*2.3. X-ray Crystallography*

The single-crystal diffraction data of **1**–**3** were collected on a Gemini A Ultra CCD diffractometer with graphite monochromated Mo Kα (Λ = 0.71073 Å) radiation at 296(2) K. The structures were solved by direct methods and refined by the full-matrix least-squares fitting on F<sup>2</sup> method with the SHELX-2008 program package [26]. Anisotropic displacement parameters were refined for all atomic sites except for some disordered atoms. The contribution of the disordered solvent molecules in **1** and **2** was treated with the SQUEEZE method in PLATON (Utrecht University, Utrecht, The Netherlands). In the refinements, 0, 1, and 2 lattice water molecules were found for **1**–**3** from the Fourier maps, respectively. Based on the potential solvent-accessible voids and electron counts from the SQUEEZE reports, there were 31 and 55 lattice water molecules removed for **1** and **2**, respectively. According to the elemental analyses and TGA, there are 27 and 34 lattice water molecules lost from efflorescence in **1** and **2**, respectively. In **3**, 4 absorbed water molecules were found. Basic crystallographic data and structural refinement data are listed in Table 1. Detailed crystallographic data have been deposited on the Cambridge Crystallographic Data Centre: CCDC 2171028 (for **1**), 2170965 (for **2**), and 2170966 (for **3**). These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html accessed on 29 June 2022

or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; Fax: +44-1223-336-033; or email: deposit@ccdc.cam.ac.uk.

**Table 1.** Crystallographic data and structural refinements for **1**–**3**.


<sup>1</sup> *R*<sup>1</sup> = Σ||*F*0| − |*F*c||/Σ|*F*0|. *wR*<sup>2</sup> = {Σw[(*F*0) <sup>2</sup> − (*F*c) 2] 2/Σw[(*F*0) 2] 2} 1/2.

## **3. Result and Discussion**

#### *3.1. Structure of 1 and Designed Syntheses for 2*

X-ray diffraction analyses reveal that **1** crystallizes in the trigonal space group *P*-3*c*1, consisting of the neutral [Ni6(*μ*3-OH)3(DACH)3(H2O)6(PW9O34)] (**1a**, Figure 1a) cluster. **1a** can be seen as the classical trilacunary Keggin [B-α-PW9O34] <sup>9</sup><sup>−</sup> fragment being capped by a triangular [Ni6(*μ*3-OH)3] 9+ cluster. Due to the trigonal *C*<sup>3</sup> symmetry of **1**, there are only two independent Ni2+ in the Ni6 cluster (Figure S1, Supplementary Materials). Each Ni1 and Ni2 interconnect with each other by edge-sharing, producing three edge-sharing {Ni3O4} truncated cubanes. Three Ni1O6 octahedra locate on the three lacunary sites of the {PW9} unit, while three Ni2O4N2 octahedra are on the three vertexes of the triangular Ni6 cluster, further decorated by three DACH ligands, respectively (Figure 1b). According to BVS calculations [27], the bond valance of *μ*3-O4 is 1.12, indicating its protonation. **1a** exhibits two opposite orientations, which are alternately arranged with a shoulder-toshoulder arrangement along the *a*-axis and [110] direction (Figure 1c,d). Such arrangements construct the snowflake-like supramolecular channels with *S6* symmetry and are the hydrophobic voids as well (Figure 1e).

The presence of six terminal water molecules on the Ni6 cluster provides abundant substituted sites for organic ligands. We started to incorporate organic ligands into the reaction system of **1**, attempting to construct POMCOFs with proper organic linkers. In our previous work, we have successfully made two 1D POMCOCs {[Ni6(OH)3(H2O)2- (enMe)3(PW9O34)](1,3 bdc)}[Ni(enMe)2]·4H2O (**4,** enMe = 1,2-diaminopropane, 1,3-bdc = 1,3-benzenedicarboxylate acid) and {[Ni6(OH)3(H2O)(en)4(PW9O34)](Htda)}·H3O·4H2O (**5,** en = ethylenediamine, tda = thiodiglycolic acid) based on {Ni6PW9} SBUs and V-type rigid dicarboxylate ligands (1,3-bdc and tda) [7]. To analyze these structures carefully, we found that in **4** and **5**, {Ni6PW9} SBUs are arranged in shoulder-to-shoulder and face-to-face modes, respectively, which are further bridged by the V-type dicarboxylate ligands to 1D POMCOCs. In **1**, though the opposite-orientated {Ni6PW9} units exhibit shoulder-to-shoulder arrangements along the *a*-axis, the interunit distances are too close to accommodate the organic ligands. Hence, we choose the similar V-type ligand MIP to see if the methyl group can further spread out the opposite orientated POM units and if the carboxyl groups can bridge adjacent same orientated units to 1D chains at the same time. By adding MIPA into the reaction of **1**, **2** was obtained. The observation of **2** confirms part of our speculations; though HMIP

still acts as a decoration group, it changes the orientations of adjacent POM units such that two different orientated units both arrange in shoulder-to-shoulder modes separately with moderate interunit distances.

**Figure 1.** (**a**) A polyhedral view of polyoxoanion **1a**.; (**b**) View of the Ni6 cluster in **1a**; (**c**,**d**) Shoulderto-shoulder arrangements of **1a** with opposite orientations along the *a*-axis and [110] direction; and (**e**) The 3D supramolecular framework of **1**. Color code of polyhedral: WO6: red; NiO6/NiO4N2: green; and PO4: yellow. Hydrogen atoms of the ligands are not shown for better clarity.
