Absorption of CO₂ and CS₂ into the Hofmann-Type Porous Coordination Polymer: Electrostatic versus Dispersion Interactions

Abstract

Absorption of CO2 and CS2 molecules into the Hofmann-type three-dimensional porous coordination polymer (PCP) {Fe(Pz)[Pt(CN)4]}n (Pz = pyrazine) was theoretically explored with the ONIOM(MP2.5 or SCS-MP2:DFT) method, where the M06-2X functional was employed in the DFT calculations. The binding energies of CS2 and CO2 were evaluated to be -17.3 and -5.2 kcal mol(-1), respectively, at the ONIOM(MP2.5:M06-2X) level and -16.9 and -4.4 kcal mol(-1) at the ONIOM(SCS-MP2:M06-2X) level. It is concluded that CS2 is strongly absorbed in this PCP but CO2 is only weakly absorbed. The absorption positions of these two molecules are completely different: CO2 is located between two Pt atoms, whereas one S atom of CS2 is located between two Pz ligands and the other S atom is between two Pt atoms. The optimized position of CS2 agrees with the experimentally reported X-ray structure. To elucidate the reasons for these differences, we performed an energy decomposition analysis and found that (i) both the large binding energy and the absorption position of CS2 arise from a large dispersion interaction between CS2 and the PCP, (ii) the absorption position of CO2 is mainly determined by the electrostatic interaction between CO2 and the Pt moiety, and (iii) the small binding energy of CO2 comes from the weak dispersion interaction between CO2 and the PCP. Important molecular properties relating to the dispersion and electrostatic interactions, which are useful for understanding and predicting gas absorption into PCPs, are discussed in detail.

Spin-crossover Compounds with Wide Thermal Hysteresis

“…In contrast, most other guest species strongly interact with just one of those framework sites. 77,78 Guest intercalation into some other spin-crossover materials of the Hofmann type has a similarly variable effect on their spin transitions, but no other examples leading to wide hysteresis have yet been reported. 4 ]¢1/2SC(NH 2 ) 2 .…”

Theoretical and Computational Study of a Complex System Consisting of Transition Metal Element(s): How to Understand and Predict Its Geometry, Bonding Nature, Molecular Property, and Reaction Behavior

“…Another is the position between two platinum atoms, which is called the Pt site. Because it is not easy to describe the absorption at these two sites with one model, we employed two model systems shown in Scheme 34; 152 the above was used to investigate the gas absorption at the pyrazine site and the below was used to investigate the gas absorption at the Pt site. Because the dispersion interaction plays crucial roles in the interaction between a gas molecule and the pyrazine moiety, 153 we must use a computational method which can represent well the dispersion interaction.…”

Guest Modulation of Spin‐Crossover Transition Temperature in a Porous Iron(II) Metal–Organic Framework: Experimental and Periodic DFT Studies

“…In previous experimental and theoretical works, we presented an analysis of the interaction between the host {Fe(pz)[Pt(CN) 4 ]} and the guests thiourea and SO 2 employing periodic DFT calculations. [9] Finally, Deshmukh et al [21] calculated the differences in CS 2 and CO 2 uptake in {Fe(pz)[Pt(CN) 4 ]} by means of DFT and MP2 QM/MM calculations.…”