One-,two- and three-dimensional Cu(II) complexes built via new oligopyrazinediamine ligands:from antiferromagnetic to ferromagnetic coupling

摘要

Six new pyrazine-modulated N,N'-bis(alpha-pyridyl)-2,6-diaminopyridine ligands (PMN5) were synthesized and their complexes studied.Reaction of copper(II) with the ligand that contained one pyrazine ring in its terminal position led to formation of a one-dimensional zigzag complex whereas copper(II) reactions with ligands containing three pyrazine rings or one pyrazine ring in its middle position yielded straight one-dimensional complexes.A 2-D complex was produced from the ligand with two pyrazine rings at both terminals.When nickel(II) was introduced,a 3-D network was obtained from the three-pyrazine-modulated ligand.Researches on variable-temperature magnetic susceptibility measurements revealed excellent Heisenberg chains with weak antiferromagnetic interaction of / values from -2 to -3 cm~(-1) via sigma and pi pathways in straight one-dimensional complexes between the Cu(II) centers separated by 6.8-6.9 A.The zigzag one-dimensional complex showed very poor magnetic coupling.The two-dimensional compound showed significant ferromagnetic interaction in spite of the Cu-Cu distance of 7.2 A.Ferromagnetic coupling was discussed and attributed to the unusual coordination mode of in-plane and out-of-plane linkage of bridging pyrazine rings.The three-dimensional heterometal Cu(II)-Ni(II) compound showed weak antiferromagnetic interaction,which was satisfactorily fitted with J=-2.4 cm~(-1) following a one-dimensional theoretical model including MFA.