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Structure and vibrational assignment of magnesium acetylacetonate: A densityfunctional theoretical study

Sayyed Faramarz Tayyari a,*, Tayyebeh Bakhshi a, Sayyed Jalil Mahdizadeh a, Sepideh Mehrani b,Robert Erik Sammelson c

a Department of Chemistry, Ferdowsi University of Mashhad, Mashhad 91775-1436, Iranb Department of Chemistry, Islamic Azad University, Shahrood Branch, Shahrood, Iranc Department of Chemistry, Ball State University, Muncie, IN 47306-0445, USA

a r t i c l e i n f o

Article history:Received 9 June 2009Received in revised form 29 August 2009Accepted 2 September 2009Available online 6 September 2009

Keywords:Magnesium acetylacetonateDFT calculationsFourier transform IR and Raman spectraScaling factor

a b s t r a c t

Molecular structure of magnesium bis-acetylacetonate, Mg(acac)2, has been investigated by means ofab initio and density functional theory (DFT) calculations and the results were compared with its gas-phase electron diffraction data. For comparison, the structure of Mg(acac)2 was also optimized at theMP2 level using the 6-31G* basis set.

The harmonic vibrational frequencies of Mg(acac)2 were obtained at a variety of density functionaltheory levels using the 6-31G*, 6-311G*, 6-311++G**, and lanL2DZ basis sets. The vibrational frequencies2,4-13C and 2-13C derivatives of Mg(acac)2 were also calculated at the B3LYP/6-311++G** level. The cal-culated frequencies are compared with the experimental Fourier transform IR and Raman spectra. Allof the measured IR and Raman bands were interpreted in terms of the calculated vibrational modes.The scaled theoretical frequencies and the structural parameters are in excellent agreement with theexperimental data. Analysis of the vibrational spectra indicates a strong coupling between the chelatedring modes. Four bands at the 1021, 664, 569, and 414 cm�1 are found to be mainly due to themetalAoxygen stretching motions. The very strong Raman band at 414 cm�1 is assigned to the totallysymmetric MgAO stretching mode. The corresponding band in beryllium bis-acetylacetonate, Be(acac)2,appears at a considerably higher frequency (480 cm�1). This frequency difference is consistent with theirdifferent stability constants.

� 2009 Elsevier B.V. All rights reserved.

1. Introduction

The b-diketonates of various metals are interesting compoundsfrom both applicative and theoretical points of view. Thesecompounds have been used in the preparation of supported cata-lysts and as precursors of heterogeneous catalysts [1–5]. The vola-tility of some acetylacetonates makes possible their use for thinfilm formation with magnetic, electrical, and high-temperaturesuperconductor properties, by metal-organic chemical vapor depo-sition techniques [5–7]. Mg(acac)2 is an important source materialfor MgO films [7]. Amirthaligam et al. [8] studied the X-ray crystal-lography of Mg(acac)2. A gas-phase electron diffraction (E.D) studyof Mg(acac)2 was also performed by Zakharov et al. [9]. Both X-rayand E.D studies are consisting with the D2d structure for Mg(acac)2.A semi empirical molecular orbital calculation in the CNDO/2approximation also predicts the D2d isomer is more stable thanthe D2h by about 10 kcal/mol [10].

Junge and Musso [11] studied the infrared spectra of Mg(acac)2and its 13C substituted analogue in the 1600–650 cm�1 region. Theresults of 13C isotopic frequency shifts are very useful for interpre-tation of the vibrational spectra of Mg(acac)2. To our best knowl-edge, there is no study on the Far-IR or Raman spectra ofMg(acac)2.

The aim of the present work is the full assignment of thevibrational spectra [harmonic wavenumbers, and relative inten-sities for Raman and IR spectra] of Mg(acac)2 by means of den-sity functional theory (DFT) levels. Attempts will also be madeto study the efficiency of some popular DFT levels and basissets in predicting the vibrational frequencies of the titled com-pound, which may be helpful in predicting the properties ofsimilar complexes. The calculated vibrational frequencies arecompared with those observed experimentally. The calculatedband assignments at the DFT level are also compared withthose given by Junge and Musso [11], based on isotopic substi-tution. The calculated geometrical parameters will be comparedwith the previously reported electron diffraction results for thiscompound [9].

0022-2860/$ - see front matter � 2009 Elsevier B.V. All rights reserved.doi:10.1016/j.molstruc.2009.09.006

* Corresponding author. Tel.: +98 5118780216; fax: +98 5118438032.E-mail address: Tayyari@ferdowsi.um.ac.ir (S.F. Tayyari).

