Cobalt and Copper Coordination Polymers Containing Acetylacetonato‐Derived Ligands and Bidentate Pyridine Coligands: Synthesis, Crystal Structures and Magnetic Properties

Abstract

AbstractOne‐dimensional chain derivatives of the general formula [M(acac)2(μ‐bipyridine)] were obtained from (acetylacetonato)cobalt(II) or (trifluoromethylacetylacetonato)copper(II) derivatives and bipyridine‐like bridging ligands: 1,2‐bis(4‐pyridyl)ethane, 4,4′‐bpa (1, Co; 2, Cu), trans‐1,2‐bis(4‐pyridyl)ethylene, 4,4′‐bpe (3, Co; 4, Cu), 1,2‐bis(2‐pyridyl)ethylene, 2,2′‐bpe (5, Co) or pyrazine (7, Cu). The reaction of the copper parent derivative with 2,2′‐bpe gives rise, however, to a dimeric species [{Cu(tfacac)2}2(μ‐2,2′‐bpe)] (6). Derivatives 4–7 were characterized by X‐ray crystallography, which showed linear (4, 7) or zigzag chains (5), depending on the bipyridine ligand shape. In the chain complexes, the metal centre is six‐coordinate; the oxygen donor atoms of the acetylacetonato ligands occupy the equatorial positions and the bridging bipyridine ligands are in trans axial positions. Compound 6 forms a dimer with the two copper atoms in a square pyramidal environment, in which the nitrogen atoms of the bridging 2,2′‐bpe ligand occupy the apical position in each pyramid. Magnetic susceptibility studies of the cobalt compounds are dominated by the spin–orbit coupling characteristic of this metal ion. At low temperatures and in the copper derivatives, weak antiferromagnetic interactions along the chain were observed.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)