John, Mariamma

Nayar, V U

Santha, N

IACS Institutional Repository

Indian J. Phys. «7B (5), 413 -  420 (1993)V ibrational spectroscopic studies of Slj(C H 2 )2(NH3 )2 ]3 P 4 0 j2 .14H 2OMariamma John, N Sanlha and V U NayarDepartment of Physics, University of Kerala, Kariavaltom, Trivandrum-695 581Kerala, IndiaandG KereszluryCentral Reseajch insiiluie for Chemistry, H-1525, Budapest, PO Box 17, Hungary Received 10 February 1993, accepted 2 Auj^ ust 1993Abstract ; IR and Uaman spectra of Sr[(CH2)2(NH 3)2l3P40|2.14H 2O have been recorded and analysed. The bands corresponding to (CH 2)2(NH^)2^ and P4OJ2 groups and water4 ,molecules are assigned, The P4O12 ion in this compound is likely to have ^4 .symmetry The absence of Fermi resonance sugge.sls weak hydrogen bonds in the ethylenediammonium ion. Multiplicity of the stretching modes'denoies the existence of atleast two crystallographically different water molecules in the compound The stretching frequencies of water molecule.s indicate that they are only weakly hydrogen bonded.Keywords ; Infrared spectra, Raman spectra, PACS Nos. : .13 20,Ea, 3120^1).1. Introductionl.iliylenediaminc forms very stable compounds by reacting with tetrametaphosphoric acid. X-ray studies of a number of such compounds have been reported 11,2]. From the crystal structure studies of (CH2 )2 (NH3 )2  ^ (ethylenediammonium) and P4 O12” sails, it is observed that a number of conformations are possible for both lhe.se groups. The structural studies on Si [(CH2 )2 (NH3 )2 ]3 P4 0 i2 .I4 H2 0  havc not yet been reported. The present study is an iiirempi to elucidate the structure of this compound and the nature of hydrogen bonding in it by an analysis of vibrational spectra of the compound,2. ExperimentalT'he sample was provided by Averbuch-PouChot M T, Univ A/Sepli Fourier, Grenoble, France.©1993IACSiri:Tit!■414 MarummiaJohn.NSantha. VVN ayart»^ G K tra timn e  compound in powder form was taken as a KBr pellet to wsord the JR spectrum usina a Nicolet 170 SX FTIR spectrometer. For recording the Raman speointm a Cary 82 specnometer connected to the data system of a Nicolet 7000 series Fourier Tiansfonn (FI) IR spwtromeier was used. A Spectra-Physics model 164-03 argon ion laser was used for the excitation and the spectra o f powder samples were recorded using the 514.5 nm line with a resolution better than 2 cm -'. Raman spectra in the range 50-2000 cm"' and 2400-3800 cm-* are presented in Figures 1 and 2 respectively. Figure 3 shows the IR spectrum of the studied compound ih the range 400-4000 cm"’.F ig u re  1. Raman spectra in the range (a) 50-1000 cm"' and(b) 1000-2000 cm"'.3. Interpretation of the spectrai.y. {CH2)2{NH3)\^ vibrations:Assignments of the observed bands of ethylenediammonium ioiv<refeiTed as eda) are carried out in terms of the vibrations of NH3, CH2 and skeletal modes.The bands in the region 3220-2990 cm"* are due to stretching modes of NH3 [3-5]. The 3002 and 2990 cm"’ bands are assigned to v^ NH^  since they are expected to be strong in Raman. Broad bands corresponding to &nd VgNHa modes appear also in the IRhil}3P40t2-»Hfi 415spectrum. The pmaiee of strong hydrogen bonding in salts of this type may lead to Luii'iidrmhlf Ftanni resonance between the NH stretching fundamentals and overtones and3800 3000 3400 3200 3000 , 2800 2000 2400WKVmmilBBRtcB'^ )Figure 2. Raman spectrum in the range 2400-3800 cm"'416 Mariamma John, N  Santha, V  U  Nayar and G  KereszJurycombinations of the NH deformation modes [3]. Three groups of combination modes, dcsignatedas 5as(NH;) + 5i,(NHj). 5„(NH;) + 5,(NHJ) and 5,(NHJ) + 5,'(NH;) can occur and they may shift their frequencies appreciably or gain in intensity by Fermi resonance. In the absence of Fermi resonance these modes can be observed [3] at5„(n h ;)  + 5^(NH;) 3180 -  3150 cm-I<5„(n h ;)  + 5,(n h )^ <5,(n H?) + 5,'(n h ;)around 3060 cm-1around 2940  cm -1In the spectra o f  the title compound these bands are observed in the region o f  N H 3  and C H 2  stretching m odes. The m ost intense bands have been som ew hat arbitrarily chosen as the fundam entals. In the observed spectrum, all bands in this region, except the sym m etric stretching N H 3  vibrations, are o f  medium or weak intensity. This indicates that hydrogen bonding in (C H 2 ) 2 (N H 3 )2  ^ ion is