Indlan JourDal of ChemistryVol. 16A, JUDe 1978, pp. 488-490

Polyanion Compounds of Iron (III) AcetateRAM C. PAUL, RAMESH C. NARULA & SHAM K. VASISHTDepartment of Chemistry, Panjab University, Chandigarh 160014

Received 25 August 1977; accepted 14 February 1978

Compounds of compositions, Fe(N03)(OH)(CH3C02).CHaCO.H Fe(NCS)(OH)(CH3CO.).-(CH3).CO, Fe(BF.)(OH)(CH3C02) and Fe(CIO.)(OH)(CH3C03) have been prepared and charac-terized on the basis of infrared, thermal analysis, molar conductance and magnetic susceptibi-lity measurements.

IRON (III) chloride is reported to react withacetic acid to form chlorobis(acetato)iron(III),FeCI(CHsC02)2 compounds--" with the elimina-

tion of HCI. Reinvestigations of this reactionreveals that no hydrogen chloride is evolved andinstead acetyl chloride is formed". Furthermore,instead of the chlorobis(acetato) moiety, a newformulation containing chlorohydroxoa ceta toiron (III)unit, FeCI(OH)(CH3C02).CH3C02H.0.5H20 (I), hasbeen proposed'' on the basis of its reactions withdifferent basess. In order to understand more fullythe nature of chlorohydroxoacetatoiron(III) unit,chloro group in (I) has been substituted by poly-anionic ligands, nitrate, thiocyanate, tetrafluoro-borate and perchlorate. Compounds thus obtainedare reported here.

Materials and MethodsChemical analyses and physical measurements

were made as already described+, Sulphur contentin thiocyanate compound was estimated as sulphate.

Fe(N03)(OJH)(CH3C02).CH3C02H, (II) - Thi com-pound, FeCl(OH)(CH3C02).CH3C02H.0·5H20, (.1)(10 mmoles) was dissolved in methylene chloride(60 ml) and an equivalent amount of AgN03

(10 mmoles) dissolved in. the mi~i!mum amount ofacetonitrile was added to It dropwise. The contentswere stirred for 2 hr and the precipitated AgCl wasfiltered out. The filtrate was concentrated in uaouoto get a brick-red residue. It. was crystallizedfrom a mixture of methylene chlonde and petroleumether. The crystals, on keeping for some days or ondrying in vacuo, crumble down to give fine powder(Found: C, 19·5; H, 2'9; Fe, 22·0. C4H8N08Ferequires C, 18·9; H, 3·1; ~e, 22·.0%). The compoun.dstarts decomposing at 82. ThiS slIghtly ~ygroscoPlccompound is soluble in methylene chlonde, chloro-form, tetrahydrofuran and acetonitrile. but is onlyslightly soluble in nitrobenzene and Dltromethan~.It is insoluble in non-polar solvents. The magneticmoment (fLeff) at room temperature is 4·8 BMper Fe atom.

Fe('NCS)(OH)(CH3C02).(CH3)2CO, (IV) - Com-pound (I), (10 mmoles] was dissolved i~ acetone(50 ml) and a solution of potassium .th!Ocyan~te(10 mmoles) in acetone was added to It dropwise.

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The dark red mixture was stirred for ",48 hr.The solution was evaporated in vacuo, the residueobtained was stirred with a large amount of etherand the solution filtered to remove solid RCI.The filtrate was evaporated in vacuo, the complexobtained was crystallized from a mixture of acetoneand n-pentane and then dried in vacuo (Found:C, 28'9; H, 3'9; N, 5'8; S, 12·8; Fe, 22·5.C6H1oN04SFe requires C, 29·0; H, 4·0; N, 5·7;S, 12·9; Fe, 22'5%). The hygroscopic black com-pound melts with decomposition at 101°. Thesolubility trends are the same as found in thecorresponding nitra te compound. !left value at roomtemperature is 4·37 BM.

