Heterometallic cubane single-molecule magnets

Two new heterometallic cubane molecules have been synthesized. High-frequency electron paramagnetic resonance and magnetization measurements indicate that [Mn(3)Ni(hmp)(3)O(N(3))(3)(C(7)H(5)O(2))(3)] (1) displays a well-isolated S = 5 ground state (DeltaE > 120 K), with g = 2.0, D = -0.23 cm(-1), and ferromagnetic Mn-Mn exchange interactions competing with antiferromagnetic Ni-Mn interactions. [Mn(3)Zn(hmp)(3)O(N(3))(3)(C(3)H(5)O(2))(3)] (2) possesses a S = 6 ground state (DeltaE > 105 K), with g = 2.0, D = -0.14 cm(-1), and ferromagnetic Mn-Mn exchange interactions. Magnetization vs magnetic field data for oriented single crystals of 1 and 2 indicate that both complexes are single-molecule magnets.     

Metal Assisted Synthesis of Cationic Sulfidobismuth Cubanes in Ionic Liquids

Bi₂S₃ was dissolved in the presence of either AuCl/PtCl₂ or AgCl in the ionic liquids [BMIm]Cl ⋅ xAlCl₃ (BMIm=1-n-butyl-3-methylimidazolium; x=4–4.3) through annealing the mixtures at 180 or 200 °C. Upon cooling to room temperature, orange, air-sensitive crystals of [BMIm](Bi₄S₄)[AlCl₄]₅ ( 1 ) or Ag(Bi₇S₈)[S(AlCl₃)₃]₂[AlCl₄]₂ ( 2 ) precipitated, respectively. 1 did not form in the absence of AuCl/PtCl₂, suggesting an essential role of the metal cations. X-ray diffraction on single-crystals of 1 revealed a monoclinic crystal structure that contains (Bi₄S₄)⁴⁺ heterocubanes and [AlCl₄]⁻ tetrahedra as well as [BMIm]⁺ cations. The intercalation of the ionic liquid was confirmed via solid state NMR spectroscopy, revealing unusual coupling behavior. The crystal structure of 2 consists of (Bi₇S₈)⁵⁺ spiro-dicubanes, [S(AlCl₃)₃]²⁻ tetrahedra triples, isolated [AlCl₄]⁻ tetrahedra, and heavily disordered silver(I) cations. No cation ordering took place in 2 upon slow cooling to 100 K.     

Cyclooctatetraenes through Valence Isomerization of Cubanes: Scope and Limitations

The scope and limitations of Eaton's rhodium(I)-catalyzed valence isomerization of cubane to cyclooctatetraene (COT) were investigated in the context of functional group tolerability, multiple substitution modes and the ability of cubane-alcohols to undergo one-pot tandem Ley–Griffith Wittig reactions in the absence of a transition metal catalyst.     

Heterometallic bismuth-transition metal homoleptic beta-diketonates

Bismuth(III) hexafluoroacetylacetonate reacts readily with the first row transition-metal species to produce trinuclear heterobimetallic coordination complexes Bi2M(beta-diketonate)8 (M = Mn, Fe, Co, Ni, Cu, Zn). This unique, general approach may offer new possibilities for developing single-source molecular precursors for advance oxide materials.     

Heterometallic Werner complexes as energetic materials

New heterometallic Werner complexes have been synthesized by combining the cobalt cationic [Co(NH3)6]3+ species with a nitrato metal fragment [M(NO3)4](x-) (M = Fe, Mn, Cu, Zn) or with metal oxides X2MO4 (M = Mo, W and X = Na, NH4). Depending on the metals, an organic and/or a water synthetic route was developed. X-Ray data on Mn and Cu precursors have shown the versatility of nitrate ligand coordination. TDA-TGA studies have been performed to demonstrate the energetic material character. The [Co(NH3)6]x[M(NO3)4]3 complexes display a good oxygen balance and, as shown by standard sensitivity tests, are suitable for automotive applications.     

Heterometallic lanthanide group 12 metal iodides

Neodymium tri-iodide reacts with Group 12 metal (M; M = Zn, Cd, Hg) iodides to form heterometallic compounds. These Lewis acidic M cleave Nd-I bonds to give either ionic ([(THF)(5)NdI(2)][MI(3)THF]; M = Zn, Cd) or charge-neutral [(THF)(5)NdI(micro(2)I)HgI(3)] compounds. Differences in structure are interpreted primarily in terms of M-L bond strengths, rather than Nd-L bond strengths. Experiments with Yb indicate that if there is any excess iodide present in these syntheses then the most readily isolated product is a triiodide salt, i.e., [(THF)(5)YbI(2)][I(3)]. In conventional solvents the presence of Lewis acid is not required for iodide displacement-from pyridine, "YbI(3)" crystallizes as [(py)(5)YbI(2)][I]. These compounds are potentially useful as heterometallic sources of lanthanide-doped iodide matrixes, they illustrate the ease with which iodides are displaced from lanthanide coordination spheres, and they underscore the complexity associated with using lanthanide iodides as Lewis acid catalysts.     

