Rao, K Mallikarjuna

Swamy, C K Narayana

English

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Infrared spectra of potassium citrate monohydrate singlecrystalsK. Mat.likarjhna RaoDepartment o f Physics, Regional Engineering College, Wai^ngalA (A.P.)ANDC. K. Narayana Swamy ;Department of Physics, Indian Institute of Technology, 'Madra^-^H (Received 5 January 1973)Indian J .  Phys. 48 , 225-235 (1974).Tho infrarod Rpootra o f potasfiiiim citrate monohydrato single crystals (001, 010 plates) have boon n ‘oordod in tlio region 4(K) -4000 cm using a Perkin-Elmor, infrared sp(H^trophotomt^tor, model 337 with a double grating dispersing unit. Tiie froo state frequencies of the citrate ion wert^  taken from the reported works o f Rao 8wamy (1970, 1971, 1972rt, 19726) and the observed frequencies in the present spectra A\cro assigned to differcuit modes of vibration of tlio citrate ion in the unit cell. The spen t^ra uero analysed according to the standard procedures o f Halford (1940) and Hornig (1948). The splittings o f the frequencies rovealod that the citrate ion must have an approximate Cg site sjininetry in the unit coll. Tlius sixty one out o f the ninety six expected fundamental frequencies o f the citrate ion in the potassium citrate monohydrate unit coll are identified in tlio sptjctra and assigned to their respective species. Tlie hj^dro- gen bond frequency range has been identified according to the details giv(m by Hadzi (1965). TJie effect of orientation o f tjie ions in the unit cell has been discussed with reference to the spectra o f different crystal plates.1. Introduction'i'ho work done on the molecular stnioturo o f the citrate ion is very meagre and honoe the authors have taken up this work. So far the authors have reported tlie tentative analysis of the infrared spectra o f anhydrous citric acid (Rao & Swamy 1970), sodium citrate and ammonium citrate (Rao & Swamy 1971), lithium citrate tetraliydrate (Rao & Swamy 1972a), and potassium citrate monohydrate (Rao & Swamy 19726). As a continuation the authors now have recorded the infrared spectra o f potassium citrate monohydrate single crystals and an assignment o f the observed frequencies is reported in this paper. Prior to the present work there is only one paper by Duval (1962) on the infrared spectrum o f potassium citrate monohydrate which did not report any analysis. Till) common frequencies in the polyorystalline spectra o f these compounds wore taken as the free state frequencies o f the citrate ion. Using this set o f frequencies2252^6 K . Mallikarjuna Rao and C. K . Narayana Swaniyof the citrate ion, the analysts of the frequencies in the single crystal spectra of potassium citrate monohydrate has carried out.2 . E x p e r i m e n t a x .Potassitan (titrate monoh>^drate of B.P. grade wa>s procjured from Eagle Pharmac6uti(5als and purified by repeated recrystallization. Single crystals were grown from a saturated >solution of* flie substance in distilUd water, at room temperature. Tlu^  crystal lias a (^ leaA^ age plane identified to be (001). Ao(;ord- ingly, (001) speciimai j)hites were ol)tainod hy cleaving and grinding the cleaved plate o\ or a sliglUly undersaturat(d acpioous solution of the salt. The(010) taco is groAvn naturally which is idontinod from the morphological details given by Groth (1910). Tlie axes identification was confirmed by taking X-ray oscillation rotation pJu)tograi)hs of (010) and (001) plates. Then tJie infrared spectra of (001) and (010) plates were rooo.rdtxl wliicli are reproduced in figures 1, 2 and 3. The observed frequencies witli assignments are given in table 2 and the citrate ion Iroquoucios for comparison are given in table 1.w*™*® monohydrate-single crystal (010) plate spectrum. 