New supramolecular hybrids based on A-type Anderson polyoxometalates and Mn–Schiff-base complexes Qiong Wu a,b,c , Shi-Wei Lin a , Yang-Guang Li a , En-Bo Wang a,⇑ a Key Laboratory of Polyoxometalate Science of Ministry of Education, Department of Chemistry, Northeast Normal University, Renmin Street No. 5268, Changchun, Jilin 130024, PR China b Department of Chemical Science and Technology, Kunming University, Yunnan, Kunming 65200, PR China c Stem Cell, Tissue and Organ Engineering Research Center, Kunming General Hospital of Chinese People’s Liberation Army, The Military Medical Institute of Chengdu Military Area CDC, Kunming 650032, PR China article info Article history: Received 5 October 2010 Received in revised form 29 September 2011 Accepted 6 October 2011 Available online 21 October 2011 Keywords: A-type Anderson Polyoxometalate Schiff-base Manganese Photocatalysis abstract By combination of metal–Schiff-base complexes and A-type Anderson heteropolymolybdates, two new metal–Schiff-base polyoxometalate hybrid compounds [Mn(salen)(H 2 O) 2 ] 2 Na 3 [IMo 6 O 24 ]18H 2 O(1) and [Mn(salpn)(H 2 O) 2 ] 2 Na 3 [IMo 6 O 24 ]10H 2 O (2) (salen = N,N 0 -ethylene-bis(salicylideneiminate) and sal- pn = N,N 0 -(1,3-propylene)bis(salicylideneiminate)) have been successfully isolated. Compounds 1 and 2 were characterized by the single crystal X-ray diffraction analysis, elemental analysis, IR spectroscopy, TG analyses and XPS spectra. Single-crystal X-ray diffraction analysis revealed that both compounds exhi- bit 3-D supramolecular networks stabilized by electrostatic attraction and/or extensive hydrogen-bond- ing interactions. Moreover, compounds 1 and 2 represent first two examples of organic–inorganic composite supramolecular compounds based on A-type Anderson polyanion and metal–Schiff-based complexes. Photocatalytic experiment indicates that both compounds exhibit good catalytic activities for photodegradation of RhB with UV irradiation. Ó 2011 Elsevier B.V. All rights reserved. 1. Introduction Supramolecular chemistry that focuses on the system made up of long-range ordered discrete organic and/or inorganic molecular subunits or components represent a modern frontier area in inor- ganic chemistry, coordination chemistry, crystal engineering and materials science offering diverse potential applications that range from molecular recognition, biomimetic catalysts, absorption, magnetic, electronic to photosensitive materials [1–7]. In this area, a vast range of novel supermolecular compounds are obtained from the combination of distinctive multitude organic and/or inor- ganic components behaving simultaneously the inherent natures and/or synergetic interactions of/between precursors. Therefore, one of the most efficient and widely adopted strategies to direct synthesis aiming products with specific properties and structures is the introduction of well defined inorganic moieties and organ- ic/metal–organic building units in the same reaction system [8,9]. Specifically, during the design and synthesis novel supramolec- ular compounds the desired ideal ionic and anionic units should not only be stabilized in various reaction systems but also have the controllable structure for the production of novel compounds. In this aspect, Schiff-base metallic complexes is a class of excellent metal–organic compounds to fabricate supramolecular materials owing to their preferable acid and base stability and the operable Schiff-base ligand that can be easily tuned to accommodation dif- ferent purposes of the various research subjects [10–24]. Numer- ous impressive studies have been made by Miyasaka, Clérac, Oshio, Yamashita, and Gao, which dramatically promotes the development of metal Schiff-base chemistry [25–28]. On the other hand polyoxometalates (POMs), as unique anionic metal–oxide clusters, have a diverse range of applications in catalysis, biology, magnetism, optics and medicine because of their variable building blocks, adjustable connection modes and tunable surface charge density which also qualified POMs units to be an outstanding cat- egory of functional inorganic building blocks in construction of supramolecular compounds [28–44]. However, up to the present the reports made on the combina- tion of these two interesting fields to construct new hybrid mate- rials have been pretty much unexplored [45–48], although Schiff- base chemistry and POMs chemistry both have touched almost unprecedented number of other fields of chemistry. It is worth mentioning that, in spite of numerous supramolecular structures based on classic POMs such as Keggin, Dawson, and Lindquist type have been successfully reported up to now, Anderson-type supra- molecular compounds remain largely unexplored. 0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2011.10.028 ⇑ Corresponding author. Tel./fax: +86 431 85098787. E-mail addresses: [email protected], [email protected](E.-B. Wang). Inorganica Chimica Acta 382 (2012) 139–145 Contents lists available at SciVerse ScienceDirect Inorganica Chimica Acta journal homepage: www.elsevier.com/locate/ica
