ISSN:
1572-8854
Keywords:
Zinc ion coordination
;
magnesium ion coordination
;
nedocromil
;
hydrates
;
water molecule channel
;
thermal analysis
;
thermal dehydration
Source:
Springer Online Journal Archives 1860-2000
Topics:
Geosciences
,
Physics
Notes:
Abstract The crystal structure of one of the hydrated forms of nedocromil zinc, the heptahydrate, and that of one of the hydrated forms of nedocromil magnesium, the pentahydrate, have been determined. Crystal data: zinc salt,a=11.769(3),b=7.000(2),c=14.022(4); Å; β=105.35(2)°; monoclinic, space groupP21,Z=2;magnesium salt,a=7.460(1),b=10.233(2),c=13.934(2) Å, α=86.54(1)°, β=79.74(1)°, γ=77.25(1)°; triclinic, space groupPĪ,Z=2. The major differences between the crystal structures are the environment and bonding of the cations. The zinc cation is linked directly to the carbonyl oxygen of the pyridone ring and to five water molecules in an octahedral coordination. The magnesium cation is linked directly to two different carboxyl oxygens, one in asyn orientation and the other in ananti orientation in different asymmetric units and to four water molecules in an octahedral coordination. Thermal analytical methods show that the zinc salt hydrate undergoes thermal dehydration at lower temperatures than the magnesium salt hydrate. This behavior may be related to the presence of continuous water channels in the zinc salt hydrate and to their absence in the magnesium salt hydrate. For each salt hydrate 1 mole of water is lost at a higher temperature than the other waters.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01673666
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