First molecular complexes of Cr(III) with 2,6-diacetylpyridine-bis(thiosemicarbazone): synthesis and crystal structures

The first molecular complexes of Cr(III) with chelating 2,6-diacetylpyridine-bis(thiosemicarbazone) Schiff-base ligand (H(2)daptsc), [Cr(Hdaptsc)(H2O)(1.4)(CH3OH)(0.6)](NO3)(2)center dot 1.4CH(3)OH (1), [Cr(Hdaptsc)(H2O)(2)](NO3)(2)center dot 1.3C(2)H(5)OH (2), [Cr(Hdaptsc)(H2O)(2)](NO3)(2)center dot H2O (3), [Cr(H(2)daptsc)(H2O)(2)](NO3)(3)center dot 2H(2)O (4), [Cr(Hdaptsc)(N-3)(2)]center dot CH3OH (5), [Cr(Hdaptsc) (N-3)(2)]center dot 1.25H(2)O (6) have been synthesized, and their crystal structures have been studied. Structural analysis has shown that in all the crystals, the Cr(III) cation is seven-coordinated by N3S2 atoms of the pentadentate ligand in the equatorial plane and two O or N atoms of water/methanol or N-3(-) axial ligands. The pentadentate ligand is fully protonated in 4 and monodeprotonated in one hydrazinic -NH group in all the other compounds. The degree of deprotonation depends on the pH of the reaction medium. The remaining proton in Hdaptsc(-) is ordered and localized on one side of the ligand. As a result, the Hdaptsc(-) ligand possesses a pronounced difference in Cr-S/N bond distances for the neutral protonated and negatively charged deprotonated halves due to the strong Jahn-Teller effect for the high-spin 3d3 configuration in the pentagonal bipyramidal (PBP) ligand field.