New Perspectives in Polyoxometalate Chemistry by isolation of compounds containing very large moieties as transferable building blocks: (NMe4)5[As2Mo8V4AsO40] · 3H2O, (NH4)21[H3Mo57V6(NO)6O183(H2O)18] · 65 H2O, (NH2Me2)18(NH4)6[Mo57V6(NO)6O183(H2O)18] · 14 H2O,and (NH4)12[Mo36(NO)4O108(H2O)16] · 33 H2O

The compounds (NMe₄)₅[As₂Mo₈V₄AsO₄₀] · 3 H₂O 2a , (NH₄)₂₁[H₃Mo₅₇V₆(NO)₆O₁₈₃(H₂O)₁₈] · 65 H₂O 3a , (NH₂Me₂)₁₈(NH₄)₆[Mo₅₇V₆(NO)₆O₁₈₃(H₂O)₁₈] · 14 H₂O 3b and (NH₄)₁₂[Mo₃₆(NO)₄O₁₀₈(H₂O)₁₆] · 33 H₂O 4a ( 3a and 4a were not correctly reported in the literature regarding to their composition, structures and the oxidation states of the metal centres) which contain large isolated anionic species, have been prepared (among them 3a, 3b , and 4a in rather high yield) and characterized by complete crystal structure analysis as well as IR/Raman, UV/VIS/NIR, ESR spectroscopy and magnetic susceptibility measurements, redox titrations, bond valence sum calculations, elemental analyses and thermogravimetric studies. Perspectives for polyoxometalate chemistry referring to the synthesis of “extremely” large nanoscaled species are discussed, together with the occurrence of a large transferable {Mo₁₇} building block in the compounds 3a, 3b and 4a which also exists in the corresponding iron compound Na₃(NH₄)₁₂[H₁₅Mo₅₇Fe₆(NO)₆O₁₈₃(H₂O)₁₈] · 76 H₂O 7a .     

Supramolecular Systems Based on Ca2+, [Mo3O2S2Cl6(H2O)3]2s-, [Mo3S4Cl6.75Br0.25(H2O)2]3s- and Cucurbit[6]uril

Adducts of cucurbit[6]uril with Ca²⁺ and trinuclear cluster chloroaquacomplexes (H₉O₄)₂(H₇O₃)₂[(Ca(H₂O)₅)2(C₃₆H₃₆N₂₄O₁₂)]Cl₈·0.67H₂O (1) and [(Ca(H₂O)₅)₂(C₃₆H₃₆N₂₄O₁₂)]× [Mo₃O₂S₂Cl₆(H₂O)₃]₂·13H₂O (2) are obtained and structurally characterized. The structures of both compounds contain polymeric [Ca(H₂O) _n ]₂² CB[6]∞ cations that form infinite columns; the space between them is filled with Cl^s- (1) and [Mo₃O₂S₂Cl₆(H₂O)₃]^2s- (2). A new (H₇O₃)₂(H₅O₂)× [Mo₃S₄Cl_6.25Br_0.25(H₂O)₂](C₃₆H₃₆N₂₄O₁₂)·CH₂Cl₂·6H₂O complex (3) is also obtained and structurally characterized.     

Synthesis and the crystal structure of a supramolecular adduct of the [Mo3O4(H2O)6Cl3]+ cluster complex with macrocyclic cavitand cucurbituril

The crystalline supramolecular compound of composition {(C₃₆H₃₆N₂₄O₁₂)[Mo₃O₄(H₂O)₆Cl₃]₂}Cl₂·14H₂O was obtained by slow concentration of a hydrochloric solution of the cluster aqua complex [Mo₃O₄(H₂O)₉]⁴⁺ and macrocyclic cavitand cucurbituril (C₃₆H₃₆N₂₄O₁₂). The molecular and crystal structure of the supramolecular adduct was established by X-ray diffraction analysis.     