4000-400 cm-» region using PBIRS, Mode) 337^Doi^le beam instru­ment Qratmg disperemg unit.Infrared spectra o f potassium citrate etc. 2274 j0 MtCRONS 50Fig. 2 Infrared spectrum of potassium citrate monohydrato-single crystal spectrum— 6-axis parallel to slit of the spectrophotometer-4000-400 cm-' region using PEIRS, model 337-Double beam instrument-Grating dispersing unit.3. Rkstjlts and DiscussionTt is known from Bums & Tball (1957) and Love et al (1960) that potassium citrate monohydrate crystallizes in the monoclinic system with four molecules in its unit cell of dimensions a -  7.06A, b -  11.72A, c =  13.69A, and ^ =  112.0“ and has a space group Full structural details are not available for thiscompound to know anything about the structure of the citrate ion in the unit cell. However, the structure o f the citrate ion in magnesium citi-ato decahydrate crystal is known from the details given by Johnson (1965). According to this, citrate ion has only site symmetry in the crystal unit cell. Data on the bond lengths and bond'angles of different bonds in the citrate ion from the details given by Johnson has been quoted in our earlier paper (Rao & Swamy 19726). The Cl point group symmetry of the citrate ion could be inferred from the spec­troscopic observations as follows.228 K . Mallikarjiina Rao and C. K . Narayana Swamy40 MICRONS SOMICRONS ISO 20 0 2S.0Fig. 3 Infrarod spectrum of potassium citrate monohydrato-single crystal (001) plate spectrum—a-axis parallel to slit of the spectrophotometer-4000~400 cm~i region using PEIR8, model 337-Double beam instrument—Grating dispersing unit.Fig. 4a Magnesium tricitrate unit call-viewed along the 6-axis.Fig. Hydrogen bonding and molecular-pack ing in the magnesium tricitrate unit cell viewed along the 6-axis.In fra red  spectra o f  potassium  citrate etc. 229Fig. 6  Structure of the tricitrate ion (CeH6 0 7 )—rTable 1 . Infrared frequencies of the citrate ion in the free state (taken from polycrystalline studies) in comparison to the frequencies df the citrate in the solid state from single crystal spectraPolyorystall ineFreq.numberSingle Crystal\ ac»T rm 4*Freq. Int. Freq.cni"^Species/v sB ig iiiz ie ii  t2937 v s >^3 2940 3 H2  asyimn. stretch.29282895 B 2900 Oft CHa 83rmm. stretch.2878 bu1572 m. Vs 1574 bu COO asymm. stretches.1566 Ou1649 m. 1555 Ctfl1548 bu1532 m. VlQ 1541 bu1533 au1501 m. vn 1502 «ti CH2 bends.1490 bu1480 m. 1487 au1477 bu1465 m. n 1472 au COO symm. stretches.1464 bu1445 m.br. V® 1455 Ou1444 bu1420 m. Vi 1433 Ou1420 bu1406 m.sh. na 1413 Ou CH2 bends.1395 bu1340 m.br. V3 5 1346 au CHa deformations.1333 bu1286 m.br. vae 1295 —1182 w. Vll 1189 au C-OH stretch.1183 buTable 1 contd.230 K . Mallikarjuna Rao and C. K . Narayana SwamyPolycrystall ineFroq,numborSingle Crystal AssignmentFreq. Int. Freq. Speciesom“^ cm”^1071 m 2^7 1075 K C-OH oscillations.1069 Ctfi1006 w. *'2H 1065 bu1057 dfi969 w Vl2 970 6 « C~C stretches.950 w 960 bu945 a„914 H 917 COO deformations.911 bu900 s 900 ciu8 6 6 m 2^3 860 bu8 6 6842 m >'24 849 au842 bu770 w >^40 777 __ CH2 rockings.764 —747 vw 749 __744 —*'2y 535 ■ -528 —>'3*i 623 — O-C bendings.611 —>'31 605 —495 —468 _ COO out of plane462 — bendings.V3H 460 __453 —>'42 428 __ C-C torsions.419 —>'43 420 __411 —From the available data on the infrarod and Raman ypoctra of sodiumin both the spectra. This is possible only when the citrate has C^ p, Cj etc., point groups. Apart from this the