Triol-Ligand Modification and Structural ... - ACS Publications

Mar 7, 2017 - The reaction of the mother cluster [(n-C4H9)4N]3[Co(OH)6Mo6O18] and triol ligands in methanol resulted in a codecoration of methanol wit...
2 downloads 0 Views 2MB Size
Download PDF
Article pubs.acs.org/IC

Triol-Ligand Modification and Structural Transformation of Anderson−Evans Oxomolybdates via Modulating Oxidation State of Co-Heteroatom Yang Wang,† Xiaoting Liu,†,‡ Wei Xu,§ Ying Yue,† Bao Li,*,†,‡ and Lixin Wu† †

State Key Laboratory of Supramolecular Structure and Materials, ‡Institute of Theoretical Chemistry, and §State Key Laboratory of Inorganic Synthesis & Preparative Chemistry, Jilin University, Changchun 130012, P. R. China S Supporting Information *

ABSTRACT: Various covalent decorations and structural transformations of a series of R−C(CH2OH)3 triol ligands on CoII/CoIIIcentered Anderson−Evans polyoxomolybdates were studied in aqueous and/or organic solution. Single-crystal X-ray structural analysis demonstrated that four manners, including (1) double-sided χ/χisomer and (2) double-sided δ/χ-isomer with CoII central heteroatom, and (3) single-sided δ-isomer and (4) double-sided δ/δ-isomer with CoIII central heteroatom, appeared on the decoration of the mother polyanion [CoII/III(OH)6Mo6O18]4−/3−. Through careful manipulation of the reaction conditions, a gradual oxidation process from CoII to CoIII was disclosed to happen in air, and accompanying that process, the CoIIcentered double-sided δ/χ-isomer that formed in the initial stage transformed into a CoIII-centered double-sided δ/δ-isomer. When the electron-withdrawing group −NO2 substituted triol ligand was used to replace CH3C(CH2OH)3, the oxidation process accelerated spontaneously. A further investigation showed that this oxidation process can be blocked by acid. While the triol ligands’ decoration on Anderson−Evans polyoxometalates (POMs) took place along with the oxidation of the central heteroatom, that codecoration of other components was also accomplished. In the presence of excess acetic acid, an unprecedented single-sided δ-isomer with an acetate ligand covalently attaching on the other side by replacing one μ3-O atom was obtained in aqueous solution. The reaction of the mother cluster [(n-C4H9)4N]3[Co(OH)6Mo6O18] and triol ligands in methanol resulted in a codecoration of methanol with the double-sided δ/δ-isomer, which has never been reported in B-type Anderson−Evans POMs. The obtained results revealed that the oxidation state of the heteroatom has a significant impact on the triol ligand decoration styles, such as the χ/χ- or δ/χ-isomer for the divalent heteroatom and the δ- or δ/δ-isomer for the trivalent heteroatom.

■

INTRODUCTION Anderson−Evans polyoxometalates (POMs) are a class of metal−oxygen polyanionic clusters1 with the general formula [Xn+M6O24Hm](12−n−m)−, in which X indicates the heteroatom and M is the coordination atom (Mo or W), while m = 0 or 6 denotes A- or B-type structure.2,3 This class of POMs possesses unique magnetic and electrochemical properties,4,5 making them ideal candidates for bio- and nanomaterials.6,7 In contrast to A-type clusters that can be grafted by only alcohols at bibridging (μ2) oxygen atoms, the B-type POMs can be modified at both tribridging (μ3) and dibridging μ2-O atoms by triol derivatives with a formula of R−C(CH2OH)3 (R: −NH2, −OH, or other substituted groups) or other ligands with multiple oxygen coordination sites.8 The covalent decoration provides numerous opportunities for utilizing the hybrid POMs in supramolecular self-assembly9−11 and bioapplications.12−17 However, the construction of versatile decoration architectures and understanding the modification chemistry still remain to be the fundamental challenges because several key factors, including heteroatoms and coordination atoms, ligands, grafting sites, and reaction conditions, affect the final hybrid products © XXXX American Chemical Society

but have not been discerned, which are not fully unmasked but in close relation to the functionalization of Anderson−Evans POMs.18 Following the initial modification of triol ligands on MnIII centered Anderson−Evans polyoxomolybdate,19 several other divalent or trivalent transition metal ions were used as heteroatoms for double-sided modification, and the formation process for a typical cluster, [MnMo6O18((OCH2)3CNH2)2]3−, prepared from TBA4Mo8O26 (TBA = tetrabutylammonium cation) was clearly analyzed.20 Accordingly, symmetric and asymmetric modifications of CrIII-, MnIII-, and AlIII-centered clusters were realized utilizing either hydrothermal conditions or by controlling the ratio of ligand.21−23 On the other hand, a dimeric structure of CrIII-centered POM that was modified on one side was also obtained,24 and we reported the single-sided decoration of AlIII-centered discrete clusters with a series of triol ligands and their recognition-induced chiral migration in aqueous solution.25,26 The single-sided modifications to FeIIIReceived: March 7, 2017

A

DOI: 10.1021/acs.inorgchem.7b00614 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

Scheme 1. Schematic Illustration for the Decoration Fashions and Synthetic Parameters in the Preparation and Transformation of Co-centered Anderson−Evans POMs 1−8a

a

The codes are added to represent corresponding compounds.

and GaIII-centered Anderson−Evans POMs were then conducted to support protein crystallization.27 In an extra acidic condition, the single-sided χ-isomer28 and diol alkoxo ligand decorated POMs could be obtained.29 In addition to oxomolybdate, triol ligand decorated Anderson−Evans oxotungstate with NiII serving as the heteroatom revealed similar modification chemistry.30 Based on all known modifications of Anderson−Evans POMs, we proposed five prominent types consisting of single-sided decoration fashions, δ-isomer and χisomer, double-sided decoration styles, axial symmetric δ/δisomer, helical symmetric χ/χ-isomer, and δ/χ-isomer in malposition, as shown in Figure S1, and succeeded in synthesizing CuII-centered Anderson−Evans POMs in a double-sided δ/χ-isomer decoration type.31 It is found that the acidity of the reaction system and the identity of the heteroatoms play crucial roles for both the activation of the reaction site and the final decoration type. In most cases (but not all), the divalent heteroatoms and acidic conditions lead to χ/χ-isomers while the trivalent heteroatoms and suitable reaction environments afford either δ- or δ/δisomers. But the principle for the regularity is still not clarified completely. As the acidity of oxometalate associates closely with the metals and its valence, the decoration type can be modulated by changing both the metal ions and their oxidation states. However, only a limited series of metal ions, such as CrIII, MnIII, FeIII, NiII, CuII, ZnII, GaIII, and AlIII,18 have been used as the heteroatoms for covalent decoration of triol ligand on Anderson−Evans POMs. Additionally, there is no example showing heteroatoms in different oxidation states that is used for adjustable triol ligand decoration. Therefore, to understand the chemistry occurring in organic decoration, our motivation is to bring a heteroatom that has changeable valence for the modification of organic components and to realize the transformation of decoration type by modulating the oxidation state of the heteroatom and the acidity of the reaction system to achieve more possible decoration types in one cluster.

