Synthese and magnetic properties of new polymetallic complexes of coordination. Margot KALISZ

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2 Synthese and magnetic properties of new polymetallic complexes of coordination. Margot KALISZ

3 Work under the direction of Prfa. Corine Mathonière (ICMCB) Introduction : definition of the photomagnetism by electron transfer. I. Photomagnetism of a 3D network : 2 [MoIV (CN) 8 ].7,5H 2 O 1) Presentation. 2) Photomagnetic cycles at 60 K, tests of relaxations. 3) Photomagnetic cycles at 10 K. I. Photomagnetism of a new cluster : [ (tren)] 6 [ (CN) 8 ][ClO 4 ] 8.16H 2 O 1) Presentation. 2) Description of the photomagnetic effect. III. Study of relaxation. 1) Tests of follow-up of the magnetic signal versus time at a given T. 2) Study of relaxation by thermal cycles. Conclusions Project of thesis Under the directin of Prfa Maria Vaz (iq-ufrj) and Prf Miguel Novak (if-ufrj) new compounds with interesting magnetic properties.

4 Introduction Definition of the photomagnetism : influence of an electromagnetic irradiation on the magnetic properties of a material excited state A hν 1 hν 2, B E A B A

5 Possible mechanisms on a molecular scale : Spin transition, centered on the metal : example of the Fe II (d 6 ) hν 1 hν 2 e g t 2g LS S=0 HS S=2 Electronic transfer : example of the Rb 0,54 Co 1,21 [Fe(CN) 6 ].17H 2 O * e - Fe II -CN-Co III LS LS hν Fe III -CN-Co II LS HS hν ET Fe III -CN-Co II LS LS ST * A. Bleuzen, M. Verdaguer, JACS, 2001, 122, 6648.

6 Photomagnetism of a network 3D : 2 [MoIV (CN) 8 ].7,5H 2 O* 1) Presentation IVCT à 450 nm hν 406 nm 10K Mo V Cu I Mo V Mo V Cu I Cu I Mo V Cu I paramagnetic ferro magnet Mo V Cu I S=1/2 S=0 S=1/2 S=1/2 S= 1/2 * Rombaut G., Mathonière, C &. al Inorg. Chem , Inorganica Chim. Acta, 2001, 326, 27. Ohkoshi S.-I., Hashimoto K. &. al Synth. Metals S=0

7 Irradiation 5 h in 60 K : (power of the laser 3 mw.cm -2 ) H=20000 Oe befor hν after hν after hν and annealing in 300 K T (cm 3.mol -1.K) hν 406 nm T (K) the curves befor and after irradition meet in 180 K. the curves befor and after irradiation + thermal annealing are identical.

8 2) Magnetic cycles in 60 K, tests of relaxations. Irradiations in 60 K T (cm 3.mol -1.K) 2 3 annealing : 180 K annealing : 200 K 4 1 annealing : 160 K the 4 irradiations are effective no fatigability of the process of photo-conversion H=20000 Oe time (s) 1,4 T(cm 3.mol -1.K) 1,3 1,2 1,1 1,0 hν 12 h annealing 160 K hν 5 h annealing 180 K hν 5h30 annealing 200 K hν 11 h 160 K : incomplete relaxation 180 K and 200 K: relaxations at the same point, but not complete 0,9 0,8 T=60 K H=20000 Oe time (u. a.) surprising bad reversibility cf. courbe χt=f(t)

9 3) photomagnetic cycles at 10 K. Irradiation 1 h at 10 K χt (cm 3.mol -1.K) hν 1 h annealing 300 K hν 1 h annealing 300 K T=10 K H=20000 Oe hν 1 h time (u. a.) χt 0,14 cm 3.mol -1.K χt after annealing χt befor hν non fatigability good reversibility

10 Conclusions of the 1 rst part : Conditions of good reversibility : hν 1 h in 10 K in this case : the photo-conversion obtained is insufficient to study of relaxation notice : the xt curve obtained after irradiation looks like that obtained for compounds organized in clusters χt (cm 3.mol -1.K) H=20000 Oe hν 406 nm Idea : to obtain systems organised in clusters - with a more important photomagnetism - allowing a simulation of magnetic properties T (K) Coord Mo = 8 ideal stoechiometry : 1 Mo / 8 Cu This compound does not exist but the compound 1 Mo / 6 Cu was synthesized by the group of Pr. Michel Verdaguer

11 Photomagnetism of a new cluster : [ (tren)] 6 [ (CN) 8 ][ClO 4 ] 8.16H 2 O 1) Presentation ligand tren N C [Cu(tren)] 6 [Mo(CN) 8 ]

12 2) Description of the photomagnetic effect. Irradiation (406 nm) à 10 K T (cm 3.mol -1.K) hν 406 nm M (Nβ) H = G T=5 K T (K) H (Oe) befor irradiation after irradiation 15 h at 10 K after irradiation + annealing à 300 K M befor hν M after hν + annealing χt = 2,3 cm 3.mol -1.K Reversibility of the photo-induiced process Photomagnetic effect important

13 short irradiation in 10 K, non-fatigability of the process M (Nβ) befor irradiation simulation «6 S=1/2» after irradiation 1 h à 10 K sim. 57 % «S=3» + 43 % «6 S=1/2» simulation «S=3» T=5 K H (Oe) hν 406 nm 6 S=1/2 S total =3 Mo V Cu I M (Nβ) hν 1 h annealing in 300 K hν 1 h annealing in 300 K Reversibility and no fatigability of a photo-induiced process H=50000 Oe good candidate for the study of the relaxation time (u.a.) M av hν M ap hν + recuit (1) M ap hν + recuit (2)

14 study of the relaxation 1) Tests of follow-up of magnetic signal versus time with T given.? 10 K 100 K 150 K 200 K 250 K hν 406 nm T = C te T = C te T C te T C te T (K) time at each temperature tested, stability of xt relaxation during the increase in T? T(cm 3.mol -1.K) 250 K 200 K 10 K time (s)

15 2) Study of relaxation by thermal cycles K 50 K 100 K 150 K 200 K 250 K 300 K hν 406 nm T (K) 1 H=20000 Oe T (cm 3.mol -1.K) hν 406 nm T (K) Relaxation from a cycle to the following Points of meeting at the end of each cycle relaxation takes place during the increase in the T

16 10 k 100 k 150 k 200 k 250 k 300 k hν 406 nm T (K) T (cm 3.mol -1.K) H=20000 Oe T (K) relaxation during the 1 rst passage only After each increase in the T, the signal is stable Creation of magnetic centers with a distribution of T relaxation A hν 1 B 1 + B 2 + B 3 B1, B2, B3

17 Conclusions 3D network Cu 2 Mo : photomagnetism reversible (hν 1 h à 10 K), but too weak photoconversion To increase the efficacity of the irradiation : - approach top-down : nano-materials (too small quantities for the moment) - approach bottom-up analogy with the molecular clusters 20 µm Cu 2 [Mo(CN) 8 ].7,5H 2 O Cluster Cu 6 Mo : - photomagnetism reversible and important, but relaxation non-conventional : independent of the time. - stability of the signal with T given. A hν B annealing with T 1 B* Example : T 1 = 150 K annealing with 300 K χt = 1,1 cm 3.mol -1.K