Stability of iron(III)-thiocyanate complexes and the dependence of absorbance on the nature of the anion

Abstract

The dependence of the colour intensity of the iron(II1)thiocyanate complex formed a t two different ratios of thiocyanate to iron on the nature and concentration of the acid anion was studied. Four different acids were tested over the concentration range 0.05-1 .O N : perchloric acid, nitric acid, hydrochloric acid and sulphuric acid. Fading of the iron(II1)thiocyanate colour was ascribed to a specific effect of the anion caused by progressive masking of iron(II1) ions of the highly dissociated iron(II1)thiocyanate by the more strongly complexing anion ligand. The results were interpreted in the light of the calculated values of side-reaction coefficients between iron(II1) and the added ligand, as well as on the magnitude of conditional stability constants of iron(II1)thiocyanate in the various media. That the order of effectiveness of the added anions towards complexing iron(II1) ions is SO,2-> C1-> NO,-> C10,was further substantiated.

Spectrophotometric study of iron oxidation in the iron(II)/thiocyanate/acetone system and some analytical applications

“…Our main objective was gather the best experimental conditions for complete oxidation and complexation reactions in the iron(II)/ thiocyanate system, making its fast spectrophotometric utilization possible. The dependence of the colour intensity of the formed iron-thiocyanate complexes on the nature and concentration of the acid anion have seen studied [14,15]. Perchloric acid has been chosen to acidify this system (and analogous ones) due to its weak coordination character.…”

“…In spectrophotometric studies, the presence of organic solvent in the reaction systems generally increases the complexes stability and consequently the molar absorptivity and the sensitivity. The fading of the iron(III)/thiocyanate colour has been a very critical photometric problem in aqueous medium and a large number of classic works have been carried towards the stabilization of such iron(III) complexes [14,15]. More recently [12], another spectrophotometric oxidation study using the iron(II)/azide/tetrahydrofuran system was done in our laboratory, which allowed us to explore a new band (396 nm), also described by our group in the literature, caused exclusively by the THF presence under a large excess of the azide ligand [7].…”

Solubility Investigations in the Na2SO4 + V2O5 + H2O System from 293 K to 323 K

“…The vanadium(V) concentration was determined by spectrophotometric analysis using the double-beam UV/VIS Hitachi U-2000 spectrophotometer. The analysis was based on the ability of vanadium(V) to form the colored complex with 4-(2-pyridylazo)resorcinol (PAR) − that is one of the most sensitive reagents for vanadium analyses. Beer's law is satisfied in the broad range of vanadium concentration (2·10 -5 to 1.8·10 -2 ) mol·dm -3 .…”

Development of a Sensitive and Selective Optical Sensor for Measuring Ultra‐Trace Amounts of Fe(II) and Fe(III) Ions in Water

“…In reality, various reagents have been utilized, each of which is specific to a single iron oxidation state. The most commonly employed ligands for Fe(II) determination are 1,10‐phenanthroline, [8] 4,7‐diphenyl‐1,10‐phenanthroline, [9] and 2,2′‐bipyridine, [10] whereas thiocyanate [11] and 3‐hydroxy‐1,2‐dimethyl‐4(1H)‐pyridinone [12] . Despite the high sensitivity allowed using these reagents, the methods require troublesome procedures for total iron determination.…”