A Series of Octahedral First-Row Transition-Metal Ion Complexes

Article Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX

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A Series of Octahedral First-Row Transition-Metal Ion Complexes Templated by Wells−Dawson Polyoxometalates: Synthesis, Crystal Structure, Spectroscopic, and Thermal Characterizations, and Electrochemical Properties Fatma Dhifallah,*,† Mohamed Salah Belkhiria,‡ Loic Parent,§ Nathalie Leclerc,§ and Emmanuel Cadot§

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†

Faculty of Sciences, Laboratoire de Physico-Chimie des Matériaux, University of Monastir, Avenue de l’environnement, 5019 Monastir, Tunisia ‡ School of Sciences and Technology, University of Sousse, Rue Lamine Abassi, 4011 Hammam Sousse, Tunisia § Institut Lavoisier de Versailles, University of Versailles Saint-Quentin-en-Yvelines, UMR 8180, 45 avenue des Etats-Unis, 78035 Versailles Cedex, France S Supporting Information *

ABSTRACT: Three Wells−Dawson polyoxotungstates-based hybrid compounds of general formula [M(C3H7NO)6][{M(C3H7NO)5}2(μ-P2W18O62)]· nC3H7NO·n′H2O [with M = MnII (1), FeII (2), CoII (3) ; n = 2, 2, 3 and n′ = 0, 0, 1, respectively] were synthesized at room temperature by a facile method and characterized by IR and 1H and 31P NMR spectroscopy studies, thermogravimetric analysis−differential scanning calorimetry thermal analyses, UV−vis, X-ray diffraction (XRD) powder and single-crystal XRD analyses, and cyclic voltammetry studies. From the X-ray study, it was established that the metal (M = Mn, Fe, Co) is located on an inversion center, being octahedrally coordinated to six dimethylformamide (DMF) molecules to form the complex cation [M(dmf)6]2+. Also, in the dinuclear complex anion [{M(dmf)5}2(μ-P2W18O62)]2−, the M atoms are coordinated to five DMF molecules through the oxygen atoms, while the sixth coordination site is occupied by a terminal oxygen atom of the Wells−Dawson anion [P2W18O62]6− that plays the role of a bridging ligand. The crystal components are connected through numerous weak C−H···O hydrogen bonds to construct a three-dimensional network. The UV−vis shows the two characteristic absorption bands for the three compounds at 266−268 and 297 nm. These two strong bands are attributed to the charge-transfer absorption band of Ot-W and Ob/c-W, respectively. Cyclic voltammetry study of compounds (1), (2), and (3) reveals at least two reduction reversible peaks ascribed to a Wells−Dawson cluster.

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magnetic properties, the organic−inorganic hybrid materials7,8 have captured considerable attention and were widely applied in many fields such as material science, catalysis, and medicine. On the basis of coordination capability of the surface oxygen atoms (bridging or terminal oxygen atoms) of POMs, novel complexes with discrete clusters, one-dimensional (1D), twodimensional (2D), or three-dimensional (3D) structures have been synthesized9−14 through metal coordination complexes being bound to the surface of POMs framework. Hence, the synthesis of novel organic−inorganic hybrid materials, based on Wells−Dawson clusters, requires choosing suitable transition metals and organic ligands, which can be considered very important for the successful of complexes formation. Of common solvents that have been used in organic and/or inorganic reactions, CH3CN, pyridine, dimethyl sulfoxide (DMSO), and dimethylformamide (DMF) may be

INTRODUCTION

Polyoxometalates (POMs) are molecularly defined as anionic metal−oxygen clusters of transition metals in their highest oxidation states (most commonly MoVI and WVI).1 In the Wells−Dawson-type POMs, the 18-metallo-2-phosphate polyanion [P2M18O62]6− (P2M18) is constituted by two subunits “PM9” related by a plane of symmetry perpendicular to a trigonal symmetry axis passing through phosphorus atoms.2,3 The two subunits PM9 are linked together by six oxygen atoms situated in the mirror plane. The most commonly encountered isomers of (P2M18) polyoxoanions are α isomer4 and the β isomer,5 which have D3h and C3v symmetry, respectively. Sasaki6 postulated that β isomer is derived from the α one by rotating a PM9 subunit by π/3. Over the past few decades, POMs have been considered as interesting building blocks for the construction of organic−inorganic hybrid materials because of their nanosize, abundant topologies, controllable shape, and high negative charges. Because of their unique properties, for example, redox, catalytic, photochemical, and © XXXX American Chemical Society

Received: May 9, 2018

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DOI: 10.1021/acs.inorgchem.8b01207 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry Table 1. Crystal Data and Refinement Parameters of (1), (2), and (3) empirical formula formula mass temperature [K] system space group a [Å] b [Å] c [Å] α [deg] β [deg] γ [deg] volume [Å3] Z μ (Mo Kα) (mm−1) ρcalcd (g·cm−3) θ range [deg] index ranges

parameters/restraints reflections collected/unique R1 [FO > 4σFO] WR2 GOF residual density [e/Å3]

complex 1

complex 2

complex 3

C54 H126 Mn3 N18 O80 P2 W18 5843.78 203 monoclinic C2/c 26.9702(5) 14.3845(2) 34.1762(7) 90 111.896(2) 90 12 302.3(4) 4 17.178 3.155 3.27 to 27.88 −35 ≤ h ≤ 35 −18 ≤ k ≤ 18 −44 ≤ l ≤ 44 804/7 110 388/14 565 0.0348 0.0715 1.116 2.044/−2.050

C54H126Fe3N18O80P2W18 5846.52 203(2) monoclinic C2/c 26.8005(3) 14.4004(2) 34.2726(3) 90 111.779(1) 90 12 283.0(2) 4 17.251 3.162 2.71 to 27.88 −35 ≤ h ≤ 32 0 ≤ k ≤ 18 0 ≤ l ≤ 45 756/202 63 963/14 509 0.0567 0.1364 0.873 4.159/−1.762

C57H133Co3N19O82P2W18 5944.85 298(2) monoclinic C2/c 26.8825(4) 14.4944(3) 34.3294(8) 90 111.811(1) 90 12 418.7(4) 4 17.108 3.180 2.42 to 27.10 −21 ≤ h ≤ 34 −16 ≤ k ≤ 18 −43 ≤ l ≤ 31 756/321 34 110/13 606 0.0563 0.1435 0.940 1.904/−2.455

R1 = ∑||Fo| − |Fc||/∑|Fo|. bwR2 = [∑w(Fo2 − Fc2)2/∑w(Fo2)2]1/2.

