1D pure inorganic helical chain framework built upon banana-shaped molybdovanadates: Synthesis, crystal structure, and magnetic properties

    1D pure inorganic helical chain framework built upon banana-shaped molybdovanadates: Synthesis, crystal structure, and magnetic properties Qiao Gao, Fengyan Li, Lin Xu PII: DOI: Reference:

S1387-7003(15)30007-1 doi: 10.1016/j.inoche.2015.06.029 INOCHE 6034

To appear in:

Inorganic Chemistry Communications

Received date: Revised date: Accepted date:

1 April 2015 23 June 2015 27 June 2015

Please cite this article as: Qiao Gao, Fengyan Li, Lin Xu, 1D pure inorganic helical chain framework built upon banana-shaped molybdovanadates: Synthesis, crystal structure, and magnetic properties, Inorganic Chemistry Communications (2015), doi: 10.1016/j.inoche.2015.06.029

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ACCEPTED MANUSCRIPT 1D pure inorganic helical chain framework built upon banana-shaped molybdovanadates : Synthesis, crystal structure, and magnetic properties Qiao Gao, Fengyan Li, Lin Xu*

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Key Laboratory of Polyoxometalate Science of Ministry of Education, Department of

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Chemistry, Northeast Normal University, Changchun, Jilin 130024, P. R. China

Abstract A

new

molybdovanadate,

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(NH4)12[Na(H2O)5][Na(H2O)2]2[Fe5CoMo22V2O87(H2O)]·19H2O (1) was synthesized and structurally characterized by elemental analysis, IR spectra, UV electronic

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spectroscopy and X-ray diffraction. Compound 1 exhibits a one-dimensional (1D) pure inorganic chain-like framework based on banana-shaped molybdovanadate [Fe5CoMo22V2O87(H2O)]15-.

Ferther,

compound

1

exhibits

good

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anions

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electrocatalytic activity for nitrite reduction. The magnetic investigation reveals a distinct occurrence of ferromagnetic interactions among its Fe5Co cluster.

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Keywords: Molybdovanadate; 1D helical chain; Electrocatalysis; Magnetic property

Polyoxometalates (POMs), a fascinating class of metal–oxygen cluster

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compounds with a unique structural variety and interesting physicochemical properties, have been found to be extremely versatile inorganic building blocks in view of their potential applications in catalysis, magnetism, gas sorption, medicine and materials science [1-6]. Among them, the sandwich-type species are an important subfamily because of their interesting magnetic and electrochemical properties, which usually consist of two trivacant Keggin or Wells--Dawson moieties (e.g., XW9O33-34n-, X'2W15O56 12-, X = PV, AsV, SbIII, BiIII, GeIV, SiIV, CoII, ZnII, etc.; X'= PV, AsV) linked together by transition-metal centers [7-14]. However, little progress has been gained for the synthesis of sandwich-type heteropolymolybdates. Recently, several double-sandwich or banana-shaped polyoxotungstates have been reported, such as [Co7(H2O)2(OH)2P2W25O94]16-

[15],

[Ni4Mn2P3W24O94(H2O)2]17−

and

[Ni6As3W24O94(H2O)2]17- [16], and [((MOH2)M2PW9O34)2(PW6O26)]17- (M=Co2+, 1

ACCEPTED MANUSCRIPT Mn2+) [17], [M6Ge3W24O94(H2O)2]n− (M=FeIII, n=14; M=CoII, n=20; M=MnII / MnIII, n=18) [18].

In 2009

Mialane et

al. addressed a novel banana-shaped

nonairon(II)-containing polyoxometalate-based single-molecule magnets (SMMs),

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[(Fe4W9O34(H2O))2(FeW6O26)]19- [19]. In 2013 Hill et al. reported a hexa-nuclear cobalt(II) cluster incorporated in a banana-shaped tungstovanadate showing catalytic

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activity for the H2O2-based epoxidation of 1-hexene and cyclohexene [20]. However, the heteropolymolybdates analogues are still scarce [21], because the lacunary heteropolymolybdate behaves with structural lability in aqueous solution, so that the

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isolation of a stable complex of lacunary heteropolymolybdate is considerably difficult [22].

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Taking account of catalytic applications, our recent interest has directed to the preparation of heteropolymolybdates incorporating VV as the central tetrahedrally heteroatom.

