Journal of Molecular Structure 970 (2010) 139–146

Contents lists available at ScienceDirect

Journal of Molecular Structure

journal homepage: www.elsevier .com/ locate /molst ruc

Molecular structure and vibrational spectrum of [Mg((CH3)2SO)6](ClO4)2 studiedby infrared and Raman spectroscopies and DFT computations

El _zbieta Szostak, Kacper Dru _zbicki *, Edward MikuliDepartment of Chemical Physics, Faculty of Chemistry, Jagiellonian University, Ingardena 3, 30-060 Kraków, Poland

a r t i c l e i n f o a b s t r a c t

Article history:Received 23 January 2010Accepted 24 February 2010Available online 1 March 2010

Keywords:Hexadimethylsulphoxidemagnesiumchlorate(VII)Vibrational spectroscopy (FT-IR and FT-RS)DFTB3LYP/6-311++G(3df,p)Phase-change materialsPCM

0022-2860/$ - see front matter � 2010 Elsevier B.V. Adoi:10.1016/j.molstruc.2010.02.063

* Corresponding author. Tel.: +48 12 6632265; fax:E-mail address: druzbick@chemia.uj.edu.pl (K. Dru

The Fourier-transform Raman and infrared spectra were recorded in the solid state and interpreted bycomparison with theoretical spectra derived from density functional theory (DFT) calculations. The[Mg((CH3)2SO)6]2+ cation equilibrium geometry under S6 symmetry, harmonic vibrational frequenciesand related infrared and Raman scattering intensities were determined using B3LYP/6-311++G(3df,p)level of theory. Very good agreement between the theoretical and the experimental spectra justify anappropriateness of the used approach. Analogous, additional calculations were performed separatelyfor the ClO�4 anion within Td point group, at the same level of theory.

� 2010 Elsevier B.V. All rights reserved.

1. Introduction

We recently investigated the phase polymorphism of several[M((CH3)2SO)6](ClO4)2 compounds, where M = Cd, Co, Mn, Zn, Niand Mg, using the differential scanning calorimetry (DSC) method[1–6] and found that all these substances had several crystallineand rotational solid phases. Some of these phases can be very eas-ily super-cooled and indicate metastable character. The com-pounds with M = Ni, Co and Zn crystallize in an orthorhombicsystem (space group: P31c, no. 159, Z = 2) [7,8] and those withM = Mn and Cd crystallize in a trigonal system (space group:Fdd2, no. 43, Z = 2) [9–11]. Unfortunately, the crystal structure of[Mg((CH3)2SO)6](ClO4)2 is so far unknown. However, the crystallattice structure of all of these compounds consist of two kinds ofcomplex ions: [M((CH3)2SO)6]2+ and ClO�4 , where the cations areslightly deformed octahedrons, in which the metal(II) cation iscoordinated by six oxygen atoms derived from the dimethylsulph-oxide (DMSO) ligands and tetrahedral (point symmetry Td) ClO�4anions. The DMSO ligands are built like pyramids (p. s. C2v).

In the present work we want to focus on vibrational spectrum ofthe title compound inclusive its interpretation based on the theo-retical spectrum calculated by means of density functional theory(DFT). The presented results bring a reliable theoretical view onthe vibrational spectrum with a fully described picture of the inter-nal vibrational dynamics, which may dispels any possible doubts

ll rights reserved.

+48 12 6340515._zbicki).

and controversies about the band assignment of this and analogouscompounds. We are currently exploring the temperature-depen-dent infrared and Raman scattering spectra of several[M(DMSO)6](ClO4)2 type complexes, and the results of these stud-ies will be reported elsewhere.

It is well known that vibrational spectroscopy is a relativelycheap and efficient method of studying phase transitions and reori-entational dynamics in this class of compounds, which are inter-esting from a point of view of new technology applications,particularly as phase-change materials for thermal storage.

2. Experimental details

The Fourier-transform middle infrared (FT-MIR) vibrationalspectrum of polycrystalline [Mg(DMSO)6](ClO4)2 was recorded atroom temperature (RT) in the range of 4000–400 cm�1 at a resolu-tion of 4 cm�1 on Bruker EQUINOX 55 spectrometer, equipped witha Nernst lamp as the light source and with a deuterium triglycinesulphate (DTGS) detector. Two different samples were measured.One was prepared as a pellet with KBr, and the second was pre-pared as a Nujol mull. Fourier-transform far-infrared (FT-FIR) spec-trum at RT was recorded in the frequency range of 600–50 cm�1 ata resolution of 1 cm�1 on Nicolet Magna-IR 760 spectrometer,equipped with a DTGS detector and a Globar lamp as the lightsource. The sample was mixed with powdered polyethylene andpressed to obtain a pellet.

