Further Insights into the Structure of [M(η²(<i>C,C</i><i>‘</i>)-C₃O₂)(PPh₃)₂] (M = Ni, Pd, Pt) by Quasi-Relativistic Density Functional Calculations and Solid-State CP/MAS NMR

The molecular and electronic structures of [M(η2(C,C‘)-C3O2)(PPh3)2] (M = Ni, Pd, Pt) have been investigated by means of quasi-relativistic gradient-corrected density functional calculations and solid-state CP/MAS NMR spectroscopy. Theoretical outcomes are consistent with a square-planar coordination around the central metal atom and are in very good agreement with the bonding scheme emerging from IR and NMR data

Structure and Stability of TiO₂-B Surfaces: A Density Functional Study

We investigate the structure and energetics of low-index surfaces of the TiO2-B polymorph by means of periodic density functional theory calculations within the generalized gradient approximation. The bulk structure contains two nonequivalent Ti ions, one of them exhibiting an octahedral coordination, while the other is square-pyramidal. When exposed at the surface, these two types of ions display different relaxation schemes, which ultimately tend to make them more similar. On the basis of the computed surface energies and of the Wulff construction, we predict for TiO2-B a pseudohexagonal prismatic equilibrium shape and an average surface energy practically identical to that of TiO2-anatase

Experimental and Theoretical Investigation of the Molecular and Electronic Structure of [Zn₄(μ₄-S){μ-S₂As(CH₃)₂}₆] and [Cd₄(μ₄-S){μ-S₂As(CH₃)₂}₆]: Two Possible Molecular Models of Extended Metal Chalcogenide Semiconductors^†

The molecular and electronic structure of hexakis[μ-(dimethylarsinodithioate-S:S‘)]-μ4-thioxotetrazinc has been investigated by combining X-ray diffraction measurements, electrospray mass spectrometry (ESI), UV absorption spectroscopy, and density functional calculations. The polynuclear zinc complex consists of discrete “tetrazinc sulfide” moieties held together by van der Waals interactions. The unit cell contains four independent molecules and four solvent molecules. Each independent unit is characterized by a central μ4-S coordinated to four Zn ions, each of them at the center of an irregular tetrahedron of S atoms. ESI measurements point out that the synthesis of the analogous Cd derivative was successful. Crystal data are as follows:  chemical formula, C12H36As6Cl1.5S13Zn4; monoclinic space group P21/n (no. 14); a = 30.4228(7) Å, b = 18.3720(5) Å, c = 32.3758(8) Å, β = 95.857(1)°; Z = 16. Theoretical calculations indicate that, despite their structural arrangement, neither the Zn nor the Cd complex can be considered molecular models of the extended ZnS and CdS. Nevertheless, the electronic transitions localized in the Zn4(μ4-S) and Cd4(μ4-S) inner cores of the title compounds have the same nature as those giving rise to the maxima in the excitation spectra of the extended Zn4S(BO2)6 and Cd4S(AlO2)6 [Blasse, G.; Dirksen, G. J.; Brenchley, M. E.; Weller, M. T. Chem. Phys. Lett. 1995, 234, 177]

Molecular Dynamics Simulations of the Self-Assembly of Tetraphenylporphyrin-Based Monolayers and Bilayers at a Silver Interface

A theoretical study of the adsorption and dynamics of tetraphenylporphyrins on a Ag(111) substrate and the subsequent aggregation of the formed monolayers with fullerene molecules is reported. Classical molecular dynamics simulations were able to reveal the various phases of monolayer and bilayer formation and succeeded in identifying all the interactions responsible for self-assembling and surface binding. Possible supramolecular configurations extracted from the molecular dynamics trajectories were classified and characterized in detail and revealed to be in satisfactory agreement with experimental data

Experimental and Theoretical Investigation of the Molecular and Electronic Structure of [Zn₄(μ₄-S){μ-S₂As(CH₃)₂}₆] and [Cd₄(μ₄-S){μ-S₂As(CH₃)₂}₆]: Two Possible Molecular Models of Extended Metal Chalcogenide Semiconductors^†

