Photosynthesis of a cyanocomplex containing molybdenum(IV) and molybdenum(VI): Photosynthesis of K6[Mo2Mo(CN)8O6]2H2O

A photochemical method for the preparation of K₆[Mo₆[Mo₂^IVMo^IV(CN)₈O₆]2H₂O is discussed. The synthesis of this complex was achieved by photolysing aqueous solutions of K₄Mo(CN)₈ in contact with atmospheric oxygen.     

High‐Field Pulsed EPR Spectroscopy for the Speciation of the Reduced [PV2Mo10O40]6− Polyoxometalate Catalyst Used in Electron‐Transfer Oxidations

An in‐depth spectroscopic EPR investigation of a key intermediate, formally notated as [PV^IVV^VMo₁₀O₄₀]^6? and formed in known electron‐transfer and electron‐transfer/oxygen‐transfer reactions catalyzed by H₅PV₂Mo₁₀O₄₀, has been carried out. Pulsed EPR spectroscopy have been utilized: specifically, W‐band electron–electron double resonance (ELDOR)‐detected NMR and two‐dimensional (2D) hyperfine sub‐level correlation (HYSCORE) measurements, which resolved ⁹⁵Mo and ¹⁷O hyperfine interactions, and electron–nuclear double resonance (ENDOR), which gave the weak ⁵¹V and ³¹P interactions. In this way, two paramagnetic species related to [PV^IVV^VMo₁₀O₄₀]^6? were identified. The first species (30–35 %) has a vanadyl (VO²⁺)‐like EPR spectrum and is not situated within the polyoxometalate cluster. Here the VO²⁺ was suggested to be supported on the Keggin cluster and can be represented as an ion pair, [PV^VMo₁₀O₃₉]^8?[V^IVO²⁺]. This species originates from the parent H₅PV₂Mo₁₀O₄₀ in which the vanadium atoms are nearest neighbors and it is suggested that this isomer is more likely to be reactive in electron‐transfer/oxygen‐transfer reaction oxidation reactions. In the second (70–65 %) species, the V^IV remains embedded within the polyoxometalate framework and originates from reduction of distal H₅PV₂Mo₁₀O₄₀ isomers to yield an intact cluster, [PV^IVV^VMo₁₀O₄₀]^6?.     

The assembly,synthesis and properties of a trinuclear cyano-bridged CuII–MoIV–CuII complex

A new trinuclear cyano-bridged Cu^II–Mo^IV–Cu^II compound has been prepared, characterized spectroscopically (UV–Vis and IR) and its structure determined by X-ray crystallography. The title complex 1 exhibits an antiferromagnetic exchange interaction between copper(II) ions mediated by [Mo(CN)₈]^4? diamagnetic units.     

Two organic–inorganic hybrid compounds constructed from [PMoV1MoVI7VIV2VV4O42]4− and different transition metal fragments

Two new organic–inorganic hybrid compounds, [Cu(phen)(prz)]₂[PMo^V₁Mo^VI₇V^IV₂V^V₄O₄₂]·4H₂O (1) and [Ag₂(phen)₄]₂[PMo^V₁Mo^VI₇V^IV₂V^V₄O₄₂] (2) (phen = 1,10-phenanthroline, prz = pyrazine), have been synthesized and characterized by IR, XPS, XRD, UV–vis, fluorescent spectra analyses, elemental analyses, X-ray diffraction analyses, TG analyses, and cyclic voltammetric measurements. Both compounds are formed by Keggin POM cores and transition metal fragments. Compound 1 exhibits an unprecedented 1-D chain structure constructed from [PMo^V₁Mo^VI₇V^IV₂V^V₄O₄₂]^4? and [Cu(phen)(prz)]²⁺ in the –A–B↑–C–B↓– linking mode. Compound 2 shows a supramolecular structure formed by [PMo^V₁Mo^VI₇V^IV₂V^V₄O₄₂]^4? and [Ag₂(phen)₄]²⁺.     

