Copper Tetramer Research Articles

An octanuclear 3-phenyl-5-(2-pyridyl)pyrazolate/phenylsilsesquioxane complex: synthesis, unique structure, and catalytic activity.

The first metallasilsesquioxane bearing pyrazolylpyridine ligands, the Cu8-based complex 1, adopts a cage-like structure with two zigzag-type copper tetramers sandwiched by two cyclic Si5 silsesquioxane ligands. The four 3-phenyl-5-(2-pyridyl)pyrazolate ligands in 1 exhibit dual (chelating and bridging) modes of ligation. Compound 1 is very active in the oxidation of alkanes and alcohols.

Oxidative dehydrogenation of cyclohexene on atomically precise subnanometer Cu4-nPdn (0 ≤ n ≤ 4) tetramer clusters: the effect of cluster composition and support on performance.

The pronounced effects of the composition of four-atom monometallic Cu and Pd and bimetallic CuPd clusters and the support on the catalytic activity and selectivity in the oxidative dehydrogenation of cyclohexene are reported. The ultra-nanocrystalline diamond supported clusters are highly active and dominantly produce benzene; some of the mixed clusters also produce cyclohexadiene, which are all clusters with a much suppressed combustion channel. The also highly active TiO2-supported tetramers solely produce benzene, without any combustion to CO2. The selectivity of the zirconia-supported mixed CuPd clusters and the monometallic Cu cluster is entirely different; though they are less active in comparison to clusters with other supports, these clusters produce significant fractions of cyclohexadiene, with their selectivity towards cyclohexadiene gradually increasing with the increasing number of copper atoms in the cluster, reaching about 50% for Cu3Pd1. The zirconia-supported copper tetramer stands out from among all the other tetramers in this reaction, with a selectivity towards cyclohexadiene of 70%, which far exceeds those of all the other cluster-support combinations. The findings from this study indicate a positive effect of copper on the stability of the mixed tetramers and potential new ways of fine-tuning catalyst performance by controlling the composition of the active site and via cluster-support interactions in complex oxidative reactions under the suppression of the undesired combustion of the feed.

Diverse coordination architectures based on a flexible multidentate carboxylate ligand and N-donor linkers: Synthesis, structure, supramolecular chemistry and related properties

Three new metal–organic framework (MOF) containing compounds, namely {Cu2(tci)(btx)0.5(µ3-OH)(H2O)}n (1), {Cu1.5(tci)(biip)}n (2), {Co1.5(tci)(biip)}n (3) [H3tci = tris(2-carboxyethyl)isocyanurate, btx = 1,4-bis(triazol-1-yl-methyl)benzene, biip = 3,5-bis(imidazole-1-yl)pyridine] have been successfully synthesized through the assembly of metal ions [Cu(II) ion for compounds 1 and 2, Co(II) for compound 3] with H3tci and two different N-donor ligands (btx and biip) under solvothermal conditions. All compounds were characterized by IR spectroscopy, elemental and thermogravimetric (TG) analyses, powder X-ray diffraction (PXRD) studies and finally, the structures of all compounds were unambiguously determined by single-crystal X-ray diffraction (SCXRD) technique. Compound 1 is a 1D coordination polymer, constructed by the connectivity of copper tetramer as a secondary building unit (SBU) with the H3tci and btx ligands. Whereas the crystal structure of compound 2 possesses two different SBUs i.e., paddlewheel and square planar involving Cu(II). The connectivity of these two SBUs results in the formation of 2D layers which are further pillared by biip ligand to result in a 3D structure. In the case of compound 3, both Co1 and Co2 exhibit distorted octahedral geometry in their SBUs. Further, the connectivity of these SBUs with tci3- and biip ligands results in the formation of a 3D framework.

Atom by atom built subnanometer copper cluster catalyst for the highly selective oxidative dehydrogenation of cyclohexene.

