Synthesis and Electrochemical Properties of a New 1D Organic–Inorganic Hybrid Compound Based on Keggin-Type Heteropolyanions and Isopolyanions Decorated by Transition Metal Fragments

A new chain-like organic–inorganic hybrid compound composed of the heteropolyanions and isopolyanions, [{Cu^II(2,2′-bpy)}₆(Mo^VMo^VI ₅O₂₂)] [PMo^VI ₁₂O₄₀] · H₂O 1 (bpy = 2,2′-bipyridine) has been hydrothermally synthesized and characterized by elemental analysis, IR spectroscopy, TG analysis, XPS spectrum and single-crystal X-ray diffraction. Crystal data for compound 1: monoclinic, space group P _2(1)/c, a = 13.9382(14) Å, b = 20.0300(19) Å, c = 17.1757(17) Å, β = 94.054(2)°, V = 4783.2(8) ų, Z = 2. The Keggin-heteropolyanion [PMo₁₂O₄₀]^3? and the Cu-supporting isopolyanion [{Cu(2,2′-bpy)}₆(Mo₆O₂₂)]³⁺ building units are bridged through the O–Cu–O bridges into 1D infinite chain. Note that, the [{Cu(2,2′-bpy)}₆(Mo₆O₂₂)]³⁺ unit, which contains a rarely reported isopolyanion [Mo₆O₂₂]^9? decorated by six [Cu(2,2′-bpy)] fragments. Furthermore, the electrochemical behavior of a 1-modified carbon paste electrode (1-CPE) and its electrocatalytic reduction of nitrite were investigated.     

The molybdenum-molybdenum triple bond—XVII. Syntheses,spectroscopic and structural characterizations of Mo4F4(O—t-Bu)8 and Mo2F2(O—t-Bu)4(PMe3)2 (MoMo)

Hydrocarbon solutions of Mo₂(O—t-Bu)₆ and PF₃ (2 equiv) yield Mo₄F₄(O—t-Bu)₈, I, and PF₂(O—t-Bu). Compound I contains a bisphenoid of molybdenum atoms with two short MoMo distances, 2.26 Å, and four long MoMo distances, 3.75 Å, corresponding to localized MoMo triple bonding and non-bonding distances, respectively. The tetranuclear compound may be viewed as a dimer, [Mo₂(μ₂-F)₂(O-t-Bu)₄]₂, and addition of PMe₃ to hydrocarbon solutions of I yields Mo₂F₂(O—t-Bu)₄(PMe₃)₂, II, which contains an unbridged MoMo triple bond of distance 2.27 Å. Each molybdenum atom is coordinated to two oxygen atoms, one fluorine atom and the phosphorus atom of the PMe₃ ligand in a roughly square planar manner. The overall central Mo₂O₄F₂P₂ skeleton has C₂ symmetry and NMR studies (¹H, ¹⁹F and ³¹P) are consistent with the maintenance of this type of structure in solution. Infrared and electronic absorption spectral data are reported. These are the first compounds containing fluorine ligands attached to the (MoMo)⁶⁺ unit.     

Synthesis,crystal structure of a new tetranuclear Ni<Stack><Subscript>2</Subscript><Superscript>II</Superscript></Stack>Cu<Stack><Subscript>2</Subscript><Superscript>II</Superscript></Stack> complex containing a macrocyclic ligand

The first inorg/organic hybrid complex incorporating the macrocyclic oxamide, of formula [(NiL)₂Cu₂(μ-NSC)₂(NSC)₂] (1), (NiL, H₂L = 2, 3-dioxo-5,6,14,15-dibenzo-1,4,8,12-tetraazacyclo-pentadeca-7,13-dien), have been synthesized and structurally characterized. The crystals crystallize in the triclinic system, space group P-1, for (1) a = 8.319(3) Å, b = 10.434(4) Å, c = 14.166(5) Å, a = 107.030(5)°, β  =  91.257(5)°, γ = 107.623(5)°. The complex involved both bridging N, S-ligand, and oxamide ligand, C–H?S interactions and NCS → Ni weak coordination interactions making the complex superamolecular.     