Two novel windmill-like tetrasupporting heteropolyoxometalates: [MoVI7MoVVIV8O40(PO4)][M(phen)2(OH)]2[M(phen)2(OEt)]2 (M=Co,Ni)

Two interesting neutral tetrasupporting heteropolyoxometalates: [Mo^VI₇Mo^VV^IV₈O₄₀(PO₄)][M(phen)₂(OH)]₂[M(phen)₂(OEt)]₂·xH₂O (phen=1,10-phenanthroline, EtOH=ethanol, M=Co, x=7, 1; M=Ni, x=6, 2) were hydrothermally prepared and structurally characterized. The mixed molybdenum–vanadium polyoxoanion [Mo^VI₇Mo^VV^IV₈O₄₀(PO₄)]⁴⁻ exist in both two complexes, which acts as a bridge to covalently link two pairs of transition metal complex fragments, generating neutral windmill-like trimetallic nanocluster polyoxometalates. Variable-temperature magnetic susceptibility measurements of complexes 1 and 2 reveal that antiferromagnetic exchange interaction exists in this type of trimetallic tetrasupporting heteropolyoxometalates.     

Two-dimensional layer polyoxometalate-based inorganic metal–organic hybrid supramolecular networks woven by Cu ··· Opolyoxoanion short contact weak interactions

Two polyoxometalate-based inorganic metal-organic hybrid supramolecular complexes [Cu(2,2′-bpy)₂]₂[V^IV ₂Mo^V ₅Mo^VI ₇O₃₈(PO₄)] (1) (2,2′-bpy?=?2,2′-bipyridine) and [Cu(2,2′-bpy)₂]₂[Mo^VMo^VI ₁₁O₃₆(PO₄)]?·?3H₂O (2), have been hydrothermally prepared and structurally characterized by single-crystal X-ray diffraction. Both complexes are constructed from polyoxoanions (the bivanadyl capped α-Keggin polymolybdate anion [V^IV ₂Mo^V ₅Mo^VI ₇O₃₈(PO₄)]^4? for 1 and the reduced 12-molybdophosphate anion [Mo^VMo^VI ₁₁O₃₆(PO₄)]^4? for 2) and copper(II) complex cations [Cu(2,2′-bpy)₂]²⁺, forming two-dimensional (2D) layer network structures, in which the polyoxoanion and the complex fragment cation connect with each other through Cu?···?O_polyoxoanion short contact weak interactions, which mediate ferromagnetic interaction.     

Photoinduced Mo−CN Bond Breakage in Octacyanomolybdate Leading to Spin Triplet Trapping

The photoinduced properties of the octacoordinated complex K₄Mo^IV(CN)₈⋅2 H₂O were studied by theoretical calculations, crystallography, and optical and magnetic measurements. The crystal structure recorded at 10 K after blue light irradiation reveals an heptacoordinated Mo(CN)₇ species originating from the light-induced cleavage of one Mo−CN bond, concomitant with the photoinduced formation of a paramagnetic signal. When this complex is heated to 70 K, it returns to its original diamagnetic ground state, demonstrating full reversibility. The photomagnetic properties show a partial conversion into a triplet state possessing significant magnetic anisotropy, which is in agreement with theoretical studies. Inspired by these results, we isolated the new compound [K(crypt-222)]₃[Mo^IV(CN)₇]⋅3 CH₃CN using a photochemical pathway, confirming that photodissociation leads to a stable heptacyanomolybdate(IV) species in solution.     

Methoxokomplexe drei-, vier- und fünfwertiger Zentralatome

The complex formation with CH₃O^? of As^III, Sb^III, Ge^IV, Nb^IV, Se^IV, Te^IV, Ti^IV, Sn^IV and Mo^V has been investigated in absolute methanolic solutions containing (CH₃)₄NCl, LiCl, or Lithiumtosylate (μ = 1; 20.0°) by means of pH-titrations. The relations between the stoichiometry of the reactions and the shape of the buffer regions, as well as the concentration-dependance of these buffer regions are discussed.     

Photoinduced Mo−CN Bond Breakage in Octacyanomolybdate Leading to Spin Triplet Trapping

The photoinduced properties of the octacoordinated complex K₄Mo^IV(CN)₈?2 H₂O were studied by theoretical calculations, crystallography, and optical and magnetic measurements. The crystal structure recorded at 10 K after blue light irradiation reveals an heptacoordinated Mo(CN)₇ species originating from the light‐induced cleavage of one Mo?CN bond, concomitant with the photoinduced formation of a paramagnetic signal. When this complex is heated to 70 K, it returns to its original diamagnetic ground state, demonstrating full reversibility. The photomagnetic properties show a partial conversion into a triplet state possessing significant magnetic anisotropy, which is in agreement with theoretical studies. Inspired by these results, we isolated the new compound [K(crypt‐222)]₃[Mo^IV(CN)₇]?3 CH₃CN using a photochemical pathway, confirming that photodissociation leads to a stable heptacyanomolybdate(IV) species in solution.     

