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

1998; Elsevier BV; Volume: 22; Issue: 1-3 Linguagem: Inglês

10.1016/s1387-1811(98)00103-6

1873-3093

Jie Xu, Zhaohua Luan, T. Wąsowicz, Larry Kevan,

Metal-Organic Frameworks: Synthesis and Applications

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 CaCl2 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 D2O and are accessible to water, but framework Mn(II) species III coordinates with only three D2O and is less accessible to water.