Hydrogen Bonding in Amorphous Alkaline Earth Carbonates

Abstract

Amorphous intermediates play a crucial role during the crystallization of alkaline earth carbonates. We synthesized amorphous carbonates of magnesium, calcium, strontium, and barium from methanolic solution. The local environment of water and the strength of hydrogen bonding in these hydrated modifications were probed with Fourier transform IR spectroscopy, H NMR spectroscopy, and heteronuclear correlation experiments. Temperature-dependent spin-lattice (T1) relaxation experiments provided information about the water motion in the amorphous materials. The Pearson hardness of the respective divalent metal cation predominantly determines the strength of the internal hydrogen-bonding network. Amorphous magnesium carbonate deviates from the remaining carbonates, as it contains additional hydroxide ions, which act as strong hydrogen-bond acceptors. Amorphous calcium carbonate exhibits the weakest hydrogen bonds of all alkaline earth carbonates. Our study provides a coherent picture of the hydrogen bonding situation in these transient species and thereby contributes to a deeper understanding of the crystallization process of carbonates.

Solid-State Phase Transformation and Self-Assembly of Amorphous Nanoparticles into Higher-Order Mineral Structures

“…First, this is evidence that the rigid hydrogen-bearing ions/molecules are homogenously distributed throughout the amorphous calcium carbonate nanoparticles; and a similar conclusion was previously reached by others 68,69 . Second, this also rules out the presence of bicarbonate ions (HCO3 -) given the absence of a distinct upfield signal at short contact time (expected in the range of δ( 13 C) ≈ 155-165 ppm 67,70,71 ).…”

Solar-driven valorisation of glycerol on BiVO4 photoanodes: effect of co-catalyst and reaction media on reaction selectivity

“…Note that no carbonate was detected in the reaction mixture as followed from the absence of the corresponding signals in 13 C NMR spectra (d ¼ 166-168 ppm). 56…”

Small Ionic Radius Limits Magnesium Water Interaction in Amorphous Calcium/Magnesium Carbonates

“…The stabilizing effect has long been thought to originate in the relatively high dehydration energy of Mg 2+ compared to Ca 2+ , arguing that magnesium ions bind water more strongly, thereby reducing mobility of the ions. , However, recent studies have shown that diffusion of water is significantly faster in amorphous magnesium carbonate (AMC) compared to amorphous calcium carbonate (ACC) and even compared to mixed phases (amorphous calcium magnesium carbonate, ACMC) with as much as 73% Mg/(Ca + Mg), suggesting that calcium reduces water mobility more effectively than magnesium, despite the lower dehydration energy. , It has also been shown that magnesium incorporates a much larger portion of hydroxide ions into the amorphous carbonate phase compared to calcium, which provides additional stabilization. ,, …”