Synthesis,structures, luminescent and dielectric properties of lanthanide coordination polymers

Under hydrothermal conditions, four lanthanide coordination polymers were synthesized based on 4-(4,5-dicarboxy-1H-imidazol-2-yl)pyridine 1-oxide (H₃DCImPyO), with the molecular forumulas [Eu(HDCImPyO)·(H₂O)₂·(CHO₂)]_n (1), [Sm(HDCImPyO)·(H₂O)₂·(HCO₂)]_n (2), {[La(HDCImPyO)·(H₂O)·(HCO₂)]·O₂}_n (3) and {[Y(HDCImPyO)·(C₂O₄)·(H₂O)₂]·H₂O}_n (4). With diverse coordination modes, they were further characterized by elemental analysis, infrared spectroscopy, dielectric measurement, and single-crystal X-ray structural analysis. Complexes 1 and 2 were isostructural and had similar structures with {4⁴, 6²} topology. Complex 1 exhibited strong fluorescent emission in the solid state at room temperature. In 3, HDCImPyO^2? adopted μ₄-kO, O′: kO′, O′′: O′′′: O′′′′ coordination to bridge four La(III) ions to form a 3-D framework with {4. 5²}₂{4². 5¹⁰. 6¹². 7. 8³} topology. In 4, both HDCImPyO^2? ligands and Y³⁺ cations were simplified as linkers to form an interpenetrating 3-D framework with {4¹³. 6²}₂{4²². 6⁶} topology.     

Synthesis and photo-/electro-catalytic properties of a 3-D supramolecular framework based on [HxAs2Mo6O26](6−x)− and {Cu-diz} complexes

Herein, an arsenomolybdate, {Cu(diz)₄(H₂O)₂}[{Cu(diz)₂(H₂O)₂}₂{As₂Mo₆O₂₆}]·2H₂O (diz = 1,2-diazole) (1), has been synthesized under hydrothermal conditions and characterized by single-crystal X-ray diffraction, elemental analysis, IR, TG, XPS, PXRD, and UV–Vis-NIR. The {Cu-diz} complexes link the [As₂Mo₆O₂₆]^6? polyoxoanions, forming a 1-D infinite chain. The 2-D layer is constructed from 1-D chains through hydrogen bonds. Adjacent layers and free {Cu(diz)₄(H₂O)₂} complexes are fused through hydrogen bonding to form a 3-D topological framework with symbol of {4¹⁴·6¹⁰·8⁴}{4}². Compound 1 exhibits luminescence at room temperature, excellent degradation activity for four different organic dyes (RhB, MB, MO, and AP) under UV irradiation. The photocatalytic mechanism of 1 is discussed in detail. Furthermore, the electrocatalytic activity of 1 toward hydrogen peroxide has also been studied.     

Stability of the Mo72Fe30 polyoxometalate buckyball in solution

The stability of the [Mo₇₂Fe₃₀O₂₅₂(CH₃COO)₁₂{Mo₂O₇(H₂O)}₂{H₂Mo₂O₈(H₂O)}(H₂O)₉₁] · ??150H₂O polyoxometalate (Mo₇₂Fe₃₀) with a buckyball framework structure in solution has been investigated as a function of the solute concentration, illuminance, the presence/absence of a polymer, and the acidity of the medium. The polyoxometalate ions can form association species with molecules of water-soluble nonionic polymers, such as polyvinyl alcohol and polyvinylpyrrolidone. Electrotransport properties of the polyoxometalate ions??mobility, transport number, and diffusion coefficient??have been measured. The catalytic activity and stability of Mo₇₂Fe₃₀ in a redox reaction have been evaluated.     

Organic‐Inorganic Hybrid Supramolecular Assemblies Based on Isomers [HxAs2Mo6O26](6–x)– Clusters

The arsenomolybdates [H₂As₂Mo₆O₂₆(H₂O)] · (H₂biyb)₂ · 2H₂O ( 1 ) and [H₃As₂Mo₆O₂₆] · (H₃pt)₂ ( 2 ) [biyb = 1,4‐bis(imidazol‐1‐ylmethyl)benzene, pt = 4′‐(3′′‐pyridyl)‐2,3′:6′3′′‐terpyridine] were synthesized via hydrothermal method. The structures of the compounds were characterized by single‐crystal X‐ray diffraction analyses, elemental analyses, IR spectroscopy, and TG analysis. Compounds 1 and 2 exhibit two isomeric forms of [H_xAs₂Mo₆O₂₆]^(6–x)–. The structure of 1 is constructed from the B‐type [H₂As₂Mo₆O₂₆(H₂O)]^4– polyanions and free biyb ligands via weak interactions to form 3D supramolecular framework with a {3 · 4 · 5³ · 6}{3 · 4³ · 5²}{3 · 5 · 6}²{3 · 5²}² topology structure. In compound 2 , the A‐type [H₃As₂Mo₆O₂₆]^3– clusters are surrounded by pt ligands through hydrogen bond interactions forming 3D supramolecular framework with a {4³ · 6³}²{4⁶ · 6⁶ · 8³} topology structure. The electrochemical behaviors, electrocatalytic and photocatalytic activities of 1 and 2 are detected.     

