Structure and electron affinity of platinum fluorides

Cryogenic Photoelectron Spectroscopic and Theoretical Study of the Electronic and Geometric Structures of Undercoordinated Osmium Chloride Anions OsCln- (n = 3-5)

A series of anionic transition metal halides, OsCln- (n = 3-5), have been investigated using a newly developed, home-constructed, cryogenic anion cluster photoelectron spectroscopy. The target anionic species are generated through collision-induced dissociation in a two-stage ion funnel. The measured vertical detachment energies (VDEs) are 3.48, 4.54, and 4.81 eV for n = 3, 4, and 5, respectively. Density functional theory calculations at the B3LYP-D3(BJ)//aug-cc-pVTZ(-pp) level predict the lowest energy structures of the atomic form of OsCln- (n = 3-5) to be a quintet triangle, quartet square, and quintet square-based pyramid, respectively. The CCSD(T)-calculated VDEs and corresponding adiabatic detachment energies agree well with our experimental measurements. Analysis of the corresponding frontier molecular orbitals and charge density differences suggests that the d-orbitals of the transition metal Os play a primary role in the single-photon detachment processes, and the detached electrons originating from different molecular orbitals are distinguishable.

Photoelectron Imaging Study of the Diplatinum Iodide Dianions [Pt2I6]2- and [Pt2I8]2

Photoelectron spectroscopy has been used to study the electronic structure, photodetachment, and photodissociation of the stable diplatinum iodide dianions [Pt₂I₆]^2– and [Pt₂I₈]^2–. Photoelectron spectra over a range of photon energies show the characteristic absence of low kinetic energy photoelectrons expected for dianions as a result of the repulsive Coulomb barrier (RCB). Vertical detachment energies of ∼1.6 and ∼1.9 eV and minimum RCBs of ∼1.2 and ∼1.3 eV are reported for [Pt₂I₆]^2– and [Pt₂I₈]^2–, respectively. Both of the diplatinum halides exhibit three direct detachment channels with distinct anisotropies, analogous to the previously reported spectra for PtI₂^– and PtI^–, suggesting a platinum-centered molecular core that dominates the photodetachment. Additionally, evidence for two-photon photodissociation and subsequent photodetachment channels producing I^– are observed for both dianions. Finally, an unexplained feature is observed at photon energies around 3 eV, whose origin is considered. Our work highlights the complex electronic structure of the heavy platinum-halide dianions that are characterized by a dense manifold of electronic states.

Photoelectron imaging of PtI2 - and its PtI- photodissociation product

The photoelectron imaging of PtI₂ ^- is presented over photon energies ranging from hν = 3.2 to 4.5 eV. The electron affinity of PtI₂ is found to be 3.4 ± 0.1 eV, and the photoelectron spectrum contains three distinct peaks corresponding to three low-lying neutral states. Using a simple d-block model and the measured photoelectron angular distributions, the three states are tentatively assigned. Photodissociation of PtI₂ ^- is also observed, leading to the formation of I^- and of PtI^-. The latter allows us to determine the electron affinity of PtI to be 2.35 ± 0.10 eV. The spectrum of PtI^- is similarly structured with three peaks which, again, can be tentatively assigned using a similar model that agrees with the photoelectron angular distributions.

Matrix Isolation Spectroscopic and Relativistic Quantum Chemical Study of Molecular Platinum Fluorides PtFn (n=1-6) Reveals Magnetic Bistability of PtF4

Molecular platinum fluorides PtF_n, n=1–6, are prepared by two different routes, photo‐initiated fluorine elimination from PtF₆ embedded in solid noble‐gas matrices, and the reaction of elemental fluorine with laser‐ablated platinum atoms. IR spectra of the reaction products isolated in rare‐gas matrices under cryogenic conditions provide, for the first time, experimental vibrational frequencies of molecular PtF₃, PtF₄ and PtF₅. Photolysis of PtF₆ enabled a highly efficient and almost quantitative formation of molecular PtF₄, whereas both PtF₅ and PtF₃ were formed simultaneously by subsequent UV irradiation of PtF₄. The vibrational spectra of these molecular platinum fluorides were assigned with the help of one‐ and two‐component quasirelativistic DFT computation to account for scalar relativistic and spin–orbit coupling effects. Competing Jahn‐Teller and spin–orbit coupling effects result in a magnetic bistability of PtF₄, for which a spin‐triplet (³B_2g, D_2h) coexists with an electronic singlet state (¹A_1g, D_4h) in solid neon matrices.

