Vibrational spectra of mono, di and trimethyl ammonium double sulphates of rare earths Pr, Nd, Ho and Eu

Spectrochimica Acta Part A 65 (2006) 278–284

Vibrational spectra of mono, di and trimethyl ammonium double sulphates of rare earths Pr, Nd, Ho and Eu R.S. Jayasree a,∗ , V.U. Nayar b , V. Jordanovska c a

Department of Radiology, Sree Chitra Tirunal Institute for Medical Sciences and Technology, Trivandrum 695011, Kerala, India b Department of Optoelectronics, University of Kerala, Kariavattom, Trivandrum 695581, Kerala, India c Institute of Chemistry, University of Skopje, Arhimedova 5, Macedonia Received 12 August 2005; received in revised form 19 August 2005; accepted 21 October 2005

Abstract Infrared and Raman spectra of four rare earth (Ho, Eu, Nd and Pr) double sulphates have been recorded and analysed based on the vibrations of methyl ammonium cations, sulphate anions and water molecules. Formation of hydrogen bonds of the type N H· · ·O and O H· · ·O are identified in all the compounds. Bifurcated hydrogen bonds are present in the compounds with dimethyl ammonium cations. The sulphate anions are distorted and occupy a lower site symmetry in the compounds. The bands obtained for (CH3 )2 NH2 and SO4 2− ions indicate that the structural bonding of (CH3 )2 NH2 Eu(SO4 )2 ·H2 O and (CH3 )2 NH2 Ho(SO4 )2 ·4H2 O is identical. Electronic transition bands of Eu3+ and Nd3+ observed in the Raman spectra of these two compounds have been identified and discussed. © 2005 Elsevier B.V. All rights reserved. Keywords: Infrared spectroscopy; Raman spectroscopy; Electronic structure; Rare earth bromates

1. Introduction

2. Experimental

Vibrational spectra of mono, di and trivalent cations with different anions have been the subject of many investigators mainly for its importance in the field of phase transitional studies and hydrogen bond strength analysis [1–4]. A series of compounds with mono, di, tri and tetramethyl ammonium cations and sulphate anions have been prepared and their thermal behaviour studied by Jordanovska and Siftar [5–7]. The vibrational spectroscopic studies of these compounds except that of tetramethyl ammonium cations are dealt with and explained in this paper. The IR and polarised Raman spectra of the double sulphate with tetramethyl ammonium cation have been reported earlier by Jayasree et al. [8]. Several studies have been reported to characterise the energy sequence of the 7FJ and 5DJ levels of rare earth ions. The electronic spectra can be used as a tool to determine the local microsymmetry of the rare earth ion in the crystal. In this paper, an attempt is made to assign the electronic transitions observed in the Raman spectra of Eu3+ and Nd3+ ions of two compounds.

The double sulphates of rare earths(III) and dimethyl ammonium (CH3 )2 NH2 Ho(SO4 )2 ·4H2 O (referred to as CHS) and (CH3 )2 NH2 Eu(SO4 )2 ·H2 O (referred to as CES) were obtained by evaporation of an aqueous mixture of rare earth(III) sulphates [Ln(SO4 )3 ] and dimethyl ammonium in molar ratio 1:4 to 1:15 at room temperature and by subsequent treatment of some concentrated reaction mixtures with ethanol [6]. By evaporating an aqueous mixture of rare earth(III) sulphate and trimethyl ammonium sulphate in molar ratio greater than 1:10 and up to 1:20, double sulphates of rare earth(III) and trimethyl ammonium (CH3 )3 NHNd(SO4 )2 ·3H2 O (referred to as CNS) were obtained [7]. Double sulphate of rare earth(III) with monomethyl ammonium CH3 NH3 Pr(SO4 )2 ·3H2 O (referred to as CPS) was obtained by evaporating at room temperature of an aqueous mixture of monomethyl ammonium sulphate and rare earth(III) sulphate in a molar ratio from 1:2 to 1:10 [5]. The crystal products were filtered off, washed with ethanol and dried in air. Raman spectra of CES and CHS were recorded using a 1401 Spex Raman spectrometer equipped with a Spectra Physics Model 165.08Ar+ ion laser. The spectra were recorded using 514.5 nm excitation wavelength at a resolution better than 3 cm−1 . The Raman spectrum of CNS was recorded using a Bruker IFS-66V-

