Mesoporous MCM-41 materials with a distinct N 2 -sorption hysteresis behavior have been prepared from pure silica and aluminosilicate-C 16 trimethylammonium (TMA)Br systems by a delayed neutralization procedure. On the basis of the analysis of transmission electron microscopy micrographs of these MCM-41 materials, we observed that the sample with large type-H4 hysteresis loop at p/p 0 between 0.5 and 1.0 contains extensive structural defect holes amid the nanochannels. These holes are irregular in shape and their size distributes between 5.0 and 30.0 nm. The pore-blocking effect leads to the hysteresis in desorption. Aluminosilicate MCM-41 often possesses a larger hysteresis loop than pure silica MCM-41. The linear channel system of MCM-41 becomes effectively interconnected through these defect holes. The unusual adsorption hysteresis is associated with the pore-blocking effect around the embedded voids in the framework structures. The size of the adsorption-desorption hysteresis loop is proportional to the volume of hole defects in the nanochannels, and it is dependent on the synthesis conditions such as water content, Si/Al ratio, and morphology. Tubular morphology is often associated with large hysteresis behavior and thus more hole defects. The interconnecting channels through defect holes thus makes the diffusion of molecules inside the MCM-41 structure more effective, which is important in catalysis applications.

I 0.0 -0.4 -0.8 E(V) vs AglAgCl F g u e 5. Cyclic voltammogram of 1.0 mmol dm-, [IC0(aet),],Zn,0]~+ (cation of 2) in 0.1 mol aqueous solution of NaNO,. The scan rate is 50 mV s-I.region (32-48) X lo3 cm-' (Figure 3). This CD spectral deviation suggests that the asymmetric bridging sulfur atoms of the central cos6 chromophore in AA-[Co(Co(aet),},13+ contribute conspicuously to the CD spectrum in the region (16-30) X lo3 cm-l.Electrochemical experiments were performed in a 0.1 mol dm-3NaNO, aqueous solution at a glassy carbon electrode. As shown in Figure 5, the cyclic voltammogram of [{C~(aet),),Zn,O]~+ (2) initiated at 0.0 V with a negative potential scan yields four consecutive reduction waves (E, = -0.44, -0.56, -0.69, -0.87 V) and coupled four oxidation waves (E, = -0.36, -0.48, -0.61, and -0.79 V). No other redox couple is observed in the potential region of +0.8 to -1.2 V (vs Ag/AgCl). The peak current is approximately proportional to the square root of the scan rate. At a scan rate of 50 mV s-I, the ratio of cathodic to anodic peak current is approximately unity and the observed peak separation (E, -E, )In order to estimate the structure of 1, its cyclic voltammetric measurement was performed under the same conditions as used for 2. The cyclic voltammogram of 1 gave broad and nonreversible four consecutive reduction waves at E, = -0.45, -0.57, -0.71, and -0.89 V. This electrochemical behavior analogies with that of 2, although the relative instability of 1 in water restricts the electrochemical characterization. In addition, the absorption spectrum of 1 is quite similar to that of 2 over the whole region, as shown in Figure 4. These facts suggest that 1 has a cage-type S-bridged structure similar to that of 2. The plasma emission spectral analysis indicates that 1 contains Co and Zn in a ratio of 4:3. Accordingly, it is likely that 1 is the cagatype S-bridged complex with a "defective" [Zn3BrI5+ core, [ { C ~( a e t ) ~} ~Z n ~B r ] ~+ , considering that the formation of 1 was achieved by the addition of a large amount of NaBr to the reaction solution of fa@')- [Co(aet),] and ZnZ+.Registry No. 1, 139100-76-8; %Br6 (A-isomer), 139100-77-9; 2. Br6.9.5H20 (A-isomer), 139236-12-7; 26+ (A-isomer), 139236-13-8; fac-(S)-[Co(aet),], 18703-22-5; A A -[ C ~( C O ( ~~~) ~) ~] (NO,)3, 129387-95-7;Table SI, listing anisotropic thermal parameters (1 page); Table SII, listing observed and calculated structure factors (8 pages). Ordering information is given on any current masthead page. ALLL-~uc(S)-K~ [ CO( L-cYs-N,~), 1, 97 8 60-43-0.

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Aluminum Keggin ion-pillared magadiite was synthesized from Na-magadiite, NazSil402y1lH20, by ion-exchange with Keggin ion solution. The precursor for this pillaring reaction is n-hexylamine-intercalated magadiite, whereby the free interlayer spacing of H-magadiite was greatly expanded by n-hexylammonium ions and free amines. The presence of Keggin ion pillars in the interlayers of the product was confirmed by 27Al and 29Si MAS-NMR studies. XRD analysis showed that the resultant pillared product is highly disordered, but NZ adsorptiondesorption analysis showed that the pillared magadiite contains both micro-and mesopores. The presence of pillars in the interlayers of magadiite was further confirmed by the higher thermal stability and surface area over Na-magadiite, as well as the possession of microporous structures. 2-Propanol dehydration studies on the acid-base properties of Keggin ion-pillared magadiite revealed that it consists mainly of acidic sites. These sites are the Si-OH groups of the silicate layers and the A1-OH groups of the Keggin ions. The latter was found to be stronger acid sites.