Hexanuclear Mixed-valence Research Articles

Synthesis, Characterization, and Modeling of Magnetic Properties of a Hexanuclear Amino Alcohol-Supported {CoII2CoIII2DyIII2} Pivalate Cluster

A heterometallic hexanuclear mixed-valence Co–Dy cluster [Co4Dy2(OH)2(O2CCMe3)8(HO2CCMe3)2(teaH)2(N3)2]·2(EtOH) (1) has been prepared from the reaction of dinuclear Co(II) pivalate with triethanolamine and azide ligands and characterized by elemental analysis, IR spectroscopy, and X-ray crystallography. The metal atoms in the {CoII2CoIII2DyIII2} cluster core are bridged by two μ3-hydroxy groups, two azide N3– anions, six pivalate residues, and two doubly deprotonated teaH2– ligands. A theoretical model has been developed to explain the magnetic behavior of 1. The model takes into account the crystal fields acting on the DyIII ions and the anti- and ferromagnetic exchange interactions in the pairs Co–Dy and Co–Co, respectively. The Stark structure for the DyIII ions is calculated with due account of the covalence effects within the frames of the exchange charge model of the crystal field. It is demonstrated that at low temperatures the magnetic properties of the cluster are determined by the interaction of...

Tri-, tetra-, and hexanuclear mixed-valence molybdenum clusters: structural diversity and catalysis of acetylene hydrogenation.

A series of novel cluster compounds comprising molybdenum in a low valence state was synthesized by means of a disproportionation of the dimeric compound [Mo+42Cl4(OCH3)4(CH3OH)2] (1). The reaction of 1 with CH3OH leads to the disproportionation of Mo+4 yielding an unusual mixed-valence cluster [Mo+3.54Cl4O2(OCH3)6(CH3OH)4] (2). By exploring this synthetic approach further, tri-{[Mo3Cl3(OCH3)7(CH3OH)3] (3)}, tetra-{[Mo4Cl4(OCH3)10(CH3OH)2] (4), [Mo4Cl3O(OCH3)9(CH3OH)3] (5), [Mo4Cl2(OCH3)12(CH3OH)2] (6)}, and hexanuclear {[Mo6Cl4O6(OCH3)10(CH3OH)2] (7)} molybdenum alkoxides were synthesized by the reaction of 1 with methanol and stoichiometric amounts of magnesium methoxide, thus providing a general facile access to the polynuclear methoxide complexes of a low-valence molybdenum. Due to the feasibility to adopt multiple oxidation states in a reversible manner and the documented competence of molybdenum alkoxide compounds to catalyze the reduction of inert molecules, including N2, the synthesized compounds were expected to function as catalysts of small molecule substrates reduction/hydrogenation. Accordingly, the reduction of acetylene (C2H2) to an ethylene (C2H4) and ethane (C2H6) mixture, in methanol (with water additives) serving as a reaction medium and a proton donor, and using sodium or europium amalgams as reducing agents, was performed in the presence of 2. Preliminary kinetic studies evidently point to a catalytic function of molybdenum species derived from 2, thus establishing the observed reactivity as a rare example of non-precious metal-catalyzed acetylene hydrogenation, providing, in addition, a convenient model for further mechanistic studies.

A Hexanuclear Mixed-Valence Oxovanadium(IV,V) Complex as a Highly Efficient Alkane Oxidation Catalyst

The new hexanuclear mixed-valence vanadium complex [V(3)O(3)(OEt)(ashz)(2)(μ-OEt)](2) (1) with an N,O-donor ligand is reported. It acts as a highly efficient catalyst toward alkane oxidations by aqueous H(2)O(2). Remarkably, high turnover numbers up to 25000 with product yields of up to 27% (based on alkane) stand for one of the most active systems for such reactions.