Journal of Molecular Structure 938 (2009) 76–81

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2. Experimental

Mg(acac)2 was prepared and purified according to the methoddescribed in the literature [12]. The anhydrous Mg(acac)2 complexhas been obtained by vacuum sublimation (at 0.2 Torr, 220 �C) andidentified by IR spectroscopy.

The IR spectra were recorded on a Bomem B-154 Fourier trans-form spectrophotometer in the region 600–4000 cm�1 by averag-ing 20 scans with a resolution of 2 cm�1. The spectra weremeasured as KBr pellets and in CH2Cl2 or CH3CN solution.

The Far-IR spectra in the region 600–100 cm�1 were obtainedusing a Thermo Nicolet NEXUS 870 FT-IR spectrometer equippedwith a DTGS/polyethylene detector and a solid substrate beamsplitter. The spectrum of the polyethylene pellet was collectedwith a resolution of 2 cm�1 by averaging the results of 64 scans.

The FT-Raman spectra were recorded employing a 180� back-scattering geometry and a Bomem MB-154 Fourier transform Ra-man spectrometer. The instrument was equipped with a ZnSebeam splitter and a TE cooled InGaAs detector. Rayleigh filtrationwas afforded by two sets of two holographic technology filters.The spectra were accumulated for 500 scans with a resolution of2 cm�1. The laser power at the sample was 400 mW.

3. Method of analysis

In this study, the molecular equilibrium geometry, harmonicforce field, and vibrational transitions of Mg(acac)2 were computedwith the GAUSSIAN 03 software system [13] by using a selection ofmodern density functionals, using 6-311G*, 6-31G*, LanL2DZ.LanL2DZ is a useful basis set for heavier metal complexes. The B[14], G96 [15], MPW1 [16], or B3 [17] exchange functionals werecombined with the PW91 [18] or LYP [19] correlation functionals,resulting in the eight different functionals BPW91, BLYP, B3PW91,B3LYP, G96PW91, G96LYP, MPW1PW91, and MPW1LYP. Applica-tions of the B3LYP and BLYP density functional were repeated withthe larger basis sets 6-311++G**, which is a triple-zeta split valenceset augmented with diffuse and polarization functions on all atoms(436 basis functions, 680 primitive Gaussians). For comparison, thegeometry of Mg(acac)2 was further optimized at the MP2 level,using the 6-31G* basis set.

Raman activities were computed by numerical differentiation ofdipole derivatives with respect to the electric field, using standardGAUSSIAN 03 procedures (Freq = Raman) and default options; thiscalculation is particularly time consuming and was not carried outfor the 6-311++G** basis set.

The assignment of the experimental frequencies are based onthe observed band frequencies and intensities in the infrared andRaman spectra confirmed by establishing one to one correlationbetween observed and theoretically calculated frequencies. Theassignment of the calculated wavenumbers is aided by the anima-tion option of the GaussView 3.0 graphical interface for Gaussianprograms [20], which gives a visual representation of the shapeof the vibrational modes.

4. Results and discussion

4.1. Molecular geometry

The optimized geometrical parameters of Mg(acac)2, obtainedat the B3LYP level (using 6-311++G**, 6-311G*, and 6-31G* basissets), and MP2 (using 6-31G* basis set) along with the gas-phaseelectron diffraction results of Mg(acac)2 [9] are given in Table 1.The geometry and the atom numbering system are shown inFig. 1. It can be clearly observed from Table 1 that the calculatedgeometrical parameters are somewhat sensitive to the choice of

level and basis sets. The calculated C1AC2 bond length was some-what shorter (0.020–0.033 Å) at all levels of theory from the GEDlength previously reported [9]. However, this is not the case forberyllium acetylacetonate, Be(acac)2 [21]. According to our calcula-tions, all methyl groups are staggered with respect to the C Obonds, which are in agreement with the Zakharov et al. [9] GED re-sults. The calculated energy differences between the staggered andeclipsed conformers are 11–13 kJ/mol (see Table 1).

