Controlled synthesis of [Fe(pyridine)2Ni(CN)4] nanostructures and their shape-dependent spin-crossover properties

Abstract

Ultrathin nanosheets of the spin crossover (SCO) coordination polymer [Fe(py)2Ni(CN)4] (py = pyridine) have been achieved through a reverse micelle route. The nanosheets possess regular square shape with a thickness less than 10 nm and a main width of 600–800 nm. Through controlling the synthetic parameters, the nanostructures of [Fe(py)2Ni(CN)4] can be tuned to be square plate-, cube- and box-like shapes, respectively. The possible formation mechanism for these diversiform nanocrystals was proposed. Magnetic measurements and differential scanning calorimetry analyses revealed an interesting morphology-dependent SCO behavior of [Fe(py)2Ni(CN)4]. The hysteresis width decreases in the order of nanoplates (ca. 22 K), nanocubes (ca. 16 K), nanoboxes (ca. 4 K) and nanosheets (ca. 2 K). The enthalpy (ΔH) and entropy (ΔS) variations associated with the spin transitions of nanosheets and nanoboxes are significantly lower than those of nanocubes and nanoplates. Thus, the nanosheets and nanoboxes exhibit stronger nano-effect and their SCO properties are largely weakened owing to the large specific surface areas resulting from their unique morphologies.