Chromium carbonyl nitrosyls: comparison with isoelectronic manganese carbonyl derivatives

Density functional methods indicate that the global minimum for Cr2(NO)2(CO)8 is a staggered D4d structure in accord with experiment and analogous to the isoelectronic Mn2(CO)10. For the unsaturated Cr2(NO)2(CO)n derivatives the lowest energy structures are very different from the lowest energy structures for the isoelectronic Mn2(CO)n+2 derivatives. Thus the global minimum for Cr2(NO)2(CO)7 is an unbridged structure with a Cr(NO)(CO)4 fragment linked to a Cr(NO)(CO)3 fragment through a Cr=Cr double bond. For Cr2(NO)2(CO)6 the global minimum is a structure with two bridging CO groups, whereas the global minimum for Mn2(CO)8 is an unbridged structure. For Cr2(NO)2(CO)5 both NO groups are bridging NO groups with one of them having a short enough Cr-O distance to be considered a formal five-electron donor eta2-mu-NO group. Thus the isoelectronic substitution of NO for CO with a necessary adjustment in the central metal atom can lead to significant shifts in the relative energies of various structural types of metal carbonyl nitrosyls, particularly for unsaturated molecules. For the mononuclear Cr(NO)2(CO)3 the theoretical structure differs from that deduced from matrix isolation experiments. Moreover, the nu(CO) and nu(NO) vibrational frequencies predicted here for Cr(NO)2(CO)3 correspond more closely with the unassigned species labeled "Cr(NO)(CO)x" in the experiments rather than the species claimed to be Cr(NO)2(CO)3.     

Formation of a reversible, intramolecular main-group metal-CO2 adduct

The P,P-chelated stannylene [(i-Pr(2)P)(2)N](2)Sn takes up 2 equiv of carbon dioxide (CO(2)) to form an unusual product in which CO(2) binds to the Sn and P atoms, thus forming a six-membered ring complex. Gentle heating of the solid product releases CO(2), indicating that CO(2) is bound as an adduct to the main-group complex. The groups bound to the CO(2) fragment are not particularly sterically crowded or highly acidic, thus indicating that "frustrated" Lewis acid-base pairs are not required in the binding of CO(2) to main-group elements.     

Mononuclear and binuclear rhenium carbonyl nitrosyls: comparison with their manganese analogues

The structures and energetics of Re(NO)(CO)n (n = 5, 4, 3, 2) and Re2(NO)2(CO)n (n = 7, 6) have been investigated using density functional theory. For Re(NO)(CO)4 the preferred structure is an equatorially substituted trigonal bipyramid analogous to the known structure of the manganese analogue. The lowest energy structures for the unsaturated Re(NO)(CO)n (n = 3, 2) species can be derived from this structure by removal of carbonyl groups. A structure is found for Re(NO)(CO)5 in which the NO ligand has attached to one of the CO ligands by forming a C-N bond to give an unprecedented eta(2)-OCNO ligand. However, this structure is predicted to undergo exothermic CO loss to give Re(NO)(CO)4. The preferred structures for the binuclear derivatives Re2(NO)2(CO)n (n = 7, 6) are structures unprecedented for the manganese analogues and consist of a Re(CO)5 unit linked to a Re(NO)2(CO)(n-5) unit. However, only slightly higher in energy are structures of the type Re2(mu-NO)2(CO)n with two bridging nitrosyl groups, similar to the global minima for the manganese analogues. These results predict extensive areas of new rhenium carbonyl nitrosyl chemistry. Thus the synthesis of Re(NO)(CO)4 by methods related to the synthesis of the manganese analogue appears to be feasible. In addition, the existence of an extensive series of Re(NO)2(CO)2X derivatives, as well as a Re2(NO)4(CO)4 dimer, is predicted.     

Molecular orbitals of the oxocarbons (CO)n, n = 2-6. Why does (CO)4 have a triplet ground state?

