Tuning dimensionality of octamolybdate structures through selecting different ligands

Accepted Manuscript Tuning dimensionality of octamolybdate structures through selecting different ligands Ai-Xiang Tian, Jia-Ni Liu, Xue-Bin Ji, Gui-Ying Liu, Ting-Ting Li, Yan Tian, Huai-Ping Ni, Guo-Cheng Liu, Jun Ying PII:

S0022-2860(17)31494-1

DOI:

10.1016/j.molstruc.2017.11.021

Reference:

MOLSTR 24507

To appear in:

Journal of Molecular Structure

Received Date: 2 September 2017 Revised Date:

5 November 2017

Accepted Date: 6 November 2017

Please cite this article as: A.-X. Tian, J.-N. Liu, X.-B. Ji, G.-Y. Liu, T.-T. Li, Y. Tian, H.-P. Ni, G.-C. Liu, J. Ying, Tuning dimensionality of octamolybdate structures through selecting different ligands, Journal of Molecular Structure (2017), doi: 10.1016/j.molstruc.2017.11.021. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Graphical Abstract Three ligands dpz, tbz and btp were used to tune dimensionality of Mo8-based compounds. When dpz and tbz were utilized, low dimensional structures were obtained, 0D for 1− −4 and 1D for 5. The btp induces a 2D→3D interpenetraing

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structure of 6.

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Tuning dimensionality of octamolybdate structures through selecting different ligands

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AI-XIANG TIAN,a,∗∗ JIA-NI LIU,a XUE-BIN JI,a GUI-YING LIU,b TING-TING LI,a YAN TIAN,a HUAI-PING NI,a GUO-CHENG LIU,a JUN YINGa,* a

Department of Chemistry, Bohai University, Jinzhou 121013, P. R. China

Liaoning Ocean and Fisheries Science Research Institute, DaLian, P.R. China

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b

By using different organic ligands, six octamolybdate hybrid compounds with

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different dimensionalities, namely, [Ag4(dpz)8(β-Mo8O26)] (1), [Cu4(dpz)8(β-Mo8O26)] (2), [Co2(tbz)4(H2O)2(β-Mo8O26)] (3), [Ni2(tbz)4(H2O)2(β-Mo8O26)] · 2H2O (4), [Cu(tbz)(H2O)(β-Mo8O26)1/2] (5), [Cu(btp)2(H2O)(β-Mo8O26)1/2]·2H2O (6) (dpz = 3,5-dimethyl-pyrazolidine,

tbz

=

2-(4-thiazolyl)benzimidazole,

btp

=

1,3-bis(1,2,4-triazol-1-yl)propane), have been synthesized under hydrothermal

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conditions and characterized by single crystal X-ray diffraction analyses, elemental analyses and IR spectra. By using a dpz ligand, two isostructural 0D compounds 1 and 2 were obtained, with four {M(dpz)2} fragments (M = Ag for 1, Cu for 2) supporting

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one anion. When rigid tbz was used, 0D compounds 3 and 4, and 1D structure of compound 5 was constructed. The tbz play a terminate chelate role in these compounds. By selecting a flexible bis(triazole) btp ligand with more N donors, a 2D

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hamburger-like layer is formed. Adjacent layers further interpenetrate with each other to construct a 3D interpenetrating framework of compound 6, realizing dimensionality from 2D to 3D. Using different ligands to tune the dimensionality of POM-based structures is rational. The electrochemical and photocatalytic properties of compounds 1–6 were researched, in which the POM subunit is regarded as active component but not organic moiety.

∗CONTACT A.-X. Tian [email protected] J. Ying [email protected] 1

ACCEPTED MANUSCRIPT Keywords: Polyoxometalate; 3,5-dimethyl-pyrazolidine; 2-(4-thiazolyl)benzimidazole; 1,3-bis(1,2,4-triazol-1-yl)propane); Electrochemical properties; Photocatalytic properties

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1. Introduction Polyoxometalates (POMs) as a large family of anionic metal oxide clusters have attracted more attention owing to their numerous in variety[1] and extensive potential applications, such as catalysis[2], electrochemistry[3] and magnetism[4]. Recently, to

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design different transition metal complexes (TMCs) for modification of diverse POM anions has become a booming branch of POM field. Up to now, a good deal of

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POM-TMC compounds has been obtained[5]. Among many POM types, the octamolybdates anions have received tremendous attention because of their abundant isomers, such as α, β, γ, δ, ε, ζ, η, and θ isomers[6]. Furthermore, the octamolybdates anions also can provide rich terminal and bridging oxygen atoms, in order to link TMCs covalently. Thus, exploring different TMCs to modify octamolybdates anions

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to construct 0D, 1D, 2D and 3D structures is appealing and challenging. In order to tune TMCs modified octamolybdates with expected dimensionalities, the selection of proper organic ligands is an essential and important factor[7]. For

