Stability effects on CO2 adsorption for the DOBDC series of metal-organic frameworks

Metal-organic frameworks with unsaturated metal centers in their crystal structures, such as Ni/DOBDC and Mg/DOBDC, are promising adsorbents for carbon dioxide capture from flue gas due to their high CO(2) capacities at subatmospheric pressures. However, stability is a critical issue for their application. In this paper, the stabilities of Ni/DOBDC and Mg/DOBDC are investigated. Effects of steam conditioning, simulated flue gas conditioning, and long-term storage on CO(2) adsorption capacities are considered. Results show that Ni/DOBDC can maintain its CO(2) capacity after steam conditioning and long-term storage, whereas Mg/DOBDC does not. Nitrogen isotherms for Mg/DOBDC show a drop in surface area after steaming, corresponding to the decrease in CO(2) adsorption, which may be caused by a reduction of unsaturated metal centers in its structure. Conditioning with dry simulated flue gas at room temperature only slightly affects CO(2) adsorption in Ni/DOBDC. However, introducing water vapor into the simulated flue gas further reduces the CO(2) capacity of Ni/DOBDC.     

Hydrogen adsorption in the metal-organic frameworks Fe2(dobdc) and Fe2(O2)(dobdc)

The hydrogen storage properties of Fe(2)(dobdc) (dobdc(4-) = 2,5-dioxido-1,4-benzenedicarboxylate) and an oxidized analog, Fe(2)(O(2))(dobdc), have been examined using several complementary techniques, including low-pressure gas adsorption, neutron powder diffraction, and inelastic neutron scattering. These two metal-organic frameworks, which possess one-dimensional hexagonal channels decorated with unsaturated iron coordination sites, exhibit high initial isosteric heats of adsorption of -9.7(1) and -10.0(1) kJ mol(-1), respectively. Neutron powder diffraction has allowed the identification of three D(2) binding sites within the two frameworks, with the closest contacts corresponding to Fe-D(2) separations of 2.47(3) and 2.53(5) ?, respectively. Inelastic neutron scattering spectra, obtained from p-H(2) (para-H(2)) and D(2)-p-H(2) mixtures adsorbed in Fe(2)(dobdc), reveal weak interactions between two neighboring adsorption sites, a finding that is in opposition to a previous report of possible 'pairing' between neighboring H(2) molecules.     

Structural and magnetic studies on cyano-bridged rectangular Fe2M2 (M = Cu, Ni) clusters

Using the tricyano precursor, (Bu4N)[(Tp)Fe(CN)3] (Tp = Tris(pyrazolyl) hydroborate) (1), four new tetranuclear clusters, [(Tp)Fe(CN)3Cu(Tp)]2.2H2O (2), [(Tp)Fe(CN)3Cu(bpca)]2.4H2O (3) (bpca = bis(2-pyridylcarbonyl)amidate anion), [(Tp)Fe(CN)3Ni(tren)]2(ClO4)2.2H2O (4) (tren = tris(2-amino)ethylamine), and [(Tp)Fe(CN)3Ni(bipy)2]2[(Tp)Fe(CN)3]2.6H2O (5) (bipy = 2,2'-bipyridine), have been synthesized and structurally characterized. The four clusters possess similar square structures, where FeIII and MII (M = CuII or NiII) ions alternate at the rectangle corners. There exist intermolecular - stacking interactions through pyrazolyl groups of Tp- ligands in complexes 2 and 4, which lead to 1D chain structures. Complex 5 shows a 3D network structure through the coexistence of - stacking effects and hydrogen-bonding interactions. Magnetic studies show intramolecular ferromagnetic interactions in all four clusters. The exchange parameters are +11.91 and +1.38 cm(-1) for clusters 2 and 3, respectively, while uniaxial molecular anisotropy can be detected in complex 3 due to the distorted core in its molecular structure. Complex 4 has a ground state of S = 3 and shows SMM behavior with an effective energy barrier of U = 18.9 cm(-1). Unusual spin-glass-like dynamic relaxations are observed for complex 5.     