∗

Corresponding author. Tel.: +91 471 2443152x124/117 (O)/+91 471 2478792 (R); fax: +91 471 2446433. E-mail address: [email protected] (R.S. Jayasree). 1386-1425/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2005.10.043

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FTIR spectrometer connected with a Raman module (Bruker, FRA-106) using radiation of 1064 nm from an Nd:YAG laser. Raman spectrum recorded for CPS was masked by high background fluorescence, and hence is not included for the analysis. FTIR spectra of all the compounds were recorded using a Bruker IFS-66V-FTIR spectrometer in the 50–4000 cm−1 with the samples taken as polyethylene pellets in the far IR region and KBr pellets in the mid IR region.

Table 2 Summary of the factor group (CH3 )2 NH2 Ho(SO4 )2 ·4H2 O

3. Factor group analysis CHS crystallises in the orthorhombic space group Pnma with 4 formula units in the unit cell. The holmium atom, occupying a special position, is co-ordinated by eight oxygen atoms (four from SO4 group and four from H2 O molecules) in the form of a bicapped trigonal prism. (CH3 )2 NH2 cations are linked by bifurcated hydrogen bond N H· · ·O directed only to the sulphate groups [9]. CPS crystallises in monoclinic space group P21 with Z = 2. Here, Pr atom is co-ordinated to nine oxygen ˚ atoms with the O Pr O distance ranging from 54.7 to 149.6 A [10]. Factor group analysis of CHS and CPS were carried out by following the correlation method developed by Fateley et al. [11]. Excluding acoustic modes at k = 0, 405 optical modes of CHS under D2h factor group are distributed as

Factor group analysis of CPS gives 165 optical modes under the space group P21 (C22 ) and they are distributed as

The summary of the factor group analysis of CPS and CHS are given in Tables 1 and 2, respectively. The factor group analysis of CNS and CES are not included in this paper due to the unavailability of detailed structural data. Table 1 Summary of the factor group analysis of CH3 NH3 Pr(SO4 )2 ·3H2 O Factor group species under C2 A

B

Translational modes Pr CH3 NH3 SO4 2− H2 O

3 3 6 9

3 3 6 9

Librational modes CH3 NH3 SO4 2− H2 O

3 6 9

3 6 9

Intramolecular modes CH3 NH3 SO4 2− H2 O

18 18 9

18 18 9

Acoustic modes

−1

−2

83

82

Factor group modes of D2h species Ag

B1g

B2g

B3g

Au

B1u

B2u

B3u

Translational modes Ho 2 (CH3 )NH2 + 2 SO4 2− 3 6 H2 O

1 1 3 6

2 2 3 6

1 1 3 6

1 1 3 6

2 2 3 6

1 1 3 6

2 2 3 6

Librational modes (CH3 )NH2 + 1 3 SO4 2− H2 O 6

2 3 6

1 3 6

2 3 6

2 3 6

1 3 6

2 3 6

1 3 6

Internal modes (CH3 )NH2 + SO4 2− H2 O

15 9 6

12 9 6

15 9 6

12 9 6

12 9 6

15 9 6

12 9 6

15 9 6

Acoustic modes

0

0

0

0

0

−1

−1

−1

53

49

53

49

49

52

48

52

4. Results and discussion The observed bands of the IR and Raman spectra of CES, CHS, CNS and CPS with assignments of various modes are given in Table 3. The spectra are analysed in terms of the vibrations of (CH3 )2 NH2 + [dimethyl ammonium (DMA)], CH3 NH3 + [monomethyl ammonium (MMA)] or (CH3 )3 NH+ [trimethyl ammonium (TMA)] cations, SO4 2− anions and water molecules. Electronic transitions observed in the Raman spectra are assigned and they are given in Table 4. The Raman and IR spectra of the compounds are shown in Figs. 1–4. 4.1. (CH3 )2 NH2 + vibrations of CES and CHS CH3 , NH2 and skeletal modes of H2 NC2 contribute to the internal modes of (CH3 )2 NH2 + ion. DMA ion has an intrinsic C2v symmetry and it occupies a centrosymmetric position in the lattice. But as the DMA+ ion cannot be centrosymmetric, the ion must be orientationally disordered to occupy the centrosymmetric site. The 27 internal modes of the free DMA ion under C2v symmetry are as given as DMA = 9A1 + 5A2 + 7B1 + 6B2 . Of these modes, the nine skeletal modes of H2 NC2 correspond

Fig. 1. Raman spectrum of (CH3 )2 NHNd(SO4 )2 ·3H2 O in the 50–3500 cm−1 region.

