SPECTROSCOPIC AND MAGNETIC-PROPERTIES OF THE PYRIDINE-2-CARBALDEHYDE THIOSEMICARBAZONATEIRON(III) COMPLEXES - [FE(C7H7N4S)(2)]X-CENTER-DOT-NH(2)O (X = CL, CLO4, NO3, PF6) - CRYSTAL-STRUCTURE OF THE HEXAFLUOROPHOSPHATE COMPOUND

The [Fe(C7H7N4S)(2)]X . nH(2)O (X = Cl (1), ClO4 (2), NO3 (3), PF6 (4) ; n = 0 (4), 1.5 (1), 0.5 (3)) compounds, where C7H8N4S is pyridine-2- carbaldehyde thiosemicarbazone, have been synthesized and characterize d. The crystal structure of compound 4 has been solved. It crystallize s in the monoclinic P2(1)/n space group with a = 13.099(2), b = 12.153 (5), c = 13.710(1) Angstrom, beta = 102.56(1)degrees, V = 2130(1) Angs trom(3), Z = 4. The framework consists of discrete monomeric cationic entities containing low-spin iron( III) ions in a distorted octahedral environment. The metal ion is bonded to one sulfur and two nitrogen a toms of each thiosemicarbazone molecule. The hexafluorophosphate molec ules act as counterions. Extended Huckel MO calculations for complex 4 reveal a high delocalization and an important charge transfer contrib ution from the ligands to the metal. EPR spectra of compounds 1, 2, 3 and 4 show rhombic signals. Their main features, which can be expresse d as a relatively low anisotropy in g values and a g(3)value which is greater than usual, are due to the low symmetry and the electronic del ocalization. (C) 1998 Elsevier Science S.A. All rights reserved.