Diverse physical functionalities of rare-earth hexacyanidometallate frameworks and their molecular analogues

Abstract

Rare-earth (RE) metal complexes exhibit attractive magnetic and optical properties related to their strong magnetic anisotropy and efficient photoluminescence. Due to the accessibility of high coordination numbers, they are useful molecular building blocks for the construction of bimetallic coordination systems. Therefore, they can be readily combined with hexacyanidometallate ions of transition metals into the d–f cyanido-bridged frameworks. This leads to the rich family of molecule-based materials varying from purely inorganic 3-D RE^III–[M^II/III(CN)₆]^4−/3− (RE = La–Lu, Y; M = Cr, Fe, Ru, Co) networks, through coordination polymers of lower dimensionality obtained with supporting organic ligands, up to strictly molecular species. The past decade brought intensive interest in the design and synthesis of rare-earth hexacyanidometallate frameworks with particular attention paid to their magnetic, optical, electronic, and mechanical properties. In this review, we discuss the most important results of this research area, including remarkable thermal expansion properties, magnetic ordering effects, single-molecule magnetism, luminescent functionalities, electrochemical activity for applications in alkali ion batteries and electroanalytical sensing, and efficient NMR relaxivity for magnetic resonance imaging, as well as photo- and pressure-induced switching of magnetic and optical characteristics. We focus on the recent advances, emphasizing also the general advantages and the future perspectives in the combination of RE(III) complexes and hexacyanidometallates within the d–f coordination frameworks towards the generation of diverse physical functionalities.