Synthesis and characterisation of first row transition metal complexes of functionalized 1,2,4-benzothiadiazines

Reaction of the novel ligand 3-(2′-pyridyl)-benzo-1,2,4-thiadiazine (L) with the transition metal chloride salts MCl₂·xH₂O (M^II = Mn, Fe, Co, Cu and Zn) in a 2 : 1 mole ratio afforded the mononuclear octahedral (high spin) complexes L₂MCl₂ (1a–1e respectively) in which L binds in a chelate fashion via N(2) and the pyridyl N atoms. In the case of CuCl₂ the intermediate 1 : 1 four-coordinate complex LCuCl₂ (2) was also isolated which adopts a polymeric structure with pseudo-square planar molecules linked via long CuS contacts (d_Cu^…S = 2.938(1) Å) in the apical position. In the presence of non-interacting ions, 3 : 1 complexes are isolated, exemplified by the reaction of L with Fe(CF₃SO₃)₂ in a 3 : 1 ratio which affords the low spin complex [L₃Fe][CF₃SO₃]₂ (3). Reaction of L with VCl₃ in a 2 : 1 mole ratio under aerobic conditions afforded the vanadyl complex [L₂V(=O)Cl][Cl] (4).