weak in this compound. M oreover, the N H 3  stretching vibrations are at higher frequencies compound to those o f (eda)CdCl4  and are similar to those in (eda)SnCl6  and (eda)PtCl6  [3]. Hydrogen bonds are also weak in hexachloro salts. \VasCH2  and V5 C H 2  appear in the region 2950 -2840  cm ”' [3 -5 ]. The lower frequency region o f  C H 2  stretching overlaps with the com bination region. But com binations and overtones are usually weaker than fundamental vibrations and they seldom  appear in Raman spectrum [6 j. These bands are sharp in both Raman and IR spectra.Oxton and Konp [3], and Powell [7] have noted the presence o f  bands o f  medium  intensity in the 21 (XV-1900 cm * region o f  the IR spectra o f  salts which contain the C - N H 3  grouping. T hese bands are identified as due to the com bination m odes involving NHJ rocking vibrations. They appear as weak broad bands at 2160  and 2120  5m~' in the IR spectrum.The 17(X)-16(X) cm"' region is expected to contain and H 2 O m odes. It isdifficult to assign these bands unambiguously. However, the bands at 1662 and 1640 cm are stronger in IR than the band at 1605 cm " '. The stretching bands o f water fall in the region from  3640  to 3 420  cm "'; nearer to those o f  a free water m olecu le . T hese favour the assignm ent o f  1605 cm ' band to water bending vibration. Therefore, 1662 cm"' and 1640 cm"' bands are assigned to 5,,j.NHt modes. The symmetric N H 3  mode is observed at 1530 cm"' in both the spectra.CH 2  bending vibrations give rise to the bands at 1470 cm"' in Raman and 1480 cm ”' in IR [3,4], T w isting and w agging m odes o f  C H 2  arc expected around 1340 cm " '. This is observed as a single band in both Raman and IR spectra. The band around 1065 cm"' in both Raman and IR is assigned to CN stretching m ode. Voc and N H 3 rocking m odes appear at lower frequencies than that o f v [ l^* ^^ tit P -O -P  stretching vibrations also appear in this region making an unambiguous assignment difficult.Vibrational spectroscopic studies d fSrl(C H 2H N H 3h h P 40i2. !4 H f i  417The possible symmetries of cthylcnediammonium ion are C2/1 (tfans structure) and C2 (gauche structure) [3J8], The bands in the region 1500-1250 cm";^  can indicate whether the ion has a trans or gauche structure. A strong or medium intense IR band at 1480 cm"^  suggests trans form of eda ion. For the gauche form this band is observed at 1460 cm'* [8]. In this compound, only a weak IR band is observed at 1480 cm"^ . If the ion has a gauche conformation, bands will appear around 1454, 1394, 1365 and 1321 cm“* in the IR spectrum. But only a very weak band is observed at 1365 cm"* in Sr(eda)3P40i2.14H20 in the IR. So from the observed spectra it is difficult to conclude the structure of ethylenediammonium ion in this compound.3.2. P4OJ2 vibrations:The frequencies of the P40]*2” anion are assigned on the basis of the characteristic vibrations of PO2* and POP groups [9-11]. The P-O bond in the PO2’ group is stronger than that in the POP bridge. Consequently, the vibrational frequencies of the PO2” group arc expected to be higher than those for the POP bridge. The asymmetric and symmetric stretching frequencies of PO2” are generally observed in the regions 1340-1220 and 1160-1100 cm"* rcsiTcctivcly [9-12J. The Raman lines at 1280, 1250 and 1225 cm'' and the IR lines at 1285 and 1250 cm'* are assigned to Vgs PO2 The stronger band at 1155cm“* and the weak band at 1110 cm'* in Raman and the IR bands at 1155 and 1105 cm"* are due to PO2”. The band at 930'cm"* in Raman and 980 ap'* in IR are assigned as the asymmetric POP stretching mode and the bands at 815, 790, 710 and 660 cm“* in IR and 715 and 670 cm"* in Raman to symmetric POP stretching modes. The bending modes of PO2' and POP arc assigned in regions,580-524 cm“* and 360-220 cm"* respectively. The Raman bands at 580 and 540 cm"' and the IR band at 524 cm”' are due to S POl~. For the POP bridge these modes are at 360, 302 and 220 cm“* in the IR.The possible symmetries of the P40j^2 anion arc Cj, C2h, S4 and D2d [9,10,13). Coincidence of most of the vibrational modes of the P40j^2 *** Raman and IR spectraindicates a non-centrosymmetric structure for the ion in this compound. Hence, the symmetry of the anion must be S4 or D2d • S4 symmetry is characterised by the presence of an IR band near or above 800 cm"' with another band between 750 and 700 cm"* and a Raman band below 700 cm"' [14]. The bands observed in the POP region of Sr(eda)3P40i2. HH2O are in agreement with this, indicating that S 4 can be the symmetry of the P40j^ ;f ion in this compound.The metal-oxygen stretching vibrations [15] occur in the POP bending region and therefore it is diAlcult to assign them unambiguously.3.3. H2O vibrations:The vibrational frequencies of a free water molecule are at 375  ^ (^as). 