J molg, nml Chem., 1974. Vol, 36. pp. 2265 2269. Pergamon Press. Printed in Great Britain A NEW SERIES OF MOLYBDENUM(V) FLUORO COMPLEXES M. C. CHAKRAVORTI and S, C. PANDIT Department of Chemistry, Indian Institute of Technology, Kharagpur, West Bengal. India (First received 3 October t973: in revised lorm 4 January 1974) Abstract The isolation and characterization of salts of a new series of fluoromolybdateslVI are described. The hydrazinium salt, NzH6[Mo(OH)F61. H20 has been obtained by reducing a solution of MoO3 in 40 per cent HF with hydrazine fluoride. The rubidium, caesium and :~-naphthyl aminium salts, MzIMo- IOHIF61, where M = Rb, Cs and C~0H10N have been obtained by crystallizing the fluorides of the respec- tive cations with the hydrazinium(II) salt in 20 per cent HF medium. A potassium salt which has been formulated as K/IMoOFdHF2) ~ or KIMoOF4]. KHF2 on the basis ofi.r, spectra, has also been prepared by the same method. All the salts are green crystalline substances and stable when dry. The hydraziniumll 1 and the potassium salts can be recrystallized from 20 per cent HF. The oxidation number of molybdenum determined by oxidation with dichromate and the magnetic moment values indicate the quinquevalency of molybdenum in the salts. The i.r. spectra of the rubidium and caesium salts give the characteristic v(O H) bands, but no 5(H-O HIband. Strongand sharp bands observed at around 980 cm t in the spectra of these hydroxo salts have been tentatively assigned as the deformation mode of Mo O H group. The hydrazinium salt undergoes dehydrohalogenation and under different conditions the complexes N 2H,- [MoOFs!, !MoIOHJF4(NzH4)I and [MoOF3(NzH,t] have been is~lated. INTRODUCTION COMPARED to an extensive volume of work done on the chloro and specially oxochloro complexes of quin- quevalent molybdenum, studies on the fluoro and oxofluoromolybdates(V) are very scanty. Salts of three such series of anionic complexes, viz., [MoFs] 3- [1, 2], [MoF6]-[2-8~ and [MoOFs]2-[4,9-12] have been reported. These compounds have been mostly prepared either by dry reactions or from nonaqueous medium. In the present communication the isolation of salts of a new anion, viz. [Mo(OH)F6] 2- from aqueous medium is reported. These have been characterized by magnetic and i.r. spectral studies. EXPERIMENTAL Molybdenum trioxide was prepared by heating ammonium molybdate (analytical reagent grade o1" J. T. Baker Chemical Co.} at 500°C. Hydrofluoric acid was E. Merck's G.R. quality {40%). Hydrazine hydrate used was of Riedel-de Hahn 180~,',). Other chemicals were B.D.H. or E. Merck's extra pure or guaranteed reagents. ~-naphthyl amine was recrystallized before use. The methods of analysis of molybdenum and fluorine were the same as described earlier[ 13, 14]. Nitrogen was estimated by Kjeldahl's method. The alkali metals were estimated gravimetrically as their sulphates after separation of molyb- denum(VI) as sulphide which was heated to MoO 3 and weighed as a check for the analysis of molybdenum. The determination of the oxidation state of molybdenum was carried out by oxidizing a known amount of the substance with known amount of potassium dichromate in hot 2N sulphuric acid medium and then estimating the excess oxidant by titration with Fe 2+ solution. I.R. spectra were recorded in Nujol mull and in KBr pellets using a Perkin Elmer spectrophotometer (No. 457). Magnetic susceptibility measurements were made by the Gouy method, the calibrant being Hg[Co[CNSL,]. The diamagnetic corrections were calculated from the data of Figgis and Lewis[151, Conductivity measurements were carried out in aqueous medium with a Philips conductivity bridge (No. PR 950t}) using platinized platinum electrodes sealed in polythene stems. Preparation of the complexes Hvdrazinium(II} hvdroxohexafluoromolvbdate(V} mono- hydrate, N2H,[Mo(OHJF~].H~O. One gram of MoO3 was dissolved in 2.5 3.0 ml of hydrofluoric acid (40 pet centJ at water bath temperature and the clear solution was treated with 3.0 ml hydrazine (80 per cent) neutralized with the same acid. On cooling a little NzH6F 2 separated out which was removed by decantation. The volume of the light green solution was reduced to one-third of its initial over a water bath. On cooling a further amount of N 2 HoF2 was separated and was removed by filtration. The deep green solution deposited green crystals on keeping in a desiccator over sulphuric acid and sodium hydroxide. The crystals were filter pressed and dried over sulphuric acid and caustic soda. The yield was 1.2 g. Potassium~rubidium~caesium hydroxohe'~qfluoromolyb- date(V), Mz[Mo(OH)Fo], M = K, Rb and Cs. IThe potassium salt has been actually formulated in a different manner. Vide discussion part on i.r. spectra.) To a concen- trated solution of N2H6[Mo(OH)F6]. H20 in 20 pet cent HF excess (hydrazinium salt :alkali fluoride = 1: 5t of con- centrated solution of potassium bifluoride/rubidium fluor- ide/caesium fluoride in 20 per cent HF was added. Free green crystals appeared on stirring. 2265
