MPS 3 Layered Intercalates as Insulating Magnets: Towards Nanocomposites Associating Ferrimagnetism and Non-Linear Optic
- PDF / 375,908 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 87 Downloads / 154 Views
obtained by our group over several years (chemistry, general magnetic properties), before describing the latest results. A UNIQUE CATION EXCHANGE INTERCALATION CHEMISTRY
The MPS 3 compounds, where M stands for a metal in the +2 oxidation state, form a class of lamellar semiconductorsl with the CdCI2 structural type (Figure 1). s N
s S
S
M
* M* Figure 1. Schematic top view of a MPS 3 slab, array of M2 + cations coordinated to P2S6 4 - bridging ligands. 319 Mat. Res. Soc. Symp. Proc. Vol. 328. @1994 Materials Research Society
When compared to other lamellar materials, these compounds possess a unique reactivity: they can form a wide range of intercalates thanks to a very unusual cation exchange process 2. Thus, for example: MnPS3(s) + 2x KClaq
-P
Mnl-xPS3K2x(H20)y (s) + x MnC12 aq
The process spontaneously takes place at room temperature in the presence of aqueous or ethanolic solutions of a great many salts, such as KCI, Me 4 NCl or organometallic salts. The reaction leads to compounds Mnl-xPS3(G)2x(H20)y, where the positive charge of the entering guest cations G+ is counterbalanced by the loss of intralayer Mn 2 + cations. As a result, the slabs in the intercalates contain metallic vacancies. Insertion often fails when the size of the guest species is too large. However, many bulky species can be inserted in two steps: (i) preinsertion of a small cation such as K+ or even Me4N+; (ii)2 exchange of the guest cations with the bulky species (for example Ru(2,2'bipy)3 +).
Other MPS3 phases (M = Mn, Cd, Zn, Fe) also give rise to a cation exchange insertion process but the reaction requires assistance by a complexing reagent (EDTA, pyridine..) which helps the M2 + cations to leave the solid. Each host material in the family has its own characteristics. Such an easy ion exchange process in the solid state appears rather unusual, as it implies that M2 + cations are able to leave their intralamellar sites and pass into the solution 3. The high mobility of the intralamellar M2 +cations cannot be explained in terms of diffusion in the solid state, which is very slow at room temperature in the chalcogenide materials (synthesis requires a temperature range about 600°C). We have suggested that ion exchange intercalation proceeds through destruction (local microdissolution of the host lattice) and subsequent reconstruction (microrecristallization of the composite). 3 This occurs 'thanks to heterogeneous equilibria 4 between solid MPS 3 and the solvated constituting units M2 + and P2S6 -, considering each 2 MPS3 slab as a polynuclear coordination compound made up of M + cations coordinated to 4 P2S6 4- bridging ligands (P2S6 - is a molecular anion stable in solution) Mn2P2S6(s)=
Mn 2 +aq + P2S64-aq +----+ Mn2-2xP2S6G4xsolvy
We have shown recently that it was also possible to insert PEO (polyethyleneoxide) macromolecules into MnPS3 and CdPS3.4 Although no specific new physical property of these MPS 3 polymer nanocomposites has been identified, it is already clear that polymer intercalation play a role for processing the
Data Loading...
