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The structures of ordered defects in thiocyanate analogues of Prussian Blue.

ABSTRACT: We report the structures of six new divalent transition metal hexathiocyanatobismuthate frameworks with the generic formula , M = Mn, Co, Ni and Zn. These frameworks are defective analogues of the perovskite-derived trivalent transition metal hexathiocyanatobismuthates M^III[Bi(SCN)₆]. The defects in these new thiocyanate frameworks order and produce complex superstructures due to the low symmetry of the parent structure, in contrast to the related and more well-studied cyanide Prussian Blue analogues. Despite the close similarities in the chemistries of these four transition metal cations, we find that each framework contains a different mechanism for accommodating the lowered transition metal charge, making use of some combination of Bi(SCN)₆ ^3- vacancies, M_Bi antisite defects, water substitution for thiocyanate, adventitious extra-framework cations and reduced metal coordination number. These materials provide an unusually clear view of defects in molecular framework materials and their variety suggests that similar richness may be waiting to be uncovered in other hybrid perovskite frameworks.

SUBMITTER: Cliffe MJ

PROVIDER: S-EPMC8159453 | biostudies-literature | 2020 Apr

REPOSITORIES: biostudies-literature

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The structures of ordered defects in thiocyanate analogues of Prussian Blue.

Cliffe Matthew J MJ Keyzer Evan N EN Bond Andrew D AD Astle Maxwell A MA Grey Clare P CP

Chemical science 20200409 17

We report the structures of six new divalent transition metal hexathiocyanatobismuthate frameworks with the generic formula , M = Mn, Co, Ni and Zn. These frameworks are defective analogues of the perovskite-derived trivalent transition metal hexathiocyanatobismuthates M<sup>III</sup>[Bi(SCN)<sub>6</sub>]. The defects in these new thiocyanate frameworks order and produce complex superstructures due to the low symmetry of the parent structure, in contrast to the related and more well-studied cyan ...[more]

PMID: 34122899

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Project description:The elucidation of the ideal coordination environment of a catalytic site has been at the heart of catalytic applications. Herein, we show that the water oxidation activities of catalytic cobalt sites in a Prussian blue (PB) structure could be tuned systematically by decorating its coordination sphere with a combination of cyanide and bidentate pyridyl groups.  K0.1[Co(bpy)]2.9[Fe(CN)6]2 ([Cobpy-Fe]), K0.2[Co(phen)]2.8[Fe(CN)6]2 ([Cophen-Fe]), {[Co(bpy)2]3[Fe(CN)6]2}[Fe(CN)6]1/3 ([Cobpy2-Fe]), and {[Co(phen)2]3[Fe(CN)6]2}[Fe(CN)6]1/3 Cl0.11 ([Cophen2-Fe]) were prepared by introducing bidentate pyridyl groups (phen: 1,10-phenanthroline, bpy: 2,2'-bipyridine) to the common synthetic protocol of Co-Fe Prussian blue analogues. Characterization studies indicate that [Cobpy2-Fe] and [Cophen2-Fe] adopt a pentanuclear molecular structure, while [Cobpy-Fe] and [Cophen-Fe] could be described as cyanide-based coordination polymers with lower-dimensionality and less crystalline nature compared to the regular Co-Fe Prussian blue analogue (PBA), K0.1Co2.9[Fe(CN)6]2 ([Co-Fe]). Photocatalytic studies reveal that the activities of [Cobpy-Fe] and [Cophen-Fe] are significantly enhanced compared to those of [Co-Fe], while molecular [Cobpy2-Fe] and [Cophen2-Fe] are inactive toward water oxidation. [Cobpy-Fe] and [Cophen-Fe] exhibit upper-bound turnover frequencies (TOFs) of 1.3 and 0.7 s-1, respectively, which are ∼50 times higher than that of [Co-Fe] (1.8 × 10-2 s-1). The complete inactivity of [Cobpy2-Fe] and [Cophen2-Fe] confirms the critical role of aqua coordination to the catalytic cobalt sites for oxygen evolution reaction (OER). Computational studies show that bidentate pyridyl groups enhance the susceptibility of the rate-determining Co(IV)-oxo species to the nucleophilic water attack during the critical O-O bond formation. This study opens a new route toward increasing the intrinsic water oxidation activity of the catalytic sites in PB coordination polymers.

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The structures of ordered defects in thiocyanate analogues of Prussian Blue.

Publications

The structures of ordered defects in thiocyanate analogues of Prussian Blue.

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