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Structure and reactivity of [RuII(terpy)(N^N)Cl]Cl complexes. Consequences for biological applications

Abstract

The crystal structures of [RuII(terpy)(bipy)Cl]Cl·2H2O and [RuII(terpy)(en)Cl]Cl·3H2O, where terpy = 2,2':6',2''-terpyridine, bipy = 2,2'-bipyridine and en = ethylenediamine, were determined and compared to the structure of the complexes in solution obtained by multi-nuclear NMR spectroscopy in DMSOd-6 as solvent. In aqueous solution, both chlorido complexes aquate fully to the corresponding aqua complexes, viz. [RuII(terpy)(bipy)(H2O)]2+ and [RuII(terpy)(en)(H2O)]2+, within ca. 2 h and ca. 2 min at 37 °C, respectively. The spontaneous aquation reactions can only be suppressed by chloride concentrations as high as 2 to 4 M, i.e. concentrations much higher than that found in human blood. The corresponding aqua complexes are characterized by pKa values of ca. 10 and 11, respectively, which suggest a more labile coordinated water molecule in case of the [RuII(terpy)(en)(H2O)]2+ complex. Substitution reactions of the aqua complexes with chloride, cyanide and thiourea show that the [RuII(terpy)(en)(H2O)]2+ complex is between 30 and 60 times more labile than the [RuII(terpy)(bipy)(H2O)]2+ complex at 25 °C. Water exchange reactions for both complexes were studied by 17O-NMR and DFT calculations (B3LYP(CPCM)/def2tzvp//B3LYP/def2svp and B97XD(CPCM)/def2tzvp//B3LYP/def2svp). Thermal and pressure activation parameters for the water exchange and ligand substitution reactions support the operation of an associative interchange (Ia) process. The difference in reactivity between these complexes can be accounted for in terms of π-back bonding effects of the terpy and bipy ligands, and steric hindrance on the bipy complex. Consequences for eventual biological application of the chlorido complexes are discussed.

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Publication details

The article was received on 08 May 2017, accepted on 03 Jul 2017 and first published on 05 Jul 2017


Article type: Paper
DOI: 10.1039/C7DT01669G
Citation: Dalton Trans., 2017, Accepted Manuscript
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    Structure and reactivity of [RuII(terpy)(N^N)Cl]Cl complexes. Consequences for biological applications

    R. van Eldik, A. Katafias, O. Impert, A. Kozakiewicz, A. Surdykowski, M. Chrzanowska, P. Brzozowska, A. Franke, R. Puchta and A. Zahl, Dalton Trans., 2017, Accepted Manuscript , DOI: 10.1039/C7DT01669G

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