Cyclobutane-1,2,3,4-tetrone has been both predicted and found to have a triplet ground state, in which a b(2g) σ MO and an a(2u) π MO are each singly occupied. The nearly identical energies of these two orbitals of (CO)(4) can be attributed to the fact that both of these MOs are formed from a bonding combination of C-O π* orbitals in four CO molecules. The intrinsically stronger bonding between neighboring carbons in the b(2g) σ MO compared to the a(2u) π MO is balanced by the fact that the non-nearest-neighbor, C-C interactions in (CO)(4) are antibonding in b(2g), but bonding in a(2u). Crossing between an antibonding, b(1g) combination of carbon lone-pair orbitals in four CO molecules and the b(2g) and a(2u) bonding combinations of π* MOs is responsible for the occupation of the b(2g) and a(2u) MOs in (CO)(4). A similar orbital crossing occurs on going from two CO molecules to (CO)(2), and this crossing is responsible for the triplet ground state that is predicted for (CO)(2). However, such an orbital crossing does not occur on formation of (CO)(2n+1) from 2n + 1 CO molecules, which is why (CO)(3) and (CO)(5) are both calculated to have singlet ground states. Orbital crossings, involving an antibonding, b(1), combination of lone-pair MOs, occur in forming all (CO)(2n) molecules from 2n CO molecules. Nevertheless, (CO)(6) is predicted to have a singlet ground state, in which the b(2u) σ MO is doubly occupied and the a(2u) π MO is left empty. The main reason for the difference between the ground states of (CO)(4) and (CO)(6) is that interactions between 2p AOs on non-nearest-neighbor carbons, which stabilize the a(2u) π MO in (CO)(4), are much weaker in (CO)(6), due to the much larger distances between non-nearest-neighbor carbons in (CO)(6) than in (CO)(4).     

Enhancement of CO2 sorption uptake on hydrotalcite by impregnation with K2CO3

The awareness of symptoms of global warming and its seriousness urges the development of technologies to reduce greenhouse gas emissions. Carbon dioxide (CO(2)) is a representative greenhouse gas, and numerous methods to capture and storage CO(2) have been considered. Recently, the technology to remove high-temperature CO(2) by sorption has received lots of attention. In this study, hydrotalcite, which has been known to have CO(2) sorption capability at high temperature, was impregnated with K(2)CO(3) to enhance CO(2) sorption uptake, and the mechanism of CO(2) sorption enhancement on K(2)CO(3)-promoted hydrotalcite was investigated. Thermogravimetric analysis was used to measure equilibrium CO(2) sorption uptake and to estimate CO(2) sorption kinetics. The analyses based on N(2) gas physisorption, X-ray diffractometry, Fourier transform infrared spectrometry, Raman spectrometry, transmission electron microscopy, scanning electron microscopy, and energy dispersive X-ray spectroscopy were carried out to elucidate the characteristics of sorbents and the mechanism of enhanced CO(2) sorption. The equilibrium CO(2) sorption uptake on hydrotalcite could be increased up to 10 times by impregnation with K(2)CO(3), and there was an optimal amount of K(2)CO(3) for a maximum equilibrium CO(2) sorption uptake. In the K(2)CO(3)-promoted hydrotalcite, K(2)CO(3) was incorporated without changing the structure of hydrotalcite and it was thermally stabilized, resulting in the enhanced equilibrium CO(2) sorption uptake and fast CO(2) sorption kinetics.     

