Context. A recent modeling study of brightness ratios for CO rotational transitions in gas typical of the diffuse ISM by Liszt found the role of H collisions to be more important than previously assumed. This conclusion was based on recent quantum scattering calculations using the so-called WKS potential energy surface (PES) which reported a large cross section for the important 0 → 1 rotational transition. This result is in contradiction to one obtained using the earlier BBH PES for which the cross section is quite small and which is consistent with an expected homonuclear-like propensity for even ∆J transitions. Aims. We revisit this contradiction with new scattering calculations using two new ab initio PESs that focus on the important longrange behavior and explore the validity of the apparent departure from the expected even ∆J propensity in H-CO rotational excitation obtained with the WKS PES. Methods. Close-coupling (CC) rigid-rotor calculations for CO(v = 0, J = 0) excitation by H are performed on four different PESs. Two of the PESs are obtained in this work using state-of-the-art quantum chemistry techniques at the CCSD(T) and MRCI levels of theory. Results. Cross sections for the J = 0 → 1, as well as other odd ∆J, transitions are significantly suppressed compared to even ∆J transitions in thermal energy CC calculations using the CCSD(T) and MRCI surfaces. This is consistent with the expected even ∆J propensity and in contrast to CC calculations using the WKS PES which predict a dominating 0 → 1 transition. Conclusions. Inelastic collision cross section calculations are sensitive to fine details in the anisotropic components of the PES and its long-range behavior. The current results obtained with new surfaces for H-CO scattering suggest that the original astrophysical assumption that excitation of CO by H 2 dominates the kinetics of CO in diffuse ISM gas is likely to remain valid.

Highly porous, polyhedral metal−organic frameworks (MOFs) of Co(II)/Ni(II), {[M 6 (TATAB) 4 (DABCO) 3 (H 2 O) 3 ]•12DMF• 9H 2 O} n (where M = Co(II) (1)/Ni(II) ( 2), H 3 TATAB = 4,4′,4″-striazine-1,3,5-triyl-tri-p-aminobenzoic acid, and DABCO = 1,4diazabicyclo[2.2.2]octane) have been synthesized solvothermally. Both MOFs 1 and 2 show a 2-fold interpenetrated 3D framework structure composed of dual-walled cages of dimension ∼ 30 Å functionalized with a high density of Lewis acidic Co(II)/Ni(II) metal sites and basic -NHgroups. Interestingly, MOF 1 shows selective adsorption of CO 2 with high heat of adsorption (Q st ) value of 39.7 kJ/mol that is further supported by theoretical studies with computed binding energy (BE) of 41.17 kJ/mol. The presence of the high density of both Lewis acidic and basic sites make MOFs 1/2 ideal candidate materials to carry out co-catalyst-free cycloaddition of CO 2 to epoxides. Consequently, MOFs 1/2 act as excellent recyclable catalysts for cycloaddition of CO 2 to epoxides for high-yield synthesis of cyclic carbonates under co-catalystfree mild conditions of 1 bar of CO 2 . Further, MOF 1 was recycled for five successive cycles without substantial loss in catalytic activity. Herein, rational design of rare examples of 3D polyhedral MOFs composed of Lewis acidic and basic sites exhibiting efficient co-catalyst-free conversion of CO 2 has been demonstrated.

The authors have performed a systematic computational study of the hydrogen storage capacity of model organometallic compounds consisting of Sc, Ti, and V transition metal atoms bound to CmHm rings (m=4-6). For all the complexes considered, the hydrogen storage capacity is limited by the 18-electron rule. The maximum retrievable H2 uptake predicted is 9.3 wt% using ScC4H4, slightly better than the 9.1 wt% hydrogen using TiC4H4, and much larger than the approximately 7 wt% hydrogen with VC4H4, where only four H2 molecules can be adsorbed. The kinetic stability of these hydrogen-covered organometallic complexes is reviewed in terms of the energy gap between the highest occupied and lowest unoccupied molecular orbitals and the strength and nature of successive H2 bindings.