Direct synthesis from MoCl3(THF)3 of a complex containing the [Mo3S4]4+ core

By reaction of MoCl₃(THF)₃ with NaSH in tetrahydrofuran, followed by addition of Me₂PCH₂CH₂PMe₂(dmpe), then chromatography on silica-gel, and finally addition of NH₄PF₆, the compound [Mo₃S₄Cl₃(dmpe)₃]PF₆·CH₃OH was prepared in moderate yield. X-ray crystallography showed the presence of a chiral cation based on a Mo₃S₄ core with chelating dmpe units arranged like the blades of a ship's screw. The three Cl atoms fill the remaining octahedral sites on each metal atom. The compound crystallizes in space group R3c with (hexagonal) cell dimensions of a = 15.310(7) Å, c = 30.640(3) Å and Z = 6. The [Mo₃S₄Cl₃(dmpe)₃]⁺ ion and the PF₆⁻ ion each have crystallographic C₃ symmetry. The principal distances and theirs esds are: MoMo, 2.766(4) Å; Mo(μ₃-S), 2.360(9) Å; Mo(μ₂-S), 2.290(7) Å, 2.336(7) Å; MoP, 2.534(8) Å, 2.605(8) Å; MoCl, 2.473(7) Å; PF, 1.56(2) Å, 1.64(3) Å. The correct enantiomer was obtained by refining both to convergence, which give R = 0.059 and R = 0.064.     

Synthesis and characterization of the organoimidopolyoxomolybdates [ n -Bu4N]2[Mo6O17(≡NAr)2] (Ar = 2-ethyl-6-methylphenyl and 2-isopropyl-6-methylphenyl)

Two new bifunctionalized arylimido derivatives of hexamolybdate, [n-Bu₄N]₂[Mo₆O₁₇(C₆H₃N-2-C₂H₅-6-CH₃)₂] (1) and [n-Bu₄N]₂[Mo₆O₁₇(C₆H₃N-2-CH(CH₃)₂-6-CH₃)₂]?·?H₂O (2), in which the two organoimido groups are covalently bonded to hexamolybdate at the cis positions, were synthesized by self-assembled metathesis of α-octamolybdate and organoimido ligands with N,N′-dicyclohexylcarbodiimide as dehydration agent, and characterized by elemental analysis, ¹H NMR, IR and electronic spectroscopy, and X-ray diffraction analysis. Both derivatives have short Mo–N bond distances [Mo(1)–N(1), 1.740(3)?Å; Mo(2)–N(2), 1.739(3)?Å for 1 and Mo(1)–N(1), 1.734(3)?Å; Mo(2)–N(2), 1.741(3)?Å for 2] and form dimers via π–π stacking in the crystalline state.     

Self-Assembly,Crystal Structure and Analysis of Intermolecular Interactions of the Supramolecular Compound Based on Hexamolybdochromate(III), Sulfate and Piperazine

A new supramolecular compound based on Anderson-B hexamolybdochromate, (H₂Pz)₃[Cr(OH)₆Mo₆O₁₈H](SO₄)₂·12H₂O (1) (Pz = piperazine) was synthesized and characterized by elemental analysis, IR spectroscopy, and single-crystal X-ray diffraction (Mo Kα). The compound crystallizes in monoclinic system, P21/c space group with a = 13.5708(6) Å, b = 17.3711(8) Å, c = 22.2387(9) Å, β = 110.631(2)°; V = 4906.3(4) Å³, Z = 4, D _c  = 2.290 g/cm³, F(000) = 3364.0; μ = 1.905, S = 1.033. The final R = 0.0398 and wR = 0.0971. The H₂pz²⁺ ions and sulfate anions in 1 are arranged through hydrogen bonds into a hexagonal network in [202] plane and hexamolybdochromates anions (CrMo₆) fill in the hexagonal vacancies. The networks stack in such a way that each anion links two sulfate ions from adjacent networks via hydrogen bonds with short (CrMo₆)O···OSO₃ distances of 2.637–2.697 Å. A lot of hydrogen bonds are formed between water molecules, sulfate, H₂pz²⁺ ions and CrMo₆ anions, which are the dominating force constructing the supramolecular structure. Hirshfeld surface analysis of 1 gives us the details of intermolecular interactions in the crystals of 1 in a visual manner and shows that the CrMo₆ anion acts as a stronger hydrogen bond donor than as an acceptor.     

