ABSTRACT
The caesium and tetraethylammonium salts of the 1-cyanocarba-closo-dodecaborate anions [1-NC-closo-1-CB(11)X(11)](-) (X = H, F, Cl, Br, I) were synthesized from CsLi[closo-1-CB(11)X(11)] and phenylcyanate. All anions are stable against aqueous acids and bases, except for the fluorinated anion [1-NC-closo-1-CB(11)F(11)](-) that immediately reacts with water. The Cs(+) and [Et(4)N](+) salts of the anions were characterized by IR, Raman and multinuclear NMR spectroscopy as well as by MALDI and ESI mass spectrometry. The thermal properties of the Cs[1-NC-closo-1-CB(11)X(11)] (X = H, Cl, Br, I) and of some of their tetraethylammonium salts were studied by differential scanning calorimetry. The crystal structures of [Et(4)N][1-NC-closo-1-CB(11)H(11)] and Cs[1-NC-closo-1-CB(11)Cl(11)] were determined and the discussion of the structural and spectroscopic properties is supported by density functional and (RI)-MP2 calculations. A first insight into the hydrolysis of the [1-NC-closo-1-CB(11)F(11)](-) anion is presented and its reactions with water are compared to those of other undecafluorinated carba-closo-dodecaborate anions. The reduced hydrolytic stability of the [1-NC-closo-1-CB(11)F(11)](-) anion in comparison to its homologues is related to differences in the carbon-boron and boron-boron bond lengths of the {closo-1-CB(11)} cage and to different partial charges of the cluster atoms.
ABSTRACT
The properties of zeolitic and related materials highly depend on their pore dimensions and topology as well as the presence and nature of framework heteroelements. Here, we present detailed insights into prenucleating solutions of zeolitic materials using two different organic structure-directing agents (SDAs) in the presence of fluoride ions. The silicate speciation was analyzed by means of electrospray ionization mass spectrometry (ESI-MS), wherein the structures of the occurring species were proven to depend on the nature of the used organic SDA. In addition, MS/MS experiments were revealed as a powerful tool to obtain detailed structural insight into the occurring silicate oligomers. With this information, we were able to locate heteroelements, namely, germanium, within these species and, furthermore, to determine the structure-directing effects of the used organic SDAs.
ABSTRACT
The properties of microporous solids can be strongly influenced during the first stages of solid-state formation from solution. Furthermore, their properties are directly related to the presence, number, and character of intra- or extraframework heteroelements. In this contribution we studied the influence of the substitution of silicon against heteroelements, such as gallium and germanium. The aqueous prenucleating solutions were obtained by hydrolysis of the silicon and heteroelement sources in the presence of tetraalkylammonium cations. The time-resolved stepwise formation of larger oligomers was studied by using electrospray ionization mass spectrometry (ESI-MS). Furthermore, the structures of the obtained signals were verified by using MS/MS experiments, which led to the conclusion that strong structure-directing effects emerge from the introduction of heteroelements into the solutions.