Catalytic Performance in CO Hydrogenation Over SiO_2-Supported Ru-M (M=Co, Fe,Mo,Ni,Rh,Mn and Cr) Bimetallic Cluster-derived Catalysts

The bimetallic Ru-M (M=Co,Fe,Ni,Mo, Rh,Cr, Mn) catalysts were prepared from SiO_2-supported bimetallic carbonyl clusters, and it was found that the Ru-Co, Ru-Fe and Ru-Mo bimetallic carbonyl cluster-derived catalysts showed higher activity and selectivity for oxygenates such as C_1-C_5 alcohols in CO hydrogenation,in contrast to catalysts prepared from SiO_2-supported homometallic Ru and Co carbonyl clusters. In situ FT-IR studies revealed that the bands at 1584 and 1555 cm~(-1) species were intermediates to produce methanol and higher oxygenates,and at higher temperatures the 1584 cm~(-1) species could react with alkyl to form 1555 cm~(-1) species. By the surface chemical reaction and the IR study of isotopic molecules,it was suggested that 1584 and 1555 cm~(-1) were assigned to surface formyl and acetyl species.     

Magnetic Susceptibilities of ThM2X2 Compounds (M = Cr,Mn, Fe,Co, Ni and Cu; X = Si and Ge)

Magnetic susceptibilities of a series of ternary intermetallic compounds of the general composition ThM₂X₂(M = Cr, Mn, Fe, Co, Ni and Cu; X = Si and Ge) were determined by means of FARADAY method in the temperature interval 100–570°K. The results confirm the previously proposed magnetic behaviour of these compounds, based on the observation of the basic crystallographic parameters as a function of the atomic number of the transition metal element. The compounds were found to be alternatively ferromagnetics and antiferromagnetics depending on the atomic number of the transition metal atom.     

Synthesis and characterization of (smif)2M(n) (n = 0, M = V, Cr, Mn, Fe, Co, Ni, Ru; n = +1, M = Cr, Mn, Co, Rh, Ir; smif =1,3-di-(2-pyridyl)-2-azaallyl)

A series of Werner complexes featuring the tridentate ligand smif, that is, 1,3-di-(2-pyridyl)-2-azaallyl, have been prepared. Syntheses of (smif)(2)M (1-M; M = Cr, Fe) were accomplished via treatment of M(NSiMe(3))(2)(THF)(n) (M = Cr, n = 2; Fe, n = 1) with 2 equiv of (smif)H (1,3-di-(2-pyridyl)-2-azapropene); ortho-methylated ((o)Mesmif)(2)Fe (2-Fe) and ((o)Me(2)smif)(2)Fe (3-Fe) were similarly prepared. Metatheses of MX(2) variants with 2 equiv of Li(smif) or Na(smif) generated 1-M (M = Cr, Mn, Fe, Co, Ni, Zn, Ru). Metathesis of VCl(3)(THF)(3) with 2 Li(smif) with a reducing equiv of Na/Hg present afforded 1-V, while 2 Na(smif) and IrCl(3)(THF)(3) in the presence of NaBPh(4) gave [(smif)(2)Ir]BPh(4) (1(+)-Ir). Electrochemical experiments led to the oxidation of 1-M (M = Cr, Mn, Co) by AgOTf to produce [(smif)(2)M]OTf (1(+)-M), and treatment of Rh(2)(O(2)CCF(3))(4) with 4 equiv Na(smif) and 2 AgOTf gave 1(+)-Rh. Characterizations by NMR, EPR, and UV-vis spectroscopies, SQUID magnetometry, X-ray crystallography, and DFT calculations are presented. Intraligand (IL) transitions derived from promotion of electrons from the unique CNC(nb) (nonbonding) orbitals of the smif backbone to ligand π*-type orbitals are intense (ε ≈ 10,000-60,000 M(-1)cm(-1)), dominate the UV-visible spectra, and give crystals a metallic-looking appearance. High energy K-edge spectroscopy was used to show that the smif in 1-Cr is redox noninnocent, and its electron configuration is best described as (smif(-))(smif(2-))Cr(III); an unusual S = 1 EPR spectrum (X-band) was obtained for 1-Cr.     