Thermal and Sensitiveness Determination of Cubanes: Towards Cubane-Based Fuels for Infrared Countermeasures

As infrared seeking technology evolves, threats are better able to distinguish defensive infrared (IR) flares from true targets. Spectrally matched flares, which generally employ carbon-based fuels, are better able to decoy some advanced missiles by more closely mimicking the IR emission of the target. Cubane is a high-energy carbon-based scaffold which may be suitable for use as a fuel in spectrally matched flares. The enthalpy of formation and strain energy of a series of cubanes was predicted in silico, and their thermal and impact stability examined. All were found to undergo highly exothermic decomposition in sealed cell differential scanning calorimetry, and two cubanes subsequently underwent quantitative sensitiveness testing. Despite their F of I values being in the secondary explosive range, cubane-1,4-dicarboxylic acid (F of I=70) and 4-carbamoylcubane-1-carboxylic acid (F of I=90) were identified as potentially useful fuels for pyrotechnic infrared countermeasure flare formulations.     

Recent Advances of Lanthanide-transition Heterometallic Coordination Polymers

With the improvement of high-tech and emergence of crossing and new fields,lanthanide-transition(Ln–M) heterometallic coordination polymers have attracted much attention of many researchers,which exhibit novel structures and unique properties with potential applications in the nonlinear optical materials,fluorescent materials,superconducting materials,magnetic materials,catalysis,bio-simulation,adsorption and separation,and so on.It is thus necessary to summarize Ln–M heterometallic coordination polymers.According to the transition metal ions,those coordination polymers are divided into six parts to explore the current applications and future developments.     

Spectroscopic Monitoring of Sol-Gel Syntheses of Heterometallic Ceramics

Multinuclear NMR spectroscopy and mass spectrometry have been used to monitor the sol-gel syntheses of heterometallic ceramics. Hydrolytic and non-hydrolytic sol-gel procedures have been used for the synthesis of NASICON, Na₃Zr₂Si₂PO₁₂. In the hydrolytic process the precursors were slowly gelated under exposure to atmospheric moisture. 1D and 2D NMR measurement allowed to follow the advancement of the reaction and determine the degree of polymerization. In the non-hydrolytic process the spectroscopic analysis allowed to establish the reaction mechanism and to optimize the synthetic conditions. After thermal treatments a very high quality NASICON phase has been obtained as shown by XRD. Three different procedures have been used with the aim of preparing thin films of -Al₂TiO₅ by hydrolysis of alkoxides of the two metals in acidic condition with or without 2,4-pentanedione (acac) as a chelating agent. Both NMR and MS indicated as the best synthesis the one carried out without acac. XRD patterns of the films obtained confirmed the results of the spectroscopic analysis.     

Structural Modulation of Coordination Polymers by Heterometallic Approach

A series of heterometallic Ni^II/Co^II coordination polymers with 2D networks were synthesized by tetrazole‐1‐acetate ligands and structurally characterized. With increasing concentration of cobalt(II), another different connectivity patterns have been observed. The influence of cobalt(II) is not only on the crystallization, but also on the variation of magnetic properties.     

Lability‐Controlled Syntheses of Heterometallic Clusters

A bulky bidentate ligand was used to stabilize a macrocyclic [Fe^III₈Co^II₆] cluster. Tuning the basicity of the ligand by derivatization with one or two methoxy groups led to the isolation of a homologous [Fe^III₈Co^II₆] species and a [Fe^III₆Fe^II₂Co^III₂Co^II₂] complex, respectively. Lowering the reaction temperatures allowed isolation of [Fe^III₆Fe^II₂Co^III₂Co^II₂] clusters with all three ligands. Temperature‐dependent absorption data and corresponding experiments with iron/nickel systems indicated that the iron/cobalt self‐assembly process was directed by the occurrence of solution‐state electron‐transfer‐coupled spin transition (ETCST) and its influence on reaction intermediate lability.     

