Rhodium gem-dicarbonyl complexes, Rh(CO) 2 , bonded within the pore structure of zeolite HY and formed by the reaction of Rh(CO) 2 (acac) (acac = acetylacetonato) with OH groups on the zeolite surface were converted in >95% yield to Rh 4 (CO) 12 by reaction with CO + water at 308 K, and the process was reversed by treatment of the supported clusters in helium at 353 K. The chemistry of these reactions was characterized by IR and X-ray absorption spectra recorded during the changes and by density functional theory. The cluster formation is driven by the water gas shift half-reaction, leading to generation of CO 2 and zeolite surface protons, and the reverse reaction proceeds via the half-reaction that completes the cycle of the water gas shift reaction. Thus, the overall process is cyclic− catalytic. The yield in the synthesis of Rh 4 (CO) 12 is the highest reported, and the high selectivity is facilitated by the confining environment for the clusters in the zeolite supercages and the low density of OH groups on the zeolite surface (the zeolite Si:Al atomic ratio was 30). The results provide insights into the first steps of sintering of atomically dispersed metals on supports.

The heats of formation of the carbonate, bicarbonate, and bicarbonate/hydroxide metal complexes, including hydrates of Mg2+, Ca2+, Fe2+, and Cd2+, and the oxides, dichlorides, and dihydroxides are predicted from atomization energies using correlated molecular orbital theory at the CCSD­(T) level extrapolated to the complete basis set limit following the Feller–Peterson–Dixon (FPD) approach. Using the calculated gas phase values and the available experimental solid-state values, we predicted the cohesive energies of selective minerals. The gas phase decomposition energies of MO, CO2, and H2O follow the order Mg ≈ Ca > Cd ≈ Fe and correlate with the hardness of the metal +2 ions. Gas phase hydration energies show that the order is Mg > Fe > Ca ≈ Cd. There are a number of bulk hydrated Mg and Ca complexes that occur as minerals but there are few if any for Fe and Cd, suggesting that a number of factors are important in determining the stability of the bulk mineral hydrates. The FPD heats of formation were used to benchmark a range of density functional theory exchange–correlation functionals, including those commonly used in solid-state mineral calculations. None of the functionals provided chemical accuracy agreement (±1 kcal/mol) with the FPD results. The best agreement to the FPD results is predicted for ωB97X and ωB97X-D functionals with an average unsigned error of 10 kcal/mol. The worst functionals are PW91, BP86, and PBE with average unsigned errors of 32–36 kcal/mol.

Low-energy minima structures for (CaCO3) n , n ≤ 28, are predicted using bottom-up genetic algorithms in conjunction with density functional theory electronic structure calculations, in comparison with the frozen and relaxed top-down clusters generated by cuts from the calcite, vaterite, and aragonite crystal structures. Similarities in structural motifs for the bottom-up and relaxed top-down are revealed using a fragment recognition technique. Fragment energy decomposition analysis shows that the bottom-up and relaxed top-down clusters belong to two classes of amorphous clusters with distinct intracluster energy distributions, despite their structural similarity. The bottom-up clusters with >20 formula units are surface stabilized with negative surface energy densities. In contrast, the top-down clusters are interior stabilized with positive surface energy densities. We prove that the sign of the surface energy density determines whether the nucleation reaction energy as a function of nuclear size has a maximum or a minimum. The surface-stabilized bottom-up clusters are proposed to be a type of prenucleation cluster at the minimum of the nucleation reaction energy. A mechanism for mineralization of CaCO3 involving prenucleation clusters and nonclassical growth pathway is proposed on the basis of our theoretical findings, which is consistent with previous titration experiments.

The gas phase heats of formation of ground-state MCO3, M(HCO3)2, and M(HCO3)(OH), where M = Mn, Co, Ni, Cu, and Zn, have been predicted using the correlated molecular orbital theory at the CCSD(T) level extrapolated to the complete basis set limit using the Feller–Peterson–Dixon (FPD) approach. Cohesive energies of the carbonates were predicted based on the calculated gas phase and experimental solid heats of formation. Coulombic dissociation energies (CDEs) between metal cations and anions show a near-linear correlation with Shannon metal cation atomic radii, yet no correlation is found with the hardness of these cations. The total reaction dissociation energies (TRDEs) of transition metals are higher than their CDEs for the di-bicarbonates, in contrast to those for Mg and Ca based on our prior work. In addition to differences in the energies needed to prepare the transition metal dications, electron donation from the ligands to the 3d orbitals of open-shell transition metal dications from lone pairs of adjacent O atoms also plays a role. No electron donation from the ligands to the fully occupied 3d orbitals of Zn and Cd was found. Decomposition energies for generating MO, CO2, and/or H2O were calculated. Gas phase metal exchange energies only partially correlate with the electrochemical series for M(s) → M2+(aq). The FPD heats of formation were used to benchmark a range of density functional theory exchange–correlation functionals, including those commonly used in solid-state mineral calculations. None of the functionals provided chemical accuracy agreement (±1 kcal/mol) with the FPD results. The best agreement with the FPD results is predicted for the τ-HCTH functional with an average unsigned error of 8.3 kcal/mol.

The chemisorption addition of CO 2 to M 3 O 6 and M 3 O 6− for M = Ti, Zr, and Hf was examined using couple cluster CCSD(T) theory using density functional theory B3LYP geometries. For neutral M 3 O 6 CO 2 , a bridge chemisorbed tridentate carbonate cluster is the lowest energy for Ti and Zr, and a terminal chemisorbed bidentate carbonate is the lowest energy for Hf. For anionic M 3 O 6 CO 2 − , the lowest energy structure is a terminal chemisorbed bidentate carbonate for all three metals. The use of correlation-consistent weighted core basis sets for the CCSD(T) calculations is shown to be necessary to obtain the correct energy ordering for the isomers. Only for Ti 3 O 6 CO 2 − is a center tridentate carbonate cluster a low energy isomer. The electron affinities of M 3 O 6 CO 2 are ∼0.2 eV larger than for M 3 O 6 . The CO 2 chemisorption binding energies increase slightly for M 3 O 6 − as compared to those for M 3 O 6 .