The Fourier-transform Raman scattering (FT-RS) measurementsat RT were performed using 1064 nm line of Nd:YAG laser as

140 E. Szostak et al. / Journal of Molecular Structure 970 (2010) 139–146

excitation wavelength in the region of 4000–100 cm�1, at a resolu-tion of 4 cm�1 on a Thermo-Nicolet FT-Raman NXR 9650 spectrom-eter equipped with germanium detector.

Fig. 1. [Mg(DMSO)6]2+ cation equilibrium geometry obtained with B3LYP/6-311++G(3df,p) level of theory.

3. Computational details

The main goal of the quantum-chemical computations was tocompute the theoretical vibrational spectra which could supportan interpretation of the experimental ones. All the computationswere carried out using Gaussian 03 package, Revision D.01. [12],implemented on BARIBAL computer in the Academic ComputerCentre, CYFRONET AGH, Kraków. Density functional theory (DFT)calculations were carried out using Becke’s three-parameter hybridexchange functional combined with Lee–Yang–Parr correlationfunctional (B3LYP) [13–15]. In the present work the calculationswere based on the isolated [Mg(DMSO)6]2+ cation model, so theenvironmental effects as well as interactions with the ClO�4 anionswere not considered. Because no crystallographic data for the titlecompound is present, the constructed initial geometry based onthe structural parameters for the [Mg(DMSO)6](C5H5)2 compound,published by Jaenschke et al. [16]. The initial [Mg(DMSO)6]2+

geometry was symmetrised and then optimized within assumedS6 symmetry [17,18]. The extended Pople’s type triple-f split-va-lence basis set 6-311++G(3df,p) includes additional diffusive func-tions on the heavy atoms, which cover a substantially larger spaceand allow for a better description of atomic interactions. Using dif-fusive basis sets is recommended for systems with a sufficient neg-ative charge, so it is appropriate for atoms with a free pair ofelectrons. Furthermore, using of diffusive functions for a propercapture of the electronic structure is necessary in this case, becauseof the close proximity of the oxygen and sulphur atoms, and be-cause of a weak coordination character of the title compound.The higher angular momentum polarization functions were useddue to the presence of sulphur atoms, for more proper descriptionof DMSO ligands geometry. Additional sets of diffusive and p-typepolarization functions were also added to the hydrogen atoms. Thegeometry optimization was followed by the harmonic frequencycalculations, which verified that the obtained geometry was a trueminimum on the potential energy surface (PES). The Raman activ-ities, calculated with Gaussian 03, were transformed into Ramanintensities using Raint program [19] by expression:

Ii ¼ 10�12 � ðm0 � miÞ4 � ð1=miÞ � RAi; ð1Þ

where Ii is the Raman intensity, RAi is the Raman scattering activi-ties, mi is the wavenumber of the normal modes and m0 denotes thewavenumber of the light of excitation laser [20].

The analogous additional calculations were performed sepa-rately for the ClO�4 anion. B3LYP calculations were performed using6-311+G(3df) basis set. The structure optimization within assumedTd point group was followed by the frequency calculations.

To account mainly for anharmonicity effects, the calculatedwavenumbers were multiplied by the scaling factor of 0.9679for the 3500–750 cm�1 region, as suggested by Andersson andUvdal [21]. The width of added Lorentzian curves in the pre-sented theoretical spectra was fitted to the experimental onesusing Gaussian v. 2.2 program [22]. We have also tried to mimicenvironmental effects induced by DMSO in the crystal lattice, byperforming the computations within the polarizable continuummodel (PCM) model of Tomasi et al. [23–25]. The PCM modeltakes account of specific molecular shape in the construction ofthe solute cavity. The PCM calculations were done choosingDMSO as a solvent and the default parameters as implementedin Gaussian 03 at B3LYP/6-311++G(3df,p) level of theory. How-ever, the obtained results have not delivered significant improve-ment. In the results presented below, we have constrained only to

signal a slight influence on the molecular structure and theoreti-cal spectrum, indicating the bands which may be especially sen-sitive on the environmental effects. The spectra computed withinvacuum and PCM models have been compared in the supplemen-tary section of this paper.