The cobalt atom has a similar atomic radius with iron, nickel, and copper; however, it has not been used yet for organic modification of Co-centered Anderson−Evans POMs, as pointed out in a recent review.18 By utilizing Co as the heteroatom, we synthesized a series of organic groupfunctionalized CoII/III-centered Anderson−Evans POMs in χ/ χ-isomer, δ/χ-isomer, δ-isomer, and δ/δ-isomer, triol ligand/ acetic acid codecorated δ-isomer, and triol ligand/methanol codecorated δ/δ-isomer. Interestingly, the utmost decoration types in one heteroatom centered POM were achieved by controlling the oxidation state and reaction conditions, as presented in Scheme 1. Meanwhile, we realized the codecoration of triol ligand/auxiliary ligands on the mother Anderson−Evans polyanion at different substitutional positions. Importantly, while it directs the rich decoration types, the oxidation of the heteroatom from CoII to CoIII is also demonstrated under different conditions.

■

EXPERIMENTAL SECTION

General Methods and Materials. All chemicals were purchased from Aladdin and were used without further purification. The two types of molybdate clusters, TBA4Mo8O26 and TBA2Mo2O7, and undecorated Anderson−Evans POM, Na3[Co(OH)6Mo6O18]·8H2O, were prepared according to the published procedures.32−34 Fourier transform IR spectra were recorded on a Bruker Vertex 80v spectrometer equipped with a DTGS detector (32 scans) under a resolution of 4 cm−1 in KBr pellets. Elemental analysis for C, H, and N was carried out on a vario MICRO cube from the Elementar Company of Germany. Elemental analysis for Cu and Mo was taken on a PLASMA-SPEC (I) inductively coupled plasma atomic emission spectrometer. Thermogravimetric analysis (TGA) was performed on a Q500 Thermal Analyzer (New Castle TA Instruments) in flowing N2 under a heating rate of 10 °C·min−1. UV−vis spectra were obtained from a Varian Cary 50 UV/vis spectrophotometer. Electrochemical experiments were carried out on a CHI 660C electrochemical workstation with a three-electrode electrochemical cell, where the work electrode is a glassy carbon electrode, the reference electrode is a Ag/Ag+ nonaqueous electrode, and the counter electrode is platinum. Oxygen was removed by purging high-purity nitrogen in the solution, B

DOI: 10.1021/acs.inorgchem.7b00614 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry Table 1. Summary of Crystal Data and Structure Refinements for 1−8 Formula

F.W. S.G. a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z Dc (g cm−3) F(000) Reflections coll./ unique Rint GOF on F2 R1a [I > 2σ(I)] wR2b(all data) a

1

2

3

4

5

6

C42H92Co Mo6N2O24 ·C8H12N4 1807.96 P21/c 13.260(3) 19.555(4) 18.213(3) 90 130.99(2) 90 3565(2) 2 1.684 1834 33534/8150

C58H127Co Mo6N3O24 ·C3H7NO•C2H6O 2004.36 P21/c 15.168(3) 25.469(5) 23.966(9) 90 110.67(3) 90 8662(4) 4 1.537 4132 47586/15130

C53H120Co Mo6N3O24 ·H20O10 1998.25 P212121 21.871(4) 25.541(5) 15.077(3) 90 90 90 8422(3) 4 1.576 4120 82356/19189

C58H126Co Mo6N3O24 ·C8H18N2O2 2058.43 P21/c 25.703(5) 13.978(3) 24.777(5) 90 92.21(3) 90 8894(3) 4 1.537 4248 79842/20126

C56H120Co Mo6N5O28 ·C4H6N2 2028.25 C2/c 22.444(5) 13.456(3) 28.656(6) 90 96.38(3) 90 8601(3) 4 1.566 4152 39919/9793

C40H86Co Mo6N4O28 ·C4H8O4 1825.80 P21/c 14.128(3) 21.185(4) 23.140(5) 90 94.29(3) 90 3301(1) 2 1.756 3684 58323/15671

C43H98Co Mo6N3O25

7

C43H93Co Mo6N2O24

8

1691.81 Pna21 18.677(4) 14.766(3) 23.686(5) 90 90 90 6532(2) 4 1.720 3424 56579/14829

1656.76 P1̅ 14.227(3) 14.569(3) 18.017(4) 112.38(3) 91.18(3) 110.04(3) 3195(1) 2 1.722 1672 31194/14327

0.0368 1.077 0.0342 0.0831

0.1110 1.048 0.0904 0.2181

0.0659 1.025 0.0530 0.1432

0.0442 1.047 0.0358 0.0914

0.0345 1.055 0.0330 0.0863

0.0806 1.036 0.0609 0.1266

0.0525 0.954 0.0393 0.0891

0.0333 1.057 0.0543 0.1892

R1 = ∑∥Fo| − |Fc∥/∑|Fo|. bwR2 = ∑[w(Fo2 − Fc2)2]/∑[w(Fo2)2]1/2. 2934, 2872, 1665, 1480, 1464, 1371, 1113, 1041, 931, 913, 895, 741, 707, 671, 598, and 418. Synthesis of [(n-C 4 H 9 ) 4 N)]3 {CoMo 6 O 18 (OH)3 [CH 3 C(CH 2 O) 3 ]}· 10(H2O) (3). Na3[Co(OH)6Mo6O18]·8H2O (1.00 g, 0.81 mmol) was dissolveded in 20 mL of boiled deionized water, and then CH3C(CH2OH)3 (0.20 g, 1.66 mmol) was added. The reaction solution was refluxed for ca. 3 h and cooled down to room temperature. After the addition of TBA·Br (1.04 g, 3.23 mmol), the reaction solution was filtered and the filtrate was maintained for several days to crystallize green product (0.70 g, yield 44.3% based on Mo). Elem anal. Calcd for CoMo6C53N3O34H117: Co, 2.98; Mo, 29.15; C, 32.23; H, 5.97; N, 2.13. Found: Co, 2.93; Mo, 29.20; C, 32.19; H, 5.91; N, 2.15. IR (KBr, cm−1): 3434, 2961, 2935, 2873, 1481, 1462, 1380, 1129, 1037, 939, 916, 899, 741, 658, 572, and 436. Synthesis of [(n-C 4 H 9 ) 4 N)] 3 {CoMo 6 O 18 [CH 3 C(CH 2 O) 3 ] 2 }·2[(CH3)2NCOCH3] (4). This compound was prepared in three approaches. In route 1, TBA3[Co(OH)6Mo6O18] (0.20 g, 0.11 mmol) and CH3C(CH2OH)3 (0.03 g, 0.22 mmol) were dissolved in 20 mL of CH3OH and the solution was heated to reflux for 12 h and then cooled down. The solution was allowed to stand at room temperature to give crude green products. The crude products were recrystallized from N,N-dimethylacetamide (DMA), giving green crystals (0.15 g, yield 63.8% based on Mo). Elem anal. Calcd for CoMo6C66N5O26H144: Co, 2.86; Mo, 27.96; C, 38.51; H, 7.05; N, 2.40. Found: Co, 2.82; Mo, 27.92; C, 38.54; H, 7.04; N, 2.43. IR (KBr, cm−1): 3658, 2960, 2933, 2872, 1667, 1470, 1460, 1385, 1114, 1043, 929, 914, 892, 751, 706, 673, 599, and 439. In route 2, Co(CH3COO)2·4H2O (0.05 g, 0.20 mmol), TBA2Mo2O7 (0.48 g, 0.60 mmol), and CH3C(CH2OH)3 (0.05 g, 0.42 mmol) were dissolved in 20 mL of DMF and the mixture was stirred at 85 °C for 72 h. The formed dark solution was allowed to stand for several days to obtain crude green products. Recrystallization from DMA gives green crystals with identical structure to that obtained in route 1 (0.15 g, yield 38.1% based on Mo). In route 3, 3 (0.20 g, 0.10 mmol) and CH3C(CH2OH)3 (0.024 g, 0.20 mmol) were dissolved in 20 mL of methanol, and the solution was heated to reflux for 12 h. The obtained green solution was aged for several days to generate crude green products. The recrystallization from DMA gives pure green crystals with identical structure to those from the other two routes (0.18 g, yield 86.5% based on Mo). Synthesis of [(n-C4H9)4N]3{CoMo6O18[O2NC(CH2O)3]2}·2(CH3CN) (5). A mixture of Co(CH3COO)2·4H2O (0.10 g, 0.40 mmol),