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example, the pyrazole ligand owns two successive N donors. These N atoms are not dispersive, which is not favor to construct extensive structures[8]. Though the rigid

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organic ligand 2-(4-thiazolyl)benzimidazole (tbz) have three N and one S donors, it usually acts as terminate ligand to prevent dimensional extension[9]. The tbz often exhibits a chelate role[10]. Compared with pyrazole and tbz that usually induced low dimensional structures, the flexible bis(triazole) ligands, such as btp, conduce to form high dimensional structures with ease[11]. The reason rests on its more N donors, dispersion of N atoms and its flexible spacer[12]. Thus, in order to construct 3D POM-based frameworks, the flexible bis(triazole) ligands can become an optimal choice. In this work, we chose a derivative of pyrazole 1H-3,5-dimethyl-pyrazole (dpz) firstly (Scheme 1). These two methyl groups increase the steric hindrance, which even

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ACCEPTED MANUSCRIPT inhibit structural extension. And then we obtained two expected discrete structures (1 and 2). Then we used the rigid tbz as organic ligand and two isostructural 0D compounds (3 and 4) and a 1D structure (5) were formed. The tbz acts as a terminate and chelate ligand in these compounds. Finally, the btp ligand is introduced to an

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octamolybdate/CuII system, an expected 2D→3D interpenetraing structure was constructed (6). So tuning dimensionalities of octamolybdate-based compounds through selecting proper organic ligands is rational, which can support meaningful experimental data for target syntheses of POM-based compounds. The POM-based

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inorganic-organic hybrid compounds usually show electrochemical and photocatalytic properties. However, diverse organic molecules in this series almost exhibit no

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influences on electrochemical and photocatalytic properties. POMs can accept and release a certain number of electrons as multi-electron relays and photocatalysis. Thus, the POM subunit is regarded as the electrochemical and photocatalytic active component for the inorganic-organic hybrid compounds[13]. But the inorganic moiety can conduce stable frameworks combined with POMs, tuning properties this series.

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Herein, in this paper, through using three kinds of organic ligands, six octamolybdate-based compounds, [Ag4(dpz)8(β-Mo8O26)] (1), [Cu4(dpz)8(β-Mo8O26)] (2),

[Co2(tbz)4(H2O)2(β-Mo8O26)]

(3),

[Ni2(tbz)4(H2O)2(β-Mo8O26)]·2H2O

(4),

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[Cu(tbz)(H2O)(β-Mo8O26)1/2] (5), [Cu(btp)2(H2O)(β-Mo8O26)1/2]·2H2O (6), have been synthesized. Moreover, we have studied the electrochemical and photocatalytic

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properties of these title compounds.

2. Experimental Section 2.1 Materials and General Methods All reagents and solvents for syntheses were purchased from commercial sources and used without further purification. Elemental analyses (C, H, N) were achieved with a Perkin-Elmer 240C elemental analyzer and the Cu, Co, Ag and Mo analyses were performed by a Leaman inductively coupled plasma (ICP). The FT-IR spectra were taken on a Varian FT-IR 640 spectrometer (KBr pellets). FT/IR spectrometer with 3

ACCEPTED MANUSCRIPT KBr pellet in the 400-4000 cm-1 region. Powder XRD investigations were carried out with an Ultima IV with D/teX Ultra diffractometer at 40 kV, 40 mA with Cu Kα (λ = 1.5406 Å) radiation. The thermal gravimetric analyses (TGA) were carried out in N2 on a Perkin-Elmer DTA 1700 differential thermal analyzer with a rate of 10.00 o

The solid-state diffuse-reflectance UV-vis spectra for powder samples were

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C/min.

monitored with a Perkin-Elmer Lambda 750 UV-Vis spectrometer equipped with an integrating sphere by using BaSO4 as a white standard. Electrochemical measurements and data collection were performed with a CHI 440 electrochemical

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workstation. A conventional three-electrode system was used with a saturated calomel electrode (SCE) as reference electrode and a Pt wire as counter electrode. The title

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compounds modified carbon paste electrodes (CPEs) were used as the working electrodes. UV-Vis absorption spectra were obtained using a Lambda 750 UV/VIS/NIR spectrophotometer. 2.2 X-ray Crystallographic Study

X-ray diffraction analyses data collection for compounds 1−6 were collected on a

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Bruker SMART APEX II with Mo Kα (λ = 0.71073 Å) by ω and θ scan mode at 293K. All the structures were solved by direct methods and refined on F2 by full-matrix least squares using the SHELXL package[14]. The detailed crystal data

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and structures refinement for 1−6 are given in Table 1. Selected bond lengths and angles are listed in Table S1. Crystallographic data for the structures reported in this

