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High‐pressure preference for reduced water content in porous zinc aspartate hydrates
Author(s) -
Roszak Kinga,
Katrusiak Andrzej
Publication year - 2020
Publication title -
acta crystallographica section b
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.604
H-Index - 33
ISSN - 2052-5206
DOI - 10.1107/s2052520620009348
Subject(s) - triclinic crystal system , monoclinic crystal system , zinc , crystallography , isostructural , chemistry , aqueous solution , molecule , water of crystallization , crystal structure , inorganic chemistry , materials science , organic chemistry
The zinc aspartate (ZnAsp 2 ) complex, a common dietary supplement, preferentially crystallizes as the dihydrate (ZnAsp 2 ·2H 2 O) from aqueous solution. Under normal conditions the dihydrate easily transforms into the sesquihydrate (ZnAsp 2 ·1.5H 2 O). The dihydrate crystal structure is triclinic, space group P 1 , and the sesquihydrate is monoclinic, space group C 2/ c . However, their structures are closely related and similarly consist of zinc aspartate ribbons parallel to pores accommodating water molecules. These porous structures can breathe water molecules in and out depending on the temperature and air humidity. High pressure above 50 MPa favours the sesquihydrate, as shown by recrystallizations under pressure and compressibility measured by single‐crystal X‐ray diffraction up to 4 GPa. This preference is explained by the reduced volume of the sesquihydrate and water compressed separately, compared with the dihydrate. The sesquihydrate undergoes an isostructural phase transition when the voids collapse at 0.8 GPa, whereas no phase transitions occur in the dihydrate, because its pores are supported by increased water content.