and a nitrogen atmosphere was maintained in the process of electrochemical measurements. Single-crystal X-ray diffraction data were collected on a Rigaku R-AXIS RAPID imaging plate diffractometer with graphite-monochromated Mo Kα (λ = 0.71073 Å) at 293 K. The empirical absorption correction based on equivalent reflections was applied. All complex crystals were solved by direct methods and refined by full-matrix-least-squares fitting on F2 using the SHELXTL-2014 software.35 All non-H atoms, except some lattice solvent molecules, were refined with anisotropic thermal parameters. A summary of the crystallographic data and structural refinements for 1− 8 is listed in Table 1. Synthesis of [(n-C4H9)4N)]2{CoMo6O16(OH)2[CH3C(CH2O)3]2}·4(CH3CN) (1). The compound was prepared through two approaches. For route 1, a mixture of Co(CH3COO)2·4H2O (0.10 g, 0.40 mmol), TBA4Mo8O26 (0.65 g, 0.30 mmol), and CH3C(CH2OH)3 (0.10 g, 0.83 mmol) was dissolved in 50 mL of acetonitrile and heated to reflux for 12 h. The orange reaction solution was cooled to room temperature and stood for several days to obtain orange crystals (0.42 g, yield 58.3% based on Mo). Through altering solvent from acetonitrile to N,N-dimethylformamide (DMF) or the mixture of methanol and DMF, the purified product was also obtained. Elem anal. Calcd for CoMo6C50N6O24H104: Co, 3.26; Mo, 31.84; C, 33.22; H, 5.80; N, 4.65. Found: Co, 3.21; Mo, 31.82; C, 33.19; H, 5.81; N, 4.65. IR (KBr, cm−1): 3620, 3442, 2962, 2934, 2873, 1480, 1468, 1381, 1108, 1048, 935, 925, 911, 733, 683, 556, and 423. For route 2, Co(CH3COO)2· 4H2O (0.05 g, 0.20 mmol), TBA2Mo2O7 (0.48 g, 0.60 mmol), and CH3C(CH2OH)3 (0.05 g, 0.42 mmol) were dissolved in 20 mL of methanol and the mixture was heated to reflux for 12 h, yielding an orange solution. The tabular orange crystals were obtained after several days (0.29 g, yield 79.0% based on Mo). The structural characterization gives identical product results as that from route 1. Synthesis of [(n-C 4 H 9 ) 4 N)] 3 {CoMo 6 O 17 (OH)[CH 3 C(CH 2 O) 3 ] 2 }· (CH3)2NCHO·CH3CH2OH (2). A mixture of Co(CH3COO)2·4H2O (0.05 g, 0.20 mmol), TBA2Mo2O7 (0.48 g, 0.60 mmol) ,and CH3C(CH2OH)3 (0.05 g, 0.42 mmol) was dissolved in 20 mL of acetonitrile and heated to reflux for 12 h. The yielded brown solution was cooled down to room temperature. To the solution was added a mixture of ethanol and DMF, and the resulting mixture was allowed to stand at room temperature for several days to obtain crystals (0.15 g, yield 38.1% based on Mo). Elem anal. Calcd for CoMo6C63N4O26H140: Co, 2.94; Mo, 28.72; C, 37.75; H, 7.04; N, 2.80. Found: Co, 2.91; Mo, 28.62; C, 37.69; H, 6.99; N, 2.82. IR (KBr, cm−1): 3658, 3427, 2960, C

DOI: 10.1021/acs.inorgchem.7b00614 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

for the synthesis of triol ligand decorated CoII/III-centered Anderson−Evans POMs. Interestingly, four triol ligand covalently decorated Co-centered Anderson−Evans POMs were obtained, and characterized carefully by elemental analysis, IR spectra, TGA, and single-crystal X-ray diffraction analysis. In the synthesis of triol ligand decorated CoII-centered POMs, we selected TBA4Mo8O26 and TBA2Mo2O7 as Mo sources to conduct one-pot reactions with CoII(CH3COO)2 and triol ligands in organic solvents following the literature and our previous work.19,31 When using TBA4Mo8O26 as the precursor in acetonitrile, product 1 is obtained as a centersymmetric χ/χ-isomer, in which triol ligand covalently decorates on [CoII(OH)6MoO18]4−. Single-crystal X-ray analysis reveals that the polyanion (Figure 1a) exhibits a

TBA4Mo8O26 (0.65 g, 0.30 mmol), and O2NC(CH2OH)3 (0.12 g, 0.80 mmol) were dissolved in 50 mL of acetonitrile and heated to reflux for 12 h. The brown solution was cooled to room temperature, and green crystals were obtained after several days (0.58 g, yield 71.6% based on Mo). Elem anal. Calcd for CoMo6C60N7O28H126: Co, 2.91; Mo, 28.38; C, 35.53; H, 6.26; and N, 4.83. Found: Co, 2.91; Mo, 28.36; C, 35.59; H, 6.21; and N, 4.85. IR (KBr, cm−1): 3432, 2963, 2938, 2874, 1480, 1466, 1381, 1077, 944, 925, 907, 741, 669, 568, and 423. Synthesis of [(n-C4H9)4N]2{CoMo6O16(OH)2[O2NC(CH2O)3]2}·2(CH3COOH) (6). A mixture of Co(CH3COO)2·4H2O (0.10 g, 0.40 mmol), TBA4Mo8O26 (0.65 g, 0.30 mmol), and O2NC(CH2OH)3 (0.12 g, 0.80 mmol), and 0.5 mL of acetic acid was added to 50 mL of acetonitrile and heated to reflux for 12 h. After cooling to room temperature, the yellow byproduct was filtered out and the orange crystalline product was obtained from the filtrate at room temperature (0.10 g, yield 15.2% based on Mo). Elem anal. Calcd for CoMo6C44N4O32H94: Co, 3.23; Mo, 31.53; C, 28.94; H, 5.19; and N, 3.07. Found: Co, 3.22; Mo, 31.55; C, 28.98; H, 5.14; and N, 3.06. IR (KBr, cm−1): 3488, 3350, 2963, 2932, 2874, 1652, 1471, 1454, 1380, 1087, 945, 923, 899, 742, 677, 553, and 424. Synthesis of [(n-C3 H 7 ) 4 N]3 {CoMo6 O 18 (OH) 2 (CH 3 COO)[CH3 C(CH2O)3]} (7). Na3[Co(OH)6Mo6O18]·8H2O (1.00 g, 0.81 mmol) was dissolveded in 20 mL of boiled deionized water. Followed by the addition of CH3C(CH2OH)3 (0.2 g, 1.66 mmol) and 3 mL of acetic acid, the solution was refluxed for 3 h. (n-C3H7)4N·Br (0.86 g, 3.23 mmol) was added to the cooled reaction solution, and after a filtration, the filtrate was allowed to crystallize out the green product in several days (0.50 g, yield 36.76% based on Mo). Elem anal. Calcd for CoMo6C53N3O34H117: Co, 3.48; Mo, 34.03; C, 30.53; H, 5.84; and N, 2.48. Found: Co, 3.45; Mo, 34.01; C, 30.54; H, 5.82; and N, 2.45. IR (KBr, cm−1): 3480, 2968, 2937, 2879, 1643, 1480, 1460, 1372, 1130, 1035, 943, 920, 904, 761, 660, 570, and 436. Synthesis of [(n-C4H9)4N)]2{CoMo6O17(CH3O)[CH3C(CH2O)3]2} (8). TBA3[Co(OH)6Mo6O18] (0.20 g, 0.11 mmol) and CH3C(CH2OH)3 (0.03 g, 0.22 mmol) were dissolved in 20 mL of CH3OH, and the solution was heated to reflux for 12 h and then cooled to room temperature. Green crystalline product was obtained in several days (0.15 g, yield 63.8% based on Mo). Elem anal. Calcd for CoMo6C43N2O24H93: Co, 3.56; Mo, 34.74; C, 31.17; H, 5.66; and N, 1.69. Found: Co, 3.55; Mo, 34.78; C, 31.15; H, 5.68 and N, 1.68. IR (KBr, cm−1): 2961, 2935, 2874, 1481, 1469, 1381, 1121, 1029, 946, 928, 911, 725, 688, 638, 573, and 436. Transformation from 2 to 4 upon Controlling the Reaction Time. Co(CH3COO)2·4H2O (0.05 g, 0.20 mmol), TBA2Mo2O7 (0.48 g, 0.60 mmol), and CH3C(CH2OH)3 (0.05 g, 0.42 mmol) were dissolved in 20 mL of DMF, and the mixture was heated to 85 °C. A brown solution was taken from the reaction solution after 12 h, and yellow crystals of 2 were obtained at room temperature in several days (0.13 g, yield 33.0% based on Mo). The products in yellow and green crystals after the reaction time of 36 h were obtained according to the same procedures (0.076 g for the yellow one and 0.057g for the green one based on Mo). When the reaction time further extended to 72 h, a dark green solution was obtained and crude green product crystallized out in several days. Recrystallization from DMA gave green crystals of 4 (0.14 g, yield 33.6% based on Mo). All products obtained were analyzed by single-crystal X-ray analysis as shown in Table 1. The detailed signal assignments of IR spectra and TGA analysis for 1−8 are listed in Table S1 and Figure S2−S10 in the Supporting Information.