4.2. Vibrational analysis

The fundamental wavenumbers obtained with different DFTprocedures were compared separately for both 1700–3100 and50–1700 cm�1 region with the experimental ones by means ofregression analysis. Simple scaling of the theoretical wavenumbersaccording to the equation mOBSD = amTHEOR generally leads to verysatisfactory agreement with the set of the observed wavenumbers;the least-square scaling factors a, regression coefficients R2, andstandard deviations SD are listed in Table 2 for both high andlow frequency regions. Superior results were obtained for the highfrequency region with the 6-31G*, 6-311G*, and 6-311++G** basissets in all levels of calculation (SD = 5.7–7.6 cm�1), except forMPW1PW91 (SD = 11.4). The best results for the lower frequency

Table 1Selected theoretical and experimental geometrical parameters for Mg(AA)2.a

Mg(acac)2

A B C D GEDb

Bond length (Å)MgAO 1.968 1.966 1.960 1.971 1.966(4)CAO 1.275 1.274 1.279 1.284 1.279(3)C2AC3 1.408 1.407 1.408 1.405 1.408(3)C1AC2 1.510 1.501 1.513 1.509 1.534(4)C1AH 1.094 1.090 1.093 1.091 1.099(4)

Bond angles (�)OMgO 91.4 91.7 93.0 93.0 93.3(4)MgOC 127.1 126.8 125.7 125.3OC2C1 115.8 115.7 115.5 115.0 116.2(5)C2C1H 109.6 109.2 109.2 108.9 108.8(10)C2C3C4 124.9 124.9 125.1 125.1 125.4(12)OC2C3 124.8 125.0 125.2 125.7DE(kJ/mol) n.c 11.6 12.3 11.1

a A, B, and C are stand for calculations at the B3LYP level using 6-311++G**,6-311G*, and 6-31G* basis sets, respectively; D is calculations at the MP2/6-31G*level; n.c., not calculated; DE, E(eclipsed)-E(staggered); M, metal.

b Data from Ref. [9].

Fig. 1. Half-structure and atom numbering system.

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region are obtained with the B3LYP, B3PW91, and MPW1LYP levelsusing 6-31G* or higher basis sets (SD = 11.7–12.9 cm�1).

The scaled wavenumbers, a equal to 0.9609 and 0.9849 for highand low frequency regions, respectively, (obtained at the B3LYP/6-311++G** level), IR intensities (obtained at the B3LYP/6-311++G**)and Raman activities (calculated at the B3LYP/6-311G* level) aregiven in Table 3 together with the experimental data. All calculatedvibrational frequencies and IR and Raman intensities are availableas supplementary data.

The Fourier transform infrared spectra of Mg(acac)2 in the solidphase and in solution are shown in Fig. 2. The solid state Ramanspectrum of Mg(acac)2 is given in Fig. 3. Lorentzian function is uti-lized for deconvolution of the infrared spectrum of Mg(acac)2 inthe 800–1800 cm�1 region and the results are shown in Fig. 4. Asshown in Table 4, the previously observed data [11] matches muchbetter with the 2-13C derivative, instead of 2,4-13C derivative,which was claimed by Junge and Musso [11].

The most calculated frequencies are slightly higher than the ob-served values for the majority of the normal modes. Two factorsmay be responsible for the discrepancies between the experimen-tal and computed spectra of Mg(acac)2. The first is caused by theenvironment. The second reason for this discrepancy is the factthat the experimental values are anharmonic frequencies whilethe calculated values are harmonic frequencies.

4.2.1. Vibrational irreducible representationAccording to D2d symmetry for the Mg(acac)2 complex, the

3N�6 = 81 vibrational modes can be classified among the symme-try species:

Cvib ¼ 13A1ðRÞ � 6A2 � 7B1ðRÞ � 13B2ðIR&RÞ � 21eðIR&RÞ

4.2.2. Band assignment4.2.2.1. CHa stretching region. The two normal modes due to theCHa stretching belong to A1 and B2 symmetry species. Comparingthe spectra of Mg(acac)2 with the previous assignments of acetyl-acetone [22] and Beryllium acetylacetonate, Be(acac)2, [21] and

considering the theoretical results, one expects to observe theCHa stretching at about 3100 cm�1. The Raman spectrum of Mg(a-cac)2 shows a band at 3079 cm�1, which is assigned to thesemodes. The corresponding bands in acetylacetone [22] and Be(a-cac)2 [21], are observed at 3098 and 3110 cm�1, respectively.

4.2.2.2. Methyl group stretching. Twelve CH stretching modes offour methyl groups can be divided into: 2A1(R) � 1A2 � 1B1(R) �2B2(IR & R) � 3E(IR & R) symmetry type. The CH stretching modesof the CH3 groups are expected to occur in the 3000–2900 cm�1 re-gion [21–25]. Three bands are observed in the Raman spectrum at2995, 2969, and 2922 cm�1. The latter band is strong and the oth-ers have weak scattering intensity in the Raman spectrum. By con-sidering our calculated Raman intensities and comparing themwith the reported results for acetylacetone [22], the band at2922 cm�1 is assigned to msCH3 and the bands at 2995 and2969 cm�1 are assigned to the in-plane and out-of-plane asymmet-ric CH3 stretching modes, respectively.