From Cs<Subscript>2</Subscript>Mo<Subscript>6</Subscript>Cl<Subscript>14</Subscript> to Cs<Subscript>2</Subscript>Mo<Subscript>6</Subscript>Cl<Subscript>14</Subscript>·H<Subscript>2</Subscript>O and Vice Versa: Crystal Chemistry Investigations

We report here the synthesis, the crystal structure and the luminescent properties of the new cluster compounds Cs₂Mo₆Cl₁₄·H₂O and Cs₂Mo₆Br₁₄·H₂O. Single-crystal X-ray diffraction performed on Cs₂Mo₆Cl₁₄·H₂O indicates that the compound crystallizes in the monoclinic space group C2/c with refined cell parameters a = 19.578 Å, b = 15.151 Å, c = 9.347 Å, and β = 115.64°. The structure can be described from discrete \(\left[ {{\text{Mo}}_{ 6} {\text{Cl}}^{\text{i}}_{ 8} {\text{Cl}}^{\text{a}}_{ 6} } \right]^{ 2- }\) anionic cluster units arranged in a “A–A’–A–A’” pseudo prismatic stacking parallel to (b, c) plane with both Cs⁺ cations and water molecules located between the layers. Moreover, the centric character of the trigonal structure of Cs₂Mo₆Cl₁₄ was also studied by combination of single-crystal X-ray diffraction and both X-ray and neutron powder diffraction. The results suggest an important influence of the sample preparation on the symmetry of the crystal structure. The crystal structure relationship between the \(\left[ {{\text{Mo}}_{ 6} {\text{Cl}}^{\text{i}}_{ 8} {\text{Cl}}^{\text{a}}_{ 6} } \right]^{ 2- }\) anionic cluster unit arrangements in Cs₂Mo₆Cl₁₄ and Cs₂Mo₆Cl₁₄·H₂O is discussed. Finally, the characterization of the luminescent properties of Cs₂Mo₆X₁₄ and Cs₂Mo₆X₁₄·H₂O (X = Cl, Br) indicates that emission profile is comparable regardless existence of water molecule in the crystal structure.     

Synthesis,Crystal Structure,and Bonding of (PCl4)2[Mo2Cl10], the First Compound in Mo–P–Cl System

An ampule reaction between Mo and PCl₅ at 200 °C yielded (PCl₄)₂[Mo₂Cl₁₀], the first ternary compound in Mo–P–Cl system. Single crystal X-ray diffraction gave a triclinic unit cell: a = 6.870(1), b = 8.892(2), c = 9.423(2) Å, α = 100.24(2), β = 95.55(2), γ = 96.12(2)° (V = 559.3(2) ų, Z = 1, sp. gr. P1, wR₂ = 0.0575 and R₁ = 0.0279. The ionic compound is built from edge sharing bioctahedra [Mo₂Cl₁₀]^2– and two tetrahedra PCl₄⁺. The averaged Mo–Cl_b distance, 2.503(1) Å, is longer than the Mo–Cl_t distance, 2.33(2) Å. The Mo … Mo distance, 3.77 Å, indicates the absence of a direct Mo–Mo interaction. Semiempirical and ab initio calculations showed the possibility for [Mo₂Cl₁₀]^2– to exist with long and short Mo to Mo distances, the letter corresponding to the Mo–Mo bond.     