Calorimetric Study on LaNi4M(M=Ni,Cu,Fe)-H Systems

The relative partial molar enthalpies and the partial molar free energiesof hydrogen dissolved in LaNi5,LaNi4Cu,and LaNi4Fe were measured respectively by acalorimetric system at 298.3K,and the partial molar entropies were also calculated By X-ray diffraction analysis the unit cell volumes V were calculated.It was found that both and vary with V according to the following linear relations     

Catalytic reduction of NOx by CO on hydrotalcites-derived mixed oxides CoAlM and MgAlM (M=Cr,Mn, Fe,Co, Ni,Cu)

Two series of mixed oxides, GIAlM and MgAlM (M= G, Mn, Fe, Co, Ni, Cu), were prepared by calcining their corresponding hydrotalcite-like compounds (HTLc). The ratio of Mg: Al: M (or Co: Al: M) was 3:1:1. The catalytic activity of all samples for the reaction of NO + CO was investigated. The results showed that the activity of CoAlM was much higher than that of MgAlM. The structure and the property of redox were characterized by XRD and H₂-TPR. The results indicated that only MgO phase was observed after calcining MgAlM hydrotalcites, and the transition metals became more stable. The spinel-like phase appeared in all of CoAlM samples after the calcination, and the transition metals were changed to be more active, and easily reduced. The activities of three series of mixed oxides CoAlCu obtained from different preparation methods, Different ratio of Co: Al: Cu and at different calcination temperatures. were studied in detail for proposing the mechanism of reaction. The ability of adsorption of NO and CO were investigated respectively for supporting the mechanism.     

XANES study of oxycarbonates Hg1−xMxSr4Cu2(CO3)O6+δ (M=Mo,Cr)

X-ray absorption measurements have been made on CuL₃ and OK edges for two transition metal substituted Hg based oxycarbonates Hg_0.5Mo_0.5Sr₄Cu₂(CO₃)O_6+δ and Hg_0.4Cr_0.6Sr₄Cu₂(CO₃)O_6+δ. Despite a much lower T_c (37 K) the Cr sample has a much higher diamagnetic fraction than the Mo sample (T_c∼74 K). CuL₃ and OK edge spectra clearly indicate the presence of substantial number of doping holes in both the samples characteristic of their superconducting properties. But interestingly, the density of holes (DOH) are almost the same for the two samples. If the DOH correlated with the T_c solely, one would expect it be nearly double in Mo sample than the Cr one. Thus the present study presents a strong evidence for the dependence of DOH upon diamagnetic fraction over and above its dependence upon their transition temperature in the cuprate perovskites. Also the results of resistivity and susceptibility studies made earlier on these samples have been mentioned briefly.     

羰基原子簇化合物M3(CO)12(M=Fe,Ru,Os)的激光解离研究

在自制的仪器上以冲激光溅射铁、钌、锇的三核羰基原子簇化合物。由原位质谱观察和分析溅射产生的正负离子。比较了解离碎片及分布发现羰基锇原子簇化合物具有特殊的结构稳定性。它们不仅具有很强的金属键,而且锇与羰基分子还形成了很强的配位键。     

配合物[M（CO）3（PPh2py）2]（M=Fe，Ru）异构体的理论研究

对PPh2py配合物[M(CO)3(PPh2py)2](M=Fe,Ru)的三种构型的异构体1-6进行了研究.其中PPh2py以两个P原子与M配位形成HH构型1(Fe)和4(Ru),以一个P和一个N原子与M配位形成HT构型2(Fe)和5(Ru),以两个N原子与M配位形成HH'构型3(Fe)和6(Ru).结果表明,(1)PPh2py中P原子对HOMO轨道的贡献最大,PPh2py作为电子给体时易以P原子与金属原子结合.(2)从分子能量和相互作用能数据表明,配合物中HH构型最稳定,HH'构型最不稳定,这与合成产物为HH构型的结果一致.(3)键长和Wiberg键级均表明P-M键比N-M键结合力强.P、M原子间存在σ键,而N、Fe原子间仅存在nN→nM或nN→σM-P的电荷转移作用.(4)HH构型中M对HOMO的贡献最大,PPh2py向M的电荷转移最强,使M的负电荷最大,故HH构型最易作为电子给体以M原子与第二个金属配位形成双核配合物.     

Stability improvement of Cu3(BTC)2 metal-organic frameworks under steaming conditions by encapsulation of a Keggin polyoxometalate

Cu(3)(BTC)(2) with an incorporated Keggin polyoxometalate was demonstrated to be stable under steaming conditions up to 483 K, while the isostructural HKUST-1 degrades and transforms into [Cu(2)OH(BTC)(H(2)O)](n)·2nH(2)O from 343 K onwards.     