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Table 3 Spectral data and assignments (CH3 )3 NHNd(SO4 )2 ·3H2 O (CNS) CPS

CHS

IR

IR

141s

52vvw 111vw 125wsh 140vssh

219sbr 260ssh 347vvw 363vvw

425m

489m

206m 235ssh 251vvs 343vvw 355vvw 382sh 434s 455vw 463vw 479m

of

CH3 NH3 Pr(SO4 )2 ·3H2 O

(CPS),

CES Raman

122 w

228w

IR

641vvs

559m 607m

647m 680wsh

Raman

135vvs 196w 212ssh 231vvs 339vvw

433s

420vw 446m 468m 495vw 510vw

602vs

434ms 455vv 468vw 474w 492m

615w 622w

650s

745m 803m

SO4 rot M O stretch

137w tCH3 233vw

␦NC2

324vvw 356vvw

␦C4 ␦NC3

44m 464m

υ2 SO4

597w 612m 640w

υ2 SO4

659ms

773vw 804vw

CH3 rock 811vw υC N

948s 1004s

1075vvs

1098vvs

1120vvs

1146vvs

1186vvs

1197wsh

1380wsh

1435m

980vs 1000vs

1001vs 1096vvs

1114m 1155m 1178sh 1250vw 1272vw 1290vw 1335w 1420w

1142vvs 1207vssh

1440w 1445w

1008m 1002s 1087m 1097w 1144m 1165vvw 1178vvw 1210vw

1335vw 1342vw 1408vw 1415vw 1437vw

1482w 1510vs 1595wsh

1500vw

1646s

1670w

2922 2986ms

Raman

912vw 938m

988m

1642vvs

2900wsh 2980m 3005w 3051m 3081w

and

370vw

594ms

815m 880vw

1643vvs 1668vs

IR

(CES)

Assignments

103 W

474w

607s 621vw 628vw 672vw 685w 706vw 734vw

(CH3 )2 NH2 Eu(SO4 )2 ·H2 O

51 w

347vw 359 372vw 388w 448m 457m 462w

(CHS),

CNS

53 w 104 w 120wsh 142vvs 200ssh 218ssh 239vvs

498w

607vvs

(CH3 )2 NH2 Ho(SO4 )2 ·4H2 O

1650w

2903m 2935w 2997vw 3051m

983vs

1130vvs 1170vvs

998vs 1011vvs 1070ns 1100ms 1130m 1130m

υ1 SO4 υ3 SO4

␦S CH3

1458 1473 1506 1522 1541 1559 1636 1685 1700 1716 1734

␦as CH3

υ 2 H2 O 1644vvw

␦as NH3

2889vw

υs CH3 υas CH3

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Table 3 (Continued ) CPS

CHS

IR

IR

3192w 3389vvsbr

3368vsbr

CES Raman

IR

3150w 3162w 3229w 3348vvw 3487vw 3518vvw 3518vvw

CNS Raman

IR

Assignments Raman υs NH2 /NH3 υas NH2 /NH3

3103ws 3143vsbr 3233ssh 3365vvsbr

3272w 3380w 3556vw 3588vw 3556vw 3588vw

3333

3247vw 3296vvw

υ 1 H2 O υ 3 H2 O

Table 4 Electronic transitions observed in the Raman spectra of (CH3 )3 NHNd(SO4 )2 ·3H2 O and (CH3 )2 NH2 Eu(SO4 )2 ·H2 O Raman shift (cm−1 ) CNS, 1064 nm excitation

