Cubane-like Core Research Articles

Tetra-μ3-selen-ido-1:2:3κ3Se;1:2:4κ3Se;1:3:4κ3Se;2:3:4κ3Se-tetrakis-[(η5-methyl-cyclo-penta-dien-yl)molybdenum(III)](6 Mo-Mo).

The title cluster compound, [Mo4(η5-C5H4Me)4(μ3-Se)4], was synthesized from the reaction of [Mo(η5-C5H4Me)(CO)3]2 with grey selenium in refluxing xylene solution under a nitro-gen atmosphere. The complete cluster is generated by a crystallographic twofold axis and contains an Mo4Se4 cubane-like core surrounded by four η5-methylcyclo-pentadienyl ligands. In the core, the four molybdenum atoms are connected to each other to form a tetra-hedron, with a selenium atom capping each face. The Mo-Mo bond lengths vary from 2.9857 (5) to 3.0083 (3) Å and the Mo-Se separations range from 2.4633 (4) to 2.4693 (5) Å.

Tetranuclear Copper Complexes with Bulky Aminoalcohol Ligands as Catalysts for Oxidative Phenoxazinone Synthase-like Coupling of Aminophenol: A Combined Experimental and Theoretical Study

The new copper(II) complexes [Cu4(pa)4(Bae)4]·H2O (1) and [Cu4(eba)4(Buae)4]·H2O (2) (Hpa = propionic acid, HBae = 2-benzylaminoethanol, Heba = 2-ethylbutyric acid and HBuae = 2-butylaminoethanol) were synthesizsed by the interaction of a copper salt with a methanol solution of the respective ligands. The single-crystal X-ray diffraction analysis reveals that both compounds have a {Cu4(μ3-O)4} cubane-like core. Both compounds show pronounced phenoxazinone synthase-like activity towards the aerobic oxidation of o-aminophenol to phenoxazinone chromophore, with the maximum initial rates W0 up to 3.5 × 10−7 M s−1, and exhibit complex non-linear W0 vs. [catalyst]0 dependences. DFT//CCSD theoretical calculations (B3LYP/ma-def2-TZVP//DLPNO-CCSD(T)/ma-def2-TZVPP) were employed to investigate the most challenging steps of catalyst-free and copper-catalysed o-aminophenol oxidation (formation of o-aminophenoxyl radical). QTAIM analysis was used to study the key intermediates and weak interactions. Geometries and energies of intermediates and transition states were benchmarked against a series of popular DFT functionals. The results of the calculations demonstrate that a CuII–OO• copper-superoxo model catalyst decreases the calculated activation barrier from 28.7 to 19.9 kcal mol−1 for the catalyst-free and copper-catalysed abstraction of the H atom from the hydroxyl group of o-aminophenol, respectively. Finally, both complexes 1 and 2 were studied as catalysts in the amidation of cyclohexane with benzamide to give N-cyclohexyl benzamide and N-methyl benzamide employing di-tert-butyl peroxide (DTBP) as the oxidant, with a conversion of 16%, and in the oxidation of cyclohexane to cyclohexanol with aq. H2O2, with a conversion of 12%.

A tetra-nuclear nickel(II) complex, [Ni4(L)4](ClO4)4·C2H3N·2H2O, with an asymmetric Ni4O4 open-cubane-like core.

A tetra-nuclear complex with an open-cubane-like core structure was synthesized from 2-meth-oxy-6-(pyridin-2-yl-hydrazonometh-yl)phenol (HL), namely, cyclo-tetra-kis-(μ-2-meth-oxy-6-{[2-(pyridin-2-yl)hydrazin-1-yl-idene]meth-yl}pheno-lato)tetra-nickel(II) tetra-kis-(perchlorate) aceto-nitrile monosolvate dihydrate, [Ni4(C13H12N3O2)4](ClO4)4·C2H3N·2H2O, and characterized using micro-analytical and spectroscopic techniques. The crystal-structure determination reveals the formation of a distorted Ni4O4 cubane-like core architecture encapsulated by four hydrazone Schiff base (HL) mol-ecules. A open-cube tetra-nuclear architecture is created in which nickel(II) ions of the NiN2O3 unit are connected by μ2-O anions of the phenolate moiety of HL. In this complex, each Ni centre has a slightly distorted square-pyramidal coordination environment. The supra-molecular architectures are stabilized via the presence of various inter-molecular hydrogen bonds and (ar-yl-aryl, ar-yl-chelate and chelate-chelate) stacking inter-actions.

