Ordered mesoporous silicas as host for the incorporation and aggregation of octanuclear nickel(ii) single-molecule magnets: a bottom-up approach to new magnetic nanocomposite materials

Abstract

Silica-based mesoporous materials have been employed as the support host for a suitably designed small octanuclear nickel(II) guest complex with a moderately anisotropic S = 4 ground spin state (D = 20.23 cm 21 ), which behaves as a single-molecule magnet at low temperature (T B = 3.0 K). Both unimodal MCM-41 and bimodal UVM-7 porous silica provide appropriate template conditions for the incorporation and aggregation of the Ni 8 complex precursor into larger complex aggregates, showing slow relaxation of the magnetization at higher blocking temperatures than the crystalline material. By playing with the initial complex vs. silica concentration, two series of samples with varying complex loading amounts have been obtained. The degree of aggregation varies, largely depending on the silica used, being higher for the bimodal UVM-7 silica series. The mesophasic and porous nature of the Ni 8 adsorbed silica samples has been verified from XRD and TEM images. N 2 adsorption-desorption isotherms show that incorporation initiates inside the small intra-particle mesopores while subsequent aggregation occurs at the external particle surface (close to the mesopore entrances). Both DC and AC magnetic susceptibility measurements have demonstrated the occurrence of such a unique silica-mediated surface aggregation process of cationic Ni 8 molecules into oligomeric [Ni 8 ] x aggregates of large spin values (S = 4x) and high blocking temperatures (T B = 4.5-10.5 K). The existence of a wide distribution of aggregates with different conformation and association degree (size distribution) and the presence of weak interactions between the aggregates leads to an exotic spin glass magnetic behavior for this family of host-guest hybrid nanocomposite materials.

Supramolecular coordination chemistry of aromatic polyoxalamide ligands: A metallosupramolecular approach toward functional magnetic materials

“…At this respect, silica-based mesoporous materials as well as clay minerals have recently been employed as support hosts for the Ni II 8 MOC [40,41]. While the incorporation of isolated Ni II 8 molecules into single clay platelets took place with the loss of the SMM behavior [41], their incorporation and further aggregation into ordered mesoporous silica led to oligomeric [Ni II 8 ] n aggregates of greater spin values (S = 4n) and blocking temperatures (T B = 4.5-10.5 K) than those of the crystalline material [40].…”

“…At this respect, silica-based mesoporous materials as well as clay minerals have recently been employed as support hosts for the Ni II 8 MOC [40,41]. While the incorporation of isolated Ni II 8 molecules into single clay platelets took place with the loss of the SMM behavior [41], their incorporation and further aggregation into ordered mesoporous silica led to oligomeric [Ni II 8 ] n aggregates of greater spin values (S = 4n) and blocking temperatures (T B = 4.5-10.5 K) than those of the crystalline material [40]. In this case, the existence of a wide distribution of aggregates with different conformation and association degrees (size distribution) and the presence of weak interactions between the aggregates led also to an exotic spin glass magnetic behavior for this family of host-guest hybrid nanocomposite materials which is reminiscent of that of multidispersed superparamagnetic nanoparticles.…”

Magnetic Nanocomposites with Mesoporous Structures: Synthesis and Applications

“…An interesting way to finely control the particle size and shape of magnetic NPs is to impregnate the magnetic NPs inside an ordered mesoporous material. By using such an impregnation and reduction method, ordered mesoporous magnetic silica nanocomposites with various magnetic NPs including Co 3 O 4 , Fe 3 O 4 , CoFe 2 O 4 , and γ‐Fe 2 O 3 have been reported with high surface areas and different mesoporous structures and pore sizes ( Figure A) 81–90. Specifically, magnetic nanocomposites with mesoporous structures and large pore sizes such as magnetic NP@SBA‐15 (pore size 6.8 nm) can be achieved using this method.…”

“…Magnetic clusters belonging to families of Mn 12 and Cr 12 ‐carboxylates were successfully incorporated into the mesoporous silicas with different pore sizes 88. Small octanuclear nickel(II) magnetic complex was also incorporated into the mesoporous silica MCM41 89. By using mesostructured hybrid silica containing ‐(CH 2 ) 2 C 5 H 4 N groups as matrices, Prussian Blue NPs magnetic iron complex Fe 2+ /[Fe(CN) 6 ] 3 , Ni 2+ /[Fe(CN) 6 ] 3 , Fe 3+ /[Mo(CN) 8 ] 3 and Ni 2+ /[Mo(CN) 6 ] 3 were incorporated into the mesoporous silicas 90…”

Fabrication of mesoporous CuO/ZrO 2 -MCM-41 nanocomposites for photocatalytic reduction of Cr(VI)

“…After the incorporation of mesoporous ZrO 2 into M-41, the intensity gradually decreases. The characteristic d-spacing values for reflections due to (1 0 1), (1 1 0), (0 1 1), (0 0 2), (1 1 2), (2 0 0), (2 1 1) and (2 0 2) planes signifies tetragonal phase of ZrO 2 [32,33]. The incorporation of copper onto the surface of mesoporous ZM-41 possess the crystalline CuO diffraction peaks (35.5 0 and 39.8 0 ) are assigned to (0 0 2) and (1 1 1) planes depending on the bulk copper content [34,35].…”