Binuclear vanadium carbonyls: the limits of the 18-electron rule

The fact that the stable mononuclear vanadium carbonyl V(CO)6 fails to satisfy the 18-electron rule has led to an investigation of the binuclear vanadium carbonyls V2(CO)n (n = 10-12) using methods from density functional theory. There are several important experimental studies of these homoleptic binuclear vanadium carbonyls. The global minimum for V2(CO)12 is a singlet structure having two V(CO)6 units linked by a long V-V single bond (3.48 A by B3LYP or 3.33 A by BP86) without any bridging CO groups. For V2(CO)11 the global minimum is a singlet structure V2(CO)10(eta2-mu-CO) with a four-electron pi-donor bridging CO group. For V2(CO)10 the global minimum is an unsymmetrical singlet (OC)4VV(CO)6 structure with three semibridging CO groups and a V-V distance of 2.54 A (B3LYP) or 2.51 A (BP86), suggesting a VV triple bond. The theoretical nu(CO) frequencies of this V2(CO)10 isomer agree approximately with those assigned by Ishikawa et al. (J. Am. Chem. Soc. 1987, 109, 6644) to a V2(CO)10 isomer produced in the photolysis of gas-phase V(CO)6. In contrast, the laboratory bridging nu(CO) frequency assigned to V2(CO)12 by Ford et al. (Inorg. Chem. 1976, 15, 1666) seems more likely to arise from the lowest-lying triplet isomer of V2(CO)11.     

Iron carbonyl sulfides, formaldehyde, and amines condense to give the proposed azadithiolate cofactor of the Fe-only hydrogenases

The azadithiolate (SCH2NHCH2S) cofactor proposed to occur in the Fe-only hydrogenases forms efficiently by the condensation of Fe2(SH)2(CO)6 (1), formaldehyde, and ammonia (as (NH4)2CO3). The resulting Fe2[(SCH2)2NH](CO)6 reacts with Et4NCN to give (Et4N)2[Fe2[(SCH2)2NH](CO)4(CN)2], for which crystallographic characterization confirmed an axial N-H and an elongated C-S bond of 1.858(3) A. Primary amines RNH2 (R = Ph, t-Bu) also participate in the condensation reaction, and Fe3S2(CO)9 can be employed in place of 1. Mechanistically, the Fe2[(SCH2)2NH] moiety is shown to arise via two pathways: (i) via the intermediacy of Fe2[(SCH2OH)2](CO)6, which was detected and shown to react with amines, and (ii) via the reaction of 1 with cyclic imines (CH2)3(NR)3 (R = Ph, Me). The reaction of 1 with (CH2)6N4 (hexamethylenetetramine) gives Fe2[(SCH2)2NH](CO)6. Trace amounts of Fe2[(SCH2)2N-t-Bu](CO)6 arise via the reaction of aqueous FeSO4, formaldehyde, NaSH, and t-BuNH2 under an atmosphere of CO.     

Low fluorine content CO2-philic surfactants

The article addresses an important, and still unresolved question in the field of CO(2) science and technology: what is the minimum fluorine content necessary to obtain a CO(2)-philic surfactant? A previous publication (Langmuir 2002, 18, 3014) suggested there should be an ideal fluorination level: for optimization of possible process applications in CO(2), it is important to establish just how little F is needed to render a surfactant CO(2)-philic. Here, optimum chemical structures for water-in-CO(2) (w/c) microemulsion stabilization are identified through a systematic study of CO(2)-philic surfactant design based on dichain sulfosuccinates. High pressure small-angle neutron scattering (HP-SANS) measurements of reversed micelle formation in CO(2) show a clear relationship between F content and CO(2) compatibility of any given surfactant. Interestingly, high F content surfactants, having lower limiting aqueous surface tensions, γ(cmc), also have better performance in CO(2), as indicated by lower cloud point pressures, P(trans). The results have important implications for the rational design of CO(2)-philic surfactants helping to identify the most economic and efficient compounds for emerging CO(2) based fluid technologies.     

Oxidation of CO by NO on planar and faceted Ir(210)