Tetranuclear Copper(I) Iodide Complexes: A New Class of X-ray Phosphors.

We report intensive visible light radioluminescence upon X-ray irradiation of archetypal tetranuclear copper(I) iodide complexes containing triphenylphosphine or pyridine ligands in the solid state. These properties, attractive for the design of X-ray responsive materials, can be attributed to the heavy {Cu4I4} cubane-like core, the absence of oxygen quenching of the emissive triplet states, and the high photoluminescence quantum yields. Radioluminescence originates from the same emissive triplet states as those produced by ultraviolet excitation as confirmed by the observed radioluminescence thermochromism. The radioluminescence properties are also preserved after incorporation of these complexes into polystyrene films, making them appealing for the development of plastic scintillators.

Synthesis, Crystal Structure, and Magnetic Properties of a New Mixed Metal (Co(II), Ni(II)) Cubane.

The mixed Co(II)/Ni(II) complex, [Co2.67Ni1.33L4(CH3COO)2][BPh4]2·0.75H2O where HL = 4-(salicylaldimine)antipyrine, was isolated as an orange solid from the reaction of 4-(salicylaldimine)antipyrine, with mixed cobalt(II) acetate and nickel(II) acetate in ethanol. The complex was characterized by Frustrated Total Internal Reflection (FTIR), UltraViolet Visible spectroscopy (UV-Vis), X-ray single crystal diffraction, and by elemental analysis. The complex is composed of two symmetry independent cationic units, A and B. The two units are essentially isostructural; nevertheless, small differences exist between them. The units contain four metal atoms, arranged at the corners of a distorted cubane-like core alternately with phenoxy oxygen of the Schiff base. The overall eight corners occupied by metal ions in the asymmetric unit are shared between cobalt and nickel in a 5.33:2.67 ratio. Each metal divalent cation binds three coordinated sites from the corresponding tridentate Schiff base ligand, the fourth one is bound by the acetate oxygen, the fifth and the sixth donor sites come from the phenolate oxygens of other Schiff base ligands. Intermolecular hydrogen bonds join the complexes to the water molecules present in the crystal packing. The magnetic characterization was carried out for this new complex and for its isostructural counterpart containing only cobalt ions. The magnetic measurements for the cobalt(II)/nickel(II) mixed compound indicate either antiferromagnetic interactions among the two cubanes or an anisotropic contribution, whereas a ferromagnetic interaction is observed within the cubane, for both the complexes, as expected by geometrical considerations. A comparison between the magnetic properties of the pure cobalt(II) derivative and similar systems discussed in literature, is presented.

Crystal structure of tetra-kis-(μ3-2-{[1,1-bis-(hy-droxy-meth-yl)-2-oxidoeth-yl]imino-meth-yl}-6-meth-oxy-phenolato)tetra-kis-[aqua-copper(II)]: a redetermination at 200 K.

The crystal structure of the tetra-nuclear title compound, [Cu4(C12H15NO5)4(H2O)4], has been previously reported by Back, Oliveira, Canabarro & Iglesias [Z. Anorg. Allg. Chem. (2015), 641, 941-947], based on room-temperature data. In the previously published structure, no standard uncertainties are recorded for the deprotonated hy-droxy-methyl group and water mol-ecule O atoms coordinating to the metal atom indicating that they were not refined; furthermore, the H atoms of some OH groups and water mol-ecules have not been positioned accurately. Since the current structure was determined at a lower temperature, all atoms, including the H atoms of these hy-droxy groups and the water mol-ecule, have been determined more accurately resulting in improved standard uncertainties in the bond lengths and angles. Diffraction data were collected at 200 K, rather than the more usual 100 K, due to apparent disordering at lower temperatures. In addition, it is now possible to report intra- and inter-molecular O-H⋯O inter-actions. In the title complex molecule, which has crystallographic -4 symmetry, the Cu(II) ions are coordinated by the tridentate Schiff base ligands and water mol-ecules, forming a tetra-nuclear Cu4O4 cubane-like core. The Cu(II) ion adopts a CuNO5 elongated octa-hedral environment. The coordination environment of Cu(II) at 200 K displays a small contraction of the Cu-N/O bonds, compared with the room-temperature structure. In the crystal lattice, the neutral clusters are linked by inter-molecular O-H⋯O hydrogen bonds into a one-dimensional hydrogen-bonding network propagating along the b axis.