The effect of particle size and support on the catalytic performance of supported subnanometer copper clusters was investigated in the oxidative dehydrogenation of cyclohexene. From among the investigated seven size-selected subnanometer copper particles between a single atom and clusters containing 2-7 atoms, the highest activity was observed for the titania-supported copper tetramer with 100% selectivity toward benzene production and being about an order of magnitude more active than not only all the other investigated cluster sizes on the same support but also the same tetramer on the other supports, Al2O3, SiO2, and SnO2. In addition to the profound effect of cluster size on activity and with Cu4 outstanding from the studied series, Cu4 clusters supported on SiO2 provide an example of tuning selectivity through support effects when this particular catalyst also produces cyclohexadiene with about 30% selectivity. Titania-supported Cu5 and Cu7 clusters supported on TiO2 produce a high fraction of cyclohexadiene in contrast to their neighbors, while Cu4 and Cu6 solely produce benzene without any combustion, thus representing odd-even oscillation of selectivity with the number of atoms in the cluster.

CO2 Methanation on Cu-Cluster Decorated Zirconia Supports with Different Morphology: A Combined Experimental In Situ GIXANES/GISAXS, Ex Situ XPS and Theoretical DFT Study

Subnanometer copper tetramer–zirconia catalysts turn out to be highly efficient for CO2 hydrogenation and its conversion to methane. The cluster size and substrate morphology are controlled to opti...

Dynamic Interplay between Copper Tetramers and Iron Oxide Boosting CO2 Conversion to Methanol and Hydrocarbons under Mild Conditions

Atomically precise subnanometer catalysts are of significant interest because of their remarkable efficiency in a variety of catalytic reactions. However, the dynamic changes of active sites under ...

A long-range ordered array of copper tetrameric units embedded in an on-surface metal organic framework.

We report on the assembly of a highly ordered array of copper tetrameric clusters, coordinated into a metal-organic network. The ordered cluster array has been achieved by the deposition of tetrahydroxyquinone molecules on the Cu(111) surface at room temperature, and subsequent thermally activated dehydrogenation with the formation of tetraoxyquinone tetra-anions with a 4 × 4 periodicity. The supramolecular organic network acts as a spacer for the highly ordered two-dimensional network of copper tetramers at the very surface.

New copper(II) tetramer with arylhydrazone of barbituric acid and its catalytic activity in the oxidation of cyclic C5–C8 alkanes

2-(2-(2,4,6-Trioxotetrahydropyrimidin-5(2H)-ylidene)hydrazinyl)terephthalic acid (H5L) was synthesized by azocoupling of diazonium salts of 2-aminoterephthalic acid with barbituric acid and characterized by IR, 1H and 13C NMR spectroscopies and ESI-MS analysis. In solution and solid state, H5L exists in the hydrazone form. The reaction of H5L with copper(II) nitrate hydrate in methanol affords the tetramer species [Cu2(μ2-1κNOO′:2κO′O″-H3L)2]2 (1) where carboxylate groups bridge two Cu(II) centers in a bridging chelate μ2-(O,O′,O′) fashion, giving rise to a cyclic Cu4O4 core. A rare and intense intermolecular non-covalent interaction of the type Ocarboxylic(lone pair)⋯π(pyrimidine), with O⋯centroid distance of 2.705Å, was found in 1. In addition, medium intense NH⋯O and OH⋯O contacts expand the structure to a 3D network. Compound 1 behaves as efficient catalyst in the mild oxidation, by aqueous H2O2 in acidic MeCN/H2O media, of different cyclic C5–C8 alkanes to produce the corresponding alcohols and ketones. Overall product yields up to ca. 25% (based on alkane) were achieved.

