Synthesis and property of a layer vanadium oxide with transition metal coordination complexes

TIAN Shufang, LIU Yun, LI Jie

(College of Chemistry and Chemical Engineering, Henan University, Kaifeng 475004, Henan, China))

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Synthesis and property of a layer vanadium oxide with transition metal coordination complexes

TIAN Shufang, LIU Yun, LI Jie*

(CollegeofChemistryandChemicalEngineering,HenanUniversity,Kaifeng475004,Henan,China))

The hydrothermal reaction of ammonium vanadate as starting materials with divalent first-row transition metal cations in the presence of nitrogen donor chelating ligands at 160 ℃ yielded the brown block solid of [Co(dien)2]2[V6O17]·3H2O (1) (dien = diethylenetriamine), which was structurally characterized by elemental analysis, IR and single-crystal X-ray diffraction analysis. Results indicate that the product 1 belongs to monoclinic system of space groupP2(1) /c, and its crystal data are determined to bea= 1.613 4(4) nm,b= 0.866 8(2) nm,c= 1.398 1(4) nm,β= 103.070(4)°,V= 1.904 7(9) nm3,ρ= 2.016 g/cm3,Z= 2. The crystal structure is composed of vanadium oxide layers and [Co(dien)2]2+fragments. These vanadium oxide layers are composed of a {VO}nhelical chain.

polyoxometalate; hydrothermal; crystal structure; hexavanadates

Although polyoxovanadates constitute an important subclass of metal oxide cluster with an exceptional capacity to form mixed-valence compounds that exhibit rich electronic and magnetic properties and have relevance to catalysis, medicine, and materials science[1], it is only recently that attention has been drawn to the synthesis and structure of such new compounds templated by organic amines[2-8]. Until now the examples of polyoxovanadates templated or coordinated by transition metal complexes are still few. They include one-dimensional metavanadate chain compounds[9-10], in which the co-ordination groups are attached to the V-O chains. Some new vanadium oxide layers have also been observed in [Ni(en)2][V6O14][11], (L2M)y[VOx] (L = bidentate amine, M = Cu or Zn, 0.16 ≤y≤ 0.33 and 2.335 ≤x≤ 12.8)[12], [Cd(enMe)2][V8O20][13], Ni(dien)V2O6[14], and K{V12IVV6VO42Cl[Ni(en)2]3}[15]. KHAN et al. have also reported some three-dimensional frameworks which consist of spherical [V18O42(XO4)] cages linked by bridging [M(H2O)4] groups (X = V, S; M = Fe, Co, Mn, Zn)[16]. Vanadium adopts so many co-ordination geometries and multifarious oxidation states, therefore the metal ions as well as the organic ligands also influence on the structures. Recently we have always devoted ourselves to the systemative investigation of polyoxovanadates in order to find the effective pathways to design and synthesize the metal oxide clusters with the neoteric and intriguing structures. In this paper, we report on the hydrothermal synthese, structure and thermal property of a layered vanadium oxide with interlayer metal coordination complex: [Co(dien)2]2[V6O17]·3H2O (1) (dien = diethylenetriamine).

1 Experiment

1.1 Materials and physical measurements

All reagents were purchased commercially and used without further purification. C, H, and N elemental analyses were performed on a Perkin-Elmer 240C elemental analyzer. Inductively coupled plasma (ICP) analysis was performed on a Perkin-Elmer Optima 2000 ICP-OES spectrometer. Infrared spectra were recorded on a Bruker VERTEX 70 IR spectrometer using KBr pellets from 400 to 4 000 cm-1.