Synthesis, structure and DFT calculation of a hexanuclear mixed-valence copper cluster supported by 2,3-disulfidobenzoate and 3-carboxybenzene-1,2-bis(thiolate)

A homoleptic hexanuclear Cu cluster, [(Cu(DSB)(CBT)) 2(Cu 2Br) 2][PPh 4] 2 ( 1-PPh 4 ) [DSB = 2,3-disulfidobenzoate; CBT = 3-carboxybenzene-1,2-bis(thiolate)] was synthesized as dark green crystals by the reaction of CuCl 2 with 2,3-dimercaptobenzoic acid in acetate buffer solution. The X-ray crystal study of 1-PPh 4 revealed its unique structural features: (1) one of two types of crystallographically distinct Cu centers adopted a square planer geometry and the other center had a tetrahedral geometry, and (2) intermolecular H-bonding interactions connected between carboxylic acid group of CBT and the carboxylate group of DSB led to the construction of an unprecedented topologic architecture of a zigzag patterned infinite sheet. In addition, taking into account the total charge of the molecule, which contained 2,3-disulfidobenzoate and 3-carboxybenzene-1,2-bis(thiolate), and the diamagnetic nature of 1-PPh 4 , 1-PPh 4 led to it is assignment as a mixed-valence Cu(I)/Cu(III) cluster. Such mixed valence states of Cu atoms were also examined by density functional theory calculation.

Bis-Tris Propane as a New Polydentate Linker in the Synthesis of Iron(III) and Manganese(II/III) Complexes

We describe the synthesis, structure, and magnetic properties of two new complexes, one decanuclear iron(III) cluster and one hexanuclear mixed-valence manganese(II/III) cluster, where the previously unexplored polydentate ligand Bis-tris propane {(CH2OH)3CNH(CH2)3NHC(CH2OH)3} is used to link small cluster fragments into high-nuclearity complexes.

Excited-state electronic coupling and photoinduced multiple electron transfer in two related ligand-bridged hexanuclear mixed-valence compounds.

The synthesis, characterization, electrochemical, photophysical, and photochemical properties of two hexanuclear mixed-valence compounds are reported. Each supramolecular species consists of two cyano-bridged [(NC)(5)Fe(II)-CN-Pt(IV)(NH(3))(3)L-NC-Fe(II)(CN)(5)] triads that are linked to each other through a Pt(IV)-L-Pt(IV) bridge, where L = 4,4'-dipyridyl (bpy) or 3,3'-dimethyl-4,4'-dipyridyl (dmb). The major difference between the two compounds is the electronic nature of the bridging ligand between the two Pt atoms. Both species exhibit a broad Fe(II) --> Pt(IV) intervalent (IT) absorption band at 421 nm with an oscillator strength that is approximately four times that for [(NC)(5)Fe(II)-CN-Pt(IV)(NH(3))(5)] and twice that for [(NC)(5)Fe(II)-CN-Pt(IV)(NH(3))(4)-NC-Fe(II)(CN)(5)].(4-) When L = bpy, the resonance Raman spectrum obtained by irradiating the IT band at 488 nm exhibits several dipyridyl ring modes at 1604, 1291, and 1234 cm(-1) which are not present in the spectrum when L = dmb. In addition, femtosecond pump-probe spectroscopy performed at 400 nm yields a transient bleach of the IT absorption band with a single exponential decay of 3.5 ps for L = bpy, compared with only 1.8 ps for L = dmb and 2.1 ps for [(NC)(5)Fe(II)-CN-Pt(IV)(NH(3))(4)-NC-Fe(II)(CN)(5)].(4-) Last, prolonged irradiation of the complexes at 488 nm leads to the formation of 4 equiv of ferricyanide with a quantum efficiency of 0.0014 for L = bpy and 0.0011 for L = dmb. The transient absorption, resonance Raman, and photochemical data suggest that the degree of excited electronic coupling in these compounds is tunable by changing the electronic nature of the Pt-L-Pt bridging ligand.

Synthesis and structure of [Mn 6O 2(O 2CPh) 10(EtOH) 4(H 2O)] ·. EtOH, a manganese aggregate containing three types of benzoate ligation. Isomerism in [Mn 6O 2(O 2CPh) 10] complexes

The reaction of Mn(O 2CPh) 2·.4H 2O with KMnO 4 in warm ethanol in the presence of benzoic acid has been found to give, in addition to the previously reported “manganic benzoate”, the new hexanuclear mixed-valence manganese cluster [Mn 6O 2 (O 2CPh) 10(EtOH) 4(H 2O)]·.EtOH ( 1) in 40% yield. X-ray crystal structure determination at −172°C shows that the complex contains a distorted [Mn II 4Mn III 2O 2] 10+ core and, in addition to terminal EtOH and H 2O groups, three different types of benzoate ligation viz. μ 3-bridging, μ 2-bridging and monodentate terminal forms.