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paper have been deposited in the Cambridge Crystallographic Data Center with CCDC Numbers of 1528061−1528066 for 1−6. (Insert Table 1)

2.3 Preparation of compounds 1−6 2.3.1 Synthesis of [Ag4(dpz)8(β-Mo8O26)] (1). A mixture of (NH4)6Mo7O24·4H2O (0.124 g, 0.1 mmol), dpz (0.027 g, 0.1 mmol), AgNO3 (0.075 g, 0.3 mmol) was dissolved in 10 mL of distilled water and stirred for 0.5 h at room temperature. When the pH of the mixture was adjusted to about 4.7 with 1.0 mol L-1 NaOH, the suspension was put into a 25 mL Teflon-lined autoclave and

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ACCEPTED MANUSCRIPT kept under autogenous pressure at 160 °C for 5 days. After slow cooling to the room temperature, yellow block crystals of 1 were filtered and washed with distilled water with a final pH of 3.8 (36% yield based on Mo). Anal. Calcd. for C40H56Ag4Mo8N16O26(2319): C 20.70, H 2.41, N 9.66, Ag 18.60, Mo 33.10%. Found: C 20.78, H 2.46, N 9.74, Ag 18.36, Mo 32.45%.

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2.3.2 Synthesis of [Cu4(dpz)8(β-Mo8O26)] (2).

Compound 2 was prepared with similar process to 1, except for changing the AgNO3 to Cu(CH3COO)2·H2O (0.06 g, 0.3 mmol). The pH was 5.2. Dark red block crystals of

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2 were filtered and washed with distilled water with a final pH of 4.0 (28% yield based on Mo). Anal. Calcd. for C40H64Cu4Mo8N16O26(2206): C 21.76, H 2.90, N

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10.15, Cu 11.52, Mo 34.79%. Found: C 21.85, H 2.95 N 10.22, Cu 11.27, Mo 35.18%.

2.3.3 Synthesis of [Co2(tbz)4(H2O)2(β-Mo8O26)] (3).

A mixture of CoCl2·6H2O (23.8 mg, 0.10 mmol), tbz (0.020 g, 0.1 mmol) and (NH4)6Mo7O24·4H2O (0.124 g, 0.1 mmol) was dissolved in 10 mL of distilled water

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and stirred for 0.5 h at room temperature. When the pH of the mixture was adjusted to about 2.4 with 1.0 mol L-1 NaOH, the suspension was put into a 25 mL Teflon-lined autoclave and kept under autogenous pressure at 160 °C for 5 days. After slow

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cooling to room temperature, dark red block crystals of 3 were filtered (final pH = 2.8) and washed off the white precipitate with distilled water, and dried at room temperature

in

a

desiccator

(34%

yield

based

on

Mo).

Calcd.

for

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C40H32Co2Mo8N12O28S4 (2143): C 22.42, H 1.51, N 7.85, Co 5.50, Mo 35.82%. Found: C 22.49, H 1.47 N 7.92, Co 5.35, Mo 35.46%. 2.3.4 Synthesis of [Ni2(tbz)4(H2O)2(β-Mo8O26)]·2H2O (4). Compound 4 was prepared with similar process to 3, except for changing CoCl2·6H2O to the Ni2SO4 (0.033 g, 0.1 mmol). The pH was 5.2. Blue-green block crystals of 4 were filtered and washed with distilled water with a final pH of 4.0 (28% yield based on Mo). Anal. Calcd. for C40H36Mo8N12Ni2O28S4 (2146): C 22.39, H 1.69, N 7.83, Ni 5.47, Mo 35.77%. Found: C 22.46, H 1.61, N 7.91, Ni 5.26, Mo 35.42%. 2.3.5 Synthesis of [Cu(tbz)(H2O)(β -Mo8O26)1/2] (5). 5

ACCEPTED MANUSCRIPT A mixture of (NH4)6Mo7O24·4H2O (0.124 g, 0.1 mmol), tbz (0.033 g, 0.1 mmol), CuCl2·2H2O (0.085 g, 0.5 mmol) was dissolved in 10 mL of distilled water and stirred for 0.5 h at room temperature. When the pH of the mixture was adjusted to about 3.3 with 1.0 mol L-1 NaOH, the suspension was put into a 25 mL Teflon-lined autoclave

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and kept under autogenous pressure at 160 °C for 5 days. After slow cooling to the room temperature, blue block crystals of 5 were filtered and washed with distilled water with a final pH of 3.8 (36% yield based on Mo). Anal. Calcd. for C10H9CuMo4N3O14S (875): C 13.73, H 1.04, N 4.80, Cu 7.26, Mo 43.86%. Found: C

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13.81, H 1.01, N 4.87, Cu 7.41, Mo 43.49%. 2.3.6 Synthesis of [Cu(btp)2(H2O)(β-Mo8O26)1/2]·2H2O (6).

