Distinct Short-Range Order Is Inherent to Small Amorphous Calcium Carbonate Clusters (<2 nm).
Amorphous intermediate phases are vital precursors in the crystallization of many biogenic minerals. While inherent short-range orders have been found in amorphous calcium carbonates (ACCs) relating to different crystalline forms, it has never been clarified experimentally whether such orders already exist in very small clusters less than 2 nm in size. Here, we studied the stability and structure of 10,12-pentacosadiynoic acid (PCDA) protected ACC clusters with a core size of ca. 1.4 nm consisting of only seven CaCO3 units. Ligand concentration and structure are shown to be key factors in stabilizing the ACC clusters. More importantly, even in such small CaCO3 entities, a proto-calcite short-range order can be identified but with a relatively high degree of disorder that arises from the very small size of the CaCO3 core. Our findings support the notion of a structural link between prenucleation clusters, amorphous intermediates, and final crystalline polymorphs, which appears central to the understanding of polymorph selection.
Physical Chemistry, University of Konstanz, Universitätsstrasse 10, 78457, Konstanz, Germany.|School of Chemical Engineering, State Key Laboratory of Chemical Engineering, Shanghai Key Laboratory of Multiphase Materials Chemical Engineering, East China University of Science and Technology, 130 Meilong Road, Shanghai, 200237, P.R. China.
Shengtong
S
Sun
Department of Chemistry and Institute for Research in Materials, Dalhousie University, Halifax, Nova Scotia, B3H 4R2, Canada.
Daniel M
DM
Chevrier
Department of Chemistry and Institute for Research in Materials, Dalhousie University, Halifax, Nova Scotia, B3H 4R2, Canada.
Peng
P
Zhang
Physical Chemistry, University of Konstanz, Universitätsstrasse 10, 78457, Konstanz, Germany. denis.gebauer@uni-konstanz.de.
Denis
D
Gebauer
Physical Chemistry, University of Konstanz, Universitätsstrasse 10, 78457, Konstanz, Germany. helmut.coelfen@uni-konstanz.de.
Helmut
H
Cölfen
EXAFS; amorphous materials; calcium carbonate clusters; carboxylate ligands; short-range order