Probing the SO₂Adsorption Mechanism in Hofmann Clathrates via Inelastic Neutron Scattering and Density Functional Theory Calculations

Abstract

The adsorption mechanism of SO2 in the Hofmann-like coordination polymer Fe­(pz)­[Pt­(CN)4] is studied using inelastic neutron scattering and density functional theory calculations. We find that the most important spectral change upon gas adsorption is the blue shift of the low-energy peak found at 100 cm–1, a feature that is fully confirmed by the computed neutron-weighted phonon density of states. Our calculations suggest that the origin of this change is twofold: (i) an increase in the force constant of the cyanide out-of-plane movement due to the binding of the gas onto the Pt­(CN)4 plane and (ii) the hampered rotation of the pyrazine due to steric hindrance. The high-energy region of the neutron scattering data whose spectral weight is dominated by the internal vibrations of the pyrazine is negligibly affected by the presence of the gas as expected from a physisorption type of binding.

CO and CO2 Adsorption Mechanism in Fe(pz)[Pt(CN)4] Probed by Neutron Scattering and Density-Functional Theory Calculations

“…The gas adsorption results in a larger shift for CO (37 cm −1 ) than CO2 (20 cm −1 ) and the previously studied SO2 molecule (29 cm −1 , see ref. 48). This is well reproduced by the computed S(ω) (see Fig 6).…”

“…We note that at low energy the assignation of the vibrational modes from the calculations is more challenging compared to higher energy (see for example the intense peak at 100 cm −1 as compared to that at 400 cm −1 ). While at around 400 cm −1 a good agreement between experiment and DFT is found, 48,51 low energy modes present larger relative errors possibly due to the underlying approximations (basis set and functional choice may affect this part of the spectra).…”

“…For the bare material the pyrazines are considered perpendicular in agreement with previous calculations and experimental findings. 48,49 The scattering function upon CO adsorption in Figure 4 is computed by adopting the configuration described in the previous section with 2 molecules per f.u. and pyrazines in a parallel orientation.…”

Hidden ordered structure in the archetypical Fe(pyrazine)[Pt(CN)4] spin-crossover porous coordination compound

“…It deserves to be noted that the perpendicular configuration is also the one found compatible with the experimental results and calculations when certain types (and quantities) of molecules are adsorbed. 13,32 In the high-spin state, the diffractogram does not show any signal of superstructure reflections and can be satisfactorily fitted with the disordered model with the space group P 4/ mmm (Fig. 3c).…”

Hidden ordered structure in the archetypical Fe(pyrazine)[Pt(CN)4 ] spin-crossover porous coordination compound

“…It deserves to be noted that the perpendicular configuration is also the one found compatible with the experimental results and calculations when certain types (and quantities) of molecules are adsorbed. 13,32 In the high-spin state, the diffractogram does not show any signal of superstructure reflections and can be satisfactorily fitted with the disordered model with space group P 4/mmm (Fig. 3c).…”