Discrete dinuclear complexes and two-dimensional architectures from bridging polynitrile and bipyrimidine (bpym) ligands: Syntheses, structures and magnetic properties of [M-2(bpym)(dcne)(4)(H2O)(2)] (M = Mn-II, Co-II) and [M-2(bpym)(dcne)(4)(H2O4]center dot 2H(2)O (M = Fe-II, Cu-II) (dcne(-) = [(CN)(2)CC(O)OEt)](-))
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abstract
One-pot reactions in aqueous solutions of the polynitrile anion dcne - (2,2-dicyano-1-ethoxyethenolate = [(CN)2-CC(O)OEt)] -] with the MII ions (M = Mn, Fe, Co, Cu) in the presence of bpym (2,2-bipyrimidine) afford the first mixed dcne/bpym compounds [M2(bpym)(dcne)4(H2O)2] (1: M = Mn; 2: M = Co) and [M2(bpym)(dcne)4(H2O) 4]2H2O (3: M = Fe; 4: M = Cu). The new compounds have been characterized by IR spectroscopy and X-ray crystallography. Compounds 1 and 2 are isostructural, with each metal ion being located in an MN 5O pseudo-octahedral environment with three N atoms coming from three dcne- ligands, two nitrogen atoms from bpym and one oxygen atom from a water molecule. The extended structures of 1 and 2 are best described as dcne-bridged zigzag chains of MII ions running along the [100] direction; connections of these chains in the [010] direction, by the bis(chelating) bpym ligand, afford 2D structures. Compounds 3 and 4 are isostructural, and consist of discrete dinuclear units involving MN 4O2 octahedrally coordinated MII ions bridged by bis(bidentate) 2,2-bipyrimidine and terminal dene ligands. Magnetic measurements for the 2D compounds 1 and 2 exhibit maxima in the m vs. T plots (at about 4.5 K for 1 and about 20 K for 2) which are characteristic of weak antiferromagnetic exchange interactions between the high-spin metal centres. While the dinuclear iron complex 3 presents a similar behaviour (maximum in m vs. T plot at 12 K), the antiferromagnetic exchange interactions are stronger in the copper complex 4. Fits of magnetic data for compounds 1, 3 and 4 with appropriate models led to J values of -0.6, -1.5 and -99.0 cm-1 respectively. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.