Transcript
Inorganica Chimica Acta 382 (2012) 139–145
Contents lists available at SciVerse ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier .com/locate / ica
New supramolecular hybrids based on A-type Anderson polyoxometalatesand Mn–Schiff-base complexes
Qiong Wu a,b,c, Shi-Wei Lin a, Yang-Guang Li a, En-Bo Wang a,⇑a Key Laboratory of Polyoxometalate Science of Ministry of Education, Department of Chemistry, Northeast Normal University, Renmin Street No. 5268, Changchun,Jilin 130024, PR Chinab Department of Chemical Science and Technology, Kunming University, Yunnan, Kunming 65200, PR Chinac Stem Cell, Tissue and Organ Engineering Research Center, Kunming General Hospital of Chinese People’s LiberationArmy, The Military Medical Institute of Chengdu Military Area CDC,Kunming 650032, PR China
a r t i c l e i n f o
Article history:Received 5 October 2010Received in revised form 29 September2011Accepted 6 October 2011Available online 21 October 2011
By combination of metal–Schiff-base complexes and A-type Anderson heteropolymolybdates, two newmetal–Schiff-base polyoxometalate hybrid compounds [Mn(salen)(H2O)2]2Na3[IMo6O24]�18H2O (1) and[Mn(salpn)(H2O)2]2Na3[IMo6O24]�10H2O (2) (salen = N,N0-ethylene-bis(salicylideneiminate) and sal-pn = N,N0-(1,3-propylene)bis(salicylideneiminate)) have been successfully isolated. Compounds 1 and 2were characterized by the single crystal X-ray diffraction analysis, elemental analysis, IR spectroscopy,TG analyses and XPS spectra. Single-crystal X-ray diffraction analysis revealed that both compounds exhi-bit 3-D supramolecular networks stabilized by electrostatic attraction and/or extensive hydrogen-bond-ing interactions. Moreover, compounds 1 and 2 represent first two examples of organic–inorganiccomposite supramolecular compounds based on A-type Anderson polyanion and metal–Schiff-basedcomplexes. Photocatalytic experiment indicates that both compounds exhibit good catalytic activitiesfor photodegradation of RhB with UV irradiation.
� 2011 Elsevier B.V. All rights reserved.
1. Introduction
Supramolecular chemistry that focuses on the system made upof long-range ordered discrete organic and/or inorganic molecularsubunits or components represent a modern frontier area in inor-ganic chemistry, coordination chemistry, crystal engineering andmaterials science offering diverse potential applications that rangefrom molecular recognition, biomimetic catalysts, absorption,magnetic, electronic to photosensitive materials [1–7]. In this area,a vast range of novel supermolecular compounds are obtainedfrom the combination of distinctive multitude organic and/or inor-ganic components behaving simultaneously the inherent naturesand/or synergetic interactions of/between precursors. Therefore,one of the most efficient and widely adopted strategies to directsynthesis aiming products with specific properties and structuresis the introduction of well defined inorganic moieties and organ-ic/metal–organic building units in the same reaction system [8,9].
Specifically, during the design and synthesis novel supramolec-ular compounds the desired ideal ionic and anionic units shouldnot only be stabilized in various reaction systems but also have
the controllable structure for the production of novel compounds.In this aspect, Schiff-base metallic complexes is a class of excellentmetal–organic compounds to fabricate supramolecular materialsowing to their preferable acid and base stability and the operableSchiff-base ligand that can be easily tuned to accommodation dif-ferent purposes of the various research subjects [10–24]. Numer-ous impressive studies have been made by Miyasaka, Clérac,Oshio, Yamashita, and Gao, which dramatically promotes thedevelopment of metal Schiff-base chemistry [25–28]. On the otherhand polyoxometalates (POMs), as unique anionic metal–oxideclusters, have a diverse range of applications in catalysis, biology,magnetism, optics and medicine because of their variable buildingblocks, adjustable connection modes and tunable surface chargedensity which also qualified POMs units to be an outstanding cat-egory of functional inorganic building blocks in construction ofsupramolecular compounds [28–44].
