Immobilization of uranyl Schiff base in mesoporous MCM-41 Sushanta K. Badamali a , Arvind K. Tripathi a ,DimpleP.Dutta b ,VimalK.Jain b ,andNarendraM.Gupta a; * a Applied Chemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085, India b Novel Material and Structural Chemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400 085, India Received 23 July 2002; accepted 12 September 2002 A uranyl Schiff base complex [UO 2 {OC 6 H 4 N¼C(H)C 6 H 4 O} : H 2 O] has been immobilized inside the periodic mesopore channels of MCM-41 by the impregnation route. The samples have been characterized by XRD, N 2 adsorption/desorption, TG-DTA, DR UV–vis, 29 Si MAS NMR and FTIR techniques. While the host is found to retain its structural integrity, the surface area and the pore volume decrease considerably as a result of the intrapore confinement of complex molecules. The spectroscopy results indicate that the complex molecules are anchored with the silanol groups of MCM-41 via hydrogen bonding. KEY WORDS: MCM-41; uranyl Schiff base; immobilization. 1. Introduction Mesoporousmolecularsieveshavereceivedmuchatten- tion during recent years owing to their very high surface area (800–1000m 2 g ÿ1 ), tailored pore sizes (20–100A ˚ ) andgoodthermalstability[1].Thesecharacteristicsmake mesoporous materials ideal candidates as shape-selective catalysts, as hosts for the heterogenization of homoge- neous catalysts and as supports for metal/metal oxide catalysts [2,3]. Also, the internal surface hydroxyl groups inMCM-41provideconvenientanchoringsitesonwhich inorganicmetalcomplexescanbeimmobilized.Thephysi- calentrapmentofmetalcomplexesinthemicro-/mesopore spaceprovidesmanyadvantages,suchasshapeselectivity, enhancedactivity,siteisolation,stability,etc.,thatcannot be realized in the homogeneous phase or using conven- tional supports. Although recent reports on the catalytic performance of uranium complexes are quite promising [4–6], no report on the heterogenization of uranyl com- plexesinmolecularsievesisavailablesofar.Inpursuance ofourinterestinuranium-basedcatalysts[7,8],wereport here a study of the encapsulation of a uranyl Schiff base complex in MCM-41 silicate molecular sieves. The natureofthehost–guestinteractionintheensuingmaterial hasbeeninvestigatedbyDRUV–vis, 29 SiMASNMRand FTIRspectroscopy. 2. Experimental 2.1. Preparationofligand[HOC 6 H 4 N¼C(H)C 6 H 4 OH] Theligandwaspreparedbycondensing2-aminophenol with salicylaldehyde in benzene, according to the procedure reported in the literature [9,10]. The sample was characterized on the basis of chemical analysis (experimental composition: C, 73.0%; H, 5.42%; N, 6.40%; calculated values: C, 73.2%; H, 5.57%; N, 6.57%), melting point (185 8C) and 1 H NMR in CDCl 3 (:7.4–7.0ppm). 2.2. Preparation of uranyl Schiff base complex [UO 2 {OC 6 H 4 N¼C(H)C 6 H 4 O} : H 2 O] The uranyl Schiff base was prepared by dropwise addition of a benzene suspension of uranyl acetate, UO 2 (OAc) 2 : 2H 2 O (772mg (1.82mmol) in 25ml), to a benzene solution of the ligand (388mg, 1.82mmol in 25ml) under constant stirring at room temperature. The solution was evaporated in vacuo to give an orange- colored solid (850mg, 94% yield). The product was characterized as [UO 2 {OC 6 H 4 N¼C(H)C 6 H 4 O} : H 2 O]. The chemical composition of the product was found to be: C, 32.0%; H, 1.8%; N, 2.7%, against the following values calculated for the above formula: C, 31.3%; H, 2.2%;N,2.8%. 2.3. Complex encapsulation Mesoporous MCM-41 was synthesized hydrother- mallyaccordingtothereportedprocedure[1].Theimmo- bilizationoftheuranylSchiffbasecomplexwasachieved by the impregnation method. Prior to impregnation, the template-free MCM-41 was heated under vacuum (10 ÿ4 torr, 493K, 5h) followed by cooling to ambient temperature. The uranyl Schiff base complex (12mg in 20ml of CH 2 Cl 2 ) was added without any exposure to air and the mass was kept overnight under agitation. The buff-yellow solid was subsequently recovered by evaporating the solvent under ambient conditions. In order to ensure the removal of excess complex from the Catalysis Letters Vol. 85, Nos. 1–2, January 2003 (# 2003) 13 1011-372X/03/0100-0013/0 # 2003 Plenum Publishing Corporation *To whom correspondence should be addressed. E-mail: nmgupta@magnum.barc.ernet.in