Ground State Geometries Research Articles

Multi-state and Multi-mode Vibronic Coupling Effects in the Photoionization Spectroscopy of Acetaldehyde.

Multi-state and multi-mode vibronic dynamics in the seven energetically low-lying (, , , , , , and ) electronic states of the acetaldehyde radical cation is theoretically studied in this article. Adiabatic energies of these electronic states are calculated by ab initio quantum chemistry methods. A vibronic coupling model of seven electronic states is constructed in a diabatic electronic basis to carry out the first-principles nuclear dynamics study. The vibronic spectrum is calculated and compared with the experimental findings reported in the literature. The progressions of vibrational modes found in the spectrum are assigned. The findings reveal that the and electronic states are energetically well-separated from the other electronic states and the remaining states ( to ) are energetically very close or even quasi-degenerate at the equilibrium geometry of the reference electronic ground state of acetaldehyde. The energetic proximity of to electronic states results in multiple multi-state conical intersections. The impact of electronic nonadiabatic interactions due to conical intersections on the vibronic structure of the photoionization band and nonradiative internal conversion dynamics is discussed.

Understanding interactions between graphene and local anesthetic molecules applied in dentistry – Towards the prolonged effects of local anesthesia

Recent findings have shown that the controlled release of anesthetic molecules via adsorption by nanomaterials is a promising approach to prolonging the effects of local anesthesia. In this work, we have addressed the interactions between graphene and the best-known dental anesthetic molecules: novocaine, lidocaine, and articaine, intending to contribute to developing drug-carrier agents suitable for pain management. A computational study employing various atomistic calculations has been performed to understand in detail how typical representatives of dental anesthetic molecules interact with graphene. The combination of quantum mechanical calculations and molecular dynamics simulations was applied to identify and quantify the non-covalent interactions between graphene and selected anesthetic molecules. Periodic density-functional tight-binding (DFTB) calculations were used to obtain ground state geometries of the system consisting of graphene and adsorbing molecule and calculate the binding energies. Density functional theory (DFT) calculations were used to identify and quantify noncovalent interactions between graphene and adsorbing molecules. Last but not least, molecular dynamics simulations were performed to investigate interactions in water medium, which is important for biomedical applications. It was found that the most prominent prolongation of the anesthetic effect via adsorption by graphene could be potentially achieved in the case of articaine.

Experimental and theoretical studies on prototropic tautomerism of 1-tetralone-2-carbothioamides and synthesis of regioselectively designed fused 2H-indazole derivatives

Condensation of 1-tetralones with phenylisothiocyanate in presence of sodium hydride produced 1-oxo-N-phenyl-1,2,3,4-tetrahydronaphthalene-2-carbothioamides 2a–b. The structure of carbothioamides 2 was established on the basis of spectral data. Prototropic tautomerism studies of carbothioamide 2a were investigated in solution by NMR (1H and 13C NMR), electronic spectroscopy and gas chromatography techniques. The proton transfer behaviour in solid state and gaseous phase was studied utilizing FT-IR and Mass spectral studies, respectively. DFT approach was used to accomplish the theoretical computations. The ground state geometries of different tautomers were optimized using B3LYP method and 6-31G(d) basis set. The vibrational and NMR spectra of different tautomers were calculated and correlated with the experimental results. HOMO-LUMO studies of different probable tautomers of carbothioamide 2a were employed in determination of chemical reactivity descriptors.The dynamic photoisomerization experiments were performed in chloroform under UV irradiation (UV lamp, 15W) and spectra were recorded to investigate the photo dynamic keto ⇌ enol ⇌ thioenol tautomerization. Further, condensation of carbothioamides 2 with hydrazine and its aryl derivatives regioselectively furnished 4,5-dihydro-2H-benzo[g]indazole derivatives 3. Spectrochemical characterizations and single crystal X-ray diffraction analysis of representative indazole derivative 3b resolved the structural ambiguity between the possible 2H-indazole 3 and 1H-indazole 4 regioisomers. Also, the optimized geometric bond lengths and bond angles, obtained by using DFT studies, were compared with the values obtained from X-ray diffraction. The regioselectivity of 3 was justified by root mean square deviations (RMSD) calculations which shows the minimum deviation for 2H-indazole derivative 3.