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A mixture of (NH4)6Mo7O24·4H2O (0.124 g, 0.1 mmol), btp (0.027 g, 0.1 mmol), CuCl2·2H2O (0.085 g, 0.5 mmol), was dissolved in 10 mL of distilled water and stirred for 0.5 h at room temperature. When the pH of the mixture was adjusted to about 2.8 with 1.0 mol L-1 NaOH, the suspension was put into a 25 mL Teflon-lined autoclave and kept under autogenous pressure at 160 °C for 4 days. After slow

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cooling to the room temperature, blue block crystals of 6 were filtered and washed with distilled water with a final pH of 3.8 (30% yield based on Mo). Anal. Calcd. for C14H26CuMo4N12O16 (1066): C 15.78, H 2.46, N 15.77, Cu 5.96, Mo 36.00%. Found: C 15.86, H 2.41, N 15.85, Cu 5.78, Mo 36.35%.

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2.4 Preparation of compounds 1−6 bulk-modified CPEs

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Compound 1 modified carbon paste electrode (1−CPE) was made as follows: compound 1 (10 mg) and graphite powder (0.10 g) were mixed and grinded about 40 min by agate mortar and pestle to achieve a uniform mixture. And then add 0.1 mL of liquid paraffin to the mixture with stirring. The homogenized mixture was packed into a quartz rod with a 1.5 mm inner diameter and smoothed the tube surface with weighing paper. At last, a copper rod was assembled through the back of the electrode compactly. In a similar manner, 2− to 6−CPEs were made with compounds 2−6. 2.5 Information about photocatalytic degradation procedure Under UV light irradiation from a 125 W Hg lamp, the photocatalytic activities of compounds 1–6 were studied in the methylene blue (MB) and rhodamine B (RhB) 6

ACCEPTED MANUSCRIPT solutions. Experimental processes are as follows: 100 mg of compounds 1–6 were decentralized in 0.02 mmol L−1 MB/RHB aqueous solution (90 mL), respectively. Magnetically stirred for about 15 min in the dark to make sure the solution equably. Then the mixed solution was stirred continuous under a UV Hg lamp. Every interval

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30 min, 5.0 mL samples were taken out for analysis by Lambda 750 UV/VIS/NIR spectrophotometer.

3. Results and Discussion

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3.1 Synthesis

In this work, we tuned the dimensionality of POM-based compounds by changing

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different ligands. Moreover, we also tried to discuss whether different transition metal cations exhibit influence on the structures. For the β-Mo8O26/dpz system, we used Co2+ and Ni2+ ions instead of Ag+ (1) and Cu2+ (2). However, only blue-green precipitate was obtained. For the β-Mo8O26/tbz system, we used Ag+ cations instead of Co2+ (3), Ni2+ (4) and Cu2+ (5). But tiny yellow crystals with rather poor quality were

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obtained. When we used Ag+, Co2+ and Ni2+ cations instead of Cu2+ (6), only precipitate was obtained. Further study on other TM cations introduced to β-Mo8O26 system is underway.

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3.2 Structure Description

Crystal Structure of Compound 1. Single-crystal Xray diffraction analysis shows

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that the asymmetric unit of 1 contains four AgI ions, eight dpz ligands and one

β-[Mo8O26]4- anion (abbreviated to Mo8) (Fig. 1). The valence sum calculations[15] show that all the Mo atoms are in the +VI oxidation states and all the Ag atoms are in the +I oxidation states.

(Insert Fig. 1) There are two crystallographically independent AgI ions in 1. Both the Ag1 and Ag2 ions are four-coordinated by two N atoms (N1, N5 for Ag1; N3, N7 for Ag2) from two dpz ligands and one O atom (O10 for Ag1 and O11 for Ag2) from one Mo8 anion, exhibiting a T-type coordination mode. The bond distances and angles around Ag ions

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ACCEPTED MANUSCRIPT are 2.588(3) and 2.62995) Å for Ag-O, 2.106(5)−2.132(6) Å for Ag-N, and 161.69(18)o and 168.2(2)o for N-Ag-N, 88.03(16)o−100.35(17)o for N-Ag-O, 80.97(15)o−108.05(13)o for N-Ag-Ag, 126.2(6)o−128.2(6)o for C-N-Ag. In compound 1, the dpz ligand provides its one N donor to link one AgI ion. Each AgI

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ion is fused by two dpz ligands to form a {Ag(dpz)2} fragment. Furthermore, one Mo8 molecule offers four symmetrical O atoms to connect four {Ag(dpz)2} fragments and a discrete structure is formed. The Mo8 becomes a four-supporting anion. Considering the Ag-C weak interactions (Ag2···C6 = 3.334 Å, Ag2···C7 = 3.089 Å), A

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supramolecular 1D chain is constructed, as shown in Fig. 2. Furthermore, the hydrogen bonding interactions (C5···O14 = 3.194 Å) connect adjacent layers to form