Figure 1. Polyanionic structures of (a) 1 and (b) 2 with thermal ellipsoids as the atoms at a 30% probability level. All H atoms are omitted for clarity.

classical characteristic of an Anderson−Evans cluster with one {CoO6} octahedron surrounded by six {MoO6} octahedra with all metal ions located in the same plane. All seven {MO6} (M = Co or Mo) octahedra are connected by sharing two O atoms, yielding 12 terminal O atoms, 6 μ2-O atoms, and 6 μ3-O atoms. Two μ3-O and one μ2-O atoms on each side of the disk-like polyanion are replaced by one triol ligand, forming a triol ligand double-sided decorated fashion like those architectures with NiII, ZnII, and CuII heteroatoms.19,31 In the crystal structure of 1, each polyanion links with two lattice acetonitrile molecules via strong O−H···N hydrogen bonds through two unbounded protonated μ3-O atoms, as shown in Figure S11. It is demonstrated that when using TBA2Mo2O7 as a Mo source, a δ/χ-isomer with a CuII heteroatom in acetonitrile is obtained,31 which is also applicable in the present cobalt system. When TBA2Mo2O7 is used as precursor to react with CoII(CH3COO)2 in the presence of triol ligand in acetonitrile, product 2 is obtained. As shown in Figure 1b, in the polyanion, one triol ligand replaces three μ3-O atoms on one side and another triol ligand replaces two μ3-O atoms and one μ2-O atom on the other side, forming the center-asymmetric δ/χisomer. The product here further demonstrates that the method for achieving this type of decoration fashion is common and easily controlled. Thus, as summarized in Figure 2, we realize the site modulation of the triol ligand’s decoration on the polyanion by simply changing Mo sources. The possible mechanism has been studied in our previous work,31 and the decoration difference could be explained to derive from the acidity in the reaction according to the reaction equations for the synthesis of products 1 and 2 (see Supporting Information). While in an

■

RESULTS AND DISCUSSION Synthesis and Characterization of Triol Ligand Decorated CoII/III Anderson−Evans POMs. To understand the influence of the heteroatom’s oxidation state, cobalt was selected due to its stable divalent and trivalent ions in Anderson−Evans POMs, which have not yet been used for organic modification. Based on the solubility of the starting materials, one-pot and step-by-step methods were both applied D

DOI: 10.1021/acs.inorgchem.7b00614 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

product 3 in the δ-isomer is formed successfully, in which only three μ3-O atoms on one side of the mother cluster are replaced by one triol ligand, just like those observed in AlIII-, CrIII-, FeIII-, and GaIII-centered Anderson−Evans POMs.24,25,27 In the crystal structure, three counterions indicate that CoII has been oxidized into CoIII by Na2S2O8. Additionally, of all ten lattice water molecules (Figure S12), seven form direct hydrogen bonds with the undecorated side of the polyanions while the other three construct direct hydrogen bonds with the decorated side. As shown in Figure S13, these hydrogen bonds link the polyanions into a two-dimensional network in the (010) plane. To verify the influence of surrounding media, we conducted the same reaction in organic solvents. Due to the poor solubility of bare Anderson−Evans POMs in the state of sodium salt, the reaction cannot be carried out in organic solvents directly. To improve the solubility, the sodium counter cations are substituted by TBA cations, and after that procedure, the reaction of TBA3[Co(OH)6Mo6O18] and the triol ligand is carried out in methanol. As expected, a doubleside decorated δ/δ-isomer is obtained, which possesses a different decoration type from that in aqueous solution. Due to the poor diffraction data, only the polyanion and partial cations can be distinguished from the Fourier transformation electronic density map. To improve the quality of crystals, we recrystallized the product from DMA, and succeeded to obtain product 4, which has the same polyanion but different lattice molecules. As shown in Figure 3b, two triol ligands replace all six μ3-O atoms surrounding the central CoIII heteroatom. Similar to the widely investigated triol ligand-decorated MnIII-centered Anderson−Evans POMs,19 all six hydroxyls were symmetrically replaced by triol ligands. It is interesting that the product 4 in the δ/δ-isomer can also be prepared from the product 3 in the δ-isomer following a stepwise reaction, just like preparation of CrIII-, AlIII-, or MnIIIcentered clusters.23 With the addition of an extra triol ligand into the methanol solution of product 3 and after several hours of stirring, the precursor of product 4 with TBA counterions was obtained, as presented in Figure 4. It is obvious that the

Figure 2. Preparation of product 1 and 2 following different routes, which indicates the influence of starting materials and solvents.