a

slight variations observed over successive runs are attributed to the uncertainty associated with the detection limit of our equipment (potentiostat, hardware, and software) rather than to the working electrode pretreatment or to possible variations in temperature. IR at High Temperature. This technique allowed us to study the stability of hybrid compounds at the heat. Infrared radiation emitted is analyzed by a Thermo Scientific spectrometer with high-resolution Fourier transform Nicolet iS10 FT-IR. Spectra were thus recorded for temperatures between 291 and 849 K at a rate of 4 °C. UV−Visible Absorption Measurements. The UV−visible spectra were recorded on a PerkinElmer Lambda 19 spectrophotometer. Matched 1.000 cm optical path quartz cuvettes were used. X-ray Powder Diffraction. The X-ray powder diffractogram were recorded at room temperature using a Siemens D5000 X-ray diffractometer. The typical recording conditions were 40 kV and 40 mA for Cu Kα (λ = 1.5418 Å), and the diffractogram was recorded in 2θ/θ mode, between 3° and 83° (3120 measurements) with a step size of 0.025° and a scan time of 52 min. The calculated pattern was produced using the Fullprof and WinPLOTR software programs.18−20 Thermal Behavior. A coupled differential scanning calorimetric (DSC) and thermogravimetric analyses (TGA) were done using a Mettler-Toledo TGA/DSC1 apparatus in the temperature range from 25 to 700 °C with a heating rate of 5 °C·min−1 and under a flow of oxygen gas at 50 mL·min−1. Synthesis of Compound 1. This was prepared, at room temperature, by dissolving, successively, the potassium salt K6[αP2W18O62]·11H2O, (0.606g, 0.125 mmol) synthesized by a literature method16 and the manganese(II) chloride MnCl2·4H2O (0.099 g, 0.5 mmol) in DMF solvent (25 mL) under stirring. The clear solution obtained was allowed to stand for at least one night, until it took a stable color indicating that the kinetics of the reaction was complete. Yellow crystals of (1), suitable for XRD analysis, were obtained by diffusion of ethanol in the dimethylformamide solution (yield 71% based on W element). Anal. Calcd for C54H126Mn3N18O80P2W18 (5843.78): C 11.10, H 2.17, N 4.31; found C 11.12, H 2.20, N 4.35%. UV/Vis [DMF]: λmax (log ε) = 266(4.87), 297(4.74) nm. IR (polyoxometalate region): ṽ = 1645 (vw), 1435 (s), 1418 (s), 1378

the most likely ones that can act as ligands and therefore perhaps to divert the reactions using a catalyst from their intended goal.15 Herein, we report on three new organic− inorganic hybrid complexes, namely, [M(C3H7NO)6][{M(C3H7NO)5}2(μ-P2W18O62)]·nC3H7NO·n′H2O [with M = MnII (1), FeII (2), CoII (3); n = 1, 2, 3 and n′ = 0, 0, 1 respectively].

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EXPERIMENTAL SECTION

Materials and Measurements. General Information. All reagents and dimethylformamide solvent employed were commercially available and were used as received without further purification. The potassium salt K6[α-P2W18O62]·11H2O was prepared according to the literature method and identified by Fourier transform infrared (FTIR) and 31P NMR spectroscopies.16 IR and 1H and 31P NMR spectra were recorded using, successively, a Nicolet 6700 FTIR spectrometer without KBr pellet in the 4000−350 cm−1 range and a Bruker 300 MHz Spectrometer. Electrochemistry. Electrochemical data were obtained using Ecochemie BV-type Autolab PGSTAT 302N, a potentiostat driven by a personal computer (PC) with the Nova1.7. A one-compartment cell with a standard three-electrode configuration was used for cyclic voltammetry experiments. The reference electrode was a saturated calomel electrode (SCE), and the counter electrode was platinum gauze of large surface area; both electrodes were separated from the bulk electrolyte solution via fritted compartments filled with the same electrolyte. The working electrode was a 3 mm OD glassy carbon disc (GC, Le Carbone Lorraine). The pretreatment of this electrode before each experiment has been described elsewhere.17 The polyanion concentration was 5 × 10−4 M. Prior to each experiment, solutions were deaerated thoroughly for at least 30 min with pure Ar. A positive pressure of this gas was maintained during subsequent work. All cyclic voltammograms were recorded at a scan rate of 10 mV s−1 unless otherwise stated. All experiments were performed at room temperature, which is controlled and fixed for the lab at 20 °C. Results were very reproducible from one experiment to another, and B


Article

Inorganic Chemistry

Figure 1. ORTEP drawing of [Mn(C3H7NO)6][{Mn(C3H7NO)5}2(μ-P2W18O62)], showing the labeling of atoms with thermal ellipsoids drawn at 30% probability level. Hydrogen atoms are omitted for clarity. [Symmetry code: (i) −x + 1, y, −z + 1/2; (ii) −x + 1/2, −y − 1/2, −z]. (m), 1251 (s), 1109 (s), 1090 (vw), 1020 (s), 959 (vw), 911 (w), 782 (vw), 599 (vs), 567 (vs), 527(m), 477 (vs), and 429 (vs) cm−1. 31P NMR (300 MHz, D2O, 330 K): δ = −12.71 ppm. 1H NMR (300 MHz, D2O, 330 K): δ = 7.78 (s, 1 H, DMF), 2.86 (s, 3 H, DMF), 2.70 (s, 3 H, DMF) ppm. Synthesis of Compounds 2 and 3. Compounds 2 and 3 were prepared following the procedure described for compound 1, but FeCl3·6H2O (0.135 g, 0.5 mmol) and CoCl2·6H2O (0.121 g, 0.5 mmol) were used instead of MnCl2·4H2O. Good-quality crystals of 2 and 3 were prepared by slow diffusion of ethanol into the dimethylformamide solutions. Complex 2: Anal. Calcd for C54H126Fe3N18O80P2W18 (5846.52): C 11.09, H 2.17, N 4.31; found C 11.13, H 2.19, N 4.34%. UV/Vis [DMF]: λmax (log ε) = 267(4.70), 297(4.58), and 466(3.61) nm. IR (polyoxometalate region): ṽ = 1639 (vw), 1430 (s), 1418 (s), 1360 (m), 1249 (s), 1115 (s), 1087 (vw), 1019 (s), 958 (vw), 910 (w), 780 (vw), 526(m) cm−1. 31P NMR (300 MHz, D2O, 330 K): δ = −12.68 ppm. 1H NMR (300 MHz, D2O, 330 K): δ = 7.76 (s, 1 H, DMF), 2.80 (s, 3 H, DMF), 2.64 (s, 3 H, DMF) ppm. Complex 3: Anal. Calcd for C57H133Co3N19O82P2W18 (5944.85): C 11.51, H 2.25, N 4.47; found C 11.53, H 2.20, N 4.50%. UV/Vis [DMF]: λmax (log ε) = 268(4.74), 297(4.62), and 532(2.14) nm. IR (polyoxometalate region): ṽ = 1643 (vw), 1434 (s), 1418 (s), 1378 (m), 1251 (s), 1109 (s), 1090 (vw), 1020 (s), 959 (vw), 910 (w), 782 (vw), 597 (vs), 566 (vs), 527(m), 474 (vs), and 426 (vs) cm−1. 31P NMR (300 MHz, D2O, 330 K): δ = −12.77 ppm. 1H NMR (300 MHz, D2O, 330 K): δ = 7.78 (s, 1 H, DMF), 2.86 (s, 3 H, DMF), 2.70 (s, 3 H, DMF) ppm. The crystallographic data and structural refinement details of 1−3 are shown in Table 1.

