Theoretical studies on titanium pentafulvene complexes

A series of six titanium pentafulvene complexes are thoroughly investigated using the B3LYP/6-31G(d) level of theory. Excellent agreement with the available structural data is obtained. Relevant structural parameters indicate that a gradual change of the fulvene ligand coordination to the titanium center. Depending on the nature of the exocyclic fulvene substituents dianionic η⁵, η¹-and olefinic η⁶-coordination modes are found. This behavior is further supported by NBO and AIM population analyses which predict differences in the bond nature meanly of the contacts between titanium and the exocyclic carbon atom. In an excitation study, several theoretical approaches are evaluated against the available recorded UV-Vis spectra of the six complexes. The “best” approach, time-dependant DFT calculations reproduce the experimental UV data reasonably well, although systematically slightly too small values (abut 50 cm⁻¹) are obtained. The other levels of theory are significantly more erratic. It could further be testified that the absorption maxima correspond to a ligand-to-metal charge transfer from the HOMO to the LUMO+1 of the complexes.     

Fluxional behavior of methyl-substituted tricarbonyl(tropone)iron complexes and their different reactivity

The compositions of regioisomeric mixtures of tricarbonyliron complexes of 2-methyltropone (1a,b), 3-methyltropone (2a,b) and 2,6-dimethyltropone (3a,b) are studied and compared with the results of ab initio computations. The structures, frontier orbitals, and population analysis are evaluated by means of density functional theory. The thermodynamic and kinetic parameters of regioisomerizations are determined using dynamic ¹H NMR technique. The influence of methyl-substituent(s) on the equilibrium ratio of regioisomers resulting from the haptotropic rearrangement is discussed. Significant differences in the reactivity of C-protonized methyl- and dimethyl-substituted tricarbonyl(tropone)iron complexes 4–6 in nucleophilic additions and corresponding O-trimethylsilylated complexes 7–9 in [3+2] cycloadditions are explained in terms of electronic and steric effects of the methyl group(s). Various hydroazulenone cycloadducts of tricarbonyl(η⁴-2,6-dimethyltropone)iron 3a,b have been prepared by stereoselective [3+2] cycloaddition with Fp-reagents 12–14 and characterized. Formerly proposed mechanism of [3+2] cycloaddition was approved.     

Theoretical study of the protonation of square-planar palladium(II) complexes. Assessment of basis set and correlation effects

The protonation of the [Pd(H)₂(Cl)(NH₃)]^– and [Pd(H)₂(NH₃)₂] taken as models of anionic and neutral square-planard ⁸ palladium complexes is investigated through SCF, MP2, MP4, CASSCF and CASPT2 calculations, using various basis sets on the metal and the ligands. It is shown that correlation effects, mainly those associated with the covalent character of the metal hydrogen and metal ligand bonds, are important. The importance of diffuse functions on the ligands, especially for the anionic system, is stressed.     

A density functional study of alizarin two of its isomers and its transition metals and rare-earth complexes

Electronic structure of Alizarin, two of its isomers, 11 different transition metal complexes and five rare-earth complexes are studied using density functional theory (DFT). Complexation energies are evaluated and it is found that chelation has a negligible influence on the structure of the anthraquinone backbone; the molecule keeps a planar conformation except for some metals such as Cr, Al, and Zn where the metal atom M and the oxygen atoms are slightly out of the plane by few degrees. The M–O bonds involve p or d metal orbitals depending on whether the d shell is full or empty. The complexation effect leads to a red shift and hence to a colour change of the solutions of the complexes.

The calculated complexation energies are of the same order for metal transition and for rare-earth elements.     

Preparation and protonation reactions of aryl complexes of manganese and rhenium

Aryl M(κ¹-Ar)(CO)_nP_5−n [M = Mn, Re; Ar = C₆H₅, 4-CH₃C₆H₄; n = 2, 3; P = P(OEt)₃, PPh(OEt)₂, PPh₂OEt] and Re(κ¹-C₆H₅)(CO)₃[Ph₂PO(CH₂)₃OPPh₂] complexes were prepared by allowing hydrides MH(CO)_nP_5−n to react first with triflic acid and then with the appropriate aryl lithium (LiAr) compounds. The complexes were characterized spectroscopically (IR and ¹H, ³¹P, ¹³C NMR) and by the X-ray crystal structure determination of Re(κ¹-C₆H₅)(CO)₃[Ph₂PO(CH₂)₃OPPh₂] derivative. Protonation reaction of the aryl complexes with HBF₄ · Et₂O lead to free hydrocarbons Ar-H and the unsaturated [M(CO)_nP_5−n]⁺ cations, separated as solids in the case of [Re(CO)₃P₂]BF₄ derivatives.     