Oxidation of CO by pre-adsorbed NO has been studied on planar Ir(210) and nanofaceted Ir(210) with average facet sizes of 5 nm and 14 nm by temperature programmed desorption (TPD). Both surfaces favor oxidation of CO to CO(2), which is accompanied by simultaneous reduction of NO with high selectivity to N(2). At low NO pre-coverage, the temperature (T(i)) for the onset of CO(2) desorption as well as CO(2) desorption peak temperature (T(p)) decreases with increasing CO exposure, and NO dissociation is affected by co-adsorbed CO. At high NO pre-coverage, T(i) and T(p) are independent of CO exposure, and co-adsorbed CO has no influence on dissociation of NO. Moreover, at low NO pre-coverage, planar Ir(210) is more active than faceted Ir(210) for oxidation of CO to CO(2): T(i) and T(p) are much lower on planar Ir(210) than that on faceted Ir(210). In addition, faceted Ir(210) with an average facet size of 5 nm is more active for oxidation of CO to CO(2) than faceted Ir(210) with an average facet size of 14 nm, i.e., oxidation of CO by pre-adsorbed NO on faceted Ir(210) exhibits size effects on the nanometer scale. In comparison, at low O pre-coverage planar Ir(210) is more active than faceted Ir(210) for oxidation of CO to CO(2) but no evidence has been found for size effects in oxidation of CO by pre-adsorbed oxygen on faceted Ir(210) for average facet sizes of 5 nm and 14 nm. The TPD data indicate the same reaction pathway for CO(2) formation from CO + NO and CO + O reactions on planar Ir(210). The adsorption sites of CO, NO, O, CO + O, and CO + NO on Ir are characterized by density functional theory.     

Hexanuclear cobalt carbonyl carbide clusters: the interplay between octahedral and trigonal prismatic structures

The six-vertex cobalt carbonyl clusters [Co6C(CO)n](2-) (n = 12, 13, 14, 15, 16) with an interstitial carbon atom have been studied by density functional theory (DFT). These DFT studies indicate that the experimentally known structure of [Co6C(CO)15](2-) consisting of a Co6 trigonal prism with each of its edges bridged by carbonyl groups is a particularly stable structure lying more than 20 kcal/mol below any other [Co6C(CO)15](2-) structure. Addition of a CO group to this [Co6C(CO)15](2-) structure gives the lowest energy [Co6C(CO)16](2-) structure, also a Co6 trigonal prism with one of the vertical edges bridged by two CO groups and the remaining eight edges each bridged by a single CO group. However, this [Co6C(CO)16](2-) structure is thermodynamically unstable with respect to CO loss reverting to the stable trigonal prismatic [Co6C(CO)15](2-). This suggests that 15 carbonyl groups is the maximum that can be attached to a Co6C skeleton in a stable compound. The lowest energy structure of [Co6C(CO)14](2-) has a highly distorted octahedral Co6 skeleton and is thermodynamically unstable with respect to disproportionation to [Co6C(CO)15](2-) and [Co6C(CO)13](2-). The lowest energy [Co6C(CO)13](2-) structure is very similar to a known stable structure with an octahedral Co6 skeleton. The lowest energy [Co6C(CO)12](2-) structure is a relatively symmetrical D3d structure containing a carbon-centered Co6 puckered hexagon in the chair form.     

Precursors to [FeFe]-hydrogenase models: syntheses of Fe2(SR)2(CO)6 from CO-free iron sources

This report describes routes to iron dithiolato carbonyls that do not require preformed iron carbonyls. The reaction of FeCl 2, Zn, and Q 2S 2C n H 2 n (Q (+) = Na (+), Et 3NH (+)) under an atmosphere of CO affords Fe 2(S 2C n H 2 n )(CO) 6 ( n = 2, 3) in yields >70%. The method was employed to prepare Fe 2(S 2C 2H 4)( (13)CO) 6. Treatment of these carbonylated mixtures with tertiary phosphines, instead of Zn, gave the ferrous species Fe 3(S 2C 3H 6) 3(CO) 4(PR 3) 2, for R = Et, Bu, and Ph. Like the related complex Fe 3(SPh) 6(CO) 6, these compounds consist of a linear arrangement of three conjoined face-shared octahedral centers. Omitting the phosphine but with an excess of dithiolate, we obtained the related mixed-valence triiron species [Fe 3(S 2C n H 2 n ) 4(CO) 4] (-). The highly reducing all-ferrous species [Fe 3(S 2C n H 2 n ) 4(CO) 4] (2-) is implicated as an intermediate in this transformation. Reactive forms of iron, prepared by the method of Rieke, also combined with dithiols under a CO atmosphere to give Fe 2(S 2C n H 2 n )(CO) 6 in modest yields under mild conditions. Studies on the order of addition indicate that ferrous thiolates are formed prior to the onset of carbonylation. Crystallographic characterization demonstrated that the complexes Fe 3(S 2C 3H 6) 3(CO) 4(PEt 3) 2 and PBnPh 3[Fe 3(S 2C 3H 6) 4(CO) 4] feature high-spin ferrous and low-spin ferric as the central metal, respectively.     

