Indian Journal of ChemistryVol. 34A, June 1995, pp. 454-458

Synthesis and characterization of nonaisopropoxodizirconatotin(IV)complexes

Sanjay Mathur, Anirudh Singh" & Ram C Mehrotra

Department of Chemistry, University of Rajasthan, Jaipur 302 004

Received 18 October 1994; revised and accepted 2 January 1995

A number of novel heteroleptic nonaisopropoxodizirconatotin(IV) complexes of the type[Sn{Zr2(OPri)9}nCl4_nl(where n= 1-3) have been synthesised by the reactions of SnCl4 with KZr2(OPri)9'in benzene in requisite (1:1, 1:2, or 1:3) molar ratios. Replacement of chloride in these derivatives by anappropriate alkoxide affords volatile, heterobimetallic derivatives of the type [Sn{Zr2(OPri )9}n(OR)4.nl(R = Pr', But, n = 2 or 3). These novel heterometal alkoxides have been characterized by elemental ana-lyses, molecular weight measurements, IR and multinuclear (lH, l3C and 119Sn)NMR spectral studies.

Metal alkoxides continue to attract a great deal ofinterest in view of their potential as precursors forSoI-Gep-4 and MOCVD5 processes. In view ofthis, a number of reviews=" on synthesis and char-acterization of heterometal alkoxides of severalmetals throughout the periodic table have ap-peared recently. In spite of wide applications? oftin containing oxide ceramics, progress in the fieldof utilisation of stannic alkoxides as precursors hasreceived scant attention due to difficulties in theirsynthetic procedures 10,11.Despite the synthesis ofMSn2(ORW (M=Na, K; R=Et, Pri), in 1957 byWardlaw and coworkers, the heterometallic alkox-ides of tin(IV) remain relatively rare!'. Only dur-ing the last few years a number of interesting he-terometallic alkoxides of tin(IV) have been report-ed and some of these have been characterised bysingle crystal Xeray diffraction studies 14-17.

In continuation to our recent report'" on alko-xoaluminates of tin(IV), we report in this papersome newly synthesised nonaisopropoxodizircona-totin(IV) complexes.

Materials and MethodsStringent precautions were taken to exclude

moisture throughout the experimental procedure.Tin tetrachloride (Aldrich) was distilled

(114°/756 mm) before use. Zirconium isopropox-ide isopropanolate, Zr(OPrikPriOH, and alumini-um isopropoxide, Al(OPri h, were prepared byliterature methods".

Zirconium was estimated as Zr02 after precipi-tation as mandelate and ignition to oxide. Tin inthe filtrate was estimated as 8002 by ignition ofthe precipitated cupferrate.

Isopropoxy contents were estimated by an oxid-imetric method 19 using NK2Cr207 solution in12.5% H2S04, Chloride was estimated byVolhard's method/",

The infrared spectra (4000-200 cm-I) were re-corded as Nujol mulls using CsI optics on CARLZEISS JENA specord M80 spectrophotometer.The lH (89.55 MHz), l3C (22.49 MHz), and 119Sn(33.35 MHz) NMR spectra were recorded atroom temperature on a JEOL FX90Q spectro-meter. Il9Sn NMR chemical shifts were measuredusing SnMe4 as external reference. The molecularweights were determined ebullioscopically in ben- I

zene using GallenKamp ebulliometer with thermis-ter sensing.

Synthesis of heterobimetallic alkoxides of tin(IV)In view of similarities in the procedures for syn-

theses, only typical preparations are described be-low, and details of analytical data and some physi-cal data are listed in Table 1.