Models for the Active Center of Pterin-Containing Molybdenum Enzymes: Crystal structure of a molybdenum complex with sulfur and pterin ligands

The first crystal structure of a molybdenum complex 9 with a hydrogenated pterin and a sulfur ligand contributes to the discussion about the active center of molybdenum and tungsten enzymes containing a molybdopterin cofactor. Complex 9 was synthesized through a redox reaction of [Mo^VIO₂ (LN-S₂)] ( 8 ; LN-S₂ = pyridine-2, 6-bis(methanethiolato)) with 5, 6, 7, 8-tetrahydropterin ( 7 ). 2 HCl (H₄Ptr.2 HCl). The complex crystallizes, with a non-coordinating Cl-atom acting as a counterion, in the monoclinic space group C2/c (No. 15) with cell dimensions a = 22.900(5), b = 10.716(2), c = 17.551(4) Å, β = 120.36(3)°, and Z = 8. We interpret 9 as [Mo^IVO(LN-S₂)(H⁺-q-H₂Ptr)]Cl (q = quinonoid; H₂Ptr = dihydropterin), i.e., a Mo^IV monooxo center coordinated by a pyridine-2, 6-bis(methanethiolato) ligand and a protonated dihydropterin. The spectroscopic properties of this new complex are comparable to those of other crystalline molybdenum complexes of hydrogenated pterins without additional S-coordination. The slightly H₂O-soluble complex 9 reacts with the natural enzyme substrate DMSO very slowly, possibly due to the lack of easily dissociable ligands at the metal center.     

Theoretical study on photoinduced magnetization process: Possible meta-stable molecular structure for a photomagnetic high-spin molecule [MoIV(CN)2(CN-CuL)6]8+

An intermediate in photoinduced magnetization process for the photomagnetic high-spin molecule [Mo^IV(CN)₂(CN-CuL)₆]⁸⁺ is studied with quantum chemistry calculations of the density functional theory and the ab initio multireference configuration interaction methods. It is found that the intramolecular electronic transfer from Mo^IV to Cu^II leads one trigonal-bipyamid coordinated Cu^II to be changed to the tetrahedral coordinated Cu^I with the light irradiation. The calculated magnetic properties show that the paramagnetic system [Mo^IV(CN)₂(CN-Cu^IIL)₆]⁸⁺ with six isolated spin 1/2 Cu ions is changed to ferromagnetic coupling high-spin system [Mo^V(CN)₂(CN-Cu^IIL)₅(CN-Cu^IL)]⁸⁺. These calculations will help to understand photoinduced magnetization phenomenon and provide a clue for the synthesization of new reversible photoinduced magnetic compounds.     

Octacyanidotungstate(IV) Coordination Chains Demonstrate a Light‐Induced Excited Spin State Trapping Behavior and Magnetic Exchange Photoswitching

A huge increase in the magnetization of two coordination chains based on tetravalent octacyanidometalates (W^IV and Mo^IV) is observed on irradiation with 436 nm light, while no such behavior is observed for the Nb^IV analogue. A photomagnetic response based solely on [W^IV(CN)₈]⁴⁻ is demonstrated for the first time. The observed behavior is attributed to the light‐induced excited spin state trapping (LIESST) effect at the octacyanidometalate, and to the resulting magnetic exchange ON/OFF photoswitching between the Mn^II center and the photoinduced high‐spin (S =1) W^IV or Mo^IV centers.     

Kinetics and mechanism of oxidation of benzoic acid hydrazide by bromate catalyzed by octamolybdomanganate(II)

Oxidation of benzoic acid hydrazide by bromate in the presence of octamolybdomanganate(II), [Mn^IIMo₈O₂₇]⁴⁻, was studied in hydrochloric acid medium. The mechanism of the reaction involves oxidation of the catalyst to [Mn^IVMo₈O₂₇]²⁻ by bromate which then forms a complex with the unoxidized catalyst. Both the complex and [Mn^IVMo₈O₂₇]²⁻ react with the substrate in rate-determining steps to generate an intermediate acyl diimide, RCONNH. The reaction of water with the diimide then leads to the formation of benzoic acid and nitrogen as products through an NH–NH intermediate. There was no formation of free radical, indicating the involvement of only two-electron transfer steps in the mechanism. The order of more than unity in catalyst concentration is due to the formation of complex between the catalyst and the oxidized form of the catalyst. A rate law explaining all the kinetic results has been derived and verified. The effects of ionic strength and solvent polarity have also been studied, and the thermodynamic parameters were determined. A less solvated transition state as a result of interaction between the complex and oxidized form of the catalyst satisfactorily explains all the effects observed. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