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The phase purity was monitored by powder X-ray diffraction (Figures S1−S3 in the Supporting Information; intensity differences between experimentally determined and simulated patterns are due to preferred orientation effects). Crystal Structure Description. Single-crystal X-ray diffraction analysis reveals that compounds (1), (2), and (3) are isomorphic with only slight differences in bond lengths, bond angles, and the number of lattice dimethylformamide molecule. The three compounds crystallize in the monoclinic C2/c space group (Table 1). Compound (1) is described as an example below. X-ray single-crystal structural analysis indicates that a molecular structure unit of the compound consists of 0.5 dinuclear complex anions [{Mn (1)(DMF) 5 } 2 (α P2W18O62)]2−, 0.5 [Mn(2)(DMF)6]2+ complex cation, and one free DMF molecule. The connection mode between the complex anions and cations is illustrated in Figure 1. Each [αP2W18O62]6− coordinates with two manganese atoms through two terminal oxygen atoms from equatorial WO6 octahedra, which constitutes a novel coordination mode for a Wells− Dawson cluster with a transition-metal atom.21 Each manganese atom adopts distorted octahedral geometry, defined by one terminal oxygen atom from [α-P2W18O62]6− anions and five DMF ligands. The organic component plays an important role in determining the packing arrangements of organic−inorganic assemblies along b-axis and c-axis (Figure 2). The Wells−Dawson polyanion [α-P2W18O62]6−, which has point symmetry close to D3h, contains two categories of W atoms: 6 at polar positions and 12 at equatorial positions. The two central P atoms are tetrahedrally coordinated by four bridging oxygen atoms, forming two {PO4} clusters. The corresponding P1−O bond distances vary from 1.528(5) to 1.577(5) Å (mean value 1.545 Å), and the O−P1−O bond angles range from 106.5(2) to 112.7(2)°. The W−O distances vary over a wide range: 1.700(5)−2.384 (4) Å and can be divided into three groups: (i) The W−Ot (Ot = terminal oxygen atom) bonds are in the usual range of 1.700(5)− 1.725(5) Å (mean value 1.710 Å); (ii) W−Ob/c (Ob/c = bridging oxygen atom) distances vary from 1.881(4) to

RESULTS AND DISCUSSION

Synthesis. In the solution of dimethylformamide, a 1:4 molar ratio reaction of Wells−Dawson POM α-K6P2W18O62· 11H2O and M (MnCl2·4H2O, FeCl3·6H2O, CoCl2·6H2O) was stirred and successively produced the three compounds (1), (2), and (3). The obtained compounds were characterized by FTIR, 1H and 31P NMR, and UV−vis spectroscopies, powder and singlecrystal XRD, and coupled TGA/DSC. C


Article

Inorganic Chemistry

range from 2.137(6) to 2.205(5) Å (mean value 2.1623 Å) and from 2.134(7) to 2.214(9) Å (mean value 2.174 Å) for Mn1 and Mn2 atoms, respectively. The O−Mn−O bond angles vary from 82.9(2)° to 100.0(2)° for Mn1, from 84.2(3)° to 90.6(3)° for Mn2, and from 169.7(2)° to 174.5(3)° for bond angles with O atoms in trans positions in the Mn1 complex. These bond length and angle values for manganese coordination sphere are in good agreement with bibliographic data.24 The Fe−O bond distances of compound 2 range from 2.101(11) to 2.155(9) Å and from 2.094(14) to 2.117(14) Å for Fe1 and Fe2 atoms, respectively. The O−Fe−O bond angles vary from 84.1(5)° to 99.0(5)° for Fe1, from 82.7(8)° to 97.3(8)° for Fe2, and from 170.6(5)° to 175.5(5)° for bond angles with O atoms in trans positions in the Fe1 complex.25 In compound 3, the two cobalt atoms Co1 and Co2 have a distorted octahedral environment. The Co−O bond lengths are in the ranges of 2.039(11)−2.124(11) Å for Co1 atom, located in general position, and 2.001(17)−2.052(14) Å for Co2 atom, located on the inversion center. The O−Co−O bond angles are in the range from 85.4(5)° to 97.6(5)° for Co1, from 87.9(7)° to 92.1(7)° for Co2, and from 171.9(5)° to 175.3(5)° for bond angles with O atoms in trans positions in the Co1 complex.26 During refinement, we found that the DMF solvent molecules for complexes 2 and 3 are completely disordered and therefore difficult to model. For this reason these molecules were excluded by the squeeze command for platon program. FT-IR, NMR, and UV/Vis Spectroscopy. The IR spectra of (1), (2), and (3) exhibit characteristic peaks of metal− oxygen stretching and deformation modes of the POM, in the region 1000−251 cm−1 16,27 (Figure S4). The characteristic vibration bands attributable to ν(P−Oa), ν(W−Ot), ν(W−Oe), and ν(W−Oc) appear at 1090 cm−1 for (1) and (3) and at 1087 cm−1 for (2); at 959 cm−1 for (1) and (3) and at 958 cm−1 for (2); at 911 cm−1 for (1) and at 910 cm−1 for (2) and (3); at 782 cm−1 for (1) and (3) and at 780 cm−1 for (2).28−30 Bands in the 1700−1110 cm−1 region are attributed to DMF groups. These bands appear at 1645 cm−1 for (1), at 1639 cm−1 for (2), and at 1643 cm−1 for (3); at 1498 cm−1 for (1), at 1490 cm−1 for (2), and at 1497 cm−1 for (3); at 1435 cm−1 for (1), at 1430 cm−1 for (2), and at 1434 cm−1 for (3); at 1418 cm−1 for (1), (2), and (3); at 1378 cm−1 for (1) and (3), and at 1360 cm−1 for (2); at 1251 cm−1 for (1) and (3) and at 1249 cm−1 for (2); at 1109 cm−1 for (1) and (3) and at 1115 cm−1 for (2), and they are attributed, respectively, to the ν(CO), δas(CH3), δ(CH), δs(CH3), νas(C′N), r(CH3).31 IR spectra studies indicate that there is strong interaction between the polyanions and organic groups in the solid state. Hundreds of spectra were thus recorded for temperatures between 291 and 849 K at a rate of 4 °C, among which we chose a few to compare at different temperatures to know the thermal stability domain of the POM, and it was found at the end of measurements that the colors of iron and cobalt complexes became gray and that this color is homogeneous on the whole pellet. Figure 4 shows some IR spectra of iron compounds at different temperatures. The stability of the well-known αDawson anion can be followed by the bands located at 691 cm−1 attributed to νs(W−Oc) and at 1023 cm−1 attributed to νs(P−Oa), which disappear from the temperature of 540 °C.

