Indian Journal of ChemistryVol. 30A, September 1991, p .793-798

Halide alk xides of yttrium, gadolinium, erbium and ytterbium

R C Mehrotra*, J M Batwara, U D Tripathi & U M Tripathi

Chemical Laboratories, University of Rajasthan, Jaipur- 302004

Received 2 April 1991 ; accepted 10 May 1991

Reactions of ytt ium, gadolinium, erbium and ytterbium isopropoxides with acetyl halides (chlo-ride and bromide) in different molar ratios lead to respective halide isopropoxides containing in-creasing amounts ester in the form of addition products. Chloride isopropoxides have also beenprepared by radic interchange reactions between lanthanide trihalides and triisopropoxides. A typi-cal 'gadolinium bre 'is observed in the solubilities of these products. The reactions of lanthanide t-butoxides with ace I chloride are rather complex; the lanthanide chlorides formed initially tend toreact with the side- roduct t-butyl acetate to form acetoxy derivatives, indicating an interesting varia-tion with the chang in the electronegativity values of the metals.

Halide alkoxides of m tals including lanthanides Iand yttrium? serve as important intermediates inthe synthesis of hetero olymetal alkoxide systems,which are proving to e excellent precursors forsuperconducting and ther oxide ceramics. Exist-ence of a number of c oride z-butoxies of yttriumhave been reported+i the reactions of YCl3 withNaOBut in differ nt molar ratios. TheNd6(OPri)17CI, isolate by the reaction of NdCl3with NaOl'r" in 1:3 lar ratio, has been report-ed" to have an interesti g structure. However, theformation of Nd(OPri) , reported" earlier has beenreconfirmed recently" in our laboratories by thereaction of crystallize NdCI3.3PriOH with threemoles of KOPri; this tris-isopropoxide has beenconverted" into Nd6( Pri)17CI, by reaction withacetyl chloride in 6:1 olar ratio. We present her-ein the results of 0 investigations on the reac-tions of lanthanide is propoxides and t-butoxideswith acetyl halides. attempt has also beenmade to correlate interesting variations ob-served with the electr egativity of the metal.

Following methods are available in the litera-ture" for the prepar tion of halide alkoxides ofmetals: (a) reaction f dry hydrogen halides onmetal alkoxides; (b) eaction of acetyl halides onmetal alkoxides; and ( ) radical interchange reactionsbetween anhydrous alides and metal alkoxides.Method (a) being fa exothermic tended to leadto precipitation of t e chloride isopropanolates,LnCI3.3PriOH, inst of chloride isopropoxides.The latter two me ods have, therefore, beenpursued for the prep ation of halide alkoxides ofthe lanthanides.

Materials and MethodsAdequate precautions were taken to exclude

moisture, while carrying out the reactions.Lanthanide chlorides were obtained by heating

a mixture consisting of hydrated lanthanide chlo-ride and ammonium chloride in a current of dryhydrogen chloride and chlorine gas under stricttemperature control to avoid the formation of fus-ible oxychloride (LnOCI). Acetyl chloride andbromide (BDW AR) were freshly distilled. Theisopropoxides of yttrium, gadolinium erbium andytterbium were prepared by reported proce-dures/-".

Metals were weighed as oxides after igniting theprecipitated oxalates. Halides were determined assilver halides and isopropoxy groups were esti-mated by dichromate oxidation". Acetoxy groupwas estimated by titrating the weighed samplewith N/10 caustic soda using phenolphthalein asindicator.

Reactions of yttrium, gadolinium, erbium andytterbium isopropoxides and t-butoxides with ace-tyl halides in different molar ratios (1:1, 1:2, 1:3,1:excess): General procedure

Requisite amount of acetyl halide was added toa cold solution of the respective isopropoxide inbenzene. The reaction of gadolinium isopropoxideand acetyl halide led to the formation of a whiteprecipitate immediately on mixing the reactants.However, no precipitation occurred in the reac-tions of yttrium, erbium and ytterbium isopropox-ides with acetyl halide. All the reaction mixtureswere shaken at room temperature for some time,

793

C.Ln(OPri)3+ 3CH3COX

(or excess)

LnX3·

INDIAN J CHEM, SEe. A, SEPTEMBER 1991

rollowed by refluxing for 1 hr at SO-90°C. Thevolatiles were then removed under reduced pres-sure ( - 2soC/0.l mm).