4.2.2.3. 1700�1000 cm�1 region. In this region, in addition to theCH3 deformation and rocking and also the CH in-plane bendingmodes, we expect to observe four bands due to the C O and C Cstretching modes. The Raman spectrum of Mg(acac)2 shows twovery weak bands at 1633 and 1610 cm�1, which the former is inac-tive and the latter is very strong in the IR spectrum. This result is inexcellent agreement with the calculation, which attributes the for-mer to the A1 and the latter to the B2 species of the msC O +msC C C. The assignment for the former, as far as we know, hasnot been reported, but the latter is assigned by Junge and Mussoto msC O [11]. The corresponding bands in Be(acac)2 spectra areobserved at 1602 and 1569 cm�1 [21]. The very strong IR band at1521 cm�1, which according to the theoretical calculation belongsto E species, is assigned to the asymmetric C C C stretching cou-pled strongly to the CAHa in-plane bending mode. Junge and Mus-so observed a low frequency shift of 8 cm�1 upon 2,4-13Csubstitution, which is very different from our calculations(16 cm�1). However, this frequency shift is in agreement with the

Table 2Mg(acac)2 scaling factors a, regression coefficients R2, and standard deviations SD (cm�1) for regressions of observed vibrational wavenumbers on theoretical ones (see text).

Regression, high frequency Regression, low frequency

a R2 SD a R2 SD

B3LYP/6-311++G** 0.9609 0.999997 5.7 0.9859 0.999858 11.9B3LYP/6-311G* 0.9600 0.999997 5.8 0.9781 0.999836 12.8B3LYP/6-31G* 0.9539 0.999995 7.1 0.9705 0.999839 12.7B3LYP/LANL2DZ 0.9509 0.999978 14.9 0.9764 0.999410 24.3BLYP/6-311++G** 0.9863 0.999997 5.6 1.0207 0.999713 16.9BLYP/6-311G* 0.9862 0.987789 6.7 1.0120 0.999673 18.0BLYP/6-31G* 0.9807 0.999994 7.5 1.0042 0.999692 17.5BLYP/LANL2DZ 0.9773 0.999982 13.6 1.0115 0.999219 27.9B3PW91/6-311G* 0.9559 0.999992 9.2 0.9763 0.999856 12.0B3PW91/6-31G* 0.9498 0.999988 11.0 0.9691 0.999842 12.6B3PW91/LANL2DZ 0.9455 0.999969 17.7 0.9716 0.999503 22.3BPW91/6-311G* 0.9792 0.999989 10.3 1.0080 0.999792 14.4BPW91/6-31G* 0.9733 0.999986 12.0 1.0004 0.999782 14.7BPW91/LANL2DZ 0.9686 0.999970 17.5 1.0039 0.999361 25.2G96LYP/6-311G* 0.9847 0.999996 6.4 1.0097 0.999692 17.5G96LYP/6-31G* 0.9795 0.999994 7.6 1.0023 0.999698 17.3G96LYP/LANL2DZ 0.9758 0.999980 14.1 1.0088 0.999230 27.7G96PW91/6-311G* 0.9779 0.999989 10.6 1.0058 0.999786 14.6G96 PW 91/6-31G* 0.9721 0.999985 12.3 1.0088 0.999230 27.7G96 PW 91/LANL2DZ 0.9671 0.999967 18.2 1.0013 0.999362 25.2MPW1LYP/6-311G* 0.9557 0.999998 5.0 0.9718 0.999832 12.9MPW1LYP/6-31G* 0.9495 0.999996 6.6 1.0064 0.999639 19.7MPW1LYP/LANL2DZ 0.9467 0.999978 14.8 0.9706 0.999432 23.8MPW1PW91/6-311G* 0.9499 0.999991 9.7 0.9691 0.999845 12.4MPW1PW91/6-31G* 0.9437 0.999987 11.4 0.9621 0.999840 12.6MPW1PW91/LANL2DZ 0.9393 0.999967 18.0 0.9644 0.999530 21.6

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frequency shift upon 2-13C substitution. The corresponding Ramanband appears as a medium band at 1521 cm�1.