The molecular and electronic structure of hexakis[μ-(dimethylarsinodithioate-S:S‘)]-μ4-thioxotetrazinc has been investigated by combining X-ray diffraction measurements, electrospray mass spectrometry (ESI), UV absorption spectroscopy, and density functional calculations. The polynuclear zinc complex consists of discrete “tetrazinc sulfide” moieties held together by van der Waals interactions. The unit cell contains four independent molecules and four solvent molecules. Each independent unit is characterized by a central μ4-S coordinated to four Zn ions, each of them at the center of an irregular tetrahedron of S atoms. ESI measurements point out that the synthesis of the analogous Cd derivative was successful. Crystal data are as follows:  chemical formula, C12H36As6Cl1.5S13Zn4; monoclinic space group P21/n (no. 14); a = 30.4228(7) Å, b = 18.3720(5) Å, c = 32.3758(8) Å, β = 95.857(1)°; Z = 16. Theoretical calculations indicate that, despite their structural arrangement, neither the Zn nor the Cd complex can be considered molecular models of the extended ZnS and CdS. Nevertheless, the electronic transitions localized in the Zn4(μ4-S) and Cd4(μ4-S) inner cores of the title compounds have the same nature as those giving rise to the maxima in the excitation spectra of the extended Zn4S(BO2)6 and Cd4S(AlO2)6 [Blasse, G.; Dirksen, G. J.; Brenchley, M. E.; Weller, M. T. Chem. Phys. Lett. 1995, 234, 177]

Metal-Free on-Surface Photochemical Homocoupling of Terminal Alkynes

On-surface synthesis involving the homocoupling of aryl-alkynes affords the buildup of bisacetylene derivatives directly at surfaces, which in turn may be further used as ingredients for the production of novel functional materials. Generally, homocoupling of terminal alkynes takes place by thermal activation of molecular precursors on metal surfaces. However, the interaction of alkynes with surface metal atoms often induces unwanted reaction pathways when thermal energy is provided to the system. In this contribution we report about light-induced metal-free homocoupling of terminal alkynes on highly oriented pyrolitic graphite (HOPG). The reaction occurred with high efficiency and selectivity within a self-assembled monolayer (SAM) of aryl-alkynes and led to the generation of large domains of ordered butadiynyl derivatives. Such a photochemical uncatalyzed pathway represents an original approach in the field of topological C–C coupling at the solid/liquid interface

Spin−Orbit Relativistic Time-Dependent Density Functional Calculations of the Metal and Ligand Pre-Edge XAS Intensities of Organotitanium Complexes: TiCl₄, Ti(η⁵-C₅H₅)Cl₃, and Ti(η⁵-C₅H₅)₂Cl₂

Time-dependent density functional theory (TDDFT) coupled to the relativistic two-component zeroth-order regular approximation, both available in the last version of the ADF package, have been successfully used to simulate X-ray absorption spectra of TiCl4, Ti(η5-C5H5)Cl3, and Ti(η5-C5H5)2Cl2 in terms of their oscillator strength distributions. Besides allowing a first principle assignment of Ti 1s, Cl 1s, and Ti 2p (L2,3 edges) core excitation spectra, theoretical outcomes provide a rationale for deviations from the expected L3/L2 branching ratio

<i>Ab Initio</i> and Experimental Studies on the Structure and Relative Stability of the <i>cis</i>-Hydride−η²-Dihydrogen Complexes [{P(CH₂CH₂PPh₂)₃}M(H)(η²-H₂)]⁺ (M = Fe, Ru)