Iridium-iron-monocarborane clusters from oxidative insertion reactions of [IrCl(CO)(PPh3)2] with ferracarborane anions

The nine-vertex ferracarborane salt [N(PPh3)2][7,7,7-(CO)3-closo-7,1-FeCB7H8] (1) reacts with an excess of [IrCl(CO)(PPh3)2] in the presence of Tl[PF6] to form, successively, the bimetallic species [7,7,9,9,9-(CO)5-7-PPh3-closo-7,9,1-IrFeCB6H7] (3), in which one {BH}- vertex has formally been subrogated by an {Ir(CO)2(PPh3)} unit, and the trimetallic complex [6,7,9-{Ir(CO)(PPh3)2}-7,9-(mu-H)2-7,9,9-(CO)3-7-PPh3-closo-7,9,1-IrFeCB6H6] (5), which contains an {FeIr2} triangle. The {FeIrCB6} core in 5 resembles that in 3 with, in addition, the Fe...Ir connectivity being spanned by an {Ir(CO)(PPh3)2} fragment and the consequent Fe-Ir and Ir-Ir bonds bridged by hydrido ligands. In contrast to the above, treatment of the 10-vertex diferracarborane salt [N(PPh3)2][6,6,6,10,10,10-(CO)6-closo-6,10, 1-Fe2CB7H8] (2) with the same reagents yields two very different, trimetallic complexes, namely [8,10-{Ir(mu-PPh2)(Ph)(CO)(PPh3)}-8-(mu-H)-6,6,6,10,10-( CO)5-closo-6,10,1-Fe2CB7H7] (6) and [6,7,10-{Fe(CO)3}-6-(mu-H)-6,10,10,10-(CO)4-6-PPh3-closo-6,10,1-IrFeCB7H7] (7). In 6, an exo-polyhedral {IrPh(CO)(PPh3)} moiety is attached to a {closo-6,10,1-Fe2CB7} framework via a PPh2-bridged Fe-Ir bond and a B-HIr agostic-type linkage, the iridium center formally having inserted into one P-Ph bond of a PPh3 unit. Complex 7 contains an {IrFeCB7} cluster core, with an exo-polyhedral {Fe(CO)3} moiety bridging a {BIrFe} triangular face and with an additional Ir-H-Fe bridge. However, this metal atom arrangement reveals that iridium and iron moieties have exchanged exo- and endo-polyhedral sites with respect to the 10-vertex metallacarborane. X-ray diffraction studies upon 3, 5, 6, and 7 confirmed their novel structural features; some preliminary reactivity studies upon these compounds are also reported.     

Binuclear manganese and rhenium carbonyls M2(CO)n (n = 10, 9, 8, 7): comparison of first row and third row transition metal carbonyl structures

The equilibrium geometries, thermochemistry, and vibrational frequencies of the homoleptic binuclear rhenium carbonyls Re2(CO)n (n = 10, 9, 8, 7) were determined using the MPW1PW91 and BP86 methods from density functional theory (DFT) with the effective core potential basis sets LANL2DZ and SDD. In all cases triplet structures for Re2(CO)n were found to be unfavorable energetically relative to singlet structures, in contrast to corresponding Mn2(CO)n derivatives, apparently owing to the larger ligand field splitting of rhenium. For M2(CO)10 (M = Mn, Re) the unbridged structures (OC)5M-M(CO)5 are preferred energetically over structures with bridging CO groups. For M2(CO)9 (M = Mn, Re) the two low energy structures are (OC)4M(micro-CO)M(CO)4 with an M-M single bond and a four-electron donor bridging CO group and (OC)4M[double bond, length as m-dash]M(CO)5 with no bridging CO groups and an M[double bond, length as m-dash]M distance suggesting a double bond. The lowest energy structures for Re2(CO)8 have Re[triple bond, length as m-dash]Re distances in the range 2.6-2.7 A suggesting the triple bonds required to give the Re atoms the favored 18-electron configuration. Low energy structures for Re2(CO)7 are either of the type (OC)(4)M[triple bond, length as m-dash]M(CO)3 with short metal-metal distances suggesting triple bonds or have a single four-electron donor bridging CO group and longer M-M distances consistent with single or double bonds. The 18-electron rule thus appears to be violated in these highly unsaturated Re2(CO)7 structures.     