Coordination Chemistry of the Magic Inorganic Building Block {Fe<Superscript>II</Superscript>[Mo<Subscript>6</Subscript>P<Subscript>4</Subscript>O<Subscript>31</Subscript>]<Subscript>2</Subscript>}: Hydrothermal Synthesis and Crystal Structure of a New Reduced Ferrous Molybdophosphate

A new reduced ferrous molybdophosphate composite solid of the formula, [(C₁₀H₁₄N₂)H]₄[Fe^II ₁₀Mo^V ₂₄(H₂PO₄)₄(HPO₄)₁₂(PO₄)₄(H₂O)₁₆(OH)₁₆O₄₄]·12H₂O, has been synthesized from a reaction mixture of MoO₃, FeSO₄·7H₂O, C₂H₂O₄·2H₂O, nicotine, H₃PO₄, and H₂O under hydrothermal conditions. The crystal data: monoclinic, space group C2/m, a = 24.4349(124), b = 12.9935(66), c = 14.7281(74) Å, β = 104.87(1) Å, V = 4520(4) Å³, Z = 2, R ₁  = 0.0874, wR ₂  = 0.2179. The structure is built from the building blocks of the formula, {Fe^II[Mo₆P₄O₃₁]₂}, consisting of a network of MO₆ (M = Fe, Mo) octahedral and PO₄ tetrahedral linked through their vertices. The connectivity of the building blocks with two pairs of face-sharing dinuclear Fe(II) clusters of the formula of [Fe^II ₂(H₂O)₄O₅] on which a phosphate group is hanging gives rise to one-dimensional chains with eight-membered apertures. The remarkable hydrogen bonded interactions between the chains form a unique and interesting framework with three-dimensional intersecting tunnels where the protonated nicotine molecules as structuring templates and crystallization water molecules are situated.     

<Emphasis Type="Italic">cis</Emphasis>-Dioxomolybdenum(VI) complexes of sterically encumbered phenol-based tetradentate N<Subscript>2</Subscript>O<Subscript>2</Subscript> ligands: Structural,spectroscopic, and electrochemical studies

Two cis-dioxomolybdenum(VI) complexes [MoO₂L] (L: L ¹, 2 and L: L ², 3) in a phenol-based sterically encumbered N₂O₂ ligand environment have been synthesized, and their crystallographic characterizations are reported. The orange crystals of 2 are monoclinic, space group P2₁/a with unit cell dimensions as a=16.2407(17) Å, b=7.2857(8) Å, c=18.400(2) Å, β=98.002(9)°, Z=4, and d _cal=1.486 g cm^?3. The light orange crystals of 3, however, are orthorhombic, space group, Pbcn, with unit cell dimensions a=8.3110(12) Å, b=12.637(3) Å, c=34.673(5) Å, Z=4, and d _cal=1.187 g cm^?3. The structures were refined by a full-matrix least-squares procedure on F ² to a final R=0.046 (0.055 for 3) using 4944 (3677) all independent data. In both the cases, the Mo atom exists in a distorted octahedral geometry defined by a N₂O₄ donor set, which features a cis-Mo(–O)₂ and a trans-Mo(OPh)₂ arrangement. Compound 2 undergoes a quasireversible one-electron reduction at ?1.3 V vs Ag/AgCl reference due to Mo^VIO₂/Mo^VO₂ electron transfer and thus providing a rare example of steric solution to the comproportionation–dimerization problem encountered frequently in the development of valid biomimetic models for the active sites of oxomolybdenum enzymes.     

A New Three-Dimensional Framework Based on K<Subscript>2</Subscript>Zr<Subscript>3</Subscript>-Substituted Sandwich-Type Polyoxometalate Clusters and K–O Chains

A new Zr-substituted sandwich-type polyoxometalate, H₈K₃[Zr₃K₂(μ₃-O)₂(μ₂-OH)(H₂O)₂(A-α-PW₉O₃₄)₂]·2Cl^?·7H₂O (1), has been made under hydrothermal conditions. 1 was characterized by IR spectrum, thermogravimetric analysis, powder X-ray diffraction and single-crystal X-ray diffraction, respectively. Crystal data for 1: tetragonal space group P4₂2₁2, a = 24.0096(3), b = 24.0096(3), c = 14.7416(3) Å, V = 8498.0(2) Å³ and Z = 4. Single crystal X-ray structure analysis reveals that 1 exhibits a three-dimensional framework structure based on Zr₃K₂-substituted sandwich-type polyanions [Zr₃K₂(μ₃-O)₂(μ₂-OH)(H₂O)₂(PW₉O₃₄)₂]^9? linked by K–O chains. UV–Vis spectrum indicates that 1 is a wide-gap semiconductor. In addition, the SHG of 1 was also investigated.     