However, up to the present the reports made on the combina-tion of these two interesting fields to construct new hybrid mate-rials have been pretty much unexplored [45–48], although Schiff-base chemistry and POMs chemistry both have touched almostunprecedented number of other fields of chemistry. It is worthmentioning that, in spite of numerous supramolecular structuresbased on classic POMs such as Keggin, Dawson, and Lindquist typehave been successfully reported up to now, Anderson-type supra-molecular compounds remain largely unexplored.
In order to explore such systems, the choice of metal–Schiff-base precursors and POM building block is important step thatwas guided by the need of their stable environment, their specificproperties as well as their electrical properties. In this area, wehave recently demonstrated that B-type Anderson POM tertiarystructure can be used for separation of magnetic precursor to ob-tain novel polyoxometalate-based Schiff-base composite materials[49]. As an extension of our proceeding work, we start the investi-gation of different POM units and Schiff-base ligands to constructnovel organic–inorganic hybrids.
In this paper, we carefully choose A-type polyoxoanion [IM-o6O24]5� which processes identical structure motif but differentelectrical properties with B-type polyoxoanion as inorganic–anionicbuilding block to future investigates the electrical impact of differentinorganic tertiary structure on the dinuclear metal–Schiff-baseprecursors: [Mn(salen)(H2O)]2(ClO4)2�H2O, [Mn2(salpn)2(H2O)2]�(ClO4)2 (see Scheme 1) and successfully obtained two novel mono-nuclear Mn–Schiff-base complexes constructed supramolecularcompounds [Mn(salen)(H2O)2]2Na3[IMo6O24]�18H2O (1) and[Mn(salpn)(H2O)2]2Na3[IMo6O24]�10H2O (2). To the best of ourknowledge, 1 and 2 represent two rare examples of POM–metal–Schiff-base supramolecular compounds and the first two hybridcompounds based on A-type Anderson polyoxometalates andSchiff-base metal complexes, furthermore our work may also showsthat A-type Anderson polyanion can be used for structure templatesfor directing Schiff-based {Mnsalen}2 precursor into mononuclearmotif.
2. Experimental
2.1. Synthesis
The reaction between A-type Anderson polyoxoanions {IMo6}and Schiff-base type {Mn2} clusters lead the isolating of two neworganic–inorganic hybrid compounds. As to the design and assem-bly this kind of new type supramolecular architectures there areseveral key factors should be emphasized. Firstly, considering thepolyoxoanions Na3[XMo6(OH)6O18] were synthesized in aqueoussolution and dimeric MnIII-salen complexes were isolated fromthe mixed methanol–water solution, the mixed methanol–watersolution was employed as reaction media. Secondly, parallel exper-iments indicate that when using pure methanol or water as solventmerely amorphous state precipitate instead of crystalline product
can be obtained. Meanwhile suitable heating can increase the pro-ductivity of compound 1 and 2 but when the temperature is higherthan 80 �C, no crystalline phase was formed from the reactionsystem.
2.2. Materials and methods
All chemicals were commercially purchased and used withoutfurther purification. The starting materials [Mn(salen)(H2O)]2
(ClO4)2�H2O, Na5[IMo6O24]�3H2O were synthesized according tothe literatures [50–52] and characterized by IR spectra. Elementalanalyses Cr, Al, Mn and Mo were analyzed on a PLASMA-SPEC (I)ICP atomic emission spectrometer. IR spectra were recorded inthe range 400–4000 cm�1 on an Alpha Centaurt FT/IR Spectropho-tometer using KBr pellets. TG analyses were performed on a Per-kin–Elmer TGA-7 instrument in flowing N2 with a heating rate of10 �C min�1. An UV–Vis absorption spectrum was obtained usinga PC 756 UV–Vis spectrophotometer.
2.2.1. [Mn(salen)(H2O)2]2Na3[IMo6O24]�18H2ONa5[IMo6O24]�3H2O (1.26 g, 1.0 mmol) in distilled water was
added to a solution of freshly prepared [Mn(salen)(H2O)]2
(ClO4)2�H2O (0.88 g, 1.0 mmol) in 20 ml methanol solution. Afterleft to stir overnight in a conical flask at 60 �C for 12 h, the cleardark-brown solution was obtained. After filtration, the filtratewas sealed with parafilm containing tiny pores for facilitating slowevaporation at room temperature. Brown stick-like crystals ofcompound 1 were isolated after 2 weeks. In 26% yield by filtration,washed with methanol, and dried in air. Anal. Calc. forC34H56Mn2N7IMo6O45 1: C, 19.49; N, 4.68; I, 5.98; Mn, 6.05; Mo,27.36. Found: C, 19.11; N, 5.16; I, 5.26; Mn, 5.76; Mo, 29.12%. TGanalysis confirms ca. 18 water molecules in complex 1.