Herein,

we

report

a

1D

pure

inorganic

chain

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coordinated

(NH4)12[Na(H2O)5][Na(H2O)2]2[Fe5CoMo22V2O87(H2O)]·12H2O

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molybdovanadate

(1). To the best of our knowledge, compound 1 is the first example of 1D pure

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inorganic helical chain framework based on banana-shaped molybdovanadates. Compound 1 was synthesized by a facile one-pot self-assembly reaction under mild condition. NaVO3 (2.4 mmol) and (NH4)6Mo7O24 (1 mmol) were successively

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dissolved in water (20 mL), and then CoCl2 (1 mmol) was added. The pH was adjusted to 5.0 by 4 M ammonium hydroxide. The resulting suspension was heated to about 90℃, and then FeCl3 (0.4 mmol) was added to the hot solution with continued heating for 30 min. The mixture was filtered and allowed to cool to ambient temperature. The brown crystals were isolated after one week (yield: 23% based on Mo). Elemental analysis (%) calc (found): V 2.22 (2.01), Mo 46.01 (45.24), Fe 6.08 (5.92), Co 1.28 (1.12) , Na 1.51 (1.42) , N 3.63 (3.48), H 2.01 (1.82). IR (2% KBr pellet, ν/cm−1): 927(W), 886(s), 772(s), 653(s), 556(m). Single crystal X-ray analysis‡ reveals that 1 crystallizes in the triclinic space group

P

1

and

consists

of

a

polyoxoanion

unit

{[Na(H2O)2]2[Na(H2O)5][Fe5CoMo22V2O87(H2O)]}12-, twelve [NH4]+ cations and 2

ACCEPTED MANUSCRIPT twelve lattice water molecules [23]. The polyoxoanion [Fe5CoMo22V2O87(H2O)]15unit can be considered as a banana-shaped structure containing two {VMo7O28} fragments and a unique central {FeMo7O28} fragment linked via two trimeric moieties,

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{Fe2MoO(μ2-O)2} and {Fe2Co(H2O)}. The Na+ in [Na(H2O)5]+ possesses octahedral coordination environment formed by oxygen atoms from water molecules and unit

(see

Fig.

1a).

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{Fe5CoMo22V2O87(H2O)}

The

neighboring

{[Na(H2O)5][Fe5CoMo22V2O87(H2O)]}14- polyoxoanion units connect alternately via [Na2(H2O)4]2+ units to form a 1D pure inorganic helical chain-like structure (see Fig.

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1b).

The bond valence sum (BVS) calculations for 1 confirmed the oxidation states of

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the Mo and V atoms are +6, and +5, respectively, while those for four octahedral coordination Fe atoms are in the range of 3.036–3.072 with the average value of 3.053,

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and that in the FeO4 group is 2.923. The value of octahedral coordination Co atom is

Electrochemistry

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2.248, which suggests that the valency of all the atoms remains unchanged.

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The electrochemical behavior of compound 1 was investigated using compound 1-modified carbon paste electrode (1-CPE) in 0.4 M HAc–NaAc buffer solution (pH = 4.8) under a scan rate of 0.02 V/s. As shown in Fig. 2a, in the potential range of +1

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V to -1 V, three semi-reversible redox peaks can be observed and the mean peak potentials E1/2 = (Epa + Epc)/2 are 0.715(I), 0.098(II) and -0.42 (III). Each edox peak can be ascribed to redox process of molybdenum. The expected redox peaks of the iron and cobalt ions have not been observed, although the scans were repeated under different conditions for compound 1. The electrocatalytic reduction of nitrite for 1-CPE were studied in 0.4M CH3COONa+CH3COOH buffer solution (pH=4.8). Upon the addition of modest amounts of nitrate, the reduction peak currents of II and III increased while the corresponding oxidation peak currents decreased, suggesting that nitrite was reduced by the reduced POM species (Fig. 2b). The results indicate that compound 1 displays excellent electrocatalytic activity toward the reduction of nitrite. Magnetic properties 3

ACCEPTED MANUSCRIPT The plots of χmT versus T and 1/χm versus T of compound 1 measured from 2 to 300 K in an applied magnetic field of 1000Oe are shown in Figure 3. The experimental χmT value of 1 at room temperature is 21.13 cm3 K mol-1, which is

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slightly lower than the expected value 23.75 cm3 K mol-1 for five isolated Fe3+ ions (S

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= 5/2, g = 2.00) and one Co2+ ion (S = 3/2, g = 2.00) [24-25]. The χmT values

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gradually increase with decreasing temperature, and reach a maximum value of 65.23 cm3 K mol−1 at T = 6K，which is closed to 66.0 cm3 Kmol−1 based on a ground-state spin ST = 11 of antiferromagnetic coupling between Co II and FeIII atoms, and

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ferromagnetic coupling between FeIII atoms. In addition, the 1/χm versus T plot for 1 obeys the Curie–Weiss law [χm =C/(T – θ)] from 100 to 300 K with C = 17.62 cm3 K

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mol–1 and θ = 52.91 K for 1. The positive Weiss constant suggests dominant ferromagnetic interactions.