Figure 2. Polyhedral representation of the crystal structure of (1), viewed along the b axis and c axis.

1.955(5) Å (mean value 1.910 Å); (iii) the longest W−Oa (Oa = oxygen coordinated to P atom) bonds are in the range of 2.306(4)−2.384(4) Å (mean value, 2.365 Å). The bond angles O−W−O are in the range from 71.6(2) to 103.8(2)°. These bond lengths and angles are within the normal ranges and are consistent with those described in the literature for the α-isomer of the well-known Dawson anion.22,23 Selected bond lengths and angles for these compounds (1), (2), and (3) are listed in Table 2. The first metal atom Mn1, located in general position, forms a dinuclear complex anion [{Mn(dmf)5}2(μ-P2W18O62)]2−, and it is coordinated to five DMF molecules through the oxygen atom, while the sixth coordination site is occupied by a terminal oxygen atom of the Wells−Dawson anion [P2W18O62]6− that plays the role of a bridging ligand. The second metal atom Mn2, located in special position, is octahedrally coordinated to six DMF molecules and forms the complex cation [Mn(dmf)6]2+. The cohesion of the crystal structure is ensured by electrostatic interactions between the ions and by numerous weak C−H···O hydrogen bonds that organize all the structure components into a three-dimensional framework (Figure 3). The Mn1 atoms have an octahedral coordination that is distorted toward a trigonal pyramid having three short Mn1− O bonds trans to three longer ones; for example, this atom has three bonds at 2.137(6), 2.143(6), and 2.153(6) Å, two bonds at 2.163(5) and 2.173(6) Å, and one bond at 2.205(5) Å. The Mn2 octahedron, which is located in special position on an inversion center, is characterized by three bond lengths: one longer at 2.214 (9) Å, one medium at 2.175(7) Å, and one shorter at 2.134 (7) Å. Furthermore, the Mn−O bond lengths D


Article

Inorganic Chemistry Table 2. Selected Bond Lengths (Å) and Angles (deg) for 1−3 complex 1

complex 2

W1−O11 1.700(5) W1−O1 1.910(5) W1−O13 2.373(4) W2−O12 1.708(5) W2−O13 2.380(5) W3−O10 1.715(5) W3−O3 1.904(5) W3−O13 2.392(4) W4−O8 1.955(5) W4−O14 2.384(4) P1−O16 1.528(5) P1−O14 1.543(5) P1−O15 1.533(5) P1−O13 1.577(5) O11−W1−O4 103.8(2) O4−W1−O1 90.1(2) O11−W1−O13 169.8(2) O1−W1−O13 73.32(17) O16−P1−O15 112.7(2) O16−P1−O14 111.5(2) O15−P1−O14 111.9(3) O16−P1−O13 107.1(2) O15−P1−O13 106.6(3) O14−P1−O13 106.5(2) manganese coordination octahedron Mn2−O37 2.133(7) Mn2−O38 2.175(7) Mn2−O39 2.214(9) Mn1−O34 2.137(6) Mn1−O36 2.153(6) Mn1−O31 2.205(5) O37−Mn2−O37 180.0 O37−Mn2−O38 89.4(3) O37−Mn2−O38 90.6(3) O37−Mn2−O39 84.2(3) O37−Mn2−O39 95.8(3) O38−Mn2−O39 90.4(3 O34−Mn1−O36 96.2(3) O36−Mn1−O35 82.9(2) O36−Mn1−O33 174.5(3) O35−Mn1−O33 100.0(2) O32−C1 C1−N1 C1−H1 N1−C2 N1−C3 C1−O32−Mn1 O32−C1−N1 C1−N1−C2 C1−N1−C3 C2−N1−C3

1.245(9) 1.322(10) 0.9300 1.439(11) 1.454(11) 125.6(5) 123.3(8) 122.0(8) 120.6(7) 117.3(7)

complex 3

polyoxotungstate Wells−Dawson W1−O1 1.713(9) W1−O10 1.910(10) W1−O31 2.382(8) W2−O2 1.709(10) W2−O31 2.366(9) W3−O3 1.726(11) W3−O13 1.904(9) W3−O31 2.388(9) W4−O26 1.930(10) W4−O28 2 0.362(9) P1−O30 1.535(9) P1−O29 1.538(9) P1−O28 1.566(9) P1−O31 1.601(9) O1−W1−O15 103.7(4) O12−W1−O10 89.5(4) O1−W1−O31 170.4(4) O10−W1−O31 71.5(4) O30−P1−O29 112.1(5) O30−P1−O28 111.7(5) O29−P1−O28 112.6(5) O30−P1−O31 107.1(5) O29−P1−O31 105.6(5) O28−P1−O31 107.3(5) iron coordination octahedron Fe1−O32 2.101(11) Fe1−O34 2.130(12) Fe1−O34 2.130(12) Fe1−O7 2.155(9) Fe2−O38 2.094(14) Fe2−O37 2.112(15) Fe2−O39 2.117(14) Fe2−O39 2.117(14) O32−Fe1−O35 90.3(5) O32−Fe1−O36 86.6(5) O35−Fe1−O36 96.6(5) O36−Fe1−O33 175.5(5) O38−Fe2−O38 180.0(7) O38−Fe2−O37 91.9(6) O38−Fe2−O39 8 2. Seven (8) O38−Fe2−O39 97.3(8) DMF ligand O32−C1 1.209(15) C1−N1 1.251(17) C1−H1 0.9300 N1−C2 1.452(18) N1−C3 1.485(19) C1−O32−Fe1 129.0(11) O32−C1−N1 130.2(15) C1−N1−C2 124.9(14) C1−N1−C3 118.8(15) C2−N1−C3 116.2(14)

W1−O1 1.749(9) W1−O13 1.922(10) W1−O23 2.379(9) W2−O2 1.678(10) W2−O23 2.363(9) W3−O3 1.712(10) W3−O10 1.919(9) W3−O23 2.384(9) W4−O28 1.930(9) W4−O22 2.372(10) P1−O22 1.537(10) P1−O30 1.549(10) P1−O24 1.557(10) P1−O23 1.594(9) O1−W1−O14 103.2(5) O10−W1−O14 87.7(4) O1−W1−O23 170.5(4) O11−W1−O23 72.5(4) O22−P1−O30 112.5(6) O22−P1−O24 112.7(5) O30−P1−O24 111.4(5) O22−P1−O23 107.3(5) O30−P1−O23 105.9(5) O24−P1−O23 106.5(5) cobalt coordination octahedron Co1−O35 2.039(11) Co1−O34 2.054(12) Co1−O36 2.079(11) Co1−O32 2.094(12) Co1−O7 2.123(11) Co2−O37 2.001(17) Co2−O38 2.030(17) Co2−O39 2.052(14) O35−Co1−O36 86.7(5) O34−Co1−O36 175.3(5) O36−Co1−O32 96.8(6) O34−Co1−O7 90.5(5) O37−Co2−O37 180.0(11) O37−Co2−O39 91.4(6) O 37 −C o2−O39 88.6(6) O38−Co2−O39 92.1(7) O32−C1 C1−N1 C1−H1 N1−C3 N1−C2 C1−O32−Co1 O32−Ci−Nj C1−N1−C3 C1−N1−C2 C3−N1−C2