Preparation of[Sn{Zr2( OPf)9lzCh ](Ib)Potassium nonaisopropoxodizirconate obtained

by the reaction of potassium isopropoxide (pre-pared by reacting potassium (0.38 g, 9.77 mmol)and isopropyl alcohol) with Zr(OPri)4.PrcOH (7;58g, 19.55 mmol) in a mixture of isopropyl alcohol(- 5 ml) and benzene (-15 ml] followed by remo-val of the volatiles) was dissolved in benzene ( -20 ml) and added slowly to a solution of SnCl4(1.27 g, 4.86 mmol) in benzene ( - 15 ml). Afterstirring the reaction mixture for - 6 h, the precipi-tated KCI (0.70 g, 9.38 mmol) was filtered off.The removal of volatiles from the filtrate under

MATHUR et al.: STUDIES ON SOME NONAISOPROPOXODIZIRCONATOTIN COMPlEXES 455

Table I-Analytical, l19Snchemical shifts and physical data of new heterometallic alkoxides of tin(IV)

Product" Yield" Volatility Found (Calcd), % 119Snchemical Mol.Wt.(OC/mm) shifts in C6H6 Obs.

Sn Zr AI OPri Cl (lI,ppm) (Calc.)

[SnZr2CI3(OPri)9] (Ia) 90 d 12.5 19.5 56.1 11.1

(undistilled) (12.63) (19.42) (56.61) (11.34) (939)

[SnZr4Cl2(OPri)18] (Ib) 70 180/0.1 7.2 22.6 65.2 4.2 -588.66 1708'(7.33) (22.55) (65.73) (4.39) (1618)

[SnZr6Cl(OPri)d (Ie) 65 205/0.1 5.1 23.9 68.9 1.4 -647.35 2380(5.17) (23.83) (69.46) (1.54) (2299)

[SnZr4(OPriho] (Id) 60 210/0.1 7.0 22.1 70.1 -624.16 1830(7.13) (22.90) (70.97) (1665)

[SnZri OPri)18(OBu'h] (Ie) 65 215/0.1 6.8 21.7 62.2 -635.36 1867(7.00) (21.54) (62.82) (1693)

[SnZr6(OPri)28] (If) 70 200.10.1 5.0 23.6 70.7 -633.31 2481(5.12) (23.58) (71.30) (2321)

[SnZr6(OPrib(OBu')] (Ig) 60 200/0.1 4.9 23.3 68.0 -634.62(5.09) (23.44) (68.34) (2335)

[AISnZr6(OPri)31]c (lIa) 98 b 4.6 21.7 1.0 71.9 -633.45(undistilled) (4.70) (21.68) (1.07) (72.55) (2525)

"All are white soft solids except the derivative Ia which is a highly viscous liquid; "disproportionates into Al(OPrih and[SnZr 6(OPrihs]; cthe instability of this product depicted by its dissociation into Al(OPri)3 and [SnZr6(OPrihs] (If) and hence, thealmost identical l19Sn chemical shift (-633.45 ppm) with that observed for (If) appears to indicate a similar dissociation in solu-tion also; ddecomposed; ·yields refer to sublimed product unless otherwise stated.

reduced pressure (1 mm) yielded a white soft solid[Sn{Zr2(OPri)9!zCI2].The compound was purifiedin 70% yield by sublimation at 180°CI0.1 mm.

In an analogous procedure, compoundsof compositions [Sn{Zr2(OPri)9}CI3] (Ia) and5n{Zr2(OPri)9hCI] (Ic) were prepared in quantita-

tive yields starting from SnCl4 and KZJ,"2(OPri)9inappropriate molar ratios.

Preparation vf[Zn{Zr2( OPI)9lz( OPI}z] (Id)To a benzene (20 mI)solutioJ\of[Sn{Zr2(OPri)9!zCI2]

(7.36 g, 4.54 mmol) was added slowly, a benzene( - 10 ml) suspension of KOPri (prepared by react-ing potassium (0.35 g, 9.10 mmol) with isopropylalcohol (- 5 ml) followed by removal of excess'isopropyl alcohol). The reaction mixture was ref-luxed for - 1 h, after stirring for - 4 h. The pre-cipitated KCI (0.64 g, 4.28 mmol) was removed byfiltration. The volatiles were removed from thefiltrate under reduced pressure (1 mm) to yield thetitle product (7.72 g, 98%) as sticky solid, whichwas purified by sublimation at 210%.1 mm in60% yield.