4. Results

4.1. Molecular structure

The equilibrium [Mg(DMSO)6]2+ geometry, belonging to the S6

point group, has been illustrated in Fig. 1. No significant differ-ences in the calculated cation geometry can be observed in com-parison with the experimental data for the analogous[Mg(DMSO)6](C5H5)2 compound [16]. However, the experimentalgeometry of the cation is slightly distorted. Mg–O bonds lengthsdetermined for this compound vary from 2.069 to 2.090 Å, whilethe calculated Mg–O bond length equals 2.101 Å. The calculatedS–O bond length is 1.522 Å, while these determined by Jaenschkeet al. vary from 1.520 to 1.525 Å. The computed S–C bond length is1.802 Å and the corresponding experimental values differ from1.777 to 1.784 Å. No significant differences in the angle valueswere also observed. The computed C–S–C angle equals 98.31�and the corresponding experimental values fluctuate between97.9� and 98.6�. The calculated O–S–C angle values are 105.25�and 105.51� while the experimental ones alternate from 104.9�to 105.7�. The relatively biggest, however, still only slight differ-ence was observed for the Mg–O–S angle, where the computed va-lue is 127.40� and corresponding values vary from 120.7� to123.1�. The calculated O–Mg–O angles amount to 89.10�, 90.90�and 180�, while the corresponding experimental ones are 88.81�,91.19� and 180�, respectively.

Computations within the assumed PCM approach have notdelivered any noticeable changes in the geometric parameters. Itmay be noticed that the calculated metal–ligand distance has beenshortened for 0.012 Å, which gives a value of 2.089 Å. The S–O, C–Sand C–H bonds have been shortened for �0.001–0.003 Å. No signif-icant differences in the angle values were observed. The corre-sponding C–S–C angle value is lower for 0.1�. The O–S–C anglevalue is also smaller for 0.2–0.3� in this case.

E. Szostak et al. / Journal of Molecular Structure 970 (2010) 139–146 141

4.2. Band assignments of vibrational spectra

Experimental FT-RS and FT-MIR spectra of [Mg(DMSO)6](ClO4)2,with comparison to the theoretical results, are presented in Figs. 2and 3, respectively. The intensive bands linked to the water vibra-tions may be found in the FT-MIR spectrum recorded in KBR pelletat about 3300 and 1600 cm�1, due to a hygroscopic properties ofthe title compound and the sample preparation process. Thus thespectrum of the sample in Nujol is also presented to draw a com-parison, and it clearly shows that the adsorbed water has no influ-ence on the vibrational spectrum of [Mg(DMSO)6](ClO4)2.

The comparison of the theoretical and experimental spectraldata, with the assignment of the bands, is presented in Table 1.The complex vibrational motions of [Mg(DMSO)6]2+ cation can beresolved into 177 normal modes, including 108 modes belongingto the 12 methyl groups (also –CH3 torsions). According to grouptheory [17], the vibrational representation of [Mg(DMSO)6]2+ un-der S6 point group is

Cvib ¼ 29Ag þ 29Eg þ 30Au þ 30Eu: ð2Þ

All the symmetric modes (g) should be Raman-active whereas theasymmetric ones (u) should be IR-active.

If the methyl groups are considered as point masses, then thevibrational representation becomes

Cvib0 ¼ 11Ag þ 11Eg þ 12Au þ 12Eu: ð3Þ

Under this assumption, the internal modes of the ligands formthe representation:

CðaÞvib0¼ 6Ag þ 6Eg þ 6Au þ 6Eu: ð4Þ

Simultaneously, the modes unique for the complex are distrib-uted among the following species:

CðbÞvib0¼ 5Ag þ 5Eg þ 6Au þ 6Eu: ð5Þ

The possible symmetry lowering in the solid state, from S6 atleast to C3, can cause all vibrations to be both infrared- andRaman-active [17]. However, the complementary character of the

Fig. 2. Comparison of the experimental FT-RS spectrum of [Mg(DMSO)6](ClO4)2 (a) wisymmetry (b) and the ClO�4 anion with assumed Td symmetry (c). The bands due to the chmost intensive bands. Theoretical frequencies were multiplied by the scaling factor of 0

presented spectra and the very good agreement between the the-ory and the experiment show that MgðDMSOÞ2þ6 geometry can besuccessfully described within S6 symmetry, which indicates ab-sence of any significant geometric distortions.

The tetrahedral ClO�4 anion has nine normal modes. The vibra-tional representation of ClO�4 under Td point group is

Cvib ¼ A1 þ Eþ 2F2: ð6Þ

All of them are Raman-active but only 2F2 are infrared-active [26].Most of the vibrations contain contributions from many internalcoordinates and involve the motion of a relatively large numberof atoms; however, the obtained spectra can be clearly divided intofew ranges connected with the sets of characteristic vibrations. Thevery good agreement between theoretical and experimental spectrais achieved, with the overall root mean square deviation (RMSD)value for the frequencies equals 20 cm�1.

