Bist, H D

Khandelwal, D P

Tayal, V P

English

IACS Institutional Repository

Temperature dependence of external modes of water in infrared spectra of monohydrates of some divalent transition metal sulfatesV. P. T aYAL and D. P. KlIANDhLWAL//. H. Technological Inslilute, Kanpur ANDH. D. B istIndian Institute o f Technology, KanpurThe IR spectra of MvSQj.H-O (M™:Mn, Co, Ni) which arc isomorphous have been recorded in the region 1000-250 cm  ^ at liquid nitrogen temperature (L N T ). I ’hc overlapping contours have been analyzed into Lorentzian components and the positions half-widths and integrated intensities have been reported for different components of external modes of water. All compo­nents show an increase in intensity and a shift towards higher frequency at LNT over their loom temperature (R T ) values.In the region around 300 cm ’ one dominant temperature sensi' live band is attributed to stretch. Correlation curvesarc given for H-O (rock), H-O (Wag) and M -O ^ stretch frequency against M -O ^  distances.Iiitiim Ph>y 52B, 122-127 (1977)1. iN T R O D U n iO NThe hydrates IVIvSOj. Ih.O (M i-M n , Co, Ni) are isosiructural belonging to the space group having four formula units per unit cell^’ “\ Infraredstudies of these salts have been reported in the past *^' at room temperature (\<T) above 600 cm \ In a previous paper by the authors^’  ^ an analysis of the overlapping bands with half widths and relative integrated intensities of the internal and librational modes of water along with the internal modes of SOr at room temperature were reported and a linear con elation of the frequency of the nx:king mode of H-O with M-O,^ distance was given, being the oxygen of the water. In the present piiper the effect of changing the temperature from room temperature to liquid nitrogen icinpeiaturc (LN T) on the water librational and stretch blinds is presented, and the corre­lation with M-O^v distance is extended to HjO wag and M-O^y stretching frequencies (at LN T) also.2. hXPI'RIMI NTAI.Infrared spectra of transition metal sulfates 123The monohydrates of Mn and Co sails were prepared by ervstalli/alion from aqueous solution at ^  8(>®C and drying the precipitate in an oven al 100*C, while that of Ni was prepared by baking the hcxahvdrate at -- 120'’C. ITie hydration level was checked by the wciglu loss method Spectra were recorded in Nujol mull on Perkin-Fdmer 521 speclrophomeicr. For low tehperatures (L T ) a modified Wagner Homig type cell was used, which could be directly inserted in the sample beam without anv material change of the optical path. Prior to cooling the cell was evacuated to 10 '' cm of Hg. The temperatures were measured by a ihcrmcKouple and the s^Kctra at different temperatures were recorded without disturbing the geometry.3. R h S U L I S  AND D lS ( OSSION (a) Analysis o f  the SpectraFigure 1 gives the spectra in region 250-1000 cm ’ al R T  and FN T for the three salts. Considerable overlapping of the bands will at once be observed. The contours were subjected to analysis inU) Lorcnlzian components, which is justified when band widths arc much larger than instrumental iv olulion. TheFig. l. Infrared absorption spectra al room temperature (RT) and Liquid Nitrogen Temperature (LNT) of (a) MnS0 4 .Ho0  (b) CoSO^.Hp (c) NiSO, H / )  m Nujol mull. N denotes bands due to nujol.124 V, P. Tayal, D. P. Khandelwal and H. D. Bistbasis was to fit the minimum number of components warranted by the observed contours and in most cases the positions were reproducible within 5 cm~’ and intensities within 10% . In those cases where the choice was between one component slightly departing from T..orcntzian shape and two compo­nents with gtxxl Lorentzian shapes the first was preferred, unless there was other evidentx favouring the second alternative. F'igurc 2 gives the typical resolution of a contour mlo l.oienlzian components in the latter category. In the cases of Co and Mn salts the S04- '  (v i) bands have Lorent/ian shapes and two water librations are found well separated. Hence in this spectrum of Ni salt the SO*- bands were kept in Lorentzian shapes and the residue led necessarily to two components on the lower Irequcncy tail.Fig. 2 Typical analysis of the absorption band contour in the region 5W-7.SO cm -i (solid curve) into Lorent/ian components (broken curves) for NiSO^.H^.O spectrum LNT. The water wagging components at low' frequency tail ire marked by arrowsTabic 1 iiives the results of analysis cxclucUnii the internal modes of S O r " . Band positions, half widths and integrated intensities are given.