Bifunctional [Fe6Co7] cyanide bridged assemblies: electron transfer coupled spin transition and liquid crystal properties

Abstract

Mesostructuring of Prussian blue analogues (PBAs) can impart high surface area and anisotropic magnetic behavior, making them desirable for practical applications as switches, sensors and display devices. Herein, we present the first report of alkylated {[Fe₃Co₃]₂Co} tridecanuclear PBAs exhibiting magnetic bistability co-existing with thermochromism (green → red) and crystal to liquid–crystal phase change. The rational design strategy led to the isolation of these tridecanuclear complexes with general formula {[Fe^IITp(CN)₃]₃[Co^III(L-C_n)₂]₃}₂Co^II·A⁻·ysolvents (For 1-C_n; A⁻ = 7BF₄⁻·[Fe^IIITp(CN)₃]⁻, y = 64H₂O and for 2-C_n; A⁻ = 8ClO₄⁻, y = 8H₂O), where n = carbon chain length, i.e. 4, 6, 8, 10, 12, 14, 16; Tp = hydrotris(1-pyrazolyl)borate and L-C_n = N-alkylated 2,2′-dipyridylamine with the respective carbon chain lengths. The transition and melting temperatures of the complexes are in synchronisation and decrease with increasing carbon chain length. This occurs due to higher flexibility of longer alkyl chains. The flexible chains not only induce liquid crystalline properties in the complexes, but also allow their fabrication into thin films with nearly no compromise in the magnetic bistability and thermochromic behavior. This strategy to functionalise PBAs with flexible alkyl chains provides an array of mesostructures with tunable magnetic, optical, and electronic properties.