DFT and CBS Study of Ethyl Acetate Conformers in the Neutral Hydrolysis

First-principles calculations are commonly used to search for possible transition states in reaction kinetics studies, which are such a challenge to observe experimentally. However, computationally studying the reaction is also challenging because of, inter alia, the Basis Set Incompleteness Error (BSIE). Accordingly, we utilized density functional theory-based calculations and the complete basis set method, to confirm the conformational effect in the neutral hydrolysis of three ethyl acetate analogs: ethyl formate, ethyl acetate, and ethyl fluoroacetate. The results showed that both methods yielded activation energy span, which implies that the conformational effect in the ethyl acetate neutral hydrolysis is not due to the BSIE. The results also demonstrated the importance of polarization and diffuse function in a basis set. The former was to improve the ground state geometry, and the latter was to increase the activation energy.

Studying the Formation of Choline Chloride- and Glucose-Based Natural Deep Eutectic Solvent at the Molecular Level.

The liquid waste is the major source of waste, which usually generated from academic laboratories and industry during the extraction, separation, chemical synthesis, and pretreatment processes. These chemical and engineering processes require more solvents. In this regard, there is a need to develop more environmentally friendly, cheaper, non-toxic solvents that are harmless to humans and the environment. In this regard, deep eutectic solvents (DES) and their derivatives so-called natural deep eutectic solvents (NADES) are a new field in the search for green alternative solvents. In our work, the formation of choline chloride-based NADESs using density functional theory (DFT) calculations, and classical all-atom molecular dynamics (MD) simulation was studied in detail using Gaussian09 and Gromacs software's. Next, the ground state geometry optimizations were performed in the gas phase using DFT B3LYP 6-31 + G(d) level of theory. Moreover, classical all-atom MD simulations were implemented using Gromos force field. After the modeling and simulations, the DFT calculation results revealed the formation of NADESs via formation (creation) of binding between chlorine and choline, and chlorine and glucose. At the same time, the results of classical all-atom MD simulations, based on the time average of the equilibrated production run of MD simulations, stated that the nitrogen atom of choline ion and chloride ion has greater interactions, while chloride ion has also greater interaction with glucose during formation of NADES. The outcomes of both DFT and classical all-atom MD simulations are in good agreements.

Spectroscopic Investigation, DFT Calculations, anti-Inflammatory Activity and Molecular Dynamic Simulation Study on Fagaramide Alkaloid

Fagaramide (FA) alkaloid was investigated experimentally using FT-IR, FT-Raman and NMR (1H and 13C) spectra, also theoretically studied using density functional theory (DFT) calculations. To obtain the ground state geometry and vibrational frequencies of FA molecule, DFT calculations were performed at the B3LYP/6-31++G(d,p) level. The potential energy distribution (PED) analysis of the title molecule was obtained with the help of normal co-ordinate analysis (NCA) and these assignments were compared with the experimental FT-IR and FT-Raman spectrum. The natural bond orbital (NBO), reduced density gradient (RDG) and Hirshfeld surface analysis were applied to evaluate the relative strength of hydrogen bond interaction and to represent their effect on the stabilization of molecular arrangements. Electron localization function (ELF) and localized orbital locator (LOL) maps were generated to show electron delocalization in the molecule. The reactivity of the molecule was studied by the investigation of frontier molecular orbital analysis, density of states (DOS), molecular electrostatic potential (MEP) and chemical reactivity descriptors. Furthermore, through molecular docking, the anti-inflammatory activity of FA was studied and discussed. A molecular dynamic simulation (MDS) was employed to explore biomolecular stability.

Hydrogen and halogen bonding in H2O-HF and H2O-F2 complexes

Five-dimensional morphed potentials have been generated for the prototype hydrogen-bonded H2O-HF and halogen-bonded H2O-F2. These determined morphed potentials formed the basis for modeling the dynamics of the complexes and predicting accurate intermolecular rovibrational frequencies. The discrepancy between previous experimental and ab initio predictions for the dissociation energy of the H2O-HF complex is discussed. Predictions based on the morphed potential and application of the Badger-Bauer rule give better estimates for the dissociation energy of the H2O-HF complex, that are in better agreement with the experimental prediction. It is found that the H2O-HF and H2O-F2 complexes have similar equilibrium and ground state geometries. This is in agreement with recent developed canonical approaches to potential energy surfaces, which demonstrated that there are no fundamental distinctions between hydrogen and halogen bonds.