Radical interchange reactions: General procedureFreshly prepared anhydrous lanthanide chloride

(1-2 g) were suspended in dry benzene. To thiswas added a respective isopropoxide (stoichiomet-ric amount) in benzene. The reaction was slightlyexothermic. On refluxing turbid solutions becameclear in the reaction of yttrium, erbium and yt-terbium chlorides, whereas a white suspension re-mained in the reaction of gadolinium chloridereactants. Prolonged refluxing did not bring aboutany change in the above solutions. The solventwas removed under reduced pressure and pro-ducts finally dried at - 2soC/0.l mm. Quantita-tive yields were obtained. The analyses of theproducts were almost unaltered after their recrys-tallization in two typical cases.

Reaction of anhydrous gadolinium chloride withisopropyl acetate

Freshly prepared anhydrous gadolinium chlo-ride (1.56 g) was added to freshly distilled isopro-pyl acetate (- 38 g). Exothermic reaction tookplace with slow dissolution of the chloride. Thereaction mixture was refluxed for 2 hr, the vola-tile fractions were then removed under reducedpressure and the product was finally dried at -2soC/0.l mm. A white solid (2.70 g) of the com-position, GdCI3.2CH3COOPri, sparingly solublein benzene was obtained. (Found: Gd, 33.S; CI,22.9, GdCl3.2CH3COOPri, requires Gd, 33.6; Cl,22.7%).

Results and Discussion

Reactions of lanthanide isopropoxides with acetylhalides

Reactions of lanthanide (Ln = Y, Gd, Er or Yb)isopropoxides with acetyl chloride and bromide(CH3COX) in different molar ratios yield pro-ducts according to Eqs. (1-4 ):

Ln(OPri)3+ CH3COCl ~ LnCl{OPrilz.(I)

O.5CH3COOPri + 0.5CH3COOPri ... (1)

Ln(OPri)3+ CH3COBr ~LnBr(OPrilz + CH3COOPri ... (2)

(II)

C.H.Ln(OPri)3+ 2CH3COX -

LnX2{ OPri).CH3COOX ... (3)(III)

794

... (4)

All these reactions are q ite facile and exother-mic in nature: and afford he products, (I)-(IV),corresponding in analyses and in quantitativeyields except in 1:3 molar r tios in which the iso-lated products tended to co respond in analysis toLnX2.7-2.8(OPri)03_0.22CH3C Ol'r' (when Ln = Gdor Er). It is noted that wi the gradual replace-ment of isopropoxide by more electronegativechloridelbromide group, th adduct forming tend-ency of the product with e liberated ester in-creases; the actual number f molecules of the es-ter which form adducts va es with the tempera-ture and pressure at whic these are removedfrom the products and the alyses reported here-in are of the products obt . ed at room tempera-ture ( - 2S°C) and 0.1 mm pr ssure.

A striking difference is 0 served in the solubi-lities of the products in be ene. All the productsformed in the reactions of y rium and gadoliniumare sparingly soluble, while those of erbium andytterbium are soluble. The r ason for this changein solubility of halide alkoxi es of lanthanides up-to gadolinium is not very cl ar. However, a sud-den change of many physic as well as chemicalproperties in the lanthanide eries beyond gadoli-nium has been mentioned' the Iiterature'P:". Asimple plausible explanation or the observed sol-ubility behaviour may be th change of structureof chloride-isopropoxides f lanthanides uptogadolinium, similar to the c ange in structure ofanhydrous chlorides of gado ium in comparisonto other lanthanides beyond g dolinium-Y".

It is evident that the halid alkoxides of lantha-nides have a tendency to for adducts with isop-ropyl acetate, which has be n confirmed by thereaction of isopropyl acetate with anhydrous lan-thanide chlorides (Eq. 5):

GdCl3 + 2CH3COOPri ....•GdC .2CH3COOPr'(excess) ... (5)

It may be observed that the reactions of lantha-nide isopropoxides with acet halides are similarto those reported in the prep ation of some thio-cyanates of titanium 19, niobium and tantalum/".

Radical interchange reactio of lanthanide iso-propoxides with chlorides

Radical interchange reactio have been used inthe synthesis of lanthanide c oride cyclopentadi-enides'". The formation and isolation of single

MEHROTRA et al.: HALIDE ALKOXIDES OF Y, Gd, Er & Yb

It is interesting to note that the reactions ofA1(Olsu'), with CH3COCI can be represented+ by

ide t-butoxides with acetyl Eqs (12-14).

stoichiometric produ ts in the reactions (1H4)suggests ready radic interchangeability. This hasbeen confirmed by study of reaction betweenlanthanide 'isopropo des and chlorides in differ-ent stoichiometric ra .os. It is observed that a fa-cile radical interchan e takes place and chloride-isopropoxides are ob ained in almost quantitativeyields. These reacti ns may be represented byEqs (6) and (7):

... (6)

... (7)

The products in th se cases (see Table 1) differfrom those obtained in the reactions of isopro-poxides with acetyl chloride in not having anycoordinated ester m ecules. The solubility differ-ence in gadolinium d erbium chloride isopro-poxides has already een explained elsewhere inthe paper.