1.237(14) 1.289(14) 0.9300 1.441(14) 1.470(15) 134.4(14) 125.3(15) 123.5(13) 117.7(12) 118.8(12)

The IR spectra as a function of temperature for the cobalt compound (Figure 5) shows that the POM remains stable at a temperature of 560 °C, while the DMF begins to degrade at a temperature of 460 °C. The stability of the POM can be followed by the bands located at 599 and 689 cm−1 attributed to νs(W−Oc) and at 1022 cm−1 attributed to νs(P−Oa). This

This constitutes a proof of the degradation of the Wells− Dawson {P2W18}. The study of the stability of DMF can be followed by bands at 1195 and 1648 cm−1. The appearance of the new bands on either side of these bands shows that the DMF undergoes decomposition from a temperature of 325 °C. E


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Inorganic Chemistry

Figure 3. Representation of an anionic row connected through hydrogen bonds C−H···O.

UV/Vis spectra of (1), (2), and (3) were recorded in 1 × 10−5 M DMF solution in the 800−200 nm range (Figure 6). The spectra have in common two characteristic absorption bands at 266−268 and 297 nm (Table 3). The two strong bands near 266−268 and 297 nm are attributed to the chargetransfer absorption bands of Ot−W and Ob/c−W, respectively. These bands correspond, respectively, to the transitions π−π * and n−π *.24,34 Further, the bands at 466 and 532 nm in the visible region might originate from the d−d electron transition of, respectively, FeII 35 and CoII (1 × 10−2 M) ions.36 The energy difference between the levels of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) (optical band gap Eg)37 is obtained from the UV−visible spectrum. This energy is calculated by the relation Eg optic (eV) = hc/λgap = 1241/λgap (λgap in nm) from the value of the intersection of the two tangents to the absorption curve (baseline and absorption band). Thermal Behavior. The thermal stability of compounds (1), (2), and (3) was established by TG and DSC analyses, which were simultaneously performed under O2 atmosphere between 25 and 700 °C, with a heating rate of 5 °C min−1. The thermograms are depicted in Figure 7. The TGA curve of compound 1 gives a first mass loss of 9.47% (calcd 9.99%), in the temperature range of 30−200 °C, parallel to an endothermic peak centered at 144 °C on the DSC curve. This manifestation can be attributed to the loss of two DMF molecules of crystallization and six DMF molecules coordinated to manganese ions. A second loss of 12.16% (calcd 12.49%) exhibited by endothermic peaks between 221 and 661 °C corresponding to the loss of 10 DMF molecules coordinated with manganese ions that are bound to the [P2W18O62]6− anion followed by a decomposition of the heteropolyanion. The TGA and DSC thermograms of compound 2 are shown in Figure 8. The TGA curve shows a first mass loss of 7.26% (calcd 7.49%) in the temperature range of 30−200 °C parallel to an endothermic peak centered at 190 °C on the DSC curve. This manifestation can be attributed to the loss of two DMF molecules of crystallization and four DMF molecules coordinated with the iron ion. The structure then loses seven DMF molecules in the temperature range of 210−350 °C, as demonstrated by a corresponding mass loss of 8.09% (calcd 8.74%) evidenced by endothermic peaks between 292 and 548 °C. A third mass loss of 6.24% (calcd 6.24%) occurred in the temperature range of 360−700 °C relative to five DMF molecules and the degradation of the Wells−Dawson heteropolyanion.

Figure 4. IR spectra of C54H126Fe3N18O80P2W18 at high temperature.

Figure 5. IR spectra of C57H133Co3N19O82P2W18 at high temperature.

constitutes a proof of the degradation of the POM, whereas the stability of DMF can be followed by the disappearance of the bands located at 1114 cm−1 attributed to r(CH3), at 1254 cm−1 attributed to νas(C′N), and at 1420 cm−1 attributed to δ(CH), which shows that the DMF undergoes decomposition. The 31P NMR spectra of compounds 1−3 show a single peak at −12.71 ppm (Figure S5). This chemical shift value is close to −13.00 ppm, which is characteristic of the α-isomer of Wells−Dawson polyanions.32 The three compounds have almost identical 1H NMR spectra. They have two singlets of three protons with chemical shifts slightly below 3 ppm and a singlet at 7.80 ppm (Figure S6). As the rotation around the C−N bond is not entirely due to the free relocation of the doublet nitrogen giving the CN bond is partial to double bond, methyl protons give resonant two singlets instead of one. The protons of methyl trans to the oxygen appear around 2.85 ppm, and those of methyl cis appear around 2.70 ppm; these chemical shifts are in accordance with the values provided by the databases33 for free DMF dissolved in deuterated chloroform: 2.883, 2.970, and 8.019 ppm. F


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Inorganic Chemistry

Figure 6. UV/Vis absorption spectra of compound 1, 2, and 3 in DMF solution at concentrations of ca. 1 × 10−5 and 1 × 10−2 M.

Table 3. UV/Vis Data of Compounds 1−3 in DMF Solution compound 1 2

3

λ [nm] (log ε) 266 297 267 297 466 268 297 532

(4.87) (4.74) (4.70) (4.58) (3.61) (4.74) (4.62) (2.14)

λgap (nm)

Eg optic (eV)

351

3.53

570

2.17

609

2.03

Figure 9 groups the TGA and DSC thermograms recorded for this hybrid 3. A first loss of 11.82% (calcd 11.65%) of the mass of the sample is observed between 27 and 200 °C, parallel to the two endothermic peaks centered at 109 and 198 °C. This manifestation is attributed to a loss of two water molecules, three DMF molecules of crystallization, and six DMF molecules coordinated to cobalt ions. The structure then loses 10 DMF molecules that are bound to the Wells−Dawson anion in the temperature range of 210−560 °C, as demonstrated by a corresponding mass loss of 12.02% (calcd 12.27%). The DSC curve presents some strong endothermic peaks between 325 and 555 °C. No loss of mass occurs at temperatures above 600 °C. These results illustrate that three compounds decompose at ca. 584 °C. From the above analyses, we can surmise that the

Figure 7. TGA-DSC curves of compound 1.

frameworks of polyanions of this kind of compound decompose at ca. 590 °C. The TGA results confirm, inter alia, the number of solvents in the lattices of 1−3. Cyclic Voltammetry. The electrochemical behavior of compounds 1−3 was studied by cyclic voltammetry (CV) in 0.5 M Na2SO4 + H2SO4 solutions under argon atmosphere, using reference electrode (saturated calomel electrode (SCE)). Compound 1. [Mn(C3H7NO)6][{Mn(C3H7NO)5}2(μP2W18O62)]·2C3H7NO. The study of the manganese species G