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a 2D supramolecular layer of 1 (Fig. S1). (Insert Fig. 2)

Crystal Structure of Compound 2. Compound 2 is isostructural with 1, containing four CuI ions, eight dpz ligands and one Mo8 anion (Fig. S2). The bond distances and angles around Cu ions are 1.878(7) to 1.889(7) Å for Cu-N, 2.351(4)−2.364(5) Å for

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Cu-O, and 164.2(3)o and 163.5(3)o for N-Cu-N, 90.1(2)o−99.4(2)o for N-Cu-O. The valence sum calculations[15] show that all the Mo atoms are in the +VI oxidation states and all the Cu atoms are in the +I oxidation states. Crystal Structure of Compound 3. Single-crystal Xray diffraction analysis shows

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that the asymmetric unit of 3 contains two CoII ions, four tbz ligands, one Mo8 anion and two coordinated water molecules (Fig. 3). The valence sum calculations[15] show

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that all the Mo atoms are in the +VI oxidation states and all the Co atoms are in the +II oxidation states.

(Insert Fig. 3)

There is only one crystallographically independent Co1 ion in compound 3. The Co1 ion are six coordinated, defined by four N atoms (N1, N3, N4, N6) from two tbz ligands and two O atoms from one Mo8 anion and one water molecule. The bond distances and angles around Co ions are 2.0593(14) and 2.1667(13)Å for Co-O, 2.1239(17)−2.1975(17) Å for Co-N, and 78.54(7)o−170.87(6)o for N-Co-N. In compound 3, the tbz ligand offers two N donors from the thiazole and 8

ACCEPTED MANUSCRIPT benzimidazole groups respectively to chelate one CoII ion. The tzb in 3 plays the terminater role to prevent dimensional extension. The CoII ion is fused by two tbz ligands and one water molecule to form a {Co(tbz)2(H2O)} subunits. The Mo8 anion offers two symmetric terminal O13 atoms to link two {Co(tbz)2(H2O)} subunits.

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Namely, the Mo8 is a bi-supporting anion by two {Co(tbz)2(H2O)} subunits. Thus, compound 3 is a discrete 0D structure. Furthermore, the hydrogen bonding interactions (N2···O7 = 2.906 Å) connect adjacent bi-supporting anions to build a 1D supramolecular chain, as shown in Fig. 4.

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(Insert Fig. 4)

Crystal Structure of Compound 4. Compound 4 is isostructural with 3, containing

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two NiII ions, four tbz ligands, one Mo8 anion, two coordinated and two crystal water molecules (Fig. S3). The bond distances and angles around Cu ions are 2.073(6) to 2.086(6) Å for Ni-N, 2.134(18) and 2.082(2) Å for Ni-O, and 79.85(9)o and 178.80(9)o for N-Ni-N, 87.72(8)o−171.82(8)o for N-Ni-O. The valence sum calculations[15] show that all the Mo atoms are in the +VI oxidation states and all the

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Ni atoms are in the +II oxidation states.

Crystal Structure of Compound 5. Single-crystal Xray diffraction analysis shows that the asymmetric unit of 5 contains one CuII ion, one tbz ligand, half a Mo8 anion

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and one coordinated water molecule (Fig. 5). The valence sum calculations[15] show that all the Mo atoms are in the +VI oxidation states and all the Cu atoms are in

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the +II oxidation states.

(Insert Fig. 5)

There is only one crystallographically independent Cu1 ion in compound 5. The Cu1 ion is five-coordinated by two N atoms (N1 and N3) from one tbz ligand three O atoms from two Mo8 anions and one water molecule. The Cu1 ion exhibits a distorted square pyramid geometry. The τ value for Cu1 is 0.18 (τ = (β-α)/60)[16]. For Cu1 the angles are N3-Cu1-O1W = 173.9o (β) and N1-Cu1-O8 = 163.0o (α). The bond distances and angles around Cu ion are 1.947(2) and 2.209(2)Å for Cu-O, 1.987(3) and 2.003(3) Å for Cu-N, and 81.65(11)o for N-Cu-N. In compound 5, the anion is different in 1− −4 and 6, becoming one of structural 9

ACCEPTED MANUSCRIPT features of 5. In 5, adjacent Mo8 anions link each other through sharing O10 atoms to construct an infinite octamolybdate chain (Fig. S4). The tbz ligand shows the same coordination mode with 3 and 4, using two N donors from the thiazole and benzimidazole groups respectively to link a CuII ion. One CuII is fused by only one tbz

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to form a {Cu(tbz)} subunit. The {Cu(tbz)} subunit further connects two O atoms (O3 and O8) from two Mo8 anions respectively. Namely, the {Cu(tbz)} subunits cover this inorganic infinite octamolybdate chain up and down, as shown in Fig. 6. The tbz ligands terminate the dimensional extension in compound 5. So compound 5 is only a

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1D structure. Considering the hydrogen bonding interactions, a 2D suparmolecular layer is formed through the linkage of N2···O7 =2.694 Å (Fig. S5).