Structures of [(CO2)n(CH3OH)m](-) (n = 1-4, m = 1, 2) cluster anions

The infrared photodissociation spectra of [(CO 2) n (CH 3OH) m ] (-) ( n = 1-4, m = 1, 2) are measured in the 2700-3700 cm (-1) range. The observed spectra consist of an intense broad band characteristic of hydrogen-bonded OH stretching vibrations at approximately 3300 cm (-1) and congested vibrational bands around 2900 cm (-1). No photofragment signal is observed for [(CO 2) 1,2(CH 3OH) 1] (-) in the spectral range studied. Ab initio calculations are performed at the MP2/6-311++G** level to obtain structural information such as optimized structures, stabilization energies, and vibrational frequencies of [(CO 2) n (CH 3OH) m ] (-). Comparison between the experimental and the theoretical results reveals the structural properties of [(CO 2) n (CH 3OH) m ] (-): (1) the incorporated CH 3OH interacts directly with either CO 2 (-) or C 2O 4 (-) core by forming an O-HO linkage; (2) the introduction of CH 3OH promotes charge localization in the clusters via the hydrogen-bond formation, resulting in the predominance of CO 2 (-).(CH 3OH) m (CO 2) n-1 isomeric forms over C 2O 4 (-).(CH 3OH) m (CO 2) n-2 ; (3) the hydroxyl group of CH 3OH provides an additional solvation cite for neutral CO 2 molecules.     

An ab initio investigation on (CO2)n and CO2(Ar)m clusters: geometries and IR spectra

An ab initio investigation on CO(2) homoclusters is done at MPWB1K6-31++G(2d) level of theory. Electrostatic guidelines are found to be useful for generating initial structures of (CO(2))(n) clusters. The ab initio minimum energy geometries of (CO(2))(n) with n=2-8 are T shaped, cyclic, trigonal pyramidal, tetragonal pyramidal, tetragonal bipyramidal, pentagonal bipyramidal, and pentagonal bipyramid with one CO(2) molecule attached to it. A test calculation on (CO(2))(20) cluster is also reported. The geometric parameters of the energetically most favored (CO(2))(n) clusters match quite well their experimental counterparts (wherever available) as well as those derived from molecular dynamics studies. The effect of clustering is quantified through the asymmetric C-O stretching frequency shift relative to the single CO(2) molecule. (CO(2))(n) clusters show an increasing blueshift from 1.8 to 9.6 cm(-1) on increasing number of CO(2) molecules from n=2 to 8. The energetics and geometries of CO(2)(Ar)(m) clusters have also been explored at the same level of theory. The geometries for m=1-6 show a predominant T type of the argon-CO(2) molecule interaction. Higher clusters with m=7-12 show that the argon atoms cluster around the oxygen atom after the saturation of the central carbon atom. The CO(2)(Ar)(m) clusters exhibit an increasing redshift in the C-O asymmetric stretch relative to CO(2) molecule of 0.7-5.6 cm(-1) with increasing number of argon atoms through m=1-8.     

