Coordination chemistry
Rotating pyrazine rings put a kink in Xe isotherms
Open access · cc by · source: Europe PMC
SIFSIX-3-Fe takes up more Xe than Kr because its pores match Xe, while an inflection in SIFSIX-3-Ni’s Xe isotherm is attributed to pyrazine rings ordering from disordered to aligned rotations.
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Rotating pyrazine rings put a kink in Xe isotherms
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SIFSIX-3-Fe Xe/Kr uptakes at 1 atm and 298 K were 54.9 and 30.8 cm3 STP g−1.
Xe uptake of SIFSIX-3-Fe at 1 atm and 298 K was found to be 54.9 cm 3 STP g –1 , whereas Kr uptake is 30.8 cm 3 STP g –1 .
What MOF platform was studied?
Herein, we present experimental observations and computational studies of the influence of rotating pyrazine rings in the pillared square grid platform, SIFSIX-3-M, of formula [M(pyz) 2 SiF 6 ] (M = Fe or Ni; pyz = pyrazine)
Key findings
At 1 atm/298 K, SIFSIX-3-Fe adsorbs 54.9 cm3 STP g−1 Xe vs 30.8 Kr; Ni analogue 56.2 vs 12.6. Xe Qst at infinite dilution is 27.4 kJ mol−1 (Fe) vs 18.9 (Ni). The Ni inflection tracks a disordered-to-ordered ring rotation, not breathing.
Methodology
Authors synthesised pillared [M(pyz)2SiF6] (M = Fe, Ni), measured Xe/Kr isotherms and isosteric heats, and used computation of IN/OUT pyrazine configurations to explain a non-Langmuirian inflection.
Limitations
The rotational model is inferred from isotherms and computation, not a single-crystal movie of rings flipping under Xe.
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