4.2.1. Ligand vibrationsDespite the harmonic approximation and a lack of the Fermi

resonance effect consideration in the theoretical approach, thebands in the range of 3020–2910 cm�1, connected with the C–Hstretching modes, are quite well reproduced by theoretical calcula-tions. These frequencies are overestimated by the calculations;however, using scaling factor 0.9679 brings the reduction of theoverestimation down to about 30–40 cm�1. It rather suggests exis-tence of only weak, dispersive interactions in the crystal phase. TheC–H stretching band intensities are very well reproduced in thetheoretical Raman spectrum. According to the theory, these bandsshould be IR inactive; however, due to the environmental effectsthey were observed with very low intensity in the experimentalFT-MIR spectrum. The PCM calculation brought a slight reductionof the underestimation for about 10 cm�1. It should be also notedthat the used scale factor is fixed for all the spectral area and theoverestimation may be further reduced by using a scale factor clo-ser to 0.96 for the range over 2000 cm�1.

The medium and weak bands representing the CH3 deformationvibrations manifest in the spectral range of 1435–900 cm�1, wherethe bands corresponding to the v(S–O) and v(ClO�4 ) stretching

th the theoretical spectra calculated for the MgðDMSOÞ2þ6 cation with assumed S6

lorate(VII) anion are designated with an asterisk. Intensities were normalized to the.9679 for the spectral range of 3500–750 cm�1.

Fig. 3. Comparison of the experimental FT-MIR (in KBr and Nujol) and FT-FIR spectra (separated by the dotted line) of [Mg(DMSO)6](ClO4)2 (a) with the theoretical spectracalculated for the MgðDMSOÞ2þ6 cation with assumed S6 symmetry (c) and for the ClO�4 anion with assumed Td symmetry (d). The bands due to the chlorate(VII) anion aredesignated with an asterisk. Intensities were normalized to the most intensive bands. Theoretical frequencies were multiplied by the scaling factor of 0.9679 for the spectralrange of 3500–750 cm�1.

142 E. Szostak et al. / Journal of Molecular Structure 970 (2010) 139–146

modes, can also be observed. The bands are generally well restoredby the calculations. The anti-symmetric deformation modes mani-fest in the spectra as the bands in the range of 1435–1410 cm�1.The symmetric deformation vibrations (‘umbrella modes’) manifestin the spectra as the bands lying near 1300 cm�1. The related theo-retical frequencies are generally underestimated by 5–15 cm�1.The PCM calculation brought a slight enhancement of the underesti-mation for ca. 10 cm�1.

The CH3 rocking modes are spread in the range of 1030–900 cm�1.It should be underlined, that these modes are mixed with the v(S–O)stretching modes down to ca. 950 cm�1, which makes the assignmentof the connected bands questionable.

The shoulder bands assigned to the CH3 torsion modes were re-corded in the FT-RS spectrum at 215 and 197 cm�1 – which is alsoobserved as a very weak band in FT-IR spectrum. These bands areconnected, respectively, to the in-phase and out-of-phase torsionsof the adjacent methyl groups in DMSO. The theoretical frequen-cies for the in- and out-of-phase modes are overestimated forabout 5 and 30 cm�1, respectively.

It is known from the literature [27,28], that oxygen coordinationdecreases and that sulphur coordination increases the S–O stretch-ing vibration frequency in the dimethyl sulfoxide complexes. Thespectrum indicates that the v(S–O) bands of free DMSO have down-shifted from wavenumbers 1056 cm�1 (FT-RS) and 1042 cm�1 (FT-IR) to 966 and �955 cm�1, respectively [28]. According to our stud-ies, we believe that the character of the weak band, observed in theFT-RS spectrum at 966 cm�1, is dominated by the collective, sym-metric vs(S–O) stretching mode, while the band at about 955 cm�1

corresponds to the set of asymmetric vas(S–O) stretching modes.Simultaneously, due to the metal–ligand coordination, the v(C–S)

frequency shifting occurs. The blue-shifts from 698 and 667 cm�1,respectively, up to 715 and 675 cm�1 have been observed. The bandsrecorded with a medium intensity in the FT-RS spectrum at309 cm�1 and with a weak intensity in the FT-IR spectrum were as-signed to the d(C–S–C) scissoring modes.

In comparison with the experimental values, the theoretical fre-quencies corresponding to the v(S–O), v(C–S) and d(C–S–C) modesare slightly underestimated for ca. 5–25 cm�1. The PCM calcula-tions did not bring any reduction of an error. In the solid state, thiseffect may be induced by the interactions with ClO�4 anions; how-ever, it may be also partially caused by the selection of an ex-change–correlation functional, which has been signalized by ourbackground calculations, carried out using several hybridfunctionals.

4.2.2. Metal–ligand vibrationsSix v (Mg–O)stretching modes manifest in the spectra as the

medium and weak peaks within the range of 450–395 cm�1, inboth FT-RS and FT-IR spectra. It should be noted that although itis symmetry forbidden, the weak band in FT-RS spectrum at394 cm�1 was also observed in the FT-IR spectrum. The bands ob-served in the FT-RS spectrum at 364 and 343 cm�1 were assignedto the set of nine d(O–Mg–O) bending modes. The FT-IR corre-sponding bands were recorded at 366 and 345 cm�1, respectively.Due to a dominant character of the vibrations, the bands recordedat 180 and 119 cm�1 by FT-RS, and also at 170 and 126 cm�1 by FT-IR, were assigned to the b(Mg–O–S) and c(Mg–O–S) types of me-tal–ligand deformation modes, respectively.

