Ultraviolet spectrophotometric properties of ferric complexes of 2:2'-dipyridines in glacial acetic acid

Talama,

1958, Vol

1, PP 153-158.

Per@m~on

Press

Ltd..

London

ULTRAVIOLET SPECTROPHOTOMETRIC PROPERTIES OF FERRIC COMPLEXES OF 2:2’-DIPYRIDINES IN GLACIAL ACETIC ACID Whl. M. BANICK, JR. and G. FREDERICK SMITH William Albert Noyes Laboratory, Department of Chemistry, Umverslty of Ilhnon, Urbana, Ilhnols, U S A (Recewed 14 February 1958) Summary-2 2’-Dlpyrldme forms a stable, yellow-green complex with lrox$I m glacial ace& acid with a hgand to n-on mole ratio of 1 60 to 1 (3 to 2). The 4.4’-dnubstltuted derlvatlves also form a yellow-green complex Solutions of these complexes are characterlsed by a strong absorption maximum m the 250-350 rnp region of the spectrum. The spectrophotometrlc constants of the lronTII complexes were evaluated at tlus maximum The lronlI1 complex of the dlphenyl derlvatlve has the largest molar absorptivity of all the 2 2’-dlpyrldmes studled INTRODUCTION

direct chelation of Fe”’ with 1: lo-phenanthrohne and Its derrvatrves m aqueous solutron 1s in general not possible over a pH range of 1 to 12. An exception to this condition is that of Fen1 with 1 :lO-phenanthroline to form a complex wrth a hgand to metal mole-ratio of 3 to 2 as employed by Manning and Harvey’ in the srmultaneous spectrophotometrlc determination of ferrous and ferric Iron Brandt and Howsmon2 studied the Fe”‘-1 : lo-phenanthrohne system in glacral acetrc acid and found the complex to have a hgand to metal ratro of 1 to 1. They isolated an orangeyellow salt which was of the composltton Fe(phen)Cl,. The study has been made3 of 2:2’-drpyrrdine and eleven 4:4’-duubstituted dipyridines as their Fe” complexes by Smrth and Bamck in aqueous solutions at pH 1 to 12 and m glacial acetic acid by the authors4 of the present study. The reactron of Fen1 m direct chelation with a group of the same ligands m glacial acetic acid is the subject of the present work. The hgands included are unsubstituted 2:2’drpyridine and the 4:4’-substrtuted drpyrrdines of the following types: ethyl, bromo, chloro, ethoxy, phenoxy, drcarbethoxy and phenyl groups. THE

PREPARATION

OF

REAGENT

SOLUTIONS

Solutions of 2 2’-drpyndme and derwatwes. 0 OlOF solution m glacial acetic acid The 4:4’dlcarboxy and -dlcarboxamlde-2,2’-dlpyrldlnes are quite msoluble m glacial acetlc acid and were not mvestlgated as m the previously cited ‘s4 studies The procedures involved m this study required 0 002OF and 0 OOlOF solutions of the various hgands m glacial acetlc acid. Ferric chlorrde solutrons A weighed amount of reagent grade ferric chloride hexahydrate was dissolved m glacial acetlc acid to give 0 002OF solutions IDENTIFICATION

OF

THE

IRONIII-2

2’-DIPYRIDINE

COMPLEX

Smce 2 2’-dlpyrldme and its 4 4’-dlsubstltuted derlvatlves all reacted with lronlI1 to give the same yellow-green coloured complex m glacial acetlc acid, stable over a period of at least 48 hours, It was reasonable to assume that the nature of the complex m each case was the same Hence, ldentlfication of the 2 2’-dlpyrldme complex would serve to ldentlfy the nature of the lronlI1 complex with its derlvatlves The first step m the ldentlficatlon of the ironIT complex of 2 2’-dlpyrldme m glacial acetlc acid was to obtam a spectrum of a solution of the complex, a solution of 2 2’-dlpyrldme, and a solution of 153

154

WM. M. BANICK, JR. and G. FREDERICKSMITH

ferric chloride m order to select a sultable wavelength for spectrophotometrlc exammatlon of the complex The 22’-dlpyndme solution was prepared by dllutmg 0 50ml of the 0 002OOF2 2’-dlpyndme solution to 25ml m a glass-stoppered volumetric flask wth glacial acetic acid. The ferric chloride solution was prepared m the same manner usmg 0 50ml of the 0 002OOFferric chloride solution. The solution of the complex was prepared by ddutmg 0 50ml of the 0 002OOF2 2’-dlpyrldme sohmon and

300

340 Wavelength,

380 ~-I/L

FIG 1. A-O 50 ml of 0 00200F 2 2’-dlpyndme (a) dduted to 25 ml, B-O 50 ml of 0.002OOF ferric chloride @) diluted to 25 ml, C-O.50 ml of (a) and 0.50 ml of (b) dduted to 25 ml.