Correlation between hydration and deprotonation in hexaaqua metal complexes

The hydration energy of metallic cations determined with density functional calculations using a double-numerical plus p-polarization basis set, related to the acidity constants of hexaaqua metal complexes, was investigated in the present study. From the results calculated by Vosko-Wilk-Nusair (VWN), Becke-Perdew (BP) and Becke-Lee-Yang-Parr (BLYP) density functionals, a global linear correlation with the observed acidity constants in both main group [Mg(II), Ca(II) and Al(III)] and (post-)transition group [Mn(II), Zn(II), Cd(II), Sc(III), Cr(III), Fe(III), Ga(III) and In(III)] hexaaqua metal complexes has been established:

VWN density functional: pK_a = 16.5760 + 0.0173E_hydr kcal mol⁻¹

BP density functional: pK_a = 15.7329 + 0.0182E_hydr kcal mol⁻¹

BLYP density functional: pK_a = 15.9448 + 0.0185E_hydr kcal mol⁻¹     

Transition metal clusters and supported species with metal-carbon bonds from first-principles quantum chemistry

We discuss the impact of density functional electronic structure calculations for understanding the organometallic chemistry of transition metal (TM) surface complexes and clusters. Examples will cover three types of systems, mainly of interest in the context of heterogeneous catalysis: (i) supported carbonyl complexes of rhenium on MgO and of rhodium in zeolites, (ii) TM clusters with CO ligands and adsorbates, and (iii) metal clusters exhibiting chemical bonds with atomic carbon. The first group of case studies promotes the concept that surface groups of oxide supports are bonded to TM complexes in the same way as common (poly-dentate) ligands are bonded in coordination compounds. The second group of examples demonstrates various “ligand effects” of TM clusters. Finally, we illustrate how carbido centers stabilize TM clusters and modify the propensity for adsorption at the surface of such clusters.     

Crystal structure studies and antimicrobial activities of transition metal complexes of pyridine-2,6-dicarboxylic acid and imidazole containing water clusters

Two new copper(II) and chromium(III) complexes of tridentate 2,6-pyridinedicarboxylic acid (H₂pydc) with imidazole (im), (Him)[Cu(Hpydc)(pydc)]?H₂pydc?5H₂O (1) and (Him)[Cr(pydc)₂]?H₂pydc?5H₂O (2), have been prepared and characterized by elemental analysis, TGA measurements, FT-IR, and UV–Vis spectroscopy, powder and single crystal X-ray crystallography. Crystal structure analyses reveal that both copper(II) and chromium(III) ions are in a distorted octahedral environment. The optimized geometrical parameters were calculated using methods based on the density functional theory (DFT). These calculations agree closely with the X-ray structure. The antimicrobial activities of the ligand and the complexes were evaluated in vitro and compared with drugs in use. The results show that the complexes had stronger antibacterial activity than the corresponding ligand and the effectiveness was confirmed against Bacillus subtilis (gram positive) and Klebsiella pneumoniae (gram negative) for 1, and Escherichia coli and K. pneumoniae (gram negative) for 2 by the well diffusion method.     

Syntheses,structures, photoluminescence,and theoretical studies of a novel class of d10 metal complexes of 1H-[1,10]phenanthrolin-2-one

A novel asymmetric monosubstituted 1,10-phenanthroline, Hophen.0.5 H(2)O (1, Hophen=1H-[1,10]phenanthrolin-2-one), was generated by a facile route, and a novel class of crystalline, d(10)-metal, monomeric or oligomeric complexes of this ligand, namely [Hg(ophen)(2)].4 H(2)O.CH(2)Cl(2) (2), [Cd(3)Cl(ophen)(5)].1.5 H(2)O.2 CH(2)Cl(2) (3), and [Zn(4)O(ophen)(4)(OAc)(2)].4H(2)O.2 CH(2)Cl(2) (4), were obtained by means of liquid diffusion, and were characterized by X-ray crystallography and photoluminescence studies. Complex 1 exhibits a hydrogen-bonded dimeric structure, 2 is a neutral monomeric complex, 3 has a trinuclear structure with the ophen ligand acting as a bridge through the ketone groups, and 4 features a tetranuclear Zn(4)O core that is consolidated further by bridging ophen and acetate ligands. All the complexes display photoluminescent properties in the blue/green region. The photoluminescent mechanisms were investigated by means of molecular orbital calculations, which showed that the photoluminescent properties are ligand-based and can be tuned upon ligation to different metal ions.     