The computed values of v(Mg–O) frequencies are overestimatedby the theory for �15 cm�1, while the theoretical b(Mg–O–S) and

Table 1Theoretical B3LYP/6-311++G(3df, p) and experimental FT-IR and FT-RS spectral data (cm�1).

vIR vRS vDFT vscaled Cvib IIR IRS Assignment

18 18 Eu 0.1 0.0 Skeletal torsional deformations (T(–S–O–))18 18 Eu 0.1 0.023 23 Ag 0.0 1.530 30 Au 0.2 0.031 31 Eg 0.0 18.331 31 Eg 0.0 18.4

57w 36 36 Eu 1.1 0.0 Skeletal torsional deformations (T(–Mg–O–))39 39 Eu 0.1 0.039 39 Au 0.1 0.040 40 Ag 0.0 4.443 43 Eg 0.0 6.643 43 Eg 0.0 6.6

80w89w

48 48 Eu 0.6 0.0 Skeletal bending deformations48 48 Eu 0.6 0.050 50 Au 0.0 0.064 64 Eg 0.0 12.964 64 Eg 0.0 13.091 91 Ag 0.0 2.094 94 Eu 0.5 0.094 94 Eu 0.5 0.0

126vw 119w 113 113 Eg 0.0 2.6 c(Mg–O–S)113 113 Eg 0.0 2.6121 121 Au 2.4 0.0126 126 Ag 0.0 1.4

170vw 180m 160 160 Au 0.2 0.0 b(Mg–O–S)167 167 Eu 3.8 0.0167 167 Eu 3.8 0.0169 169 Eg 0.0 4.9169 169 Eg 0.0 5.0174 174 Ag 0.0 9.4

194vw 197sh 197 197 Eu 0.0 0.0 T(–C–S–)a�T(–C–S–)b

197 197 Eu 0.0 0.0198 198 Eg 0.0 0.4198 198 Eg 0.0 0.4199 199 Ag 0.0 0.4200 200 Au 0.0 0.0

215sh 241 241 Eu 0.1 0.0 T(–C–S–)a+T(–C–S–)b

241 241 Eu 0.1 0.0243 243 Eg 0.0 0.3243 243 Eg 0.0 0.3243 243 Au 0.1 0.0243 243 Ag 0.0 0.0

280w 267 267 Au 3.5 0.0 d(C–S–C)307vw 309m 277 277 Eu 6.0 0.0

277 277 Eu 6.0 0.0297 297 Eg 0.0 10.2297 297 Eg 0.0 10.2301 301 Ag 0.0 5.1

345s 343m 317 317 Au 0.0 0.0 d(O–Mg–O)325 325 Eu 0.8 0.0325 325 Eu 0.8 0.0327 327 Eg 0.0 12.8327 327 Eg 0.0 12.8

366s 365w 337 337 Eu 15.4 0.0 d(O–Mg–O)337 337 Eu 15.5 0.0338 338 Ag 0.0 15.7347 347 Au 27.6 0.0

396w 394w 409 409 Eg 0.0 1.9 vs(Mg–O)409 409 Eg 0.0 2.0

405w 422 422 Ag 0.0 1.0435m 430 430 Au 23.6 0.0 vas(Mg–O)

437 437 Eu 34.0 0.0437 437 Eu 34.0 0.0

456w 446 446 E 0.0 13.49 d2(ClO4)446 446 E 0.0 13.49

629m 623m 616 616 F2 5.20 9.64 d1(ClO4)616 616 F2 5.20 9.64616 616 F2 5.20 9.4

673w 680vst 661 661 Eg 0.0 8.4 vs(C–S)661 661 Eg 0.0 8.4661 661 Ag 0.0 100.0661 661 Au 0.3 0.0661 661 Eu 0.7 0.0661 661 Eu 0.7 0.0

(continued on next page)

E. Szostak et al. / Journal of Molecular Structure 970 (2010) 139–146 143

Table 1 (continued)

vIR vRS vDFT vscaled Cvib IIR IRS Assignment

720w 714w 694 694 Eg 0.0 9.8 vas(C–S)694 694 Eg 0.0 9.8694 694 Eu 1.3 0.0694 694 Eu 1.3 0.0694 694 Ag 0.0 31.0695 695 Au 7.4 0.0