Coordination of Phenylsulfinate PhSO2— to Mo3MS44+ Clusters (M = Ni,Pd)

Reaction of heterometal cuboidal clusters [Mo₃(MCl)S₄(H₂O)₉]³⁺ (M = Ni, Pd) with PhSO₂Na in aqueous HCl leads to the substitution at Ni or Pd to give the [Mo₃(M(PhSO₂))(H₂O)_9—xCl_x]^(3—x)+species, isolated as supramolecular adducts with cucurbituril (Cuc) [Mo₃(Ni(PhSO₂))S₄Cl_1.17(H₂O)_7.83][Mo₃(Ni(PhSO₂))S₄Cl_2.22(H₂O)_6.78]Cl_2.61 · Cuc · 15H₂O ( 1 ) and [Mo₃(Pd(PhSO₂))S₄Cl_1.12(H₂O)_7.88][Mo₃(Pd(PhSO₂))S₄Cl_2.29(H₂O)_6.71]Cl_2.59 · Cuc · 11H₂O ( 2 ), respectively. Crystal structure of 1 and 2 was determined, revealing that the PhSO₂ is coordinated via its sulfur atom (Ni — S 2.182 Å, Pd — S 2.305 Å). The structure of these isostructural compounds is built from triple aggregates {(cluster)(Cuc)(cluster)} united into zigzag chains via hydrogen bonds between coordinated PhSO₂ and H₂O ligands.     

Synthesis and Properties of Complexes with Unusual {MnIII4} and {MnII4} Cages

Two types of manganese complexes with [Mn₄] cores featuring the unusual distorted cube topology are presented, the first of which comprises new modifications of the reported complex [Mn^III₄(sao)₄(saoH)₄]·3CHCl₃: [Mn₄(sao)₄(saoH)₄]·1.32(C₄H₁₀O)·0.43(CH₄O) ( 1a ) and [Mn(sao)₄(saoH)₄]·0.5(CH₄O)·0.5(C₂H₃N) ( 1b ) sao = salicylaldoxime. The second, 0.55[Mn₄Cl₄(C₁₂H₉N₂O)₄(CH₃OH)₂(H₂O)₂]·0.45[Mn₄Cl₄(C₁₂H₉N₂O)₄(CH₃OH)₄] ( 2 ), is the first reported case of a {Mn^II₄} core of this topology besides known {Mn^III₄} compounds. Differences between the {Mn^II₄} and {Mn^III₄} situation are discussed, and so far overlooked differences in magnetic properties between different {Mn^III₄} compounds are pointed out.     

A New Member of Giant Polyoxomolybdate Containing Bridging Hydroxylamine Moieties: Synthesis and Crystal Structure of (NH4)4Na2[MoVI 36O108(NH2OH)2(OH)6(H2O)12]⋅35H2O

A new member of giant polyoxomolybdate containing bridging hydroxylamine groups has been unexpectedly obtained during the preparation of the material of {Mo₅₇V₆}, (NH₄)₄Na₂[Mo^VI ₃₆O₁₀₈(NH₂OH)₂(OH)₆(H₂O)₁₂]35H₂O. The title compound crystallizes in the monoclinic space group P2(1)/n, a=16.7886(2), b=18.4309(3), c=24.49950(10) Å, =99.58°, V=7475.18(15) ų, Z=2, and D _calc =2.817. Each giant cluster anion [Mo^VI ₃₆O₁₀₈(NH₂OH)₂(OH)₆(H₂O)₁₂]^6– ({Mo ₃₆ (NO) ₂ }) consists of two large [Mo^VI ₁₅O₅₀(MoO)⁴⁺ ₂(-NH₂OH)(-OH)(t-OH)₂(t-OH₂)₆]^5– ({Mo₁₇} units linked together by two {MoO₂}²⁺ centers; these anions {Mo ₃₆ (NO) ₂ } are further connected via distorted mono-capped pentagonal-pyramidal sodium into a three-dimensional structure with channels that filled with lattic water molecules and NH⁺ ₄ ions.     

