Basis Set Combinations Research Articles

Adsorption of Industrial Gases (CH4, CO2, and CO) on Olympicene: A DFT and CCSD(T) Investigation.

Olympicene C19H12, an organic semiconductor, is investigated as an adsorption material for toxic industrial gas molecules such as CH4, CO2, and CO. A deep insight of complexation of CH4, CO2, and CO with olympicene (analyte@OLY) was obtained by interaction energy, symmetry-adopted perturbation theory (SAPT2+), quantum theory of atoms in molecules (QTAIM), density of states (DOS), noncovalent interaction (NCI), and frontier molecular orbital and natural bond orbital analysis. Domain-based local pair natural orbital coupled cluster theory single-point energy calculations were performed using the cc-pVTZ basis set in combination with corresponding auxiliary cc-pVTZ/JK and cc-pVTZ/C basis sets. For all property calculations of doped olympicene complexes, the ωB97M-V functional was employed. The stability trend for interaction energies is CO2@OLY > CH4@OLY > CO@OLY. QTAIM and NCI analysis confirmed the presence of NCIs, where the dispersion factor (in CH4@OLY) has the highest contribution, as revealed from SAPT2+. The chemical sensitivity of the system was evidenced by the origination of new energy states in DOS spectra. The recovery time for the analyte@OLY complex was calculated at 300 K, and an excellent recovery response was observed. All results evidently indicated weak interactions of the olympicene surface with CH4, CO2, and CO.

Tuning the optoelectronic properties of cross conjugated small molecules using benzodithiophene as a core unit with favorable photovoltaic parameters: a DFT study

In a recent study, cross conjugated molecules (BDT-C1 to BDT-C6) based on Benzo [1,2-b:4,5-b'] (BDT) as core units linked with different acceptor moieties are designed for encouraging photovoltaic applications. The optoelectronic study has been conducted by density functional theory (DFT) at B3LYP 6-31G (d, p) basis set combination by equating them with recently reported cross conjugated reference (BDT-CR) molecule and to study basic parameters such as frontier molecular orbital, the density of states, reorganization energy, maximum absorption, dipole moment, transition density matrix (TDM) and open-circuit voltage (V OC). Six new cross conjugated molecules (BDT-C1 to BDT-C6) with modified acceptor moieties are designed to evaluate their photophysical behavior in photovoltaic cells and the optoelectronic analysis of designed molecules indicates that among all cross conjugated molecules, BDT-C3 molecule exhibited the lowest bandgap value (1.84 eV) and broad absorption (747 nm) spectrum in dichloromethane due to extended conjugation in molecule than BDT-CR. TDM results reveal the easy dissociation of exciton due to the transfer of electron density in a diagonal direction from donor to acceptor moieties. The lowest value of electron mobility (0.0030 eV) and hole mobility (0.0027 eV) of BDT-C4 indicates its excellent electron and hole transfer behavior. The newly architecture molecule BDT-C1 displayed the highest V OC value of 1.52 eV concerning PC61BM. All above-mentioned outcomes reflect that our newly architecture cross conjugated molecules are suitable applicants for photovoltaic cells and can exhibit wonderful results in the quest of power conversion efficiency.

Spectroscopic, conformational analysis, structural benchmarking, excited state dynamics, and the photovoltaic properties of Enalapril and Lisinopril