898vw 908w 907 878 Eg 0.0 0.0 q2(CH3)907 878 Eg 0.0 0.0908 879 Eu 0.4 0.0

916w 908 879 Eu 0.4 0.0 q2(CH3)908 879 Au 2.9 0.0908 879 Ag 0.0 0.0

931vst 919 890 A1 0.0 100 vs(ClO)A1

942sh 946 916 Eg 0.0 0.7 q2(CH3)946 916 Eg 0.0 0.7946 916 Eu 1.1 0.0946 916 Eu 1.1 0.0947 917 Ag 0.0 0.3947 917 Au 8.9 0.0

955vst 966w 971 940 Eg 0.0 4.2 vs(S–O) asymmetric, q1(CH3), q2(CH3)971 940 Eg 0.0 4.3973 942 Eu 25.6 0.0973 942 Eu 25.6 0.0973 942 Au 18.4 0.0975 944 Ag 0.0 1.6 vs(S–O) symmetric, q1(CH3)

1000vst 1015sh 1028 995 Eg 0.0 5.8 q1(CH3), v(S–O)1028 995 Eg 0.0 5.81034 1001 Au 53.5 0.01035 1002 Eu 100.0 0.01035 1002 Eu 100.0 0.01036 1003 Ag 0.0 4.6

1021vst 1039 1006 Eg 0.0 1.0 q1(CH3)1039 1006 Eg 0.0 1.01040 1007 Au 13.3 0.01040 1007 Eu 28.1 0.01040 1007 Eu 28.1 0.0

1027w 1066 1032 Ag 0.0 11.3 v(S–O)1075m 1093 1058 F2 100 13.64 vas(ClO)F2

1094vst 1095w 1093 1058 F2 100 13.641116vst 1105w 1093 1058 F2 100 13.641298vw 1297vw 1332 1290 Eg 0.0 0.0 ds(CH3)

1332 1290 Eg 0.0 0.01332 1290 Eu 0.1 0.01332 1290 Eu 0.1 0.01333 1290 Au 1.0 0.01333 1290 Ag 0.0 0.0

1320w 1314vw 1352 1309 Eu 6.2 0.0 ds(CH3)1352 1309 Eu 6.2 0.01352 1309 Eg 0.0 0.11352 1309 Eg 0.0 0.11353 1310 Ag 0.0 0.41353 1310 Au 4.6 0.0

1399sh 1438 1392 Eg 0.0 0.5 d2as(CH3)

1438 1392 Eg 0.0 0.51439 1393 Eu 1.7 0.01439 1393 Eu 1.7 0.01439 1393 Au 9.8 0.01439 1393 Ag 0.0 0.1

1413m 1420m 1450 1403 Ag 0.0 0.5 d1as(CH3), d2

as(CH3)1451 1404 Au 2.3 0.01452 1405 Eu 2.3 0.01452 1405 Eu 2.3 0.01453 1406 Eg 0.0 10.01453 1406 Eg 0.0 10.01454 1407 Eu 2.6 0.01454 1407 Eu 2.6 0.01454 1407 Ag 0.0 0.41455 1408 Eg 0.0 1.51455 1408 Eg 0.0 1.51455 1408 Au 0.2 0.0

1432m 1437sh 1471 1424 Ag 0.0 0.3 d1as(CH3)

1471 1424 Au 3.2 0.01472 1425 Eg 0.0 0.71472 1425 Eg 0.0 0.71472 1425 Eu 15.8 0.01472 1425 Eu 15.8 0.0

144 E. Szostak et al. / Journal of Molecular Structure 970 (2010) 139–146

Table 1 (continued)

vIR vRS vDFT vscaled Cvib IIR IRS Assignment

2912w 3044 2946 Au 0.1 0.0 vs(CH3)a�vs(CH3)b

3044 2946 Ag 0.0 2.03044 2946 Eg 0.0 0.23044 2946 Eg 0.0 0.23044 2946 Eu 0.0 0.03044 2946 Eu 0.0 0.0

2920vst 3046 2948 Au 0.0 0.0 vs(CH3)a+vs(CH3)b

3046 2948 Ag 0.0 77.63046 2948 Eg 0.0 0.93046 2948 Eg 0.0 0.93046 2948 Eu 0.3 0.03046 2948 Eu 0.3 0.0

2993w 3138 3037 Ag 0.0 0.3 vas(CH3)a�vas(CH3)b

3138 3037 Eu 0.1 0.03138 3037 Eu 0.1 0.03138 3037 Au 0.4 0.03138 3037 Eg 0.0 1.03138 3037 Eg 0.0 1.0

3004st 3142 3041 Ag 0.0 0.7 vas(CH3)a+vas(CH3)b

3142 3041 Eu 0.4 0.03142 3041 Eu 0.4 0.03142 3041 Au 0.1 0.03142 3041 Eg 0.0 12.53142 3041 Eg 0.0 12.5