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(Insert Fig. 6)

Crystal Structure of Compound 6. Single-crystal Xray diffraction analysis shows that the asymmetric unit of 6 contains one CuII ion, two btp ligands, half a Mo8 anion and two crystal water molecules (Fig. 7). The valence sum calculations[15] show that all the Mo atoms are in the +VI oxidation states and all the Cu atoms are in the +II

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oxidation states.

(Insert Fig. 7)

There is one crystallographically independent Cu1 ion in compound 6. The Cu1 ion is

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six-coordinated by three N atoms(N1, N9 and N12) from three btp ligands and two O atoms from one anion and one H2O molecule, exhibiting an octahedral coordination geometry. The bond distances and angles around Cu ions are 1.971(5)−2.019(6) Å for

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Cu-N, 2.404(5) and 2.622(5) Å for Cu-O and 88.0(2)o-175.1(2)o for N-Cu-N. In compound 6, the btp offers its two apical N donors to link two CuII ions. Each CuII ion is fused by four btp ligands. Thus, the coordination features of btp and CuII induce the 2D grid-like layer of 6 (Fig. S6). Two adjacent layers cover Mo8 anions covalently. Namely, the Mo8 anions pillar two adjacent layers to form a 2D hamburger-like structure, as shown in Fig. S7. Furthermore, adjacent 2D hamburger-like subunits interpenetrate with each other (Fig. S8), which become the structural feature of 6. This interpenetration mode increases the dimensionality from 2D to 3D, which is

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ACCEPTED MANUSCRIPT scarcely observed in POM-based compounds. Tuning dimensionality of POM-based compounds through using different ligands. Selection of proper organic ligands is an important factor to construct POM-based compounds with expected dimensionality. In this work, we introduced three kinds of

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ligands with distinct coordination features to a Mo8 system, such as dpz, tbz and btp (Scheme 2). Firstly, we used dpz to modify Mo8 aions, which owns two additional methyl groups compared with pyrazole molecule. This feature can increse the steric hindrance, which may avoid forming high dimensional structures. Fortuantely, two

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0D discrete structures of 1 and 2 were obtained. Secondly, a rigid ligand tbz was unsed, which usually acts as a terminate molecule. The tbz only offers its two N

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donors from the thiazole and benzimidazole groups respectively to chelate one TM ions. And then isostructural 0D compounds 3 and 4 and a 1D structure of 5 were constructed. The flexible bis(triazole) ligands conduce to construct high dimensional structures. Both the more N donors and flexible backbone can build 3D frameworks with ease. Thus, we finally introduced btp to modify Mo8 anions and a 2D

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hanberger-like layer is formed. Interestingly, adjacent layers further interpenetrate with each other and a 3D interpenetrating structure is obtained, realizing dimensionality update 2D→3D. Thus, changing different ligands to tune the

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dimensionality of POM-based compounds is a rational and effective method, which may support experimental data for target syntheses.

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3.3 FT-IR spectra, UV-vis absorption spectra and powder X-ray diffractions Fig. S9 shows the IR spectra of compounds 1−6. In the spectra, characteristic bands at 936, 840, 705 and 655 cm-1 for 1, 929, 880, 752 and 681 cm-1 for 2, 944, 845, 743 and 671 cm-1 for 3, 928, 865, 758 and 625 cm-1 for 4, 965, 865, 743 and 648 cm-1 for 5, 972, 873, 737 and 648 cm-1 for 6, are attributed to the ν(Mo=O), ν(Mo-O-Mo)[17], respectively. Bands in the regions of 1587−1144 cm-1 for 1, 1636−1051 cm-1 for 2, and 1623−1108 cm-1 for 3 and 1623−1015 cm-1 for 4 and 1644−1038 cm-1 for 5 and 1614−1102 cm-1 for 6 are attributed to the dpz, tbz and btp ligands, respectively. The UV-vis absorption spectra of compounds 1–6 were measured in the crystalline

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ACCEPTED MANUSCRIPT state at room temperature (Fig. S10). The energy bands from 200 to 300 nm may be assigned to the pπ (O terminal)→dπ* (Mo) electronic transitions in the Mo=O bonds and dπ-pπ-dπ electronic transitions between the energetic levels of the Mo-O-Mo bonds, respectively [13].

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The powder X-ray diffraction (PXRD) patterns indicate that the synthesized compounds match with the simulated ones except for some intensity differences (Fig. S11), proving the purity of the crystalline phase 1–6. The intensity differences can be owed to the different orientation of the crystals in the powder samples.