1.2 Synthesis of compound 1

Raw materials used in the synthesis were NH4VO3, Co(NO3)2· 6H2O, dien, 1, 4-Bis(imidazole-l-ylmethyl)benze, and distilled water. In a typical synthesis of compound 1, 0.34 g of NH4VO3was added to 20 mL of distilled water, to which 0.58 g of Co(NO3)2· 6H2O, 0.25 mL of dien and 0.12 g of 1, 4-bis(imidazole-l-ylmethyl)benze were added with stirring. The reaction mixture was sealed in a 30 mL Teflon-lined autoclave and heated under autogenous pressure at 160 ℃ for 3 d. The crystals were separated mechanically, washed with water and dried in air at ambient temperature. The yield of compound 1 was ca. 12% based on vanadium. Anal. Calc. for C16H52Co2N12O20V6: C, 16.62; H, 4.53; N, 14.54. Found: C, 16.45; H, 4.67; N, 14.46.

1.3 Single-crystal X-ray diffraction (XRD)

The crystal structure of 1 was determined by single crystal X-ray diffraction methods. The data on a crystal with dimensions 0.31 mm × 0.27 mm × 0.23 mm were collected on a Bruker Smart Apex-II CCD diffractometer with graphite monochromated Mo Kαradiation (λ= 0.071 073 nm). Cell constants and an orientation matrix for data collection were obtained from least-squares refinements of the setting angles in the range of 1.30° ≤θ≤ 25.09°. Routine Lorentz polarization and an empirical absorption correction were applied to intensity data. On the basis of systematic absences and statistics of intensity, the space groups wereP2(1)/c. Their structures were determined and the heavy atoms were found by direct methods using the SHELXTL-97 program package[17]. The remaining atoms were found from successive full-matrix least-squares refinements onF2and Fourier syntheses. No hydrogens associated with water molecules were located from the difference Fourier map. Positions of the hydrogens attached to carbon and nitrogen were geometrically placed. All hydrogens were refined isotropically as a riding mode using the default SHELXTL parameters. A total of 9 425 reflections were collected, of which 3 393 unique reflections (Rint= 0.022 0) were used for structural elucidation. A summary of the crystallographic data is given in Table 1. CCDC reference number is 1542235.

Table 1 Crystal data and structural refinements for compound 1

2 Results and discussion

2.1 Synthesis

The simple hydrothermal route is an effective way to synthesize a great variety of inorganic solid-state materials, which contain amine-ligated transition metal cations situated between vanadium oxide layers. The vanadium oxide [Co(dien)2]2[V6O17]·3H2O (1) is prepared in the hydrothermal method by the reaction of the transition metal element, the mixed ligands, and NH4VO3in aqueous solution at 160 ℃, and is isolated as thin brown block crystalline.

2.2 Structure determination

Compound 1 shares similar structural features of vanadium oxide layers as well as six-coordinate interlayer cations with [Zn(bipy)2]2[V6O17][12]. Fig. 1 shows the coordination environments around the Co and V atoms in 1. The Co atoms reside in a six-coordinate and very regular CoN6octahedral environment with the Co-N bond lengths [0.194 9(3)-0.196 6(3) nm], which are similar to those of the previously reported compounds[18-19]. The coordination atoms of Co atom in 1 are different from that of the Zn atoms in [Zn(bipy)2]2[V6O17], which are four N atoms from two bidentate amine ligands and two O atoms from the VO layer. The layers are built up in all cases from VO4te-trahedra or VO5square pyramids, connected by edge- or corner-sharing interactions. The three vanadium atoms V1, V2 and V3 of 1 are crystallographically distinct. They adopt distorted tetrahedral environments and are corner-shared by O1, O4 and O7 atoms to form VO4helical chains instead of V4O12tetramer rings as in the case of Cu(dien)V2O6· H2O[14]. The bond distances of the bridging oxygen and the vanadium atoms (V-μ2-O) are the V-O1 [mean: 0.180 3(2) nm], V-O4 [mean: 0.180 5(3) nm] and V-O7 [mean: 0.178 9(3) nm], which are close to each other, however these values are very much smaller than those in [Ni(en)2][V6O14] [mean: 0.213 7(2) nm][11]. The remaining terminal oxygen atoms have V=O distances between 0.160 7(3) and 0.164 0(3) nm, which are bigger than those of [Ni(en)2][V6O14] [1.576(6)-1.603(8) nm]. The the O-V-O angles vary from 105.15(13)° to 111.53(13)°, which are comparable to the reported vanadates data.