DFT and TD-DFT studies of 1,3,5-Tris (dipheny1amino) benzene derivatives based hole transport materials: application for perovskite solar cells

The current study examined a series of 1,3,5-tris (diphenylamino) benzene derivatives used as hole transport materials in perovskite solar cells (HTM1-HTM9). All calculations were performed utilizing the density functional theory (DFT) and TD/DFT procedures at B3LYP/6-311G level. The ground state geometry, frontier molecular orbital (FMO), photoelectric properties and reorganization energies and the absorption spectra were investigated. The energy levels of highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecular orbitals (LUMOs) were calculated for HTM1-HTM9, compared to all of the compounds under investigation and the spiro-OMeTAD, HTM 8 has the lowest HOMO energy level, indicating a favourable overlap with the MAPbI3 perovskite active layer.

Synthesis, crystal structures, DFT calculations, and catalytic application in hydrosilylation of acetophenone derivatives with triethylsilane of novel rhoduim-N-heterocyclic carbene (NHCs) complex

N-Heterocylic carbenes (NHCs) and their role as universal spectator ligands in transition metal compounds have recently sparked a wide interest in the broader field of green chemistry because of their astounding catalytic properties in reactions involving organic synthesis. In this study, a new rhodium based complex has been developed that incorporate an N-heterocyclic carbene ligand. This rhodium(I) N-heterocyclic carbene complex was characterized fully and the solid-state single crystal X-ray structure of the complex was discussed. Single-crystal X-ray diffraction analysis indicates that this complex crystallizes in the centrosymmetric space group Pbca of the orthorhombic system. The carbene complex exhibits the same general structural motif with slightly distorted square-planar geometry. The ground state geometry of the complex was optimized using density functional theory (DFT) at mixed double ζ basis set, 6-31G(d) for H, C, N, O and Cl and LANL2DZ for Rh. The presence of the different functional groups and the nature of their vibrations were identified by the experimental and theoretical infrared spectra. The optical properties of the studied complex were determined experimentally using UV-visible and photoluminescence techniques in solid state and theoretically using the TD-DFT method. Hirshfeld surface analysis employing 3D molecular surface contours and 2D fingerprint plots has been used to analyze intermolecular interactions present in the solid state.The utility of this complex as catalyst precursor for in the hydrosilylation of acetophenone derivatives with triethylsilane at 80 °C for 2 h using 1 mol% of the rhodium complexes was studied.The new rhodium(I) N-heterocyclic carbene complex 3 were also tested against MCF7 and MDA-MB-231 cancer cells, as well as Micrococcus luteus LB 14,110, Listeria monocytogenes ATCC 19,117, S. Typhimurium ATCC 14,028, Staphylococcus aureus ATCC 6538, Pseudomonas aeruginosa, and Candida albicans microorganisms.

A novel copper (II) complex containing pyrimidine-4-carboxylic acid: Synthesis, crystal structure, DFT studies, and molecular docking

A new Cu(II) complex of pyrimidine-4-carboxylic acid was synthesized and characterized through a combination of single-crystal XRD, Ultraviolet-Visible (UV-Vis), and Fourier Transform Infrared Spectroscopy (FT-IR). The Cu(II) complex adopts six-coordinate, distorted octahedral geometry around the Cu (II) center. The ground state geometry of the copper compound was optimized using the Density Functional Theory (DFT) method with unrestricted hybrid density functional B3LYP. The vibrational spectra of the Cu(II) complex and similar molecules were described and compared with calculated data obtained by the DFT/UB3LYP/6–31G(d,p) method. The experimental UV-Vis absorption spectrum was compared to the simulated data using time-dependent (TD)-DFT. The effect of the solvent was carried out using the integral equation formalism-polarized continuum model (IEF-PCM). Global reactivity descriptors (ionization potential, chemical hardness, electron affinity, etc.) were surveyed by using the DFT/UB3LYP and DFT/UCAM-B3LYP methods. The non-linear optical (NLO) parameters of the complex were calculated by using the UB3LYP method with 6–31G(d,p) basis set. Furthermore, the molecular docking study was also performed to display interactions between the B-DNA and the Cu(II) complex.

Revealing the exotic structure of molecules in strong magnetic fields.

A novel implementation for the calculation of molecular gradients under strong magnetic fields is employed at the current-density functional theory level to optimize the geometries of molecular structures, which change significantly under these conditions. An analog of the ab initio random structure search is utilized to determine the ground-state equilibrium geometries for Hen and CHn systems at high magnetic field strengths, revealing the most stable structures to be those in high-spin states with a planar geometry aligned perpendicular to the field. The electron and current densities for these systems have also been investigated to develop an explanation of chemical bonding in the strong field regime, providing an insight into the exotic chemistry present in these extreme environments.