0 50 ml of the 0.002OOF ferric chloride solution to 25 ml with glacial acetlc acid m a glass-stoppered volumetric flask All solution transfers were made with measurmg pipettes These solutions were then examined spectrophotometrlcally on the Cary Recording Spectrophotometer, Model 14 M, usmg I-cm sihca cells The 270-400 rnp region of the spectrum was scanned employmg glacial acetic acid m the reference cell The spectrum of each of these solutions IS shown m Fig 1. The wavelength of 340 rnp was selected as the most sultable for use m the spectrophotometrlc ldentdicatlon of the mole ratio of hgand to non m soiutlons of the complex. Two more solutions of the complex m glacial acetic acid were prepared usmg the procedure described above The amount of 2 2’-dlpyrldme solution used, however, was 2 00 ml for one of the solutions and 3 00 ml for the other The absorbance of each of these solutions of the complex at 340 rnp was exactly the same and of such magmtude as to discount a hgand to iron mole ratlo of 3 to 1 for the complex m solution The mole ratio method described by Yoe and Jones6 was used for the quantltatlve ldentdicatlon of the lronlI1 complex of 2 2’-dlpyrldme m glacial acetic acid The procedure used m this mole ratio study was as follows to each of a series of 25-ml glass-stoppered volumetric flasks contammg 2 00 ml of the standard ferric chloride solution was added a known volume of the 0 002OOF 2:2’-dlpyndme solution Dilution to volume was then made with glacial acetic acid The volume of the 2 2’-dlpyndme solution added to each flask was varied so that the mole ratlo of 2 2’-dlpyndme to iron ranged from 5 0 to 0 75. All volume measurements were made with measurmg pipettes. The solutions of the complex thus prepared were exammed spectrophotometrlcally on the Cary Recordmg Spectrophotometer. Model 14 M, usmg l-cm sihca cells For those solutions m which the mole ratlo of hgand to Iron was 2 to 1 or greater, glacial acetic acid was used m the reference cell For solutions m which the ratlo was less than 2 to 1, the reference cell contained solutions of ferric ehlorlde m order to compensate for absorbance due to uncomplexed Iron Calculations of the amount of uncomplexed u-on were made assuming a complex wluch had a llgand to non mole ratlo of 2 to 1. The absorbance values of these solutions at 340 rnp were plotted agamst the hgand to Iron mole ratlo. An excellent mole ratlo plot was obtamed which indicated, however, a hgand to iron mole ratio of 1 75 to 1 These same solutions were re-exammed usmg different ferric chloride blank solutions (where necessary). The amounts of ferric chloride used m preparmg the ddferent blank solutions were calculated assummg a hgand to iron mole ratlo of 3 to 2 (1 67 to 1)

Ferrtc complexes of 2:2’-dtpyridmes

155

m acetic actd

The spectrophotometrrc data obtamed from these measurements are given m Table I These data were used to construct the mole ratto plot shown m Frg 2. The mole ratio plot gives a value of 1.60 for the hgand to iron mole ratto, mdtcatmg a hgand to iron mole ratto of 3 to 2 for the complex m solution 0 Q-

A=340

q.8 ----

/ 1.0

/I 1.6 2.0

Mole ratm -hgand

I 3.0

I 4.0

I 5.0

to Iron

FIG 2. Mole ratto plot

An orange-yellow crystalline salt was isolated from a solution containing 2.2’-dtpyndme and ferric chloride usmg the followmg procedure a stoichtometrtc amount of ferric chlortde was added The resultant to 25 ml of hot glacial acetic acid contammg 0 630 g of dissolved 2:2’-dtpyrtdme orange-coloured solutton was cooled and the orange-yellow salt which precipitated was collected by tiltratron and washed with glacial acetic acid The salt was then dried at 85” for four hours Tlus salt was soluble m water and m 95 % ethanol, yreldmg brown-coloured soluttons Aqueous soluttons of the salt gave a white precipitate with silver nitrate. A quantttattve determmation of iron m this salt was carried out spectrophotometrtcally using 2.2’-dipyrrdme. Duplicate analyses gave TABLE I