2.2.2. [Mn(salpn)(H2O)]2 Na3[IMo6O24]�10H2O (2)A colorless solution of Mn(OAc)2�4H2O (2.0 g) in 10 mL distill
water was add to the yellow mixture of salicylaldehyde (0.122 g,1.0 mmol), N,N0-(1,3-propylene)bis(salicylideneiminate) (0.121 g,1.0 mmol) and triethylamine (0.101 g, 1.0 mmol), and the mixturewas stirred for 30 min at room temperature. At this point 0.20 gNaClO4 was then added, after this 20 mL aqueous solution contain-ing 1.06 g Na5[IMo6O24]�3H2O (1.0 mmol) was added leading to adark-brown solution. Kept the solution stirring for 12 h and fil-tered. The filtrate was sealed with parafilm containing tiny pores
for facilitating slow evaporation at room temperature. Brown stick-like crystals were obtained after two weeks. In 32% yield by filtra-tion, washed with methanol, and dried in air. C34H56Mn2N7IMo6O38
1: C, 20.59; N, 4.94; I, 6.40; Mn, 5.54; Mo, 29.03. Found: C, 21.96; N,5.16; I, 6.55; Mn, 5.56; Mo, 30.12%. TG analysis confirms ca. 10water molecules in complex 2.
2.3. X-ray crystallography
A dark-brown single crystal of 1 with dimensions of0.28 � 0.26 � 0.23 mm was sealed to the end of a glass capillarywith vaseline. The data were collected on a Rigaku R-AXIS RAPIDIP diffractometer with Mo Ka (k = 0.71073 Å) at 150 K in the rangeof 3.15 < h < 26.88�. A total of 15179 (6941 unique, Rint = 0.0535)reflections were measured (�11 5 h 5 11, �12 5 k 5 12, �24 5l 5 24). The flake-shaped brown crystal of 2 with dimensions of0.35 � 0.26 � 0.23 mm was also sealed in a glass capillary withvaseline for X-ray diffraction test. The data were collected on a Rig-aku R-AXIS RAPID IP diffractometer with Mo Ka (k = 0.71073 Å) at150 K in the range of 3 < h < 27.48�. A total of 16275 (7519 unique,Rint = 0.0478) reflections were measured (�13 5 h 5 13, �15 5k 5 15, �18 5 l 5 18).
The crystal structures of compounds 1 and 2 were solved by thedirect method and refined by the full-matrix least squares on F2
using the SHELXTL-97 software. During the refinement, all non-hydrogen atoms in 1, and 2 were refined anisotropically refined.H atoms on the C atoms were fixed on the calculated positions. Hatoms on the disordered water molecules can not be determinedfrom the difference Fourier maps and directly included in the finalmolecular formula. The highest residual peak and the deepest holeare 1.518 and �1.943 e �3 for 1 and 2.078 and �1.298 e �3 for 2.The detailed crystal data and structure refinement for 1 and 2 were
Table 1Crystal data and structure refinement for 1 and 2.
1 2
Empirical formula C32H64IO45N4Mn2Mo6Na3 C34H56Mn2N7IMo6O38
R1 (I > 2r(I))a 0.0612 0.0509wR2 (all data)b 0.1395 0.1336Goodness-of-fit (GOF) on
F21.042 0.910
Dqmax,min (e �3) 1.518, �1.943 2.078, �1.298
a R1 =P
||F0| � |FC||/P
|F0|.b wR2 =
P[w(F0
2 � FC2)2]/
P[w(F0
2)2]1/2.
given in Table 1. Selected bond lengths and angles of 1 and 2 werelisted in Tables S1 and S2, respectively.
It is worthy mention that, the polyoxoanion and partial sodiumcations in 1 and 2 were all anisotropically refined, while the rest ofthe sodium cations and the solvent water molecules were just re-fined isotropically because of their unusual anisotropic thermalparameters and obvious disorder problems.
