cg049944g_si_004.txt (22.27 kB)

Heteropolymetallic Supramolecular Solid-State Architectures Constructed from [Cr(AA)(C2O4)2]- Tectons, and Sustained by Coordinative, Hydrogen Bond and π−π Stacking Interactions (AA = 2,2‘-Bipyridine; 1,10-Phenanthroline)

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posted on 05.01.2005, 00:00 by Gabriela Marinescu, Marius Andruh, Miguel Julve, Francesc Lloret, Rosa Llusar, Santiago Uriel, Jacqueline Vaissermann
The paper reports on four novel solid-state architectures constructed by using tectons having the general formula:  [Cr(AA)(C2O4)2]- [AA = 2,2‘-bipyridine (bipy) and 1,10-phenanthroline (phen)]. These building blocks are involved in various intermolecular interactions:  coordinative, hydrogen bonds, and π−π contacts. Two new crystallohydrates in the Ba[Cr(AA)(C2O4)2]2·nH2O family have been characterized:  [BaCr2(bipy)2(C2O4)4(H2O)2]·4H2O (1) and [BaCr2(phen)2(C2O4)4(H2O)2] (2). Because of the different numbers of water molecules, their crystal structures are completely different from those of two others previously reported, [BaCr2(bipy)2(C2O4)4(H2O)]·H2O and [BaCr2(phen)2(C2O4)4(H2O)2]·4H2O. The crystal structure of 1 consists of neutral chains, with diamond-shaped units sharing the barium atoms, with the two other corners occupied by chromium atoms. The barium and chromium ions are connected by bis(bidentate) oxalato ligands. Compund 2 exhibits a two-dimensional structure with irregular octagonal meshes. The Ba(II) and Cr(III) ions are connected by two types of oxalato bridges:  bis(bidentate) toward chromium and barium, and bidentate toward chromium, monodentate toward barium. The supramolecular solid-state architectures of two new Mn(II)−Cr(III) heteropolymetallic systems are discussed:  [Mn(4,4‘-bipy)2(H2O)4][Cr(phen)(C2O4)2]2·9H2O (3) and [Mn(MAC)(H2O)2][Cr(phen)(C2O4)2]2 (4) [4,4‘-bipyridine = 4,4‘-bipy, MAC = a pentaaza macrocyclic ligand, 2,13-dimethyl-3,6,9,12,18-pentaazabicyclo-[12.3.1]octadeca-1(18),2,12,14,16-pentaene]. These complexes have been obtained from the corresponding barium precursors through transmetalation reactions, in the presence of organic ligands (4,4‘-bipy or the macrocyclic ligand, MAC). The cationic entities in 3, [Mn(4,4‘-bipy)(H2O)4]2+, are interconnected through O−H···N hydrogen bonds and face-to-face π−π stacking interactions between pairs of 4,4‘-bipy ligands affording supramolecular chains. Crystal 4 is built up by cationic, [Mn(MAC)(H2O)2]2+, and anionic, [Cr(phen)(C2O4)2]-, entities. Each aqua ligand from the cationic units is hydrogen bonded to two oxygen atoms arising from the oxalato ligands belonging to two different anionic species, resulting in supramolecular chains. The cryomagnetic properties of the two Ba−Cr polynuclear complexes have been investigated. Very weak antiferromagnetic interactions occur between the chromium(III) ions in 1 and 2.