In a similar procedure, the reaction of[Sn{Zr2(OPri)9lzC12] (6.96 g, 4.30 mmol) with

KOBu' (0.96 g, 8.59 mmol) in refluxing benzeneyielded [Sn{Zr2(OPti)9lz(OBut)2](6.9 g, 95%) as awhite soft solid (b.p, 215%.1 mm; yield, 65%).

The following compounds were also preparedin the same manner as described above startingfrom Ie and KOR (R = Pri or But).

[Sn{Zrz(OPri)9b(OPri )] (If): from Ie (6.36 g; 2.76. mmol) and \KOPr1 (0.27 g, 2.75 mmol), yield6.4 g(94%).

[Sn{Zr2(OPri)9h(OBut)] (Ig): from Ie (4.67 g, 2.03mmol) and KOBu,t (0.22 g, 2.03 mmol),yield 4.3 g(90%). The analytical data are summarized inTable 1.

(If) has also been prepared by the reaction of[Sn{Zr2(OPri)9lz(OPri}z] (Id) (3.71 g, 2.22 mmol)and Zr(OPrikPriOH (1.73 g, 2.23 mmol) in ref-luxing benzene. Yield 4.6 g, (94%). Analysis:[Found Sn 5.0, Zr 23.6, OPr; 70.7; Calc. Sn 5.12,Zr 23.58, OPri 71.30%].

tCaJculated on the basis of potassium metal used.

456 INDIAN J CHEM, SEe. A, JUNE 1995

Attempted preparation Of[{Zr2( OPI)9bSn{A~ OPI)411(lIa)

To a benzene ( - 20 ml) solution of[Sn{Zr2(OPri)9bCl] (8.59 g, 3.74 mmol) was addeda suspension of KAl(OPri)4 (freshly prepared bythe reaction of potassium (0.14 g, 3.74 mmol) andAl(OPrih (0.76 g, 3.72 mmol) with isopropyl alco-hol (- 5 mI) in benzene, followed by removal ofvolatiles) with continuous stirring. The reactionmixture after stirring for - 3 h was refluxed for- 1 h. The precipitated KCI (0.25 g, 3.35 mmol)was filtered off. The volatiles were stripped offfrom the filtrate under reduced pressure (1 mm) toyield (9.3 g, 98%) [{Zr2(OPri)9bSn{Al(OPri)4ll as asoft solid.

lH NMR (CDCI3, b ppm):/b 1.21 (d, J=6 Hz,6H), 4.28 (Sept, J = 6 Hz, 1H), 13C PH} NMR(COCl3): b 24.37, 26.16, 27.46, (~-carbon), and66.47,67.87,70.53 (a-carbon).

119SnNMR (C6H6): b - 633.45 ppm, On heatingthe above compound in vacuo (0.1 mm), it dispro-portionates at 190°C yielding AI(OPri)3 and on in-creasing the temperature to 210°C a pale yellowsolid sublimes which on analysis gave: [Found Sn4.9, Zr 23.8, or- 71.1 Calc. for[Sn{Zr2(OPri)9bOPri] I Sn 5.12, Zr 2358, OPri71.50].

Structurally relevant infrared spectral data(ern - I) for the complexes synthesized during thepresent investigations are given below:

Ia: 305 v(Sn-Cl); 540, 565 v(Zr-O); 585,675, 710 v(Sn -0); 945, 970, 1000, 1015v(C - 0); 810, 890,1150,1170 v(alkoxy).

Ib: 320 v(Sn-CI); 555, 585 v(Zr-O); 590,680, 710 v(Sn - 0); 930, 960, 1010, 1030v((C - 0); 805, 835,1150, 1170 v (alkoxy).

Ie: 335 v(Sn-CI); 520, 570 v(Zr-O); 575,665, 700 v(Sn-O); 920,. 955, 1015 v(C-O);820,855, 1125, 1170 v(alkoxy).