Fig.1 Co-ordinations around the Co and V atoms with the atomic labeling scheme in compound 1 with H atoms omitted for clarity

Fig.2 displays the framework structure of compound 1. The inorganic layers formulated by [V6O17]4-are composed solely of VO4tetrahedra. All of VO4te-trahedra have two vanadyl oxygen groups (V=O) toward opposite sides of the layer and share two corners with two neighboring VO4units to form a ‘V’ shape V3O10building group. The V3O10groups are connected through sharing corners in the alternating “up” and “down” orientations, which leads to the information of a helical chain. This unique characteristic of the polyhedral arrangement has not been reported for any other single-layer vanadium oxide, and it has even been suggested that this arrangement of two corner-shared vanadium tetrahedra oriented in the same direction is not possible[20]. The screw pitch of the inorganic framework helical chain is about 0.727 nm.

Fig.2 Projection of compound 1 along the b axis, showing the vanadium oxide layers with [Co(dien)2]2+ complexes located in the interlayer positions. The hydrogen atoms are omitted for clarity

On the basis of valence sum (∑s) calculations[21], the oxidation states of the two Co atoms are +2 (∑s= 2.15-2.19) and the six V atoms are +5 (∑s= 5.22-5.24) in 1. The oxidation states of the Co and V atoms are consistent with the formula of compound 1.

2.3 IR spectrum

In the IR spectrum of compound 1, strong bands at 1 012 and 983 cm-1are assigned to the terminal V=O stretching in VO4tetrahedra. Features at 883 and 761 cm-1are related to the symmetric and antisymme-tric stretching of V-O-V (Fig. 3). In addition, stretches of -OH, -NH2, and -CH2are observed at 3 437, 3 302 and 3 210, 2 938 and 2 880 cm-1for 1. Bands at 1 629, 1 570, and 1 451 cm-1for 1 are assigned to bending vibration of -OH, -NH2, and -CH2, respectively[22]. The vibration pattern ofν(C-N) is at 1 390 cm-1for 1. The occurrence of these resonance signals confirms the presence of organic amine groups, which are consistent with the single-crystal structural analyses.

Fig.3 IR spectrum of 1

3 Conclusion

In conclusion, this work describes the structure of a new vanadium oxide with transition metal coordination complexes. The result demonstrates that compound 1 bears such a kind of structure type with vanadium oxide layers. These vanadium oxide layers are composed of a {VO}nhelical chain. The V-O-V linkages play a critical role in constructing the layer structure.

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[責任編輯:吳文鵬]

含有過渡金屬配合物的層狀釩氧化物的合成和性質

田淑芳，劉 云，李 杰*

(河南大學 化學化工學院,河南 開封 475004)

以釩酸銨為起始原料，在螯合配體存在下，利用水熱合成法將其與二價第一行過渡金屬陽離子在160 ℃反應得到了一個棕色塊狀化合物[Co(dien)2]2[V6O17]·3H2O (1) (dien = 二乙烯三胺)，并用元素分析、紅外光譜和X 射線單晶衍射對之進行了定性分析. 結果表明,化合物1 屬于單斜晶系,P2(1) /c空間群;其晶格參數為：a= 1.613 4(4) nm,b= 0.866 8(2) nm,c= 1.398 1(4) nm;β= 103.070(4)°;V= 1.904 7(9) nm3;ρ= 2.016 g/cm3;Z= 2. 化合物1是由釩氧層和[Co(dien)2]2+構成. 這些釩氧層是由{VO}n螺旋鏈組成.

多金屬氧酸鹽；水熱合成；晶體結構；六釩酸鹽

The Foundation of Education Department of Henan Province(15A150037).

, E-mail：lllijie2007@henu.edu.cn.

O614.5 Document code： A Article ID： 1008-1011(2017)03-0321-05

Received date： 2007-04-13.

Biography： TIAN Shufang (1982-)，female，lecturer，research field: polyoxomolybdate chemistry.*