由砷鉬酸鹽和鎳配合物構筑而成的有機-無機雜化的化合物

李　杰，田淑芳，劉　云

(河南大學化學化工學院，河南開封475004)

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由砷鉬酸鹽和鎳配合物構筑而成的有機-無機雜化的化合物

李杰*，田淑芳，劉云

(河南大學化學化工學院，河南開封475004)

摘要:利用水熱合成法得到了一個結構新穎的砷鉬酸鹽［Ni( dien)2］2［As6NiMo6O30］·2H2O ( 1) ( dien =二乙烯三胺)，并用紅外光譜、元素分析、熱重分析和X射線單晶衍射對之進行了表征．化合物1屬于單斜晶系，P2( 1) /n空間群．化合物1是由［As6NiMo6O30］4－陰離子簇和［Ni( dien)2］2+配合物構成．

關鍵詞:多金屬氧酸鹽;水熱合成;晶體結構;砷鉬酸鹽

The polyoxomolybdates ( POMs) are of interest，because of their unusual structural chemistry［1－2］and properties that make them attractive for applications in catalysis，materials science，photochemical and electrochemical［3－5］．In this field，arsenatomolybdates show a great variety of unique structures and properties owing to the redox-active nature of both molybdenum and arsenic［2，6］．Such arsenatomolybdates could be molecularly fine-tuned and provide potential new types of catalyst systems，as well as interesting functionalized materials with other properties．Arsenatomolybdate fragments have a large number of terminal and bridge oxygen atoms，so arsenatomolybdate fragments not only could coordinate with metal ion by their terminal and bridge oxygen atoms，but also can act as inorganic ligands multiply to bind several transition-metal complexes ( TMCs)．So far the reports on arsenatomolybdates have been mainly concentrated on several Keggin-type polyanions［7－9］，Dawson-type polyanions［10］，sandwich-like polyanions［11］and other types of polyanions［12－16］．However，in contrast to the rich information on inorganic arsenatomolybdates，the organic-inorganic hybrid arsenatomolybdates remain relatively undeveloped［17－20］．Herein，we report the synthesis and structural characterization of a new organic-inorganic hybrid arsenatomolybdate，［Ni( dien)2］2［As6Ni-Mo6O30］·2H2O ( 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．Thermogravimetric analyses were performed using a Perkin－Elmer7 thermal analyzer from 25 to 800℃under a dry nitrogen atmosphere with a heating rate of 10℃/min．

1．2 Synthesis of compound 1

Hydrothermal treatment of the mixture of Na2MoO4·2H2O ( 0．48 g，2．0 mmol)，As2O3( 0．12 g，0．6 mmol)，Ni( NO3)2·6H2O ( 0．36 g，1．2 mmol)，dien ( 0．20 mL，1．86 mmol)，imidazole ( 0．02 g，0．33 mmol) and 18 mL H2O at 160℃for 5 d with pH = 5．87 gave rise to a quantity of purple block crystals，in about 36% yield ( base on Mo)．Elemental analysis ( %) calculated for C16H52As6Mo6N12Ni3O32: C 9．04，H 2．47 and N 7．90; found: C 8．87，H 2．65 and N 7．62．

1．3 Single-crystal X-ray diffraction ( XRD)

A purple block crystal with dimensions 0．32 mm× 0．23 mm×0．21 mm for 1 was stuck on a glass fiber and intensity data were collected at 296( 2) K on a Bruker Smart Apex-II CCD diffractometer with graphite-monochromated Mo Kαradiation (λ= 0．071 073 nm)．The structure was solved by direct methods and refined by the full-matrix least-squares method on F2using the SHELXTL-97 package［21］．Intensity data was corrected for Lorentz and polarization effects，as well as for multi-scan absorption．All of the non-hydrogen atoms were refined anisotropically．The crystallographic data are listed in Table 1．The atomic coordinates and other parameters of structure have been deposited with the Cambridge Crystallographic Data Centre ( No．1 415278 ; deposit@ ccdc．cam．ac．uk)．

