Tetrameric Clusters Research Articles

Observation of a water–anion tape constructed from unusual trimeric and tetrameric water clusters embedded in a copper(II) complex

Unusual trimeric and tetrameric water clusters have been observed in a complex of [Cu(DBA)(phen)2·(H2O)4·(NO3)] (1), (HDBA=benzilic acid, phen=1,10-phenanthroline), which was prepared under solvothermal conditions and characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis (TGA), UV–Vis spectroscopy, powder X-ray diffraction and single-crystal X-ray diffraction. In 1, a butterfly-like water–nitrate trimer formed by two water molecules and one nitrate anion, as well as a cyclic tetrameric water cluster are observed. The uncoordinated carboxylate oxygen atoms of DBA ligands, water molecules and nitrate anions interact via hydrogen bonds and extend 1 into a water–anion–cation tape, which in turn join to form a double water–anion–cation tape viaπ···π stacking interactions involving neighboring pyridyl and phenyl groups of DBA ligands.

Supramolecularly assembled tetrameric water cluster stabilized by a mixed complex of Ni(II) and 5-aminoisophthalate

In this study, a novel Ni(II)-5-aminoisophthalate (aip) complex with 5-methylimidazole (5-meim), [Ni(5-meim)6]2(aip)2⋅8H2O (1) has been synthesized. Elemental analysis, magnetic susceptibility, IR and UV–Vis. spectroscopic studies have been performed to characterize the compound. The molecular structure of 1 has been determined by the single crystal X-ray diffraction technique. The complex consists of two hexa(5-methylimidazole)nickel(II) cations, two uncoordinated 5-aminoisophthalate anions and eight uncoordinated water molecules. The molecular structure of (1) has been determined by the single crystal X-ray diffraction technique. In (1) Ni(II) ion has distorted octahedral geometry. The complex (1) is further constructed to form three-dimensional framework by hydrogen bonding, CH⋯π and π⋯π stacking interactions.

Synthesis, spectroscopic characterization and molecular modeling of a tetranuclear platinum(II) complex with thiazolidine-4-carboxylic acid

The synthesis, spectroscopic characterization and molecular modeling of a novel tetranuclear platinum(II) complex with thiazolidine-4-carboxylic acid (THC) are described. Elemental analysis is consistent with the composition PtCl2C4H7NO2S·H2O. Infrared (IR) spectroscopic results and solid-state 13C and 15N nuclear magnetic resonance (NMR) data indicate coordination of the ligand to Pt(II) through the nitrogen and sulfur atoms. The square planar geometry of the platinum(II) complex is completed by chlorine atoms. Density functional theory (DFT) suggests the formation of a tetrameric cluster as the most probable structure, where each THC molecule bridges between two metal centers. The compound is insoluble in water.

Synthesis, Structure, and Crystallization Study of a Layered Lithium Thiophene-Dicarboxylate

A layered lithium carboxylate, Li4[C4H2S(CO2)2]2[C3H7NO]2, crystallizes under solvothermal conditions (160–180 °C) from lithium nitrate and the ligand 2,5-thiophenedicarboxylate in N,N-dimethylformamide as solvent. Single-crystal X-ray diffraction (Pbca a = 10.0216(18) A, b = 18.327(4) A, c = 24.871(5) A) shows that the material is constructed from lithium-centered tetrahedral units linked by edge- and corner-sharing to give tetrameric clusters. These inorganic building units are linked in two dimensions by the bidentate ligand to give a layered structure in which additionally coordinated dimethylformamide projects into the interlayer region. A study of the crystallization of the material using time-resolved in situ energy-dispersive X-ray diffraction reveals that the material crystallizes directly from solution at the reaction temperature following an induction period. Analysis of the crystallization curves suggests that nucleation does not extend far into the crystallization period and that crystal grow...