Interfacial Contact is Required for Metal-Assisted Plasma Etching of Silicon

For decades, fabrication of semiconductor devices has utilized well-established etching techniques to create complex nanostructures in silicon. The most common dry process is reactive ion etching which fabricates nanostructures through the selective removal of unmasked silicon. Generalized enhancements of etching have been reported with mask-enhanced etching with Al, Cr, Cu, and Ag masks, but there is a lack of reports exploring the ability of metallic films to catalytically enhance the local etching of silicon in plasmas. Here, metal-assisted plasma etching (MAPE) is performed using patterned nanometers-thick gold films to catalyze the etching of silicon in an SF6/O2 mixed plasma, selectively increasing the rate of etching by over 1000%. The catalytic enhancement of etching requires direct Si-metal interfacial contact, similar to metal-assisted chemical etching (MACE), but is different in terms of the etching mechanism. The mechanism of MAPE is explored by characterizing the degree of enhancement as a function of Au catalyst configuration and relative oxygen feed concentration, along with the catalytic activities of other common MACE metals including Ag, Pt, and Cu.

After 20 Years, Theoretical Evidence That “AuF7” Is Actually AuF5·F2

Quantum-chemical calculations at the DFT (BP86, PBE, TPSS, B3LYP, PBE0), MP2, CCSD, and CCSD(T) levels have been carried out to characterize the putative AuF(7) reported in 1986 by Timakov et al. Our calculations indicate clearly that the species claimed to be AuF(7) had not been synthesized. Instead, a new gold fluoride complex AuF(7) x F2 was prepared. This complex is 205 kJ mol(-1) more stable than the proposed AuF(7) species, and the elimination of F(2) is calculated to be endothermic. This is consistent with the reported stability of the product. A reported experimental vibrational frequency at 734 cm(-1) was verified computationally to be the F-F stretching mode of the end-on coordinated F2 molecule. This result is in line with the recently published trends in the highest attainable oxidation states of the 5d transition metals where Au(V) remains the highest oxidation state of gold.

On the Existence of Molecular Palladium(VI) Compounds: Palladium Hexafluoride

A theoretical study of the accessibility of hexacoordinate palladium(VI) compounds is presented. Species such as [Pd(SiR3)6], [PdCl6], and [Pd(OH)6] are predicted to be unstable toward reductive elimination of the ligands. In contrast, the presence of a stable palladium(VI) center is expected in [PdF6], a low-spin nearly octahedral molecule with a weak Jahn-Teller distortion and highly covalent Pd-F bonds. A vibrational analysis confirms such a geometry as an energy minimum, and a special distribution of its spin density makes PdF6 a highly interesting synthetic target.

Solid State Molecular Structures of Transition Metal Hexafluorides

Single-crystal structure determinations of all nine transition metal hexafluorides (Mo, Tc, Ru, Rh, W, Re, Os, Ir, and Pt) at -140 degrees C are presented. All compounds crystallize alike and have the same molecular structure. The bond length sequence r(w-F) congruent with r(Re-F) congruent with r(Os-F) < r(Ir-F) < r(Pt-F) is confirmed and paralleled by the sequence r(Mo-F) congruent with r(Tc-F) congruent with r(Ru-F) < r(Rh-F). Within the limits of precision, no systematic deviation from octahedral symmetry can be established. DFT and ab initio calculations predict octahedral structures for MoF6 and RhF6 and tetragonally distorted structures for ReF6 and RuF6. The energy barrier toward octahedral structures is only 2.5 kJ mol(-1) in the two latter cases. Calculated electron affinities are in the sequence MoF6 < TcF6 < RhF6 < RuF6 with a value of 6.98 eV for the latter. O2+RhF6- crystallized in an undisordered manner in P, isostructural to the low-temperature form of O2+AuF6-. RhF6- has a D4h compressed octahedral structure, while AuF6- is essentially octahedral. The absorption spectrum of TcF6 and the 19F and 195NMR spectra of PtF6 are presented.

Has AuF7 Been Made?

Quantum chemical calculations at DFT (BP86, B3LYP, BHLYP), MP2, CCSD, and CCSD(T) levels have been carried out on various fluoro complexes of gold in oxidation states +V through +VII to evaluate the previously claimed existence of AuF7. The calculations indicate clearly that elimination of F2 from AuF7 is a strongly exothermic reaction with a low activation barrier. This is inconsistent with the reported stability of AuF7 up to room temperature. A reported experimental vibrational frequency at 734 cm(-1) for AuF7 could not be verified computationally. It is concluded that the reported observation of AuF7 was probably erroneous. As the calculations indicate also an extremely large electron affinity and little stability for AuF6, Au(V) remains the highest well-established gold oxidation state.

Synthesis and structure of formally hexavalent palladium complexes

Formally hexavalent palladium complexes have been isolated and structurally characterized for the first time. Thermal condensation reaction of three molecules of 1,2-C6H4(SiH2)2PdII(R2PCH2CH2PR2) (where R is defined as a methyl or ethyl) provided trinuclear palladium complexes. Single-crystal x-ray analysis revealed that each of the central palladium atoms of the complexes is ligated by six silicon atoms and is hexavalent, whereas the other palladium atoms are divalent.