La5Mo6O21: a novel ternary reduced molybdenum oxide containing {MoIV}3 clusters and isolated MoV centres

The crystal structure of La₅Mo₆O₂₁ (penta­lanthanum hexa­molybdenum henicosa­oxide) is made up of Mo₃O₁₃ units containing triangular {Mo^IV}₃ clusters, three distorted Mo^VO₆ octa­hedral units and six inter­stitial La^III atoms. The Mo₃O₁₃ unit consists of three edge‐sharing Mo^IVO₆ units involving Mo—Mo bonding. The three Mo^VO₆ octa­hedra share their corners or edges with each other and with the Mo₃O₁₃ units.     

Reversible Dihydrogen Activation and Hydride Transfer by a Uranium Nitride Complex

Cleavage of dihydrogen is an important step in the industrial and enzymatic transformation of N₂ into ammonia. The reversible cleavage of dihydrogen was achieved under mild conditions (room temperature and 1 atmosphere of H₂) by the molecular uranium nitride complex, [Cs{U(OSi(O^tBu)₃)₃}₂(μ‐N)] 1, leading to a rare hydride–imide bridged diuranium(IV) complex, [Cs{U(OSi(O^tBu)₃)₃}₂(μ‐H)(μ‐NH)], 2 that slowly releases H₂ under vacuum. This complex is highly reactive and quickly transfers hydride to acetonitrile and carbon dioxide at room temperature, affording the ketimide‐ and formate‐bridged U^IV species [Cs{U(OSi(O^tBu)₃)₃}₂(μ‐NH)(μ‐CH₃CHN)], 3 and [Cs{U(OSi(O^tBu)₃)₃}₂(μ‐HCOO)(μ‐NHCOO)], 4 .     

Three novel octacyanomolybdate(IV)–M(II) [M = Mn and Cu] bimetallic assemblies: crystal structures and magnetic properties

Synthesis, structure characterization, and magnetic properties of three novel cyano-bridged complexes {[Mn^II(bpy)(DMF)₂]₂[Mo^IV(CN)₈]·1.5H₂O} _n (1), [Cu^II(L)]₂[Mo^IV(CN)₈]·6.75H₂O (2), and [Mn^II(bpy)₂]₄[Mo^IV(CN)₈]₂·4MeOH·4H₂O (3) (where DMF = N,N′-dimethylformamide; bpy = 2,2-bipyridine and L = 1,3,6,8,11,14-hexaazatricyclo[12.2.1.1^8,11]octadecane) have been studied. The X-ray single-crystal structure reveals that 1 is a cyanide-bridged 1D infinite chain with the alternating of Mn^II(bpy)(DMF)₂ and Mo^IV(CN)₈ moieties. The neighboring chains interact with each other by hydrogen bonding to form a sheet-like network, and the layers further extend to a 3D network due to the face-to-face π···π stack interactions. For 2, the Mo^IV center adopts a distorted square antiprism coordination environment, while the Cu^II center adopts a distorted square pyramidal geometry. The weak Mo–CN···Cu interactions between neighboring molecules lead to a 2D network structure of 2. For 3, basic structural unit is centrosymmetric and contains four Mn^II centers bridged by two octacyanomolybdate(IV). Here, their magnetic properties have also been studied. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

High Intensity Trip-Multiplet Transitions,a Reality! Synthesis,Properties, and Crystal Structure of l-Bis(triphenylphosphine)iminium trans-Dibromophthalocyaninato(2–)molybdate(III)