observed infrared frequencies in the spectra of potassium citrate monohydrate single crystals could bo satisfactorily explained only when wo take C, point group for the free citrate ion. Thus we were lead by the above facts to the conclusion that (7j must be the point group of the freeInfrared spectra o f potassium  citrate etc. 231citrate ion. The citrate ion has eighteen atoms and must have forty eight fre­quencies. The number of frequencies of different bond stretchings, l)endings etc., were calculated according to the proccxiure ol* Decius (194y9). TJie commtm infrared froquonoios in the spectra of sodium citrate potassium citrate, ammo­nium citrate and lithium citrate tetiahydrato were noted. Those frequencies sliould belong to tiie citrate ion having i\ point group symmetry. TIk^  fre­quencies are assigned to tlieir respective group»s using the tabtes for tlc^  charac­teristic group frequencies. Tiie fn^quonoios numb^od r, ...,fn assigning the froqiKUKnos to etc., tluvn^  wa>s some diflfKiuJty regardiTig assign­ment' wjionever two groups of frequencies are vc^ ry jiear and ttiis ditficulty w^ as overcome hy observing the single crystal sp(K?tra of potassium citrate mono- hydrate. Thus the free state citrak  ^ ion froquencios havii been identified and are given in table 1. We liave ident-ifi(^ d tjiirty one fundamental froquencios out- of forty eigJit tjiat are tlieorctically expected. Using tJus set of froquencios of tj\(^  (htrate ion, the ijilrand sp( c^tra of ]>otassium citrate monohydrate single cjystals w(u*e sul>j<ictod to an analysis as given below.From the available structural data on (Bums & Tball 1954) potassium citrate monohydrate and tlxe symmetry of the free citrate ion, wo (?an conclude that tho site of symmetry of citrates ioji in tho potassium (titrate monoliydrate crystal must be (\. According to the details given by Johixson (19(>5) on the structure (xf the citrate ion in tlio unit coll of magnesium citrate decaliydrate, all the atoms of the ion are a-iTanged on two planes which an^  nearly perpendi(uiIar to oacli otlier. Tlio fine structure and specially tlxi^  splitting of the fundamental froquencios in tJu^  spoctriun reveal tlio fact tliat ilio (utrato ion may bo coixsidored to Jxavo an aj)proximate site symmetry Cs ic,, tho citrate ion may be considered approxi- juiit(4y to consists of two Cg groups ((tojLsidt^ ring the atoms on each plane form­ing a Cs group and the two groups being porpendioulaj* to each other the interao- tiorx will be negligible). TJxe observed frequencies are assigned accordingly and discussed below. The correlation table betwreon (tixo point group), (site group) and C2h (Bpace group) is given in table 2.According to tlxo orientations of the citrate ions in the unit cell as reported by Johnson (1965) for magnesium trioitrate it is concluded that T,., Ty^  Tz, the dipole moment transition vectors, are parallel to c, a and b crystallographic axes respectively, and Ty are of h species and Tz is of a species. According lo the selection rules a and h species are only permitted in the infrared. Thore- fom in the (010) plate spectrum it is expected that only b species should be present ‘^'Ud in the (001) plate spectrum both a and b species should be present.A free state fundamental like wall split into foui* components duo to the pi'c.seuce of four molecules in the unit cell. According to tho correlation table 2 ouly two frequencies of a and b species appear in the infrared, out of the four232 K . Mallikarjuna Rao and C. K . Narayana Swamy%3T3 §08o9 e523>togffi I “oa-aS fi ^20 .c^1n °o■ §1s_ dI s  guQDw**otafiIII9 «K t47 Oa•coooIi'%» 1  9 9dw > ► !