Theoretical studies on the influence of metallic cations on ring opening of propylene oxide catalyzed by metal-salen complexes

We studied the ring opening of propylene oxide (PO) by salen-M coordinated OH⁻ group [M = Al(III), Sc(III), Cr(III), Mn(III), Fe(III), Co(II), Co(III), Ni(II), Cu(II), Zn(II), Ru(III) and Rh(III)]. The results show that the ring-opening energy barriers for M(II) complexes are much lower than those with M(III) complexes in the gas phase, and the barriers correlate linearly with the negative charges on the OH⁻ group and the Fukui function condensed on the OH⁻ group. The nucleophilicity ordering in the gas phase can be rationalized by the ratio of formal positive charges/radius of M cations. Solvent effect greatly increases the barriers of M(II) complexes but slightly changes the results of M(III) ones, making the barriers similar. Analysis indicates that the reaction heats are linearly proportional to the reverse reaction barriers. The relationships established here can be used to estimate the ring-opening barriers and to screen epoxide ring-opening catalysts.     

Prediction of the reduction potential in transition‐metal containing complexes: How expensive? For what accuracy?

Accurate computationally derived reduction potentials are important for catalyst design. In this contribution, relatively inexpensive density functional theory methods are evaluated for computing reduction potentials of a wide variety of organic, inorganic, and organometallic complexes. Astonishingly, SCRF single points on B3LYP optimized geometries with a reasonably small basis set/ECP combination works quite well‐‐B3LYP with the BS1 [modified‐LANL2DZ basis set/ECP (effective core potential) for metals, LANL2DZ(d,p) basis set/LANL2DZ ECP for heavy nonmetals (Si, P, S, Cl, and Br), and 6‐31G(d') for other elements (H, C, N, O, and F)] and implicit PCM solvation models, SMD (solvation model based on density) or IEFPCM (integral equation formalism polarizable continuum model with Bondi atomic radii and α = 1.1 reaction field correction factor). The IEFPCM‐Bondi‐B3LYP/BS1 methodology was found to be one of the least expensive and most accurate protocols, among six different density functionals tested (BP86, PBEPBE, B3LYP, B3P86, PBE0, and M06) with thirteen different basis sets (Pople split‐valence basis sets, correlation consistent basis sets, or Los Alamos National Laboratory ECP/basis sets) and four solvation models (SMD, IEFPCM, IPCM, and CPCM). The MAD (mean absolute deviation) values of SCRF‐B3LYP/BS1 of 49 studied species were 0.263 V for SMD and 0.233 V for IEFPCM‐Bondi; and the linear correlations had respectable R ² values (R ² = 0.94 for SMD and R ² = 0.93 for IEFPCM‐Bondi). These methodologies demonstrate relatively reliable, convenient, and time‐saving functional/basis set/solvation model combinations in computing the reduction potentials of transition metal complexes with moderate accuracy. © 2017 Wiley Periodicals, Inc.     

Theoretical study of the structural character of weakly bonding silicon carbonyl complexes

