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  1. Experimentally conducted reactions between CO 2 and various substrates ( i.e. , ethylenediamine (EDA), ethanolamine (ETA), ethylene glycol (EG), mercaptoethanol (ME), and ethylene dithiol (EDT)) are considered in a computational study. The reactions were previously conducted under harsh conditions utilizing toxic metal catalysts. We computationally utilize Brønsted acidic ionic liquid (IL) [Et 2 NH 2 ]HSO 4 as a catalyst aiming to investigate and propose ‘greener’ pathways for future experimental studies. Computations show that EDA is the best to fixate CO 2 among the tested substrates: the nucleophilic EDA attack on CO 2 is calculated to have a very small energy barrier to overcome (TS1EDA, Δ G ‡ = 1.4 kcal mol −1 ) and form I1EDA (carbamic acid adduct). The formed intermediate is converted to cyclic urea (PEDA, imidazolidin-2-one) via ring closure and dehydration of the concerted transition state (TS2EDA, Δ G ‡ = 32.8 kcal mol −1 ). Solvation model analysis demonstrates that nonpolar solvents (hexane, THF) are better for fixing CO 2 with EDA. Attaching electron-donating and -withdrawing groups to EDA does not reduce the energy barriers. Modifying the IL via changing the anion part (HSO 4 − ) central S atom with 6 A and 5 A group elements (Se, P, and As) shows that a Se-based IL can be utilized for the same purpose. Molecular dynamics (MD) simulations reveal that the IL ion pairs can hold substrates and CO 2 molecules via noncovalent interactions to ease nucleophilic attack on CO 2 . 
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  2. null (Ed.)
    An ab initio molecular dynamics investigation of the solvent effect (water) on the structural parameters, 195 Pt NMR spin–spin coupling constants (SSCCs) and chemical shifts of a series of pyridonate-bridged Pt III dinuclear complexes is performed using Kohn–Sham (KS) Car–Parrinello molecular dynamics (CPMD) and relativistic hybrid KS NMR calculations. The indirect solvent effect ( via structural changes) has a dramatic effect on the 1 J PtPt SSCCs. The complexes exhibit a strong trans influence in solution, where the Pt–Pt bond lengthens with increasing axial ligand σ-donor strength. In the diaqua complex, where the solvent effect is more pronounced, the SSCCs averaged for CPMD configurations with explicit plus implicit solvation agree much better with the experimental data, while the calculations for static geometry and CPMD unsolvated configurations show large deviations with respect to experiment. The combination of CPMD with hybrid KS NMR calculations provides a much more realistic computational model that reproduces the large magnitudes of 1 J PtPt and 195 Pt chemical shifts. An analysis of 1 J PtPt in terms of localized and canonical orbitals shows that the SSCCs are driven by changes in the s-character of the natural atomic orbitals of Pt atoms, which affect the 'Fermi contact' mechanism. 
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