There have been numerous attempts to theoretically design a better photovoltaic property with much interest on how to improved absorption and emission parameters of most reactive compounds in respect to dye – sensitized solar cells (DSSCs). This is regardless of the promising futures of the photovoltaic properties. However, for such effective design, it is necessary to understand the electronic and photophysical properties of the dye systems. Herein detailed density functional theory (DFT) and time – dependent DFT (TD-DFT) investigation of the excited state characteristics and the influence of various solvents: water, acetone, ethanol and chloroform on the photophysical properties of enalapril and lisinopril were investigated along with the experimental spectral (UV–vis and FT-IR) analysis. The electronic structure calculations were conducted using the 6–311++G(d,p) basis set in combination with B3LYP, M06-2X, and ꞷB97XD DFT functionals for the structural benchmarking investigations of the studied compounds. Results of the excitation electronic analysis of enalapril was observed to have wavelength absorption in the order gas > chloroform > ethanol > water which correspond to 229.19, 228.81, 228.85, 229.03 nm respectively while Lisinopril have the order of chloroform > gas > water > ethanol which present ethanol have the highest transition energy. In all the studied structured, the transition assignment corresponds to π → π* all corresponding to the Frank -Condon local excitation. It can be inferred from the photovoltaic properties that among the studied compounds in four different phases enalapril have the highest oscillator strength, but the values of light-harvesting efficiency (LHE) varies and show greater stability in Lisinopril. Lisinopril was observed to have the highest value of VOC compared to Enalapril this further confirmed the result obtained from the frontier molecular orbitals.

Exchange Functionals and Basis Sets for Density Functional Theory Studies of Water Splitting on Selected ZnO Nanocluster Catalysts.

In this communication, we use density functional theory (DFT) to study the structural (geometry) and electronic properties (vertical detachment energy and electron affinity) of ZnO monomers and dimers that can be used to form ZnO clusters of different sizes, with a view to adapting one or more of them as catalysts or photocatalysts, standing alone or on suitable substrates like graphene, to split water. We also investigate different pairs of exchange functionals and basis sets to optimize their choice in our DFT calculations and to compare the singlet–triplet energy gaps of small ZnO clusters of different sizes to select an optimal cluster size for water splitting. We find that the B3LYP/DGDZVP2 exchange functional/basis set is a reliable combination for use with DFT to calculate the geometry and electronic properties of small ZnO nanoclusters from among several other combinations of exchange functionals and basis sets. Comparisons of the singlet–triplet energy gaps show that the trimer (ZnO)3 has an energy gap of 58.66 k cal/mol. which is approximately equal to the energy of a visible photon at a wavelength of 500 nm, and a HOMO–LUMO gap of 4.4 eV, making it a suitable choice of photocatalyst for the oxidation of water from among six (ZnO)n nanoclusters of monomers, with n ranging from 1 to 6. We used this exchange functional/basis set to study the structural and energetic details of hydration and hydrolysis of water absorbed on the (ZnO)3 nanocatalyst and calculated the corresponding potential energy profiles to identify three sets of singlet–triplet pathways for water splitting. Detailed study of a pathway showed that oxygen is produced after hydrogen, and the rate-determining step is the formation of hydrogen.

Towards Elucidating Structure-Spectra Relationships in Rhamnogalacturonan II: Computational Protocols for Accurate 13C and 1H Shifts for Apiose and Its Borate Esters.

Apiose is a naturally occurring, uncommon branched-chain pentose found in plant cell walls as part of the complex polysaccharide Rhamnogalacturonan II (RG-II). The structural elucidation of the three-dimensional structure of RG-II by nuclear magnetic resonance (NMR) spectroscopy is significantly complicated by the ability of apiose to cross-link via borate ester linkages to form RG-II dimers. Here, we developed a computational approach to gain insight into the structure–spectra relationships of apio–borate complexes in an effort to complement experimental assignments of NMR signals in RG-II. Our protocol involved structure optimizations using density functional theory (DFT) followed by isotropic magnetic shielding constant calculations using the gauge-invariant atomic orbital (GIAO) approach to predict chemical shifts. We evaluated the accuracy of 23 different functional–basis set (FBS) combinations with and without implicit solvation for predicting the experimental 1H and 13C shifts of a methyl apioside and its three borate derivatives. The computed NMR predictions were evaluated on the basis of the overall shift accuracy, relative shift ordering, and the ability to distinguish between dimers and monomers. We demonstrate that the consideration of implicit solvation during geometry optimizations in addition to the magnetic shielding constant calculations greatly increases the accuracy of NMR chemical shift predictions and can correctly reproduce the ordering of the 13C shifts and yield predictions that are, on average, within 1.50 ppm for 13C and 0.12 ppm for 1H shifts for apio–borate compounds.