Presence of Gap States at Cu/TiO2Anatase Surfaces: Consequences for the Photocatalytic Activity

Copper-modified titania is a system of interest for its potential for photocatalytic applications in the production of solar fuels. Still, the role of copper in the process is unclear. In this work, small copper clusters on the (101) and (100) surfaces of anatase have been investigated by first-principles simulations based on density functional theory, to shed light on their atomic and electronic structure, and to understand their effect on the photocatalytic process. The main effects of copper on the electronic structure are to provide states above the edge of the valence band of titania and to lead to the formation of midgap states. There are two types of midgap states, respectively, associated with direct Cu–Ti bonds and to Ti3+ polarons. The latter are the result of charge donation from copper and lie in the vicinity of the surface. Moreover, the copper tetramer (Cu4) displays empty states at the bottom of the conduction band that play a key role in accommodating excess electrons. We discuss how these...

Synthesis, Structure and Reactivity of the Compound [Cu(C7H7NH2)Cl]4 derived from CuCl and Benzylamine (C7H7NH2)

AbstractThe facile synthesis, molecular structure, and reactivity of [Cu(C7H7NH2)Cl]4 (1) towards dioxygen and derivatives is reported. The compound could easily be prepared in good yields by mixing CuCl and benzylamine under inert conditions in dichloromethane. Surprisingly this copper(I) compound, a copper(I) tetramer with CuI···CuI interactions of 2.89 Å, was formed instead of an expected cubane cluster. Oxidation reactions led to formation of μ‐oxido‐species as intermediates, however 1 did not show any catalytic activity in the activation of CH bonds. In contrast it turned out that 1 was quite stable towards oxidation. Analogous reactions with CuBr or CuI were different and neither cluster units or polynuclear copper(I) complexes were obtained.

Heavier carbene analogues and their derivatives as κ-El, κ2-El,N, and κ2-N,N′ ligands: different reactivity patterns for acyclic and cyclic diamidogermylenes and -stannylenes

Because of the increasing importance of N-heterocyclic carbenes in organometallic chemistry we investigated the ligand properties of structurally-related acyclic and cyclic heavier carbene analogues with transition metal chlorides. Acyclic {(Me(3)Si)(2)N}(2)El, El = Ge and Sn, react with CuCl with transfer of one (Me(3)Si)(2)N ligand to yield the known copper tetramer {(Me(3)Si)(2)NCu}(4). The cyclic Me(2)Si(μ-N(t)Bu)(2)Ge, by contrast, binds copper through germanium only, furnishing a tetranuclear ladder structure with both terminal and bridging germylenes. The tin homologue, however, inserts into the CuCl bond, and the ensuing {Me(2)Si(μ-N(t)Bu)(2)SnCl}(-) ions then coordinate one copper ion via their tin atoms while sandwiching the remaining three copper ions in an unprecedented κ(2)-N,N' fashion. Chemically-harder Cr(II)--created in a redox reaction of Me(2)Si(μ-N(t)Bu)(2)Sn with CrCl(3)(THF)(3)--is not coordinated by tin, but chelated by both nitrogen atoms of one {Me(2)Si(μ-N(t)Bu)(2)SnCl}(-) ion and more weakly through the tin-bound chloride.

CH3OH + 2H (2Sg) hydrogen abstraction reactions occurring in the presence of a copper tetramer: A DFT study

AbstractThe density functional approximation M05 with 6‐31G** and m‐6‐31G* basis sets were used to calculate the classical barrier heights, structures, reaction energies, and enthalpies of the hydrogen abstraction reaction paths of 2H + (CH3OH)·Cu4 → 2H2 + (COH2)·Cu4, which is a prototype system for dehydrogenation of methanol catalyzed by copper clusters, consisting of two sequential elementary reactions of the methanol combustion mechanism. Electronic structure and intermolecular/intramolecular bond energies were computed as well as the energy variations for the reaction both free and in the presence of the tetramer copper cluster. It was observed that the first dehydrogenation path, related to the abstraction from hydroxyl group of methanol, shows no classical barrier in this level of calculation. We have demonstrated that the planar rhombus cluster Cu4 has bonding properties which mimic quantitatively catalytic properties for some elementary reactions in the methanol combustion mechanism. © 2012 Wiley Periodicals, Inc.