MOLE-RATIO STUDY OF THEIRON~*~COMPLEX IN GLACIAL ACETIC ACID 7

ml of 2:2’-dtpyrtdme solutton

OF 25!'-DIPYRIDINE

T

Mole-ratio, hgand to iron

Absorbance

at 340 rnp

-

5 00 400 300 2 00 1 50 100 0 75

100 80 60 40 30 20 15 _I-

I

0 769 0 770 0 712 0764 0 738 0.497 0 346

17.7 % and 17 8% iron These results suggested the formula of the salt to be Fe(dtpy)CI, or possibly Fe,(dtpy),Cl,-m which compounds the iron content is 17 5 % DETERMINATION

OF

SPECTROPHOTOMETRIC

DATA

Soluttons of the tronlI1 complex of 2:2’-dipyrtdme and its 4 4’-disubstttuted derivattves were prepared for spectrophotometrrc exammatton using the following procedure: 0 50 ml of the standard ferric chloride solutton and 1.67 ml of the 0 OOlOOFdtpyridme solutton were transferred to a 50-ml glass-stoppered vohunetrrc flask using measuring pipettes The contents of the flask were diluted The 250-350 rnp regton of to volume with glacial acetic acid and exammed spectrophotometrically. the spectrum was scanned usmg glactal acetic acid m the reference cell.

156

WM M

BANICK, JR and G

FREDERICKSMITH

The absorption spectra of glacial acetlc acid solutions of the 2.2’~dlpyrldmes were also obtamed m the same region of the spectrum The solutions of the 2*2’-dlpyndmes were prepared by ddutmg 1 00 ml of the 0 OOlOOFsolutions of the dlpyrldmes to 25 ml m a glass-stoppered volumetric flask. Spectrophotometrlc exammatlon of these solutions was carried out usmg the same instrument and procedure as described above The ultraviolet absorption spectra of the 2 2’-dlpyndmes and their lronlIr complexes are shown in Figs 3 to 10 The spectrophotometrlc constants of the hgands and complexes are summarlsed m Table II All calculations of the molar absorptlvltles of the complexes were based on the amount of iron added TABLE II AND

SPECTROPHOTOMETRIC DATA FOR THE 2

THEIR

IRON”’

COMPLEXES

IN

GLACIAL

2’-DIPYRIDINES

ACETIC

ACID

Substitution derivative Substitution derivative of 2:2’-dlpyrldme

1 2 3. 4 5. 6. 7 8

unsubstltuted 4,4’-dlethyl4,4’-dlbromo4,4’-dlchloro4,4’-dlethoxy4,4’-dlphenoxy4,4’-dlcarbethoxy4,4’-dlphenyl-

1msx

288 rnp 295 m,u 283 m,u 282 m,u 283 rnp 280 rnp 301 rnp 295 m,u

Molar absorptlvlty 11,100 13,100 12,700 12,800 12,400 12,500 11,600 19,800

IrorP

complex

i-_ 297 m,u 295 rnp 294 rnp 292 m,u 285 rnp 286 rnp 308 rnp 305 rnp

25,200 26,800 24,500 23,000 24,800 26,300 20,900 38,400

DISCUSSION

The n-on”’ complexes of the 4:4’-disubstltuted 2:2’-dlpyridmes like the ironlI1 complex of 2:2’-dlpyndme have one strong absorption maximum m the 250-350 rnp region of the spectrum. In this respect the spectra of the complexes resemble the spectra of the free hgands The spectra of 2:2’-dlpyndme and the 4:4’-dlethyl, -dlphenoxy, and -dlphenyl derivatives m glacial acetic acid are quite similar to the spectra of then n-onlI1 complexes m this same solvent over the spectral range of 250-350 m,u. On the other hand, the absorption spectra for glacial acetic acid solutions of the dlbromo, dlchloro, diethoxy, and dlcarbethoxy derivatives are somewhat different from the spectra of their iron”’ complexes m this same solvent over the spectral range of 250-350 m,u. For all the dlpyrldmes studied, however, the lron’r’ complex has a longer wavelength of maximum absorption than the corresponding ligand Only three of the derivatives studied ylelded an iron”’ complex which had a molar absorptivity greater than the molar absorptlvlty of the 2*2’-dlpyndme-lronln complex This might be considered unusual m view of the fact that the molar absorptlvltles of all the derlvatlves were greater than the molar absorptivity of the unsubstltuted hgand. As expected the iron”’ complex of the diphenyl derivative has the largest molar absorptivity. The hgand to metal mole-ratio of 1 60 to 1 (3 to 2) for the iron”’ complex of 2:2’-dipyndine in glacial acetic acid differentiates it from the iron”’ complex of 1 :lO-phenanthrolme, which has a hgand to metal mole ratio of 1 to 1 m glacial acetlc acide3 It is perhaps of interest that the mole ratio value of 1.60 obtained here for the

Ferric complexes of 2 2’-dlpyndines

157

m acetic acid

ABSORPTION SPECTRA OF 7m DIPYRIDINEs AND THEIR FERRIC COMPLEXES IN GLACIAL ACETIC ACID

300

260

Wavelength, 3

FIG

I

1

260

A-2

,

I

380

340

300

FIG. 4 A4 4 4’-dlethyl-2

2’-dlpyndme, B-2.2’d1pyr1dmelronm complex.