Article

Inorganic Chemistry

surface of the working electrode. Furthermore, the waves of {P2W18} remain stable over cycling. For the interval [0.3 V; 1.3 V] of the voltammogram, the position of the Mn redox waves are located at exactly the same potential values (Epa = 0.96 V and Epc = 0.74 V) independently of the cycle. Epa, Epc, and Ipa (oxidation current) remained unchanged over successive cycles, while Ipc (reduction current) increased. We can conclude that the Mn oxides adsorbed on the working electrode surface during the oxidation step are not completely redissolved during the consecutive reduction step but require going down to 0.07 V. This results in an increase, albeit small but gradual, in the thickness of this film over successive cycles, hence the increase in Ipc that corresponds to its redissolution. This film seems not to cause a significant modification of the working electrode (Epa and Ipa are almost invariant). After restricting the cycling within the interval [0.3 V; 1.3 V] (Figure 10B) a slight increase in Ipc over the following cycle is observed, while Epc remained almost constant. Meanwhile, between the first and the second cycle, Epa shifted by ∼40 mV in the direction of negative potentials. As observed for Ipc, there was a slight increase of Ipa. Regarding the behavior of the reduction wave, a gradual increase of the thickness of the Mn oxide film leads to an increase of Ipc. However, the nature of this oxide film seems to be different, as the behavior of the working electrode is significantly modified during the subsequent cycle, which made the oxidation of Mn easier. In other words, scanning the potential down to 0.07 V is necessary but may be not sufficient to regenerate an active working electrode surface and minimize changes of Mn waves during cycling (potentials and currents). If the scanning is stopped before this limit (at +0.3 V, e.g.), this significantly modifies the working electrode surface, altering its reactivity toward oxidation of MnII centers. In fact, exploration of potential up to the MnII/IV redox wave always irreversibly modifies the working electrode surface, and a full polishing procedure is required if one wants to recover its initial activity and collect reliable data.38 Compound 2. [Fe(C 3 H 7 NO) 6 ][{Fe(C 3 H 7 NO) 5 } 2 (μP2W18O62)]·2C3H7NO. The CV of the iron species is restricted to the reduction of the two first monoelectronic waves of the Wells−Dawson {P2W18} and iron centers. The comparison of the two CVs obviously shows that the reduction of FeIII centers happens at nearly the same potential as that of



is limited to the reduction of the two first monoelectronic waves of the Wells−Dawson {P2W18} and the oxidation of Mn centers. The global voltammogram (Figure 10A) can be cut in two zones. For the interval [−0.35 V; 0.3 V] of the voltammogram, the first cycle in black shows the typical two first waves of {P2W18}, whereas the second one in red exhibits a new irreversible reduction wave (R1′) (Epc = 0.12 V) due to the reduction of Mn species, which appears further to the oxidation of MnII centers creating a Mn oxide film on the

Figure 10. Cyclic voltammograms of 1 at pH 3. The solvent is 0.5 M Na2SO4 + H2SO4, POM concentration is 0.5 mM, and the scan rate is 10 mV s−1. (A) Potentials were initially scanned down to −0.35 V and then up to +1.3 V. (B) Potentials were scanned between +0.3 and +1.3 V. H


Article

Inorganic Chemistry tungsten framework and leads to the merging of the iron and tungsten first wave (R2), as it is still manifested by the wave (R1), while the second wave of the tungsten (R3) framework is not influenced by the presence of iron centers. The reduction of FeIII can be observed (Figure 11) even if the initial oxidation state of iron centers is +II because of the

Figure 12. Cyclic voltammograms of Co3P2W18 at pH 3 (0.5 M Na2SO4 + H2SO4), POM concentration 0.5 mM. Scan rate 10 mV s−1; reference electrode SCE.

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CONCLUSION Three new organic−inorganic hybrid polyoxotungstates have been synthesized and characterized. X-ray single-crystal structural analysis indicates that a molecular structure unit of these compounds consists of 0.5 dinuclear complex anions [{M(dmf)5}2(μ-P2W18O62)]2−, where M = Mn, Fe, Co atoms are coordinated to five DMF molecules through the oxygen atom, while the sixth coordination site is occupied by a terminal oxygen atom of the Wells−Dawson anion [P2W18O62]6− that plays the role of a bridging ligand; 0.5 [M(dmf)6]2+ complex cation, located on an inversion center, is octahedrally coordinated to sixth DMF molecules and n free solvent molecules. In addition to the electrostatic interactions between the ions, the structure is stabilized by numerous weak C−H···O hydrogen bonds that organize all the structure components into a three-dimensional framework. An innovative study on the electrochemical behavior of d-metalcontaining Wells−Dawson-type complexes has been performed. In most of the cases, the reduction of the three M(III) centers takes place in two successive single-electron steps, each electron being delocalized over the three centers.

Figure 11. Cyclic voltammograms of P2W18 (blue line) and Fe3P2W18 (black line) at pH 3 (0.5 M Na2SO4 + H2SO4) and POM concentration 0.5 mM. Scan rate 10 mV s−1; reference electrode SCE. Start potential 0.8 V.

starting potential, which causes the oxidation of FeII along the equilibrium time just before the measurement. The reduction of the iron centers also leads to a decrease of the current intensity 0.41 V (R1). The oxidation of tungsten framework is the same for the two compounds (Epa stays the sames). The oxidation of iron centers is observed at 0.64 V.39−41 The electrochemical data for all three complexes 1−3 with P2W18 are collected in Table 4. It would be necessary to make several measurements to fully understand the formed species after the reduction of iron centers (iron oxides, iron hydroxides, etc.) and the different mechanisms between these species. Compound 3. [Co(C3H7 NO) 6][{Co(C 3 H7NO)5 }2 (μP2W18O62)]·3C3H7NO·H2O. Electrochemical behavior of (3) was investigated by cyclic voltammetry in (0.5 M Na2SO4 + H2SO4) at pH = 3, using a glassy carbon working electrode. The obtained cyclic voltammogram shows, in the explored potential domain from −1.000 to 1.200 V (Figure 12), four well-defined redox couples with approximate electron ratios of 1:1:2:2. The two one-electron waves followed by two consecutive two-electron waves were reversible attributable to the [P2W18O62]6− polyoxoanion.42 No electrochemical activity was detected for Co(II).