Rapid degradation of the tetrameric Mn cluster in illuminated, PsbO-depleted photosystem II preparations

A "decoupling effect" (light-induced electron transport without O2 evolution) was observed in Ca-depleted photosystem II (PSII(-Ca)) membranes, which lack PsbP and PsbQ (Semin et al. (2008) Photosynth. Res., 98, 235-249). Here PsbO-depleted PSII (PSII(-PsbO)) membranes (which also lack PsbP and PsbQ) were used to examine effects of PsbO on the decoupling. PSII(-PsbO) membranes do not reduce the acceptor 2,6-dichlorophenolindophenol (DCIP), in contrast to PSII(-Ca) membranes. To understand why DCIP reduction is lost, we studied light effects on the Mn content of PSII(-PsbO) samples and found that when they are first illuminated, Mn cations are rapidly released from the Mn cluster. Addition of an electron acceptor to PSII(-PsbO) samples accelerates the process. No effect of light was found on the Mn cluster in PSII(-Ca) membranes. Our results demonstrate that: (a) the oxidant, which directly oxidizes an as yet undefined substrate in PSII(-Ca) membranes, is the Mn cluster (not the Y(Z) radical or P680(+)); (b) light causes rapid release of Mn cations from the Mn cluster in PSII(-PsbO) membranes, and the mechanism is discussed; and (c) rapid degradation of the Mn cluster under illumination is significant for understanding the lack of functional activity in some PSII(-PsbO) samples reported by others.

Tetranuclear stiboxanes (RSb)4O6, exhibiting an adamantane-type structure

Depolymerization reactions of organostibonic acids with protic ligands have been investigated. Reaction of arylstibonic acids with 8-hydroxyquinoline (8-HQ), or {2-[1H-pyrazol-5(3)-yl]naphthalene-1-ol} (H(2)naphpz) in a 1 : 1 stoichiometry in refluxing toluene affords adamantane-like L(4)(RSb)(4)O(6) clusters [(p-XC(6)H(4)Sb)(4)(O)(6)(Q)(4)] (where X = Cl (1), Br (2), QH = 8-hydroxyquinoline), [(p-ClC(6)H(4)Sb)(4)(O)(6)(Hnaphpz)(4)]·H(2)naphpz (3) and [(p-Br-C(6)H(4)Sb)(4)(O)(6)(Hnaphpz)(4)](2)·H(2)naphpz (4). Further a tetrameric organoantimony oxo cluster, L(4)(RSb)(4)O(4) [(p-ClC(6)H(4)Sb)(4)(O)(4)(naphpz)(4)] (5) has also been isolated as a side product in the reaction of arylstibonic acid with naphthylphenolic pyrazole. Interestingly 1-4 structurally resemble the dimeric form of the antimony oxide Sb(2)O(3) and its mineral senarmontite.

Redox-active polyoxometalate-based crystalline material-immobilized noble metal nanoparticles: spontaneous reduction and synergistic catalytic activity

A 3D eight-connected redox-active polyoxometalate (POM)-based crystalline material, IFMC-101, has been synthesized based on reduced {P4Mo6O31H6}-based tetrameric clusters. IFMC-101 was used as a reducing agent and stabilizer to prepare Au and Pt nanoparticles (NPs) by auto-redox reactions without extra reduction assistance. For the first time, we have demonstrated a new strategy to prepare noble metal NP-loaded POM-based crystalline catalysts. These crystalline catalysts were employed toward the reduction of 4-nitrophenol by NaBH4 and the efficiency of the Au NP-loaded material, Au@IFMC-101, was nearly 9 times higher than that of the POM-based crystalline material, IFMC-101. This result reveals that Au@IFMC-101 exhibits enhanced activity owing to the synergistic catalysis of noble metal NPs and crystalline POM components.

Low temperature Raman and DFT study of creatinine

The Raman spectra of creatinine powder in the wavenumber region of 500–3500 cm−1 have been recorded as a function of temperature ranging from 293 K to 83 K and different clusters of creatinine were optimized with DFT method to determine hydrogen bonding network in crystalline creatinine. The accurate vibrational assignment of all vibrational bands of creatinine has been done on the basis of the calculated vibrational spectra and the potential energy distribution. The calculated Raman spectra of hydrogen bonded tetramer cluster matches nicely with the experimentally observed spectra confirming four molecules in unit cell as reported by crystallographic data. In addition signature of dimer, which is just half of the tetramer, has also been observed. The bands associated with CH3, CH2, ν(CO), ν(CN) and ν(CH) have been given more focus to see the behavior of hydrogen bond network with temperature. The analysis of these bands reveals that a gradual change (increase/decrease) in linewidth and peak position occurs with temperature as a consequence of the anharmonic coupling of internal modes with phonon mode and intermolecular interaction. The behavior of hydrogen bond network on cooling has been explained in terms of contraction of unit cell.

