Goel, (Mrs) S.

Mehrotra, R. C.

Sharma, (Miss) C. K.

English

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IncUan Joul'Dal of Chemi8tryVol. 14A, November 1976, pp. 878·879Synthesis of Apparently Covalent Double Alkoxides ofRubidium & CaesiumR. C. MEHROTRA*, (Miss) C. K. SHARMA & (Mrs) S. GOELDepartment of Chemistry. University of Rajasthan. Jaipur 302004Received 30 April 19i6A number of volatile double metal isopropoxides of rubidium and caesium of the formulaeM[Al(OPrj).], M[Zr.(Opr)9]' M[Ta(Opr).] (where M = Rb or co, Cs.[Zr3(OPr')u]. Cs[Hf.(OPri).].Cs2[Hf3(opr),.] and Cs[Nb(OPri).] have been synthesized by the reaction of the respectivemetal alkoxides in different stoichiometric proportions in isopropanol. Tentative struc-tures based on NMR data have been suggested.SYNTHESIS of apparently covalent volatiledouble alkoxy derivatives of electropositivemetals lithium, sodium and potassiumv+ hasgenerated an interest regarding the synthesis ofcompounds of even more strongly electropositiveelements rubidium and caesium. Here we reporta number of apparently covalent double isoprop-oxides of Cs and Rb with AI, Zr, Ta, Hf and Nb.'Materials and Methods•... All the preparations were carried out underanhydrous conditions.Aluminium isopropoxide was procured from NCL,Poona. Benzene (BDH) and isopropanol (BDH)were dried as usual.Zirconium, hafnium, niobium and tantalum iso-propoxides were prep~red by t~e ammonia method="using the corresponding chlondes (Fluka AG).Zirconium, hafnium, niobium and tantalum wereestimated as oxides, Aluminium was estimatedas oxinate.The alkoxy groups were estimated by oxidationwith potassium dichromates.Preparation of double alkoxides of Rb and Cs-Rubidium or caesium isopropoxide was preparedby dissolving the corresponding metal in isopropanol.The resultant reaction was exothermic. The S0111-tion obtained was cooled to the room temperatureand stoichiometric quantities of AI{OPri)a, Zr{OPri)(,Hf(OPri)" Nb(OPri)5 or Ta(OPrih were added,The reaction mixture was refluxed for 1-2 hr.Excess of the solvent was removed by distillationand the product was dried in vacuo. The productscould be sublimed under reduced pressure. AI! a-lytical results are summarized in Table 1.Results and DiscussionThese reactions are facile and can be representedby following equations:M(OPri) -i-Al(OPrih~:\i[Al(OPri)413f(OPri) .J..2M'(OPri)4~:\f[:\I~(OP~i)9J:\f(OPri) ~-Ta(OPrih~:\I[Ta(OPri)6~*Present address: Vice-Chancellor. University of Delhi,Delhi 11 0007_8782Cs(OPri) +3M'(OPr )4~CS2[M\(OPr;)l(JCs(OPri) ~-Nb(OPrih~CSLNb(OPr;)6J(M = Rb or C5; M' = Zr or Hf)The products are white crystalline solids. sparinglysoluble in isopropanol and benzene. The compoundswere purified either by recrystallization from iso-propanol or by sublimation/distillation under reducedplessure in yields between 40 and 75% (Table 1).Ebullioscopic determination of molecular weightsof some of the present double alkoxides soluble inbenzene showed them to be monomeric,In the present series of the double isopropoxides,the solubility goes on increasing from lithium toTABLE 1- REACTIONS OF RUBIDIUM AND CAESIUMISOPROPOXlDES WITH AI. Zr, Hf, Nb AND Ta ISOPROPOXlDESReaction of Molar· b.p. Found 0/ (calc.)