,

I 38(

340

Wavelength,

m/i

rnp

4’-dlethyl-2 2’-dlpyrldme, B2’-dlpyndm+nonIII complex

I

300 Wavelength,

300

380

m,u

Wavelength,

FIG 5 A4 4’dlbromo 2 2’ dlpyrldme, B4 4’-dlbromo-2 2’-dlpyndme-Iron111 complex

260

260

300 Wavelength,

340

rn,u

FIG 6. A4 4’-dlchloro-2 2’-dlpyndme, 4 4’-dlchloro-2 2’-dlpyndm+lronIIIcomplex

380 m/i

FIG 7 A4 4’-dlethoxy-2 2’-dlpyndme, B4 4’-cbethoxy-2 2’-dlpyndme-lronm complex

260

300 Wavelength,

340

B-

38r

rnp

FIG. 8 A-4 4’-dlphenoxy-2 2’-dlpynchne; B4 4’-dlphenoxy-2 2’-dlpyndme-Iron111 complex

158

WM. M. BANICK,JR. and G. FREDERICKSMITH

rron’rr complex of 2:2’-dipyridine ratio value of 1.63 reported 1: IO-phenanthroline The

almost

derivative

in aqueous

mstantaneous

m glacral acetrc acid is almost identical

by Mannmg

and Harvey

for the

iront’r

to the mole complex

of

solution. fading

of the yellow-green

could possrbly be a result of the reduction

complex

of the rronnl

of the diamino by the chelation

reagent.

A 270 Wavelength,

Wavelength,

mp

FIG 9. A4 4’-dlcarbethoxy-2 2’-dqyrulme, B4 4’-dlcarbethoxy-2 2’-dlpyndme-lronm complex.

310

35( 3 mp

FIG 10. A--4.4’-dlphenyl-2 2’-dlpyrldme B4,4’dlphenvl-2,2’dlpyrldme-lronm compl:r.

Zusanunenfassung-2 2’-Dlpyrldm blldet mlt Elsen-III m Elsesslg emen stabllen gelb-grunen Komplex worm es em Ltgand-zu-Elsen mol-Verhaltms von 1,60 : 1 (3 : 2)glbt Die4 4’-dlsubstltmertenDerlvate bllden such emen gelb-grunen Komplex Losungen dleser Komplexe werden durch em starkes Absorptlonsmaxlmum lm 250-350 m,u Spektrumsgeblet charakterlslert Die spektrofotometrlschen Konstanten der Elsen-III Komplexe werden an dlesem Maximum ausgearbeltet Der Elsen-IIIKomplex des Dlphenyl-Derivats hat die grosste Molabsorptlvltat von allen studierten 22’-Dlpyrldmen R&um&-La 2 2’-dlpyndme donne avec le fer-III en milieu aclde ac&que glacial un complexe Jaune-vert stable dont le rapport mol&ulalre du hgand il fer est 1,60 : 1 (3 2) Les d&v& 44’&substltu& forment kgalement un complexe Jaune-vert. Les solutions de ces complexes sont caract6nles par un maximum d’absorphon pronon& dans la rkgglon du spectre 250 g 35Omp. On a tvalut, g ce ma-urn, les co&antes spectrophotom&lques des complexes dufer-III De toutes les 2:2’-dlpyrldmes qu’on a Ctud&es c’est le complexe fer-III du d&iv6 du dlphknyle qm a la plus grande absorptlvitC molaire REFERENCES 1 2 3 4 5

D L Mannmg and A E. Harvey, Jr , J. Amer Chem Sot , 1952, 74,4144 W. W, Brandt and W B Howsman, Jr, zbrd, 1954, 76, 6319. Frederick G Smith and Wm M Bamck, Jr , Analyt Chrm Acta, in press. Wm M Bamck, Jr, and G. Frederick Smith, zbld, in press J H Yoe and A L Jones, Ind Eng. Chem. Anal, 1944,16, 11