A New Molybdophosphate Constructed From {Mo<Stack><Subscript>2</Subscript><Superscript>V</Superscript></Stack>O<Subscript>4</Subscript>(H<Subscript>2</Subscript>O)<Subscript>6</Subscript>}<Superscript>2+</Superscript> and 1-Hydroxyethylidenediphosphonate

A new molybdophosphate (NH₄)₈{Mo₂^VO₄[(Mo₂^VIO₆)CH₃C(O)(PO₃)₂]₂}·14H₂O (1), has been synthesized by the reaction of {Mo₂^VO₄(H₂O)₆}²⁺ fragments with 1-hydroxyethylidenediphosphonate (hedp HOC(CH₃)(PO₃H₂)₂), and it is characterized by ³¹P NMR, IR, UV, element analysis, TG and single-crystal X-ray analysis. The structure analysis reveals that the polyoxoanion can be described as two {(Mo₂^VIO₆)(CH₃C(O)(PO₃)₂} units connected by a {Mo₂^VO₄}²⁺ moiety. In the structure, the six Mo atoms are arranged into a new “W-shaped” structure, which represents a new kind of molybdophosphate.     

Synthesis and Crystal Structure of Two New Molydenum(V) Pyrophosphate Complexes

Two new reduced molybdenum pyrophosphates, Na₂₈[Na₂{(Mo₂O₄)₁₀(P₂O₇)₁₀(HCOO)₁₀}]·108H₂O ( 1 ) and Na₂₂(H₃O)₂[Na₄{(Mo₂O₄)₁₀(P₂O₇)₁₀(CH₃COO)₈(H₂O)₄}]·91H₂O ( 2 ) have been synthesized and characterized by single‐crystal X‐ray diffraction. Red crystals of 1 are triclinic, space group , with a = 17.946(4) Å, b = 18.118(4) Å, c = 21.579(4) Å, α = 114.47(3)°, β = 93.54(3)°, γ = 114.39(3)° and V = 5581.8(19) ų, and orange crystals of 2 are monoclinic, space group P2₁/n, with a = 21.467(4) Å, b = 23.146(5) Å, c = 24.069(5) Å, β = 101.76(3)° and V = 11708(4) ų. They are both constructed by Mo^V dimers ({Mo₂O₄(O_P)₄(HCOO)} in 1 , {Mo₂O₄(O_P)₄(CH₃COO)} and {Mo₂O₄(O_P)₄(H₂O)₂} in 2 ) and pyrophosphoric groups. Their structures can be described as two interconnected nonequivalent wheels which are approximately perpendicular, delimiting a large cavity. The larger wheel contains six Mo^V dimers, while the smaller one has four dimers.     

Molybdänhalogenidcluster mit sechs terminalen Alkoholatliganden: (C18H36N2O6Na)2[Mo6Cl8(OCH3)6] · 6CH3OH und (C18H36N2O6Na2)2[Mo6Cl8(OC6H5)6]

Molybdenum(II) Halide Clusters with six Alcoholate Ligands: (C₁₈H₃₆N₂O₆Na)₂[Mo₆Cl₈(OCH₃)₆] · 6CH₃OH and (C₁₈H₃₆N₂O₆Na)₂[Mo₆Cl₈(OC₆H₅)₆] . The reaction of Na₂[Mo₆Cl₈(OCH₃)₆] and 2,2,2-crypt yields (C₁₈H₃₆N₂O₆Na)₂[Mo₆Cl₈(OCH₃)₆] · 6 CH₃OH ( 1 ), which is converted to (C₁₈H₃₆N₂O₆Na)₂[Mo₆Cl₈(OC₆H₅)₆] ( 2 ) by metathesis with phenol. According to single crystal structure determinations ( 1 : P3 1c, a=14.613(3) Å, c=21.036(8) Å; 2 : P3 1c, a=15.624(1) Å, c=19.671(2) Å) the compounds contain anionic clusters [Mo₆Cl₈ⁱ(OR^a)₆]^2? ( 1 : d(Mo—Mo) 2.608(1) Å to 2.611(1) Å, d(Mo—Cl) 2.489(1) Å to 2.503(1) Å, d(Mo—O) 2.046(4) Å; 2 : d(Mo—Mo) 2.602(3) Å to 2.608(3) Å, d(Mo—Cl) 2.471(5) Å to 2.4992(5) Å, d(Mo—O) 2.091(14) Å). Electronic interactions of the halide cluster and the phenolate ligands in [Mo₆Cl₈(OC₆H₅)₆]^2? is investigated by means of UV/VIS spectroscopy and EHMO calculations.     

