Tuning of the charge in octahedral ferric complexes based on pyridoxal-N-substituted thiosemicarbazone ligands.

Four novel mononuclear coordination compounds namely: Fe(Hthpy)(2)(1/2).3.5H(2)O , [Fe(Hthpy)(2)]NO(3).3H(2)O , Fe(H(2)mthpy)(2)(3).CH(3)CH(2)OH and [Fe(Hethpy)(ethpy)].8H(2)O , (H(2)thpy = pyridoxalthiosemicarbazone, H(2)mthpy = pyridoxal-4-methylthiosemicarbazone, H(2)ethpy = pyridoxal-4-ethylthiosemicarbazone), were synthesized in the absence or presence of organic base, Et(3)N and NH(3). Compounds and are monocationic, and were prepared using the singly deprotonated form of pyridoxalthiosemicarbazone. Both compounds crystallise in the monoclinic system, C2/c and P2(1)/c space group for and , respectively. Complex is tricationic, it is formed with neutral bis(ligand) complex and possesses an interesting 3D channel architecture, the unit cell is triclinic, P1[combining macron] space group. For complex , the pH value plays an important role during its synthesis; is neutral and crystallises with two inequivalent forms of the ligand: the singly and the doubly deprotonated chelate of H(2)ethpy, the unit cell is monoclinic, C2/c space group. Notably, in and , there is an attractive infinite three dimensional hydrogen bonding network in the crystal lattice. Magnetic measurements of and revealed that a rather steep spin transition from the low spin to high spin Fe(iii) states occurs above 300 K in the first heating step. This transition is accompanied by the elimination of solvate molecules and thus, stabilizes the high spin form due to the breaking of hydrogen bonding networks; compared to and , which keep their low spin state up to 400 K.