Fe (BF4)(OH) (CH3C02), (V) -Silver t etrafluorobo-rate (10 mmoles) solution in the minimum amountof acetonitrile was added to a solution of (I), (10mmoles) in ether (60 ml). The mixture was stirredfor 6 hr and AgCl removed by filtration. Thefiltr~te was treated with n-pentane to precipitate outthe Iron compound. It was filtered and the residuewashed with ether and dried in vacuo (Found:C, 11·0; H, 2·0; Fe, 25·6. C2H4BF4Fe requires C,11·0; H, 1·8; Fe, 25'6%). The compound meltswith decomposition at 210°. The light brick-red~ompound is non?ygroscopic. Its solubility is lowin polar solvents like methylene chloride, chloroform,nitrobenzene and nitrornethane. It is soluble inTHF, acetonitrile and DMSO. The !leff value is4·0 BM.

Fe(Cl04)(OH)(CH3C02). (VI) - Silver perchlorate(10 mrnoles) dissolved in minimum amount ofacetonitrile was added dropwise to a solution of (I)(10 mmoles) in ether (60 ml). The rest of theprocedure is the same as in fluorobora te complex(Found: C, 10'5; H, 1·8; Fe, 24·0. C2H4ClO Ferequires C, 10·4; H, 1'7; Fe, 24'1%). The c~m-pound decomposes quite vigorously at --,220°. Thesolubility trends are similar to those of fluorobora tscomplex. The fLeff value is 3·54 BM.

All the manipulations were done on a vacuumline and under an atmosphere of dry nitrogen.

Results and DiscussionAnthranilic and salicylic acids (XH) react with

FeCl(OH) (CH3C02).CH3C02H.0·5H20, (I), to form

PAUL et al.: POLYANION COMPOUNDS OF Fe(II!)

substitution products of the type FeCIX2.H20 andas a result both hydroxo and acetate groups in (I)get replaceds. The chloro group in (I), however,remains intact. In order to understand more fullythe nature of chlorohydroxoacetatoiron(III) unit,chloro group in (I) has been substituted by poly-anionic ligands having tendency to form ioniccompounds. If coordinated, these polyanions canact as monodentate, bidentate or bridging ligands.lR spectra of all the compounds (Table 1) show abroad band in the region 3300-3500 crrr? which may'be assigned to the hydroxo group" .. In addition,.the compounds show va.COO and v.COO bands dueto the coordinated acetate group in the regions1575-1580 and 1440-1450 ern"! respectivelyt-".

Silver nitrate reacts with (I) to give Fe(N03)-(OH)(CHaC02).CH3C02H, (II). Compound (II), onkeeping at 150°/10-3 torr for 6 hr, loses acetic acidto give Fe(N03)(OH)(CH3C02), (III). The nitrato'Compound (II) shows bands due to monodentatenitrato group9-11 and Fe-O mode (Table 1). Inaddition, a band at 1675 crrr" due to coordinatedacetic acidl2 is also observed. The IR spectrum of·(III) shows almost no change in the position ofbands due to acetato and hydroxo groups but the'13 bands of (nitrate group) (II) at 1440 and 1280.cm"! disappear. These are replaced by new bandsat 1530 and 1250 cnr- with a Llv3 value of 280'Cm-l which indicates that (III) has probably abidentate or bridging nitra to group9-11.

Molecular weight of (II) in nitrobenzene is doublethat of the formula weight but this cannot beconsidered very reliable as (II) has a low solubility.A precipitate starts separa ting out On increasing the-concentra tion of (II) in nitrobenzene. Compound(II) and subsequent ones are quite soluble in aceto-nitrile, DMF, DMSO and THF but due to theirtendency to form complexes, the molecular weightscannot be determined. Molecular weight of (II)in DMSO is 1/4 of formula weight. The low valuesof its molar conductance (1'9 and 9·1 cm2 ohrrr?mole+) in nitrobenzene and nitromethane, respec-tively. show that compound (II) behaves as anon-electrolyte in solution.