Integrated Approach to Interaction Studies of Pyrene Derivatives with Bovine Serum Albumin: Insights from Theory and Experiment.

This work aimed to investigate the interaction of bovine serum albumin with newly synthesized potent new pyrene derivatives (PS1 and PS2), which might prove useful to have a better antibacterial character as found for similar compounds in the previous report [Low et al. Bioconjugate Chemistry2014, 12, 2269−2284]. However, to date, binding studies with plasma protein are still unknown. Steady-state fluorescence spectroscopy and lifetime fluorescence studies show that the static interaction binding mode and binding constants of PS1 and PS2 are 7.39 and 7.81 [Kb × 105 (M–1)], respectively. The experimental results suggest that hydrophobic forces play a crucial role in interacting pyrene derivatives with BSA protein. To verify this, molecular docking and molecular dynamics simulations were performed to predict the nature of the interaction and the dynamic behavior of the two compounds in the BSA complex, PS1 and PS2, under physiological conditions of pH = 7.1. In addition, the free energies of binding for the BSA-PS1 and BSA-PS2 complexes were estimated at 300 K based on the molecular mechanics of the Poisson–Boltzmann surface (MMPBSA) with the Gromacs package. PS2 was found to have a higher binding affinity than PS1. To determine the behavior of the orbital transitions in the ground state geometry, we found that both compounds have similar orbital transitions from HOMO–LUMO via π → π* and HOMO–1–LUMO+1 via n → π*, which was included in the FMO analysis. A cytotoxicity study was performed to determine the toxicity of the compounds. Based on the MD study, the stability of the compounds with BSA and the dynamic binding modes were further revealed, as well as the nature of the binding force components involved and the important residues involved in the binding process. From the binding energy analysis, it can be assumed that PS2 may be more active than PS1.

Nonlinear optical response of 9,10-bis(phenylethynyl)anthracene mediated by electron donating and electron withdrawing substituents: A density functional theory approach

Herein, we report linear polarizibilty (α) and hyperpolarizibility (β) of anthracyl-based organic materials containing electron acceptor (NO2) and electron donor (NH2) moieties. Six compounds (a–f) were designed by structural modification of a reported chromophore 9,10-bis(phenylethynyl)anthracene (R). Ground state geometries, HOMO-LUMO energies polarizability, first hyperpolarizability and natural bond orbital (NBO) analyses of all compounds (R and a–f) were studied through density functional theory. FMO's results showed that the energy gaps of designed molecules a–f (1.791–2.215eV) were much lower than parent molecule R (2.606 eV). UV Visible analysis of designed compounds showed a red shift in the absorption spectrum as compared with reference molecule (R). The highest λmax was observed for compound c (816.7 nm). NLO analysis and hyper polarizibility values computed for compounds a-f were much higher than reference compound R (0.023 a.u.). The observed red shifts in the absorption spectra indicated the decrease in excitation energy, an important factor in enhancing NLO response. Overall, compound c showed larger αtotal and βtotal values of 575.9 a.u. (LC-BLYP/6–31++G(d,p), and 58156.8 a.u. (LC-BLYP/6–31++G(d,p), respectively. The findings of our study provide a theoretical platform for useful conversion of centrosymmetric compounds to non-centrosymmetric materials for enhancing the NLO behavior through structural modifications for modern technological applications.

Photoluminescent complexes of Eu(III), Tb(III) and Gd(III) with 3-thiopheneacetate and 4,4′-dimethyl-2,2′-bipyridine: Synthesis, characterization and photophysical properties

Three crystals of lanthanide complexes with 3-thiophenoacetic acid (3-HTAA) and 4,4′-dimethyl-2,2′-bipyridine (dmbpy) ligands were synthesized. The structures of the complexes [Ln2(3-TAA)6(dmbpy)2] [Ln = Eu(III), Tb(III), Gd(III)] were determined by single crystal X-ray diffraction, where all crystals are isostructural and belong to the triclinic crystal system with P-1 space group. The complexes were characterized by CHN elemental analysis and spectroscopic techniques in the Infra-red region and Raman scattering. The dimeric structures have different modes of coordination using carboxylic and nitrogen groups present in the ligands. To investigate the photoluminescence properties, the Eu(III) and Gd(III) complexes was selected. The triplet state (23,529 cm−1) was determined by the emission spectrum of the Gd(III) complex. Sparkle/PM3 model was also used to predict the ground state geometries of the Eu(III) complex. The intensity parameters (Ω2, Ω4 and Ω6), energy transfer rates, radiative and non-radiative rates (Arad and Anrad), quantum efficiency (η) and quantum yield (q) were determined by quantum mechanics calculation using the LUMPAC software. Crystal structures, spectroscopic properties and their photoluminescence behavior are discussed.