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In summary, an unprecedented 1D pure inorganic helical chain molybdovanadate was

obtained,

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(NH4)12[Na(H2O)5][Na(H2O)2]2[Fe5CoMo22V2O87(H2O)]·12H2O

representing the first example of 1D architecture containing banana-shaped

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molybdovanadate building units. The results of electrocatalytic experiments for 1 suggest good electrocatalytic activity for nitrite reduction. The result of a magnetic investigation for 1 suggests antiferromagnetic interactions.

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Supplementary material

Selected bond lengths (Å) and angles (deg), IR spectrum, UV/Vis Spectroscopy, XRD data and the TG curve are available for 1. Supplementary data associated with this article can be found, in the online version. Acknowledgments. The authors are thankful for the financial support from the Natural Science Foundation of China (Grant No. 21273031 and 21361027), Jilin Provincial Science and

Technology

Development

Foundation

(Grant

No.

201201068

and

20140101120JC).

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ACCEPTED MANUSCRIPT 69-71. (b) R. Tong, L. Chen, Y. Liu, B. Liu, L.G. Xue, H. Hu, F. Fu, J. Wang, Inorg. Chem. Commun. 13 (2010) 98-100.

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(c) N. Jiang, F.Y. Li, L. Xu, Inorg. Chem. Commun. 13 (2010) 372-375. [19] J.D. Compain, P. Mialane, A. Dolbecq, Angew. Chem. Int. Ed. 48 (2009)

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Dalton Trans. 42 (2013) 58-62.

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[23] Crystal data and structure refinements for 1: Mr = 4624.57 g mol-1, brown blocks, triclinic, space group P 1 , a = 15.5930 Å, b = 17.3436 Å, c = 26.5827 Å, α = 99.9040°, β = 95.6790°, γ = 109.6520°, V = 6573.4 Å3 ,

Z = 2, R1 = 0.0529, wR2

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= 0.1843. Crystal data were measured on a Oxford Diffraction using Mo Kα radiation (λ = 0.71073 ) at 293(2) K. CCDC-1054334 contains the supplementary crystallographic data. [24] M.H. Zeng, Z. Yin, Y.X. Tan, W.X. Zhang, J. Am. Chem. Soc. 136 (2014) 4680−4688. [25] Y.Q. Hu, M.H. Zeng, K. Zhang, S. Hu, J. Am. Chem. Soc. 135 (2013) 7901−7908.

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ACCEPTED MANUSCRIPT Figure Captions

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Fig.1. Combined polyhedral/ball-and-stick representation (a) and Ball and stick

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representation (b) of the 1D chain structure in 2. Color code: MoO6 blue octahedra,

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VO4 yellow terahedra, CoO6 green octahedra, FeO6 dark green octahedral, NaO6 pink octahedral.

Fig. 2. (a) Cyclic voltammograms of 1 in 0.4 M HAc–NaAc buffer solution (pH = 4.8)

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at a scan rate of 10 mV s-1; (b) Cyclic voltammograms of 1-CPE in 0.4 M HAc–NaAc buffer solution (pH = 4.8) containing 0.0–40 mM NaNO2. Scan rate: 0.02

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V/s.

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Fig. 3. χm and χmT versus T curves of 1. Insets: 1/χm versus T curves.

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Figure 1

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Figure 2

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Figure 3

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Graphical Pictogram

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Graphical abstract

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novel

molybdovanadate

consisting

of

banana-shaped

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Graphical Synopsis

molybdovanadate

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[Fe5CoMo22V2O87(H2O)]15- anions arise from a pH-dependent self-assembly process, in which {[Na(H2O)5][Fe5CoMo22V2O87(H2O)]}14- anions could be bridged by

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[Na2O10] unit to form the 1D helical chain framework.

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Research Highlights

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 Compound 1 exhibits a 1D pure inorganic helical chain framework based on

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banana-shaped molybdovanadate anions.  A high electrocatalytic activity on nitrite reduction was demonstrated.  The magnetic investigation reveals a distinct

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occurrence of ferromagnetic interactions in compound 1.

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