Institut de Chimie Moléculaire et des Matériaux d'Orsay

Laboratoire de Chimie Inorganique - LCI

Coordination Nanoparticles

Laure Catala, Talal Mallah, Sandra Maszerat
Mauricio Lopez (post-doc), Gabriella Paul (Ph.D. candidate)


The introduction of Ni(II) within the photomagnetic coordination nanoparticles based on Mo(CN)8 allows controlling their size and shape leading to 3 nm objects. We demonstrated, for the first time, light-induced blocking of the magnetization of the isolated objects opening the perspectives of using light to tune the magnetic bistability at the nanoscale.

 

Fig. 1Transmission Electronic Microscopy image of the NiCuMo(CN)8 nanoparticles (left) and magnetization vs. applied magnetic field before (black) and after (red) light irradiation

 

References:Photoinduced superparamagnetism in trimetallic coordination nanoparticles. D. Brinzei, L. Catala, C. Mathonière, W. Wernsdorfer, A. Gloter, O. Stéphan and T. Mallah, J. Am. Chem. Soc., 2007, 129, 3778-3779.

One of the important questions in the area of spin transition complexes before 2008 was the critical size below which the bistability of a spin transition compound vanishes, since the bistabilty is he result of a collective behaviour due to long range elastic interactions. The expertise of my group in the area of coordination nanoparticles allowed us to prepare size-controlled nanocrystals of one spin transition system. We demonstrate, for the first time, that, for this system, the bistability remains for the14 nm objects but disappears below 7 nm. These results, with others that have been reported the same year, opened a whole domain of research experimental and theoretical aiming at the understanding of the relation between size, shape, surface effect of nanocrystals of spin transition compounds. Furthermore, the design of nanometric (or at least micrometric) devices become possible.

 

Figure 3 : Variation of the magnetic response as a function of temperature  (middle) for spin transition nanocrystals of 7 nm (left) and 14 nm (right) size.

References: Spin-crossover coordination nanoparticles. F. Volatron, L. Catala, E. Riviere, A. Gloter, O. Stephan and T. Mallah, Inorg. Chem., 2008, 47, 6584-6586.

We have discovered a new route for the preparation of nanocrystals of coordination networks in 2006, using electrostatic stabilization. The water « soluble » nanocrystals can then be used as seeds for the controlled growth of core-multishell particles. In this paper, we set the routes for such synthesis and demonstrated that the shell thickness may be controlled at the molecular level. We used Electron Energy Loss Spectroscopy (EELS) to prove the growth control by performing a chemical mapping of individual nanocrystals (see Figure 1). In addition, High Resolution Transmission Electronic Microscopy allowed examining the core-shell interface confirming the stability of the different networks at least within 1 nm resolution. The direct application was the preparation of core-shell particles with a shell of 1 nm thickness containing the anisotropic Co(II) ion, which led to a dramatic enhancement of the magnetic anisotropy of the nanocrystals in comparison to the same objects without the anisotropic ion (see fIgure 2). This paper open the perspectives of a controlled tuning of the magnetic behaviour of the nanocrystals and particularly the design of multifunctional nanoscale objects including magnetic, photomagnetic, electroactive components whose properties may be changed by an external perturbation.

Figure 4 : HAADF-STEM (a) and High Resolution Transmission Electronic Microscopy (b) image of a CsCoCr@CsFeCr@CsNiCr core-bishell particle. c) Comparison between the EELS spectra of the core and shell parts (S1and S2) of the particle. d) A line profile across another particle shows that Cr and Cs are present throughout the whole particle while Co, Fe, Ni are only in domains.

Figure 5 :HAADF-STEM (a) HRTEM (b) images of a CsNiCr@CsCoCr particle (d=12 nm). c) Plot of magnetization versus field for CsNiCr@CsCoCr particles (circles) and CsNiCr particles (d=12 nm; triangles).

Reference: Core-Multishell Magnetic Coordination Nanoparticles: Toward Multifunctionality on the Nanoscale. L. Catala, D. Brinzei, Y. Prado, A. Gloter, O. Stéphan, G. Rogez and T. Mallah, Angew. Chem. Int. Edit., 2009, 48, 183-187 (VIP).

 

 

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