The ligand, the metal and the 'Holey'-host: Synthesis, structural and magnetic characterisation of Co(ii), Ni(ii) and Mn(ii) metal-organic frameworks incorporating 4,4'-dicarboxy-2,2'-bipyridine

Tynan, Eithne, Jensen, Paul, Kelly, Niamh R., Kruger, Paul E., Lees, Anthea C., Moubaraki, Boujemaa and Murray, Keith S. (2004) The ligand, the metal and the 'Holey'-host: Synthesis, structural and magnetic characterisation of Co(ii), Ni(ii) and Mn(ii) metal-organic frameworks incorporating 4,4'-dicarboxy-2,2'-bipyridine. Dalton Transactions, (21), 3440-3447. (doi:10.1039/B408961H).

Abstract

We report herein the single crystal structures of four metal–organic framework complexes incorporating the 4,4?-dicarboxy-2,2?-bipyridine ligand, H2dcbp: ?-[Co(dcbp)(H2O)2], 1; ?-[Co(dcbp)(H2O)2], 2, [Ni(dcbp)(H2O)2], 3 and {[Mn(dcbp)]·½DEF}, 4 (DEF = diethylformamide). In each complex the ligand is deprotonated giving neutral species with 1 ? 1 stoichiometry that form three-dimensional coordination polymers. Supramolecular isomerism (polymorphism) in 1 and 2 arises from the different ligand connectivity around the octahedral Co(II) centres. The two coordinated water molecules in 1 occupy cis positions, which are trans to the chelating bipyridine nitrogen atoms, leaving the carboxylate oxygen atoms in axial trans positions. In 2 all like donors occupy cis positions. Different modes of carboxylate coordination in 1 and 2 give dissimilar network topologies. A rare example of two interpenetrating 6482-b (quartz-like) chiral networks in 1 results from both dcbp carboxylate groups coordinating in a monodentate fashion to adjacent Co(II) centres, whereas in 2 only one carboxylate group bridges between adjacent Co(II) centres giving rise to a single chiral (10,3)-a net. In 1 and 2 the coordinated water molecules hydrogen bond to the non-coordinated carboxylate oxygen atoms. These interactions give rise to water–carboxylate double helices in 1, and support the coordination network in 2. Strikingly for a pair of dimorphs the crystal densities of 1 and 2 differ by ca. 0.3 g cm?3 (1.654 vs. 1.940 g cm?3, respectively). Compound 3 is isomorphous with 1 and likewise features two chiral interpenetrating nets of quartz topology. In 4, chelating bipyridine nitrogen atoms and four carboxylate oxygen atoms from a total of five adjacent dcbp ligands provide distorted octahedral geometry around Mn(II). The carboxylate groups bridge adjacent Mn(II) centres to produce bis-carboxylato chains which cross-link and generate a 3D network that is perforated with channels. The channels are occupied with disordered DEF molecules. The network topology in 4 is quite different to 1–3 and has a (4.62)(42.6)(43.66.86) Schläfli notation. Magnetic susceptibility studies performed on 1, 2, {[Mn(dcbp)]·½DMF} 5 (DMF = dimethylformamide) and {[Mn(dcbp)]·2H2O} 6 reveal very weak antiferromagnetic coupling between the metal centres in each case.

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