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3.4 TG analyses

TG analysis was carried out under N2 with a heating rate of 10 oC min–1. The TG

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curves of compounds 1−6 (Fig. S12) are measured in the range 25–880 oC. A total weight loss of 37.84% agrees well with the calculated value of 38.64% for compound 1. A total weight loss of 44.23% agrees well with the calculated value of 43.53% for compound 2. For the compound 3, the first weight loss is 1.68% and the second is 46.55%, corresponding to the release of crystal water and the tbz ligands. The first

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weight loss is 3.36% and the second one is 44.97%, corresponding to the release of crystal water and tbz ligands for compound 4. A total weight loss of 37.18% agrees well with the calculated value of 36.08% for compound 5 with the first weight loss is

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2.05% and the second one is 34.03%, corresponding to the release of crystal water and tbz ligands. For 6, the first weight loss is 5.06% and the second one is 42.47%,

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corresponding to the release of crystal water and btp liagands. 3.5 Voltammetric behavior of 1−CPE to 5−CPE in aqueous electrolyte and its electrocatalytic activity For investigate the electrochemical behaviors of compounds 1−6, the title compounds bulk-modified CPEs were made. Because of the similar electrochemical behaviors of 1– to 6–CPEs, so 6–CPE has been taken as an example. The electrochemical behaviors of 6–CPE in 0.1 M H2SO4 + 0.5 M Na2SO4 aqueous solution at different scan rates are presented in Fig. 8 (a). The 6–CPE exhibits three pairs of redox peaks in the potential range of –230 to + 400 mV, which can be attributed to three consecutive 12

ACCEPTED MANUSCRIPT two-electron processes of Mo, respectively[18]. The mean peak potentials E1/2 = (Epa + Epc)/2 are +259 (I–I'), +158 (II–II') and –68 mV (III–III') (100 mVs–1) for 6–CPE, respectively. The peak potentials change gradually with the scan rates increasing: the cathodic peak potentials shift toward the negative direction and the corresponding

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anodic peak potentials to the positive direction. The peak currents are proportional to the scan rates up to 500 mVs-1, indicating that the redox processes of the 6–CPE is surface-controlled (Fig. S13).

For 6–CPE, with the addition of bromate and nitrite, all the reduction peak currents

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increase gradually and the corresponding oxidation peak currents decrease, suggesting that the three reductive species of Mo8 all possess electrocatalytic activities for the

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reduction of BrO3– and NO2- (Fig. 8 (b), (c)). Namely, the bromate and nitrite are reduced by two-, four- and six-electron reduced species of Mo8 in 6–CPE. (Insert Fig. 8)

3.6 Photocatalytic activities

Recently, the POM-based compounds have been proved good photocatalysts in

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degradation of some organic substances under the UV light[19]. At this point, we selected two organic dyes methylene blue (MB) and rhodamine B (RHB) as model pollutants. As shown in Fig. 9, with passage of time the degradation percentage of

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MB photocatalyzed by compounds 1− −6 increased obviously. After 120 min, the degradation ratios of MB reach 74.0 % for 1, 79.1 % for 2, 82.9 % for 3, 85.2 % for 4,

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63.9 % for 5 and 90.0 % for 6. Fig. 10 shows the photocatalytic degradation of RHB and the degradation ratios of RHB reach 80.6% for 1, 85.9 % for 2, 57.9 % for 3, 71.5 % for 4, 39.9 % for 5 and 50.5 % for 6 after 120 min. The results suggest that the title compounds exhibit good photocatalitic properties for photodegradation of MB and RHB. The high degradation ratios of RHB photocatalyzed by POM-based compounds is scarcely observed, especially compounds 1, 2 and 4. After photocatalytic process, recycled compounds 1− −6 were used for photocatalytic degradation of MB and RHB for three times, respectively (Fig. S14). Fig. S14 exhibit that the reproducibility of repeated runs is good, especially for degradation results. (Insert Fig. 9) 13

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4. Conclusions In this work, six Mo8-based compounds have been constructed. Tuning dimensionality of POM-based compounds through changing different ligands is

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rational and effective for design and syntheses of these compounds. This work may support meaningful experimental data for target syntheses of POM-based compounds with different dimensionalities. Compounds 1−6 show good photocatalytic activities and reproducibility for degradation of dyes, which may expand applicable range of

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compounds with appealing properties is underway.

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POM-based compounds. Further study on target syntheses of novel POM-based

Acknowledgements

Financial supports of this research by the National Natural Science Foundation of China (No. 21571023, 21401010 and 21471021) and Talent-supporting Program

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ACCEPTED MANUSCRIPT Table 1. Crystal data and structure refinements for compounds 1-6.