3010w 3016sh 3150 3049 Au 0.2 0.0 vas(CH3)3150 3049 Ag 0.0 0.13150 3049 Eg 0.0 4.83150 3049 Eg 0.0 4.83150 3049 Eu 0.3 0.03150 3049 Eu 0.3 0.03152 3051 Au 0.1 0.03152 3051 Eg 0.0 1.13152 3051 Eg 0.0 1.13152 3051 Eu 0.1 0.03152 3051 Eu 0.1 0.03152 3051 Ag 0.0 7.9

vw – very weak, w – weak, sh – shoulder, m – medium, st – strong, vst – very strong, v – stretching, q – rocking, d – scissoring, b – bending-in-plane, c – bending-out-of-plane,T – torsion, Cvib – normal mode symmetry, mscaled – scaled theoretical frequencies (sf = 0.9679 for the range of 3500–750 cm�1); IRel (%) – percentage relative intensity.a,b Adjacent parts of DMSO.

E. Szostak et al. / Journal of Molecular Structure 970 (2010) 139–146 145

d(O–Mg–O) frequencies are shifted down with respect to theexperiment for about 5 cm�1 and 20–30 cm�1, respectively. ThePCM calculations brought a slight reduction of the d(O–Mg–O) fre-quency error for �10 cm�1.

4.2.3. Skeletal vibrationsDue to the theoretical results, the bands connected with a

deformational motion of the most complicated nature should beobserved below 100 cm�1. According to the theoretical results,the torsion character of the deformational vibrations rises with de-crease of the wavenumber. The torsion motions over the S–Obonds within the DMSO ligands are found to be energetically thelowest ones. In the range down to 50 cm�1, explored by our FT-FIR measurements, we were able to observe three bands at 89,80 and 57 cm�1, which were assigned to the cation skeletal bend-ing deformation modes.

4.2.4. ClO�4 vibrationsAll vibrations connected with tetrahedral ClO�4 normal modes

were recorded in the Raman spectrum, while only F2 type vibra-tions are recorded in the infrared spectrum. The related infraredbands were recorded at 629 and 1100 cm�1. The Raman-activemodes were linked to the bands recorded in spectrum at the fol-lowing wavenumbers: 456 cm�1 (E), 623 cm�1 (F2), 931 cm�1 (A1)and 1100 cm�1 (F2). The distortion of the ClO�4 anion is reflectedwith the split of the 1100 cm�1 (F2), what may indicate the ClO�4symmetry lowering. Otherwise, this effect may be also caused bythe presence of more than one ClO�4 atom in the unit cell [29].

The theoretical frequencies were found at the following frequen-cies: 446 cm�1 (E), 616 cm�1 (F2), 890 cm�1 (A1) and 1058 cm�1

(F2). Thus, the values are visibly shifted with respect to the exper-imental ones.

The PCM computations upshifted the E and A1 modes, anddownshifted the frequencies of the F2 symmetry modes. We be-lieve that the visible deviations indicate an importance of theClO�4 repulsive interactions in the solid state, which were not in-cluded in the present approach.

5. General remarks

Although, the vibrational spectra of [Mg(DMSO)6](ClO4)2 werecalculated within the isolated molecule in vacuum model and com-pared with the experimental spectra recorded in the solid state, thevery close agreement between the theoretical and experimentalspectra have been obtained, with very good overall reproductionof the frequencies as well as the intensity relations. It confirmsthe appropriateness of the used approach. An overall RMSD valuedetermined for the frequencies equals 20 cm�1, which suggestsexistence of rather weak interactions in the studied system,excluding existence of strong intermolecular interactions.

Due to the restrictions of the theoretical approach some slightdeviations in the frequency values occurred. Computations withinthe polarizable continuum model using DMSO as a solvent, per-formed as the second approach, did not bring significant improve-ment of the results. Some slight geometric differences reflect in thetheoretical spectra by small frequency shifts; however, the differ-

146 E. Szostak et al. / Journal of Molecular Structure 970 (2010) 139–146

ences did not reflect in the overall RMSD value. Thus, we believethat the possible differences with respect to the experiment maybe induced rather by the interactions with ClO�4 anions, includingweak hydrogen bondings, not by the neighbouring cations.

Acknowledgements

We are grateful to J. Chrusciel PhD, Dr. habil from the Universityof Podlasie and M. Baranska PhD, Dr. habil from our Faculty fortheir help in the spectroscopic measurements. Computations wereperformed at the Academic Computer Centre CYFRONET AGH, Cra-cow, Poland (Grant number: MNiSW/SGI3700/UJ/032/2009).

Appendix A. Supplementary data

Supplementary data associated with this article can be found, inthe online version, at doi:10.1016/j.molstruc.2010.02.063.

