Hydrogen dissociative chemisorption and desorption on small lowest energy Nin clusters up to n = 13 as a function of H coverage was studied using density functional theory. H adsorption on the clusters
was found to be preferentially at edge sites followed by 3-fold hollow sites and on-top sites. The minimum energy path calculations
suggest that H2 dissociative chemisorption is both thermodynamically and kinetically favorable and the H atoms on the clusters are mobile.
Calculations on the sequential H2 dissociative chemisorption on the clusters indicate that the edge sites are populated first and subsequently several on-top
sites and hollow sites are also occupied upon full cluster saturation. In all cases, the average hydrogen capacity on Nin clusters is similar to that of Pdn clusters but considerably smaller than that of Ptn clusters. Comparison of hydrogen dissociative chemisorption energies and H desorption energies at full H-coverage among the
Ni family clusters was made. 相似文献
Catalytic activities of neutral and charged palladium (Pd) nanoparticles are compared for hydrogen reduction half-reaction. In this work the sequential H2 dissociation from the surface of a Pd13H24 cluster is systematically studied by ab initio molecular dynamics (AIMD) at the density functional theory level. AIMD simulation is launched by preparing initial values of momenta of all nuclei in the model corresponding to a temperature range of 0–1700 K. AIMD simulation provides the trajectories of all the atoms in the cluster. A sequential H2 desorption up to seven molecules is observed from the cluster surface due to thermal motion of nuclei. Modifications of total charge on the neutral Pd13H24 cluster model are found to affect surface H2 desorption behaviour. A desorption rate of H2 molecule on both neutral and charged Pd13H24 clusters is compared to the data of Pt13H24 cluster reported previously. The H2 desorption energy on all the investigated clusters is also determined. The results reveal that Pd13 cluster presents a higher catalytic activity than Pt13 cluster. 相似文献
Heteroleptic triphenylphosphine carbonyl palladium clusters of different nuclearities were prepared under mild conditions by only varying the amount of ligand (PPh3) used in the synthesis: three different clusters were successfully isolated after CO bubbling in a solution of [Pd2(dba)3] (dba = dibenzylideneacetone) with 3, 1 or 0.5 equiv of PPh3, which led, respectively, to [Pd4(CO)5(PPh3)4] (1), [Pd10(CO)12(PPh3)6] (2) and [Pdn(CO)x(PPh3)y] (3) (n ≈ 24). The molecular structures of compounds 1 and 2 were determined by X-ray crystallography. The metal cores in these compounds were shown to consist in a butterfly for 1 and a bridged octahedron for 2. Compound 3 was shown to be at the boundary between molecular clusters and colloidal particles with tentative formulation arising from characterization data. These three clusters and the known [Pd10(CO)12(PBu3)6] and [Pd12(CO)15(PBu3)7] were submitted to NaBH4 reduction. The Pd4 cluster 1 did not react. The colloidal Pdn species led to no isolable product. By contrast, the two Pd10 and the Pd12 clusters led to reduction products, isolated as salts. In the case of the reduced Pd12 cluster, its structure was resolved by X-ray crystallography: the metal core consists of a face-capped octahedron. The reduced species reacted readily with Au(PPh3)+, confirming their anionic nature. 相似文献
The development of dual catalysts with high efficiency toward oxygen reduction and evolution reactions (ORR and OER) in acidic media is a significant challenge. Here an active and durable dual catalyst based upon cubic Pt39Ir10Pd11 nanocages with an average edge length of 12.3 nm, porous walls as thin as 1.0 nm, and well‐defined {100} facets is reported. The trimetallic nanocages perform better than all the reported dual catalysts in acidic media, with a low ORR‐OER overpotential gap of only 704 mV at a Pt‐Ir‐Pd loading of 16.8 µgPt+Ir+Pd cm?2geo. For ORR at 0.9 V, when benchmarked against the commercial Pt/C and Pt‐Pd nanocages, the trimetallic nanocages exhibit an enhanced mass activity of 0.52 A mg?1Pt+Ir+Pd (about four and two times as high as those of the Pt/C and Pt‐Pd nanocages) and much improved durability. For OER, the trimetallic nanocages show a remarkable mass activity of 0.20 A mg?1Pt+Ir at 1.53 V, which is 16.7 and 4.3 fold relative to those of the Pt/C and Pt‐Pd nanocages, respectively. These improvements can be ascribed to the highly open structure of the nanocages, and the possible electronic coupling between Ir and Pt atoms in the lattice. 相似文献