> «!»a a a 1 i ti  i® S  • S ; : ; -® -?a■ i r ^  r " " «tMlO O  © © t -  10 ©  c  o  ©  CO JO :o CO CO©  C  OO^  o t ^©  ©  00 01 <N <Mc c  ©1 ©iM (N (M (M©  ©  lO 10 QC lO ©  QC QOI-l 1—t I-H00.2‘Sa c  cdHs g  1 >  > l ‘^  d . g - -  0 .2,S >-M a ?tH10 ©04 0  1 -♦< CO 1 CO CO00 ©01 ©  ©  ©  CM <No  ©  01 ©  »0 OC ©  lO 01 ©CO ©  CO 01 (M 01 (M CM 01 01 01 0101 ©  01 10 ©  >  ^©  ©  00 —t —1 1—<cn01JS »•o *o(Xm•pdtH f  p5 i j £1 on 00 a 8 a 5fH^  1. f i d  . g ®  OQ S 2 '-"® ^©  h* M ©  h- cC I-- ©  l> ©  ©  CO CO CO CO co©  QC1 ©  OO (N (N© 10 w  »d © © OQ © »o CO © 01 01 01 ^  (M 01 01 01o  «  ©© © © PH^ l-M »«H1a * ^  g03 > CO > i i  ag g gr4 ja4• S «- l 3 s . p lCO o  © >0 ‘0 © ©  © <N CO © © lO ^  «-<l © 00 CO CO CO eo N  CMo ©  «dh-10 ©© © oi oi 01 01lO © © CO © 01r> r*fH iH rH00 O  ^ CO <0 COi£5 O O O t't- »f5 rH lO lO »0 »o« e c1-1 OC QC cO li!5 COin CO ?o m CO;0 CO CO 10)0^•€g.fic«woO  CO I <N © ca I WO 10I—• iH I»M © t - O © CC ,10 ^  I0) oCOlOUOlO ^oco©2SS10 2Infrared spectra of potassium citrate etc. 233OQI§ sIwocl)® g . a (p ®ooS 05 S 'S H,S A5 0-g| ?rXi g O w 533 a a a a0 ^  O .o ^  53CO 1-^ O C<l iO r- o lo (M rj- Tf  ^ I OSTti I (Mfcl)I3 . S-^©.2 iccfi -2 S - o-o-l ? » 5;'-' gS-ft*■|2c8 . a Q  5.21 5 ?H r a uw s •^ '8 p5 §5 a ? l i lOD OQ ^<N ica CO CO <£> OSCO pH •H 00'»t ''t CO pHpH  pH  rH pH pH pHI II I•SguJD10 PH Os§?s00 oc8aw01oa00 (M O o00 GO r- «opH COaQO I" ICo oIft» ft ftvi^  w uv w r"CO W  pH  PH O  Ol«|  PH h M PH PH PH■|  ^  ^  ^^. <M pH  0>1ee1 1 CO' VflO1n T3 10opQ4J00sO,(op C^1OOoo uP o o 6N C3 1 O H a o 60 C9;T r ,^r ;T aTa a 1 ^ 1 1 <1 1 1 1 1 I 1O  pO 1 Q 1 I 1 1 1 1 1 1 1^ > 1 1 h to  o lO © to ©  CM o  ©  © ©t -  «5 «Z! A  1 1 ^  1 <N <M ©  ©  © CMOS OS ©  ©  1 1 l> 1 ©  © Tti ^-? < ?a a a a a 0  >o 0  O 0 1 1 u1>  a f t f t f t |JS^  ^  ^ 1 ^o  r - ©  M  ©  t -  © ©  © ©  ©  © ©  CM ©r - PH PH O  © © CM PH © j ©  © pHo s OS ©  ©  ©  ©  © t> t> ©  ©  ^ 1a a a 1 1 1 1 1 1 1*o >o •o 1 1 1 1 1 1 1fe 1^  1 1 1 ^ a ^  1 1©  ©  t -  lo s  S S  1© ©CM S 1 1©  © ©  ©  ©  1 1 © 1«  a f t ^ i J oa a 1 ^©  © •«34 o  ©  N o  t - ©  ©I SpH©  ©  ©  ©pH  ©  us ©  ©  ©  ©©  PHi> i> ©  © 1split frequencies mentioned above. Of those two, the a component could be identified first since it sjiould bo present in (001) plate spectrum and should be absent in (010) plate. When once the a component was identified the remain­ing split component should bo the b component. Since we have recorded the spectra of (001) plate witli a and b axis parallel to the slit of the spectrophoto­meter, the assignmcuits of tJie speci(\s have boon done witix ease. But in the 1300-1600 cm“  ^ region none of tlu^  single <;rystal spectra are resolved very well and so in this region assignments hav(^  boon offecUxi with the help of the KBr pellet specbnim. In the case of the spectnun of an unorionted specimen the symmetric sp<x?ios will usually appear with liigh intensity compared to the anti­symmetric species of the sajne group or bond. Tliis principle w^ as nised wliiJe making the assigjiments with th<^  KBr pellet spootrum. It was not possible to assign the split components of some of the frequencies like etc., to theirspecies because of the fact, that the 6-axis spectrum is taken wdtli random orienta­tion. TJxus iJxe split components of tlie availal)Je fundamentals of the citrate ion are assigned and the assigned frecpioii(?ios are tliscussexi bolow^  :CHg Frequencies :The stretching»s of this group appear in the region 2937-2895 cin~ ;^ the bend­ings at 1501, 1480, 1406 cm*"^  