Synthesis and Structure of the Tetrameric [Cp*V(μ‐F)2]4 (Cp* = C5Me5); Preparation of the Imido Molybdenum Fluoride [(2,6‐i‐Pr2C6H3N)2MoF2] · THF and the Structural Investigation of [(2,6‐i‐Pr2C6H3N)6Mo4(μ3‐F)2Me2(μ‐O)4]

Treating [Cp*V(μ‐Cl)₂]₃ (Cp* = C₅Me₅) and [(2,6‐i‐Pr₂C₆H₃N)₂MoMe₂], respectively, with Me₃SnF afforded the title compounds [Cp*V(μ‐F)₂]₄ ( 1 ) and [(2,6‐i‐Pr₂C₆H₃N)₂MoF₂] · THF ( 2 ). 1 has a tetrameric structure, in which four V atoms can be regarded as being arranged at the vertices of a distorted tetrahedron, with four long edges bridged by one F atom and each of the other two short edges bridged by two F atoms with a mean V–F bond length of 2.00 Å. A hydrolyzed product of 2 , [(2,6‐i‐Pr₂C₆H₃N)₆Mo₄(μ₃‐F)₂Me₂(μ‐O)₄] ( 3 ) was characterized by elemental analyses and X‐ray single crystal study. The X‐ray diffraction analysis reveals that 3 has a unique tetranuclear structure, containing two five and two six coordinated Mo atoms connecting each other by four μ‐O and two μ₃‐F atoms. The geometries around the two Mo atoms can be described having distorted trigonal bipyramidal and distorted octahedral coordination spheres, respectively. The Mo–(μ‐O) bond lengths are 1.813 Å (average) for five coordinated Mo atoms and 2.030 Å (average) for those of six coordinated, respectively, indicating an additional π bonding between five coordinated Mo atoms and the μ‐O atoms. The Mo–(μ₃‐F) distances range from 2.291 to 2.352 Å.     

A New Sandwich Polyoxometalate Constructed from a Zn<Stack><Subscript>6</Subscript><Superscript>12+</Superscript></Stack> Hexagon Cluster Sandwiched by Two B-α-[BiW<Subscript>9</Subscript>O<Subscript>33</Subscript>]<Superscript>9−</Superscript>

A new sandwich polyoxometalate Na₄Zn₂[Zn₂(H₂O)₁₀(ZnCl)₆(B-α- BiW₉O₃₃)₂] · 40.5H₂O (1) has been obtained in aqueous solution and characterized by IR, UV, element analysis, TG and single-crystal X-ray analysis. Polyoxoanion 1 is composed of a Zn ₆ ¹²⁺ hexagon sandwiched by two [BiW₉O₃₃]^9? units, which is firstly observed in tungstobismutate. The crystal data for compound 1: Triclinic, space group P–1, a = 15.426(3) Å, b = 15.467(3) Å, c = 15.526(3) Å, α = 74.24(3)°, β = 64.37(3)°, γ = 60.73(3)°, V = 2905.3(1) ų, Z = 1.     

Synthesis and structure of an open-type trinuclear molybdenum cluster compound[Mo_3(μ_3-S)(μ-S)_2-(μ-OAc)(S_2CNC_4H_8)_3(O)_2]·0.5CH_2Cl_2·2H_2O

