Alkali metal (K, Rb, Cs) doped methylammonium lead iodide ...
Synthesis of Alkali Metal...
3
Indian Journal of Chemistry Vol. 21A, October 1982, pp. 977-979 Synthesis of Alkali Metal Trifluoroaquomanganates(II) MANABENDRA N BHATTACHARJEE & MIHIR K CHAUDHURI* Department of Chemistry, North-Eastern Hill University, Shillong 793003 Received 12 April 1982; revised and accepted 26 June 1982 The electron transfer reaction between hydrazine hydrate and KMn0 4 in the presence of alkali metal bifluorides, AHF 2 (A = NH 4 , Na orK) readily gives light pinkish-white alkali metal trifluoroaquomanganates(II). A[MnF 3(H 2 0)] in very high yields. The corresponding Rb + and Cs + salts have been obtained by reacting 20"0 hydrofluoric acid solution of NH 4 [MnF 3(H 2 0)] with Rb 2 C0 3 and Cs 2 CO) respectively. The compounds have been characterised by elemental analyses, chemical determination of oxidation states of manganese in the compounds, room temperature magnetic susceptibility measurements, pyrolysis and infrared spectral studies. There is a growing current interest in the study of fluoro-manganese chemistry! ~6. It is now well established that F ~ ions stabilise Mn3+ and it is also generally believed that the reduction of higher valent manganese below + 3 state through electron transfer reactions in the presence of F ~ Iigands is rather a difficult task! -5, eventhough + 2 oxidation state of manganese is a more common one. Moreover, complex formation tendency of Mn2+ seems to be comparatively less pronounced than that of Mn 3 + (ref. 7). In view of this and in continuation of our work on the synthesis and structural assessment of fluoromanganates'v", we thought it important to carry out the electron transfer reaction between K M nO 4 and a strong reducing agent, like hydrazine hydrate (N 2H4.H 20) in the presence of alkali metal bifluorides and to synthesise and characterise fluoro- manganates(II) directly from Mn 7 +. This paper incorporates results of such an ·investigation. Materials and Methods All the chemicals used were reagent grade products. Alkali metal bifluorides, AHF 2 were synthesised by the method developed in this laboratory". The oxidation state of manganese in each of the alkali metal trifluoroaquomanganates(II) was determined chemically by the reaction of a known amount of the compound with aqueous acidic Fe 2 + solution followed by estimation of unreacted Fe 2 + in solution. Synthesis or alkali metal trifluoroaquo- manganates(ll), A[MnF 3(H 2 0)]--Ammonium, sodium and potassium trifluoroaquomanganatestl l) were synthesised by the following general method. Alkali metal bifluoride, AHF 2 (A = NH 4 , Na or K) (19.3mmol) and solid KMn0 4 (3.16mmol) were mixed, powdered and dissolved in a minimum volume of water by slightly warming over a steam-bath and filtered. The filtrate was collected in a polythene beaker and an excess of hydrazine hydrate (3 ml) added in one lot with constant stirring. A highly exothermic reaction set in and readily gave a light pinkish-white microcrystalline product with the mother liquor becoming colourless. The reaction mixture was cooled to room temperature, solid separated by centrifugation and purified by washing with n-heptane and finally dried in vacuo. The yield was between 80 and 90%' Synthesis of rubidium trifluoroaquomanganateilh, Rb[MnF 3(H 20)]~ NH 4 [MnF 3(H 20)] (2 m mol) was dissolved in a minimum volume of 20% hydrofluoric acid to get a clear solution. To this solution was added powdered Rb 2 C0 3 (1 m mol) in portions with stirring. After addition was over, the light pinkish-white Rb[MnF 3(H 2 0)] appeared, which was separated by centrifugation and purified by washing with n-heptane and finally dried in vacuo; yield 91 %. Synthesis of cesium trifluoroaquomanganateif Ii, Cs[MnF iH20)]~ The above metathesis reaction was carried out with NH4[MnF 3(H 2 0)] (2 m mol) and CS 2 C0 3 (I m mol) to get Cs[MnF 3(H 2 0)] in 91 '1~ yield. Results and Discussion The experimental conditions employed for the synthesis of various alkali metal trifluoroaquo- manganates successfully brought about the reduction of manganese below its + 3 state, inspite of difficulties recorded earlier! ~5. On the addition ofN 2 H 4 .H 2 0 to excess of alkali metal bifluorides and potassium perrnanganate the temperature went up to about 80- 90 c C. This temperature was strategically maintained in order to facilitate the reduction of manganese below its + 3 state. The analysis of the reaction products shows the reduction of manganese below its + 3 state. Thus the method leading to trifluoroaquomanganates(II) of alkali metals indicates that hydrazine hydrate reductions could be developed for the synthesis of other types of compounds of manganese in its + 2 state 977
Transcript of Synthesis of Alkali Metal...
