Synthesis of Microcrystals of the [Fe(L)(bipy)] Spin Crossover Coordination Polymer in a Poly‐4‐vinylpyridine Matrix

Abstract

Microcrystals of the spin-crossover coordination polymer [FeL(bipy)] (L=[3,3']-[1,2-phenylenebis(iminoethylidyne)]bis-(2,4-pentanedionato)(2-), bipy=4,4'-bipyridine) have been prepared in a poly(4-vinylpyridine) (P4VP) matrix. This was done by sequential addition of the iron(II) precursor complex and the bridging ligand bipy to a P4VP matrix, and by repetition of this cycle. The obtained composite material was characterized using TEM, SEM, XRPD, and SQUID measurements, and Mössbauer spectroscopy. With repeating cycles, the size of the [FeL(bipy)] crystals in the P4VP matrix increases from submicrometer to micrometer dimensions. A strong dependence on the number of cycles is observed. Above a critical size and concentration, the microcrystals show the same cooperative spin transition as the bulk material. No indication for a gradual spin transition is observed, but the remaining iron centers are either high-spin or low-spin depending on the coordination environment.

Synthesis of [Fe(Leq)(Lax)]ncoordination polymer nanoparticles using blockcopolymer micelles

“…For sample 3e only one doublet is observed that can be assigned to an iron(II) HS species. It concludes that in the case of [FeL eq (bpey)] n @BCP the HS fraction increases with higher cycles since more or longer coordination polymer is formed in the BCP micelle, in agreement with previous observations for [FeL eq (bipy)] n @BCP[13,58]. In the case of [FeL eq (bpea)] n @BCP a different behaviour is observed that is indicative for differences in the sample composition.…”

“…Sample 1d shows two different doublets which correspond to an iron(II) HS and iron(II) LS species (75% and 25%). The LS species derives from two P4VP units coordinated to the iron centre as already shown [13,58], with the formula [Fe(L eq )(VP) 2 ] (VP = vinyl pyridine) The HS species corresponds to the desired [Fe(L eq )(bpea)] unit. For sample 1e again two doublets are observed with a similar HS/LS ratio (Supporting Information File 1 ,Table S2).…”

Synthesis of Coordination Polymer Nanoparticles using Self‐Assembled Block Copolymers as Template

“…Above a critical size of the particles, a cooperative spin transition with hysteresis is observed as for the bulk material. Interestingly, below this size the spin transition is quenched and no indications for a gradual transition are observed …”

“…Interestingly,b elow this size the spin transition is quenched andn oi ndications for ag radual transition are observed. [67] Based on those results in af ollow-up approachs pherical nanoparticles were synthesized using polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP, M = 150 000 gmol À1 ,1 5w% P4VP) copolymer micelles as template. [57] Ther esults are summarized in Figure 2.…”

“… Left: General approach for the synthesis of micro‐ and nanoparticles of iron(II) coordination polymers in a polymer matrix through successive addition of iron complex and bridging axial ligand to the polymer. Right: TEM of microcrystals obtained in poly‐4‐vinylpyridine after 1 and 3 cycles of addition of complex and ligand and the results from magnetic measurements …”