Syntheses, crystal structures and magnetic properties of four-coordinate Ni(II) and Cu(II) complexes

•Two mononuclear four-coordinate Ni(II) and Cu(II) complexes have been synthesized.•Both complexes adopt severely distorted coordination geometries.•The Cu(II) complex exhibits a structure closer to a tetrahedral configuration.•The Ni(II) complex adopts a structure closer to a seesaw configuration.•The dc magnetic data show the Ni(II) complex possesses a large easy-plane anisotropy. In this work, two mononuclear four-coordinate complexes of Ni(II) and Cu(II), formulated as (HNEt3)2[Ni(L)2] (1) and (HNEt3)2[Cu(L)2]·H2O (2) (H2L = N,N′-bis(p-toluenesulfony1)oxamide), have been synthesized and characterized. These complexes are coordinated by two doubly deprotonated oxamide ligands. The crystal structures of both complexes were determined using single-crystal X-ray diffraction, revealing highly irregular coordination geometries around the central metal ions. Complex 1 exhibits a structure closer to a tetrahedral configuration, whereas complex 2 adopts a structure closer to a seesaw configuration. Direct-current (dc) magnetic data demonstrate that 1 possesses an easy-plane anisotropy with a large value for the zero-field splitting (ZFS) parameter D of +66.3 cm−1. Two mononuclear four-coordinate Ni(II) and Cu(II) complexes have been prepared and characterized. Both complexes exhibit highly irregular coordination geometry, among them, the Ni(II) complex possesses a large easy-plane anisotropy. [Display omitted]