The structures, properties and the bonding character for sub-carbonyl Si, SiCO and Si(CO)₂, in singlet and triplet states have been investigated using complete-active-space self-consistent field (CASSCF), density functional theory and second-order M?ller–Plesset methods with a 6-311+G* basis set. The results indicate that the SiCO species possesses a ³∑⁻ ground state, and the singlet ¹Δ excited state is higher in energy than the ³∑⁻ state by 17.3 kcalmol⁻¹ at the CASSCF–MP2/6-311+G* level and by 16.4 kcalmol⁻¹ at the CCSD(T)/6-311+G* level. The SiCO ground state may be classified as silene (carbonylsilene), and its CO^δ− moiety possesses CO⁻ property. The formation of SiCO causes the weakening of CO bonds. The Si–C bond consists of a weak σ bond and two weak π bonds. Although the Si–C bond length is similar to that of typical Si–C bonds, the bond strength is weaker than the Si–C bonds in Si-containing alkanes; the calculated dissociation energy is 26.2 kcalmol⁻¹ at the CCSD(T)/6-311+G* level. The corresponding bending potential-energy surface is flat; therefore, the SiCO molecule is facile. For the bicarbonyl Si systems, Si(CO)₂, there exist two V-type structures for both states. The stablest state is the singlet state (¹A₁), and may be referred to the ground state. The triplet state (³B₁) is energetically higher in energy than the ¹A₁ state by about 40 kcalmol⁻¹ at the CCSD(T)/6-311 + G* level. The bond lengths in the ¹A₁ state are very close to those of the SiCO species, but the SiCO moieties are bent by about 10°, and the CSiC angles are only about 78°. The corresponding ³B₁ state has a CSiC angle of about 54° and a SiCO angle of about 165°, but its Si–C and C–O bonds are longer than those in the ¹A₁ state by about 0.07 and 0.03 ?, respectively. This Si(CO)₂ (¹A₁) has essentially silene character and should be referred to as a bicarbonyl silene. Comparison of the CO dissociation energies of SiCO and Si(CO)₂ in their ground states indicates that the first CO dissociation energy of Si(CO)₂ is smaller by about 7 kcalmol⁻¹ than that of SiCO; the average one over both CO groups is also smaller than that of SiCO. A detailed bonding analysis shows that the possibility is small for the existence of polycarbonyl Si with more than three CO. This prediction may also be true for similar carbonyl complexes containing other nonmetal and non-transition-metal atoms or clusters. Received: 17 April 2002 / Accepted: 11 August 2002 / Published online: 4 November 2002 Acknowledgements. This work was supported by the National Natural Science Foundation of China (29973022) and the Foundation for Key Teachers in University of the State Ministry of Education of China. Correspondence to: Y. Bu e-mail: byx@sdu.edu.ch     

Theoretical investigation of the coordination of dibenzazepine to transition-metal complexes: A DFT study

DFT calculations with full geometry optimizations have been carried out on a series of hypothetical compounds of the CpM(C₁₄NH₁₁) and (CO)₃M(C₁₄NH₁₁) (M = transition metal and C₁₄NH₁₁ = dibenzazepine ligand) type. A rationalization of the bonding in hypothetical complexes is provided. Depending on the electron count and the nature of the metal, the dibenzazepine ligand can bind to the metal through the η¹, η², η³, η⁴ , η⁵, η⁶ , or η⁷ coordination mode adopting structures of types a or b. In the investigated species, the most favored closed-shell count is 18-MVE except for the Sc and V models which prefer the 16-MVE configuration.     

Theoretical study of oxidation of molecular nitrogen with vanadium peroxo complexes

The structure and reactivity toward molecular nitrogen of vanadium diperoxo complexes, as well as the influence of the protonation and coordination of trifluoroacetate on the reactivity, were studied using the density functional method. The most stable form of the starting complex is the ozonide [V(O₃)O₂]^–. The triplet state of the complex is formed with small energy expenses for electron transfer from the peroxo ligand to the vanadium atom to form V^IV. The transfer of the O atom to the N₂ molecule to form N₂O is possible for several transition states. The nature of possible complexes and transition states retains upon protonation but the number of different structures increases depending on the ligand and the site of proton addition. Upon protonation the reactivity increases and the lowest activation barrier decreases from 27 to 20 kcal mol^–1. The coordination of trifluoracetate anion also decreases the activation barrier for the intermolecular transfer of oxygen to the nitrogen molecule.     