Internal dynamics of methyl p-tolyl sulfoxide in the gas phase: Rotational spectroscopy and theoretical studies.

A pure rotational spectrum of methyl p-tolyl sulfoxide (MTSO) was studied using chirped-pulse Fourier transform microwave spectroscopy in the frequency range of 18-26GHz. A single conformer was unambiguously observed in the supersonic jet expansion, which is consistent with the conformational analysis performed using quantum-chemical calculations. Rotational transitions were split into two components of A and E symmetries due to the low-barrier internal rotation of the ring methyl group [V3 = 11.0178(23) cm-1]. The low energy barrier for the methyl top internal rotation implies an electron-withdrawing effect of the group at the opposite side of the phenyl ring, in comparison with other para-substituted toluenes. The effective ground state (r0) geometry was derived using the rotational constants from the parent species and the 34S and eight 13C singly substituted isotopologues. Compared to two other sulfoxides, methyl phenyl sulfoxide and methyl 4-nitrophenyl sulfoxide, the sulfoxide group in MTSO is slightly more twisted with respect to the plane of the phenyl ring, which could be attributed to the moderate electron-donating effect of the p-methyl group. Furthermore, the pyramidal inversion that interconverts the handedness at the sulfur stereogenic center was explored in the electronic ground (S0) and excited (S1) states with nudged elastic band and time-dependent density functional theory methods. It was found that the pyramidal inversion in S1 is easier than in S0, showing that optical excitation to S1 will facilitate an effectively barrier-free inversion.

Crystal structure, optical properties, spectroscopic characterization and density functional theory studies of a new rhodium(i)-imidazolidin-2-ylidene complexes: Synthesis, characterization and cytotoxic properties

Rhodium(I) complexes bearing imidazolidin-2-ylidene ligands have been widely used in catalytic chemistry, but there are very few reports of the biological properties of these type complexes. A series of [RhCl(COD)(NHC)] complexes were synthesized. The structures of all compounds were characterized by 1H NMR, 13C NMR, IR and elemental analysis techniques, which supported the proposed structures. The single-crystal structures of complexes 1a and 1c have been determined. Single-crystal X-ray diffraction analysis indicates that complexes 1a and 1c crystallize in the centrosymmetric space groups P n m a and I 1 2/a 1 of the orthorhombic and monoclinic systems respectively. The ground state geometry of these complexes was optimized using density functional theory (DFT) at mixed double ζ basis set, 6-31G(d) for H, C, N, O and Cl and LANL2DZ for Rh. The presence of the different functional groups and the nature of their vibrations were identified by the experimental and theoretical infrared spectra. The optical properties of the studied complex were determined experimentally using UV–visible and photoluminescence techniques in solid-state and theoretically using the TD-DFT method. Hirshfeld surface analysis employing 3D molecular surface contours and 2D fingerprint plots has been used to analyze intermolecular interactions present in the solid-state. The cytotoxic properties of the rhodium(I)–NHC complexes have been assessed in various human cancer lines, including cisplatin-sensitive and resistant cells. IC50 values of these four complexes were determined by the MTS-based assay on three human cancer cell lines; brain (SH-SY5Y), colon (HTC116), and liver (Hep 3B). Substances 1a-d showed 100% anticarcinogenic effect in cancer cell lines at 50 and 100 µM.

Effect of Exchange–correlation Functionals on Ground State Geometries, Optoelectronic and Charge Transfer of Triphenylamine-based Dyes

The importance of the Density Functional Theory (DFT) calculation approach lies in their ability to provide a highly accurate prediction of structural and optoelectronic properties. However, the traditional methods of DFT failed to predict optoelectronic properties satisfactorily. Therefore, it will be necessary to examine methods containing different percentages of Hartree-Fock exchange and correlation in order to find the most suitable functionals. DFT and Time-Dependent-DFT (TD-DFT) calculations was carried out using four different functionals approximations incorporating a different amount of Hartree Fock exchange (B3LYP, BHandHLYP, CAM-B3LYP and LCωPBE), in order to evaluate their accuracies to predict the geometrical, optoelectronic and charge transfer properties of four triphenylamine-based dyes for Dye-Sensitized Solar Cells (DSSCs) applications. The functional hybrid B3LYP was the best among adopted functional that reproduced the geometrical, optoelectronic and charge transfer properties. On the other hand, it has been shown that the Hartree-Fock exchange percentage for BHandHLYP, significantly improved TD-DFT results in the case of organic dyes. Moreover, the corrected long-range functionals (CAM-B3LYP and LC-wPBE) present valuable tools for giving results of comparable precision with experimental optical data. In terms of the choice of the most appropriate functional for computational calculation, the obtained results can be useful for future DSSC applications. DOI: http://dx.doi.org/10.17807/orbital.v14i1.1682