New trans-[Pd(sac)2(PPhMe2)(DMSO)]·H2O (Pd) and trans-[Pt(sac)2(PPhMe2)2]·H2O (Pt) complexes (sac = saccharinate and PPhMe2 = dimethylphenylphosphine) were synthesized and characterized by elemental analysis, IR, NMR, ESI-MS spectral analyses and X-ray diffraction. The complexes were evaluated for their in vitro cytotoxicity against breast (MCF-7), colon (HCT116) and lung (A549) human cancer cell lines. The ATP viability assay displayed that Pd was biologically inactive, but Pt showed significant anticancer potency on MCF-7 cancer cells, similar to cisplatin. The results suggested that Pt targeted DNA, whereas Pd displayed higher binding affinity towards human serum albumin (HSA). Mechanism of action studies of Pt suggested apoptotic cell death due to significant increase in intracellular ROS (reactive oxygen species) levels, mitochondrial damage and formation of DNA double-strand breaks. Finally, this work represents a new example of potent transplatin anticancer complexes. 相似文献
Structural, chemical, magnetic and thermodynamic properties of palladium clusters Pdn with n = 2–11 are studied using density functional methods. The average bond length, entropy, enthalpy and polarisability are observed to increase as the cluster grows in size. The binding energy per atom also increases with cluster size. Stability function and atom addition energy change predict that Pd4, Pd6 and Pd9 are relatively more stable than their neighbouring clusters. Electron affinity, electronegativity and electrophilicity values suggest that larger clusters have stronger tendency to accept electrons, thereby supporting the relative stability of Pd4 and Pd6. Chemical hardness is also seen to decrease with cluster size, which suggests that large clusters are more prone to changes in their electronic structure. The magnetic properties of these clusters are reported. 相似文献
The reaction between Pd3(OOCMe)6 and Ag2(OOCMe)2 afforded the first palladium-silver heterometallic acetate-bridged complex PdII[(μ-OOCMe)2AgI(HOOCMe)2]2 (1). The molecular geometry and electronic structure of 1 were studied by single-crystal XRD and quantum-chemical DFT calculations. Thermal transformations of 1in vacuo and under Ar, H2 produced PdAg alloy nanoparticles characterized with powder XRD and EXAFS. 相似文献
Understanding the bond-cleavage ability of metal clusters is very important in various fields, such as catalysis and surface science. In this work, we performed density functional theory calculations on the first dehydrogenation process (also the key step) of methanol on Ptnq (n = 1–3, q = 0, +1, ?1) clusters in varied charge states using quantum chemical calculations. It is shown that methanol is adsorbed much more easily to the cationic Ptn+ than to the neutral and anionic Ptn0/?. By contrast, the intrinsic bond cleavage barriers of both C–H and O–H on the cationic Ptn+ are significantly higher than on Ptn0/? (the only exception is the C–H bond cleavage on Pt+). Promisingly, injecting an electron to the neutral Ptn0 to give Ptn? can greatly reduce the C–H/O–H bond scission barrier while maintaining appreciable adsorption energy. The charging effect can be nicely interpreted by the nature of the frontier orbitals of Ptnq. 相似文献
Cinnamaldehyde (CAL) belongs to the group of aromatic α,β-unsaturated aldehydes; the selective hydrogenation of CAL plays an important role in the fine chemical and pharmaceutical industries. Using Ptn clusters as catalytic models, we studied the selective hydrogenation reaction mechanism for CAL catalyzed by Ptn (n?=?6, 10, 14, 18) clusters by means of B3LYP in density functional theory at the 6-31+?G(d) level (the LanL2DZ extra basis set was used for the Pt atom). The rationality of the transition state was proved by vibration frequency analysis and intrinsic reaction coordinate computation. Moreover, atoms in molecules theory and nature bond orbital theory were applied to discuss the interaction among orbitals and the bonding characteristics. The results indicate that three kinds of products, namely 3-phenylpropyl aldehyde, 3-phenyl allyl alcohol and cinnamyl alcohol, are produced in the selective hydrogenation reaction catalyzed by Ptn clusters; each pathway possesses two reaction channels. Ptn clusters are more likely to catalyze the activation and hydrogenation of the C?=?O bond in CAL molecules, eventually producing cinnamic alcohol, which proves that Ptn clusters have a strong reaction selectivity to catalyze CAL. The reaction selectivity of the catalyzer cluster is closely related to the size of the Ptn cluster, with Pt14 clusters having the greatest reaction selectivity.
