RESUMO
The understanding of crystal stepwise transformation is very important to enclose the "black box" in the preparation of crystal materials. In this work, different structural intermediates were isolated prior to the formation of the final alkali earth coordination polymers (CPs) during the preparation of three pairs of alkali earth CPs through solvothermal method and convenient oil-bath reactions. Single crystal X-ray diffraction analysis demonstrated the structural transformation from a 0â D to 1â D inorganic connectivity for the Ca-CPs and Sr-CPs, but a 1â D to 0â D inorganic connectivity for Ba-CPs, involving the breakage/formation of chemical bonds in the reaction solutions. Further analyses indicated that these two different structural transformation pathways are determined by the deprotonation of organic acid, competitive balance between the inorganic and organic connectivity, and the twist of the linker. FT-IR spectra, thermogravimetric and luminescence behaviors agree with their structural characteristics.
RESUMO
In this work, two 1-carboxymethyl-1-methyl-pyrrolidinium bromides (N-methylpyrrolidine betaine hydrobromides) with the stoichiometry of betaine:hydrobromic acid as 1:1 and 2:1, denoted as CMPRHBr-I and CMPRHBr-II, respectively, were prepared and crystallographically determined. The large difference in these two structures is the type of hydrogen bonds, resulting in the different thermal stability. A strong OHâ¯Br hydrogen bond was observed in CMPRHBr-I, whereas Oâ¯Hâ¯O hydrogen bond in CMPRHBr-II. Both these two crystals can mutually transform by changing the pH value of the aqueous solution. Vibrational spectroscopic studies shows that these two structures can be easily distinguished by the characteristic bands such as νCO stretching vibration and the D-type bands. Our studies indicate that it should be cautious of the structural change as this type of organic salts was purified and recrystallized.