have split up as expocttKl and their species are assigned. Four CHg bending frequencies (free static) are expected but we could identify only three in the KBr spectrum and this region is not resolved w-ell in the single crystal spectra, The deformaljons appear at. 1340, 1285 cm""^  and the rooking frequencies appear at 770, 747 cm~h TJie CHg group according to the crystallographi(? details on magnesium citrate, is known to be situated out of the back-bone plane and tiie frequencies pertaining to this groiip must appear in the spectra of both tlie Cs groups, as was observed.COO Group Frequencies :Stretchings of this group appear at 1572, 1549 and 1532 om~ ,^ 1465 1445 and 1420 cm~  ^ and the deformations appear at 914, 900, 856, 842 cm "^ . The out of piano bendings appear at 453, 460 om“ .^ From the crystallographic details it is knowm that there are tw o COO groups in (010) plane which is the back-bone plane and the other COO group is in (001) plane which is perpendi­cular to the back-bone plane. These two planes represent two Cg groups. This group frequencies clearly proved that the point group consists of two Cg groups. The stretching region is not well resolved but the other regions are in oonfoimity with a Gs site symmetry.C-OH Frequencies :The frequencies at 1182, 969, 1071, 1065 om '^  are attributed to the vibra­tions of this group. The 1182 cm *^ is identified to be the stretching frequency of this group. The other frequencies are due to the bending modes of this group.234 K . Mallikarjuna Rao and C. K . Narayana SwamyInfrared spectra o f potassium citrate etc. 235According to th,o structural details, this group vibrations should appear only in (0()1) plato spectrum, since this group is in tlio (001) plane. But C-OH group frequencies may also appear in (010) plate spectrum, since the O-H-O type of bonds attached to some (7-atom also will have C-OH group vibrations.0" C Frequencies :The frequencies of this group appear at 950, 530, 523, h08 cm^' and the split components an^  identifif^d and duly assigned.0 -C Torsional Vibrations :Tho>so are due to torsional vibrations of the molecular frfiiine and identified at 420 and 411 cm~^Hydrogen Bond Frequencies :Tlie frequency regions of this group wore reporttxi by U8 in the previous ])aper on potassium citrate at 2370, 1760, 1645 cm  ^ The O -H -0  frequencies of tlio polycjystalline spoctnim li.ave split up into a number of components in tJio present single cj'ystal spectra. Duo to tjie lack of full details regarding the miraher and arrangement of hydrogen bonds, we wore unable to derive maximum useful information from the spcxdra and could only identify the regions.K e f e r e n c e sBurns D. M. & Jball J. 1954 Acta, Cryst. 7, 137.DociuH J. C. 1949 Chem, Fhys. 17. 1315.Dubttl O. 1962 Milcro, Chem, Acta. P262.(Jroth F. 1910 Ckemische Krystalloyraphic, Publisher : Wilhelm Engolmann, Toil 3, 478.Hadzi D. 1965 Parc & Appl. Chem. 11, 435.Halford R. S. 1946 J, Chem. Phys. 14, 8 .Hornig D. F. 1948 J. Chem, Phys, 16, 1063..luhnson C. K. 1965 .4c/a. Cryst. 18. 1014,Love E. W. & Patterson A. L. 1960 Acta. Cryat. 13, 426.Kao K. M. & Swamy C. K. N, 1970 Indian J, Phys, 44, 34.Rao K. M. & Swamy C. K. N. 1971 Indian J, Phys. 45, 455.Kao K. M. & Swamy C. K. N. 1972a Ind. J, Pure & Appl, Phys. 10, 176.Kao K. M. & Swamy C. K. N. 19726 Indian J. Phys, 46, 236.

Infrared Spectra of Potassium Citrate Monohydrate Single Crystals

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Infrared Spectra of Potassium Citrate Monohydrate Single Crystals

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