title: Sodium complexes containing 2-iminopyrrolyl ligands: the influence of steric hindrance in the formation of coordination polymers.
abstract: Iminopyrrolyl complexes of sodium were prepared from the reaction of 2-arylformiminopyrrole ligand precursors (aryl = C(6)H(5) (I); 2,6-Me(2)C(6)H(3) (II); 2,4,6-Me(3)C(6)H(2) (III); 2,6-(i)Pr(2)C(6)H(3) (IV)) with one equivalent of sodium hydride. The resulting corresponding compounds 1-4, [{Na(mu(2):kappa(2)N,N'-iminopyrrolyl)}(2n)(OEt(2))(2x)] (n > or = 1; x = 0 or 1), were obtained in moderate to high yields and were characterised by NMR spectroscopy, high resolution mass spectrometry and X-ray diffraction, when suitable crystals were obtained. The X-ray structure of compound 1 (n >> 1; x = 0) reveals the formation of a coordination polymer with repeating units consisting of dimers that contain two iminopyrrolyl ligands chelating two sodium atoms, where both pyrrolyl rings exhibit bridging sigma + sigma coordination to the Na atoms within the dimer; the self-assembling of the polymer is established by additional pi-bonds (eta(5)-coordination) of each of the pyrrolyl rings to the sodium atoms of the adjacent dimer units. Conversely, the structure of complex D(IV) (n = x = 1) shows it as one of such dimers capped by two diethyl ether molecules, each coordinated to the sodium atoms (n = 2; x = 1). DFT calculations indicate that the differences between the structures 1-4 of arise from the increasing bulkiness imposed by the corresponding substituents of the iminic aryl groups.
authors.affiliation: Centro de Química Estrutural, Departamento de Engenharia Química e Biológica, Instituto Superior Técnico, Av. Rovisco Pais, 1049-001 Lisboa, Portugal.
authors.forename: Clara S B
authors.initials: CS
authors.lastname: Gomes
authors.forename: D
authors.initials: D
authors.lastname: Suresh
authors.forename: Pedro T
authors.initials: PT
authors.lastname: Gomes
authors.forename: Luis F
authors.initials: LF
authors.lastname: Veiros
authors.forename: M Teresa
authors.initials: MT
authors.lastname: Duarte
authors.forename: Teresa G
authors.initials: TG
authors.lastname: Nunes
authors.forename: M Conceição
authors.initials: MC
authors.lastname: Oliveira