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.8b01207. Experimental and simulated powder XRD data, IR spectra, NMR spectra (PDF)

Table 4. Electrochemical Dataa for the Two First Monoelectronic Waves of the Wells−Dawson Polyanion and for Complexes 1−3 at pH 3.00 (0.5 M Na2SO4 + H2SO4) ring oxidations 1st oxidation Epa P2W18 Mn3P2W18 Fe3P2W18 Co3P2W18

b

0.966

Epc

c

0.739

ring reductions 1st reduction

E1/2d 0.852

2nd reduction

3rd reduction

Epc

Epa

E1/2

Epc

Epa

E1/2

−0.009 −0.007 0.412 −0.008

0.042 0.065 0.648 0.048

0.033 0.058 0.530 0.040

−0.176 −0.173 0.055 −0.178

−0.118 −0.105 0.074 −0.110

−0.294 −0.278 0.064 −0.288

Epc

Epa

E1/2

−0.159

−0.103

−0.131

a

The potentials are reported versus SCE. bEpa = anodic peak potential. cEpc = cathodic peak potential. dE1/2 = half-wave potential. I


Article

Inorganic Chemistry Accession Codes

on Wells-Dawson POM/Ag Chemistry. Inorg. Chem. 2008, 47, 5145− 5153. (11) Tian, A. X.; Ying, J.; Peng, J.; Sha, J. Q.; Zhu, D. X.; Pang, H. J.; Zhang, P. P.; Chen, Y.; Zhu, M. Assembly of a new Wells-Dawson polyoxometalate-templated compound based on Fe-btb complex. Inorg. Chem. Commun. 2008, 11, 1132−1135. (12) Tian, A. X.; Ying, J.; Peng, J.; Sha, J. Q.; Han, Z. G.; Ma, J. F.; Su, Z. M.; Hu, N. H.; Jia, H. Q. Assembly of the Highest Connectivity Wells-Dawson Polyoxometalate Coordination Polymer: the Use of Organic Ligand Flexibility. Inorg. Chem. 2008, 47, 3274−3283. (13) Yang, H. X.; Guo, S. P.; Tao, J.; Lin, J. X.; Cao, R. Hydrothermal Syntheses, Crystal Structures, And Magnetic Properties of a Series of Complexes Constructed from Multinuclear Copper Clusters and Polyoxometalates. Cryst. Growth Des. 2009, 9, 4735− 4744. (14) Wang, X. L.; Li, Y. G.; Lu, Y.; Fu, H.; Su, Z. M.; Wang, E. B. Polyoxometalate-Based Porous Framework with Perovskite Topology. Cryst. Growth Des. 2010, 10, 4227−4230. (15) Crabtree, R. H. The Organometallic Chemistry of the Transition Metals, 2nd ed.; Wiley: New York, 1994. (16) Mbomekalle, I. M.; Lu, Y. W.; Keita, B.; Nadjo, L. Simple, high yield and reagent-saving synthesis of pure α-K6P2W18O62.14H2O. Inorg. Chem. Commun. 2004, 7, 86−90. (17) Vilà, N.; Aparicio, P. A.; Sécheresse, F.; Poblet, J. M.; López, X.; Mbomekallé, I. M. Electrochemical Behavior of α1/α2-[Fe(H2O)P2W17O61]7‑ Isomers in Solution: Experimental and DFT Studies. Inorg. Chem. 2012, 51, 6129−6138. (18) Rodriguez-Carvajal, J. Recent advances in magnetic structure determination by neutron powder diffraction. Phys. B 1993, 192, 55− 69. (19) Roisnel, T.; Rodriquez-Carvajal, J. Mater. Sci. Forum 2001, 378, 118−123. (20) Roisnel, T.; Rodriguez-Carvajal, J. WinPLOTR: a Windows tool for powder diffraction patterns analysis. In Materials Science Forum, Proceedings of the Seventh European Powder Diffraction Conference (EPDIC7), 2000; Delhez, R., Mittenmeijer, E. J., Eds.; Trans Tech Publications, 2001; pp 118−123. (21) Dhifallah, F.; Belkhiria, M. S. Crystal structure of hexakis(dimethylformamide-κO)manganese(II) decakis(dimethylformamide)-1κ5O,2κ5O-[μ-octadecatungstodiphosphato(V)-κO:κO′]dimanganate(II) dimethylformamide disolvate. Acta Crystallogr. 2016, E72, 841−844. (22) Dhifallah, F.; Belkhiria, M. S.; Leclerc, N.; Cadot, E. A new Wells−Dawson heteropolyoxotungstate functionalized by nickeldimethylformamide complex: Synthesis, spectroscopic and thermal characterizations, and X-ray crystal structure. Inorg. Chim. Acta 2016, 441, 15−19. (23) Niu, J. Y.; Zhao, J. W.; Guo, D. J.; Wang, J. P. Preparation, electrochemistry and crystal structure of a derivative of 18tungstophosphate with Dawson structure: K 16 H[Yb(α-2P2W17O61)2].44H2O. J. Mol. Struct. 2004, 692, 223−229. (24) Niu, J. Y.; Guo, D. J.; Wang, J. P.; Zhao, J. W. 1D polyoxometalate-Based Composite Compounds Derived from the Wells-Dawson Subunit: Synthesis and Crystal Structure of [{Ce(DMF)4(H2O)3}{Ce(DMF)4(H2O)4}(P2W18O62)]·H2O and [{La(DMF)6(H2O)}{La(DMF)4.5(H2O)2.5}(P2W18O62)]. Cryst. Growth Des. 2004, 4, 241−247. (25) Rojas-Dotti, C.; Moliner, N.; González, R.; Martínez-Lillo, J. Hexakis(dimethylformamide)iron(II) complex cation in hexahalorhenate(IV)- based salts: Synthesis, X-ray structure and magnetic properties. J. Coord. Chem. 2018, 71, 737−747. (26) Zhao, X.; Liang, D.; Liu, S.; Sun, C.; Cao, R.; Gao, C.; Ren, Y.; Su, Z. Two Dawson-Templated Three-Dimensional Metal-Organic Frameworks Based on Oxalate-Bridged Binuclear Cobalt(II)/Nickel(II) SBUs and Bpy Linkers. Inorg. Chem. 2008, 47, 7133−7138. (27) Contant, R.; Thouvenot, R. A reinvestigation of isomerism in the Dawson structure: syntheses and 183W NMR structural characterization of three new polyoxotungstates [X2W18O62]6‑ (X = PV, AsV). Inorg. Chim. Acta 1993, 212, 41−50.

CCDC 1028991 and 990228 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Phone/Fax: +216 53 724 104/+216 73 500 278. ORCID

Fatma Dhifallah: 0000-0001-7065-9642 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors gratefully acknowledge the Ministry of Higher Education and Scientific Research of Tunisia for financial support.