Theoretical Studies of Inorganic Compounds. 27 Quantum Chemical Investigations of Transition Metal Nitrido Complexes with a TM‐N‐E Linkage (E = Main Group Element)

It is reported about quantum chemical DFT calculations of various transition metal (TM) nitrido complexes which contain a TM‐N‐E linkage. The goal is to elucidate the nature of the TM‐N‐E bonding situation with modern quantum chemical tools. Five comparative investigations have been carried out. (a) Comparison of the N‐donor ability in the nitrido complexes Cl₃W‐N‐ECl_n where ECl_n = NaCl, MgCl₂, AlCl₃. (b) Comparative analysis of the bonding situation in Cl₄W‐N‐X where X = Na, MgCl, AlCl₂, SiCl₃, PCl₂, SCl, Cl. (c) Comparison of the structure and bonding in Cl₅W‐NPH₃, Cl₅W‐OPH₃⁺, Cl₄W‐(NPH₃)(OPH₃)⁺. (d) Comparative analysis of the bonding situation in Cl₅Ta‐OPH₃, Cl₅W‐NPH₃, Cl₅Re‐CPH₃. (e) Energy decomposition analysis of the bonding of the isolobal ligands NPH₃ and Cp with WCl₅.     

Density functional theory assessment of the thermal degradation of diclofenac and its calcium and iron complexes

Thermogravimetric analyses of diclofenac sodium, its Ca²⁺ and Fe³⁺ complexes manifested a decreasing trend of the onset decomposition temperatures at which these compounds dissociated. The drop in the temperature was metal ion dependent; the sodium salt showed thermal stability up to 245 °C, whereas the complexes started their degradation processes at temperatures starting from 90 °C. While G* for the cleavage of the acetate moiety in the sodium salt was 63.76 kJmol⁻¹, it was 82.06 and 140.57 kJmol⁻¹ in the cases of Ca²⁺ and Fe³⁺, respectively. However, their complete fusion took place at 187.65, 150.34 and 98.77 °C, respectively, displaying a reversed trend which is probably indicative of some catalytic part on the binding metals.

Using the Gaussian 98 W package of programs, ab initio molecular orbital treatments were applied to diclofenac and its Ca²⁺ and Fe³⁺ metal complexes to study their electronic structure at the atomic level. The thermochemistry of diclofenac sodium was followed through the TG fragmentation peak temperatures using the density functional theory calculations at the 6-31G(d) basis set level. The FT-IR data were in good agreement with the theoretically calculated values.

Single point calculations at the B3LYP/ 6-311G(d) level of theory, were used to compare the geometric features, energies and dipole moments of these compounds to detect the effect of the binding metal ions on the thermal dissociation of their diclofenac complexes.     

Electronic structures of tetragonal nitrido and nitrosyl metal complexes

The standard oxidation states of central metal atoms in C _4v nitrido ([M(N)(L)₅] ^z ) complexes are four units higher than those in corresponding nitrosyls ([M(NO)(L)₅] ^z ) (L=CN: z = 3−, M = Mn, Tc, Re; z = 2−, M = Fe, Ru, Os; L = NH₃: z = 2+, M = Mn, Tc, Re; z = 3+, M = Fe, Ru, Os). Recent work has suggested that [Mn(NO)(CN)₅]³⁻ behaves electronically much closer to Mn(V)[b ₂(xy)]², the ground state of [Mn(N)(CN)₅]³⁻, than to Mn(I)[b ₂(xy)]²[e(xz,yz)]⁴. We have employed density functional theory and time-dependent density functional theory to calculate the properties of the ground states and lowest-lying excitations of [M(N)(L)₅] ^z and [M(NO)(L)₅] ^z . Our results show that [M(N)(L)₅] ^z and [M(NO)(L)₅] ^z complexes with the same z value have strikingly similar electronic structures.     

Broken symmetry approach to calculation of exchange coupling constants for homobinuclear and heterobinuclear transition metal complexes

The application of broken symmetry density functional calculations to homobinuclear and heterobinuclear transition metal complexes produces good estimates of the exchange coupling constants as compared to experimental data. The accuracy of different hybrid density functional theory methods was tested. A discussion is presented of the different methodological approaches that apply when a broken symmetry wave function is used with either Hartree–Fock or density functional calculations. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 1391–1400, 1999     

About the calculation of exchange coupling constants in polynuclear transition metal complexes

The application of theoretical methods based on the density functional theory with hybrid functionals provides good estimates of the exchange coupling constants for polynuclear transition metal complexes. The accuracy is similar to that previously obtained for dinuclear compounds. We present test calculations on simple model systems based on H. He and CH(2). He units to compare with Hartree-Fock and multiconfigurational results. Calculations for complete, nonmodeled polynuclear transition metal complexes yield coupling constants in very good agreement with available experimental data.