The Excited State and Charge Transfer of Two Nonfullerene Acceptors from First-Principles Many-Body Green’s Function Theory

Nonfullerene acceptors (NFAs) have shown an outstanding performance upon producing highly efficient and sustainable organic solar cells (OSC). Recently, a growing group of researchers denoted to modify the structures of acceptor−donor−acceptor-type NFAs to raise the power conversion efficiencies (PCEs) when they are blended with a variety of polymer donors in OSC. In 2020, the ketone on the ending groups of BTP-IC were substituted for sulfonyl; the new NFA named BTP-IS was synthetized. The PCE of BTP-IS based OSC is 5.25% higher than that of the BTP-IC device. Based on this, the many-body Green’s function theory, combined with other quantum chemical methods, is conducted to study their ground electronic structures, excited states, and absorption spectra. The ground-state geometries, ionization energies, and the excited state energies are deeply sensitive to exchange-correlation functionals used in calculations. The lowest excited state energies calculated by full-BSE method using DFT-PBE as the starting point is 0.07~0.14 eV smaller than that by TDDFT-PBE method, which is more consistent with experimental data. This provided a methodology for future research on similar NFA systems. The first charge-transfer states and transfer mechanism of two molecules are proposed in this paper. Furthermore, we found that the reason for more efficient charge transport in BTP-IS-based OSC is the larger ionization energies and much weaker electron-hole interaction in BTP-IS. This finding is conducive to the better application of BTP-IS in OSC field.

Phytochemical, pharmacological and in silico studies on Teucrium stocksianum Bioss

A new triol-based compound, teucriol (1) and eleven others (2–12), were first time isolated from the ethanol extract of Teucrium stocksianum Bioss using bioassay guidelines, and their structures were established using various spectroscopic techniques. Antibacterial, antifungal, insecticidal, cytotoxic, phytotoxic, and antioxidant properties of ethanol extract fractions and a novel isolate were tested. When compared to the standard ceftriaxone, the extract, fractions, and novel isolate demonstrated good antibacterial potential against Streptococcus pneumonia, Staphylococcus aureus, Klebsiella pneumonia and Escherichia coli bacteria, while all were inert against Fusarium solani, Candida albicans, Candida glabrata, Microsporum Canis and Aspergillus flavus fungi, and Tribolium castaneum and Rhyzopertha dominica insects.All fractions showed promising antioxidant activity. Density functional theory was used to optimize the ground state geometry of teucriol (1) at the B3LYP/TZ2P level. The global molecular descriptors, electronic characteristics, molecular electrostatic potential, and Hirshfeld surface analyses were studied to investigate the biological activity of the investigated molecule.

Coordination Chemistry of the Parent Dithiocarbamate H2NCS2-: Organometallic Chemistry and Tris-Chelates of Group 9 Metals.

Two tris-chelate complexes of cobalt and rhodium and two complexes of Ru(II) of dithiocarbamate, [S2CNH2]-, were synthesized. The complexes were spectroscopically characterized by IR, NMR, UV-vis, and MS and structurally characterized by X-ray diffraction. The structural features of the rhodium complex were compared to those of other tris-chelate Rh(III) dithiocarbamate complexes and are characterized by a change in the ground-state geometry in comparison to expected octahedral tris-chelate complexes. This was confirmed both experimentally by X-ray diffraction and theoretically using DFT calculations. The inversion barriers of Rh(Bz2dtc)3, Ir(Bz2dtc)3, and Rh(Et2dtc)3 were determined using VT-NMR in DMSO. These barriers were found to be surprisingly low for heavy group 9 elements of d6 tris-chelate complexes: values of 16.7, 17.1, and 16.4 kcal/mol were calculated, respectively. By comparing structural features, we are able to determine that the activation barrier for the inversion of stereochemistry of Rh(H2dtc)3 must have a similarly low value. A modified version of the Bailar twist involving an intermediate with C3h geometry was proposed as the mechanism of inversion.