A yellow-green tetranuclear Cd(II) (8-quinolinolato) chelate with thiophene group: synthesis, crystal structure, photophysical properties and DNA binding

One novel tetranuclear Cd(II) complex with formula [Cd4L6(NO3)2] (1) is accessible by solvothermal reaction of Cd(NO3)2 with a (E)-2-[2-(3-thienyl)ethenyl]-8-quinolinol ligand (HL), which was characterized by means of 1H NMR, ESI-MS, elemental analysis, IR and TGA. X-ray structural analysis indicated that 1 exhibited a double open cubane-like core structure, which was bridged by six 8-hydroxyquinolinate-based ligand. Rich aromatic stacking interactions and non-classical C–H···O weak interactions sustain the packing structure. The coordination behavior of cadmium salt and HL in solutions was performed by UV–vis and photoluminescence (PL). The experimental results corroborate that emission spectrum of the title complex in the solid state at room temperature gives strong yellow-green luminescence. In addition, the thermal stability, fluorescent lifetime, electronic calculation and quenching behaviors of C60 and EtBr-DNA interacted with the compound were also investigated.

Synthesis, structures, and magnetic properties of tetranuclear nickel and cobalt complexes with 2-mercaptobenzoxazole

The synthesis and magnetic properties of two tetranuclear Ni complex Ni4(L)4(CH3CN)4(OCH3)41 and Co complex Co4(L)4(CH3CN)4(OCH3)42 (HL=2-mercaptobenzoxazole) are reported. The X-ray structures reveal that 1 and 2 are isostructural with [Ni4O4] 1 and [Co4O4] 2 cubane-like cores. Analysis of the temperature dependent magnetic measurements data shows that both complexes are paramagnetic with weak antiferromagnetic coupling. One-J model and two-J model are both applied to fit the experimental magnetic data of 1 and the results indicate the exchange coupling between the type A Ni(II) ions affected by NCS three atoms bridge in 2-mercaptobenzoxazole ligand.

Synthesis, Characterization, and Crystal Structure of [Co4(CH3CO2)2L4]2[BPh4]4·0.5H2O, Where HL = 4-(Salicylaldiminato)antipyrine

The title complex was isolated as a red solid from the reaction of 4-(salicylaldiminato)antipyrine, HL, and cobalt (II) acetate in ethanol. The complex has been characterized by elemental analysis, FTIR, UV-Vis, and X-ray single crystal diffraction. Two crystallographically different cationic units, A and B, of the title complex are found. Both units are essentially isostructural; nevertheless, small differences exist between them. Both units contain four cobalt atoms arranged at the corners of distorted cubane-like core alternatively with phenoxy oxygen of the Schiff base. In both cases, one cobalt binds to three coordinated sites from the corresponding tridentate Schiff base ligand, and the fourth one was bonded by the acetate oxygen, and the fifth and the sixth donor sites come from the phenolate oxygen of another Schiff base ligand.

Synthesis, crystal structure, and photophysical properties of a double open cubane-like Cd(II) complex based on 2-substituted-8-hydroxyquinoline

A 2-substituted-8-hydroxyquinoline (E)-2-[2-(3-thienyl)ethenyl]-8-quinolinol (HL) was synthesized and characterized by ESI-MS, NMR spectroscopy, and elemental analysis. Using solvothermal method, a tetranuclear complex [Cd4L6Br2]·6DMF (1) was fabricated by assembly of Cd(II) with HL. X-ray structural analysis shows that 1 exhibits a double open cubane-like core structure, which is bridged by six 8-hydroxyquinolinate-based ligands. The supramolecular structure of 1 features a 3-D porous solid constructed by aromatic stacking interactions, C–H···π interactions and C–H···O hydrogen bonds. The assembly of cadmium salts and HL in solution was investigated by UV–vis and photoluminescence. We also studied the thermal stability and photophysical properties (fluorescent emission, lifetime, and quantum yield) of 1. The results show that 1 emits yellow luminescence in the solid state.

