Luminescent complexes of Re(I) and Ru(II) with appended macrocycle groups derived from 5,6-dihydroxyphenanthroline: cation and anion binding
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Lazarides, T.
(EN)
Πανεπιστήμιο Ιωαννίνων. Σχολή Θετικών Επιστημών. Τμήμα Χημείας
(EL)
Lazarides, T.
(EN)
A range of ligands in which a macrocyclic unit is fused to a 1, 10- phenanthroline unit has been prepared starting from 5,6- dihydroxyphenanthroline. The ligands are L(1) in which the pendant ligand is 18- crown- 6; L(2), in which the pendant ligand is benzo- 24- crown- 8; and L(3), in which the macrocycle contains two carboxamide units. Ligands L(1) and L(2) can bind Group 1 and 2 metal cations in their crown- ether cavities; L(3) contains two H- bond ( amide) donors and is suitable for anion- binding. Luminescent complexes of the form [ Ru( bipy) (2)L] (2+), [ ReL( CO)(3)Cl] and [ RuL( CN) (4)] (2-) were prepared and some were structurally characterised; their interactions with various guest species were investigated by luminescence and NMR spectroscopy. For complexes with the crown ethers ( L(1) and L(2)), binding of K(+) was rather weak, but the electrostatic effect due to the charge on the host complex was clear with [ RuL(1) ( CN)(4)] (2-) binding K(+) more strongly than [ Ru( bipy)(2)L(1)] (2+). Binding to the pendant crown ethers was much stronger with Ba(2+), and both [ ReL(1) ( CO) (3)Cl] and [ ReL(2) ( CO)(3)Cl] showed substantial luminescence quenching in MeCNon addition of Ba(2+) ions, with binding constants of 4. 5 x 10(4) M(-1) for [ ReL(1) ( CO)(3)Cl] /Ba(2+) and 1. 3 x 10(5) M(-1) for [ ReL(2) ( CO)(3)Cl] / Ba(2+). Complexes [ Ru( bipy)(2)L(3)] (2+) and [ ReL(3) ( CO)(3)Cl], due to their H- bond donor sites, showed binding of dihydrogenphosphate to the macrocycle. Whereas [ ReL(3) ( CO)(3)Cl] showed 1 : 1 binding with ( H(2)PO(4))(-) in dmso with a binding constant of 65 M(-1), [ Ru( bipy)(2)L(3)] (2+) showed 1 : 2 binding, with microscopic association constants of ca. 1 x 10(6) and 1. 6 x 10(6) M(-1) in MeCN. The fact that K(2) > K(1) suggests a cooperative interaction whereby binding of the first anion makes binding of the second one easier to an extent which overcomes electrostatic effects, and a model for this is proposed which also accounts for the substantial increase in luminescence from [ Ru( bipy)(2)L(3)] (2+) ( 5- fold enhancement) when the second ( H(2)PO(4))(-) anion binds. Both [ Ru( bipy)(2)L(3)] (2+) and [ ReL(3) ( CO) (3)Cl] undergo complete luminescence quenching and a change in colour to near- black in the presence of ( anhydrous) fluoride in MeCN, probably due to deprotonation of the carboxamide group. These changes are however irreversible on a long timescale and lead to slow decomposition.
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