Equivalent energy

Assignments

CES, 514.6 nm excitation

1643vw 1775sh 1837vs 1912vvs 1992ssh 2033w 2061wsh 2076ms 2355w 2385w 2473vvvsbr 2549vvsbr 2600vvvsbr 2885m 2895m 2903m 2935w 2983m 2997m 3068m 3103vs 3143vvsbr 3252vvs 3272ssh

to Γ = 4A1 + A2 + 2B1 + 2B2 . The remaining 18 degrees of freedom correspond to the modes of two methyl groups. The stretching frequencies of CH3 are expected in the wide range of 2800–2950 cm−1 depending upon the type of compounds [12]. The methyl group attached to a nitrogen atom shifts these modes to 2805–2780 cm−1 region [13]. In CES and CHS, the bands observed between 2900 and 3005 cm−1 in the Raman spectra and between 2900 and 2980 cm−1 in the IR spectra are assigned to the stretching modes of CH3 . The Raman spectrum of CES is masked by the fluorescence spectrum of Eu3+ appearing as very intense and broad band in the 2300–3300 cm−1 region. Only one band corresponding to the stretching vibration of CH3 is observed in the IR spectrum of CHS while two bands are observed in this region for CPS. Symmetric and asymmetric bending modes are assigned in the 1475–1340 cm−1 region. The C N stretching mode is observed as weak bands at 880 cm−1 for CHS and at 912 cm−1 for CES

7756 7624 7562 7487 7407 7366 7338 7323 17081 17051 16963 16887 16836 16551 16541 16533 16501 16453 16439 16421 16333 16293 16184 16164

4F3/2 → 4I13/2

5D1 → 7F3 5D0 → 7F1 5D0 → 7F1

5D0 → 7F1 5D1 → 7F4 5D0 → 7F2 5D0 → 7F4 5D0 → 7F2 5D1 → 7F4

in the Raman spectrum. This mode is not observed in the IR spectrum. In primary amines, in dilute solutions, the stretching modes of NH2 are observed in the 3300–3500 cm−1 region [13]. In solids these modes may shift to lower wavenumbers due to hydrogen bonding. In primary amines the symmetric and asymmetric stretching modes are linearly related by the expression, υs NH2 = 345.5 + 0.876υas NH2 . The assignments of symmetric and asymmetric stretching modes of NH2 are made on the basis of this relation and are observed at 3051 and 3081 cm−1 as medium intense and weak bands, respectively, in the Raman spectrum of CHS. The high intensity of the bands observed in the IR spectrum of NH stretching region and the observed shift towards high wavenumber region of the NH bending and rocking modes suggest that the amine group forms strong hydrogen bonds in both the compounds. The intensity of this band is significantly large in CHS compared to CES. The stretching frequency

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Fig. 2. Raman spectra of (CH3 )2 NH2 Ho(SO4 )2 ·4H2 O in the: 50–1350 cm−1 (a) and 1400–3550 cm−1 (b) regions.

of the methyl group attached to nitrogen atoms shifting to lower wavenumbers to around 2800 cm−1 is not observed in the present case, even though the observed frequencies are at lower wavenumbers compared to free methyl groups. The absence of band near 2800 cm−1 is due to the presence of bifurcated hydrogen bonds, since bent hydrogen bonds show large deviation from linearity and are always associated with high stretching frequencies [13]. This is in good agreement with the X-ray data of CHS where the hydrogen bonds from (CH3 )2 NH2 + are found to be bifurcated and directed to the O(1) and O(2) of sulphate groups [9]. The assignments of various bands to different modes are in good agreement with the assignments made for the vibrations of DMA+ ion in (CH3 )2 NH2 ClO4 , (CH3 )2 NH2 NO3 and dimethyl ammonium halides [14,15].

Fig. 4. FT-IR spectra of: (CH3 )2 NH2 Ho(SO4 )2 ·4H2 O (a), CH3 NH3 Pr(SO4 )2 ·3H2 O (b), (CH3 )2 NH2 Eu (SO4 )2 ·H2 O (c) and (CH3 )3 NHNd (SO4 )2 ·3H2 O (d).