Heterometallic compounds assembled from ferrocene-containing bisthiosemicarbazone clips

Heteropolynuclear organometallic compounds have been constructed by using the ferrocene-based ligand H(2)L, [NH(2)SCNHN=C(CH(3))(C(5)H(4))](2)Fe. Reaction of the ligand H(2)L with the cobalt(II) salt gave a tetranuclear helicate Co(2)Fe(2) (1) with two ferrocene-based clips wrapped around the two cobalt atoms. The chiral helicates recognized the neighbors with same chirality through intermolecular hydrogen bonding between the thiosemicarbazone moieties to form a one-dimensional chiral channel. Reaction of the ligand H(2)L with the cadmium(II) salt afforded a tetranuclear dimeric compound Cd(2)Fe(2) (2), with two symmetric related parts bridged through two sulfur atoms. Reaction of the ligand H(2)L with the copper(I) salt, in the presence of triethylamine, resulted in a hexanuclear compound Cu(4)Fe(2) (3) with a crownlike Cu(4)S(4) octagon similar to that of S(8) sited inside and two ferrocene-containing ligands positioned outside. Electrochemical measurements were displayed to investigate the redox communications between the ferrocene moieties through metal centers.     

基于立方烷结构的分子催化剂在光催化水氧化中的研究进展

随着化石燃料大量使用带来的气候变化和环境污染问题日趋严重,寻找清洁高效的可再生能源用做传统化石燃料的替代品,已经成为当前的研究热点。光驱动的水分解反应被认为是太阳能制氢的可行途径。水的全分解包括两个半反应-水的氧化和质子还原。其中水的氧化反应是一个涉及四个电子和四个质子转移的复杂过程,需要很高的活化能,被认为是全分解水反应的瓶颈步骤。因此,开发高效、稳定、廉价丰产的水氧化催化剂是人工光合作用突破的关键因素。立方烷具有类似自然界光合作用酶光系统II(PSII)活性中心Mn_4CaO_5簇的结构,世界各国的科学家受自然界光合作用的启发,开发出了许多基于过渡金属的立方烷结构的催化剂,常见的有锰、钴和铜等立方烷催化剂。本文简要地综述了近年来立方烷分子催化剂在光催化水氧化中的研究进展。首先介绍了立方烷基光催化水氧化反应历程,继而详细介绍了基于有机配体的立方烷配合物和全无机的多金属氧酸盐立方烷水氧化催化剂,其次是半导体(BiVO4或聚合的氮化碳(PCN))为捕光材料复合立方烷分子催化剂的水氧化体系最新研究进展。最后总结并展望了该领域所面临的挑战及其前景。     

Molecular Design of Novel Heterometallic Alkoxides as Precursors

In view of the advantages of employing heterometallic alkoxides as precursors for ceramic materials by the sol-gel process, efforts are being made to develop novel routes for their synthesis and to design single source precursors suited to the final targeted material. Three such new pathways are briefly presented in this paper: (i) varying the ratio of constituent metals; (ii) dissolution of metal chlorides in alkoxides of tetravalent metals; and (iii) reactions of acidic protons of metal glycolate derivatives with alkoxides of another metal yielding derivatives containing other alkoxometallates in cationic form.     

Functionalization of Cubanes and Homocubanes via Oxidative Displacement of Iodine Using Hypervalent Iodine

The iodo group in 4-iodo-1-carbomethoxycubane (1) can be replaced by mesyloxy, tosyloxy and chloro by oxidative displacement with C₆H₅I(OH)OMs, C₆H₅I(OH)OTs and C₆H₅ICl₂, respectively. Similarly, the iodo group in the homocubyl compound 4-iodo-1-bromopentacyclo[4.3.0.0^2,5.0^3,8.0^4,7]nonane-9-one ethylene acetal (2) was analogously replaced by mesyloxy, tosyloxy and chloro. Possible pathways for these reactions are discussed.     

Radical-Bridged Heterometallic Single-Molecule Magnets Incorporating Four Lanthanoceniums

The syntheses and magnetic properties of organometallic heterometallic compounds [K(THF)₆]{Co^I[(μ₃-HAN)RE₂Cp*₄]₂} ( 1-RE ) and [K(Crypt)]₂{Co^I[(μ₃-HAN)RE₂Cp*₄]₂} ( 2-RE ) containing hexaazatrinaphthylene radicals (HAN⋅³⁻) and four rare earth (RE) ions are reported. 1-RE shows isolable species with ligand-based mixed valency as revealed by cyclic voltammetry (CV) thus leading to the isolation of 2-RE via one-electron chemical reduction. Strong electronic communication in mixed-valency supports stronger overall ferromagnetic behaviors in 2-RE than 1-RE containing Gd and Dy ions. Ac magnetic susceptibility data reveal 1-Dy and 2-Dy both exhibit slow magnetic relaxation. Importantly, larger coercive field was observed in the hysteresis of 2-Dy at 2.0 K, indicating the enhanced SMM behavior compared with 1-Dy . Ligand-based mixed-valency strategy has been used for the first time to improve the magnetic coupling in lanthanide (Ln) SMMs, thus opening up new ways to construct strongly coupled Ln-SMMs.