ISSN:
1573-1111
Keywords:
bis(benzo-15-crown-5 ether)s
;
potassium
;
rubidium
;
caesium
;
thallium(I)
;
complexation
;
thermodynamics
;
spectrophotometry
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
Notes:
Abstract The complexation thermodynamics of polymethylene andm-phenylene bridged carbonylhydrazones of 4′-formylbenzo-15-crown-5 with K+, Rb+, Cs+ and Tl+ was investigated by spectrophotometric titrations in methanol at 283–313 K. The carbonylhydrazone sequences in the bridge of the bis(benzocrown ether)s are optical sensors for the sandwich complexation of metal ions. Within the homologous series of polymethylene bridged carbonylhydrazones a stability peak was found for the sandwich complexes of the ‘propylene bridged’ compound with K+, Rb+ and Tl+. The potassium complex of this ligand shows the highest stability constant compared to all other known bis(benzo-15-crown-5) complexes with K+ in methanol. In terms of thermodynamics the formation of intramolecular sandwich complexes is driven by a gain of enthalpy. The unusual high gains of enthalpy and losses of entropy on formation of the most stable sandwich complexes allow us to propose an additional stabilization of the sandwich arrangement by intramolecular hydrogen bridge bonds. The ΔH o-TΔS o diagram gave an excellent straight line allowing discussion of the enthalpy-entropy compensation effect at these complexation reactions.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00708792
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