Architectural Isomerism in the Three-Dimensional Prussian Blue Analogue {[Co^II(TPA)]₃[Fe^III(CN)₆][Co^III(CN)₆]}: Synthesis, Crystal Structures, and Magnetic Properties

Abstract

Prussian Blue analogues (PBAs) with unusual properties such as spin crossover (SCO) and metal-to-metal electron transfer (MMET) are of great interest. However, the construction of new three-dimensional (3D) PBAs is a formidable challenge. Herein, two mixed-valence 3D PBAs, {[CoII(TPA)]3­[FeIII(CN)6]­[CoIII(CN)6]}­3DMF·7H2O (1·S) and {[CoII(TPA)]3­[FeIII(CN)6]­[CoIII(CN)6]}­2DMF·1H2O (2·S) (TPA = tris­(2-pyridylmethyl)­amine, DMF = N,N-dimethylformamide), were synthesized by a solvothermal method. Complexes 1 and 2 are architectural isomers with different crystal structures, electronic absorption spectra, and magnetic properties, one of which (1·S) showed reversible thermochromism accompanied by metal-to-metal electron transfer (MMET). Compound 1·S crystallizes in the monoclinic space group P21/c with a = 17.2227(8), b = 23.1538(10), c = 22.5074(12) Å, β = 90.388(5)°, V = 8975.17(7) Å3, and Z = 4. Compound 2·S crystallizes in the tetragonal space group P4/nnc with a = b = 33.1374(5), c = 31.7381(10) Å, V = 34851.2(15) Å3, and Z = 16. In both isomers, the 3D structures are constructed with heptanuclear heterometallic units, {[CoII(TPA)]6­[FeIII(CN)6]}9+, which are interconnected by [Fe­(CN)6]3– and [Co­(CN)6]3– anions in the trans μ-bridge mode. This work may provide a new perspective for the design of functional PBAs materials.

Phase Transition and Switchable Dielectric Properties of a Three-Dimensional Hydrogen-Bonding Framework Based on Cobalt (Ⅲ), o-Bromoaniline, and 18-Crown-6

“…Typically, electrical, magnetic, or optical responses tend to change abruptly close to the phase transition temperature. Organic-inorganic hybrids have emerged as favorable candidates for integrating phase transition properties with diverse switching response characteristics [24][25][26][27][28]. For responsive dielectrics, the dipolar orientation (e.g., order-disorder or melting/frozen-like transition) is the primary contributor to the dielectric constant.…”

Manipulating Metal-to-Metal Electron Transfer in Cyano-Bridged [Fe2Co]-Assembled Coordination Polymers

“…In 2004, Dunbar and co-workers reported a discrete pentanuclear [Fe 2 Co 3 ] complex realizing thermally induced ETCST at the molecular level . Until now, numerous cyano-bridged FeCo polynuclear complexes − and coordination polymers − ,− exhibiting the ETCST phenomenon have been reported. The systematic study of the structure–property relationships in the ETCST complexes is invaluable for exploring and strategically fabricating the electron transfer materials with switchable characteristics and functions.…”