acidic environment, once the μ2-O is activated through protonation, it will be preferentially replaced by triol ligands to form the χ/χ-isomer. To further understand this phenomenon, we conducted the two reaction routes in different organic solvents other than acetonitrile. When using TBA4Mo8O26 as starting material, the product 1 in χ/χ-isomer was obtained in both the protic solvent methanol and the aprotic solvent DMF, indicating that the solvents have no obvious influence on this decoration because the precursor itself plays an acid during its decomposition in the reaction. However, when TBA2Mo2O7 is used, the reaction becomes sensitive to the solvent environment. In contrast to the previous system, the reaction conducted in acetonitrile leads to the formation of product 2 in δ/χ-isomer, while the same reaction in methanol just results in the product 1 in χ/χ-isomer. Since TBA2Mo2O7 is a subunit of the Anderson−Evans structure and no change in acidity occurs during the reaction, the added acidity of methanol helps assist the protonation of μ2-O and then the preferential formation of the χ/χ-isomer 1. The result also reveals that CoII as a heteroatom is a bit weaker in activating μ2-O and μ3-O atoms because the reaction in methanol not only results in the χ/χ-isomer, but also drives the replacement of two μ3-O atoms by methanol in CuII-centered POMs.31 Due to the lower reactivity of μ3-O atoms in CoIIcentered POMs, the methanol molecule fails to replace μ3-O atoms in forming the triol ligand/methanol codecorated product. To evaluate the dependence of decoration type on the oxidation state of the central atoms, we studied the reaction of a CoIII-centered Anderson−Evans cluster. In a typical procedure, a Na3[CoIII(OH)6Mo6O18] mother cluster is synthesized from CoSO4 and Na2MoO4 while Na2S2O8 is added as the oxidant. The obtained undecorated POM is then refluxed in the aqueous solution of triol ligand. As shown in Figure 3a, the

Figure 4. Synthetic routes and reaction environments of products 3 and 4 starting from undecorated Co-centered Anderson−Evans POM and the transformation between them.

solvent environment has a significant influence on the triol ligand decoration of Anderson−Evans clusters, and the singlesided isomers prefer to form in aqueous solutions while doublesided isomers are easy to obtain in organic solvents, which is in agreement with the general results in the literature24,25,27−29 though a few examples dealing with double-sided decorated Fe-

Figure 3. Polyanionic structures of (a) product 3 and (b) 4 with thermal ellipsoids as the atoms at a 30% probability level. All H atoms are omitted for clarity. E

DOI: 10.1021/acs.inorgchem.7b00614 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

Figure 5. Gradual oxidation process of the Co-central heteroatom from +2 to +3 in air and the accompanying decoration fashion change of the triol ligand on an Anderson−Evans POM.

products 1 and 2 exhibit obvious redox peaks at positive potential (Figure S14a and S14b). For products 3 and 4, only one redox peak appears at a quite lower positive potential (Figure S14c and S14d). To verify the electrochemical signals deriving from products 1−4, parallel experiments were carried out in blank solution and in the presence of CH3C(CH2OH)3, undecorated CoII- and CoIII-centered clusters, TBA4[CoIIMo6(OH)6O18], and TBA3[CoIIIMo6(OH)6O18] (Figure S15). The detailed comparison of CV curves of products 1−4 with the references indicates that all products have their own redox properties differing from each other. Both the decoration fashion of triol ligand and oxidation state of the Co heteroatom have a significant influence on the electrochemical behaviors. Unfortunately, the observed redox signals in products 1−4 are also different from the only redox wave of a Co-contained POM, which make the assignment of signals become difficult.38 As reported in the literature,39,40 the electrochemical signals of cobalt centered or substituted POMs are normally difficult to be detected. The present results provide new examples of the electrochemical potentials of Co-containing Anderson−Evans POMs. Controlled Oxidation of Co-Heteroatom for Triol Ligand’s Decoration. To track the oxidation process of heteroatoms and the influence of oxidation state on decoration fashion, we tried the combination of oxidation and triol ligand decoration in air without the presence of an additional oxidant. Following the oxidation from air, we may modulate the triol ligand’s decoration fashion by simply controlling the valence of the central heteroatom. Though CoII is quite stable under neutral condition, it becomes easier to be oxidized into CoIII in a coordination state or a basic environment.41 Thus, we selected a weaker basic reaction environment by using TBA 2 Mo 2 O 7 as a Mo source for the reaction with CoII(CH3COO)2 and triol ligand in DMF, which is a nucleophilic agent and serves as a base solvent compared to methanol and acetonitrile, for the evaluation of CoII/CoIII oxidation. Only yellow crystals of product 2 (CoII center) in δ/χ-isomer, the same product as that prepared in acetonitrile, were obtained within 12 h. Interestingly, when the reaction time was extended to ca. 36 h, a mixture of yellow and green crystals with a ratio of ca. 57.1:42.9 were collected. Apparently, the yellow crystal affords the product 2 with a CoII center corresponding to the initial state, but the structural characterization of the green crystals indicates the formation of the δ/δisomer of 4, in which the central heteroatom CoII has been oxidized into CoIII. Thus, it is inferred that the longer reaction time triggers the oxidation of CoII and finally leads to a transformation of decoration fashion. Further extending the reaction up to ca. 72 h yields only green crystals, indicating that the CoII heteroatoms have fully been oxidized to CoIII, forming product 4, as illustrated in Figure 5. Noticeably, from the weight ratio change of 2 and 4 in the obtained products against

and Cr-centered Anderson−Evans POMs are found in aqueous solution.27,36 But on the other hand, no triol ligand single-sided decoration on Anderson−Evans POMs in organic solvents has ever been reported. By summarizing the published results, it is clear that the reaction environment including solvent and acidity, central heteroatom, and triol ligand terminal group plays an important role in the formation of single- and doublesided isomers. In short, by controlling the valence state of the central Co heteroatom, we successfully obtained four decoration fashions of triol ligand on the Anderson−Evans cluster with one heteroatom. Actually, the triol ligand decoration of MIIcentered (transition metal) Anderson−Evans oxomolybdates usually forms the χ/χ-isomer, but the intermediate δ/χ-isomers can be realized from the clusters with CuII and present CoII heteroatoms under a nonacidic or aprotic environment.31,37 By summarizing the present results and published decorations, the reason yielding preferential fashion of the χ/χ-isomer can be ascribed to the protonation at the μ2-O atom, resulting in the activation of this position and the following easier reaction with triol ligand than that with the μ3-O atom, forming a malposition structure. When the solution environment becomes less acidic, the hard protonation of the μ2-O atom decreases the activity at this position so that part of the grafting reaction moves to the μ3-O atom, forming the δ/χ-isomer. It can be predicted that if a more basic environment is applied, it would be possible to obtain a full δ-isomer for MII centered heteroatoms. It should be noted that, only if the reaction solution is very carefully controlled, is the target product type able to be reached because all POM clusters only maintain their chemical architectures in a limited acidity range. However, for those highly charged metal heteroatoms, such as MnIII, AlIII, CrIII, GaIII, FeIII, and the present CoIII, the MIII-centered (transition metal) Anderson− Evans oxomolybdates generally form either δ- or δ/δisomers.19,24,25,27 By comparing the difference of Co2+ and Co3+ ions on the ligand decoration, one can see that the valence state of the central heteroatom has a crucial influence on the activation of the μ2-O atom by protonation and its competition with the third μ3-O atoms in grafting reactions. In the situation of a trivalent heteroatom, only the residue μ3-O atom reacts with triol ligand because of the hard activation of the μ2-O atom, thus leading to the formation of δ-isomer. Only in a more acidic environment, such as HCl, can the μ2-O atom be activated and grafted preferentially by triol ligand to form χisomer, like those containing MnIII and CrIII heteroatoms obtained by adding excess strong acid.28 However, the increased acidity has to be precisely controlled, as the excess acid could result in the formation of (Mo6O19)2−.29 The cyclic voltammetric (CV) performance of 1−4 in acetonitrile solution was conducted to demonstrate the roles of Co heteroatom and its valence as well as the decoration fashions of triol ligand in electrochemical behaviors. The F

