From the reactions between Mo2(DAniF)3pivalate (DAniF = N,N'-di(p-anisyl)formamidinate) and the carboxylic acids LH, the title compounds Mo2(DAniF)3L have been prepared and characterized: compounds I (L = O2CC≡CPh), II (L = O2CC4H2SC≡CH), and III (L = O2CC6H4-p-CN). The new compounds have been characterized in their ground states by spectroscopy ((1)H NMR, ultraviolet-visible absorption, near-infrared absorption, and steady state emission), cyclic voltammetry, and density functional theory calculations. The compounds show strong metal Mo2 to ligand L δ-π* transitions in their visible spectra. The nature of the S1 (1)MLCT and T1 states has been probed by time-resolved (femtosecond and nanosecond) transient absorption and infrared spectroscopy. The observed shifts of the C≡C and C≡N vibrational modes are found to be consistent with the negative charge being localized on the single L in the S1 states, while the T1 states are (3)Mo2 δδ*. The present results are compared to earlier studies of the photoexcited states of trans-Mo2(2,4,6-triisopropylbenzoate)2L2 compounds that have been assigned as either localized or delocalized.
The compounds trans-M 2 (T i PB) 2 (L) 2 and trans-M 2 (T i PB) 2 (L 0 ) 2 have been prepared from the reactions between M 2 (T i PB) 4 (T i PB ¼ 2,4,6-triisopropylbenzoate, M ¼ Mo or W) and LH or L 0 H ($2 equiv.), respectively, whereThese cyanoacrylate ligands promote intense M 2 d to L or L 0 p*-transitions that span the range 550-1100 nm. The two molybdenum complexes have been characterized by single crystal X-ray studies that reveal the extensive L-M 2 -L or L 0 -M 2 -L 0 M 2 d-ligand p-conjugation. The new compounds have been characterized by electronic structure calculations employing density functional theory (DFT) and time-dependent-DFT, cyclic voltammetry, electronic absorption and steady state emission spectroscopy and femtosecond (fs) and nanosecond (ns) time resolved transient absorption (TA) and fs time-resolved infrared spectroscopy (TRIR). The latter allows the determination of the S 1 states as 1 MLCT that are delocalized over both L and L 0 . For molybdenum the T 1 states are 3 MoModd* whereas for tungsten they are 3 MLCT.
Repetitive syntheses of six AuPt/Vulcan carbon (VC) and six AuPd/VC nanocomposites by NaBH4 solution reduction of equimolar mixtures of HAuCl4 · xH2O and H2PtCl6 · 6H2O salts or HAuCl4 · xH2O and Na2PdCl4 salts gives nanocomposites having highly dispersed metal alloy nanoparticles of similar average size (4–7 ± 2 nm). Significant variation in nanocomposite physical and electrochemical properties is observed. AuM alloy stoichiometries and total metal wt% vary by as much as ±11 at% and ±5 wt%, respectively. Activities toward electrocatalytic oxidation of formic acid, evaluated by cyclic voltammetry, reveal one electrochemically inactive nanocomposite, higher activities for AuPd/VC nanocomposites than for AuPt/VC nanocomposites, and a maximum mass‐specific current of 3.8 mA cm−2 per mg total metal for one AuPd/VC nancomposite.
TEM image of AuPt/Vulcan carbon (left image) and AuPd/Vulcan carbon (right image) nanocomposites. Bar represents 20 nm.
Evidence, based on femtosecond transient absorption and time resolved infrared spectroscopy, is presented for photoinduced charge transfer from the Mo2δ orbital of the quadruply bonded molecule trans-Mo2(T(i)PB)2(BTh)2, where T(i)PB = 2,4,6-triisopropyl benzoate and BTh = 2,2'-bithienylcarboxylate, to di-n-octyl perylene diimide and di-n-hexylheptyl perylene diimide in thin films and solutions of the mixtures. The films show a long-lived charge separated state while slow back electron transfer, τBET ~ 500 ps, occurs in solution.
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