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REFERENCES

(1) (a) Pope, M. T., Müller, A., Eds. Polyoxometalate Chemistry from Topology via Self-Assembly to Applications; Springer, 2001; p 427. (b) Pope, M. T.; Müller, A. Polyoxometalate Chemistry: An Old Field with New Dimensions in Several Disciplines. Angew. Chem., Int. Ed. Engl. 1991, 30, 34−48. (c) Special thematic issue on polyoxometalates: Chem. Rev. 1998, 98, 1−388. (d) Long, D. L.; Burkholder, E.; Cronin, L. Polyoxometalate clusters, nanostructures and materials: from self assembly to designer materials and devices. Chem. Soc. Rev. 2007, 36, 105−121. (e) Long, D. L.; Tsunashima, R.; Cronin, L. Polyoxometallate als Bausteine für funktionelle Nanosysteme. Angew. Chem. 2010, 122, 1780−1803;(e1) Polyoxometalates: building blocks for functional nanoscale systems. Angew. Chem., Int. Ed. 2010, 49, 1736−1758. (f) Special Issue: Frontiers in Metal Oxide Cluster Science. Isr. J. Chem. 2011, 51, 169−302. (2) Dawson, B. The structure of the 9(18)-heteropoly anion in potassium 9(18)-tungstophosphate, K6(P2W18O62).14H2O. Acta Crystallogr. 1953, 6, 113−126. (3) d’Amour, H. Vergleich der heteropolyanionen [PMo9O31(H2O)3]3‑, [P2Mo18O62]6‑ und [P2W18O62]6‑. Acta Crystallogr., Sect. B: Struct. Crystallogr. Cryst. Chem. 1976, 32, 729−740. (4) Pope, M. T. Structural isomers of 1:12 and 2:18 heteropoly anions. Novel and unexpected chirality. Inorg. Chem. 1976, 15, 2008− 2010. (5) Weakley, T. J. R. Some aspects of the heteropolymolybdates and heteropolytungstates. Struct. Bonding (Berlin) 1974, 18, 131−176. (6) Matsumoto, K. Y.; Sasaki, Y. Crystal structure of α-P2W18O626‑ anion. J. Chem. Soc., Chem. Commun. 1975, 16, 691−692. (7) Niu, J. Y.; Guo, D. J.; Zhao, J. W.; Wang, J. P. Controlled assembly of polyoxometalate-based composite materials containing zero-and one-dimensional structures. New J. Chem. 2004, 28, 980− 987. (8) Wang, J. P.; Zhao, J. W.; Niu, J. Y. A novel 1D zigzag chain organic-inorganic polymer with Dawson-type polyoxometalates as building blocks: synthesis and crystal structure of H1.5[Sm(H2O)8]0.5[Sm(DMF)6(H2O)(α-P2W18O62)].DMF.3H2O. J. Mol. Struct. 2004, 697, 191−198. (9) Cao, R.; Sun, D. F.; Liang, Y. C.; Hong, M. C.; Tatsumi, K.; Shi, Q. Syntheses and Characterizations of Three-Dimensional Channellike Polymeric Lanthanide Complexes Constructed by 1,2,4,5Benzenetetracarboxylic Acid. Inorg. Chem. 2002, 41, 2087−2094. (10) Sha, J. Q.; Peng, J.; Lan, Y. Q.; Su, Z. M.; Pang, H. J.; Tian, A. X.; Zhang, P. P.; Zhu, M. pH-Dependent Assembly of Hybrids Based J


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Inorganic Chemistry (28) Jin, H.; Qi, Y.; Xiao, D.; Wang, X.; Chang, S.; Wang, E. Two novel inorganic−organic hybrids based on saturated Wells−Dawson polyoxoanion and copper−organonitrogen coordination polymer. J. Mol. Struct. 2007, 837, 23−29. (29) Cao, X.; He, L.; Lin, B.; Chen, Z.; Liu, P. Synthesis and characterization of a polyoxotungstate-supported metal compound [{Cu(enMe)2(H2O)}{Cu(enMe)2}3P2W18O62]·nH2O. Inorg. Chim. Acta 2009, 362, 2505−2509. (30) Dong, B.; Peng, J.; Chen, Y.; Zhang, P.; Tian, A.; Chen, J. A novel wavelike chain constructed from Wells−Dawson type polyoxoanions and mixed-ligand decorated transition metal complex cations [Ni(phen)(bbi)2]2+. J. Mol. Struct. 2008, 875, 75−79. (31) Durgaprasad, G.; Sathyanarayana, D. N.; Patel, C. C. Infrared Spectra and Normal Vibrations of N, N-Dimethylformamide and N, N-Dimethylthioformamide. Bull. Chem. Soc. Jpn. 1971, 44, 316−322. (32) Graham, C. R.; Finke, R. G. The Classic Wells−Dawson Polyoxometalate, K6[α-P2W18O62]·14H2O. Answering an 88 YearOld Question: What Is Its Preferred, Optimum Synthesis? Inorg. Chem. 2008, 47, 3679−3686. (33) Spectral Data Base for Organic Compounds (SDBS); National Institute of Advanced Industrial Science and Technology; SDBS No. 324HSP-04-529. (34) Niu, J. Y.; Wang, J. P. Introduction of Heteropoly Compounds; Henan University Press: Kaifeng, P. R. China, 2000; p 189. (35) Kim, Y. J.; Park, C. R. Analysis of Problematic Complexing Behavior of Ferric Chloride with N,N-Dimethylformamide Using Combined Techniques of FT-IR, XPS, and TGA/DTG. Inorg. Chem. 2002, 41, 6211−6216. (36) Kalb, A. J.; Pecht, I. Biochim. Biophys. Acta, Protein Struct. 1973, 303, 264−268. (37) Colladet, K.; Nicolas, M.; Goris, L.; Lutsen, L.; Vanderzande, D. Low-band gap polymers for photovoltaic applications. Thin Solid Films 2004, 451-452, 7−11. (38) Lebrini, M.; Mbomekallé, I. M.; Dolbecq, A.; Marrot, J.; Berthet, P.; Ntienoue, J.; Sécheresse, F.; Vigneron, J.; Etcheberry, A. Manganese(III)-Containing Wells−Dawson Sandwich-Type Polyoxometalates: Comparison with their Manganese(II) Counterparts. Inorg. Chem. 2011, 50, 6437−6448. (39) Mbomekalle, I. M.; Keita, B.; Nadjo, L.; Berthet, P.; Hardcastle, K. I.; Hill, C. L.; Anderson, T. M. Multi-Iron Tungstodiarsenates. Synthesis, Characterization, and Electrocatalytic Studies of αββα(FeIIIOH2)2FeIII2(As2W15O56)212‑. Inorg. Chem. 2003, 42, 1163−1169. (40) Keita, B.; Mbomekalle, I. M.; Nadjo, L.; Anderson, T. M.; Hill, C. L. Multi-Iron Wells−Dawson Heteropolytungstates. Electrochemical Probing of Siderophoric Behavior in Sandwich-Type Complexes. Inorg. Chem. 2004, 43, 3257−3263. (41) Keita, B.; Nadjo, L. Electrochemistry of Isopoly and Heteropoly Oxometalates 2007, 22, 607−700. (42) Mal, S. S.; Dickman, M. H.; Kortz, U.; Todea, A. M.; Merca, A.; Bogge, H.; Glaser, T.; Muller, A.; Nellutla, S.; Kaur, N.; van Tol, J.; Dalal, N. S.; Keita, B.; Nadjo, L. Nucleation Process in the Cavity of a 48-Tungstophosphate Wheel Resulting in a 16-Metal-Centre Iron Oxide Nanocluster. Chem. - Eur. J. 2008, 14, 1186−1195.

K


A Series of Octahedral First-Row Transition-Metal Ion Complexes

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