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The strong CO ligand vibrations of an octahedral complex, fac- [Re (CO) 3 (bpy)(CH 3 CN)] + , in acetonitrile are observed at 2040 and 1932 cm -1 . Facial rhenium tricarbonyl systems offer very strong and isolated CO vibrations with the potential for interactions between these vibrations. This work first identifies the dominant ion-pair species using attenuated total reflection infrared (ATR-IR) absorption spectra on a dilution series and then determines the strength of these CO ligand vibrations (as isolated vibrations) with a combination of ATR-IR and etalon-based measurements that determine the absolute complex index of refraction of the solution. Finally, the etalon experiments are modeled to study the interaction between vibrations, which is a property not embedded in the solution's complex index of refraction. The ATR-IR spectra are accomplished on a dilution series as well as a larger set of spectra as these solutions evaporated. The A'(1) CO ligand band at 2040 cm -1 is fit with a sum of three Lorentzian functions characterizing the distribution of free, solvent-separated, and contact ion pairs of this octahedral complex vs concentration. The other CO ligand band at 1932 cm -1 is broader and complicated by the dynamics of vibrational interactions, the unresolved splitting of the A'(2) and A″ CO vibrations, and ion-pair speciation. The etalon transmission measurements vs angle were on a 0.029 M solution, and Rabi splittings of 19 and 38 cm -1 were observed for the A'(1) CO vibration and the unresolved A'(2) + A″ CO vibrations, respectively. The great strength of the CO ligand vibrations is evident despite the use of a dilute solution. Integrated band intensities are reported in comparison to hybrid density functional calculations for isolated vibrations. Then, the observed Rabi splittings are modeled to obtain the coupling strength of the CO ligand vibration with etalon cavity modes and with each other. In summary, this work develops a method to determine the concentration of these solutions from the ATR-IR spectrum, characterizes the ion-pairing, shows that the index of refraction is not constant in the IR spectral region of interest, and develops an interaction Hamiltonian that characterizes cavity-vibration and vibration-vibration coupling.

A new method is established using an etalon cavity to assist in the determination of the wavelength-dependent complex index of refraction of a solution throughout the mid-infrared range. The results are used to study the cavity-vibration polaritons of PF 6 - in acetonitrile. Mixed states are formed by placing solution inside a pair of parallel plate mirrors with a wavelength-scale spacing, i.e ., within an etalon, such that there are cavity states that are angle-tuned into resonance with the strong P-F vibrations. The dominant ν 3 vibrations of PF 6 - consist of nearly triply degenerate oscillations of the partial-positively charged phosphorous against antisymmetric concerted motions of different sets of fluorine atoms with partial negative charges. These vibrations are dominant even though the solute is 29 times less concentrated than the solvent on a molar basis. The first part of the paper describes the method of determining the complex index of refraction of the solution from a combination of etalon transmission maxima and the attenuated total reflection (ATR) absorption spectrum of the solution. The results are presented as an analytical function including a sum of 37 vibrational contributions. Absolute integrated isolated band intensities were determined to be 463 ± 4, 462 ± 7, and 266 ± 4 km/mol for the three ν 3 PF 6 - vibrations at 841.4, 847.4, and 854.0 cm -1 , respectively, which sum to 1191 ± 9 km/mol for the ν 3 band. Then, the results are used to simulate the measured etalon transmission using the transfer matrix (TM) method with and without the ν 3 target vibrations. The etalon transmission simulations reconstruct the position of cavity modes in the absence of target vibrations. They provide input data for the testing of simple quantum mechanical models for the interaction of vibrations with cavity modes and the interactions of vibrations with other vibrations within the molecule and between solute and solvent. The model shows that the nearly degenerate ν 3 vibrations interact with each other with a vibration-vibration coupling of 33 ± 5 cm -1 . This is comparable to the cavity-vibration coupling of 30.4 ± 2.9 cm -1 of the two strongest vibrations of PF 6 - .

Ligand-stabilized platinum nanoparticles (Pt NPs) can be used to build well-defined three-dimensional (3-D) nanostructured electrodes for better control of the catalyst architecture in proton exchange membrane fuel cells (PEMFCs). Platinum NPs of 1.7 +/- 0.5 nm diameter stabilized by the water-soluble phosphine ligand, tris(4-phosphonatophenyl)phosphine (TPPTP, P(4-C6H4PO3H2)3), were prepared by ethylene glycol reduction of chloroplatinic acid and subsequent treatment of the isolated nanoparticles with TPPTP. The isolated TPPTP-stabilized Pt NPs were characterized by multinuclear magnetic resonance spectroscopy (31P and 195Pt NMR), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and extended X-ray absorption fine structure (EXAFS). The negatively charged TPPTP-Pt NPs were electrostatically deposited onto a glassy carbon electrode (GCE) modified with protonated 4-aminophenyl functional groups (APh). Multilayers were assembled via electrostatic layer-by-layer deposition with cationic poly(allylamine HCl) (PAH). These multilayer films are active for the key hydrogen fuel cell reactions, hydrogen oxidation (anode) and oxygen reduction (cathode). Using a rotating disk electrode configuration, fully mass-transport limited kinetics for hydrogen oxidation was obtained after 3 layers of TPPTP-Pt NPs with a total Pt loading of 4.2 microg/cm2. Complete reduction of oxygen by four electrons was achieved with 4 layers of TPPTP-Pt NPs and a total Pt loading of 5.6 microg/cm2. A maximum current density for oxygen reduction was reached with these films after 5 layers resulting in a mass-specific activity, i(m), of 0.11 A/mg(Pt) at 0.9 V. These films feature a high electrocatalytic activity and can be used to create systematic changes in the catalyst chemistry and architecture to provide insight for building better electrocatalysts.