4.2. CH3 NH3 + vibrations of CPS A free CH3 NH3 + ion has a C3v symmetry and has 18 normal modes which are distributed as . A broad band extending from 2800 to 3600 cm−1 is observed in the IR spectrum corresponding to the stretching mode region of NH3 and CH3 . Since this band is not well resolved, it is difficult to assign the stretching modes of NH3 from the IR spectrum. The weak shoulder bands appearing at 2986 and 2850 cm−1 are assigned, respectively, to the asymmetric and symmetric stretching vibrations of CH3 . The deformation band of NH3 is observed at 1643 cm−1 as an intense band. The rocking mode NH3 which is expected to appear around 1260 cm−1 is not observed in the present study. The symmetric and asymmetric bending modes of CH3 are assigned, respectively, to the bands at 1435 and 1473 cm−1 . The appearance of NH3 deformation mode at higher wavenumbers compared to free state value of NH3 is an indication of the weakening of N H bond due to the formation of N H· · ·O type hydrogen bonds in the compound. 4.3. (CH3 )3 NH+ vibrations of CNS

Fig. 3. Raman spectra of (CH3 )2 NH2 Eu (SO4 )2 ·H2 O in the: and 2200–3600 cm−1 (b) regions.

50–1750 cm−1

(a)

CH3 , NH and skeletal modes contribute to the internal modes of (CH3 )3 NH+ cation. The assignments are in good agreement with that of the vibrations of trimethyl ammonium

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hexachloroantimonate [16]. A free trimethyl amine molecule has a C3v symmetry with the normal modes of vibrations distributed as 8A1 + 4A2 + 12E. A weak band observed at 2889 cm−1 in the Raman spectrum is assigned to the symmetric stretching mode of CH3 . An unresolved broad band is observed in the IR spectrum in the stretching mode region of CH3 and NH3 . The NH stretching mode is assigned to the band observed at 3247 cm−1 in the Raman spectrum. The asymmetric bending mode of CH3 is observed as a weak band at 1473 cm−1 in the IR spectrum. The symmetric bending mode of NH is observed at 1458 cm−1 in the IR spectrum. From the observed IR and Raman bands, it is clear that TMA also forms hydrogen bonds similar to those of MMA and DMA ions. 4.4. SO4 2− vibrations The normal mode vibrations of a free tetrahedral SO4 2− ion under Td symmetry have frequencies at 981, 451, 1104 and 613 cm−1 for υ1 (A1 ), υ2 (E), υ3 (F2 ) and υ4 (F2 ) modes, respectively. All these modes are Raman active whereas only υ3 and υ4 modes are IR active [17]. In all the compounds, the IR inactive symmetric stretching mode is observed as medium intense to highly intense bands in the IR spectra. In CPS and CNS, the υ1 mode appears at 988 and 983 cm−1 without much deviation from the free state value whereas in CES, this mode appears at higher wavenumbers 1001 cm−1 . In CHS, two equally intense bands are observed in the Raman spectrum at 1003 and 987 cm−1 for this mode. In the Raman spectra, this mode splits into two in CES and CNS also with an order of splitting of 6 and 13 cm−1 , respectively. In CHS, the order of splitting is 20 cm−1 . A complete lifting of degeneracy is observed in the triply degenerate asymmetric stretching mode (υ3 ) of CHS, CES and CNS in the Raman spectra, with additional splitting in CNS and CES. A broad intense band extending from 1050 to 1230 cm−1 with distinct peaks are observed in the IR spectra of all compounds. The bands observed in the 430–500 cm−1 are assigned to the symmetric deformation vibration (υ2 ) of SO4 in all the compounds. Additional bands observed in this region in the Raman spectra are assigned to the Raman active ␦(NC3 ) vibrations. The bands observed between 550 and 690 cm−1 are assigned to the asymmetric bending (υ4 ) mode of SO4 2− . The degeneracy of this mode is found to be partially lifted in the IR spectra of CPS, CES and CNS whereas complete lifting of degeneracy is observed in the IR and Raman spectra of CHS. In MoO4 crystals, Hardcastle and Wachs have shown that the Mo O stretching frequency appears at lower frequencies for the shortest metal–oxygen bond when the tetrahedron is more regular [18]. Following the same principle, it can be inferred that the SO4 2− ion in CES is more distorted than those in CPS, CHS and CNS as the υ1 mode appears at higher frequency. The complete lifting of degeneracy of the υ2 , υ3 and υ4 modes and the appearance of IR inactive υ1 and υ2 modes indicate that the sulphate tetrahedron has linear as well as angular distortion in all the compounds [19,20]. The splitting observed in the non-degenerate stretching mode is due to the correlation field splitting since the order of splitting is less than 20 cm−1 in all