Surface dependence of CO2 adsorption on Zn2GeO4

An understanding of the interaction between Zn(2)GeO(4) and the CO(2) molecule is vital for developing its role in the photocatalytic reduction of CO(2). In this study, we present the structure and energetics of CO(2) adsorbed onto the stoichiometric perfectly and the oxygen vacancy defect of Zn(2)GeO(4) (010) and (001) surfaces using density functional theory slab calculations. The major finding is that the surface structure of the Zn(2)GeO(4) is important for CO(2) adsorption and activation, i.e., the interaction of CO(2) with Zn(2)GeO(4) surfaces is structure-dependent. The ability of CO(2) adsorption on (001) is higher than that of CO(2) adsorption on (010). For the (010) surface, the active sites O(2c)···Ge(3c) and Ge(3c)-O(3c) interact with the CO(2) molecule leading to a bidentate carbonate species. The presence of Ge(3c)-O(2c)···Ge(3c) bonds on the (001) surface strengthens the interaction of CO(2) with the (001) surface, and results in a bridged carbonate-like species. Furthermore, a comparison of the calculated adsorption energies of CO(2) adsorption on perfect and defective Zn(2)GeO(4) (010) and (001) surfaces shows that CO(2) has the strongest adsorption near a surface oxygen vacancy site, with an adsorption energy -1.05 to -2.17 eV, stronger than adsorption of CO(2) on perfect Zn(2)GeO(4) surfaces (E(ads) = -0.91 to -1.12 eV) or adsorption of CO(2) on a surface oxygen defect site (E(ads) = -0.24 to -0.95 eV). Additionally, for the defective Zn(2)GeO(4) surfaces, the oxygen vacancies are the active sites. CO(2) that adsorbs directly at the Vo site can be dissociated into CO and O and the Vo defect can be healed by the oxygen atom released during the dissociation process. On further analysis of the dissociative adsorption mechanism of CO(2) on the surface oxygen defect site, we concluded that dissociative adsorption of CO(2) favors the stepwise dissociation mechanism and the dissociation process can be described as CO(2) + Vo → CO(2)(δ-)/Vo → CO(adsorbed) + O(surface). This result has an important implication for understanding the photoreduction of CO(2) by using Zn(2)GeO(4) nanoribbons.     

CO-migration in the ligand substitution process of the chelating diphosphite diiron complex (mu-pdt)[Fe(CO)3][Fe(CO){(EtO)2PN(Me)P(OEt)2}

Selective synthetic routes to isomeric diiron dithiolate complexes containing the (EtO) 2PN(Me)P(OEt) 2 (PNP) ligand in an unsymmetrical chelating role, for example, (mu-pdt)[Fe(CO) 3][Fe(CO)(kappa (2)-PNP)] ( 3) and as a symmetrically bridging ligand in (mu-pdt)(mu-PNP)[Fe(CO) 2] 2 ( 4), have been developed. 3 was converted to 4 in 75% yield after extensive reflux in toluene. The reactions of 3 with PMe 3 and P(OEt) 3 afforded bis-monodentate P-donor complexes (mu-pdt)[Fe(CO) 2PR 3][Fe(CO) 2(PNP)] (PR 3 = PMe 3, 5; P(OEt) 3, 7), respectively, which are formed via an associative PMe 3 coordination reaction followed by an intramolecular CO-migration process from the Fe(CO) 3 to the Fe(CO)(PNP) unit with concomitant opening of the Fe-PNP chelate ring. The PNP-monodentate complexes 5 and 7 were converted to a trisubstituted diiron complex (mu-pdt)(mu-PNP)[Fe(CO)PR 3][Fe(CO) 2] (PR 3 = PMe 3, 6; P(OEt) 3, 8) on release of 1 equiv CO when refluxing in toluene. Variable-temperature (31)P NMR spectra show that trisubstituted diiron complexes each exist as two configuration isomers in solution. All diiron dithiolate complexes obtained were characterized by MS, IR, NMR spectroscopy, elemental analysis, and X-ray diffraction studies.     

