Synthesis and spectroscopic properties of two pyridine-2-carbaldehyde thiosemicarbazonecopper(II) compounds: [CuX₂(C₇H₈N₄S)] · H₂O (X = Br, Cl). Crystal structure of the bromo complex

The [CuX₂(C₇H₈N₄S)] · H₂O (C₇H₈N₄S = pyridine-2-carbaldehyde thiosemicarbazone; X = Cl, Br) complexes have been synthesized and characterized. The crystal structure of the bromo compound has been solved. It crystallizes in the monoclinic system space group P2₁/c with a = 8.750(1), b = 9.834(1), c = 14.838(2) Å, β = 99.37(1)°, V = 1259.7(3) Å Z = 4, A = 0.050, R_w = 0.047. The framework consists of discrete monomeric molecules with five-coordinate square-pyramidal copper(II) ions. One sulfur and two nitrogen atoms of the thiosemicarbazone ligand and one bromide ion are in the basal position, with another bromide ion in the apical one. Bond lengths are compared with those of other thiosemicarbazone complexes. The chloro complex is isostructural with the bromo one. Considering the electronic delocalization along the thiosemicarbazone ligand and the geometry of its chelating centers, an important influence in the copper orbitals sequence has been shown from the spectroscopic studies and molecular orbital calculations.