Theoretical study of the structure, bonding and electronic spectrum of the tetrameric copper (I) amide complex [CuN(SiMe3)2

The tetrameric copper amide cluster, [CuN(SiMe3)2]4, has been previously shown to exhibit interesting spectral properties including a large Stokes shift in the emission spectrum. The photoluminescence has been suggested to arise from phosphorescence from an excited state involving enhanced Cu–Cu bonding. In this study the molecular structure and bonding of [CuN(SiMe3)2]4 are studied in the ground state and excited states using density functional theory. Density functional theory calculations are shown to accurately reproduce the geometry of the complex using both the full structure and using a model complex. Time dependent density functional theory calculations are used to simulate the electronic spectrum of the model complex and assign the observed absorption bands to specific electronic transitions. It is found that the two observed near-UV absorption bands arise from transitions between the HOMO and LUMO/LUMO+1 of the complex. Both excited states involve population of orbitals with Cu–Cu bonding character. ΔSCF optimization of the lowest lying 3Eu state indicates significant Cu–Cu bonding enhancement and short Cu–Cu distances in a Jahn–Teller distorted structure. QTAIM analysis also support enhanced Cu–Cu bonding in the excited state.

Synthesis, Structure, Photochemical [2 + 2] Cycloaddition, Transformation, and Photocatalytic Studies in a Family of Inorganic–Organic Hybrid Cadmium Thiosulfate Compounds

Three new inorganic–organic hybrid cadmium thiosulfate compounds, [Cd(C12H11N2)2(H2O)(S2O3)2] (I), [Cd2(C12H10N2)3(H2O)4(S2O3)2] (II), and [Cd(C12H10N2)S2O3] (III), have been prepared using bispyridylethene (bpe) as a coligand. The compounds have connectivity between the Cd centers, the bpe, and the thiosulfate units, giving rise to molecular (zero) (I), two (II), and three dimensionally (III) extended structures. The formation of Cd4S4 tetrameric cluster units in III is noteworthy. The two-dimensional compound, II, was found to be a reactive intermediate and transforms to the three-dimensional compound, III, as a function of reaction time. The [2 + 2] photochemical reactions carried out on all of the compounds suggest the facile formation of the cyclized products. The photodimerization studies resulted in a one-dimensional structure (Ia) from the molecular complexes of I and rigid cyclized products in II and III. The present study illustrates the usefulness of the photochemical method as a viable alterna...

Ni5, Ni8, and Ni10 Clusters with 2,6-Diacetylpyridine-dioxime as a Ligand

In the present work, novel coordination possibilities for the system dapdoH(2)/Ni(II) (dapdoH(2) = 2,6-diacetylpyridine-dioxime) have been explored. Depending on the starting reagents and solution conditions, several clusters with nuclearities ranging from Ni(5) to Ni(10) were achieved and structurally characterized, namely, [Ni(5)(R-COO)(2)(dapdo)(2)(dapdoH)(2)(N(CN)(2))(2)(MeOH)(2)] in which R-COO(-) = benzoate (1) or 3-chlorobenzoate (2), [Ni(8)(dapdo)(4)(NO(3))(4)(OH)(4)(MeOH)(4)] (3), and [Ni(10)(dapdo)(8)(N(CN)(2))(2)(MeO)(MeOH)](NO(3)) (4). For the first time, pentadentate coordination for the dapdo(2-) ligand has been established. All compounds show a combination of square-planar and octahedrally coordinated nickel atoms. According to the Ni(2)(sp)Ni(3)(Oh) (1 and 2), Ni(4)(sp)Ni(4)(Oh) (3), and Ni(4)(sp)Ni(6)(Oh) (4) environments, these systems magnetically behave as trimer, tetramer, and hexanuclear clusters, respectively. dc magnetic measurements in the 2-300 K range of temperature reveal antiferromagnetic coupling for all compounds, and the correlation of the superexchange interaction with the torsion angles involving the oximato bridges is experimentally confirmed.

