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Structures of [Cd(C2H8N2)Cl2]n(1)and [Cd(C2H8N2)Br2]n(2)were solved from powder diffraction data. Compound (1)crystallizes in the space group Pbam(No. 55), a= 9.9021(7) Å, b= 7.8186(6) Å, c= 4.0705(3) Å, V= 315.13(3) Å3, Z= 2. (2)is isostructural: space group Pbam(No. 55), a= 10.405(2) Å, b= 7.8634(8) Å, c= 4.2079(5) Å, V= 344.28(6) Å3, Z= 2. The investigated compounds are examples of two-dimensional hybrid coordination polymers, in which neighboring metal centers are bridged via both organic and inorganic moieties: ethylenediamine molecules and halide anions. Both crystal structures were solved ab initiofrom powder data using direct methods.

In this study, the nature of the hydroxyl groups present on γ-alumina, γ-Al2O3, pretreated at various temperatures has been reinvestigated by 1H NMR spectroscopy. The peaks are assigned by comparison between experimental and simulated spectra, in agreement with previous IR studies. The lowest chemical shifts δ correspond to OH groups strongly bound to the most acidic Al atoms (AlIVand AlV). High chemical shifts δ are assigned to OH groups making hydrogen bonds. A large range of values is found depending on the strength of these bonds. The structure of the surface complexes obtained by grafting Hf(CH2tBu)4, 1, on γ-Al2O3at various pretreatment temperatures T (350, 500, 700 °C), referred to as 1-γ-Al2O3-(T), and of their thermolysis products has been determined, by a combined experimental (mass balance, in situ IR,) and theoretical (DFT calculations) study. These results unambiguously prove the presence of two kinds of neopentyl–metal bonds, Hf–CH2tBu and Al–CH2tBu for 1-γ-Al2O3-(500)and 1-γ-Al2O3-(700), hence the existence of surface cationic low coordinated hafnium complexes. In contrast, for 1-γ-Al2O3-(350), only neutral species exist. Hence, temperature pretreatment has a key role for controlling the chemistry of the alumina surface (density of OH groups, presence of highly Lewis acidic Al), the grafting mode of the Hf precursor, and the formation of cationic low coordinated active centers.

Abstract: This review describes the work of two laboratories in the field of the modification of micro- and mesoporous molecular sieves through reactions with organometallic complexes. The modification of zeolites can occur inside the pore channels or on the external surface, depending on the size of the organometallic complex. When the modification occurs on the external surface, it results in a decrease of the pore entrance, which will lead in turn to a modification of the sorption properties of the zeolite, by decreasing the rate of the adsorption (mainly by a kinetic control). Such a material can be also used in catalysis, because the external acid sites, which are responsible for side-reactions, have been removed upon grafting. When small organometallic complexes are used, they can fill the channels and cages of the zeolite and react with internal hydroxyl groups. Due to the high acidity of zeolites, the reaction occurs very easily (for example at −100 °C on faujasite), in contrast to what is observed on the external surface, therefore leading to high metal loadings. In that case, the modification of the sorption properties will be mainly related to a thermodynamic control. The resulting materials can be useful in catalysis, by combining the activity of the organometallic complex and properties (for example shape-selectivity) of the zeolite. Modification of mesoporous molecular sieves occurs always in the pores and results in altering of the sorption properties of the solid, by changing the interaction type between the sorbent and the sorbate. For example the sorption isotherm of alkanes is changed from type II to type III according to the IUPAC nomenclature.