The first mixed-valent octanuclear platinum blue compounds with bridging acetamidate and 2-fluoroacetamidate ligands, [(H3N)2Pt(CH3CONH)2Pt(NH3)2]4(NO3)10·4H2O (1) and [(H3N2Pt(CH2FCONH)2Pt(NH3)2]4(NO3)8.66·4H2O (2), are crystallographically characterized. Compound 1 crystallizes in triclinic space group. Z = 1, with a = 12.091 (2) Å, b = 13.557 (3) Å, c = 10.983 (4) Å,α = 100.62 (2)°, β = 97.12 (2)°, γ = 89.79 (2)°, and V = 1756 (1) Å3. Compound 2 crystallizes in triclinic space group. Z = 1, a = 12.214 (5) Å, b = 15.517 (9) Å, c = 10.794 (4) Å, α = 106.86 (4)°, β = 97.92 (3)°, γ = 103.01 (4)°, and V = 1862 (2) Å3. Each octaplatinum complex cation is made up of a zigzag platinum chain formed by the tetramerization of four acetamidate-bridged head-to-head dimers. A new interdimer bonding mode, which has not been observed in the previous amidate-bridged tetranuclear compounds, is achieved between the N4Pt and the N2O2Pt coordination planes in 1 and 2. The Pt-Pt distances in 1, 2.778 (1), 2.880 (2), 2.934 (1), and 2.900 (1) Å, are relatively shorter than those in 2, 2.938 (6), 2.835 (5), 2.979 (5), and 2.962 (5) Å, probably due to thehigher average platinum oxidation state of 1. Compound 1 has been confirmed to be diamagnetic with ESR spectroscopy. The magnetic susceptibility measurement of 2 revealed that the compound has a magnetic moment of μeff = 1.41 μ and is a mixture of two isostructural compounds, diamagnetic [(H3N)2Pt(CH2FCONH)2Pt(NH3)2]48+ and paramagnetic [(H3N)2Pt(CH2FCONH)2Pt(NH3)2]49+, with the weight ratio of 65.77% for the latter. The diffuse reflectance spectrum of 1 shows strong broad absorption bands in the ranges of 450-650 nm with λmax = 500 nm, 650-750 nm and at around 1200 nm with λmax = 1140 nm. The former two bands in the visible region were also observed in the previously reported mixed-valent tetranuclear platinum blues, whereas the third absorption band in the near infrared region does not have its counterpart in the tetranuclear compounds. Extended Hückel molecular orbital calculation of 1 shows that all of the bands arise from the transitions between the MOs which have significant contributions of the Pt 5d-orbitals, and, therefore, the absorption bands can be regarded as the intervalence charge transfers between the Pt atoms. The X-ray photoelectron spectra of 1 and 2 exhibit Pt 4f5/2 and 4f7/2 binding energies at 76.5 and 73.3 eV for 1 and 76.4 and 73.4 for 2, respectively. The comparison of the X-ray photoelectron spectra of several binuclear, tetranuclear, and octanuclear amidate-bridged platinum blue compounds with various average platinum oxidation states shows that, although the 4f7/2 binding energies of 1 and 2 are almost identical with those of the amidate-bridged Pt(II) binuclear compounds, the more broadened and less dented Pt 4f5/2 and 4f7/2 peak profiles compared to those of the binuclear and tetranuclear compounds suggest that several Pt(III) components overlap on the Pt(II) components in these octanuclear compounds.
All Science Journal Classification (ASJC) codes
- Colloid and Surface Chemistry