Sonocrystallization as an Efficient Way to Control the Size, Morphology, and Purity of Coordination Compound Microcrystallites: Application to a Single-Chain Magnet

Abstract

Size, morphology and purity control of coordination compounds powders is a key stage for their conversion into materials and devices. In particular, surface science techniques require highly pure bulk materials with a narrow crystallite-size distribution together with straightforward, scalable and reproducible crystallization procedures. In this work we demonstrate how sonocrystallization, i.e. application of ultrasounds during the crystallization process, can afford, very quickly, powders made of crystallites with controlled size, morphology and purity. We show that this process drastically diminishes the crystallite-size distribution (low Polydispersity Indexes, PDI) and crystallite aspect ratio. By comparing sonicated samples with various silent crystallization conditions, we unambiguously show that the improvement of the crystallite morphologies and size-distribution is not due to any thermal effect but to the sonication of the crystallizing media. The application of sonocrystallization on crystallization batches of Single-Chain Magnets (SCM) maintains SCMs chemical integrity together with their original magnetic behavior. Moreover, luminescent measurements show that sonocrystallization induces an efficient micromixing that drastically enhances the purity of the SCMs powders. We thus propose that sonocrystallization, which is already used on organic or MOF compounds, can be applied to (magnetic) coordination compounds to readily afford bulk powders for characterization or shaping techniques that require pure, morphology-and crystallite-size-controlled powder samples.

Optimized Local Synthetic Conditions Induce Size Reduction and Phase Purification in {[Fe(Htrz)2(trz)](BF4)}n Spin Crossover Particles

“…This clearly shows that, under these operating conditions, and contrary to what was previously observed on similar 1D coordination compounds, 34 the sonication does not operate in a sonocrystallization regime that is known to reduce particle size distribution. Sonofragmentation (breakage of large crystallite) 35 may occur here.…”

Sonocrystallization of CMONS Needles and Nanocubes: Mechanistic Studies and Advanced Crystallinity Characterization by Combining X-ray and Electron Diffractions with DNP-Enhanced NMR

“…The other effect of the ultrasonic radiation is to provoke the formation of cavitation bubbles, which can promote the nucleation process either in the bubbles, associated with very high local pressure, or at their interface with the solution through heteronucleation. 20 To estimate appropriate concentrations for the synthesis of NCs, an approximate calculation shows that a spherical droplet with a diameter of 5 µm of an organic solution at 2.5 ×10 -4 M should lead to a 0.15 µm wide nanocube. Thus, the first trials of sonocrystallization were intended by injecting 100 mL of a methanol solution of CMONS at a concentration of 2.5 ×10 -4 M into 600 mL of water under standard precipitation conditions.…”

“…Indeed, the probability d P of forming a stable nucleus in a volume of solution V during a period of time dt is d P = J V d t , where J is the stationary nucleation rate or nucleation frequency. The other effect of the ultrasonic radiation is to provoke the formation of cavitation bubbles, which can promote the nucleation process either in the bubbles, associated with very high local pressure, or at their interface with the solution through heteronucleation …”

“…Furthermore, amorphous or ill-crystallized nanoprecipitates are often obtained, 14 while size and size distribution of molecular NPs are often difficult to master. In order to transition from amorphous to crystalline particles, 14 and to provoke early nucleations to control the NC size dispersity, 20 ultrasounds may be applied to initiate the nanocrystallization process. Indeed, ultrasounds are known to decrease the free energy necessary for the nucleation to take place thanks to the transient formation of cavitation bubbles with very high local pressure and temperature.…”

Particle Size and Crystal Habit Modification of Active Pharmaceutical Ingredient Using Cooling Sonocrystallization: A Case Study of Probenecid

“…In Table 5, the sonication intensity and sonication duration were operated at a low‐to‐intermediate extent to avoid the considerable thermal energy input by applying power ultrasound. [ 37 ] Four operating parameters, namely solution concentration, sonication intensity, sonication duration and cooling rate, were investigated. In Table 5, recrystallization experiment without applying power ultrasound was denoted as Exp.…”