The title compound was prepared by the reaction of Mo_3S_4(dtp)_4(H_2O)[ctp=S_2P(OEt)_2]with NaOAc·3H_2O and C_4H_8NCS_2NH_4.Crystallographic data:[Mo_3(μ_3-S)(μ-S)_2(μ-OAc)-(S_2CNC_4H_8)_3(O)_2]·0.5CH_2CI_2·2H_2O,Mr=980.18,triclinic,space group P,α=12.360(3),b=16.653(6),c=9.206(2)A,α=101.97(2),β=108.32(2),γ=86.14(3)°.V=1759.6(9)A~3,Z=2,Dc=1.85 g/cm~3,F(000)=962,μ(Mo K_α)=16.53 cm~(-1).Final R=0.044 for 4301 reflections with I≥3σ(I).This compoundmay be regarded as a mixed-valent trinuclear molybdenum cluster{Mo_2(V)Mo(Ⅳ)(μ_3-S)(μ-S)_2-(μ-OAc)(S_2CNC_4H_8)_3(O)_2}.The Mo-Mo distances are 2.783(1),2.833(1)and 3.374(2)A in the Mo_3non-equilateral triangle and there exist only two Mo-Mo bonds.The cluster was obtained by oxi-dation and ligand substitution of{Mo_3(μ_3-S)(μ-S)_3[μ-S_2P(OEt_2)][S_2P(OEt)_2]_3(H_2O)}.     

Multiply Bonded Dimolybdenum Cation Immobilized in Mesoporous Silica: XAFS Analysis and Catalytic Activity in Cyclopentadiene Polymerization

MCM‐41 derivatized with the cis‐[Mo₂(μ‐O₂CMe)₂(MeCN)₆]²⁺ cation has been characterized by means of XAFS spectroscopy and shown to be active as an initiator for the cationic polymerization of methylcyclopentadiene. The Mo‐Mo quadruple bond is not disrupted during the fixation on the surface.     

Synthesis,crystal structures,and antimicrobial activity of a pair of isostructural dinuclear copper(II) complexes derived from 4-nitro-2-[(2-diethylaminoethylimino)methyl]phenol

A pair of isostructural azido- or thiocyanato-bridged centrosymmetric dinuclear copper(II) complexes, [Cu₂L₂(μ_1,3-N₃)₂] (1) and [Cu₂L₂(μ_1,3-NCS)₂] (2), derived from the Schiff base ligand 4-nitro-2-[(2-diethylaminoethylimino)methyl]phenol (HL), have been synthesized and characterized by elemental analysis, IR spectra and single crystal X-ray diffraction. Each Cu atom in the complexes is five-coordinate in a square pyramidal geometry by one O and two N atoms of one Schiff base ligand, and by two terminal donor atoms from two bridging azide or thiocyanate ligands. Both the azide and thiocyanate ligands adopt end-to-end bridging mode in the complexes. The distance between the two copper atoms is 5.205(2) Å for (1) and 5.515(2) Å for (2). The antimicrobial activity of the complexes has been tested.     

In Situ: 2-D Inorganic Layer Lead-MOF Built from [(<Emphasis Type="Italic">μ</Emphasis><Subscript>4</Subscript>-O)Pb<Subscript>4</Subscript>] Core

In situ lead-MOF derived from 2-Methyl-3-acetylnaphtho[2,3-b]furan-4,9-dione (MAFD), [Pb₇O₂(OH)₂(1,2-BDC)₄(H₂O)] 1, 1,2-BDC = C₆H₄(COOH)₂, phthalic acid, has been synthesized and characterized by elemental analysis, IR, TG-DTA, powder X-ray diffraction (XRD) and single crystal X-ray diffraction. Compound 1 possesses 2-D inorganic layer structure built from rare tetranuclear unit [(μ ₄-O)Pb₄]. In 1, both crystallographic distinct Pb(1) and Pb(4) ions adopt six-coordination geometry, and the other two crystallographic distinct Pb(2) and Pb(3) ions display eight-coordination geometry under the condition of Pb–O bond length extended to 3.10 Å. A 3-D supramolecular network is also formed by hydrogen bonds (C–H···O). Result of photoluminescence measurement indicates an emission band at 385 nm (λ _excitation = 209 nm).     

Di‐μ‐methoxy‐bis[(η5‐cyclopentadienyl)(nitrosyl‐κN)(trimethylsilylmethyl)molybdenum(II)]

The title complex, [Mo₂(C₅H₅)₂(CH₃O)₂(C₄H₁₁Si)₂(NO)₂], is formed in high yield by treating [CpMo(NO)(CH₂SiMe₃)₂] (Cp is cyclo­penta­dienyl) with methanol. The nitro­syl ligands are nearly linear [O—N—Mo 170.1 (4) and 170.1 (5)°], with short Mo—N bonds [1.769 (4) and 1.776 (4) Å] and long N—O bonds [1.216 (5) and 1.201 (4) Å]. The central four‐membered Mo₂O₂ ring exhibits an average Mo—O bond length of 2.15 Å.     

