Template synthesis and crystal structure of an asymmetric square-planar complex: Pyridine-2,6-dicarbaldehyde-bis(<Emphasis Type="Italic">S</Emphasis>-methylisothiosemicarbazonato)nickel(II) iodide

The asymmetric complex Ni(HL)]I (where H₂L is pyridine-2,6-dicarbaldehyde-bis(S-methylisothiosemicarbazone)) is synthesized by the 2 + 1] template condensation of S-methylisothiosemicarbazide hydroiodide with pyridine-2,6-dicarbaldehyde in the presence of nickel(II) acetate. The crystal structure of the Ni(HL)]I complex (where HL is C₁₁H₁₄N₇S₂) is determined using X-ray diffraction. The square-planar coordination of the nickel(II) central atom is provided by four N donor atoms of the chelating ligand, namely, one N atom of the pyridine residue and three N atoms of the isothiosemicarbazide fragments. The deprotonated isothiosemicarbazide fragment in the imino form and the neutral ammonium isothiosemicarbazide fragment differ in the degree of deprotonation, the mode of coordination to the central atom (N¹N³ and N², respectively), and the conformation (E and Z, respectively). The structural features of the ammonium isothiosemicarbazide fragment are associated with the formation of zwitterions. It is established that the crystal structure of the compound under investigation contains centrosymmetric dimers. These dimers participate in the formation of the second coordination sphere N₄S of the central atom.