Electric quadrupole and hexadecapole moment, dipole polarizability and hyperpolarizability of the copper tetramer (Cu4) from pseudopotential calculations and a comparison with all-electron ab initio results

We have obtained the electric quadrupole and hexadecapole moment, dipole polarizability and hyperpolarizability of copper tetramer from finite-field ab initio and density functional theory (DFT) calculations performed with a systematic sequence of basis sets built upon the Stevens/Basch/Krauss effective core potential triple-split basis set CEP-121G. Our present ab initio values show significant discrepancies with previous all-electron results [G. Maroulis, A. Haskopoulos, J. Comput. Theor. Nanosci. 6 (2009) 418]. Representative calculations yield self-consistent field (SCF) values (second-order Møller–Plesset results in parentheses) for (hyper)polarizability invariants: mean polarizability α¯=187.41(147.04) and anisotropy Δα=158.95 (128.09) e2a02Eh-1, mean hyperpolarizability 10-3×γ¯=551.7(123.5)e4a04Eh-3. Analogous all-electron results are α¯=196.23(161.24) and anisotropy Δα=165.71 (138.68) e2a02Eh-1, mean hyperpolarizability 10-3×γ¯=631(271)e4a04Eh-3.

Tetranuclear copper(i) carboxylates: the effect of a stepwise increase in Lewis acidity on solid-state structures and photoluminescence

X-Ray diffraction studies of three aliphatic copper(I) carboxylates revealed a tetranuclear core structure for [Cu(4)(O(2)CCH(2)CH(3))(4)] (1), [Cu(4)(O(2)CCF(3))(O(2)CCH(2)CH(3))(3)] (2), and [Cu(4)(O(2)CCF(2)CF(3))(4)] (3). The effect of a stepwise increase in electrophilicity on solid-state interactions of copper(I) tetramers as well as the implications of structural variations on photoluminescent properties of the above copper(I) propionates have been discussed.

Electric Polarizability and Hyperpolarizability of the Copper Tetramer (Cu<SUB>4</SUB>) from <I>Ab Initio</I> and Density Functional Theory Calculations

Electric Polarizability and Hyperpolarizability of the Copper Tetramer (Cu<SUB>4</SUB>) from <I>Ab Initio</I> and Density Functional Theory Calculations

Four coordination polymers constructed from a multicarboxylate ligand and metal centers various from Ba 2+, Cu 2+, Zn 2+ to Gd 3+: Syntheses, crystal structures and properties

Hydrothermal reactions between H 4ODPA (2,2′,3,3′-oxydiphthalic acid) and metal ion salts of Ba 2+, Cu 2+, Zn 2+ and Gd 3+ afford four novel coordination polymers [Ba(H 2ODPA)(H 2O) 4] · H 2O ( 1), [Cu 2(ODPA)(H 2O) 3] · H 2O ( 2), Zn 2(ODPA)(H 2O) 2 ( 3) and [Gd(HODPA)(H 2O) 3.5] · H 2O ( 4), accordingly. These polymers show great differences in regard to their structures and properties originated from the variation of size and coordination geometry of the metal ions. Compound 1 presents puckered achiral layer structure with (4.8 2) topology with helices, 2 has a 6 3 topology with copper tetramer as SBUs, 3 has chiral layer with two kinds of helices built up from Zn-binuclear “paddle-wheel” like SBUs, and 4 features a simple 1D helix with opposite chirality. Compound 3 shows obvious fluorescent emissions upon excitation. Compound 2 shows ferromagnetic interactions between Cu II centers bridged by carboxylate groups, whereas compound 4 presents weak ferromagnetic interaction between Gd III ions.

