title: Transition metal quinone-thiosemicarbazone complexes 3: Spectroscopic characterizations of spin-mixed iron (III) of naphthoquinone-thiosemicarbazones.
abstract: An interesting series of iron (III) complexes with naphthoquinone-thiosemicarbazones are synthesized and physico-chemically characterized by elemental analysis, UV-vis, IR, EPR and magnetic susceptibility measurements. They possess a cationic octahedral [FeL2]+ species and a tetrahedral [FeCl4]- anion and exhibit unusual spin-mixed states involving high-spin and low-spin ferric centers as revealed from magnetic behavior with significant amount of exchange interactions mediated by intermolecular associations. The magnetic susceptibility data is fitted with S1=5/2 and S2=1/2 Heisengberg's exchange coupled model; H=-2JS1S2 and the magnetic exchange interactions are found to be of the order of -13.6 cm-1 indicating the moderate coupling between two paramagnetic centers present in different chemical and structural environment. The presence of spin-paired iron (III) cation having dxz2dxz2dxz1 ground state is revealed from the EPR spectra with three prominent peaks while the high-spin tetrahedral iron (III) anion exhibits characteristics g=4 signal whose intensity increases with lowering the temperature suggesting its influence on the magnetic properties of the complex molecule. FTIR measurements indicate tridentate ONS donor systems involving quinone/hydroxyl oxygen, imine/hydrazinic nitrogen and thione/thiol sulfur atoms as binding sites for naphthoquinone-thiosemicarbazones.
authors.affiliation: Department of Chemistry, University of Pune, Pune 411 007, India. rajuchikate@rediffmail.com
authors.forename: Rajeev C
authors.initials: RC
authors.lastname: Chikate
authors.forename: Subhash B
authors.initials: SB
authors.lastname: Padhye
mesh_terms: D004578:Electron Spin Resonance Spectroscopy; D004583:Electrons; D007501:Iron / Q000737:chemistry*; D008024:Ligands; D008280:Magnetics; D009285:Naphthoquinones / Q000737:chemistry*; D013055:Spectrophotometry, Infrared; D013113:Spin Labels; D013696:Temperature; D013882:Thiosemicarbazones / Q000737:chemistry*; D028561:Transition Elements / Q000737:chemistry*
chemical_list: D008024:Ligands; D009285:Naphthoquinones; D013113:Spin Labels; D013882:Thiosemicarbazones; D028561:Transition Elements; D007501:Iron