N,N′-bis(substituted-phenyl)oxamides and their dinuclear pentacoordinate nickel(II) complexes

The preparation, spectroscopic characterization and magnetic study of N,N′-bis(substituted-phenyl)oxamidate-bridged nickel(II) dinuclear complexes of formula {[Ni(N3-mc)]2(μ-CONC6H4-X)}(PF6)2 (N3-mc = 2,4,4-trimethyl-1,5,9-triazacyclo-dodec-1-ene (Me3-N3-mc) or 2,4,4,9-tetramethyl-1,5,9-triazacyclododec-1-ene (Me4-N3-mc), X = 2-Cl, 4-Cl, 2-OCH3, 4-OCH3) are reported. These paramagnetic nickel(II) complexes have been characterized by both one- and two-dimensional (COSY) 1H NMR techniques. The COSY spectrum of 5 has allowed to achieve the assignment of the phenyl protons of the N,N′-diphenyloxamidate. The crystal structures of [Ni(Me3-N3-mc)(μ-CONC6H4-4-Cl)]2(PF6)2 (6), [Ni(Me3-N3-mc)(μ-CONC6H4-4-OMe)]2(PF6)2 (8) and [Ni(Me4-N3-mc)(μ-CONC6H4-2-Cl)]2(PF6)2 (9) have been determined and their magnetic properties have been studied. The value of magnetic coupling between the two nickel(II) ions across the oxamidate bridge [J = − 37.6 (6), −39.9 (8) and −39.7 cm−1 (9)] is sensitive to the distortion of the coordination sphere of the metal ions and the topology of the molecular bridge.