Graphical Abstract The reaction mechanism for the selective hydrogenation reaction ofcinnamaldehyde catalyzed by Ptn clusters was studied by densityfunctional theory. The reactionselectivity of cluster catalyzer was concluded to be closely related to the size of Ptn clusters, with Pt14 clusters having the greatest reaction selectivity
Reaction of the metalloligand [Pt2(μ-S)2(PPh3)4] with the N-heterocyclic carbene (NHC) complexes IPrAuCl, IMesAuCl and IMesAgCl in methanol gave the first examples of metal adducts of [Pt2(μ-S)2(PPh3)4] that contain NHC ligands, namely [Pt2(μ-S)2(PPh3)4AuL]+ (L = IPr, IMes) and [Pt2(μ-S)2(PPh3)4AgIMes]+. The complexes were isolated as hexafluorophosphate salts. Reaction of [Pt2(μ-S)2(PPh3)4] with excess IPrAuCl in refluxing methanol yielded only the mono-adduct, in contrast to the behaviour with the gold(I) phosphine complex Ph3PAuCl, which undergoes double addition giving [Pt2(μ-SAuPPh3)2(PPh3)4]2+. The X-ray structure of [Pt2(μ-S)2(PPh3)4AuIPr]PF6 was determined and reveals that the ‘free’ sulfide is substantially sterically protected by the IPr ligand, accounting for the low reactivity towards addition of a second AgIPr+ moiety. 相似文献
[Pd(dppf)(MeCN)2](OTf)2 [dppf = 1,1′-bis(diphenylphosphino)ferrocene, OTf = triflate] reacts with pyridyl acetic acid (PyAcOH) to yield a dipalladium ring structure, [Pd2(dppf)2(μ-PyOAc)2](OTf)2 (1). The doubly-bridging ligands exhibit basicity at the pendant carboxyl oxygen to attract AgX (X = OTf or CF3CO2) to form [Pd2Ag2(dppf)2(PyOAc)2(OTf)4] (2) and [Pd2Ag2(dppf)2(PyOAc)2(OTf)2(CF3CO2)2] (3), respectively. Complexes 1 and 2 have been crystallographically characterized. Similar spacer-guest affinity is not found in the Pt(II) or isonicotinate analogues. 相似文献
Direct ethanol fuel cells (DEFCs) have great activity as a green energy conversion device. However, the weak activity of most anode electrocatalysts for the C? C bond cleavage is an obstacle to the DEFCs development. Herein, a simple galvanic replacement reaction strategy to synthesize hollow and porous PtRhCu trimetallic nanoboxes (CNBs) with a tunable Pt/Rh atomic ratio is developed. For the ethanol oxidation reaction (EOR), PtRhCu CNBs show morphology and composition‐dependent electrocatalytic activity. The composition optimized Pt54Rh4Cu42 CNBs exhibit excellent specific and mass activity and stability for the EOR, which is attributed to its unique geometric structure and synergistic effects. The hollow porous structure can effectively enhance the atomic utilization and mass transfer. The introduction of Cu improves the antipoisoning capability for CO. The introduction of Rh elevates the self‐stability of PtRhCu CNBs. More importantly, further electrochemical results confirm that the introduction of Rh significantly promotes the cleavage of C? C bonds, leading to the transformation of the main catalytic pathway for EOR from C2 to C1 pathway. The real concentration detection for C2 products (CH3COOH and CH3CHO) shows Pt54Rh4Cu42 CNBs have a nearly 11.5‐fold C1 pathway enhancement compared to Pt nanoparticles, showing an obvious selectivity enhancement for the C1 pathway. 相似文献
The reactions of [Pt2(μ-S)2(PPh3)4] with α,ω-dibromoalkanes Br(CH2)nBr (n = 4, 5, 6, 8, 12) gave mono-alkylated [Pt2(μ-S){μ-S(CH2)nBr}(PPh3)4]+ and/or di-alkylated [Pt2(μ-S(CH2)nS}(PPh3)4]2+ products, depending on the alkyl chain length and the reaction conditions. With longer chains (n = 8, 12), intramolecular di-alkylation does not proceed in refluxing methanol, with the mono-alkylated products [Pt2(μ-S){μ-S(CH2)nBr}(PPh3)4]+ being the dominant products when excess alkylating agent is used. The bridged complex [{Pt2(μ-S)2(PPh3)4}2{μ-(CH2)12}]2+ was accessible from the reaction of [Pt2(μ-S)2(PPh3)4] with 0.5 mol equivalents of Br(CH2)12Br. [Pt2(μ-S){μ-S(CH2)4Br}(PPh3)4]+ can be cleanly isolated as its BPh4− salt, but undergoes facile intramolecular di-alkylation at −18 °C, giving the known