ESR and ESEM studies of Mn-containing MCM-41 materials

Abstract

Abstract Through electron spin resonance (ESR) and electron spin echo modulation (ESEM) studies, three Mn(II) species are found in three kinds of Mn-containing MCM-41 materials: ion-exchanged Mn-MCM-41, synthesized MnMCM-41 and synthesized MnMCM-41(Ca) with subsequent CaCl 2 exchange. Mn(II) species I with a well-resolved sextet centered at g =2.007 has distorted 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; attributed to zero field interactions. Both species I and II correspond to extra-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 2 O and are accessible to water, but framework Mn(II) species III coordinates with only three D 2 O and is less accessible to water.