283

the compounds [17]. The bands obtained for (CH3 )2 NH2 + and SO4 2− ions in both CHS and CES indicate that the structural bonding of CES is similar to that of CHS. 4.5. Water vibrations A very intense broad band extending from around 3600 to 2800 cm−1 is observed in the IR spectra of all the compounds along with the stretching modes of methyl and amine groups of the cations. Several weak bands are identified in the Raman spectrum in this region. In the bending mode region, an intense band is observed around 1640 cm−1 in the IR spectra of CHS and CES. This band is more intense in CPS and CNS with additional bands appearing as shoulders. The appearance of the stretching mode of water at lower wavenumbers and bending modes at higher wavenumbers compared to the free state value of water molecules indicate that these water molecules form strong hydrogen bonds in the compounds [8]. The enhanced intensity of these modes in the FTIR spectra further confirms this result. 5. External modes External modes of the ions and the metal oxygen stretching modes appear below 300 cm−1 . The translational and librational modes of NH2 are assigned at higher wavenumbers than those of SO4 ions [21]. The bands observed below 125 cm−1 are assigned to the translational and librational modes of SO4 . Rotational modes of CH3 are observed around 250 cm−1 . 6. Electronic Raman spectra The triply ionised Eu and Nd have six and three 4f electrons, respectively, outside the closed orbitals in their ground state configuration. Transitions relating to changes in electronic states within the 4fn configuration may appear in the Raman spectra depending on the symmetry of the rare earth ion. The transitions between these levels are restricted by the selection rules for electric and magnetic dipole moments [22]. The electronic bands observed in the Raman spectra of CES and CNS along with the equivalent energy and assignment for the transitions are given in Table 4. The very high intensity of the bands in the specified region compared to normal modes of sulphate ions indicate that these bands are not due to pure vibrational modes. In the triply ionised configuration, the ground state is the isolated 7FJ and the next state is 5DJ for Eu3+ whereas the ground state of Nd3+ is 4IJ/2 and the next is 2HJ/2 . The spin orbit coupling splits the 7F term into seven multiplets with J = 0–6 and 5D term into five multiplets with J = 0–4. The ground state of Nd3+ is split into four multiplets such as 4I9/2 , 4I11/2 , 4I13/2 and 4I15/2 . Since the fluorescence transition of Eu3+ originate from 5D0 and 5Dn1 levels, simplified electronic spectra could be obtained even at room temperature. For Nd3+ , excited state electronic transitions may be induced from the metastable 4F3/2 state because this state is longer lived than the higher lying crystal field components of 4F5/2, 7/2, 9/2 Stark manifolds. The selection rules for

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electronic transitions between the intermanifold levels is given by the J = 2, while those between J = 3/2 and 5/2 manifolds are not allowed. The energy of the exciting line (514.5 nm in the case of Eu and 1064 nm in the case of Nd) being well above the emitting levels of Eu and Nd ions, fluorescence transitions from these levels to the ground state are observed in the Raman spectra in the 2300–3300 cm−1 for Eu and 1600–2100 cm−1 for Nd. The highly intense bands observed at 2549 and 2600 cm−1 are assigned to the 5D0 → 7F1 transitions of the Eu3+ . Transitions due to 5D0 → 7F0 is not observed in the spectrum of Eu3+ . This transition is strictly forbidden by the selection rules (J = 0 ↔ 0) and parity rules. This transition will have measurable intensity only if the Eu3+ ion occupies sites of symmetry Cn , Cs or Cnv [23]. The absence of this transition confirms that the ion occupies site symmetries other than those mentioned above. There remains some ambiguity in the identification of the different 5DJ → 7FJ transitions because of the superposition of several transitions originating from different emitting levels. Assignments are made by considering the fact that the 5D0 → 7FJ transitions are stronger than the 5D1 → 7FJ transitions since 5D0 level is more populated than 5D1 . Out of the eight electronic bands observed in the Raman spectrum of Nd3+ ion, six bands are assigned to the 4F3/2 → 4I13/2 transition. The two bands at 1643 and 1775 cm−1 do not correspond to any of the allowed transitions of the Nd3+ ion. 7. Conclusion The amine groups of the dimethyl ammonium cation of (CH3 )2 NH2 Eu(SO4 )·H2 O and (CH3 )2 NH2 Ho(SO4 )2 ·4H2 O form strong hydrogen bonds in the compounds. Formation of bifurcated hydrogen bonds have been confirmed in these compounds. The amine group of monomethyl and trimethyl ammonium cations of CH3 NH3 Pr(SO4 )2 ·3H2 O and (CH3 )3 NHNd(SO4 )2 ·3H2 O are also found to form hydrogen bonds of the type N H· · ·O. The spectral pattern of water vibrations confirms the presence of O H· · ·O type hydrogen bonds in the compounds. In all the four compounds, the sulphate anions are distorted both linearly and angularly. The distortion is more in the compounds with dimethyl ammonium cations. The bands obtained for (CH3 )2 NH2 and SO4 2− ions indicate

