Inorganic self-assembly through sequential complexation in the formation of bimetallic and trimetallic architectures from multisite ligands based on 5,5'-disubstituted 2,2'-bipyridines

Abstract

Dois pré-ligantes 2,2'-bipiridínicos 5,5'-dissubstituídos apresentando em sua estrutura dois ou três sítios de coordenação [5,5'-bis(ácido N-metil-hidroxâmico)-2,2'-bipiridina (4) e 5-metil-5'-(ácido N-metil-hidroxâmico)-2,2-bipiridina (10)] foram sintetizados. Estes ligantes foram empregados no estudo de uma estratégia de automontagem por complexação seqüencial. De acordo com este conceito, o primeiro metal adicionado organiza os substituintes-ligantes das posições 5,5' para a complexação do segundo íon metálico adicionado seqüencialmente. A adição de Fe 2+ a uma solução contendo 4 levou à formação do complexo Fe 2+ -tris(bipiridil). A adição de Fe 3+ a este complexo rendeu uma arquitetura trimetálica. O ligante 10 levou à formação de uma mistura de arquiteturas bimetálicas pela adição seqüencial de íons Fe 2+ e Fe 3+ . No entanto, quando a ordem de adição foi alterada, somente um complexo bimetálico foi obtido. Isto se deve ao fato de que o primeiro metal adicionado (Fe 3+ ) age como um molde, organizando os ligantes bipiridínicos e pré-formando uma cavidade adequada para o íon Fe 2+ .Two multisite 5,5'-disubstituted 2,2'-bipyridine ligands containing N-methyl hydroxamic acids as substituents [5,5'-bis(N-methylhydroxamic)-2,2'-bipyridine (4) and 5-methyl-5'-(Nmethylhydroxamic)-2,2-bipyridine (10)] were synthesized. These ligands were used in order to illustrate the strategy of self-assembly through sequential complexation. According to this concept, the first metal added organizes the ligands disposed in 5,5'-positions to accomodate the second metal ion that is sequentially added. Thus, addition of Fe 2+ to a solution of 4 led to a Fe 2+ -tris(bipyridine) complex. Addition of Fe 3+ to this solution yielded a trimetallic architecture, which was characterized. Ligand 10 yielded a mixture of bimetallic architectures through complexation with Fe 2+ followed by Fe 3+ ions. However, if the order of metal addition is changed, only one bimetallic complex is obtained. This is due to the fact that the first metal ion added (Fe 3+ ) acts as a template, organizing the bipyridine ligands and preforming an adequate cavity for the Fe 2+ ion.Keywords: inorganic self-assembly, sequential ligands, sequential complexation, metalloexoreceptors IntroductionSelf-assembly of inorganic architectures from programmed components has been an extensively investigated field of supramolecular chemistry in recent years. [1][2][3][4][5][6] Such processes involve the design of programmed supramolecular species, which are spontaneously formed from carefully constructed ligands and metal ions able to read the binding sites according to their coordination algorithm. 1,2,6 This strategy has allowed the synthesis of a great variety of inorganic architectures, 1-6 such as double-7 and triple-helical 8 complexes, rack-, 9 grid-10 and cagetype 11 arrays of metal ions synthesized by our own group. The design of ligands containing different coordination sites has spontaneously yielded structures having different metal ions at specific locations, as in h...

Metal-directed assembly of combinatorial libraries—principles and establishment of equilibrated libraries with oligopyridine ligands

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Influence of the Reaction Sequence on the Complexation of an NS4-Macrocycle with CdII and CuI Salts Leading to the Formation of Supramolecular Isomers and an Endo/Exocyclic CuI Complex

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