Tetra-kis(μ3-2-{[1,1-bis-(hy-droxy-meth-yl)-2-oxidoeth-yl]imino-meth-yl}-6-nitro-pheno-lato)tetra-copper(II).

The title cluster, [Cu4(C11H12N2O6)4], was obtained from the Cu0–FeCl2·4H2O–H4 L–Et3N–DMF reaction system (in air), where H4 L is 2-hy­droxy­methyl-2{[(2-hy­droxy-3-nitro­phen­yl)methyl­idene]amino}­propane-1,3-diol and DMF is di­methyl­formamide. The asymmetric unit consists of one Cu2+ ion and one dianionic ligand; a -4 symmetry element generates the cluster, which contains a {Cu4O4} cubane-like core. The metal ion has an elongated square-based pyramidal CuNO4 coordination geometry with the N atom in a basal site. An intra­molecular O—H⋯O hydrogen bond is observed. The solvent mol­ecules were found to be highly disordered and their contribution to the scattering was removed with the SQUEEZE procedure in PLATON [Spek (2009 ▶). Acta Cryst. D65, 148–155], which indicated a solvent cavity of volume 3131 Å3 containing approximately 749 electrons. These solvent molecules are not considered in the given chemical formula.

Conversion of tetranuclear Ni complexes from a defect dicubane core to a [Ni4O4] cubane-like core via addition of 2-hydroxymethylpyridine: Synthesis, crystal structures, and magnetic properties

Abstract A defect dicubane-like complex, [Ni4{(2-py)2C(OH)O}2{(2-py)2C(OCH3)O}2 (N3)4]·2CH3CN·2H2O (1) and a cubane-like complex, [Ni4{(2-py)2C(OH)O}3(hmp)3(NO3)].(NO3)·3H2O (2) (Hhmp = 2-hydroxymethylpyridine), were prepared by reacting NiCl2·6H2O with (py)2CO, NaN3 and NMe4OH in MeOH/MeCN and the similar reaction exception the N3− anion replaced by multidentate chelating ligand Hhmp, respectively. X-ray analysis revealed that four Ni2 + ions, four O atoms and two N atoms in 1 were located at the vertices of a defect dicubane; by contrast, four Ni2 + ions and four O atoms in 2 occupied alternate vertices of a [Ni4O4] cubane. Magnetic studies indicated the presence of overall ferromagnetic interactions between Ni2 + ions within both complexes.

Synthesis, structure and magnetism of three cubane Cu(II) and Ni(II) complexes based on flexible Schiff-base ligands

Three cubane Ni(II) and Cu(II) complexes, namely [Cu4L14]·CH3CN (1), [Ni4L14(CH3OH)4]·4H2O (2), [Ni4L24(CH3OH)4]·6H2O (3), have been synthesized from flexible polydentate Schiff bases (H2L1 and H2L2) based on o-vanillin. X-ray single-crystal analyses reveal that all three complexes own a cubane-like core M4O4 in which Cu ions in 1 are five-coordinated and Ni ions in 2 and 3 are six-coordinated. Variable-temperature magnetic susceptibility data display dominant ferromagnetic interactions in complexes 1–3 while antiferromagnetic and ferromagnetic couplings coexist in the cubane core, thus resulting in a nonzero spin ground state. The magnitude of the exchange coupling constants correlates with the geometrical parameters arising from the minor ligand modifications.