Cation-templated 2-D Mn(II)–oxalate framework with an acyclic tetrameric water cluster

The single-crystal X-ray structure of a cation-templated manganese–oxalate coordination polymer [NH(C2H5)3][Mn2(ox)3] · (5H2O)] (1) is reported. In 1, triethylammonium cation is entrapped between the cavities of 2-D honeycomb layers constructed by oxalate and water. The acyclic tetrameric water clusters and discrete water assemble the parallel 2-D honeycomb oxalate layers via an intricate array of hydrogen bonds into an overall 3-D network. The magnetic susceptibility, with and without the water cluster, are reported with infrared and EPR studies.

Structural stabilities and diffusion of small Fe clusters on Fe (1 1 0) surface: A molecular dynamics study

Using Embedded-atom-method (EAM) potential of iron, structural stabilities of small Fe clusters on a Fe (1 1 0) surface have been investigated by molecular dynamics studies. It is presented that a tetramer and heptamer clusters are more stable than other sizes. These two clusters have high transition energies. They can be a critical nucleus at low and high temperature, respectively. A dimer diffuses more easily with lower energy barrier than single adatom. The trimer's rotation and dimer shearing mechanisms have been investigated in this paper.

Anion currents in yeast K+ transporters (TRK) characterize a structural homologue of ligand-gated ion channels

Patch clamp studies of the potassium-transport proteins TRK1,2 in Saccharomyces cerevisiae have revealed large chloride efflux currents: at clamp voltages negative to -100 mV, and intracellular chloride concentrations >10 mM (J. Membr. Biol. 198:177, 2004). Stationary-state current-voltage analysis led to an in-series two-barrier model for chloride activation: the lower barrier (α) being 10-13 kcal/mol located ~30% into the membrane from the cytoplasmic surface; and the higher one (β) being 12-16 kcal/mol located at the outer surface. Measurements carried out with lyotrophic anions and osmoprotective solutes have now demonstrated the following new properties: (1) selectivity for highly permeant anions changes with extracellular pH; at pH(o)= 5.5: I(-)≈ Br(-) >Cl(-) >SCN(-) >NO (3)(-) , and at pH(o) 7.5: I(-)≈ Br(-) > SCN(-) > NO(3)(-) >Cl(-). (2) NO(2)(-) acts like "superchoride", possibly enhancing the channel's intrinsic permeability to Cl(-). (3) SCN(-) and NO(3)(-) block chloride permeability. (4) The order of selectivity for several slightly permeant anions (at pH(o)= 5.5 only) is formate>gluconate>acetate>>phosphate(-1). (5) All anion conductances are modulated (choked) by osmoprotective solutes. (6) The data and descriptive two-barrier model evoke a hypothetical structure (Biophys. J. 77:789, 1999) consisting of an intramembrane homotetramer of fungal TRK molecules, arrayed radially around a central cluster of four single helices (TM7) from each monomer. (7) That tetrameric cluster would resemble the hydrophobic core of (pentameric) ligand-gated ion channels, and would suggest voltage-modulated hydrophobic gating to underlie anion permeation.

Carbophosphazene-Based Multisite Coordination Ligands: Metalation Studies on the Pyridyloxy Carbophosphazene, [NC(NMe2)]2[NP(p-OC5H4N)2

The pyridyloxycarbophosphazene, [NC(NMe2)]2[NP(p-OC5H4N)2] (L), reacted with Cd(OAc)2·4H2O to afford a rail-road-like double-strand coordination polymer, [{Cd(CH3COO)2(L)}(CH3OH)(H2O)2]n (1). The c...

