The Synthesis, Structure And Magnetism On Mn And Lanthanide Clusters

With the development of material,biology,superchemistry and physical technology , Mn and Rare Earth compound,as a new field appeal many scientists more and more interest.Researches on bridged Mn and 4f heteronuclear complexes have significant values,which have many applications, such as airoplane,microwave absorption , photo-magnetic button, information storage materials. And it can put forward the Molecular and Crystal engineering ,such as planning the design of molecular magnet in theroy. Although there are many reports on heteronuclear complexes with carboxylate or hydroxide as ligands, there is little reports about Pivalate and Methacrylic acid as ligands.With Pivalate as bridged ligand, four novel Mn—4f heteronuclear clusters or 4f cluster have been synthesized and characterized. The structure and magnet of the complexes have also been measured, having following results.(1),According to the ordinary synthesis method, two new Pivalic—bridged Mn—4f heteronuclear complexes with the formulas ofâ‘ Mn₂Tb₂O₂(piv)₆(pivH)₂(CH₃OH)₂å'Œâ‘¡C e6O4(OH)4(piv)12 , have been synthesized under the acidic solution of CH3OH and MeCN with the reaction of n-Bu4NMnO4 and LnCl₃. Another two new MA-clusters ofâ‘¢[Tb₂Mn₃(MA)₁₂(bipy)₂]å'Œâ‘£[ CeMn(MA)₅(bipy)(H₂O)]₂ can be synthesized at PH=4.1 in the aqueous solution..X—ray diffraction analysis reavealed that the complexes were crystaled in different crystal synsterm and space group . The core structure ofâ‘ is parallelogram , twoμ₃-O are on both sides of which with the same distance. The Tb³⁺ ions have 9 coordinates,to be the three-face centred trigonal prism configuration and the Mn^â…¢have 6 coordinates with distort octahedron because of Jahn-Teller effect .The complex can still be formed by changing the ratio of the meteraials,which reveals that the cluster is stable. The structure ofâ‘¡is octahedron with 12 piv in the same coordination environment,eight O shared four H formedμ₃-OH on the top of the eight face of the octahedron with the same distance, in which the Ce^â…£is 8 coordinations , to be square anti prism configuration. Complexesâ‘¢can also be synthesized under acidic conditions with the difference of more than 25% Mn(NO₃)₃ to be used thanâ‘£in the synthetic process.The mental center in the core structure arrange to be zigzag,and the 2,2'-bipyridine as the terminal ligand prevent the formation of one-dimensional structure. The clusterâ‘¢is penta-nuclcar with two Tb^â…¢and three Mn^â…¡, in which the Mn^â…¡have 8 coordinations, though Mn—O distance is longer than Mn—N distance, and Tb^â…¢also have 8 coordinations, to be square anti prism configuration. The mental center arranged to be Mn^â…¡-Ce^â…¢-Ce^â…¢-Mn^â…¡in compoundâ‘£,in which the Ce^â…¢have 9 coordinations of MMA and water molecular, to be the one-face centred square anti prism configuration. Compoundsâ‘¢andâ‘£crystaled very well because of theÏ€-Ï€packing effect.(2),Temperature dependent magnetic susceptibilities of complexesâ‘ ,â‘¢,â‘£were measured in 10000 Oe (DC). At low temperature, theχ_MT values for complexeâ‘ decreases with the temperature decreased and decresed rapidly after 5K, The Plots of 1/χ_M vs T of the complexe [Tb(â…¢)₂Mn(â…¢)₂] is well fit for the Curie—Weiss Law, the Weiss values (θ) is -9.84K, which reaveals that there is antiferromagnetic interaction between Mn…Mn,Mn…Tb ions. The effective manetic momentμ_eff is 14.08 B.M, which is little smaller than the calculated spin value of 15.39 B.M. In order to further research the special magnetic behavior of complexeâ‘ at low temperature, the ac Magnetic Susceptibility is also characterized between 13 and 9999Hz , showing the frequency-dependant superparamagnatic phenomenon of SMM.Theχ_MT values for complexeâ‘¢[Tb₂Mn₃]decreases with the temperature decreased. The Plots of 1/χ_M vs T is well fit for the Curie—Weiss Law and the Weiss values (θ) is-5.69K, which reaveals that the complexe [Tb₂Mn₃] exhibited antiferromagnetic interaction.The effective magnetic momentμ_eff , at 300K, is 16.82 B.M, which is little smaller than the calculated spin value of 17.14 B.M.The effective magnetic momentμ_eff is 13.28B.M at 4K.Theχ_MT values for complexeâ‘£[MnCe]₂decreases little with the temperature decreased above 5K. The effective magnetic momentμ_eff , at 300K, is 16.35B.M, and is 8.23B.M at 4K,which is markedly smaller than the theoretical value.