3. Results and discussion
3.1. Structural analysis of 1
Single-crystal X-ray structural analysis reveals that compound 1consists of a well-defined A-type heteropolyoxoanion [IMo6O24]5�
building blocks, two typical [Mn(salen)(H2O)]+ cation moieties,three Na+ ions and ten solvent water molecules. As is shown inFig. 1 and Fig. S1, each polyoxoanion [IMo6O24]5� and neighboring[Mn(salen)(H2O)]+ segments stabilized by the electrostatic force ofattraction further connect each other forming a regular threedimensional packing arrangement (see Fig. 2).
There is a half typical A-type polyanion [IMo6O24]5� structuremotif in the asymmetric unit of compound 1, which heteroatom si-ted in special position possessing 50% occupancy rate. The [IM-o6O24]5� segment is composed of seven edge-sharing {XO6}octahedra one {IO6} octahedron locates in the center of polyanionsurrounding by six {MoO6} octahedra. The lengths of the I–Ocbonds are in the range of 1.876(5)–1.897(5). In addition, accordingto the oxygen atoms coordination environments, four type of oxy-gen atoms exist in the cluster: terminal oxygen Ot, terminal oxygenOt0 linked to sodium ions, double-bridging Ob, central oxygen Oc.
Thus, the Mo–O bond lengths can be classified into four types:1.699(6)–1.703(5) Å, 1.697(6)–1.716(6), 1.928(5)–1.939(5), Mo–Oc 2.297(5)–2.361(5) Å. Bond valence sum (BVS) calculations indi-cate that all of these Mo centers exhibit 6+ oxidation state [53].
There is only one crystallographically independent manganeseatom residing in the center of distorted octahedra, which is com-pleted by the N2O2 donor atoms from one Salen2� ligand in the equa-torial mode and two oxygen atoms derived from the water ligands. Inthe equatorial plane, Mn1, O1, O2, N1, and N2 are nearly coplanar.The Mn1–O20, Mn1–O21, Mn1–N1, and Mn1–N2 bond lengths are
Fig. 1. The ball-and-stick representation of the molecular structure unit of 1. All thehydrogen and sodium atoms have been omitted for clarity.
Fig. 2. Polyhedral and ball-and-stick representations of the packing diagram of compound 1 along b-axis. All the hydrogen and sodium atoms have been omitted for clarityand (b) polyhedral representation of the {Na(H2O)3}2[IMo6O24]3� chain in 1.
1.865(1), 1.873(1) Å, 1.986(2), and 1.963(2), respectively. Both of theaxial position of the MnIII are occupied by oxygens coming fromwater molecules, as usually observed for octahedral Mn(III) ions,the Jahn–Teller distortion at the high-spin d4 metal center leads toelongated axial (Mn(1)–O(23) and Mn(1)–O(22) bonds length are2.259 and 2.331 Å, respectively.
Two crystallographically independent sodium ions reside in theunit cell of compound 1, one of which is coordinated by three sol-vent water molecules and three terminal oxygen atoms derivingfrom [IMo6O24]5� unit, leading to the formation of one-dimen-sional chain structure, see Fig 2. The other sodium ion with 50%occupancy is three-coordinated, defined by one terminal oxygenatom deriving form heteropolyoxoanion, one coordinated watermolecule from [Mn(salen)(H2O)]+ as well as a solvent watermolecule.
As shown Fig. S3a, in the packing arrangement of compound 1,every Anderson-type [IMo6O24]5� unit is surrounded by six[Mn(salen)(H2O)]+ moieties, all the heteropolyoxoanion and man-ganese mononuclear complexes are well separated on the a + cplanes. Furthermore, the structure of compound 1 exhibits alter-nate arrangement mode of inorganic and metal–organic layers. Itis noteworthy that, the cationic layers are composed of successiveinterlaced ringent [Mn(salen)(H2O)]+ units by means of strong p–pinteractions with distances of 3.75, 3.66 and 3.74 Å (Fig. S6a).According to the result of H-bond analysis of PLATON software,there is no classic H-bond in the unit cell, thus the p–p stackinginteractions and electrostatic attraction forces play an importantrole in stabilizing the crystal structure of compound 1.
Fig. 3. The ball-and-stick representation of the molecular structure unit of 2. All thehydrogen and sodium atoms have been omitted for clarity.
