Synthesis, X-ray and Mössbauer study of iron(II) complexes with trithiocyanuric acid (ttcH3).The X-ray structures of [Fe(bpy)3](ttcH)·2bpy·7H2O and [Fe(phen)3](ttcH2)(ClO4)·2CH3OH·2H2O

Abstract

Mixed-ligand Fe(II) complexes involving the trithiocyanurate anion and nitrogen-donor ligands have been prepared and characterized by Mössbauer, IR and UV–Vis spectroscopies. All the complexes are low spin with a deformed octahedral arrangement as was also proved by X-ray analysis, in the case of two complexes. DFT calculations were used for IR bands assignment. Iron(II) complexes with a combination of nitrogen-donor ligands and trithiocyanuric acid (ttcH 3 ) of the composition [Fe(bpy) 2 (ttcH)] · 2H 2 O ( 1 ), [Fe(bpy) 3 ](ttcH) · 2bpy · 7H 2 O ( 2 ), [Fe(terpyCl) 2 ](ttcH 2 ) 2 · H 2 O ( 3 ), [Fe(phen) 2 (ttcH)] · 2H 2 O ( 4 ), [Fe(nphen) 2 (ttcH)] · 4H 2 O ( 5 ) and [Fe(phen) 3 ](ttcH 2 )(ClO 4 ) · 2CH 3 OH · 2H 2 O ( 6 ), where bpy = 2,2′-bipyridine, terpyCl = 4′-chloro-2,2′:6′,2′-terpyridine, phen = 1,10-phenanthroline, nphen = 5-nitro-1,10-phenanthroline, have been prepared. The compounds, except for 6 , have been characterized by elemental analysis, 57 Fe Mössbauer, IR and UV–Vis spectroscopies. It has been found that the trithiocyanurate ion is either coordinated to the metal centre ( 1 , 4 and 5 ) or situated outside the inner coordination sphere of the iron(II) ion ( 2 , 3 and 6 ). The X-ray crystal structures of complexes 2 and 6 demonstrate that the ligands enforce a distorted octahedral geometry on the Fe II ions with monoanionic 2 and dianionic 6 forms of uncoordinated trithiocyanuric acid. Density-functional theory (DFT) calculations (B3LYP/6-31 + G*) were used for the geometry optimisation and infrared frequencies calculations of differently protonated forms of the acid (ttcH 3 , ttcH 2 − and ttcH 2− ).