Epitaxial Thin-Film vs Single Crystal Growth of 2D Hofmann-Type Iron(II) Materials: A Comparative Assessment of their Bi-Stable Spin Crossover Properties

Abstract

Integration of the ON-OFF cooperative spin crossover (SCO) properties of Fe II coordination polymers as components of electronic and/or spintronic devices is currently an area of great interest for potential applications. This requires the selection and growth of thin films of the appropriate material onto selected substrates. In this context, two new series of cooperative SCO two-dimensional Fe II coordination polymers of the Hofmann-type formulated {Fe II (Pym)2[M II (CN)4]•xH2O}n and {Fe II (Isoq)2[M II (CN)4]}n (Pym = pyrimidine, Isoq = isoquinoline; M II = Ni, Pd, Pt) have been synthesized, characterized and the corresponding Pt derivatives selected for fabrication of thin films by liquid-phase epitaxy (LPE). At ambient pressure, variable-temperature single-crystal, magnetic and calorimetric studies of the Pt and Pd microcrystalline materials of both series display strong cooperative thermal induced SCO properties. In contrast, this property is only observed for higher pressures in the Ni derivatives. The SCO behavior of the {Fe II (L)2[Pt II (CN)4]}n thin films (L = Pym, Isoq) were monitored by magnetization measurements in a SQUID magnetometer and compared with the homologous samples of the previously reported isostructural {Fe II (Py)2[Pt II (CN)4]}n (Py = pyridine). Application of the theory of regular solutions to the SCO of the three derivatives allowed us to evaluate the effect on the characteristic SCO temperatures and the hysteresis, as well as the associated thermodynamic parameters when moving from microcrystalline bulk solids to nanometric thin films.

Extreme downsizing of spin crossover nanoparticles towards stable colloids in water: a detailed nano-topographic study

“…Comparison of the magnetic data between bulk materials and nanoparticles 4, 5 and 6 showed different magnetic response. Based on the literature of 2D SCO nanoparticlesnanocrystals 19,43,76,77 it is difficult to rationalize the influence of composition of the compound on the cooperativity of SCO phenomenon. Having in mind that the SCO is in origin a molecular phenomenon, its actual demonstration is adjusted by solid-state effects based on the special characteristics of each material.…”

“…As we pointed out, the increase of molar fraction of inactive HS centres is due to the extreme downsizing of the dimensions of the nanoparticle and the actual increase of the surface/volume ratio creating a large number of defects at the periphery where the Fe II ions complete their axial coordination. [76][77] Table 2 presents a correlation between nanoparticle size distribution and the characteristics emanated from thermal susceptibility measurements.…”

Reversible guest-induced gate-opening with multiplex spin crossover responses in two-dimensional Hofmann clathrates

“…These mutual interactions in turn affect the Fe II environments and determine varying and predictable SCO behaviours. The interplay between SCO and gate-opening adsorption, together with their likely suitability to be processed as nanometric thin lms, as other related compounds, 21,27,30 evidence the potential of the reported 2D amino-functionalized HCPs for sensing and/or gas separation applications.…”

2-D spin crossover materials at the nanometric scale: the effects of the size-reduction on the magnetic properties

“…Recently Bartual-Murgui et al 45 ) synthesized in the bulk form. Their respective Pt counterparts were chosen for the fabrication of thin films through the LBL method.…”

“…Fig.6Temperature dependence of the susceptibility data of the whole mass contained in the thin films and solid red lines present the results of the magnetic simulations. Adapted from ref 45. with permission from the American Chemical Society, copyright 2020.…”