3.2. Structural analysis of 2
Crystal structure analysis reveals that the cell unit of compound2 consists of one A-type Anderson polyanion [IMo6O24]5�, two
Schiff-based metal–organic complex [Mn(salpn)(H2O)]+ moietiesthree Na+ ions and 10 water molecules leading to an unusual
Similarly with compound 1, the center atom of heteropolyanion[IMo6O24]5� in 2 is also half-occupied iodine atom. The lengths ofthe I–O bonds are in the range of 1.879(4)–1.878(4) Å, and thelengths of Mo–O bonds are, 1.699(4)–1.709(4) Å; Mo–Ot
The mononuclear cationic fragment of 2 constitute of N,N0-(1,3-propylene)bis(salicylideneiminate) and manganese(III) which leadto slightly change of the unit cell dimensions, volumes, bond dis-tances as well as packing arrangement. As shown in Fig. 3 andFig. S2, the MnIII ion has a hexacoordinated octahedral geometrywhich is defined by sapln2� ligand in the equatorial sites and watermolecules on the axial sites. The coordination bond lengths aboutMnIII ions are in the range of 1.882(4)–2.038(5) Å for the equatorialsites(Mn1–N1, N2, O1,O2), and 2.240(5) and 2.269(5) Å for the ax-ial sites(Mn–O1W, O2W). It is noteworthy that, the adjacent inter-laced {Mnsalpn}+ units extend to a dimeric structure by p–pstacking interactions between adjacent benzene ring of Schiff-baseligands with centroid–centroid distance of 3.88(1) Å (Fig. S6b).Consequently, all the {Mnsalpn}+ units possess the same easy-axisdirection and are well dispersed into the interspaces of adjacentinorganic POM layers (Fig. 4).
In compound 2, two crystallographiclly unique Na+ ions exhibitdifferent coordination environments, one of which actes as bridgeslink the A-type Anderson [IMo6O24]5� unit into chain runningalong a axis (Fig. 5), while the other do not take part in extendingthe 1-D structure but hang on the two sides of {Mnsalpn}+ unitsinto 2D layer.
Different from compound 1, analysis result of PLATON softwarepackage indicates that typical intermolecular hydrogen bond (O–H. . .O) interaction exists between terminal oxygen atom O5 and
Fig. 4. Polyhedral and ball-and-stick representations of the packing diagram of compoun
coordination water molecule O1W in compound 2 with a lengthof 2.81(8) Å (Fig. S7). Thanks to the coexist of H bonds, p–p stack-ing interactions and electrostatic attraction forces the whole 3-Dcrystal structure of compound 2 were thus stabilized (Figs. 4 andS5).
3.3. Thermal stability analysis
The TG curves of both complexes show three weight loss steps.The first two weight loss steps are in the temperature range of 40–220 and 40–210 �C, respectively, which are attributed to the loss oflattice and coordinated water molecules (found: 16.62%, Calc.15.28% for 1 and found: 9.12%, Calc. 7.26% for 2). The third weightloss of both complexes all occur from 300 to 570 �C, which are as-signed to the decomposition of the organic components and theloss of H and O atoms in the water molecule form (found:22.86%, Calc. 22.00% for 1 and found: 23.26%, Calc. 25.33% for 2)see Figs. S10 and S11.
3.4. FT-IR, UV–Vis spectroscopy and XPS spectra
The IR spectrum of compound 1 is shown in Fig. S8. A verybroad band in the region between 3600 and 3200 is assigned toO–H stretch characteristic peak indicating the presents of latticewater molecules. The medium strong absorption at 1062 and1544 belong to benzene ring and C@N vibration, respectively. Fourcharacteristic peaks at 906, 849, 797, and 657 are attribute tom(Mo–Ot) and m(Mo–Ob) vibrations of the polyanion, which aresimilar to those in Ref. [42]. The IR spectrum of compound 2 isshown in Fig. S9. The first three strong peaks occur at 3419, 2941and 1062 are attribute to O–H stretch vibration, C@C vibration ofbenzene skeleton and C@N stretch vibration, respectively. Fourcharacteristic peaks at 901, 860, 798, 755, 625 and 589 cm�1 are
d 2 along a-axis. All the hydrogen and sodium atoms have been omitted for clarity.
Fig. 5. XPS spectrum of compound 1.
Fig. 6. Changes in UV–Vis absorption spectra of RhB solutions (2.0 � 10�5 M at pHof 2.0) in the presence of 1.6 mg compound 1.