(h) IJhrafional Trades o f WaterAmongst the tibrational modes of water, ilic rocking mode has lowest frequency 820 env^ in the Mn salt which increases to 860 cni-^ in the Co salt and 930 cm^  ^ in the Ni salt. In all the three cases the lowering of temperature results in an increase in peak intensity and shift towards higher frequency. The observed curves cannot be resolved into components in the case of Co and Ni salts but in the case of Mn salt the contour shows the presence of an additional compi/ncnt at both R T  and LNT. In this spectrum a new sharp band (Av.i =^ 2^0 cm~^) appears at 892 at LN 'r. SpectraInfrared spectra of transition tnetal sulfates 12515>■g<JS*80<»ou0^q, o oX71!E iA S  c  so  gfE -VM cd^  c«cd _"Swl i" I si i eS a aw i  3• s  *  2 V3 Ca 45 a•O rj^  Q> c  UO 00.2 •-< -IT3Gcdi i“S -  !Ss  2 H xiO71IEo'(/5H^ i ;cou<I  ^H > o< <© r- r* f»'> © o8 »Air^ . ? § ?i ^  orr,»/•. r^ iO'»Ov 8*T)»/-,IT,ir. r- l lSf",r i \D r.. VO ©8 ? C © 8  39c^Vc©in n-e'Or*',y-n  r i r-.$v,rj<uC»« Ir 1— r-§iTi.C ^3  s•oa5 T) rCO^  »-l3 32SgK0 Oc l  •S e1  &r l 00 vr, r i Vir<-|M VO 00ri VD II li> ^<J S 8  8O ©r i©V, OV, ©-d->«s ;008  8  00 -d*i/'i©ITi©»8r i 8riodH0f^JTj » VO VO »n ri ri<S 8 S©m §©TT 8 ©8  8oo K9 ,Vi©»nly*!s©8rk©i/'irfat intermediate temperatures show that this band appears suddenly at ~  — 1(X)*C and increases in intensity as the temperature is progressively lowered to LNT. The origin of this band is at present not clear.The wagging mode region also has frequencies in the increasing order M n —> C o -» N i. One result of this is that while this region is well separated from the region of v» of wSOr in the Mn salt it penetrates into the tail of the Vi region of SO4- in the case of Ni salt. The main wagging component in R T  spectra falls at 560 and 585 cm ’ in Mn, Co and Ni salts respectively. At LN T each of them shifts by about 20 cm ’ towards higher frequency and also increases in intensity. A low frequency component occurs at 510 cni“  ^in the Mn salt, not shifting with change of temperature. The analysis of the corresponding bands in Co and Ni sidls is less certain due to heavy over- laping. At low temperature a band at 695 cm  ^ appears distinctly in the Ni salt. Tf the corresponding band exist for the Mn and C o salts, they would fall in the region of vi of S(^,- and would not be ovserved because of overlapping.126 V . P . T a y a l, D . P . K h an d elw al an d  H . D . B is l(d) Af-O Si retchingIn the region around 300 cm  ^ there arc four components for Mn and Ni salts and two in the case ol Co salt at RT. As there are three lyj^es of oxygens (Oi and O- of the sulfate group and of the water) and three different M-O distances in the coordination octahedra around onewould expect three bands due to M-C> stretch in this region. Besides these, bands due to combination with low lying lattice modes can also occur. It is no'liced that one comp(ment (falling at 290, 310 and 332 enr^ in ease ofPig. 3. Carrelation of TR Frequencies at 1 NT of stretch, H.>0 Wag, andH.O Rtx:k with distance in M SO,.H.,0 (MzzrMn. Co,“Ni).Mn, Co and Ni respectively) shows the greater temperature variation in intensity or half-width while the others show marginal changes. As thebands associated with internal modes of SO4- are affected to much lesser degree by lowering of temperaaure, it may be inferred that the components showing marked dependence on temperaluie arc asswiated with M -0 ,v  stretch. These are also the dominana bands in the region.(e) Correlation oj Frequencies with ilisumcesCorrelation of v (rock) with M -0^^ distances has already been reported earlier'-’*. Now we find that such correlation applies also to v (wag) and V (M -0 ^ y )  stretch, l igure s gives the coi relation curves using the low temperature data.Infrared spectra of transition metal sulfates 127Rl-tKRIiNCFSI Yiivclte Lc Fur, Jean Coing-Boyanl and ticraki Bassi. ('oinpl, Rendj Ser ( ',  269, (1966).2. H R. Oswald. Helv. Chim. Acta. 48, 490 (1 % ‘i). ^ H. R Oswald, Hciv. ( ’him .^cUl. 48, (lOO (1% S)4 Claude dc Rocchiccioli, ( ompt Rend. 257, 38*'l (l% .J)5 V P Tayal. D, P. Khandclwal and H D. Bi.sl, Solid Stale Physics (India) 17C,263 (1974).

Temperature Dependence of External Modes of Water in Infrared Spectra of Monohydrates of Some Divalent Transition Metal Sulfates

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Temperature Dependence of External Modes of Water in Infrared Spectra of Monohydrates of Some Divalent Transition Metal Sulfates

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