Two New Hybrid Organic/Inorganic Copper(II)−Oxovanadate(V) Diphosphonates: [Cu2(phen)2(O3PCH2PO3)(V2O5)(H2O)]·H2O and [Cu2(phen)2(O3P(CH2)3PO3)(V2O5)]·C3H8. Synthesis, Structure, and Magnetic Properties

Two new hybrid organic/inorganic copper oxovanadium diphosphonates [Cu2(phen)2(O3PCH2PO3)(V2O5)(H2O)] x H2O (1) and [(Cu2(phen)2(O3P(CH2)3PO3)(V2O5)] x C3H8 (2) have been obtained by hydrothermal synthesis. The compounds are monoclinic, and they crystallize in the space group P2(1)/n with cell parameters of a = 11.788(2) A, b = 17.887(3) A, c = 14.158(2) A, and beta = 93.99(0) degrees and in the space group C2/c with cell parameters of a = 11.025(1) A, b = 18.664(2) A, c = 15.054(2) A, and beta = 90.06(0) degrees, respectively. Both compounds present two-dimensional frameworks built up from infinite chains of corner-sharing vanadium tetrahedra and diphosphonate groups connected by copper tetramers for (1) and copper dimers for (2). The remarkable feature of (2) is the encapsulation of propane molecules, stabilized by strong hydrogen bonding between the layers. The magnetic properties of the compounds have been investigated showing antiferromagnetic coupling with Tmax = 64 K for (1) and Curie-like paramagnetic behavior for (2).

Comparative DFT study of electronic structure and geometry of copper and silver clusters: Interaction with NO molecule

A comparative analysis of geometry and electronic characteristics, namely, vertical detachment energies (VDE) and excitation energies of neutral clusters with geometry of anions (Te) of anionic silver and copper clusters has been carried out within DFT model using a new functional developed recently [Vitaly E. Matulis, O.A. Ivashkevich, V. S. Gurin, J. Mol. Struct. (Theochem) 664–665 (2003) 291]. The obtained data show that the most stable anionic silver and copper clusters have very similar geometry. It has been shown, that properties defined by mainly s-electrons should be very similar for copper and silver clusters. However, the molecular orbitals with large contribution of d-atomic orbitals lie considerably closer in energy to the HOMO for copper clusters than for silver ones. Therefore, a substantial difference should be observed in such properties of silver and copper where d-electrons play an important role, for example, in their catalytic activity. The role of d-electrons along with VDE and ionization potential in catalytic activity is discussed in context of interaction of silver and copper tetramers with NO molecule. To study the influence of “ionic” versus “metallic” bonding on NO adsorption, the reactivity of Cu2Au2 cluster towards NO molecule has been studied and compared with the data obtained for Cu2Ag2 cluster.

A novel 2D coordination polymer based on a copper(II) tetramer with p-sulfonated thiacalix[4]arene

X-ray structural determination of the title complex shows it containing a phenoxy and sulfato-bridged Cu(II) tetramer coordinating to fully deprotonated p-sulfonated thiacalix[4]arene with its cavity occupied by a pyridinium cation and forming a 2D coordination polymer. Variable temperature susceptibility measurement reveals an antiferromagnetic coupling of four Cu(II) ions formed.

High-field magnetization of an [formula omitted] F–F–AF–AF tetramer chain

We performed magnetic susceptibility and high-field magnetization measurements on a powder sample of a copper tetramer chain compound Cu(3-Clpy) 2(N 3) 2 (3-Clpy=3-Chloropyridine). Magnetic susceptibility ( χ) times temperature ( T) decreases gradually with decreasing temperature from 300 K and increases steeply after reaching a minimum at 10 K. The high-field magnetization of this compound at 1.3 K shows a plateau at a half of the saturation magnetization up to 250 kOe and a successive abrupt increase near the saturation field. We compare these experimental data with those calculated for the S= 1 2 ferromagnetic–ferromagnetic–antiferromagnetic–antiferromagnetic (F–F–AF–AF) tetramer chain and obtained fairly good agreement between them when the ratio of the ferromagnetic exchange constant to the antiferromagnetic one is −0.5. The abrupt increase of magnetization near the saturation field is discussed.