Indian Journal of ChemistryVol. 21A, October 1982, pp. 977-979
Synthesis of Alkali Metal Trifluoroaquomanganates(II)
MANABENDRA N BHATTACHARJEE & MIHIR K CHAUDHURI*Department of Chemistry, North-Eastern Hill University, Shillong 793003
Received 12 April 1982; revised and accepted 26 June 1982
The electron transfer reaction between hydrazine hydrate and KMn04 in the presence of alkali metal bifluorides, AHF 2 (A=NH4, Na orK) readily gives light pinkish-white alkali metal trifluoroaquomanganates(II). A[MnF 3(H20)] in very highyields. The corresponding Rb + and Cs + salts have been obtained by reacting 20"0 hydrofluoric acid solution ofNH4[MnF 3(H20)] with Rb2C03 and Cs2CO) respectively. The compounds have been characterised by elemental analyses,chemical determination of oxidation states of manganese in the compounds, room temperature magnetic susceptibilitymeasurements, pyrolysis and infrared spectral studies.
There is a growing current interest in the study offluoro-manganese chemistry! ~6. It is now wellestablished that F ~ ions stabilise Mn3+ and it is alsogenerally believed that the reduction of higher valentmanganese below + 3 state through electron transferreactions in the presence of F ~ Iigands is rather adifficult task! -5, eventhough + 2 oxidation state ofmanganese is a more common one. Moreover,complex formation tendency of Mn2+ seems to becomparatively less pronounced than that of Mn3 + (ref.7). In view of this and in continuation of our work onthe synthesis and structural assessment offluoromanganates'v", we thought it important to carryout the electron transfer reaction between K M nO 4 anda strong reducing agent, like hydrazine hydrate(N 2H4.H 20) in the presence of alkali metal bifluoridesand to synthesise and characterise fluoro-manganates(II) directly from Mn 7 +. This paperincorporates results of such an ·investigation.
Materials and MethodsAll the chemicals used were reagent grade products.
Alkali metal bifluorides, AHF 2 were synthesised bythe method developed in this laboratory".
The oxidation state of manganese in each of thealkali metal trifluoroaquomanganates(II) wasdetermined chemically by the reaction of a knownamount of the compound with aqueous acidic Fe2 +solution followed by estimation of unreacted Fe2 + insolution.
Synthesis or alkali metal trifluoroaquo-manganates(ll), A[MnF 3(H20)]--Ammonium,sodium and potassium trifluoroaquomanganatestl l)were synthesised by the following general method.
Alkali metal bifluoride, AHF 2 (A = NH4, Na or K)(19.3mmol) and solid KMn04 (3.16mmol) weremixed, powdered and dissolved in a minimum volumeof water by slightly warming over a steam-bath andfiltered. The filtrate was collected in a polythene
beaker and an excess of hydrazine hydrate (3 ml) addedin one lot with constant stirring. A highly exothermicreaction set in and readily gave a light pinkish-whitemicrocrystalline product with the mother liquorbecoming colourless. The reaction mixture was cooledto room temperature, solid separated bycentrifugation and purified by washing with n-heptaneand finally dried in vacuo. The yield was between 80and 90%'
Synthesis of rubidium trifluoroaquomanganateilh,Rb[MnF 3(H 20)]~ NH4[MnF 3(H 20)] (2 m mol) wasdissolved in a minimum volume of 20% hydrofluoricacid to get a clear solution. To this solution was addedpowdered Rb2C03 (1 m mol) in portions with stirring.After addition was over, the light pinkish-whiteRb[MnF 3(H20)] appeared, which was separated bycentrifugation and purified by washing with n-heptaneand finally dried in vacuo; yield 91%.