species [Pt2(μ-S(CH2)4S}(PPh3)4]2+. The reaction of I(CH2)6I with [Pt2(μ-S)2(PPh3)4] similarly gives [Pt2(μ-S){μ-S(CH2)6I}(PPh3)4]+, which is fairly stable towards intramolecular di-alkylation once isolated. These reactions provide a facile route to ω-haloalkylthiolate complexes which are poorly defined in the literature. X-ray crystal structures of [Pt2(μ-S){μ-S(CH2)5Br}(PPh3)4]BPh4 and [Pt2(μ-S(CH2)5S}(PPh3)4](BPh4)2 are reported, together with a study of these complexes by electrospray ionisation mass spectrometry. All complexes fragment by dissociation of PPh3 ligands, and the bromoalkylthiolate complexes show additional fragment ions [Pt2(μ-S){μ-S(CH2)n−2CHCH2}(PPh3)m]+ (m = 2 or 3; m ≠ 4), most significant for n = 4, formed by elimination of HBr. 相似文献
Nicotinate-N-oxide and isonicotinate-N-oxide have been employed to synthesize four heterometallic metallamacrocycles [(dppf)2Pd2(nicotinate-N-oxide)2](OTf)2 (1), [(dppf)2Pt2(nicotinate-N-oxide)2](OTf)2 (2), [(dppf)2Pd2(isonicotinate-N-oxide)2](OTf)2 (3) and [(dppf)2Pt2(isonicotinate-N-oxide)2](OTf)2 (4). The complexes represent the first examples of metallamacrocycles driven by solely Pd(II)/Pt(II)-O coordination using carboxylate-N-oxide donor. All the complexes 1-4 are characterized by IR, UV-Vis, multinuclear NMR spectroscopic and ESI-MS studies. The molecular structures of the complexes 1 and 3 are unambiguously determined by single crystal X-ray diffraction analysis. Despite the possibility of formation of several linkage isomers due to ambidentate nature of the donors, exclusive formation of [2 + 2] self-assembled single isomeric metallamacrocycle in each case is interesting observation. 相似文献
Coordination polymers of [2.2]paracyclophane (pcp) with in situ silver(I) perfluoro-dicarboxylates characterized by single crystal X-ray analysis are described. Structures are found to strongly depend on the dicarboxylate spacer (n). With disilver(I) tetrafluorosuccinate ((CF2)n(COOAg)2, n = 2), 3D network with composition of [Ag4(pcp)(C2F4(CO2)2)2] (1) forms in which silver salts afford infinite double chains and pcp act as linkages between chains. Changing the silver salt to disilver hexafluoroglutarate ((CF2)n(COOAg)2, n = 3) produces 3D pillared-layer structure of composition of [Ag4(pcp)(C3F6(CO2)2)2] · THF (2) (THF = tetrahydrofuran), in which silver salts form 2D sheets and pcp act as pillars between the sheets. With silver octafluoroadipate (HO2C(CF2)nCO2Ag, n = 4), 2-fold interpenetrated diamond structure, [Ag2(pcp)2(HO2CC4F8CO2)2]2 · 2toluene (3), is obtained in which silver-anion chains and silver-pcp chains are connected with each other in the perpendicular manner. The three complexes represent unprecedented metal-organic networks of silver(I) multicarboxylates and polycyclic aromatic compounds. Additionally, the effects of the dicarboxylate conformations as well as the solvents on the resulting structures were discussed. 相似文献
The reaction between [PtII(Ox)2]2− and an appropriate oxidant resulted in the formation of the dimeric unbridged platinum complex [{PtIII(Ox)2 }2]2− where (Ox) is oxalate. This complex was moderately stable under ambient conditions and was studied via a variety of NMR and spectrophotometric techniques. Reaction of the [{PtIII(Ox)2}2]2− complex with [PtII(Ox)2]2− in the presence of H+ lead to the formation of a series of longer platinum oligomers with non-integral oxidation states, culminating in the formation of partially oxidized platinum polymers of general formula [{Pt(Ox)2}n]n−. The concentration of H+ was an important factor leading to higher oligomers and the approximate number of protons associated with each oligomer was determined. The analogous [{PtIII(Mal)2}2]2− complex, where (Mal) is the malonate anion, was also synthesized and studied but was shown to be significantly less stable. 相似文献