New supramolecular adducts of chloroaquacomplexes [M3(μ3-S)S3?xSexCly(H2O)9?y](4?y)+ (M = Mo, W) with cucurbit[6]uril

New supramolecular adducts of cucurbit[6]uril with triangular cluster chloroaquacomplexes of Mo and W with mixed sulfido-selenido bridging ligands, {[W₃S₃Se(H₂O)₇Cl₂]₂(C₃₆H₃₆N₂₄O₁₂)}Cl₂·15H₂O (1), {[W₃S_1.5Se_2.5Cl_1.5(H₂O)_7.5]₂(C₃₆H₃₆N₂₄O₁₂)}Cl₅·18.5H₂O (2), and {[Mo₃SSe₃(H₂O)_7.5Cl_1.5]₂× (C₃₆H₃₆N₂₄O₁₂)}C_l5·11H₂O (3) are obtained treating the mixture of products in Mo-S-Se-Br and W-S-Se-Br systems, isolated, and structurally characterized. In all compounds, the supramolecular structure is based on hydrogen bonded associates of cucurbit[6]uril molecule with two cluster cations.     

Hydrothermal synthesis and structural characterization of two new reduced phosphomolybdates based on an organoamine template and copper ion

Two new compounds, (H₂en)₃(H₂enMe)₄(H₃O){Cu^I[Mo^V ₆O₁₂(OH)₃(HPO₄)(PO₄)₃]₂}?·?6H₂O (1) and (H₂enMe)₄{Cu^ICu^II[Mo^V ₆O₁₂(OH)₃(PO₄)(HPO₄)₂(H₂PO₄)]₂}?·?3H₂O (2), were hydrothermally synthesized and characterized by elemental analysis, IR, TGA, and single-crystal X-ray diffraction analysis. Crystallographic analysis reveals that 1 is constructed from cluster anions {Cu^I[Mo^V ₆O₁₂(OH)₃(HPO₄)(PO₄)₃]₂}^15?, protonated organic amines, and water molecules. Each cluster is bridged through hydrogen bonds to form a 3-D supermolecular structure. For 2, {Cu^I[Mo^V ₆O₁₂(OH)₃(PO₄)(HPO₄)₂(H₂PO₄)]₂}^11? are connected by Cu^II cations to form an infinite chain. The formation of 1 and 2 reveals that organoamines influence the structures of the crystals.     

Tetranuclear Manganese Complex Incorporating 2‐Pyridyloximate Ligand: Synthesis,Crystal Structure and Magnetic Property

A tetranuclear manganese complex of the composition {Mn₄[(Py)C(Ph)NO]₄(CH₃CH₂OH)₃(CH₃CH₂O)Cl₃}·2H₂O ( 1 ) was synthesized by solvothermal reaction, and characterized by X‐ray single crystal diffraction, IR spectroscopy, and elemental analysis. X‐ray analysis revealed that complex 1 contains a [Mn₄(NO)₄]⁴⁺ core with three Mn^II atoms displaying distorted octahedral arrangements and one Mn^II ion exhibiting a trigonal bipyramidal arrangement. Low‐temperature magnetic susceptibility measurement for the solid sample of 1 revealed antiferromagnetic Mn^II ··· Mn^II interactions.     

Study of the stability of solid polyoxometalate Mo72Fe30 with a buckyball structure

Samples of polyoxometalate Mo₇₂Fe₃₀: [Mo₇₂Fe₃₀O₂₅₂(CH₃COO)₁₂{Mo₂O₇(H₂O)}₂ {H₂Mo₂O₈(H₂O)}(H₂O)₉₁] · ??150H₂O with a buckyball structure, which can be both crystalline and amorphous, were synthesized. It was shown that such samples can be studied by neutron diffraction. The stability of Mo₇₂Fe₃₀ to heating and UV light exposure (in poly(vinyl alcohol) and polyvinylpyrrolidone films) was studied by IR, EPR, and electronic absorption spectroscopy; thermal analysis; and mass spectrometry. Mo₇₂Fe₃₀ was found to be less stable to heating and irradiation in a poly(vinyl alcohol) film as compared with the related polyoxometallate Mo₁₃₂ free of iron. The sorption properties of Mo₇₂Fe₃₀ to organic vapors and its stability under sorption conditions were studied. It was demonstrated that, in addition to sorption, organic substances cause the destruction of buckyballs.     