Fig. 7. Changes in UV–Vis absorption spectra of RhB solutions (2.0 � 10�5 M at pHof 2.0) in the presence of 1.6 mg compound 2.
attributed to m(Mo–Ot), m(Mo–Ob) and m(Mo–Oc) vibrations of thepolyanion, In addition, the peaks at 1455, are assigned to the vibra-tions of –CH2-group of diamine unit.
The UV–Vis spectrum of compounds 1 and 2 are recorded inaqueous solution at a concentration of 1.0–10�4 mol/L. Both com-pounds 1 and 2 exhibit main strong peaks at 240 and 293 nm,respectively, which can be attributed to the O?Mo ligand-to-metalcharge-transfer bands. The broad bands in the visible region of350–370 and 380–400 nm are mainly ascribed to the absorptionof Mn3+ ions, comparing with compound 1 the blue shift of 2 isattribute by the different ligand field effect of Schiff-base ligandsto MnIII centers.
X-ray photoelectron spectrum (XPS) was performed to furtheridentify the oxidation state of the manganese centers in com-pounds 1 and 2. The spectrum of the two compounds are very sim-ilar in the given region, therefore, the spectrum of compound 1 isdescribed here representatively. As shown in Fig 5, the XPS spec-trum of 1 exhibits one strong peak at 641.7 eV in the energy regionof Mn 2p3/2 and one strong peak at 653.2, the distance betweentwo main peaks is about 11.5 eV, which are consistent with theMn3+ oxidation state [54,55].
3.5. Photocatalysis property
It is well know that a wide range of POM possess photocatalyticactivities in the degradations of organic dyes under UV irradiationsby delivering their electrons to the organic substances [56–59]. Weinvestigated the photocatalytic performance of compounds 1 and 2for photodegradation of RhB with UV irradiation by a typical pro-cess: compounds 1 and 2 was dissolved in the presence of Rhoda-mine-B (RhB) solutions (2.0 � 10�5 mol L�1) at pH 3.5 which wasadjusted with dilute aqueous solutions of either NaOH or HClO4,then magnetically stirred in the dark for about 40 min. The solutionwas then exposed to UV irradiation from 125 W Hg lamp at a dis-tance of 4–5 cm between the liquid surface and the lamp. The solu-tion was kept stirring during irradiation. At different time intervals,3.0 mL of samples were taken out of the beaker for analysis. Asshown in Figs. 6 and 7, the A/A0 of RhB decreased obviously from1.55 and 1.6–0.2 and 0.1 in the solutions of 1 and 2 with the irra-diation time 0–480 and 0–360, respectively. These suggest thatsynergetic effect of POM units and Schiff-base segments of com-pounds 1 and 2 may be potential photocatalyst with photocatalyticactivity in reduction of some organic dye.
4. Conclusion
In conclusion, two unusual supramolecular compounds con-structed from metal–Schiff-base and A-type Anderson polyoxo-metalates have been successfully prepared by reactions betweenpolyoxoanion [IMo6O24]5� and Schiff-base cation [Mn(salen/sal-pn)(H2O)]+. Compounds 1 and 2 represent the first two hybridcompounds based on A-type Anderson polyoxometalates and me-tal–Schiff-base complexes. Interestingly, considering our previouswork [49], A/B-type Anderson polyoxoanion can be regard as struc-ture templates for the direction of Schiff-base {Mnsalen}2 precur-sor into dinuclear and mononuclear units, which may indicate anew way to rational synthesis of metal–Schiff-base complexes.Moreover, the photocatalytic performance of compound 1 and 2for photodegradation of RhB with UV irradiation were investigated,and these results indicated the photocatalytic activity in the photo-degradation of RhB.
Acknowledgments
This work was supported by the National Natural Science Foun-dation of China (Nos. 20701005/20701006), the Post-doc StationFoundation of Ministry of Education (No. 20060200002), the Testing
Foundation of Northeast Normal University and Science Founda-tion for Young Teachers of Northeast Normal University (Nos.20070312/20070302).
Appendix A. Supplementary material
CCDC 773564 and 773564 contain the supplementary crystallo-graphic data for compounds 1 and 2, respectively. These data canbe obtained free of charge from The Cambridge CrystallographicData Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplemen-tary data associated with this article can be found, in the onlineversion, at doi:10.1016/j.ica.2011.10.028.
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