Crystal Structure,Spectroscopic and Magnetic Properties of <Emphasis Type="Italic">Trans</Emphasis>-Difluoro-(1,4,8,11-Tetraazaundecane)Chromium(III) Aquatrichlorozincate

A new complex salt trans-[CrF₂(2,3,2-tet)][ZnCl₃(H₂O)] (2,3,2-tet is 1,4,8,11-tetraazaundecane), is prepared and its structure is determined by single crystal X-ray diffraction using synchrotron data at 100 K. The complex crystallizes in the space group P2₁/c of the monoclinic system with two mononuclear formula units in a cell with dimensions a = 5.6360(11) Å, b = 17.120(3) Å, c = 17.020(3) Å, and β = 94.38(3)°. The chromium(III) ion is coordinated by four N atoms of the 2,3,2-tet ligand in the equatorial plane and two F atoms in a trans axial arrangement, displaying a slightly distorted octahedral geometry. The mean Cr–N(2,3,2-tet) and Cr–F bond distances are 2.0772(11) Å and 1.8930(8) Å, respectively. The crystal packing is stabilized by hydrogen bonding interactions between N–H groups of the 2,3,2-tet, O–H groups of the anion, the F atom, and the Cl atom of the anion. The FT-infrared, UV-visible spectra, and magnetic properties are also described.     

Experimental and theoretical evidence of aromatic behavior in heterobenzene-like molecules with metal-metal multiple bonds

Binding two quadruply bonded dimolybdenum units [Mo₂(DAniF)₃]⁺ (DAniF=N,N′‐di‐p‐anisylformamidinate) with two chalcogen atoms generated two molecules with a central core composed of a cyclic six‐membered [Mo₂]₂(μ‐EH)₂ species (E=S in 1 and O in 3 , and [Mo₂] is a quadruple‐bonded [Mo₂(formamidinate)₃] unit). Aerobic oxidation of 1 and 3 followed by concomitant deprotonation gave rise to the corresponding [Mo₂]₂(μ‐E)₂ compounds 2 and 4 . The latter show a striking coplanarity and near‐bond equalization of the Mo/E cluster. The oxidized species 2 and 4 are diamagnetic in the measured temperature range of 5 to 300 K, which is somewhat unexpected for molecules that have dimetal units with a σ²π⁴δ¹ electronic configuration. This suggests there are strong interactions between the dimolybdenum units through the E atoms. The large electronic delocalization of the δ electrons over the entire Mo/E core is supported by the exceptionally large potential separation for the two successive one‐electron reductions of the linked Mo₂⁵⁺ units from the oxidized species (ΔE_1/2=1.7 V for the sulfur analogue). This large electronic delocalization has an important effect on the NMR spectroscopic signals for the two sets of methine (N‐(CH)‐N) protons from the DAniF ligands. Those essentially parallel to the core, H_∥, and those essentially perpendicular to the core, H_⊥, exhibit downfield and upfield chemical shifts, respectively, that are separated by δ=1.32 ppm. The structural, electronic, magnetic, and chemical behaviors for 2 and 4 are consistent with aromaticity, with the [Mo₂E₂Mo₂] cores that resemble the prototypical benzene molecule. Theoretical studies, including DFT calculations, natural bond orbital (NBO) analyses, and gauge‐independent atomic orbital (GIAO) NMR spectroscopic calculations, are also consistent with the aromaticity of the [Mo₂]₂(μ‐E)₂ units being promoted by d_δ(Mo₂)–p_π(E) π conjugation. The cyclic π conjugation of the central moiety in 2 and 4 involves a total of six electrons with 2e from δ(Mo₂) and 4e from p_π(E) orbitals, thereby conforming to Hückel’s rule when electrons in the MOs with δ character are considered part of the delocalized system.