DOI: 10.1021/acs.inorgchem.7b00614 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

Figure 6. UV−vis spectra of (a) 2 and (b) 4 in CH3CN at the concentration 5 × 10−5 M. The insets are the spectra showing the absorption in the visible range at a higher concentration, 1 × 10−3 M. The inserted photographs are the corresponding powders of 2 and 4.

the reaction time, it is concluded that the CoII-centered cluster generates first and the in situ oxidation of the heteroatom occurs consequently, finally giving the cluster with oxidized central atom and the changed decoration due to the increased reaction competition of the μ3-O atom at the state. The UV−vis spectra further confirm the color changes representing the different oxidation states of the cobalt central heteroatom. As shown in Figure 6, the strong absorption bands of product 2 emerge at 204 and 232 nm while those bands of 4 appear at 212 and 230 nm, which can be ascribed to the ligandto-metal charge transfer (LMCT) from the O-center to the Mo-center, according to the published results.36 To obtain useful absorbance values in the visible range, a higher concentration was applied. As shown in the insets of Figure 6, product 2 shows an absorption band at 474 nm while product 4 shows a band at 599 nm, both of which source from the d−d transition of the cobalt atom. The absorptions of the two products just explain the yellow color for 2 and the green color for 4, as seen from the photo pictures of their powder states in Figure 6. Considering the instability of POM in strongly basic environment, the enhanced coordination of the triol ligand with CoII can also be adopted by increasing the deprotonation of the hydroxyl group in organic ligand. Following this strategy, when a nitro-containing triol ligand is used to react with TBA4Mo8O26 and CoII(CH3COO)2 in acetonitrile, the δ/δisomer 5 with an oxidized CoIII heteroatom is obtained in air within 12 h. As shown in Figure 7, all six hydroxyls surrounding the heteroatom of 5 are replaced by two triol ligands on both sides, like those known Anderson−Evans clusters possessing trivalent transition metal centers. The bond valence sum (BVS) calculation also reveals that the central heteroatom is in the +3 oxidation state,42 indicating that the reaction follows the oxidation process by air. In contrast to the methyl terminated triol ligand, the substitution of an electron-withdrawing group not only is a more effective strategy in modulating the decoration fashion of Anderson−Evans clusters but also helps accelerate the oxidation of the Co-heteroatom and resist the yielded acidic environment when the acidic precursor TBA4Mo8O26 is used. Even so, the substitution-induced compensation to the acidic environment is limited and the increased acidity still plays a critical role for the oxidation of the CoII heteroatom. For example, in a designed experimental route shown in Figure 7, when a little portion of acetic acid is added to the synthesis of 5 at the unchanged reaction condition, we do not obtain any product of 5. Instead, the product 6 with a decoration fashion like 1 in the χ/χ-isomer becomes the main product, and the

Figure 7. Polyanionic structures of (a) 5 and (b) 6 with thermal ellipsoids as the atoms at a 30% probability level (all H atoms are omitted for clarity), and (c) synthetic route of 5 and 6 indicating the acidity influence in solution.

bond valence calculation42 demonstrates that the heteroatom maintains its original state. Obviously, the acidic environment restricts the deprotonation of the nitro-substituted triol ligand, which weakens the coordination of the ligand to CoII and the subsequent oxidation. This result confirms that the enhanced coordination of the triol ligand to the Co heteroatom is the prerequisite for the later oxidation process. Co-decoration of Triol/Auxiliary Ligands. In principle, it is still possible to perform a further decoration to the known five triol-ligand-decorated Anderson−Evans clusters, considering those unoccupied μ2-O and μ3-O atoms. Besides the only example of methanol’s decoration on the μ3-O atom of the χ/χisomer with a CuII heteroatom,31 no reports concern the codecoration on this kind of cluster. To figure out the reactivity of residue μ2- and μ3-O atoms in Co-centered Anderson−Evans polyanions, we added acetic acid to the reaction in synthesizing product 3 to activate the bridging O atoms of the virgin Anderson−Evans cluster and succeeded in achieving an unprecedented product 7 in aqueous solution. From the crystal structure, it is seen that 7 is a δ-isomer while an acetate ligand replaces one μ3-O atom on the opposite side of the triol ligand G

DOI: 10.1021/acs.inorgchem.7b00614 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

types, representing the utmost number of decoration fashions on the Anderson−Evans POM with one heteroatom by now. The increased decoration types were demonstrated to derive from the changeable oxidation state of the central Coheteroatom, because of the influence on neighboring oxygen atoms surrounding the deeply oxidized heteroatom, resulting in the preferential formation of δ- or δ/δ-isomer. For CoIIcentered Anderson−Evans POMs, the triol ligand is liable to replace part of the μ3-O atoms to form χ/χ- or δ/χ-isomers based on the acidity of the reaction system. The controlled oxidation from CoII to CoIII showed that the coordination state of CoII and the basic environment play key roles in the oxidation and achieving different decoration motifs. Our results also confirmed that the oxidation process was expedited when the CoII ion was in a stronger coordination state, and could be blocked by the increased acidity. In addition, the unreacted μ2O atom in triol ligand decorated clusters can also be activated in methanol after a longer reaction time for a codecoration through a stepwise reaction, which has never been discussed in B-type Anderson−Evans POMs. On the other hand, the μ2-O atom cannot be activated by addition of extra acid in aqueous solution, and thus, a δ-isomer with an acetate ligand coordination on the back face on one of the μ3-O atoms was obtained. The present achievement indicates that the central heteroatom and its valent state, the coordination atom, and the acidity and identity of the solvent (water or organic solvent) contribute to the decoration type and the further modification to the residual bridging atoms only if the resistibility of central metal ion and the cluster to the acidity in the reaction can block the creation of new decoration fashion. We are trying to find a heteroatom that is applicable for an Anderson−Evans cluster possessing five decoration types of triol ligand. As an obvious step, the obtained synthetic routes in the present study can be used for the stepped self-assemblies and functional materials.

coordination face, as shown in Figure 8a. This is quite unique from the published results because, in all known examples, the

Figure 8. Polyanionic structures of (a) 7 and (b) 8 with thermal ellipsoids as the atoms at a 30% probability level. All H atoms are omitted for clarity.

μ2-O atom is more active under strongly acidic conditions in the cases of clusters bearing CrIII and Mn III central heteroatoms.28 Therefore, we speculate that the CoIII center may cause the change of activation site among residual O atoms in aqueous solution. On the other hand, the acetic ligand has an angle of 87.4(1)° against the cluster plane and expands to the outside of the cluster edge. This coordination could be influenced by the two strong hydrogen bonds between uncoordinated oxygen atoms on the acetate ligand and two neighbor μ3-O atoms in the protonated state with the distances of O···O of 2.736 (2) and 2.730 (2) Å, as shown in Figure S16. In the crystal structure, the two hydrogen bonds also break the interactions (abundant hydrogen bonds) between cluster and crystalline solvent molecules, like the bonding state in 3, shown in Figure S13. However, we fail to activate μ2-O atom by increasing the acidity in aqueous solution for further comodification of other bridging O atoms. Conversely, the activation of the residual μ2O atom is achieved in organic solvent by extending the reaction time. With the same unmodified cluster used in the preparation of product 4, the product 8 is obtained in methanol solution when extending the reaction time to ca. 12 h. As shown in Figure 8b, all six μ3-O atoms are replaced by two triol ligands on both sides symmetrically, along with the additional coordination of a methanol molecule at one of the unreacted μ2-O atoms. So far, the coordination of methanol to the μ2-O atom was only observed in A-type Anderson−Evans clusters. The present result extends the reaction at the same site to Btype Anderson−Evans clusters.43,44 Though the μ2-O atom is activated successfully through a longer reaction time, only one of the μ2-O atoms is modified, indicating the activation is still not robust. We once achieved the modification of methanol on μ3-O atoms in the χ/χ-isomer with the CuII heteroatom, indicating the reactivity of residual μ3-O atoms.31 Combining the present and those previously reported results with all residual μ2-O and μ3-O atoms that are not yet grafted by organic ligands can be regarded as the active sizes for further decoration only if the reaction condition is controlled suitably.