that the structural bonding of (CH3 )2 NH2 Eu(SO4 )2 ·H2 O and (CH3 )2 NH2 Ho(SO4 )2 ·4H2 O is identical. Electronic transition bands observed in the Raman spectra of (CH3 )2 NH2 Eu(SO4 )2 ·H2 O and (CH3 )3 NHNd(SO4 )2 ·3H2 O have been identified and assigned. References [1] R. Jakubas, G. Bator, M. Gosniowska, Z. Ciunik, J. Baran, J. Lefebvre, J. Phys. Chem. Solids 58 (1997) 989–998. [2] T.K.K. Srinivasan, M. Mylrajan, J.B. Srinivasa Rao, J. Raman Spectrosc. 23 (1992) 21–27. [3] V.P. Mahadevan Pillai, V.U. Nayar, V. Jordanovska, J. Solid State Chem. 133 (1997) 407–415. [4] T.K.K. Srinivasan, M. Mylrajan, Phase Transit. 38 (1992) 97–113. [5] V. Jordanovska, J. Siftar, J. Therm. Anal. 39 (1993) 281–288. [6] V.B. Jordanovska, J. Siftar, Thermochim. Acta 221 (1993) 73–78. [7] V. Jordanovska, J. Siftar, Thermochim. Acta 195 (1992) 21–26. [8] R.S. Jayasree, V.U. Nayar, V. Jordanovska, J. Solid State Chem. 127 (1996) 51–55. [9] A. Arhar, L. Golic, V. Jordanovska, J. Siftar, Vestn. Slov. Kem. Drus. 28 (1981) 311–320. [10] V. Jordanovska, Ph.D. Thesis, Edvard Kardelj University of Ljubljana, Yugoslavia, 1981. [11] W.G. Fateley, F.R. Dollish, N.T. Mc Devitt, F.F. Bentley, Infrared and Raman Selection Rules for Molecular and Lattice Vibrations— Correlation Method, Wiley/Interscience, New York, 1972. [12] N.B. Colthup, L.H. Daly, S.E. Wiberley, Introduction to Infrared and Raman Spectroscopy, Academic Press, New York, 1964. [13] C.N.R. Rao, Chemical Application of Infrared Spectroscopy, Academic Press, New York, 1963. [14] T.K.K. Srinivasan, M. Mylrajan, Chem. Phys. Lett. 182 (1991) 175–179. [15] M. Mylrajan, T.K.K. Srinivasan, J. Phys. Chem. Solids 49 (1988) 929– 937. [16] R.F. Howe, M.J. Taylor, Spectrochim. Acta A 43 (1987) 73–80. [17] G. Herzberg, IR, Raman Spectra of Polyatomic Molecules, Van Nostrand, New York, 1966. [18] F.D. Hardcastle, I.F. Wachs, J. Raman Spectrosc. 21 (1990) 683–690. [19] S.P. Gupta, B. Singh, B.N. Khanna, J. Mol. Struct. 112 (1984) 41–49. [20] S.R. Sahaya Prabaharan, P. Muthusubramanian, R. Saravanan, S.K. Mohanlal, Bull. Mater. Res. 15 (4) (1992) 355–362. [21] P.M.A. Sherwood, Vibrational Spectroscopy of Solids, Cambridge University Press, Great Britain, 1977. [22] S.S. Saleem, G. Aruldhas, H.D. Bist, Spectrochim. Acta 40A (1984) 149–154. [23] F. Pelle, J.P. Denis, B. Blanzat, C. Pannel, Mater. Res. Bull. 12 (1977) 511–517.