Molecular Adsorption of H2 on Small Neutral Silver-Copper Bimetallic Nanoparticles: A Search for Novel Hydrogen Storage Materials.

In the search for novel hydrogen storage materials, neutral silver–copper bimetallic nanoparticles up to the size of eight atoms (CumAgn: m + n ≤ 8) have been computationally studied. Density functional theory with the B3LYP exchange–correlation functional and the combined basis sets of LanL2DZ and aug-cc-pVQZ were used in all of the calculations. H2 adsorption studies on the most stable cluster geometries of all of the neat and heterogeneous entities found that 12 potential candidates, CuAg4, Cu6, Cu5Ag, Cu4Ag2, Cu3Ag3, Cu2Ag4, CuAg6, Cu5Ag3, Cu4Ag4, Cu3Ag5, Cu2Ag6, and CuAg7, fall within the recommended physisorption range of −18 to −6 kJ mol–1. A correlation in the behavior of binding energy, vibrational frequency, average bond distance, highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) gap, and chemical hardness with H2 adsorption was observed. This analysis further revealed that the H2 adsorption to the cluster was either a parallel or a perpendicular alignment. The analysis of the electron configuration of each atom in the cluster and the H2 molecule and the charge transfer analysis of these 12 clusters also showed that the physisorption in the perpendicular mechanism is due to an induced dipole interaction, while that in the parallel mechanism is due to a weak ionic interaction. The clusters identified with perpendicular adsorption, CuAg4H2, Cu6H2, Cu3Ag3H2, and Cu2Ag4H2, polarized the H2 molecule but had no charge transfer with the H2 molecule and those identified with parallel adsorption, Cu5AgH2, Cu4Ag2H2, CuAg6H2, Cu5Ag3H2, Cu4Ag4H2, Cu3Ag5H2, Cu2Ag6H2, and CuAg7H2, pulled the electrons from the H2 molecule and had charge transfer with the H2 molecule. The shapes of the frontier molecular orbital diagrams of the HOMO and LUMO also followed this observation.

T-Matrix based Scattering Analysis of Photonic Materials with Periodicity in Different Dimensions

Optical devices and artificial photonic materials frequently make use of periodic arrangements of identical scatterers in 3D, 2D, and 1D, e.g. photonic crystals, meta-surfaces, or particle chains. To simplify their analysis, we present here a computational framework based on the T-matrix method that explicitly exploits spherical, cylindrical, and plane waves depending on the geometry and number of dimensions of the lattice. Due to the analytic properties of the chosen basis sets in combination with the use of Ewald’s method for the lattice summation, we obtain an efficient framework to simulate such systems. The applicability will be illustrated at the conference by means of selected examples of contemporary interest.

Synthesis, antibacterial, antifungal and computational study of (E)-4-(3-(2,3-dihydrobenzo[b][1,4]dioxin-6-yl)-3-oxoprop-1-en-1-yl)benzonitrile

