ESR AND ESEM STUDIES OF MN-CONTAINING MCM-41 MATERIALS

Through electron spin resonance (ESR) and electron spin echo modulatio n (ESEM) studies, three Mn(II) species are found in three kinds of Mn- containing MCM-41 materials: ion-exchanged Mn-MCM-41, synthesized MnMC M-41 and synthesized MnMCM-41(Ca) with subsequent CaCl2 exchange. Mn(I I) species I with a well-resolved sextet centered at g= 2.007 has dist orted octahedral symmetry and is observed in hydrated ion-exchanged Mn -MCM-41 and in synthesized calcined MnMCM-41. Mn(II) species II with g = 5.2 and 3.2 is observed in dehydrated Mn-MCM-41 and MnMCM-41; attrib uted to zero field interactions. Both species I and II correspond to e xtra-framework Mn(II). Mn(II) species III, with a symmetric line at g= 2.004 and a broad line-width of 250 to 350 G is assigned to framework sites. Extra-framework Mn(II) species I and II coordinate with four D 2O and are accessible to water, but framework Mn(II) species III coord inates with only three D2O and is less accessible to water. (C) 1998 E lsevier Science B.V. All rights reserved.