Loading-dependent structures of CO2 in the flexible molecular van der Waals host p-tert-butylcalix[4]arene with 1 : 1 and 2 : 1 guest-host stoichiometries

The adsorption of CO(2) into the low density form of p-tert-butylcalix[4]arene (tBC) has been studied by (13)C solid state NMR, single crystal X-ray diffraction and volumetric adsorption measurements. The experimental results indicate that tBC and carbon dioxide can form two distinct inclusion compounds. At low loadings the structure of the empty low-density form of the tBC framework (space group P2(1)/n) is preserved with the included CO(2) molecules located within the conical cavities of the tBC molecules. The ideal composition of this form is therefore 1 : 1 (CO(2) : tBC). With higher applied CO(2) pressures the guest loading increases and the structure of the tBC framework transforms to a well studied tetragonal (space group P4/n) form. In this form an additional CO(2) molecule is located on an interstitial site resulting in an ideal composition 2 : 1 (CO(2) : tBC). In agreement with SCXRD and the gas adsorption measurements, (13)C NMR measurements show the change in structure that takes place as a function of sample loading. Inclusion of CO(2) is a rather slow activated process that can be accelerated by increasing the temperature and the transition between crystal forms is inhomogeneous over a bulk sample. After gas release, the empty (or near empty) P4/n structure survives, thus providing another low density phase of tBC. The magnitude and temperature variation of the (13)C chemical shift anisotropy of CO(2) in both low and high occupancy complexes with tBC indicates restricted motion of the CO(2) molecules. The location and dynamics of CO(2) molecules inside the tBC structure are discussed and a motional model for CO(2) is proposed. The CO(2) molecules in the highly loaded compound are shown to exchange rapidly as a single resonance is observed for the two distinct CO(2) molecules.     

CO2在金属表面活化的UBI-QEP方法研究

应用UBI-QEP方法估算了金属表面上形成的活化吸附态CO₂^-在Cu(111),Pd(111),Fe(111)和Ni(111)表面上的吸附热,计算了各种相关反应的活化能垒.结果表明,CO₂^-在4种过渡金属表面的相对稳定性的顺序为Fe>Ni>Cu>Pd;在Fe和Ni表面上CO₂^-较易生成,且容易进一步发生解离反应,在Fe表面会解离成C和O吸附原子,而在Ni表面上解离的最终产物为CO和O;在Cu表面上,CO₂^-虽较难形成,但其加氢反应的活化能比解离反应低,因此加氢反应是其进一步活化的有效模式;在Pd表面上,CO₂^-吸附态在能量上很不稳定,所以CO₂在Pd表面上不容易活化.     

Reactivity of transition metal-phosphorus triple bonds towards triply bonded [{CpMo(CO)2}2]: formation of heteronuclear cluster compounds

Thermolysis of [Cp*P{W(CO)5}2] (1) in the presence of [{CpMo(CO)2}2] leads to the novel complexes [{(CO)2Cp*W}{CpMo(CO)2}(micro,eta2:eta1:eta1-P2{W(CO)5}2)] (6; Cp=eta5-C5H5, Cp*=eta5-C5Me5), [{(micro-O)(CpMoWCp*)W(CO)4}{micro3-PW(CO)5}2] (7), [{CpMo(CO)2}2{Cp*W(CO)2}{micro3-PW(CO)5}] (8) and [{CpMo(CO)2}2{Cp*W(CO)2}(micro3-P)] (9). The structural framework of the main products 8 and 9 can be described as a tetrahedral Mo2WP unit that is formed by a cyclisation reaction of [{CpMo(CO)2}2] with an [Cp*(CO)2W[triple chemical bond]P-->W(CO)5] intermediate containing a W--P triple bond and subsequent metal-metal and metal-phosphorus bond formation. Photolysis of 1 in the presence of [{CpMo(CO)2}2] gives 8, 9 and phosphinidene complex [(micro3-PW(CO)5){CpMo(CO)2W(CO)5}] (10), in which the P atom is in a nearly trigonal-planar coordination environment formed by one {CpMo(CO)2} and two {W(CO)5} units. Comprehensive structural and spectroscopic data are given for the products. The reaction pathways are discussed for both activation procedures, and DFT calculations reveal the structures with minimum energy along the stepwise Cp* migration process under formation of the intermediate [Cp*(CO)2W[triple chemical bond]P-->W(CO)5].