Synthesis of cesium trifluoroaquomanganateif Ii,Cs[MnF iH20)]~ The above metathesis reaction wascarried out with NH4[MnF 3(H20)] (2 m mol) andCS2C03 (I m mol) to get Cs[MnF 3(H20)] in 91 '1~yield.
Results and DiscussionThe experimental conditions employed for the
synthesis of various alkali metal trifluoroaquo-manganates successfully brought about the reductionof manganese below its + 3 state, inspite of difficultiesrecorded earlier! ~5. On the addition ofN2H4.H20 toexcess of alkali metal bifluorides and potassiumperrnanganate the temperature went up to about 80-90cC. This temperature was strategically maintained inorder to facilitate the reduction of manganese below its+ 3 state. The analysis of the reaction products showsthe reduction of manganese below its + 3 state. Thusthe method leading to trifluoroaquomanganates(II) ofalkali metals indicates that hydrazine hydratereductions could be developed for the synthesis ofother types of compounds of manganese in its + 2 state
977
INDIAN J. CHEM., VOL. 21A, OCTOBER 1982
starting from Mn 7 + and also compounds of othertransition metals starting from their stable higheroxidation states. The yields obtained by this methodare very high. It is also evident that by the use offorcing conditions the fluoro complexes of Mn2 + canbe synthesised eventhough their formation constantsin aqueous solutions are very low? -11. The alkalimetal bifluorides, AHF 2' here act as fluorinatingagents. In our previous papers4.S.8.12 we emphasisedthe role of AHF z as fluorinating agents. In fact itappears that the success of the method depended notonly on the role played by NzH4.H20 but also quiteappreciably on the presence of both H + and F - in thesolution phase arising from AHF 2' The overallreaction leading to the formation of A[MnF iH 20)]may be expressed by Eq. (1)
4KMn04 + 13AHFz + 5NzH4·H20 .....•4A[MnF3(HzO)] + 5Nz + 17HzO + HF +4KF +9AF
... (1)
The alkali metal trifluoroaquomanganates(II) areall very light pinkish-white microcrystalline productsand they attack glass in the presence of moisture. Theyare not soluble in common organic solvents.A[MnF3(HzO)] dissolves in water to some extent butthe dissolution is accompanied by dissociation ordecomposition. The compounds dissolve highly inhydrofluoric acid.
The chemically estimated oxidation states ofmanganese lie between 2.05 and 2.12 (Table I), lendingstrong support to the contention that manganese ineach of the compounds has an oxidation number of+ 2. We emphasise on the chemical determination ofoxidation state of manganese in such compoundsbecause the observed magnetic moment values(measured on a Gouy balance with Hg[Co(NCS)4] asthe calibrant) are often lower than the expected valuesowing to their pronounced antiferromagneticbehaviour. The attempts to measure the molar
conductance of various A[MnF 3(HzO)] compoundsin water were unsuccessful. The observed values werehigher than that expected for a uni-uni valent type ofelectrolyte. The higher molar conductance valuesindicate some sort of decomposition of the compoundsor the enhanced ionic character of the Mn-F bonds.
The IR spectra of ammonium, sodium, potassium,rubidium and cesium trifluoroaquomanganates(II),(recorded on a Perkin-Elmer model 125) are almostidentical. The typical features of the spectra are theoccurrence of a strong absorption .....410, a weak andbroad band - 1640, a medium intensity broad band-3350 and a medium intensity band -710cm-1,assignable to vMn-F, bH -0 - H, vO - H and rockingmodes of water arising out of coordinated fluoride andwater respectively. The occurrence of vMn-F at a muchlower frequency compared to those of MnF~ - andMnn - species4.S.13,suggests that the Mn-F bonds in[MnF 3(HzO)] - have enhanced ionic character thanthose in MnF~ - and MnF~ -. However, from the factthat the vMn-F has been observed in the present.cases- 410 ern -I, it is certain that a definite degree ofcovalency exists in the Mn-F bonds. Similarobservation was made by Peacock and Sharp13 in thecase of KMnF 3' The very weak nature of the bH -- 0- H band points to the presence of coordinatedwaterI4.IS. Moreover, the appearance of mediumintensity band - 710 crn:" which is generallyattributed to the rocking mode of coordinated wateradduces strong evidence for the presence ofcoordinated water in the compounds. Furtherevidence with regard to the presence of coordinatedwater was obtained from the pyrolysis studies ofK[MnF 3(H20)], taken as a representative. Pyrolysisof the compound at 125-30cC for 3 hr virtually did notshow any change in weight of the compound. The IRspectra of the compound recorded before and afterheating also did not indicate any change in the spectralpattern.