In the present work, synthesis, antibacterial, antifungal and computational study of synthesized (E)-4-(3-(2,3-dihydrobenzo[b][1,4]dioxin-6-yl)-3-oxoprop-1-en-1-yl)benzonitrile (DHDOBN) chalcone derivative were explored. The computational study of the DHDOBN was performed using density functional theory (DFT) with B3LYP functional and 6-31G(d,p) basis set combination. Theoretical investigations about UV–vis and FT-IR spectral investigation of the DHDOBN was reported using TD-DFT/B3LYP/6-31G(d,p) and B3LYP/6-31G(d,p) levels, respectively. The computed UV–vis and FT-IR absorption spectral properties accord well with the outcomes of the experiments. The formation of the charge separation state as a result of the successful migration of electrons from the donor to acceptor unit through the π-bridge was confirmed by the analysis of electronic properties, including the frontier molecular orbitals (FMOs) analysis, molecular electrostatic surface potential (MESP), hole density distribution (HDD), and electron density distribution (EDD) map. highest occupied molecular orbital (HOMO) and lowest occupied molecular orbital (LUMO) energy values were used to compute the ionisation potential, electron affinity, electronegativity, chemical hardness and softness, global electrophilicity, and chemical potential of the titled compound. The examined compound's significant DFT features were compared with those of other compounds that have been previously reported. In compound DHDOBN strong electron-withdrawing –CN group present at the para position makes the titled compound kinetically more reactive. The small EHOMO and ELUMO energy gap due to cyano group makes it soft and more polarizable molecule. The DHDOBN compound was tested for antibacterial activity against two Gram-negative bacterial strains namely E. coli and P. Vulgaris and two Gram-positive bacterial strains namely S. aureus and B. subtilis, whereas fungal inhibitory action was tested against A. Niger and C. albicans. The DHDOBN compound was revealed to show moderate antibacterial and antifungal potential.

Spectroscopic Identification, Structural Features and Molecular Docking Studies on 5-(4-Propoxybenzylidene)-2-[3-(4-chlorophenyl)-5-[4(propan-2-yl) phenyl-4,5-dihydro- 1H-pyrazol-1-yl]-1,3-thiazol-4(5H)-one using Pim-1 Kinase Cancer Protein

A comprehensive investigation of the molecular structure, electronic properties and vibrational spectra of 5-(4-propoxybenzylidene)-2-[3-(4-chlorophenyl)-5-[4-(propan-2-yl)phenyl]-4,5-dihydro-1Hpyrazol- 1-yl]-1,3-thiazol-4(5H)-one have been studied. Many natural and/or synthetic compounds contain, thiazole which are attractive compounds found in the building of numerous natural products and certain pharmaceutical agents. To understand the molecular-orbital interaction and structural investigation of the title compound, the density functional theory (DFT) calculation has been carried out using B3LYP/6-31G and 6-311G basis sets combination. The experimental FT-IR, FT-Raman spectral data along with theoretical quantum chemical calculation were investigated. For potential energy distributions (PED) analysis, the VEDA 4 program is utilized to do comparative frequency assignments. With the optimized structures, the highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO) energies, molecular electrostatic potential (MEP) and natural bond orbital (NBO) were applied to describe the chemical reactivity.The electron density interactions distributed in space, which exist within these compounds are analyzed by different topological methods namely, atom in molecule (AIM), localized orbital locator (LOL), electron localization function (ELF) and the reduced density gradient (RDG). Finally, the molecular docking studies of the title compound for potent Pim-1 kinase cancer PDB ID: 3A99, 1GJ8, 1XQZ was investigated using theAuto Dock program

Optimized Pseudopotentials and Basis Sets for Semiempirical Density Functional Theory for Electrocatalysis Applications.

A complete set of Goedecker, Teter, and Hutter (GTH) norm-conserving pseudopotentials (PPs) have been optimized, in conjunction with molecular optimized (MOLOPT) basis sets, for both the B97M-rV and ωB97X-V density functionals for members of the main-group elements and 3d and noble metals. The resulting small-core PPs and corresponding DZVP, TZVP, and TZV2P basis sets yield notable improvements compared to the original PBE defaults when validated against all electron calculations for redox reaction energies and geometries, binding energies, and vibrational Stark effects for metal monocarbonyls in vacuum. Further validation of the optimized PP/MOLOPT basis set combinations was performed using ab initio molecular dynamics simulations and shows greatly improved agreement with experimental trends for metal surface relaxations and the adsorption behavior of CO on solid metal surfaces.

A comparison of three DFT exchange-correlation functionals and two basis sets for the prediction of the conformation distribution of hydrated polyglycine.