Table 1 Crystal data and structural refinements for compound 1

2　Results and discussion

2．1 Syntheses

In our case，the pH value of a solution is an important factor for the formation of arsenomolybdate．A lot of parallel experiments indicated the most suitable pH value was 5．87．At lower pH values，the N-ligand groups tend to be protonated and fail to bond to the metal ions．

2．2 Crystal structure

Compound 1 has been synthesized under hydrothermal conditions and crystallizes in the monoclinic space group P2( 1) /n．The single-crystal X-ray analysis reveals that compound 1 is constructed from ［As6NiMo6O30］4－anionic clusters and ［Ni( dien)2］2+complex subunits ( see Fig．1)．

Fig．1 Polyhedral/ball-and-stick representation of the molecular structural unit of compound 1．The hydrogen atoms and lattice water molecules are omitted for clarity

The anion ［As6NiMo6O30］4－is composed of the well-known A-type Anderson anion ［NiO6Mo6O18］10－，in which a central { NiO6} octahedron is coordinated with six { MoO6} octahedra hexagonally arranged by sharing their edges in a plane．The cyclic As3O6trimers are capped on opposite faces of the Anderson-type anion plane．Each As3O6group consists of three AsO3pyramids linked in a triangular arrangement by sharing corners and bonded to the central NiO6octahedron and two MoO6octahedra via μ3-oxo groups．This kind of polyoxoanion architecture was reported for the first time by JEANNIN et al．for the cobalt( II) -containing arsenomolybdate ［Co( H2O)6］K2［As6CoMo6O30］［16］．Later，it is exploited that the polyoxoanions ［( MO6) ( As3O3)2Mo6O18］4－( M = Co，Zn，Cu) have been used as inorganic building blocks to construct extended and modified structures［6a，20，22－23］．Coordination sphere of crystallographically unique Ni in the nickel dien complexes is defined by six nitrogen atoms from two dien ligands ( Ni2－N1 = 0．211 9( 4) nm，Ni2－N2 = 0．215 6( 4) nm，Ni2－N3 = 0．213 8 ( 4) nm; Ni2－N4 = 0．213 2 ( 4) nm，Ni2－N5 = 0．216 3( 4) nm，Ni2－N6 = 0．212 4( 4) nm)．Every anionic cluster ［As6NiMo6O30］4－is surrounded by six centrosymmetric complex subunits ［Ni ( dien)2］2+along a axis ( see Fig．2)．

Fig．2 Each anionic cluster ［As6NiMo6O30］4－lies in the centre of six centrosymmetric complex subunits ［Ni( dien)2］2+in compound 1 along the a axis．The hydrogen atoms and lattice water molecules are omitted for clarity

On the basis of valence sum (∑s) calculations［24］，the oxidation states of all three Mo atoms are +6 (∑s = 5．95－5．98)，the three As atoms are + 3 (∑s = 3．00－3．03)，and the oxidation states of the two Ni atoms are +2 (∑s = 2．04－2．10) in 1．The oxidation states of the Mo，As and Ni atoms are consistent with the formula of compound 1．

2．3 IR spectrum

For 1，three groups of characteristic vibration absorption bands are observed at 925，881，804 and 661 cm－1，which are attributed to the ν( Mo－Ot)，ν( Mo－Ob)，ν( As－O)，and ν( Mo－Oc) vibrations，respectively［21，25］．The signals appearing at 3 322 and 2 899 cm－1for 1 are attributable to the ν( NH2) and ν ( CH2) stretching vibrations，while the resonances centered at 1 589 and 1 465 cm－1for 1 are assigned to the δ( NH2) and δ( CH2) bending vibration，respectively．The occurrence of these resonance signals confirms the presence of organic amine groups in 1，which are consistent with the single-crystal structural analyses．

2．4 Thermal analyses

According to the TG curve of compound 1 ( in Fig．3)，we can deduce that the thermal decomposition process of the compound is approximately divided into two steps．There is a continuous decrease in the range of 25－372℃; the weight loss of 22．9% is comparable with the calculated value of 20．9%，corresponding to the loss of two lattice water molecules and 4 molecules of dien．The second weight loss of 22% is between 372 and 673℃due to the sublimation of most As2O3molecules．

Fig．3 TG curve of compound 1

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