Oxophthalocyaninato(2–)molybdenum(IV), activated by bromine oxidation prior to use, reacts with fused triphenylphosphine in the presence of bis(triphenylphosphine)iminium bromide to yield linear-bis(triphenylphosphine)iminium trans-dibromophthalocyaninato(2–)molybdate(III), ^l(PNP)^trans[Mo(Br)₂pc^2?]. It crystallizes triclinic with crystal data: a = 10.506(1) Å, b = 12.436(2) Å, c = 12.918(2) Å, α = 76.186(1)°, β = 67.890(1)°, γ = 68.689(1)°; space group P1 (No. 2); Z = 1. Mo^III is in a pseudo-octahedral coordination geometry with the bromo ligands in trans-arrangement. The Mo? N_p and Mo? Br distance is 2.043(10) and 2.588(1) Å, respectively. The PNP cation adopts a linear conformation. In the IR spectrum v_as(Mo? Br) is observed at 218 cm^?1 and v_as(P? N) of the linear (P? N? P) core at 1406 cm^?1. Cyclic and differential-pulse voltammetry show two quasi-reversible cathodic processes at ?1.15 and ?0.53 V vs. Ag/AgCl. The first is assigned to a phthalocyaninate directed reduction (pc^2?/pc^3?), while the latter arises from a Mo directed reduction (Mo^III/Mo^II). Spectral monitoring confirms the reversible Mo^III/Mo^II reduction. Two quasi-reversible anodic processes at 0.60 and 1.27 V are assigned to the successive Mo directed oxidation with redox couples Mo^III/Mo^IV and Mo^IV/Mo^V. For the first time, three very intense spin-allowed trip-quartet transitions are observed in the electronic absorption spectra at 7140 (TQI), 16890 (TQ2) and 18700 cm^?1 (TQ3) together with a sing-quartet transition at 15850 cm^?1 and characteristic ?Q”? region with maximum at 28500 cm^?1 and ?N”? region at 37400 cm^?1. All electronic excitations are of comparable intensity. A prominent low temperature emission at 6690 cm^?1 is assigned to a spin-forbidden trip-sextet.     

Electron transfer. 109. The reaction of dimeric molybdenum(V) with carboxylato-bound chromium(V). A third mechanistic variation

The bridged dimer of molybdenum(V), Mo₂O₄²⁺ (aq) is oxidized to Mo(VI) by carboxylato-bound chromium(V). Reaction of bis(chelated) Cr(V) with excess (Mo^V)₂ yields a chelated Cr(III) complex, but this conversion proceeds through a pink Cr(IV) intermediate, indicating that the oxidation of (Mo^V)₂ entails a series of le^? steps, passing through a reactive transient, the mixed valence complex, Mo^VMo^VI. When experiments are carried out in buffers of the ligating acid, 2-ethyl-2-hydroxybutanoic acid, two stages of ligation of (Mo^V)₂ by the ligand anion, characterized by rate constants near 10⁴ and 0.14 M^?1 s^?1 (19°C; pH 3.0; μ = 0.6 M) must be considered. In quick mixing experiments, the first, but not the second, of these proceeds before the redox reaction gets under way, and autocatalytic redox profiles are observed. If the slower ligation is allowed to reach completion before Cr(V) is added, reduction to Cr(IV) is greatly accelerated and conforms to the superposition of two processes, whereas the reduction of Cr(IV) to Cr(III) is slow and exhibits a rate independent of [Cr^IV]. A proposed sequence applicable to the latter conditions includes reductions of Cr(V) at two ligation levels, slow unimolecular conversion of (Mo^V)₂ to an activated form, and rapid reduction of the latter with Cr(IV). Here Cr(IV) has assumed the role of a scavenger for the reactive form of (Mo^V)₂.     

Model oxygen-evolving center composed of polymer membrane and dimer ruthenium complex

The in situ spectrocyclic voltammetric investigations of the dimeric ruthenium complex used for water oxidation, [(bpy)₂(H₂O)Ru–O–Ru(H₂O)(bpy)₂]⁴⁺ (H₂O–Ru^III–Ru^III–OH₂), were carried out in a homogeneous aqueous solution and in a Nafion membrane under different pH conditions. The in situ absorption spectra recorded for the dimer show that the dimer H₂O–Ru^III–Ru^III–OH₂ complex underwent reactions initially to give the detectable H₂O–Ru^III–Ru^IV–OH and H₂O–Ru^III–Ru^IV–OH₂ complexes, and at higher positive potentials, this oxidized dimer underwent further oxidation to produce a presumably higher oxidation state Ru^V–Ru^V complex. Since this Ru^V–Ru^V complex is reduced rapidly by water molecules to H₂O–Ru^III–Ru^IV–OH₂, it could not be detected by absorption spectrum. Independent of the pH conditions and homogeneous solution/Nafion membrane systems, the dimer Ru^III–Ru^IV was detected at higher potentials, suggesting that the dimer complex acts as a three-electron oxidation catalyst. However, in the Nafion membrane system it was suggested that the dimer complex may act as a four-electron oxidation catalyst. While the dimer complex was stable under oxidation conditions, the reduction of the dimer Ru^III–Ru^III to Ru^II–Ru^II led to decomposition, yielding the monomeric cis-[Ru(bpy)₂(H₂O)₂]²⁺.