The performance of three density functional theory (DFT) exchange-correlation functionals, namely, Perdew-Burke-Ernzerhof (PBE), BP86, and B3LYP, in predicting conformational distributions of a hydrated glycine peptide is tested with two different basis sets in the framework of adaptive force matching (AFM). The conformational distributions yielded the free energy profiles of the DFT functional and basis set combinations. Unlike traditional validations of potential energy and structural parameters, our approach allows the free energy of DFT to be validated. When compared to experimental distributions, the def2-TZVP basis set provides better agreement than a slightly trimmed aug-cc-pVDZ basis set. B3LYP is shown to be better than BP86 and PBE. The glycine model fitted against B3LYP-D3(BJ) with the def2-TZVP basis set is the most accurate and named the AFM2021 model for glycine. The AFM2021 glycine model provides better agreement with experimental J-coupling constants than C36m and ff14SB, although the margin is very small when compared to C36m. Our previously published alanine model is also refitted with the slightly simplified AFM2021 energy expression. This work shows good promise of AFM for developing force fields for a range of proteinogenic peptides using only DFT as reference.

From Oligo(Phenyleneethynylene) Monomers to Supramolecular Helices: The Role of Intermolecular Interactions in Aggregation.

Supramolecular helices that arise from the self-assembly of small organic molecules via non-covalent interactions play an important role in the structure and properties of the corresponding materials. Here we study the supramolecular helical aggregation of oligo(phenyleneethynylene) monomers from a theoretical point of view, always guiding the studies with experimentally available data. In this way, by systematically increasing the number of monomer units, optimized n-mer geometries are obtained along with the corresponding absorption and circular dichroism spectra. For the geometry optimizations we use density functional theory together with the B3LYP-D3 functional and the 6–31G** basis set. For obtaining the spectra we resort to time-dependent density functional theory using the CAM-B3LYP functional and the 3–21G basis set. These combinations of density functional and basis set were selected after systematic convergence studies. The theoretical results are analyzed and compared to the experimentally available spectra, observing a good agreement.

Database-assisted local unitary transformation method for two-electron integrals in two-component relativistic calculations

This letter presents an efficient algorithm for local unitary transformation based on the spin-free infinite-order two-component relativistic method for the two-electron interaction, which is assisted by one-center relativistic two-electron integral (TEI) database. The database stores a set of TEIs, one for each element–basis set combination. The algorithm is numerically assessed for hydrogen halide chains, (HX)n (X = Cl and At), Aun, Ir(ppy)3, Pt3(C7H7)2(HCN)3, and PtCl2(NH3)2. The computational cost (time and memory size) at the Hartree–Fock level is lower than that of the conventional method, especially for small and medium-sized molecules.

Electronic Structures of Homodinuclear Platinum(II), Palladium(II) and Gold(I) Complexes Featuring Janus-type Benzoxazolin-2-ylidene Linkers

Electronic structures of a series of three homodinuclear platinum(II), palladium(II) and gold(I) complexes featuring Janus-type benzoxazolin-2-ylidene bridges and N,N-diisopropyl benzimidazolin-2-ylidene auxiliary ligands have been investigated. The gas-phase molecular structures of all compounds were first optimized using B3PW91 functional and SDD/6-31G(d) combination of basis sets. The nature of their frontier orbitals were then examined. The higher energy occupied molecular orbitals are predominantly d orbital of the metal in combination with p orbital of N,N-diisopropyl benzimidazolin-2-ylidene. On the other hand, the lower energy unoccupied molecular orbitals are p orbitals of the benzoxazolin-2-ylidene. TD-DFT calculations reveal that all the complexes require high energy ultraviolet photon for excitation and photoexcitations form excited state with decreased electron density on metal centers.