Id: 535, 565 v(Zr-O); 585, 670, 705v(Sn-O); 940, 965, 1060, 1010 v(C-O); 815,840, 1125,1160 v (alkoxy).

Ie: 540, 585 v(Zr-O); 595, 660, 675v(Sn - 0); 940, 975, 990, 1030, 1055 v(C - 0);795,825,1115,1140,1170 v (alkoxy);

If: 570, 595 v(Zr-O); 600, 665 v(Sn-O);935, 960, 990, 1005 v(C-O); 805, 830, 1130,1100 v (alkoxy).

Ig: 560, 590 v(Zr-O); 585, 680, 725v(Sn-O); 950, 970, 1010, 1030 v(C-O); 820,850, 1135,1180 v (alkoxy).

lIa: 480. 495 v(Al- 0); 535, 570, 590

v (Zr-O); 940, 960, 1030 v (C - 0); . 830, 860,1100,1150,1165 v (alkoxy).

Results and DiscussionInteraction of SnCl4 and KZr2(OPri)9 in differ-

ent molar ratios in benzene can be represented bythe following equation:

SnCl4 + nKZrz(OPri)9 -+ [Sn{Zr2(OPri)9InCl4_nl+nKCH

(Ia) n= 1; (Ib) n=2; (Ie) n=3

Replacement of chloride from mono and dichloroderivatives (Ib and Ie) with alkoxo groups affordedproducts according to following general equation:

[Sn{Zr2(OPri)9InCI4_n]+ (4 - n)KOR ~

[Sn{Zr2( OPri)9In(OR)4_n]+ (4-n)KCH

(Id) R=Pri, n=2; (Ie) R=Bu', n=2

(If) Rr=Pr', n= 3; (Ig) R=Bul, n= 3

The presence of free isopropanol has to beavoided in the above preparations, as the deriva-tive Zr( OPri4·Pr()H tends to crystallize out fromthe reaction mixture.

The interaction of Ic with KAl(OPri)4 in equi-molar ratio in benzene provided a derivative ofcomposition [Sn{Zr2(OPri)9b{Al(OPri4)](Ila), whichon heating under reduced pressure (190-21O°C/0.1 mm) affords [Sn{Zr2(OPri)9h(OPri)] andAI(OPri)3:

(Ic)+ KAl(OPri)4 -(Ua)+ KCI ~!~,vacuo

[Sn{Zr2(OPri)9b(OPri)]+ Al(OPri)3. (lIb)

The derivative (Ifb) could also be prepared bythe reaction of Id with Zr(OPrikPr()H in 1:2molar ratio in refluxing benzene and identified byelemental analyses and NMR spectral studies (seeExperimental section). These observations tend toindicate the reluctance of tin atom in this systemto achieve eight coordination state.

All these new heterometaI alkoxides (Table 1)are initially white soft solid which solidify slowlyand develop a yellowish tinge on storage. Most ofthese derivations could be volatilized unchangedin quantitative yields under reduced pressure, withthe exception of Ia which was obtained as a vis-cous oil, and on heating in vacuo, it disproportion-ated liberating SnCl4 and leaving a solid residue(OPr~ 36.4%; CI 6.70; Sn+Zr mixed oxide:41.3%).

MATHUR et af.: STUDIES ON SOME NONAISOPROPOXODIZIRCONATOTIN COMPLEXES 4YI

Structurally significant infrared spectral (4000-200 em -1) data of these hetero-(bi- or tri- )metallicisopropoxides have been interpreted on the basisof published data on metal alkoxides++'. For ex-ample, the bands characteristic for v (? C - O)Mappear in the range 1170-930 cm-I, whereasv(AI-O) and v(Zr-O) have been observed inthe range 720-410 em - I. On the basis of earlierobservations of alklytin alkoxides'", the absorp-tions in the range 710-535 em -I could be as-signed to v ((Sn - 0) vibrations. The chloro com-plexes exhibit additional bands in the region 335-305 em - 1 assignable to Sn - CI stretching frequen-cies26•27•