Catalytic reduction of NO_x by CO on hydro-talcites-derived mixed oxides Co AIM and MgAlM (M = Cr, Mn, Fe, Co, Ni, Cu)

Two series of mixed oxides, CoAlM and MgAlM (M= Cr, Mn, Fe, Co, Ni, Cu) , were prepared by calcining their corresponding hydrotalcite-like compounds (HTLc) . The ratio of Mg: Al: M (or Co: Al: M) was 3:1:1. The catalytic activity of all samples for the reaction of NO CO was investigated. The results showed that the activity of CoAlM was much higher than that of MgAlM. The structure and the property of redox were characterized by XRD and H2-TPR. The results indicated that only MgO phase was observed after calcining MgAlM hydrotalcites, and the transition metals became more stable. The spinel-like phase appeared in all of CoAlM samples after the calcination, and the transition metals were changed to be more active, and easily reduced . The activities of three series of mixed oxides CoAlCu obtained from different preparation methods, different ratio of Co:Al:Cu and at different calcination temperatures, were studied in detail for proposing the mechanism of reaction. The ability of adsorption of NO and CO     

Electronic structure and properties of MCO and M5CO carbonyls (M = Fe,Ni, Cu) by density functional methods

Density functional theory (DFT) calculations of the electronic structure and properties of Fe, Ni, and Cu carbonyls with one and five transition-element atoms are reported, due to their importance in heterogeneous catalysis (especially in Fischer-Tropsch synthesis). The local density approximation (LDA) with the Vosko-Wilk-Nussain (VWN) correlation functional as well as the generalized gradient approximation (GGA) using Becke's 1988 exchange functional and Perdew's 1986 correlation functional (BP method) were applied to the study of the clusters using a triple-zeta plus polarization (TZP) basis set. Triplet and quintuplet states for FeCO, singlet and triplet for NiCO, and doublet for CuCO were considered, and optimization of energy at the LDA/BP level for these cases was done. Dissociation energies in M and CO fragments, frequencies, and population analysis were performed. Geometry optimization of the distance between the C atom and the clusters M₅ (with geometries taken from the crystals) were carried out and the dissociation energy in fragments M₅ and CO as well as population analysis at the optimized geometries were also done. Comparison between our results and some others published using ab initio and density functional methods were performed. © 1996 John Wiley & Sons, Inc.     

Photochemical reactions of M(CO)6 (M = Cr,Mo, W) with Ph2P(S)P(S)Ph2

New complexes {M(CO)₄[Ph₂P(S)P(S)Ph₂]} (M = Cr, Mo and W), (1a)–(3a), [(1a), M = Cr; (2a), M = Mo; (3a), M = W] and {M₂(CO)₁₀[-Ph₂P(S)P(S)Ph₂]} (M = Cr, Mo, W), [(1b)–(3b) [(1b), M = Cr; (2b), M = Mo; (3b), M = W]] have been prepared by the photochemical reaction of M(CO)₆ with Ph₂P(S)P(S)Ph₂ and characterized by elemental analyses, f.t.-i.r. and ³¹P-(¹H)-n.m.r. spectroscopy and by FAB-mass spectrometry. The spectra suggest cis-chelate bidentate coordination of the ligand in {M(CO)₄[Ph₂P(S)P(S)Ph₂]} and cis-bridging bidentate coordination of the ligand between two metals in (M = Cr, Mo and W).     

Synergetic effect of host-guest chemistry and spin crossover in 3D Hofmann-like metal-organic frameworks [Fe(bpac)M(CN)4] (M=Pt, Pd, Ni)

