4 PULSE ELECTRON-SPIN ECHO MODULATION STUDIES OF CU(II) COMPLEXES IN MCM-41 SILICA TUBE MATERIALS

The coordination geometry of Cu(II) complexes with water and ammonia h as been studied by four pulse electron spin echo modulation spectrosco py in siliceous (L)Cu-MCM-41 and in aluminum-containing CL)Cu-AlMCM-41 where (L) denotes Cu(II) incorporation by liquid phase ion-exchange. An analysis of the proton sum peaks in the echo modulation pattern of the water and ammonia ligands reveals significant differences in the C u(II) coordination between MCM-41 and AlMCM-41. In the aluminum-contai ning material (L)Cu-AlMCM-41, Cu(II) coordinates to two molecules of w ater or ammonia and three framework oxygens in a square-based pyramida l coordination geometry The base of the pyramid is formed by two adsor bate molecules together with two framework oxygens. A third framework oxygen is located at the apex of the pyramid. The cupric ion site is s lightly shifted from the plane of the pyramid base towards the apex re sulting in an off-plane position. In the siliceous material (L)Cu-MCM- 41, [Cu(H2O)(6)](2+) and [Cu(NH3)(4)](2+) complexes are observed. The results of four pulse electron spin echo modulation experiments suppor t a distorted octahedral coordination geometry for the [Cu(H2O)(6)](2) complex in (L)Cu-MCM-41.