Transition metal complexes with thiosemicarbazide-based ligands. Part 61. Comparative analysis of structural properties of the pyridoxal thiosemicarbazone ligands. Crystal structure of PLTSC center dot HCl center dot 2H(2)O and its complex [Fe(PLTSC)Cl-2(H2O)]Cl

A novel pyridoxal thiosemicarbazone (PLTSC) compound, exhibiting ligating properties, of the formula PLTSC center dot HCl center dot 2H(2)O (1) was synthesized and characterized by X-ray analysis. The PLTSC ligand 1 displays significantly different conformation in comparison to the five previously reported compounds of this type. The structural properties of six PLTSC ligands in different conformations were compared in order to establish the structural differences and understand the factors that facilitate particular conformations. The analysis indicated great structural flexibility of the PLTSC ligands. The PLTSC ligand 1 is essentially a planar molecule with the r.m.s deviation of all non-H atoms equal to 0.06 angstrom. Consequently, the molecules of 1 form a layered three-dimensional structure which is stabilized by a variety of hydrogen bonds: O-H center dot center dot center dot O, O-H center dot center dot center dot N, O-H center dot center dot center dot Cl, O-H center dot center dot center dot S, N-H center dot center dot center dot O, N-H center dot center dot center dot N, N-H center dot center dot center dot Cl, N-H center dot center dot center dot S. In addition, the crystal structure of the Fe(III) complex with the ligand 1 of the formula [Fe(PLTSC)Cl-2(H2O)]Cl was resolved by single-crystal X-ray analysis and structural properties of this octahedral complex were discussed and compared to those of uncoordinated PLTSC ligand

(E)-4-[(2-Carbamoylhydrazinylidene)methyl]-3-hydroxy-5-hydroxymethyl-2-methylpyridin-1-ium nitrate

The title compound, C9H13N4O3+center dot NO3-, is the first structurally characterized Schiff base derived from semicarbazide and pyridoxal. Unusually for an unsubstituted semicarbazone, the compound adopts a syn conformation, in which the carbonyl O atom is in a cis disposition relative to the azomethine N atom. This arrangement is supported by a pair of hydrogen bonds between the organic cation and the nitrate anion. The cation is essentially planar, with only a hydroxymethyl O atom deviating significantly from the mean plane of the remaining atoms (r.m.s. deviation of the remaining non-H atoms = 0.01 angstrom). The molecules are linked into flat layers by N-H center dot center dot center dot O and C-H center dot center dot center dot O hydrogen bonds. O-H center dot center dot center dot O hydrogen bonds involving the hydroxymethyl group as a donor interconnect the layers into a three-dimensional structure