Table I-Analytical Data, Magnetic Moments, Estimated Oxidation States of A[MnFiH10)](A': NH •• Na, K. Rb or Cs)
Compound Jl.rr Oxidation Found (%) (Calc.)(B.M.l state of2900K Mn AorN Mn F
NH.[MnF )(H 20)] 5.3 2.05 9.61 37.52 38.21(9.46) (37.16) (38.51)
Na[MnF )(H2O)] 5.2 2.11 15.52 36.34 37.68(\ 5.03) (35.95) (37.25)
K[MnF )(H2O)] 5.2 2.12 23.43 32.89 33.51(23.08) (32.54) (33.73)
Rb[MnF )(H2O)] 5.3 2.08 40.52 25.73 26.83(39.68) (25.52) (26.45)
Cs[MnF )(H2O)] 5.3 2.12 51.61 21.38 21.48(50.55) (20.92) (21.68)
978
BHATTACHERJEE & CHAUDHLJRi: ALKALI METAL TRIFLUOROAQLJOMANGANATES
The room temperature magnetic moments of thealkali metal trifluoroaquomanganates(II),A[MnFiH20)] lie between 5.2 and 5.3 B.M. wellbelow the expected value for a high-spin dS-system.This, however, is not too surprising because similarobservations were made in the cases of A2MnF sandA2MnFs.H20 (refs 4, 5, 16, 17). Considerably lowermoments presumably owe their origin toantiferromagnetic exchange interaction betweencontinuous Mn2 + ion probably through - Mn - F- Mn-chain in the solid state. The very faint colour ofthe compounds indicates that they may haveoctahedral structure but only X-ray study wouldprovide conclusive evidence.
AcknowledgementThe authors 'thank the UGC, New Delhi for the
award of a fellowship to one of them (MNB) and Mr KP Sarma for his cooperation.
ReferencesI Massa W, Inorg nuel Chern uti. 13 (1977) 253.2 Bukovec P & Kaucic V, J chem Soc. (1977) 945.
~..1
3 Kaucic V & Bukovec P, J chem Soc, (1979) 1512.4 Bhattacharjee M N, Chaudhuri M K, Dasgupta H S & Khathing
o T, J chem SOL' Dalton Trans, (1981) 2587.5 Bhattacharjee M N, Chaudhuri M K, Dasgupta H S, Kathipri A
& Khathing 0 T, Synth React inorg met-org Chern, (I 982)(inpress).
6 Chaudhuri M K, Das J C & Dasgupta H S, J inorg nucl Chem, 43(1981) 85.
7 Wood C W & Holliday A K, Inorganic chemistry, (Butterworths,London), 1967,336.
8 Chaudhuri M K & Choudhury P K, Chemy Ind, (1979) 88.
9 Cotton FA & Wilkinson G, Advanced inorganic chemistry, (JohnWiley, New York), 1972,848.
10 Foster J J & Gill N S, J chem Soc (A), (1968) 2625.
II Colton R & Canterford J H, Halides of the first row transitionmetals, (Wiley-Interscience, New York), 1969, 212.
12 Chaudhuri M K, Dasgupta H S, Ghosh S K & Khathing D T,Synth React inorg met-org Chern, 12 (1982) 63.
13 Peacock R 0 & Sharp 0 W A, J chem Soc, (1959) 2762.
14 Thornback J R & Wilkinson G, J chem Soc Dalton Trans, (1978)110.
15 Chakravorty A R & Chakraborty A, Inorg Chern, 20(1981) 275.
16 Emori S, Inoue M, Kishita M & Kubo M, Inorg Chern, 8(1969)1385.
17 Nyholm R S & Sharpe A G, J chern Soc, (1952) 3579.
979
