150485-46-4Relevant academic research and scientific papers
Marked wavelength dependence in photolyses of dithiophosphate complexes of the [Mov2O3]4+ core through a photoactive intermediate accessed by a secondary thermal equilibrium
Thompson, Robert L.,Geib, Steven J.,Cooper, N. John
, p. 6076 - 6083 (2008/10/08)
Beer's law plots for the oxo-bridged d1-d1 dimers [Mo2O3{S2P(OR)2}4] (R = Et, 3; R = Ph, 4; R = Me, 5) exhibit positive deviations from linearity, suggestive of dissociative equilibria. In the case of 3 it has been established by 31P NMR that this is a consequence of the disproportionation equilibrium between 3 and its d2 and d0 disproportionation products [MoO{S2P(OEt)2}2] (6) and [MoO2{S2P(OEt)2}2] (7), both of which have been independently prepared. 31P NMR spectroscopy has been used to measure the dissociation constants, Kdiss, for 3, 4, and 5 at various temperatures, and hence to determine ΔG298, ΔH and ΔS values of 4.43 ± 0.05 kcal mol-1, 12.1 ± 1.0 kcal mol-1, and 25.6 ± 4.2 cal mol-1 K-1 for 3; 4.08 ± 0.06 kcal mol-1, 11.2 ± 1.3 kcal mol-1, and 23.8 ± 4.2 cal mol-1 K-1 for 4; and 3.68 ± 0.06 kcal mol-1, 12.6 ± 1.0 kcal mol-1, and 30.0 ± 4.5 cal mol-1 K-1 for 5. A single-crystal diffraction study has established that 5 (monoclinic space group P21/c; with a = 8.235(3) A?, b = 16.544(5) A?, c = 11.444(5) A?, β = 103.79(2)°, Z = 2, and R = 4.7%) has a typical [MoV2O3]4+ core with a linear bridging oxo group with an anti orientation for the terminal oxo groups. Solutions of 3, 4, and 5 are irreversibly bleached by UV light (400 nm) despite the presence of intense absorptions at 500 nm (ε500 = 11 800, 27 200, and 16 600 L mol-1 cm-1 respectively for 3, 4, and 5). Disappearance quantum yields for photolysis of 3, 4, and 5 at various irradiation wavelengths are modest in the UV (Φ = 10-3-10-2) but negligible at 510 nm (Φ510 -4, giving rise to Φ310:Φ510 ratios of >150, >180, and >60 respectively for 3, 4, and 5. It is proposed that this marked wavelength dependence arises because the d1-d1 dimers are not themselves photoactive, but are destroyed through photolysis of the d0 disproportionation products [MoO2{S2P(OR)2}2] as confirmed for the case of 3 by independent determination of the disappearance quantum yield for 7 as 0.12 at 310 nm.