Compound (II), on heating in air, loses a moleculeof acetic acid between 50° and 190° in an exo-

thermic fashion. The residue then loses all theorganic matter and oxides of nitrogen together inone exothermic step extending up to 400° to leavebehind 1/2 Fe20a (Fig. 1, curve a).The thiocyanate complex, Fe(NCS)(OH)(CHaCOz).-

(CH3)2CO, (IV), shows IR band at 1660 cm+,typical of coordinated acetone. The positions ofbands due to thiocyanate group (Table 1) indicatethat it is bonded through its terminal nitrogenatom10,14,15. The vC=N appears as a strong bandat 2040 crrr? with a strong shoulder at 1995 crrr'!arising due to crystal effects in solid state. Aband at 320 crrr? in the spectrum of IV istentatively assigned to vFe-N because no such bandis present in other compounds discussed here.

Compound (IV), on heating in vacuo (at 160°/10-3 torr) loses acetone. The IR bands due to

160

140

120

100,..,e-e'"

60

b40

20

o 100 200 300 400 SOO 600 700Ttl1)peratlll't ('°c)

Fig. 1 - TG curves for iron(III) compounds with poly-anion ligands [a, nitrate; b, thiocyanate; c, tetrafluoroborate v

TABLE 1 - IMPORTANTIR BANDS (cm") OF IRON(III) COMPOUNDS

Compound vFe-O* v and I) Fe-O Polyanion modes

Vl Vz V3 v,,Fe(N03)(OH) (CH3CO.).CH3CO.H 530wb 380sh, 360s, 350s. 1032m 802w, 14405, 1280s 766m.

305w. 285w. 255w. 838w 122m230m

Fe(NCS) (OH) (CH3CO.). (CH3)2CO 525wb 370-350sb. 305w. 2040sb, 470m 840w290w. 275w. 255w. 1995sh230m

.Fe(BF.) (OH) (CH3CO.) 525wb 375-360sb, 300w. 765m 352sh 1115sh, 1095s. 530m280m. 250w. 220m. 10405210m

,Fe(CIO.) (OH)(CH3C02) 515wb 365s, 350sh, 300w, 925m 460w 1150s. 11005. 625m280w. 250w. 220m 10455

*In hydroxy bridged ring.

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INDIAN J. CHEM., VOL. 16A, JUNE 1978

acetone are missing in the residue but other bandsshow little change. Heating in air proceeds similarlywith the loss of acetone up to 190° (Fig. 1,curve b). The last endothermic step between 3500

and 620° corresponds to the loss of 1/2 H20 toleave behind 1/2 Fe203 (Fig.!, curve b).

The molar conductance of (IV) in nitrobenzene(7·6 cm2 ohrrr'! mole'<) and nitromethane (16·7cm2 ohrrr ' mole-I) show that it undergoes a slightdissociation in these solvents.

The IR spectrum of tetrafluorobora te complex,Fe(BF4) (OH) (CHaC02) , (V), shows that the poly-anion is coordinated to the metal a tom (Table 1)and the shape of V3 is intermediate in type betweenthose of free and a covalent fluoroborate'". Inaddition to bridging acetate and hydroxo groups, itappears that the fluoroborate group bridges to givepolymeric structures in the solid sta te. The lowersolubility of (V) supports its polymeric nature. Thesemicoordination in (V) is further evidenced by themolar conductance'? value of 14·1 cm2 ohrrr+ mole"!in nitromethane. Molecular weight of (V) in DMSOis 1/2 of its formula weight.

The compound (V) on heating at 160°/10-3 torrleaves behind a black residue devoid of fluorobora tegroup. The volatile liquid in the trap gives IR bandsof ionic tetrafluorobora te. Decomposition in airproceeds almost similarly, first an endothermic stepoccurs from 60° to 180° corresponding to a weightloss equivalent to HBF4 (Fig. 1, curve c). Next,an exothermic step occurs which is attributed to theloss of organic matter to give 1/2 Fe20a at 360°.

The perchlorate, Fe(CI04)(OH)(CH3C02), (VI),shows IR bands of coordinated perchlorate groupl6(Table 1). The structure seems to be similar to thatof compound (V). Its molar conductance value is19·1 cm2 ohrrr" mole-l in nitromethane. The com-pound decomposes violently at about 220°.

490

The room temperature magnetic moment valuesare much lower than those normally observed(5'92 BM) for high-spin iron(III) compounds. Thissuggests that the present compounds, like manyother carboxylates", are antiferromagnetic.

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