Despite the possibility of inequivalent nature ofisopropoxy groups in the possible structures(Structure I) for the new derivatives, the roomtemperature IH NMR spectra (in CDCI3) of la, Ib,Ie, Id and If reveal a doublet (J = 6Hz) at b 1.23,1.20, 1.22, 1.18 and 1.23 and a septet (J = 6 Hz)at b 4.31, 4.27, 4.22, 4.29 and 4.29 ppm, respect-ively due to gem-dimethyl and methine protons.These observations indicate rapid exchange (onNMR time scale) between terminal and bridgingisopropoxy groups in the derivatives at roomtemperature.

The IH NMR spectrum of [Sn{Zr2(OPri)9b-(OButh] displays three peaks at b 1.29, 1.25,. 1.16due to gem-dimethyl protons, whereas in the caseof [Sn{Zr2(OPri)9h(OBut2)], two doublets (J = 6 Hz)at b 1.21 and 1.29 ppm are observed. The me-thine protons in both the cases appear as an aver-age septet (J = 6 Hz) at b 4.21-4.22 ppm. The tert-butoxy protons appear as a singlet at b 1.36 ppm.

In an attempt to observe better resolution in theresonances arising from isopropoxy groups presentin different (terminal-, 1l2-' and 1l3-0Pri) environ-ments, the 1H NMR spectra of a few typical deriv-atives were also recorded at low (0 to - 65°C)temperatures. For example, on cooling the samplesIe and Id to - 65°, the peaks due to gem-dimethylprotons are resolved into three doublets (J = 6 Hz)for Ie at b 1.14 (terminal), 1.17 (1l2-0Pri), and1.28'(1l3-0Prij. However, for the derivative Id onlytwo doublets (J = 6 Hz) at 6 1.12 and 1.20 ppmcould be observed. The methine protons in bothappeared as an average septet (J = 6 Hz) at 6 4.22ppm.

The l3C NMR spectra (in benzene) of the deriv-atives la, Ib, Ie, Id and If exhibit two peaks foreach 13- and a-carbon atoms at 6 23.57-26.49,26.43-27.46 and 62.28-70.39, 69.28-74.97 ppmdue to terminal and bridging isopropoxy groupsrespectively. The derivatives Ie and Ig show sig-nals at b 25.46-27.46 and 71.18-71.29 ppm due

(IB)

Cn= 2 or 3 and X = Cl,oprl or OBut)

Proposed stucture of [{Zr2(OPri)ylSnCI31 (IA) and[{Zr2(OPriylnSnX4-nl (IB)

to 13- and a-carbon atoms of the 0C(CH3)3groups.

All the new complexes (Table 1) are character-ized by high-field sharp resonances (6 - 588.56 to- 647.35 ppm) in their 119SnNMR spectra. Forexamples of the type (X = CI (Ib), Of'r' (Id), andObu' (Ie)), a correlation appears to exist for the119Snchemical shifts and the extent of donationfrom 'X' into the empty 'd orbitals on the centraltin atom. For example, the chemical shifts, in-crease in the sequence CI < OPri < OBut.

However, the 1l9Snchemical shifts increase forthe series [Sn{Zr2(OPri)9hX] (X=CI (Ie), or-: (If)and Olsu' (Ig)) do not appear to follow such a

458 INDIAN J CHEM, SEC. A, JUNE 1995

trend. Unchanged volatilization of these tri-deriva-tives lends support to their identity, but the 119Snchemical shifts for these appear to conform moretowards hexa-coordinated state for tin, whichcould be ascribed to some lengthening of the tin-isopropoxy bonds arising from steric congestion insuch molecules. Interestingly, the 119Snchemicalshifts have been. observed in the derivative[SnlAI(OPri)4b(OBu')j9 atb - 668.40 ppm, whichis more consistent with a seven-coordination fortin (Structure IB).

AcknowledgementOne of us (SM) is thankful to the CSIR, New

Delhi, for the award of a senior research fellow-ship.

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