The dinuclear complexes [Pd2(L)2(bipy)2] (1), [Pd2(L)2(phen)2] (2), [Pt2(L)2(bipy)2] (3) and [Pt2(L)2(phen)2] (4), where bipy = 2,2′-bipyridine, phen = 1,10-phenanthroline and L = 2,2′-azanediyldibenzoic dianion) dibridged by H2L ligands have been synthesized and characterized. The binding of the complexes with fish sperm DNA (FS-DNA) were investigated by fluorescence spectroscopy. The results indicate that the four complexes bound to DNA with different binding affinity, in the order complex 4 > complex 3 > complex 2 > complex 1, and the complex 3 binds to DNA in both coordination and intercalative mode. Gel electrophoresis assay demonstrates the ability of the complexes to cleave the pBR 322 plasmid DNA. The cytotoxic activity of the complexes was tested against four different cancer cell lines. The four complexes exhibited cytotoxic specificity and significant cancer cell inhibitory rate. 相似文献
The structures and energy properties for Agn (n = 1-8) metal clusters adsorbed on the perfect and oxygen vacancy MgO surfaces have been studied by using the DFT/UB3LYP
method with an embedded cluster model. The nucleation and mobility model for the Agn (n = 1-8) clusters on the perfect and oxygen vacancy MgO(100) surfaces was investigated. The results show that the Ag atoms
locate initially at the surface oxygen vacancy sites; then, with the growth of Ag cluster sizes, the large Ag clusters move
possibly out of the vacancy sites by a rolling model, and diffuse on the MgO surface under a certain temperature condition.
The relative energies needed for moving out of the oxygen vacancy region for the adsorbed Agn clusters with the rolling model have been predicted. The even-odd oscillation behaviors for the cohesive energies, nucleation
energies, first ionization potentials and HOMO-LUMO gaps of the adsorbed Agn clusters with the variation of cluster sizes have also been discussed. 相似文献
Chemical functionalization of the boron nitride nanotube (BNNT) allows a wider flexibility in engineering its electronic and magnetic properties as well as chemical reactivity, thus making it have potential applications in many fields. In the present work, the encapsulation of 13 different Pd3M (M?=?Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Pd, Pt, and Au) clusters inside the (10, 0) BNNT has been studied by performing comprehensive density functional theory (DFT) calculations. Particular attention is paid to searching for the stable configurations, calculating the corresponding binding energies, and evaluating the effects of the encapsulation of Pd3M cluster on the electronic and magnetic properties of BNNT. The results indicate that all the studied Pd3M clusters can be stably encapsulated inside the (10, 0) BNNT, with binding energies ranging from ?0.96 (for Pd3Sc) to ?5.31 eV (for Pd3V). Moreover, due to a certain amount of charge transfer from Pd3M clusters to BNNT, certain impurity states are induced within the band gap of pristine BNNT, leading to the reduction of the band gap in various ways. Most Pd3M@BNNT nanocomposites exhibit nonzero magnetic moments, which mainly originate from the contribution of the Pd3M clusters. In particular, the adsorption of O2 molecule on BNNT is greatly enhanced due to Pd3M encapsulation. The elongation of O-O bonds of the adsorbed O2 molecules indicates that Pd3M@BNNT could be used to fabricate the oxidative catalysis. 相似文献
Variable-temperature X-ray structural study of the complex [(Ph3P)2N]2[Pt2Ag4Cl2(C2Ph)8] prepared by the reaction of cis-[PtCl2(AsPh3)2] and [(Ph3P)2N][Ag(C2Ph)2] in 1:2 M ratio, revealed isolated (non-polymerised) [Pt2Ag4Cl2(CCPh)8]2− anions with a pseudo-octahedral arrangement of metal atoms. The Pt atoms (in mutually trans vertices) are each σ-bonded to four alkynyl ligands in a square planar arrangement; these moieties are bridged by four Ag atoms; each silver atom being η2-bonded to two alkynyl groups. Chloride ligands are asymmetrically bridging two opposite Ag-Ag edges. Silver atoms show strong and unusual temperature-dependent disorder. 相似文献