Reactionschloride

The reactions of I thanide tris-t-butoxides withacetyl chloride show an interesting variation. The

reactions are facile in 1:1 molar ratio and yieldessentially monochloride products, LnCl(OButh.However, in 1:2 and higher molar ratios, the reac-tions can be represented in two grounds i.e., byEqs (8, 9; Table 2) and (10,11; Table 3):

Ln'( OBut)3 + 2CH3COCI ~Ln'Cl2( OBut).0.5CH3COOBut ... (8)

Ln'( OBut)3 + 3CH3COCl ~(or excess)

Ln'CI2( OOCCH3)·CH3COOBut

Ln"(OBut)3 + 2CH3COCl--+Ln"CI(OBut)(OOCCH3)

Ln"(OBut)3 + 3CH3COCl--+Ln"CI(OOCCH3h·0.5CH3COOBut

(where Ln'= Y, Yb and Ln" = Gd, Er)

... (9)

... (10)

... (11)

... (12)

Table 1 - Radical interch ge reactions of chlorides of yttrium, gadolinium, erbium and ytterbium with respective isopropoxides inisopropanol

Sl. Reactants Molar Product; yield(%) Metal(%) Chlorine(%) lsopropoxy(%)No. ratio and its nature

Found Found Found(Calc) (Calc) (Calc)

1. Y03 1:2 YCl(OPrih.l¥OH; 28.63 11.57 59.20y(OPrih (99.2) white (29.38) (11.71) 58.54)

crystalline solid

2. YCl3 2:1 YCI2(OJ>ri).1.5J>riOH; 28.60 22.64 48.13Y(OPrih (99.9) white solid (28.77) (22.44) (47.79)

3. GdCl3 1:2 GdCl(OJ>rih; 50.11 11.43 37.70Gd(OPrih (99.7) white solid (50.58) (11.39) (38.03)

4. GdCl3 2:1 GdCI2(OJ>ri); 53.91 24.77 20.10Gd(OPrih (99.6) white solid (54.74) (24.69) (20.57)

5. ErCl3 1:2 ErCl(OJ>rih; 51.21 11.15 36.20Er(OPri)3 (99.9) pink solid (52.13) (11.03) (36.84)

6. ErCl3 2:1 ErCI2(OJ>ri); 55.44 23.92 19.50Er(OPri) (99.4 ) pink solid (56.27) (23.85) (19.88)

7. YbCl3 1:2 YbCl(OPrihO.5J>riOH; 48.05 9.80 42.53Yb(OPrih (98) white solid (48.50) (9.94) (42.11)

8. YbCl3 2:1 YbCI2(OPri)I.5PriOH; 43.82 17.83 38.51Yb(OPrih (98.7) white solid (44.11) (18.08) (38.30)

795

INDIAN J CHEM, SEe. A, SEPTEMBER 1991

Table 2 - Reactions of yttrium and ytterbium t-butoxides with acetyl chloride in b nzene

Sl. Reactants Molar Product; yield(%) Metal(%) Cho rine(%) Alkali equivNo. ratio and its nature (mole)

Found ound Found(Calc) Calc) (Calc)

1. Y(OBU')3 1:1 YCl(OBu/)2; (98.9) 33.38 2.69 0.87CH3COCI white crystalline solid (32.86) ( 3.10) (1.00)

2. Y(OBu/h 1:2 YCI2(OBU/).0.5CH3COOBu/; 30.97 3.79 2.06CH3COCI (97.6) white solid (30.80) ( 4.46) (2.00)

3. Y(OBu/h 1:3 YCI2(OOCCH3)·CH3COOBu/; 27.41 0.56 2.84CH3COCI (97.0) white solid (26.55) ( 1.18) (3.00)

4. Y(OBU/)3 1:excess YCI2(OOCCH3)·CH3COOBu/; 26.88 1.34 2.91CH3COCI (89.6) white solid (26.55) ( 1.18) (3.00)

5. Yb(OBu/h 1:1 YbCl(OBu/h; (78.8) 61.91 2.10 0.90CH3COCI white crystalline solid (61.43 ) ( 2.59) (1.00)

6. Yb(OBU/)3 1:2 YbCI2(OBu/).0.5CH3COOBu/; 47.02 8.80 2.00CH3COCI (99.8) white solid (46.13) ( 8.91) (2.00)

7. Yb(OBu/h 1:3 YbCI2(OOCCH3)·CH3COO-Bu/; 41.68 ~.61 2.90

CH3COCI (99.3) white solid (41.29) (16.92) (3.00)