3652 ( v,) and 1595 (5jB)cm"* [16]. Depending on the strength of hydrogen bonding, the stretching modes willTable 1. Spectral data (cm~^) and band aaaignmems.Raman IR Aarignments418 M ariam m a Jo h n , N  Santha, V  U  N ayar and G  Keresztury3640W  3580 m 3500 mbr 3420 m3220 w 3090 w3002 s 2990 s2950 m2920 m 2840 w2740 vw1665 vw 1640 vw1615 vwbr1530 vw1470 w1342 w1280 w 1250 wbr 1225 w1155 vs 1110 wbr1065 w930 w715 vw 670 m3640 m 3580 m 3500 w 3420 s3200 wbr3020 mbr2940 m 2860 m2790 vw 2740 vw 2700 vw 2620 w 2580 w 2480 vw 2455 w2160 wbr 2120 wbr1662 m 1640 m1605 vw1530 m1480 vw1365 vw1285 vs 1250 vs1155 m 1105 vs1068 m980 vs 81Sm  790 m 710m  660 vwand V, H2Ov„NhJCH2V,CH2Combinations and overtonesCombinations involving NH3 rock 5H20 »4 nh;«CH2Twisting and wagging of CH2v„PO^v,PO^VCNPOPV.POTRamin IR AaaignineniiVibmtiemal spectroscopic studiesTabk 1. {Contd.i419580 w540 vw475 vw 465 vw360 m 335 m 302 w 220 vw180 vw 155 vw 90 vw524 vs 455 vwtfPOjNH3 torsion6 POP and metal-oxygon stretchingLattice modesVj -  symmetry stretching, -  asymmetric stretching^  -  symmetric bending, ^  -  asymmetric bendingvs -  very strong, s -  strong, m -  medium, mbr -  medium broad, vw -  very weak, w ” weak, vwbr -  very weak broad, wbr« weak broad.shift to lower wavenumbers and bending modes to higher wave numbers [16], The bands in the region 3640-3420 cm"' are due to the stretching vibrations of H2 O and the bands at 1615 cm“' in Raman spectrum and 1605 cm'* in the IR are due to the bending vibrations of H 2O. The stretching and bending modes of water indicate that water molecules form only weak hydrogen bonds in the compound. The four bands in the stretching region and the broad bending mode show that at least two crystallographically different water molecules exist in the crystal.4 . C o n c lu s io n s1 The absence of Fermi resonance suggests weak hydrogen bonds in the eda ion.2  The P4 0 f2~ ion in the compound is likely to have S 4  symmeiiy.3 Atleast two crystallographically different water molecules are present in the compound. The stretching frequencies of water molecules indicate that they are only weakly hydrogen bonded.AcknowledgmentAuthors are grateful to Prof. M T Averbuch-Pouchot, Univ Joseph Fourier, Grenoble, France for providing the sample. NS is grateful to Council of Scientific Sl Industrial Research, New Delhi for a fellowship.References[ IJ' M Bagieu-Beucher, A Durif and J C Guitel 1988 Acta Cryst. C44 2063^f21 M T Averbuch-Pouchot and A Durif 1989 Acta Cryst. C45 46f>7B-(5)7420 Mariamma John, N  Santha, V U  Nayar and G  Keresztury[3] I A Oxion and 0  Knop 1978 J. Mol. Struct. 43 17|4] Daizy Philip and G Aruldhas 1987 J. Raman Sped rose. 21 211[5J R D McUchlan \91A Spedfochim Acta 30A 985[6 ] , E F H Brittain. W O George and C H J Wells 1970 Introduction to Molecular Spectroscopy^Theory amiExfjenment (London Academic)[7] DB Powell 1960 Spectrochim Acta 16 241[8] Y Omura and T Shiinanouchi 1973 J Mol. Spectro.se. 45 208[9] Xavier Mathew and V U Nayar 1989 J. Raman Spectrosc. 20 633110] N Santha and V U Nayar 1990 J. Raman Spectrosc. 21 517[11] V Ramakrishnan and G Aruldhas 1085 Infrared Phys 25 665[12] K Viswanathan, V U Nayar and G Aruldhas 1985 Proc. Indian Acad. Su. (Chem. Sci.) 95 463[13] C Romers, J A A Ketelaar and C H McGillary 1951 Acta Cryst 4 114[14] Kh Kh Muldagaliev, A V Lazarev and A P Mirgorodskii 1974 Inory>. Mater. 10 653[15] P F Gonzalez Diaz and M Santos 1978 Spectrochim Acta A34 241[16] S N Vinogradov and R H Linnel 1970 Hydrogen Bonding (New York ■ Van Nostrand)

Vibrational Spectroscopic Studies of Sr[(CH2)2(NH3)2]3P4O12.14H2O

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Vibrational Spectroscopic Studies of Sr[(CH2)2(NH3)2]3P4O12.14H2O

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