiltonian formalism. The ab initio calculations confirm this interpretation; however, the evaluation of the spin-Hamiltonian parameters meets difficulties owing to the quasi-degeneracy of the electronic terms.

13C NMR spectrum of crystalline [Rh(Acac) (CO)2]: A contribution to the discussion on [Rh(Acac) (CO)2] molecular structure in the solid state

13C MAS NMR spectrum of polycrystalline [Rh(Acac) (CO)2] (1) displays separate signals from all 7 carbon atoms: 2 doublets from CO ligand carbons along with 5 singlets from Acac carbons. GIPAW calculation of 13C shielding tensor values also revealed non-equivalence of all carbon atoms in molecule 1 in the anisotropic medium of the crystal lattice. Apparently, the C2v symmetry of molecule 1 is broken owing to the asymmetry of its contacts to the neighboring molecules. For example, the contacts O⋯HC of two CO ligands of molecule 1 to the CH group of the closest molecule in the adjacent stack are markedly different: the distances OH are 2.72 and 4.38 Å, the distances OC are 3.65 and 5.00 Å, the angles OHC are 164.9° and 126.4°.

Conformational analysis, infrared/Raman spectral assignment, and electronic structural studies of 1,3-dimethyl-2-imidazolidinone using quantum chemical calculations

The conformational behavior of 1,3-Dimethyl-2-imidazolidinone (C5H10N2O; DMI) was investigated by quantum chemical calculations and vibrational (IR and Raman) spectral analysis. Ab initio (MP2) and DFT (B3LYP and ωB97XD) methods combined with the 6–311++G (d,p) and aug-cc-pVTZ basis sets were used. Aided by computational outcomes, the twist form (C2) was identified to be the most stable DMI conformer while the transition state planar assumption with C2v symmetry was higher than the twist conformer by 1.5–4.24 kcal/mol. In addition, the envelope form (Cs) was converged close to the planar form after allowing the structural parameters to relax with no constraints on the dihedral angles; therefore, it is not a minimum on the potential energy surface. The observed infrared and Raman spectral data are consistent with C2 molecular symmetry for DMI; therefore, confident vibrational spectral interpretations are reported herein supported by normal coordinate analysis and potential energy distributions (PEDs). The twist-to-planar energy barrier of DMI was predicted owing to the ring puckering using a two-variable scan of the potential energy surface at the B3LYP/6–311++G (d,p) level of theory. Finally, the OVGF and P3 calculations were performed for the twist conformer to predict the vertical ionization energies (IEs) and their corresponding outer-valence HOMOs. The reported gas-phase UV photoelectron spectrum was precisely interpreted. All results were analyzed herein and compared to similar molecules whenever appropriate.