Theoretical Determination of Binding Energies of Small Molecules on Interstellar Ice Surfaces

The adsorption of a series of atoms and small molecules and radicals (H, C, N, O, NH, OH, H2O, CH3, and NH3) on hexagonal crystalline and amorphous ice clusters were obtained via classical molecular dynamics and electronic structure methods. The geometry and binding energies were calculated using a QMHigh:QMLow hybrid method on model clusters. Several combination of basis sets, density functionals and semi-empirical methods were compared and tested against previous works. More accurate binding energies were also refined via single point Coupled Cluster calculations. Most species, except carbon atom, physisorb on the surface, leading to rather small binding energies. The carbon atom forms a COH2 molecule and in some cases leads to the formation of a COH-H3O+ complex. Amorphous ices are characterized by slightly stronger binding energies than the crystalline phase. A major result of this work is to also access the dispersion of the binding energies since a variety of adsorption sites is explored. The interaction energies thus obtained may serve to feed or refine astrochemical models. The present methodology could be easily extended to other types of surfaces and larger adsorbates.

Forecasting System of Computational Time of DFT/TDDFT Calculations under the Multiverse Ansatz via Machine Learning and Cheminformatics

With the view of achieving a better performance in task assignment and load-balancing, a top-level designed forecasting system for predicting computational times of density-functional theory (DFT)/time-dependent DFT (TDDFT) calculations is presented. The computational time is assumed as the intrinsic property for the molecule. Based on this assumption, the forecasting system is established using the “reinforced concrete”, which combines the cheminformatics, several machine-learning (ML) models, and the framework of many-world interpretation (MWI) in multiverse ansatz. Herein, the cheminformatics is used to recognize the topological structure of molecules, the ML models are used to build the relationships between topology and computational cost, and the MWI framework is used to hold various combinations of DFT functionals and basis sets in DFT/TDDFT calculations. Calculated results of molecules from the DrugBank dataset show that (1) it can give quantitative predictions of computational costs, typical mean relative errors can be less than 0.2 for DFT/TDDFT calculations with derivations of ±25% using the exactly pretrained ML models and (2) it can also be employed to various combinations of DFT functional and basis set cases without exactly pretrained ML models, while only slightly enlarge predicting errors.

Thermochemistry of Tungsten-3p Elements for Density Functional Theory, Caveat Lector!

There are two primary foci in this research on WE (E = Si, P, and S) bonds: prediction of their bond dissociation enthalpies (BDEs), including σ- and π-bond energy components, and assessing the uncertainty of these BDE predictions for levels of theory commonly used in the literature. The internal standards for computational accuracy include metal-element bond lengths (mean absolute error = 1.8 ± 1.2%), main group homolog BDEs versus higher levels of ab initio theory (W1U and G4 BDEs, R2 = 0.98), and DLPNO-CCSD(T)/def2-QZVPP calculations for metal-ligand BDEs (R2 = 0.88). The W═Si first π-bond is underreported for density functional theory (DFT)/MP2 methods versus DLPNO-CCSD(T), while the latter shows negligible strength for the W;Si second π-bond, consistent with the literature. This research highlights clear issues with the underlying assumptions required for the use of perturbation theory methods for the fragments derived from W-P homolysis. The difficulties associated with modeling the metal thermochemistry with DFT (and MP2) levels of theory are manifest in the broad standard deviations observed. However, the average BDEs found using 48 popular DFT and MP2 levels of theory are reliable, 10.8 ± 6.8% mean absolute error (with W-P removed) versus DLPNO-CCSD(T), with the caveat that the individual basis set/pseudopotential/valence basis set combination can vary wildly. Analysis of the absolute error percentages with respect to the level of theory indicates little benefit to going higher on Jacob's Ladder, as simpler methods have lower error versus high-level ab initio techniques such as G4 and DLPNO-CCSD(T).

Modeling microsolvation clusters with electronic-structure calculations guided by analytical potentials and predictive machine learning techniques.