8. Yb(OBu/h 1:excess YbCI2(OOCCH3)·CH3COO-Bu/; 41.54 IP1 3.00

CH3COCI (98.3) white solid (41.29) (1r>.92) (3.00)

Table 3 - Reactions of gadolinium and erbium r-butoxides with acetyl chloride in be nzene

Sl. Reactants Molar Product; yield(%) Metai(%) Chl rine(%) Alkali equivNo. ratio and its nature (mole)

Found B)und Found(Calc) ( ralc) (Calc)

1. Gd(OBu/h 1:1 GdCl(OBu/h; (97.0) 46.80 1).40 1.00

CH3COCI white solid (46.42) (1l46) (1.00)

2. Gd(OBu/h 1:2 GdCI( OBu/X OOCCH3); (96.4) 48.20 1178 1.88

CH3COCI white solid (48.41) (lp.91) (2.00)

3. Gd(OBu/h 1:3 GdCI(OOCCH3h·0.5CH3CO- 42.70 ( .78 2.95CH3COCI OBu/; (99.3) whitt: solid (42.64) ( .61) (3.00)

4. Gd(OBu/h l:excess GdCI( OOCCH3h.0.5CH3CO- 43.01 ( .54 2.98CH3COCI OBu/; (90.6) white solid (42.64) (S .61) (3.00)

5. Er(OBu/h 1:1 ErCl(OBu/h; (98.8) 48.00 1 .00 1.00

CH3COCI pink solid (47.96) (1 .17) (1.00)

6. Er(OBu/h 1:2 ErCl(OBu/XOOCCH3); 49.36 1 .44 2.10CH3COCI (97.9) pink solid (49.97) (1 .59) (2.00)

7. Er(OBu/h 1:3 ErCl( OOCCH3h.0.5CH3CO- 44.20 Cl28 2.95CH3COCI OBu/; (98.5) pink solid (44.16) (936) (3.00)

8. Er(OBu/)3 1:excess ErCI( OOCCH3)2.0.5CH3CO - 44.71 930 2.98CH3COCI OBu/; (95.6) pink solid (44.16) (930) (3.00)

796

AI(OBUt)3+ 2CH3CO

AICldOO

MEHROTRA et al.: HALIDE ALKOXIDES OF Y, Gd, Er & Yb

AI(OBUt)3 + 3CH3COAIClo.7(OO

... (13)

... (14)

The reactions of N ~OButh and Pr(OBUt)3withCH3COCl are straigh orward'? and similar to thereactions of their isopr poxides, i.e.,

Ln{OBut)3+xCH3CO I~

Ln(OBut)3_xClx xCH3COOBut

(where Ln = Pr, Nd)... (15)

As reflected in thei electronegativity and otherrelevant characteristic , Gd and Er depict in gen-eral lesser electroposi ive behaviour than Yb andy. The observed varia .on in the reactivities of theabove two groups of etals, therefore, appears tobe in conformity with e corresponding reactionsof less electropositive and distinctly more elec-tropositive Nd and Pr.

Mechanism ofreactioBradley et aF4 s ggested that radical inter-

change plays an imp rtant role in the formationof halide-alkoxides. ul and coworkers25,26 havesuggested ionization f acetyl halides into acetyl-ium (CH3CO +)and h .de (X- ) ions.

In line with the su estions of earlier workers,the equilibria (16-18) may lead to the formationof halide alkoxides of I thanides:

Ln+{OR}z+R- +CH CO++X- ~

Ln{OR 2X+ CH3COOR

... (16)

... (17)

... (18)

Such equilibria . obviously be facilitated bythe higher electropo itive nature of lanthanides.Similarly the radical terchange reaction involvesa bimolecular mech .sm as represented by Eq.(19):

......_·(19)

In view of the markedly higher (+ I) inductiveeffect of the t-butoxy groups, the correspondingM-OBut bonds tend to be much less ionic thanthe corresponding M-OPri linkages and this tend-ency should be enhanced in halide derivatives ofthe types XaLn(OBut)3_a(where a= 1 or 2). Thisappears to be reflected in an entirely differenttype of reactivity which appears to be accentuatedby the electronegativity of the me-tal:Al{1.47)> >Gd, Er(1.11)> Yb, Y(1.11). Incontrast, the more electropositive, Nd/Pr /-butoxides (electronegativity values on Allred Ro-chow scale, 1.07) show normal replacement reac-tions characteristic of the isopropoxides of allthese metals.

AcknowledgementThe authors are grateful for financial assist-

ance by different funding agencies such as theDST, CSIR and UGC, New Delhi.

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INDIAN J CHEM, SEe. A, SEPTEMBER 1991

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