Synthesis, crystal structures and characterization of four coordination polymers based on 5-amino-2,4,6-triiodoisophthalic acid

One homochiral 1D coordination polymer [Cu(ATIBDC)(2,2′-bipy)]·3H 2O·CH 3OH ( 1) and three achiral 1D coordination polymers: [Cd(ATIBDC)(2,2′-bipy)(H 2O)]·3H 2O ( 2), [Cd(ATIBDC)(phen)(H 2O)]·4H 2O ( 3), and [Mn(ATIBDC)(phen) 2]·5H 2O ( 4) have been synthesized and characterized (H 2ATIBDC=5-amino-2,4,6-triiodoisophthalic acid, 2,2′-bipy=2,2′-bipyridine, and phen=1,10-phenanthroline). Extended high dimensional network architectures are further constructed with the help of weak secondary interactions, such as hydrogen bonding, aromatic stacking, and halogen bonding (C–I… π and C–I…N/O). Complex 1 crystallizes in the monoclinic system with chiral space group P2(1) and exhibits a right-handed 2 1 helical chain structure. The homochirality of 1 was confirmed by CD spectrum. Interestingly, two new configurations of decameric water cluster are found in 3 and 4. The acyclic tetrameric cluster (H 2O) 3(CH 3OH) in 1 and (H 2O) 4 in 2 array into highly ordered helical infinite chains. Thermal stabilities of all the complexes have been studied. Solid state fluorescent properties of the Cd(II) complexes have been explored.

Syntheses, 95Mo NMR Spectroscopy and Structures of Distorted Cubic Mo4(μ3-O)4(μ2-O2P(CH2C6H5)2)4O4 and the Open Mixed-Valent Cluster, Mo4(μ3-O)2(μ2-O2P(CH2C6H5)2)6O6

The reaction of MoO2(acac)2 and dibenzylphosphinic acid in ethanol leads to a red distorted cubic tetrameric cluster, Mo4(μ3-O)4(μ2-O2P(CH2C6H5)2)4O4, and a pink open mixed-valent cluster, Mo4(μ3-O)2(μ2-O2P(CH2C6H5)2)6O6, when the reduction is carried out at 120 and 75 °C, respectively. 95Mo NMR spectroscopy revealed a singlet for Mo4(μ3-O)4(μ2-O2P(CH2C6H5)2)4O4 (1) at 584.9 ppm (Δν1/2 = 4500 Hz) and two resonances for Mo4(μ3-O)2(μ2-O2P(CH2C6H5)2)6O6 (2) at 238.8 ppm (Δν1/2 = 1250 Hz) and 6.4 ppm (Δν1/2 = 5999 Hz), which were assigned to the Mo(V) and Mo(VI) sites, respectively. DFT geometries and 95Mo DFT-GIAO chemical shifts for Mo4(μ3-O)4(μ2-O2P(CH3)2)4O4 (3) and Mo4(μ3-O)2(μ2-O2P(CH3)2)6O6 (4) are consistent with X-ray crystallography and 95Mo NMR of 1 and 2. The open complex, Mo4(μ3-O)2(μ2-O2P(CH2C6H5)2)6O6·2(CH2Cl2), exhibits a central Mo(V)–Mo(V) single bond at 2.6217(5) A with each Mo(V) atom bonded to one oxo (trans-disposed) terminal ligand.

Nitrogen Monoxide Adsorption on Pt<SUB>4</SUB> Clusters Coated on γ-Al<SUB>2</SUB>O<SUB>3</SUB> (111) Surface

The nitrogen monoxide (NO) adsorption on platinum tetramer (Pt4) clusters supported on gamma alumina (gamma-Al2O3) with surface index (111) was investigated by using ab-initio calculation based on density functional theory. The Pt4 geometries used in this study are tetrahedron and planar rhombus. The adsorption of Pt4 on gamma-Al2O3 (111) surface in tetrahedron configuration is energetically more favorable as compared to that of the planar rhombus. However, it was found that NO molecule adheres strongly to Pt4 with planar configuration on gamma-Al2O3(111) surface. In addition, the NO adsorption calculation on the isolated Pt4 clusters also shows similar preference to planar configuration. The local density of states (LDOS) reveals that the difference in reactivity comes from the different hybridization strengths between the electronic states of nitrogen atom and those of platinum tetramers. The results are in good agreement with the experiments which show similar tendency for CO and N2O reactivity to gas-phase platinum clusters.