■

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.7b00614. Scheme for illustrating five types of triol ligand decoration fashion on Anderson−Evans polyanions, hydrogen bonds in 1, 3, and 7, TGA curves, IR spectra, cyclic voltammograms, and proposed reaction equations (PDF) Accession Codes

CCDC 1501812−1501819 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.

■

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected].

CONCLUSIONS By selecting cobalt as the central heteroatom, which was untapped in the transition metal series from Cr to Zn in the fourth period, eight triol decorated/codecorated Anderson− Evans oxomolybdates were synthesized and characterized. These Co-centered clusters collected four triol decoration

ORCID

Bao Li: 0000-0003-0727-9764 Lixin Wu: 0000-0002-4735-8558 Notes

The authors declare no competing financial interest. H

DOI: 10.1021/acs.inorgchem.7b00614 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

■

New Approach to Create Hybrid Drugs for Cancer Therapeutics. Bioorg. Med. Chem. Lett. 2013, 23, 1462−1466. (17) Yang, H. K.; Su, M. M.; Ren, L. J.; Tang, J.; Yan, Y. K.; Miao, W. K.; Zheng, P.; Wang, W. Post-Functionalization of an Anderson-Type Polyoxomolybdate Using a Metal-Free Diels−Alder Click Reaction. Eur. J. Inorg. Chem. 2013, 2013, 1381−1389. (18) Blazevic, A.; Rompel, A. The Anderson−Evans polyoxometalate: From Inorganic Building Blocks via Hybrid Organic−Inorganic Structures to Tomorrows“Bio-POM. Coord. Chem. Rev. 2016, 307, 42−64. (19) Hasenknopf, B.; Delmont, R.; Herson, P.; Gouzerh, P. Anderson-Type Heteropolymolybdates Containing Tris(alkoxo) Ligands: Synthesis and Structural Characterization. Eur. J. Inorg. Chem. 2002, 2002, 1081−1087. (20) Wilson, E. F.; Miras, H. N.; Rosnes, M. H.; Cronin, L. RealTime Observation of the Self-Assembly of Hybrid Polyoxometalates Using Mass Spectrometry. Angew. Chem., Int. Ed. 2011, 50, 3720− 3724. (21) Lin, C. G.; Chen, W.; Long, D. L.; Cronin, L.; Song, Y. F. Stepby-Step Covalent Modification of Cr-Templated Anderson-type Polyoxometalates. Dalton Trans. 2014, 43, 8587−8590. (22) Wang, X. L.; Wang, Y. L.; Miao, W. K.; Hu, M. B.; Tang, J.; Yu, W.; Hou, Z. Y.; Zheng, P.; Wang, W. Langmuir and Langmuir− Blodgett Films of Hybrid Amphiphiles with a Polyoxometalate Headgroup. Langmuir 2013, 29, 6537−6545. (23) Zhang, J. W.; Luo, J. H.; Wang, P. M.; Ding, B.; Huang, Y. C.; Zhao, Z. L.; Zhang, J.; Wei, Y. G. Step-by-Step Strategy from Achiral Precursors to Polyoxometalates-Based Chiral Organic−Inorganic Hybrids. Inorg. Chem. 2015, 54, 2551−2559. (24) Wu, P. F.; Yin, P. C.; Zhang, J.; Hao, J.; Xiao, Z. C.; Wei, Y. G. Single-Side Organically Functionalized Anderson-Type Polyoxometalates. Chem. - Eur. J. 2011, 17, 12002−12005. (25) Ai, H.; Wang, Y.; Li, B.; Wu, L. X. Synthesis and Characterization of Single-Side Organically Grafted Anderson-Type Polyoxometalates. Eur. J. Inorg. Chem. 2014, 2014, 2766−2772. (26) Zhang, B.; Liang, J.; Wang, Y.; Yang, Y.; Wu, L. X. A novel Single-Side Azobenzene-Grafted Anderson-type Polyoxometalate for Recognition-Induced Chiral Migration. Chem. Commun. 2014, 50, 10823−10826. (27) Blazevic, A.; Al-Sayed, E.; Roller, A.; Giester, G.; Rompel, A. Tris-Functionalized Hybrid Anderson Polyoxometalates: Synthesis, Characterization, Hydrolytic Stability and Inversion of Protein Surface Charge. Chem. - Eur. J. 2015, 21, 4762−4771. (28) Zhang, J. W.; Liu, Z. H.; Huang, Y. C.; Zhang, J.; Hao, J.; Wei, Y. G. Unprecedented χ Isomers of Single-Side Triol-Functionalized Anderson Polyoxometalates and Their Proton-Controlled Isomer Transformation. Chem. Commun. 2015, 51, 9097−9100. (29) Zhang, J. W.; Li, Q.; Zeng, M. Y.; Huang, Y. C.; Zhang, J.; Hao, J.; Wei, Y. G. The Proton-Controlled Synthesis of Unprecedented Diol Functionalized Anderson-type POMs. Chem. Commun. 2016, 52, 2378−2381. (30) Gumerova, N. I.; Roller, A.; Rompel, A. [Ni(OH)3W6O18(OCH2)3CCH2OH]4−: the First Tris-Functionalized Anderson-type Heteropolytungstate. Chem. Commun. 2016, 52, 9263−9266. (31) Wang, Y.; Li, B.; Qian, H. J.; Wu, L. X. Controlled TriolDerivative Bonding and Decoration Transformation on Cu-Centered Anderson−Evans Polyoxometalates. Inorg. Chem. 2016, 55, 4271− 4277. (32) Hur, N.; Klemperer, W. G.; Wang, R. C. Inorganic Synthesis; John Wiley & Sons: New York, 1990. (33) Day, V. W.; Fredrich, M. F.; Klemperer, W. G.; Shum, W. Synthesis and Characterization of the Dimolybdate Ion, Mo2O72−. J. Am. Chem. Soc. 1977, 99, 6146. (34) Nolan, A. L.; Allen, C. C.; Burns, R. C.; Craig, D. C.; Lawrance, G. A. Monomeric and Dimeric Cobalt(III) Polyoxomolybdates: Crystal Structures and Cyclic Voltammetry of Na3[H6CoMo6O24] •8H2O and K6[H4Co2Mo10O38]•7H2O. Aust. J. Chem. 1998, 51, 825− 834.

ACKNOWLEDGMENTS This work was financially supported by National Program on Key Basic Research Project (Grant 2013CB834503), National Natural Science Foundation of China (Grants 21574057), and Changbaishan Distinguished Professor Funding of Jilin Province, China.