References

[1] A. Migdal-Mikuli, E. Mikuli, E. Szostak, J. Serwonska, Z. Naturforsch. 58a (2003)341.

[2] A. Migdał-Mikuli, E. Szostak, Thermochim. Acta 426 (2005) 191.[3] A. Migdał-Mikuli, E. Szostak, Z. Naturforsch. 60a (2005) 289.[4] A. Migdał-Mikuli, E. Szostak, Thermochim. Acta 444 (2006) 195.[5] A. Migdał-Mikuli, E. Szostak, Z. Naturforsch. 62a (2007) 67.[6] E. Szostak, A. Migdał-Mikuli, J. Therm. Anal. Cal. (2010), in press.[7] E.J. Chan, B.G. Cox, J.M. Harrowfield, M.I. Ogden, B.W. Skeleton, A.H. White,

Inorg. Chim. Acta 357 (2004) 2365.[8] I. Person, Acta Chem. Scand. A 36 (1982) 7.[9] A. Migdał-Mikuli, E. Szostak, Acta Cryst. E 62 (2006) m2581–m2582.

[10] T.U. Lubeznowa, I. Ponomariew, Krystalografia 43 (1989) 862.[11] M. Sandström, Acta Chem. Scand. A 32 (1978) 519.

[12] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman,J.A. Montgomery Jr., T. Vreven, K.N. Kudin, J.C. Burant, J.M. Millam, S.S. Iyengar,J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega, G.A.Petersson, H. Nakatsuji, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa,M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J.E. Knox,H.P. Hratchian, J.B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R.E.Stratmann, O. Yazyev, A.J. Austin, R. Cammi, C. Pomelli, J.W. Ochterski, P.Y.Ayala, K. Morokuma, G.A. Voth, P. Salvador, J.J. Dannenberg, V.G. Zakrzewski, S.Dapprich, A.D. Daniels, M.C. Strain, O. Farkas, D.K. Malick, A.D. Rabuck, K.Raghavachari, J.B. Foresman, J.V. Ortiz, Q. Cui, A.G. Baboul, S. Clifford, J.Cioslowski, B.B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R.L.Martin, D.J. Fox, T. Keith, M.A. Al-Laham, C.Y. Peng, A. Nanayakkara, M.Challacombe, P.M.W. Gill, B. Johnson, W. Chen, M.W. Wong, C. Gonzalez, J.A.Pople, Gaussian 03, Revision D.01, Gaussian, Inc., Wallingford, CT, 2004.

[13] A.D. Becke, Phys. Rev. A Mol. Opt. Phys. 38 (1988) 3098.[14] C. Lee, W. Yang, R.G. Parr, Phys. Rev. B: Condens. Matter Mater. Phys. 37 (1988)

785.[15] P.J. Stephens, F.J. Devlin, C.F. Chabalowski, M.J. Frisch, J. Phys. Chem. 98 (1994)

11623.[16] A. Jaenschke, J. Paap, U. Behrens, Organometallics 22 (2003) 1167.[17] C.V. Berney, J.H. Weber, Inorg. Chem. 7 (1968) 283.[18] H.A. Patel, A.J. Carty, P.M. Boorman, Can. J. Chem. 48 (1970) 492.[19] D. Michalska, Raint Program, Wroclaw University of Technology, 2003.[20] D. Michalska, R. Wysokinski, Chem. Phys. Lett. 403 (2005) 211.[21] M.P. Andersson, P. Uvdal, Phys. Rev. Lett. 90 (2003) 076103.[22] N.M. O’Boyle, A.L. Tenderholt, K.M. Langner, J. Comp. Chem. 29 (2008) 839.[23] S. Miertus, E. Scrocc, J. Tomasi, Chem. Phys. 55 (1981) 117.[24] S. Miertus, J. Tomasi, Chem. Phys. 65 (1982) 239.[25] M. Cossi, V. Barone, R. Cammi, J. Tomasi, Chem. Phys. Lett. 255 (1996) 327.[26] K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination

Compounds, sixth ed., Part B., John Wiley & Sons, 2009.[27] G. Ma, A. Molla-Abbassi, M. Kritikos, A. Ilyukhin, F. Jalilehvand, V. Kessler, M.

Skripkin, M. Sandstrm, J. Glaser, J. Nslund, I. Persson, Inorg. Chem. 40 (2001)6432.

[28] A. Ciccarese, D.A. Clemente, A. Marzotto, G. Valle, J. Cryst. Spectrosc. Res. 23(1993) 223.

[29] R.A. Nyquist, C.L. Putzig, M.A. Leugers, R.O. Kagel, The Handbook of Infraredand Raman Spectra of Inorganic Compounds and Organic Salts, AcademicPress, 1997.