Bis[1,2-bis(ethoxycarbonyl)ethene-1,2-dithiolato-κ2S,S′]bis(η5-pentamethylcyclopentadienyl)tetra-μ3-sulfido-diiron(IV)diiron(III)(3Fe—Fe)

The title compound, [Fe4(C10H15)2(C8H10O4S2)2S4], contains a twisted Fe4S4 cubane-like core. A twofold rotation axis passes through the Fe4S4 core, completing the coordination of the four Fe atoms with two penta­methyl­cyclo­penta­dienyl ligands and two chelating dithiol­ate ligands. There are three short Fe—Fe and three long Fe⋯Fe contacts in the Fe4S4 core, suggesting bonding and non-bonding inter­actions, respectively. The Fe—S bonds in the Fe4S4 core range from 2.1523 (5) to 2.2667 (6) Å and are somewhat longer than the Fe—S bonds involving the dithiol­ate ligand.

Synthesis, structure, and catalytic activity of a new zinc complex derived from a chiral hydroxyazetidine ligand

Abstract A new chiral tetrameric zinc complex [(1)ZnEt]4 (2) has been readily prepared via alkane elimination between ZnEt2 and a chiral azetidine derivative, (2R,3R)-1-[(1S)-1-(4-methoxyphenyl)ethyl]-2-phenyl-3-hydroxyazetidine (1H). Complex 2 has been characterized by various spectroscopic techniques, elemental analyses, and X-ray diffraction analysis. Complex 2 has a cubane-like Zn4O4 core structure, and is an active catalyst for the polymerization of rac-lactide, leading to the heterotactic-rich polylactides.

Indium Complexes of Fluorinated Dialkoxy-Diimino Salen-like Ligands for Ring-Opening Polymerization ofrac-Lactide: How Does Indium Compare to Aluminum?

The reaction between InCl3 and {ONEtNO}K2 (1a), prepared from (CF3)2(OH)CCH2C(CH3)═N–R–N═C(CH3)CH2C(OH)(CF3)2 ({ONEtNO}H2, R = C2H4 (a); {ONCyNO}H2, R = rac-1,2-cyclohexylene (b)) and PhCH2K, gave {ONEtNO}InCl (2a). The reaction between InCl3 and 3 equiv of MeLi led to a mixture of [InMe3] and Li[InMe4], which upon further treatment with {ONRNO}H2 proligands gave the ate complexes [{ONRNO}Li]InMe2 (4a,b); the methyl complex {ONEtNO}InMe (3a) was also isolated from this reaction. Hydrocarbyl complexes {ONRNO}In(CH2SiMe3) (5a,b) were prepared cleanly from the 1:1 reactions between In(CH2SiMe3)3 and {ONRNO}H2. The solid-state molecular structures of mononuclear 2a, 3a, 4b, and 5b and of [(1a)2-(μ-H2O)]n, a distorted cubane-like core made up of four potassium atoms and two ligands, were determined. Compounds 5a,b are moderately active initiators/catalysts for the ring-opening polymerization of rac-lactide, giving polymers with controlled molecular weights and narrow polydispersities, especially in the presence of added isopropyl alcohol (1–10 equiv) as exogenous initiator. Isotactic-enriched (Pm = 0.62–0.69) PLAs were obtained from 5a, while 5b gave atactic materials. The heterobimetallic compounds 4a,b are also active and afforded slightly heterotactic-enriched PLAs (Pr = 0.57–0.62), but with broader polydispersities. Those results allowed us to discuss the initiation mechanisms according to the constitution of the systems (alkyl vs alkyl/iPrOH) and also stereoselective abilities as a function of the nature (In vs Al) and coordination environment (κ4-ONNO vs. κ2-NN) of the metal center.

A unique tetranuclear nickel(II) complex containing pyridine-2-carboxaldehyde derivative bearing an intramolecular acetato: Synthesis, crystal structure and magnetic property

Abstract The novel tetranuclear nickel(II) carboxylate complex formulated as [Ni4(L)2(m2-OAc)2 (m3-OAc)2]·CH3OH·H2O, (1) (where L = 2-oxo-1,2-di(pyridin-2-yl)ethyl picolinate) has been synthesized and characterized systematically. The complex crystallizes in orthorhombic system, consisting of a tetranuclear Ni(II) distorted cubane-like core, in which four Ni(II) ions are bridged by four acetato groups. Each Ni(II) ion is further ligated with nitrogen atoms of bridging pyridine-2-carboxaldehyde derivative, forming either Ni, N, N, O- or Ni, N, O-chelate macro-rings. Magnetic susceptibility studies indicate that the weak antiferromagnetic interaction is operating between the adjacent nickel ions bridged via the carboxylate oxygen atoms within the complex.

