CO₂ Coordination to Nickel Atoms:  Matrix Isolation and Density Functional Studies

Abstract

The interaction of the CO2 molecule with nickel atoms was studied by using matrix isolation spectroscopy and density functional theory. In argon dilute matrices, no reaction occurs, even after annealing the deposit. In neat CO2 matrices, it is shown that carbon dioxide forms a 1:1 complex with nickel which is characterized by its UV−visible and FTIR absorptions, including isotopically labeled species. Theory predicts the side-on coordination mode to be the most stable. The binding energy of the side-on Ni(CO2) complex is estimated to be 18 kcal/mol. The calculated OCO angle is 145°, which is quite a large value compared to those encountered in other known CO2 complexes. In dinitrogen matrices, the yield of CO2 complexation is considerably enhanced relative to that in argon dilute and neat CO2 matrices, which is attributed to the formation of unsaturated Ni(N2) n complexes prior to CO2 coordination. The CO2 binding energies calculated for the Ni(CO2)(N2) n (n = 1, 2) complexes (respectively 32 and 4 kcal/mol) suggest that CO2 probably coordinates to the Ni(N2) complex. This is a very interesting result, owing to the fact that CO2 does not react with nickel atoms in dilute argon matrices.

Ab initio study of the reaction mechanism of CO2 with Ti atom in the ground and excited electronic states

“…The reaction is endothermic by ϳ36 kcal/mol, and all intermediate steps appeared to be endothermic as well; the cyclic NiCO 2 and linear CONiO molecules lie 17-37 kcal/mol above the reactants at different levels of theory and the barrier for the last reaction step reaches ϳ50-60 kcal/mol relative to NiϩCO 2 . Earlier combined matrix isolation and density functional studies by Galan et al 25 showed that a singlet side-on ( 2 -C,O) NiCO 2 complex is the global minimum on the PES, with the binding energy of ϳ18 kcal/mol. Interestingly, the MϩCO 2 →MO ϩCO reaction mechanisms for various alkaline-earth atoms are rather similar to that for MϭNi.…”

Carbon Dioxide Fixation into Organic Compounds

“…Useful information comes from the studies on the interaction of carbon dioxide with low temperature gas matrices [8]. A great emphasis has been put in the '70s and '80s on elucidating the possible role of COz-metal complexes [6,9], bearing the cumulene either llor u-bonded to one or more metal centres, in both the carbon dioxide reduction and the reaction with organic substrates like olefins.…”

“…This issue is relevant to the more general question if the coordination of COz to a metal is a necessary pre-requisite for the COz fixation onto an organic substrate may occur. While the co-ordination to a metal system is essential for carbon dioxide reduction (C-O bond splitting [6,8] or protonation [10,11]), literature data do not show that such metal complexes have a role in the olefin-Cö, coupling. In fact, either the olefin is activated first (a) or a three centers mechanism (b) may operate.…”

“…The synthesis takes place at relatively mild temperatures ( below 373 K ) and pressures (2)(3)(4)(5)(6)(7)(8). Polymers with high molecular mass are obtained: 10 4 g/mol, from propylene oxide; 3.8 10 5 g/mol, from cyclohexene oxide.…”

Υβρίδια Οργανικών Και Ανόργανων Νανο-Υλικών Με Προκαθορισμένες Ιδιότητες

“…[107][108][109][110][111][112][113][114][115][116][117][118] Μία από τις πολλά υποσχόµενες διαδικασίες σε αυτή την κατεύθυνση είναι η µετατροπή του CO 2 σε CO ή υδρογονάνθρακες, [119][120][121][122][123] η οποία µπορεί να επιτευχθεί µε την αλληλεπίδραση του CO 2 µε διάφορους καταλύτες (κυρίως υλικά που βασίζονται σε οξείδια και µέταλλα µετάβασης). Μεταξύ αυτών των καταλυτών, ο πιο διαδεδοµένος είναι το TiO 2 146 και κυρίως η θερµοδυναµικά σταθερή (110) επιφάνεια του ρουτιλίου [147][148][149][150] (Εικόνα 7). Επίσης, µελέτες έχουν γίνει και για την προτιµητέα (101) επιφάνεια της ανατάσης, αλλά είναι περιορισµένες κυρίως λόγω της δυσκολίας απόκτησης µεγάλων Γραµµική διαµόρφωση (Ρουτίλιο) Αρθρωτή διαµόρφωση (Ανατάση)…”