pubs.acs.org/IC Published on Web 11/19/2010 r 2010 American Chemical Society 11346 Inorg. Chem. 2010, 49, 11346–11361 DOI: 10.1021/ic100928t Influence of the Synthetic Conditions on the Structural Diversity of Extended Manganese-Oxalato-1,2-bis(4-pyridyl)ethylene Systems Urko Garcı ´a-Couceiro, Oscar Castillo,* Javier Cepeda, M  onica Lanchas, Antonio Luque, Sonia P  erez-Y  a ~ nez, Pascual Rom  an, and Daniel Vallejo-S  anchez Departamento de Quı´mica Inorg  anica, Facultad de Ciencia y Tecnologı´a, Universidad del Paı´s Vasco, Apartado 644, E-48080 Bilbao, Spain Received May 10, 2010 We report herein the synthesis and physicochemical characterization of eight new manganese-oxalato compounds with 1,2-bis(4-pyridyl)ethylene (bpe): {(Hbpe) 2 [Mn 2 (μ-ox) 3 ] 3 ∼0.8(C 2 H 5 OH) 3 ∼0.4(H 2 O)} n (1), {[Mn(μ-ox)(μ-bpe)] 3 xH 2 O} n (2), [Mn 2 (μ-ox) 2 (μ-bpe)(bpe) 2 ] n (3), [Mn(μ-ox)(μ-bpe)] n (4a and 4b), and {[Mn 4 (μ-ox) 3 (μ-bpe) 4 (H 2 O) 4 ] 3 (X) 2 3 mY} n with X = NO 3 - (5a), Br - (5b), and ClO 4 - (5c) and Y = solvation molecules. The appropriate selection of the synthetic conditions allowed us to control the crystal structure and to design extended 2D and 3D frameworks. Compound 1 is obtained at acid pH values and its crystal structure consists of stacked [Mn 2 (μ-ox) 3 ] 2- layers with cationic Hbpe þ molecules intercalated among them. Compound 2 was obtained at basic pH values with a manganese/bpe ratio of 1:1, and the resulting 3D structure consists of an interpenetrating framework in which metal-oxalato chains are bridged by bpe ligands, leading to a microporous network that hosts a variable number of water molecules (between 0 and 1) depending on the synthetic conditions. Compound 3, synthesized with a manganese/bpe ratio of 1:3, shows a 2D framework in which linear metal-oxalato chains are joined by bis-monodentate 1,2-bis(4-pyridyl)ethylene ligands. The thermal treatment of compound 3 permits the release of one of the bpe molecules, giving rise to two new 2D crystalline phases of formula [Mn(μ-ox)(μ-bpe)] n (4a and 4b) depending on the heating rate. The open structures of 5a-5c were synthesized in a medium with a high concentration of nitrate, perchlorate, or bromide salts (potassium or sodium as cations). These anions behave as templating agents directing the crystal growing toward a cationic porous network, in which the anions placed in the voids and channels of the structure present high mobility, as inferred from the ionic exchange experiments. Variable-temperature magnetic susceptibility measurements show an overall antiferromagnetic behavior for all compounds, which are discussed in detail. Intoduction Metal-organic coordination polymers have attracted con- siderable interest because of their promising properties and applications in areas such as catalysis, zeolitic behavior, electrical conductivity, luminescence, nonlinear optics, and magnetism. 1 The rational design of new compounds with novel topologies and specific chemical and physical proper- ties comprises the basis and purpose of crystal engineering and involves a good understanding of the metal ion, the coordination preferences of the bridging entities, and the supramolecular self-assembly by noncovalent interactions for the development of new strategies for the synthesis of these materials. 2 Carboxylates are interesting ligands for this goal because of their versatile coordination modes and high structural stability, which has allowed the synthesis of com- pounds ranging from discrete oligonuclear species to one-, two-, and three-dimensional networks. 3 Moreover, organic carboxylate linkers and pillared polypyridines have been demonstrated to be very efficient in the construction of 3D open metal -organic frameworks (MOFs). 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