Fw crystal system space group a (Å) b (Å) c (Å) α (°) b (o) γ (°) V (Å3) Z Dc (g·cm-3)

C40H56Ag4 Mo8N16O26 2319.97 monoclinic

3

C40H64Cu4 Mo8N16O26 2206.75 monoclinic

C10H7Cu Mo4N3O14S 872.55 triclinic

C14H20Cu Mo4N12O16 1059.72 triclinic

P -1 8.330(5) 10.490(5) 12.498(5) 73.430(5) 71.558(5) 83.950(5) 992.8(9) 2 3.958 9.739 1080 0.0234 0.0555

P -1 11.4896(5) 12.1037(6) 12.5937(6) 77.4310(10) 74.5330(10) 66.9430(10) 1540.40(13) 1 2.733 6.279 1188 0.0728 0.1890

P -1 8.3295(5) 10.4899(6) 12.4982(7) 73.4300(10) 71.5580(10) 83.9500(10) 992.80(10) 2 2.919 3.696 826 0.0236 0.0562

P -1 11.6658(12) 11.7055(13) 11.8978(13) 71.114(2) 77.143(2) 85.924(2) 1498.7(3) 2 2.348 2.417 1026 0.0517 0.1200

0.940 0.0158

1.039 0.0136

1.052 0.0158

0.986 0.0370

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6

C40H24Co2 C40H24Mo8 Mo8N12O28S4 N12Ni2O28S4 2134.33 2133.89 triclinic triclinic

R1 = ∑║Fo│─│Fc║/∑│Fo│. b wR2 = {∑[w(Fo2─Fc2)2]/∑[w(Fo2)2]}1/2

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a

5

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P 21/c P 21/c 13.1827(7) 13.0725(12) 20.7227(12) 20.2825(19) 13.6873(8) 13.9436(14) 90 90 110.4990(10) 111.661(2) 90 90 3502.3(3) 3436.0(6) 2 2 2.200 2.133 -1 2.548 2.700 µ (mm ) F(000) 2224 2152 a R1 [I >2σ(I)] 0.0329 0.0489 b wR2 (all 0.0864 0.1438 data) GOF on F2 1.073 1.046 Rint 0.0289 0.0415

4

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formula

2

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1

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Scheme. 1. Three organic ligands dpz, tbz and btp used in compounds 1−6.

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Scheme 2. Schematic view of tuning dimensionality of POM-based compounds

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through chaing three ligands (pink balls: coordination N atoms).

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Fig. 1. Ball/stick view of the asymmetric unit of compound 1. The hydrogen atoms

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are omitted for clarity.

Fig. 2. The 1D supramolecular chain of compound 1 linked by weak interactions of

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Ag-C bonds.

Fig. 3. Ball/stick view of the asymmetric unit of compound 3. The hydrogen atoms are omitted for clarity.

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Fig. 4. The 1D supramolecular chain of compound 3 linked by hydrogen bonding

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interactions N2···O7 = 2.906 Å.

Fig. 5. Ball/stick view of the asymmetric unit of compound 5. The hydrogen atoms

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are omitted for clarity.

Fig. 6. The 1D chain in compound 5 with {Cu(tbz)} subunits covering inorganic infinite octamolybdate chain up and down.

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Fig. 7. Ball/stick view of the asymmetric unit of compound 6. The hydrogen atoms

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and crystal water molecules are omitted for clarity.

Fig. 8. (a) The cyclic voltammograms of the 6–CPE in 0.1 M H2SO4+ 0.5 M Na2SO4 aqueous solution at different scan rates (from inner to outer: 20, 40, 60, 80, 100, 120,

ACCEPTED MANUSCRIPT 140, 160, 180, 200, 250, 300, 350, 400, 450 and 500 mV s-1, respectively.). (b) Cyclic voltammograms of the 6–CPE in 0.1 M H2SO4 + 0.5 M Na2SO4 aqueous solution containing 0 (a); 2 (b); 4 (c); 6 (d) and 8 (e) mM KBrO3. Scan rate: 200 mV s-1. (c) Cyclic voltammograms of the 6–CPEs in 0.1 M H2SO4 + 0.5 M Na2SO4 aqueous

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solution containing 0 (a); 2 (b); 4 (c); 6 (d) and 8 (e) mM KNO2. Scan rate: 200 mV

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s-1.

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Fig. 9. Absorption spectra of the MB solution during the degradation reaction under

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UV irradiation with the compounds 1–6 as the cataldecompositionysts.

Fig. 10. Absorption spectra of the RHB solution during the degradation reaction under UV irradiation with the compounds 1–6 as the catalysts.

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Highlight 1. Tuning dimensionality of 1− −6 through changing ligands is rational and effective. 2. The POM-TMCs with 0D, 1D, 2D and 3D structures are appealing and challenging. 3. The btp induces a 2D→3D interpenetrating structure of 6.

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4. Compounds 1–6 show good electrochemical and photocatalytic properties.