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

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.