Recent joint IR and computational work (Onida et al. J. Phys. Chem B 2005) has allowed a detailed characterization of the isolated silanols at the surface of highly ordered benzene-silica hybrid material. In the present paper, a similar characterization is provided for a less ordered sample. The comparison permits the assignment of IR features to the interaction of silanols either with one another or with benzene rings of the structure. The extent of structural imperfections appears to be limited, for example, no more than pairs of interacting silanols are found, readily healed by thermal treatment. Evidence is also provided that probe molecules with simultaneous H-acceptor and H-donor properties (benzene, methylacetylene) may interact with both the acidic proton in silanols and the electronic cloud in the framework aromatic rings.

Periodic mesoporous organosilicas (PMOs), a relatively new class of mesostructured organic-inorganic hybrid materials already thoroughly characterized as it concerns acidic sites, are studied in the present paper from the viewpoint of electron-rich, potentially basic sites. Iodine was adopted as a probe molecule, as it is known that the spectral shift suffered by the I 2 band in the visible region correlates with the donor strength of solvents and solids. Iodine adsorption on ethyl-and phenylene-containing PMOs was followed by means of UV-visible spectroscopy: the results show that the electron-donor ability of oxygen atoms at the PMO surface is higher than that reported for pure siliceous materials and comparable with that of some basic zeolites, in agreement with the previously reported weaker acidity of hydroxyls. In phenylene-bridged PMOs aromatic rings are the preferential adsorption sites for iodine. Comparison between phenylene-bridged PMOs with different degrees of order in the walls reveals a lower availability of aromatic sites on the ordered surface with respect to the amorphous one.

Low-temperature adsorption of carbon monoxide on an ordered periodic mesoporous organosilica (1,4phenylenesilica PMO) was studied by means of infrared spectroscopy and theoretical calculations on cluster models. Basically, three types of adsorbed CO species were found to be simultaneously formed at a low CO coverage: (i) physisorbed species having the CO molecule interacting only with a benzene ring, (ii) hydrogenbonded species having the CO molecule interacting with a silanol group through the carbon atom, and (iii) hydrogen-bonded species having the CO molecule interacting with a silanol group through the oxygen atom. However, both hydrogen-bonded species showed also a residual (lateral) interaction of the CO molecule with a neighboring benzene ring. This residual interaction accounts for an overall adsorption enthalpy (∆H 0 ) that is significantly larger than that involving the interaction of CO with silica. Thus, the C-bonded species ii showed ∆H 0 ) -13.2 kJ mol -1 (as determined by variable-temperature infrared spectroscopy) to be compared with that of ∆H 0 ) -11 kJ mol -1 previously reported for the interaction between CO and silica silanol groups. Also remarkable is the relatively large value of adsorption enthalpy, ∆H 0 ) -10.6 kJ mol -1 , showed by the physisorbed species involving only interaction between CO and a benzene ring.