■

REFERENCES

(1) Pope, M. T.; Müller, A. Polyoxometalate Chemistry: An Old Field with New Dimensions in Several Disciplines. Angew. Chem., Int. Ed. Engl. 1991, 30, 34−38. (2) Anderson, J. S. Constitution of the Poly-Acid. Nature 1937, 140, 850. (3) Evans, H. T., Jr. The Crystal Structures of Ammonium and Potassium Molybdotellurates. J. Am. Chem. Soc. 1948, 70, 1291−1292. (4) Ouahab, L.; Golhen, S.; Yoshida, Y.; Saito, G. One Dimensional Face-to-Face Stacking of Anderson−Evans [Cr(OH)6Mo6O18]3− Polyoxometalate Anion: Synthesis, Structure, and Physical Properties of (BEDT-TTF)4[Cr(OH)6Mo6O18]·2H2O. J. Cluster Sci. 2003, 14, 193−204. (5) Adonin, A. A.; Izarova, N. V.; Besson, C.; Abramov, P. A.; Santiago-Schübel, B.; Kögerler, P.; Fedin, V. P.; Sokolov, M. N. An IrIV-Containing Polyoxometalate. Chem. Commun. 2015, 51, 1222− 1225. (6) Song, Y. F.; McMillan, N.; Long, D. L.; Kane, S.; Malm, J.; Riehle, M. O.; Padeep, C. P.; Gadegaard, N.; Cronin, L. Micropatterned Surfaces with Covalently Grafted Unsymmetrical PolyoxometalateHybrid Clusters Lead to Selective Cell Adhesion. J. Am. Chem. Soc. 2009, 131, 1340−1341. (7) Song, Y. F.; McMillan, N.; Long, D. L.; Thiel, J.; Ding, Y.; Cheng, H.; Gadegaard, N.; Cronin, L. Design of Hydrophobic Polyoxometalate Hybrid Assemblies Beyond Surfactant Encapsulation. Chem. Eur. J. 2008, 14, 2349−2354. (8) Marcoux, P. R.; Hasenknopf, B.; Vaissermann, J.; Gouzerh, P. Developing Remote Metal Binding Sites in Heteropolymolybdates. Eur. J. Inorg. Chem. 2003, 2003, 2406−2412. (9) Yvon, C.; Macdonell, A.; Buchwald, S.; Surman, A. J.; Follet, N.; Alex, J.; Long, D. L.; Cronin, L. A Collection of Robust Methodologies for the Preparation of Asymmetric Hybrid Mn−Anderson Polyoxometalates for Multifunctional Materials. Chem. Sci. 2013, 4, 3810− 3817. (10) Yan, Y.; Wang, H. B.; Li, B.; Hou, G. F.; Yin, Z. D.; Wu, L. X.; Yam, V. W. W. Smart Self-Assemblies Based on a SurfactantEncapsulated Photoresponsive Polyoxometalate Complex. Angew. Chem., Int. Ed. 2010, 49, 9233−9236. (11) Li, D.; Song, J.; Yin, P. C.; Simotwo, S.; Bassler, A. J.; Aung, Y. Y.; Roberts, J. E.; Hardcastle, K. I.; Hill, C. L.; Liu, T. B. Inorganic− Organic Hybrid Vesicles with Counterion- and pH-Controlled Fluorescent Properties. J. Am. Chem. Soc. 2011, 133, 14010−14016. (12) Wang, H. B.; Yan, Y.; Li, B.; Bi, L. H.; Wu, L. X. Hierarchical Self-Assembly of Surfactant-Encapsulated and Organically Grafted Polyoxometalate Complexes. Chem. - Eur. J. 2011, 17, 4273−4282. (13) Pradeep, C. P.; Misdrahi, M. F.; Li, F. Y.; Zhang, J.; Xu, L.; Long, D. L.; Liu, T. B.; Cronin, L. Synthesis of Modular “Inorganic− Organic−Inorganic” Polyoxometalates and Their Assembly into Vesicles. Angew. Chem., Int. Ed. 2009, 48, 8309−8313. (14) Santoni, M. P.; Pal, A. K.; Hanan, G. S.; Proust, A.; Hasenknopf, B. Discrete Covalent Organic Inorganic Hybrids: Terpyridine Functionalized Polyoxometalates Obtained by a Modular Strategy and Their Metal Complexation. Inorg. Chem. 2011, 50, 6737−6745. (15) Schaming, D.; Allain, C.; Farha, R.; Goldmann, M.; Lobstein, S.; Giraudeau, A.; Hasenknopf, B.; Ruhlmann, L. Synthesis and Photocatalytic Properties of Mixed Polyoxometalate-Porphyrin Copolymers Obtained from Anderson-Type Polyoxomolybdates. Langmuir 2010, 26, 5101−5109. (16) Yang, H. K.; Cheng, Y. X.; Su, M. M.; Xiao, Y.; Hu, M. B.; Wang, W.; Wang, Q. Polyoxometalate−Biomolecule Conjugates: A I

DOI: 10.1021/acs.inorgchem.7b00614 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry (35) Sheldrick, G. M. SHELXT−Integrated Space-Group and Crystal-Structure Determination. Acta Crystallogr., Sect. A: Found. Adv. 2015, A71, 3−8. (36) Zhang, J. W.; Huang, Y. C.; Zhang, J.; She, S.; Hao, J.; Wei, Y. G. A Direct Anchoring of Anderson-type Polyoxometalates in Aqueous Media with Tripodal Ligands Especially Containing the Carboxyl Group. Dalton Trans. 2014, 43, 2722−2725. (37) Marcoux, P. R.; Hasenknopf, B.; Vaissermann, J.; Gouzerh, P. Developing Remote Metal Binding Sites in Heteropolymolybdates. Eur. J. Inorg. Chem. 2003, 2003, 2406−2412. (38) Wang, K. Y.; Bassil, B. S.; Xing, X. L.; Keita, B.; Bindra, J. K.; Diefenbach, K.; Dalal, N. S.; Kortz, U. Incorporation of TransitionMetal-Ion Guests (Co2+, Ni2+, Cu2+, Zn2+) into the Ti2-Containing 18Tungsto-2-arsenate(III) Monolacunary Host. Eur. J. Inorg. Chem. 2016, 2016, 5519−5529. (39) Ruhlmann, L.; Nadjo, L.; Canny, J.; Contant, R.; Thouvenot, R. Di- and Tetranuclear Dawson-Derived Sandwich Complexes: Synthesis, Spectroscopic Characterization, and Electrochemical Behavior. Eur. J. Inorg. Chem. 2002, 2002, 975−986. (40) Li, B.; Yan, Y.; Li, F. Y.; Xu, L.; Bi, L. H.; Wu, L. X. Synthesis, Crystal Structure, and Properties of Two Sandwich-Type Tungstovanadates. Inorg. Chim. Acta 2009, 362, 2796−2801. (41) Song, T. Y.; Xu, J. N.; Cheng, G. Z. Inorganic Chemistry; Higher Education Press: Beijing, 2004. (42) Brown, I. D.; Altermatt, D. Bond-Valence Parameters Obtained From a Systematic Analysis of the Inorganic Crystal Structure Database. Acta Crystallogr., Sect. B: Struct. Sci. 1985, B41, 244−247. (43) Honda, D.; Ikegami, S.; Inoue, T.; Ozeki, T.; Yagasaki, A. Protonation and Methylation of an Anderson-Type Polyoxoanion [IMo6O24]5−. Inorg. Chem. 2007, 46, 1464−1470. (44) Ikegami, S.; Kani, K.; Ozeki, T.; Yagasaki, A. Methylated Molybdoplatinate−Its Unexpected Ability to Absorb Methanol. Chem. Commun. 2010, 46, 785−787.

J

DOI: 10.1021/acs.inorgchem.7b00614 Inorg. Chem. XXXX, XXX, XXX−XXX