A Novel Three-Dimensional Network Isophthalato-Bridged Lanthanide Complex: {Ln[C6H4(COO−)2-1,3](CH3COO−)(H2O)2}·H2O

The three-dimensional network of lanthanide (III) complexes with isophthalato (IPT) ligand, (Eu[C₆H₄(COO^?)₂-1,3](CH₃COO^?)(H₂O)₂}·H₂O 1 and {Sm[C₆H₄(COO^?)₂-1,3](CH₃COO^?) (H₂O)₂} H₂O 2, has been prepared by the hydro(solvo)thermal reaction of Eu(C1O₄)₃·6H₂O or Sm(C1O₄)₃·6H₂O, 1,3-dicyanobenzene and acetic acid in the presence of ethanol and H₂O. In the reaction, 1,3-dicyanobenzene was hydrolyzed to give IPT ligand. Single crystal x-ray analysis revealed that crystals 1 and 2 are isomorphous with the isostructural {M[C₆H₄(COO^?)₂-1,3](CH₃COO^?)(H₂O)₂}·H₂O unit. In 1 and 2, IPT acts as a bridging ligand to connect three adjacent metal atoms, forming a network like an undulating sheet paralleling the bc plane. The carboxylate from acetate bridges two adjacent metal atoms in a tridentate mode between the different sheets to extend the structure into a three-dimensional network.     

Chemical Adaptability: The Integration of Different Kinds of Matter into Giant Molecular Metal Oxides

Unique properties of the two giant wheel‐shaped molybdenum‐oxides of the type {Mo₁₅₄}≡[{Mo₂}{Mo₈}{Mo₁}]₁₄ ( 1 ) and {Mo₁₇₆}≡[{Mo₂}{Mo₈}{Mo₁}]₁₆ ( 2 ) that have the same building blocks either 14 or 16 times, respectively, are considered and show a “chemical adaptability” as a new phenomenon regarding the integration of a large number of appropriate cations and anions, for example, in form of the large “salt‐like” {M(SO₄)}₁₆ rings (M=K⁺, NH₄⁺), while the two resulting {Mo₁₄₆ (K(SO₄))₁₆} ( 3 ) and {Mo₁₄₆ (NH₄(SO₄))₁₆} ( 4 ) type hybrid compounds have the same shape as the parent ring structures. The chemical adaptability, which also allows the integration of anions and cations even at the same positions in the {Mo₄O₆}‐type units of 1 and 2 , is caused by easy changes in constitution by reorganisation and simultaneous release of (some) building blocks (one example: two opposite orientations of the same functional groups, that is, of H₂O{Mo?O} ( I ) and O?{Mo(H₂O)} ( II ) are possible). Whereas Cu²⁺ in [(H₄Cu^II₅)Mo^V₂₈Mo^VI₁₁₄O₄₃₂(H₂O)₅₈]^26? ( 5 a ) is simply coordinated to two parent O^2? ions of {Mo₄O₆} and to two fragments of type II , the SO₄^2? integration in 3 and 4 occurs through the substitution of two oxo ligands of {Mo₄O₆} as well as two H₂O ligands of fragment I . Complexes 3 and now 4 were characterised by different physical methods, for example, solutions of 4 in DMSO with sophisticated NMR spectroscopy (EXSY, DOSY and HSQC). The NH₄⁺ ions integrated in the cluster anion of 4 “communicate” with those in solution in the sense that the related H⁺ ion exchange is in equilibrium. The important message: the reported “chemical adaptability” has its formal counterpart in solutions of “molybdates”, which can form unique dynamic libraries containing constituents/building blocks that may form and break reversibly and can lead to the isolation of a variety of giant clusters with unusual properties.     

Neue Oxooxalatokomplexe des Molybdän(VI)

New Osooxalatocomplexes of Molybdenum (VI) The preparation of the compounds Cs₂[Mo₂O₅F₂(C₂O₄)] · H₂O and Cs₂[Mo₂O₄Cl₄(C₂O₄)] · 2 H₂O is reported. The structure of the complex anions, which are containing quadridentated oxalate ligands, is derived from their vibration spectra. The compounds [NR₄]₂[Mo₂O₄F₄(C₂O₄)] with R = CH₃ and C₂H₅ are examined for comparison.