Lanthanide Sulfate Frameworks: Synthesis, Structure, and Optical Properties

Layered lanthanide sulfate compounds with three different structures have been prepared and characterized. The compounds [C10H10N2][La(SO4)2]·2H2O (I), [C10H10N2][La(SO4)2(H2O)2]2 (IIa), [C10H10N2][Pr(SO4)2(H2O)2]2 (IIb), [C10H10N2][Nd2(SO4)4(H2O)2]2 (IIIa), [C10H10N2][Sm2(SO4)4(H2O)2]2 (IIIb), and [C10H10N2][Eu2(SO4)4(H2O)2]2 (IIIc) have anionic lanthanide sulfate layers separated by protonated bipyridine molecules. The layers are formed by the connectivity between the lanthanide polyhedra and sulfate tetrahedra. The formation of a two-dimensional La−O−La layer (Ia), Pr−O−Pr chains (IIb), and a tetramer cluster (IIIa) is noteworthy. The compounds exhibit honeycomb (I), square (IIa, IIb), and honeycomb (IIIa−IIIc) net arrangements, when the connectivity between the lanthanide ions is considered. Optical studies indicate the observation of characteristic metal-centered emission at room temperature. The Nd compound (IIIa) exhibits a two-photon upconversion behavior.

Solid-State Photoluminescence Sensitization of Tb3+ by Novel Au2Pt2 and Au2Pt4 Cyanide Clusters

The syntheses are reported for two novel Tb(3+) heterotrimetallic cyanometallates, K(2)[Tb(H(2)O)(4)(Pt(CN)(4))(2)]Au(CN)(2)·2H(2)O (1) and [Tb(C(10)N(2)H(8))(H(2)O)(4)(Pt(CN)(4))(Au(CN)(2))]·1.5C(10)N(2)H(8)·2H(2)O (2) (C(10)N(2)H(8) = 2,2'-bipyridine). Both compounds have been isolated as colorless crystals, and single-crystal X-ray diffraction has been used to investigate their structural features. Crystallographic data (MoKα, λ = 0.71073 Å, T = 290 K): 1, tetragonal, space group P4(2)/nnm, a = 11.9706(2) Å, c = 17.8224(3) Å, V = 2553.85(7) Å(3), Z = 4; 2, triclinic, space group P1, a = 10.0646(2) Å, b = 10.7649(2) Å, c = 17.6655(3) Å, α = 101.410(2)°, β = 92.067(2)°, γ = 91.196(2)°, V = 1874.14(6) Å(3), Z = 2. For the case of 1, the structure contains Au(2)Pt(4) hexameric noble metal clusters, while 2 includes Au(2)Pt(2) tetrameric clusters. The clusters are alike in that they contain Au-Au and Au-Pt, but not Pt-Pt, metallophilic interactions. Also, the discrete clusters are directly coordinated to Tb(3+) and sensitize its emission in both solid-state compounds, 1 and 2. The Photoluminescence (PL) spectra of 1 show broad excitation bands corresponding to donor groups when monitored at the Tb(3+) ion f-f transitions, which is typical of donor/acceptor energy transfer (ET) behavior in the system. The compound also displays a broad emission band at ∼445 nm, assignable to a donor metal centered (MC) emission of the Au(2)Pt(4) clusters. The PL properties of 2 show a similar Tb(3+) emission in the visible region and a lack of donor-based emission at room temperature; however, at 77 K a weak, broad emission occurs at 400 nm, indicative of uncoordinated 2,2'-bipyridine, along with strong Tb(3+) transitions. The absolute quantum yield (QY) for the Tb(3+) emission ((5)D(4) → (7)F(J (J = 6-3))) in 1 is 16.3% with a lifetime of 616 μs when excited at 325 nm. In contrast the weak MC emission at 445 nm has a quantum yield of 0.9% with a significantly shorter lifetime of 0.61 μs. For 2 the QY value decreases to 9.3% with a slightly shorter lifetime of 562 μs. The reduced QY in 2 is considered to be a consequence of (1) the slightly increased donor-acceptor excited energy gap relative to the optimal gap suggested for Tb(3+) and (2) Tb(3+) emission quenching via a bpy ligand-to-metal charge transfer (LMCT) excited state.