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Supramolecular self-assembly for designing non-centrosymmetric crystals based on Keggin polyoxometallates and crown ether

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Abstract

We report the synthesis of five novel crystals [(4-BrAni+)(DB[18]crown-6)]2[SMo12O402−]·2CH3CN (1), [(4-BrAni+)(B[18]crown-6)]2[SMo12O402−]·CH3CN (2), [(4-BrAni+)(B[18]crown-6)]3[PMo12O402−]·2CH3CN (3), [(3-AP+)3(B[18]crown-6)2][PMo12O403−] (4) and [NBu4+][(3-AP2+)(DB[30]crown-10)][PMo12O403−]·CH3CN (5) (4-BrAni+ = 4-bromoanilinium; B[18]crown-6 = benzo[18]-crown-6; DB[18]crown-6 = dibenzo[18]-crown-6; DB[30]crown-10 = dibenzo[30]-crown-10; 3-AP+ = 3-aminopyridinium; 3-AP2+ = 3-ammoniumpyridinium; NBu4+ = tetrabutylammonium). In order to construct non-centrosymmetric crystals, the five crystals were designed using a method to gradually introduce asymmetry into the building units. Crystal 1 was constructed with a symmetric supramolecular cation (SPC) [(4-BrAni+)(DB[18]crown-6)], resulting in a P21/n space group. The asymmetric SPC [(4-BrAni+)(B[18]crown-6)] was introduced into [SMo12O402−] to obtain crystal 2, which belongs to the symmetric P[1 with combining macron] space group. Introducing trivalent [PMo12O403−], [(4-BrAni+)(B[18]crown-6)] produced crystal 3 with a non-centrosymmetric Pc space group. The asymmetric sandwich SPC [(3-AP+)3(B[18]crown-6)2] was designed with multiple hydrogen bonding sites on the 3-AP+ cation, and crystal 4 was obtained with trivalent [PMo12O403−]. Crystal 4 has the properties of the chiral P1 space group. The distorted SPC (3-AP2+)(DB[30]crown-10) was constructed using flexible DB[30]crown-10, resulting in crystal 5 which matched the chiral P21 space group with trivalent [PMo12O403−]. This work focuses on strategies for the rational design of novel non-centrosymmetric crystals without a chiral synthon.

Graphical abstract: Supramolecular self-assembly for designing non-centrosymmetric crystals based on Keggin polyoxometallates and crown ether

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Publication details

The article was received on 17 Jul 2018, accepted on 24 Aug 2018 and first published on 07 Sep 2018


Article type: Paper
DOI: 10.1039/C8DT02910E
Citation: Dalton Trans., 2018, Advance Article
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    Supramolecular self-assembly for designing non-centrosymmetric crystals based on Keggin polyoxometallates and crown ether

    J. Xiong, K. Kubo, S. Lü, M. Li and T. Nakamura, Dalton Trans., 2018, Advance Article , DOI: 10.1039/C8DT02910E

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