Monitoring the spin crossover phenomenon of [Fe(2‐mpz)2Ni(CN)4] 2D Hofmann‐type polymer nanoparticles via temperature‐dependent Raman spectroscopy

Abstract

AbstractThe incorporation of spin crossover (SCO) properties into metal–organic frameworks (MOFs) has led to an appealing subclass of multifunctional MOFs. Because temperature is the most common way to manipulate the SCO phenomenon, the spin state of relevant complexes is conveniently monitored by variable‐temperature magnetic susceptibility (χMT) measurements. Other physical and spectroscopic techniques may also monitor the SCO behavior. In this context, the present work focuses on the use of variable‐temperature micro‐Raman spectroscopy. More specifically, the SCO behavior of the two‐dimensional Hofmann‐type MOF [FeII(2‐mpz)2Ni(CN)4], (2‐mpz = 2‐methylpyrazine), in the form of both bulk microcrystalline powder and nanoparticles is in depth analyzed via temperature‐dependent Raman spectroscopy. Magnetic susceptibility measurements were used in order to benchmark the vibrational spectroscopic ones. A brief introduction on the basic synthetic features of the samples and the morphological characteristics of representative samples are described, while the detailed syntheses of the MOF compounds in the microscale and the nanoscale were recently comprehensively addressed. It is unambiguously revealed for the samples in the different particle sizes that the SCO characteristics, such as Tc values, hysteretic behavior, and high spin (HS) population curves as a function of temperature, derived from Raman measurements are in close comparison with those of the magnetic susceptibility. In addition, spectroscopic analysis in the high‐ and low‐wavenumber regions suggests the 2D network structure of the specific compound and reveals the alterations at molecular level associated with the HS and low spin (LS) states. The significance of Raman spectroscopy for the study of SCO materials is demonstrated, because the technique offers combined structural characterization and detailed study of the transition.