Showing papers by "David K. Shuh published in 2009"

A comparison of 4f vs 5f metal-metal bonds in (CpSiMe3)3M-ECp* (M = Nd, U; E = Al, Ga; Cp* = C5Me5): synthesis, thermodynamics, magnetism, and electronic structure.

Abstract: Reaction of (CpSiMe3)3U or (CpSiMe3)3Nd with (Cp*Al)4 or Cp*Ga (Cp* = C5Me5) afforded the isostructural complexes (CpSiMe3)3M−ECp* (M = U, E = Al (1); M = U, E = Ga (2); M = Nd, E = Al (3); M = Nd, E = Ga (4)). In the case of 1 and 2 the complexes were isolated in 39 and 90% yields, respectively, as crystalline solids and were characterized by single-crystal X-ray diffraction, variable-temperature 1H NMR spectroscopy, elemental analysis, variable-temperature magnetic susceptibility, and UV−visible−NIR spectroscopy. In the case of 3 and 4, the complexes were observed by variable-temperature 1H NMR spectroscopy but were not isolated as pure materials. Comparison of the equilibrium constants and thermodynamic parameters ΔH and ΔS obtained by 1H NMR titration methods revealed a much stronger U−Ga interaction in 2 than the Nd−Ga interaction in 4. Competition reactions between (CpSiMe3)3U and (CpSiMe3)3Nd indicate that Cp*Ga selectively binds U over Nd in a 93:7 ratio at 19 °C and 96:4 at −33 °C. For 1 and 3, c...

Using the Antenna Effect as a Spectroscopic Tool: Photophysics and Solution Thermodynamics of the Model Luminescent Hydroxypyridonate Complex [EuIII(3,4,3-LI(1,2-HOPO))]−

Abstract: While widely used in bioassays, the spectrofluorimetric method described here uses the antenna effect as a tool to probe the thermodynamic parameters of ligands that sensitize lanthanide luminescence. The Eu3+ coordination chemistry, solution thermodynamic stability and photophysical properties of the spermine-based hydroxypyridonate octadentate chelator 3,4,3-LI(1,2-HOPO) are reported. The complex [EuIII(3,4,3-LI(1,2-HOPO))]- luminesces with a long lifetime (805 mu s) and a quantum yield of 7.0percent in aqueous solution, at pH 7.4. These remarkable optical properties were exploited to determine the high (and proton-independent) stability of the complex (log beta 110 = 20.2(2)) and to define the influence of the ligand scaffold on the stability and photophysical properties.