We propose a new methodology to study, at the density functional theory (DFT) level, the clusters resulting from the microsolvation of alkali-metal ions with rare-gas atoms. The workflow begins with a global optimization search to generate a pool of low-energy minimum structures for different cluster sizes. This is achieved by employing an analytical potential energy surface (PES) and an evolutionary algorithm (EA). The next main stage of the methodology is devoted to establish an adequate DFT approach to treat the microsolvation system, through a systematic benchmark study involving several combinations of functionals and basis sets, in order to characterize the global minimum structures of the smaller clusters. In the next stage, we apply machine learning (ML) classification algorithms to predict how the low-energy minima of the analytical PES map to the DFT ones. An early and accurate detection of likely DFT local minima is extremely important to guide the choice of the most promising low-energy minima of large clusters to be re-optimized at the DFT level of theory. In this work, the methodology was applied to the Li+Krn (n = 2-14 and 16) microsolvation clusters for which the most competitive DFT approach was found to be the B3LYP-D3/aug-pcseg-1. Additionally, the ML classifier was able to accurately predict most of the solutions to be re-optimized at the DFT level of theory, thereby greatly enhancing the efficiency of the process and allowing its applicability to larger clusters.

Ground and Excited State Electronic Structures of d8-Squared Planar Platinum(II) and Gold(III) Complexes Bearing Cyclometallated 2,6-Diphenylpyridine and Pyrene-Derived N-Heterocyclic Carbene

Electronic structures of four pyrene-derived N-heterocyclic carbene complexes of platinum(II) and gold(III) bearing cyclometallated 2,6-diphenylpyridine have been investigated theoretically. The structures of all complexes in gas phase have been first optimized. Different functionals and basis sets have been tested to find the best theoretical method. The results show that B3PW91 (LANL2DZ/6-31G*) combination give the best description of the molecules as compared with experimentally determined structural features. Using the calculation data from that best functional and mixed basis set combination, frontier molecular orbitals of the complexes have been examined. To gain understanding on the nature of electronic transitions in the UV-vis absorption spectra of the compounds, TD-DFT calculations have been carried out. A details analysis of the vertical excitation reveals that the nature of all the vertical electronic transitions in the complexes. Notably, the lowest energy transitions are πcb + dPt → $$\pi _{{{\text{cb}}}}^{{\text{*}}}$$ (for Pt1 and Pt2) and πCNC → dAu + $$\pi _{{{\text{CNC}}}}^{{\text{*}}}$$ (for Au1 and Au2) charge transfer in nature. A sharp contrast in lowest energy triplet excited state for d8‑squared planar Au1 and Pt1 has been demonstrated. While no contribution from gold(III) d orbital to the SOMO and SOMO – 1 orbital of Au1, there is significant contribution of platinum(II) dyz orbital in the SOMO – 1 orbital of Pt1, suggesting possible interaction of this singly occupied orbital with radical of π-symmetry substrates.

Structural modification of phenoxyimine titanium complexes and activation studies with alkylaluminum compounds

AbstractThe synthesis and characterization of three complexes of the type (N‐(3‐tert‐butylsalicylidene)‐R)2TiCl2 [R=2,6‐difluorophenyl 1, R=2,6‐dimethylphenyl 2, R=phenyl 3] is reported and compared with the highly active R=2,3,4,5,6,–pentafluorophenyl 4. The complexes were tested for ethylene polymerization when activated with different co‐catalysts, giving high catalytic activity when activated with methylaluminoxane for complexes 3 and 4. Complex 3 is the only catalyst to be inactive when activated with diethylaluminum chloride. Unexpectedly, for complexes 1 and 2, no catalytic activity is recorded when butylated hydroxytoluene in methylaluminoxane is used to remove the trimethylaluminum, while the catalytic activity for complex 3 is retained. NMR study on the activation of the four complexes in the presence of common alkyl aluminum co‐catalysts suggests the formation of Ti(III) species in the presence of tri‐iso‐butylaluminum, and also the formation of NR−CH2 (R: −Al(CH2CH(CH3)2)2) bond from the N=C−H bond of the ligand explaining the absence of catalytic activity. Density functional theory calculations using B3LYP and a combination of basis sets (6‐31+G and cc‐pVTZ) were performed on the catalyst precursors and the activated species showing insights into the frontier orbitals, localizing the LUMO on the imino bond elucidating their reactivity. Mulliken charges are also reported and an unexpected relationship between the nitrogen on the ligands and the molecular weight is observed.