Carboxylate clusters with the M4O4 cubane-like core: pivalate cocrystal containing CoII and NiII

Joint thermolysis of the dinuclear pivalate complexes M2(μ-H2O)(μ-Piv)2(Piv)2(HPiv)4 (M = Co (1) and Ni (2), Piv- is the pivalate anion), in decane at 174 °C at the reactant ratio 1: 1 followed by treatment of the dry thermolysis product with methanol afforded crystals of a new cocrystallization product of the molecules containing the heterometallic cubane-like core M4(Co,Ni)O4. According to the X-ray diffraction data and the results of magnetic measurements, inductively coupled plasma atomic emission spectrometry (ICP-AES), and investigations of the solid-state thermal decomposition products, the isolated cocrystallization product has the general formula [Co1.6Ni2.4(μ3-OMe)4(μ2-Piv)2(pg2 -Piv)2(MeOH)4] ·4MeOH (3·4MeOH). Thermolysis of the crystals of the solvate 3·4MeOH is a destructive process accompanied by the intramolecular redox reaction. A mixture of metallic Ni and cobalt oxide (CoO) are the final solid decomposition products of 3 · 4MeOH in an argon atmosphere, whereas a mixture of the phases NiO, Co3O4, and NiCo2O4 is formed in air.

Tetrakis(μ3-2-{[1,1-bis(hydroxymethyl)-2-oxidoethyl]iminomethyl}-6-methoxyphenolato)tetranickel(II) tetrahydrate

The title complex, [Ni4(C12H15NO4)4]·4H2O, has crystal­lographic fourfold inversion symmetry, with each NiII ion coordinated in a slightly distorted square-pyramidal coordination environment and forming an Ni4O4 cubane-like core. In the crystal structure, inter­molecular O—H⋯O hydrogen bonds connect complex and water mol­ecules to form a three-dimensional network. The O atom of one of the unique hydroxy­methyl groups is disordered over two sites, with the ratio of occupancies being approximately 0.79:0.21.

Synthesis, Structure, Spectral and Electrochemical Properties, and Catalytic Use of Cobalt(III)−Oxo Cubane Clusters

Olive-green cobalt(III) complexes having the general formula Co4O4(O2CMe)4L4 (1) where L = py (1a), 4-Mepy (1b), 4-Etpy (1c), and 4-CNpy (1d) have been prepared by the H2O2 oxidation of a mixture of Co2+, MeCO2-, and pyridine or 4-substituted pyridines in a 1:2:1 molar ratio in methanol. Spectroscopic and X-ray crystallographic studies show that these complexes contain a tetrameric cubane-like core [Co4(mu3-O)4]4+ where the four cobalt atoms form an approximate tetrahedron with edge lengths of approximately 2.75 A. Each cobalt in the crystallographically determined structure of Co4(mu3-O)4(mu-O2CMe)4L4 in 1a.NaClO4.3.5H2O and 1b.3H2O is hexacoordinate. Infrared spectra of the complexes show characteristic bands near 700, 635, and 580 cm-1 due to the central cubane-like core. 1H NMR spectra of the complexes show that the dissolved species are essentially diamagnetic and also that the complexes maintain their integrity in solution. UV-vis spectra of the green solutions have been interpreted in terms of ligand-field and charge-transfer bands. The electrochemical behavior of the complexes studied by cyclic and differential pulse voltammetric techniques indicates that the [(CoIII)4(mu3-O)4]4+ core present in the complexes undergoes a reversible one-electron oxidation to the [(CoIII)3CoIV(mu3-O)4]5+ core with an E1/2 value below 1 V. This suggests that these complexes of cobalt may be suitable as catalysts for the oxidation of organic compounds. Preliminary investigations indicate that 1a has a role to play in the cobalt-catalyzed aerobic oxidation of neat ethylbenzene and p-xylene.