The synthesis and characterization of a series of three‐dimensional (3D) Hofmann‐like clathrate porous metal–organic framework (MOF) materials [Fe(bpac)M(CN)₄] (M=Pt, Pd, and Ni; bpac=bis(4‐pyridyl)acetylene) that exhibit spin‐crossover behavior is reported. The rigid bpac ligand is longer than the previously used azopyridine and pyrazine and has been selected with the aim to improve both the spin‐crossover properties and the porosity of the corresponding porous coordination polymers (PCPs). The 3D network is composed of successive {Fe[M(CN)₄]}_n planar layers bridged by the bis‐monodentate bpac ligand linked in the apical positions of the iron center. The large void between the layers, which represents 41.7 % of the unit cell, can accommodate solvent molecules or free bpac ligand. Different synthetic strategies were used to obtain a range of spin‐crossover behaviors with hysteresis loops around room temperature; the samples were characterized by magnetic susceptibility, calorimetric, Mössbauer, and Raman measurements. The complete physical study reveals a clear relationship between the quantity of included bpac molecules and the completeness of the spin transition, thereby underlining the key role of the π–π stacking interactions operating between the host and guest bpac molecules within the network. Although the inclusion of the bpac molecules tends to increase the amount of active iron centers, no variation of the transition temperature was measured. We have also investigated the ability of the network to accommodate the inclusion of molecules other than water and bpac and studied the synergy between the host–guest interaction and the spin‐crossover behavior. In fact, the clathration of various aromatic molecules revealed specific modifications of the transition temperature. Finally, the transition temperature and the completeness of the transition are related to the nature of the metal associated with the iron center (Ni, Pt, or Pd) and also to the nature and the amount of guest molecules in the lattice.     

MII-N-diisopropoxythiophosphorylthiobenzamide complexing processes in M2[Fe(CN)6]-gelatin-immobilized matrices (M = Co,Ni, Cu)

Complexing processes in M^II-N-diisopropoxythiophosphorylthiobenzamide binary systems (M = Co, Ni, Cu) in metal(II) hexacyanoferrate(II) gelatin-immobilized matrices upon contact with aqueous–alkaline (pH = 12.0 ± 0.1) solutions of organic compounds have been studied. It has been shown that, in Co^II and Cu^II, the initial act of complexing involves destruction of the Co^II and Cu^II hexacyanoferrates(II) by OH^– ions, leading to formation of the corresponding hydroxides which react with the ligand indicated. In the both systems, successive addition of two ligand molecules per M(OH)₂ fragment occurs and [MB(OH)(OH₂)] and [MB₂] coordination compounds are formed (B^–-a singly deprotonated ligand form). In the Ni^II-N-diisopropoxythiophosphorylthiobenzamide system, the formation of three complexes, (Ni₂BOH)₂[Fe(CN)₆], [NiB(OH)(OH₂)] and [NiB₂] occurs.     

Novel electrorheological properties of a metal-organic framework Cu3(BTC)2

A metal-organic framework, Cu(3)(BTC)(2), was synthesized and applied as an electro-responsive electrorheological material dispersed in insulating oil. Powder of crystalline Cu(3)(BTC)(2) exhibited excellent chain-like structures and controllable rheological properties in an applied electric field.     

Synthesis of the New Silanediyldiphosphinite tBu2Si(OPPh2)2 and its Reactions with the Norbornadiene Complexes C7H8M(CO)4 (M = Cr,Mo, W). Crystal Structures of cis-M(CO)4[tBu2Si(OPPh2)2] (M = Cr,Mo)

Silanediyldiphosphinite tBu₂Si(OPPh₂)₂ 1 has been synthesised. 1 reacts with the norbornadiene complexes C₇H₈M(CO)₄ (M = Cr, Mo, W) to give six-membered chelate rings of the type cis-M(CO)₄[tBu₂Si(OPPh₂)₂] 2–4 . The crystal structures of the chromium and molybdenum complexes cis-Cr(CO)₄[tBu₂Si(OPPh₂)₂] 2 and cis-Mo(CO)₄[tBu₂Si(OPPh₂)₂] 3 have been determined. Both complexes crystallise in the triclinic system (space group P1 ) with unit cell parameters: ( 2 ) a = 1 093(3) pm, b = 1 477(5) pm and c = 1 542(5) pm; α = 108.4(2)°, b? = 103.87(11)° and b? = 104.57(10)°; U = 2.143(12) nm³; Z = 2; ( 3 ) a = 1 097.8(2) pm, b = 1 483.7(2) pm and c = 1 554.3(2) pm; α = 108.10(1)°, b? = 103.956(6)° and γ = 104.213(7)°; U = 2.1899(6) nm³; Z = 2. Both 2 and 3 consist of discrete, slightly distorted, octahedral monomers in which the six-membered chelate rings are essentially planar. In contrast, the conformations of the chelate rings found in crystal structures of analogous complexes vary from twist-boat to “chaise longue”.