/0Rb or Cs ratio (cC/mm),isopropoxide (M:M' yield (%) Isoprop- Metalwith isoprop- oxy (M')oxide)DOUBLE lS0PROPOXIDES OF RbA1(OPri). 1:1 180-82%-2 67-69 i-7445 (67-76) (i-73)Zr(OPri).PriOH 1: 2 160-630/0-1 66-48 22-6575 (66-51) (22-80)Ta(Opr;). 1 : 1 150-60%-2 56-49 28-9580 (57-10) (29-13)DOUBLE ISOPROPOXlDES OF CSAl (OPri)3 1 1 300-305 °;0-2 59-74 6-8440 (59-50) (6-81)Zr(OPri)._PriOH 1: 2 190-93%-1 21-44 62-i670 (21-53) (62-79)Zr(OPri) •. PriOH 2:3 220-22%-1 60·84 18-8850 (60-61) (20-04)Hf(OPri)._PriOH 1: 2 230-33%-1 51-83 34-8858 (50-43) (34-93)Hf(OPri)._PriOH 2:3 160-63%-1 50-82 32-2567 (50-79) (32-88)Nb(OPri). 1 : 1 180-85 o /0-1 61-75 16-5258 (61-09) (16-29)Ta(OPri). 1 : 1 210.12%-1 52-66 28-79iO (53-01) (27-04)*M = Rb or Cs; ],f' = AI, z-, Ta. Hf or Nb.MEHROTRA et al. : APPARENTLY COVALENT DOUBLE ALKOXIDESPI;(II (11 Jcaesium. This is unlike the other series where thecoordination compounds of potassium exhibit ano-malous stability and solubility behaviour-.NMR spectra - PMR spectra of only two products,Cs[Al(OPri)tJ and Cs[Zr2(OPr!)II], could be scanneddue to the low solubilities of other products in CC14andCDCla. The spectrum of Cs[Al(OPri)4~ showstwo types of doublets centred at 8·82 and 8·88 .• dueto the gem-dimethyl protons of bridging and terminalisopropoxy groups. The intensities of these doubletsare if' 1: 1 ratio suggesting the prese!' ce of twobridging and two terminal isopropoxy groups assnown in the probable structure (1). Mehrotraet aP have suggested structure (II) for theproducts. M[M~(OPr')IlJ (where M = Li, Na, K andM' = Zr or Hf), in which nine isopropoxy groupsare arranged around the two zirconium or hafniumatoms by sharing the faces of two octahedra. Thisstructure has been supported by the NMR spectraof the compounds K[Hfz(OPri).J and LifHf2(OPr').Jwhich give two types of isopropoxy groups (bridgingar d terminal) having the intensity ratio 1 :2.However, NMR spectrum of Cs[Zr2(OP1i).]shows two types of doublets centred at 8·71 and 8·75 .•in 5:4 ratio suggesting the presence of bridgingand terminal isopropoxy groups in the ratio of 5:4.For Cs[Zr2(OPri),], the five bridging and fourterminal isopropoxy groups can be arranged as shownin structure (III).AcknowledgementOne of lite authors (S. Goel) wishes to thankthe CSIR. New Delhi, for a senior research fellow-ship.References1. MEERWEIN. H. & EERSIN. T.. Chem, Abstr .• 24 (1930). 586.2. BARTLEY. W. G. & \\'ARDLAW. W .• j. chem, Soc .• (1958).422.3. MEHROTRA. R. C. & MEHROTR..'I., A.• Tnorg, chim. ActaRev .. 5 (197)). 127.4. KAPOOR. P. N. & MEHROTRA, R. C., Coord. chem, Rev., 14(1974). 1.5. WARDLAW, W. & BRADLEY. D. C.• Nature, 165 (1950). 75.6. BRADLEY. D. C.. MEHROTRA. R. C. & ·WARDLAW. W .• J.cbem. Soc., (1953). 1634.7. BRADLEY, D. c.. CHAKRAVORTY, B. N.• CHATTERGIE. A. K .•WARDLAW. \V. & WHITLEY, A.. j. chem, Soc., (1958).99.8. BRADLEY. D. c.. EL-HALlM. F. M. & WARDLAW. W., j.,chem, Soc., (1950), 3450.879

Synthesis of Apparently Covalent Double Alkoxides of Rubidium & Caesium

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Synthesis of Apparently Covalent Double Alkoxides of Rubidium & Caesium

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