Ab initio calculations (DMOL method) including the estimate of the total energy and the full optimization of the geometrical parameters have been used to study the electronic structures and the coordination geometries of the model systems [{P(CH2CH2PH2)3}M(H)(L)]+ (M = Fe, L = H2, C2H4, CO, N2; M = Ru, L = H2). Single crystal X-ray analyses have been carried out on the complexes [(PP3)Fe(H)(η2-H2)]BPh4·0.5THF (1·0.5THF), [(PP3)Fe(H)(CO)]BPh4·THF (3·THF), and [(PP3)Ru(H)(η2-H2)]BPh4·0.5THF (5·0.5THF) [PP3 = P(CH2CH2PPh2)3]. Crystal data:  for 1·0.5THF, triclinic P1 (No. 2), a = 17.626(3) Å, b = 14.605(3) Å, c = 12.824(4) Å, α = 90.09(2)°, β = 103.87(2)°, γ = 107.46(2)°, Z = 2, R = 0.082; for 3·THF, triclinic P1 (No. 2), a = 12.717(2) Å, b = 14.553(1) Å, c = 17.816(2) Å, α = 72.90(1)°, β = 76.82(2)°, γ = 89.71(1)°, Z = 2, R = 0.067; for 5·0.5THF, monoclinic P2/1a (No. 14), a = 19.490(5) Å, b = 19.438(2) Å, c = 16.873(5) Å, β = 110.96(2)°, Z = 4, R = 0.074. On the basis of theoretical calculations, X-ray analyses, and multinuclear NMR studies, all of the complexes of the formula [(PP3)M(H)(L)]BPh4 [M = Fe, L = H2 (1), C2H4 (2), CO (3), N2 (4); M = Ru, L = H2 (5), C2H4 (6)] are assigned a distorted octahedral structure where the hydride (trans to a terminal phosphorus donor) and the L ligand occupy mutually cis positions. The theoretical calculations indicate that the H2 ligand in the η2-dihydrogen−hydride derivatives 1 and 5 is placed in the P−M−H plane (parallel orientation) and that there is an attractive interaction between the H and H2 ligands. XPS measurements, performed on the iron complexes, show that the Fe → L back-bonding interaction plays a leading role in 3. It is concluded that the stronger metal−H2 bond in the dihydrogen−hydride complex 1, as compared to the Ru analog 5, is due to the greater d(metal) → σ*(H−H) back-donation as well as a more efficient interaction between the terminal hydride and an H of the dihydrogen ligand. This cis effect is suggested to contribute to the relative stability of the iron complexes, which increases in the order C2H4 2 2 < CO

Density Functional Theory Study of the Binding Capability of Tris(pyrazol-1-yl)methane toward Cu(I) and Ag(I) Cations

Density functional theory (DFT) has been used to look into the electronic structure of [M(tpm)]+ molecular ion conformers (M = Cu, Ag; tpm = tris(pyrazol-1-yl)methane) and to study the energetics of their interconversion. Theoretical data pertaining to the free tpm state the intrinsic instability of its κ3-like conformation, thus indicating that, even though frequently observed, the κ3-tripodal coordinative mode is unlikely to be directly achieved through the interaction of M(I) with the κ3-like tpm conformer. It is also found that the energy barrier for the κ2-[M(tpm)]+ → κ3-[M(tpm)]+ conversion is negligible. As far as the bonding scheme is concerned, the tpm → M(I) donation, both σ and π in character, is the main source of the M(I)−tpm bonding, whereas back-donation from completely occupied M(I) d orbitals into tpm-based π* levels plays a negligible role

Density Functional Theory Study of the Binding Capability of Tris(pyrazol-1-yl)methane toward Cu(I) and Ag(I) Cations

Density functional theory (DFT) has been used to look into the electronic structure of [M(tpm)]+ molecular ion conformers (M = Cu, Ag; tpm = tris(pyrazol-1-yl)methane) and to study the energetics of their interconversion. Theoretical data pertaining to the free tpm state the intrinsic instability of its κ3-like conformation, thus indicating that, even though frequently observed, the κ3-tripodal coordinative mode is unlikely to be directly achieved through the interaction of M(I) with the κ3-like tpm conformer. It is also found that the energy barrier for the κ2-[M(tpm)]+ → κ3-[M(tpm)]+ conversion is negligible. As far as the bonding scheme is concerned, the tpm → M(I) donation, both σ and π in character, is the main source of the M(I)−tpm bonding, whereas back-donation from completely occupied M(I) d orbitals into tpm-based π* levels plays a negligible role