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Publication Type
Journal Article
UWI Author(s)
Author, Analytic
Matthews, Karen D.,; Fairman, Richard A.; Johnson, A. H. M.; Spence, Kirk V.N.; Kahwa, Ishenkumba A.; McPherson, Gary L.; Robotham, H.
Author Affiliation, Ana.
Chemistry; Faculty of Pure and Applied Sciences
Article Title
The preparation and luminescence decay dynamics of coupled heterolanthanide (III) cations in dinuclear Schiff-base complexes
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Journal Title
Journal of the Chemical Society. Dalton Transactions
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Reprint Status
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Date of Publication
1993
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Issue ID
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Page(s)
1719-1723
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Abstract
Molecular recognition events in which lamthanide(III) (Ln3+) cation pairs are formed have been studied using the temple condensation crystalline products (Ln1-xEux)2L(NO3)4.H2O and (Ln1-xTbx)2L-(NO3)4.H2O (where H2L is the [2 + 2] macrocyclic Schiff base obtained from 2,6-diformyl-p-cresol and 3,6 dioxaoctane-1,8-diamine). the observed relationship between the concentrations of Eu3+ (or Tb3+) in the reaction mixture XEu or XTb (from neutron activation analyses) with corresponding concentrations in the crystalline products (x) suggest that formation of LnEuL(NO3)4.H2O heteromolecules is more favourable than that of LnTbL(NO3)4.H2O . In both cases of the caution discrimination index, comuted at the ratio of probabilities of Ln3+ incorporation into the crystalline heterolanthanide compounds, is in favour of the larger Ln3+ ion. However indiscriminate complexation of Nd3+ and Eu3+ in the (Nd1-x-Eux)2L(NO3)4.H2O system is unusual and reflects the importance of co-operative heteropair effects. Luminescene decay dynamics of the (Sm1-xEux)2L(NO3)4.H2O and (Pr1-xTbx)2L(NO3)4.H2O systems (0 < x < 1) reveal two microscopic environments for Eu3+ and Tb3+ which were attributed to homodinuclear molecules, Ln2L(NO3)4.H2O (Ln = Eu or Tb) (slow component) and heterodinuclear molecules SmEuL(NO3)4.H2O (fast component). Luminescene decay rate constants for intramolecularly coupled Eu-Sm and Pr-Tb pairs are 8200 and 12500 s-1, which yield coupling constants () of 2.9 x 10-53 and 4.7 x 10-53 m6 s-1 respectively when dominant dipolar interactions are assumed. no exchange interactions are evident despite the presence of a phenolate linkage shared by the heteroatoms only 4 apart. The ratio of Eu-Eu to Eu-Sm 'caution pairing selectivity' constant of 1:1.5 (expected ratio for random pairing is 1:2) supports the intervention of molecular recognition processes favouring the homo-to hetero-paired species in the ion pairing events leading to (Sm1-xEux)2L(NO3)4.H2O compounds....
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