The sequential growth of small titanium clusters with up to 15 atoms and the dissociative chemisorption of H2 on the minimum energy clusters have been studied within density functional theory under the generalized gradient approximation. It has been found that the low-energy clusters grow three dimensionally from Ti4 and follow a pentagonal growth pattern. The clusters Ti7 and Ti13 show a higher stability than other clusters with a configuration of pentagonal bipyramid and icosahedron structures, respectively. The second difference of binding energy plot indicates that these two clusters are highly stable; this agrees with the experimental collision-induced dissociation studies and previous theoretical calculations. For the first time, a systematic study of chemical reactivity of small Ti n clusters, with n = 2−15, toward dissociative chemisorption of H2 is performed. It is found that the chemisorption occurs preferentially at the two adjacent edges of any Ti atom. The chemisorption energy as a function of the cluster size shows considerable structural changes in the Ti n clusters due to H2 dissociation and adsorption, and the chemisorption energy of Ti13 cluster is found to be the highest.

ABSTRACT:Structures and physical properties of small palladium clusters Pd n up to n ϭ 15 and several selected larger clusters were studied using density functional theory under the generalized gradient approximation. It was found that small Pd n clusters begin to grow 3-dimensionally at n ϭ 4 and evolve into symmetric geometric configurations, such as icosahedral and fcc-like, near n ϭ 15. Several isomers with nearly degenerate average binding energies were found to coexist and the physical properties of these clusters were calculated. For several selected isomers, relatively moderate energy barriers for structural interchange for a given cluster size were found, implying that isomerization could readily occur under ambient conditions.

Highly efficient visible-light-assisted photocatalytic reduction of Cr(VI) to Cr(III) from water using multifunctional Zr(IV)-porphyrin MOFs, Zr6(μ3-OH)8(OH)8(MTCPP)2, (PCN-222(M)) (M = H2, ZnII, CuII, NiII, CoII, FeIIICl, and MnIIICl) is presented. The...

We report first-principles density functional theory calculations of the interaction between platinum subnanoclusters and the α-Al2O3(0001) surface. Energetically the most favorable adsorption sites were identified and substantial structural relaxation upon adsorption was observed. The optimized adsorption structures and the calculated average adsorption and adhesion energies were found to be size dependent. Results show that the clusters can be stably anchored on the surface with the driving force arising from the charge transfer from Pt atoms to O atoms of the substrate. Calculations of Pt atom agglomeration vs wetting suggest that metal clustering is strongly preferred.

A bifunctional, microporous Zn metal-organic framework, [Zn (NH BDC) (dpNDI)] (MOF1) (where, NH BDC=2-aminoterephthalic acid, dpNDI=N,N'-di(4-pyridyl)-1,4,5,8-naphthalenediimide) has been synthesized solvothermally. MOF1 shows an interesting two-fold interpenetrated, 3D pillar-layered framework structure composed of two types of 1D channels with dimensions of approximately 2.99×3.58 Å and 4.58×5.38 Å decorated with pendent -NH groups. Owing to the presence of a basic functionalized pore surface, MOF1 exhibits selective adsorption of CO with high value of heat of adsorption (Q =46.5 kJ mol ) which is further supported by theoretically calculated binding energy of 48.4 kJ mol . Interestingly, the value of Q observed for MOF1 is about 10 kJ mol higher than that of analogues MOF with the benzene-1,4-dicarboxylic acid (BDC) ligand, which establishes the critical role of the -NH group for CO capture. Moreover, MOF1 exhibits highly selective and sensitive sensing of the nitroaromatic compound (NAC), 2,4,6-trinitrophenol (TNP) over other competing NACs through a luminescence quenching mechanism. The observed selectivity for TNP over other nitrophenols has been correlated to stronger hydrogen bonding interaction of TNP with the basic -NH group of MOF1, which is revealed from DFT calculations. To the best of our knowledge, MOF1 is the first example of an interpenetrated Zn -MOF exhibiting selective adsorption of CO as well as efficient aqueous-phase sensing of TNP; investigated through combined experimental and theoretical studies.