Two strong IR bands at 1477 and 1414 cm�1 were not assignedby Junge and Musso. According to our theoretical calculations,these bands are attributed to the asymmetric C O stretching.The 1477 cm�1 band is coupled to the asymmetric CAH in-plane

bending and the 1414 cm�1 band is strongly coupled to the asym-metric C C C stretching.

The Raman spectrum shows a strong band at 1268 cm�1.According to our theoretical calculations, this band belongs to A1species of msC C C + msCACH3. The corresponding IR band appearsas a sharp band with medium intensity at 1263 cm�1 and belongs

Table 3Fundamental band assignment of Mg(AA)2.a

Sym. Theoretical Experimental Assignments

FScal. IIR AR IR solid IR CH2Cl2 R solid T.W Ref.[9]

A1 3075 0 157 3079(5) mCHaB2 3075 17 0.2 3074(5) 3076(2) mCHaE 3004 1 1 maCH3A1 3004 0 220 2995(4) msCH3B2 3004 68 3 2994(5) msCH3E 2971 14 1 2970(5) msCH3B1 2971 0 379 2969(6) maCH3A2 2971 0 0 maCH3A1 2916 0 698 2921(31) msCH3B2 2916 4 34 msCH3E 2916 14 2 2922(4) 2922(2) maCH3A1 1602 0 24 1633(4) msC O + msC C CB2 1582 1165 7 1612(51) 1612(55) 1610(6) msC O + msC C C msC OE 1522 421 6 1519(100) 1521(100) 1521(30) maC C C + dCHa maC C C + dCACAHE 1473 101 14 1478(31) 1476(23) daCH3 + maC OA1 1453 0 13 1453(9) dsCH3B2 1453 174 35 1457(22) 1459(12) 1453 dsCH3E 1447 14 26 1445(15) 1436(11) 1437(10) dsCH3B1 1446 0 15 1437 daCH3A2 1446 0 0 daCH3E 1416 444 1 1410(70) 1414(32) maC O maC C CA1 1372 0 41 1393(15) dsCH3B2 1372 6 65 1393(15) dsCH3E 1370 38 4 1360(15) 1364(11) 1365(28) daCH3 dsCH3A1 1264 0 29 1268(43) msC C C + msCACH3 msC C CB2 1261 102 21 1263(34) 1265(28) 1257(18) msC C C + msCACH3E 1199 18 7 1198(6) 1199(3) 1196(18) dCACAH dCACAH + maC OB1 1039 0 0.1 pCH3A2 1039 0 0 pCH3E 1025 12 1 1020(23) 1021(14) pCH3B2 1024 80 0.2 1020 1021 qCH3 + D+ qCH3A1 1023 0 22 1024(16) qCH3+E 1016 7 1 q CH3 + dCHaB2 938 9 3 942(6) 942(4) dC C C+qCH3A1 938 0 15 938(11) dC C C+qCH3E 924 21 0.1 926(21) 928(11) ma(CACH3) + D Complicated modeE 788 20 1 788(6) 781 w* cCACAH cCACAHB2 673 77 2 663(7) 664 w 664(30) msOAMgAO + D cC C CE 663 4 �0 652(7) 653 w cC C CA1 652 0 8 647(14) dC C OE 568 28 0.2 567(7) 569 m| maOAMgAOB1 570 0 6 566(25) CA2 569 0 0 CB2 529 149 4 546(12) 549s 541(22) dC C OA1 423 0 12 414(100) msOAMgAOE 402 11 2 422(21) 426 s dCACH3 + DE 345 14 2 356(16) 361 s 345(18) DB2 347 24 2 356 361 345 dOAMgAOA1 245 0 0.3 260(15) dCACH3B2 242 12 0.2 256 m 251 w dCACH3E 163 2 1 198 m n.m 172 w# cOAMgAOA1 154 0 1 165 w mAAAMgAAAE 154 9 �0 144 w n.m cOAMgAOB1 146 0 0.1 146 w sOAMgAOA2 127 0 0 cCACH3B1 96 0 0.2 107 w sCH3A2 95 0 0 sCH3E 87 1 �0 73 w n.m 75 vw sCH3B1 34 0 8 56 vw sAAAMgAAAE 37 1 3 53 w n.m cAAAMgAAA

a FScal., theoretical frequency calculated at the B3LYP/6-311++G** level, scaled by 0.9607 and 0.9819 for the 2900–3100 cm�1 and below 1700 cm�1 regions, respectively;IIR, IR intensity (in kM/mol); and AR, Raman activity (ÅA

04/amu), calculated at the B3LYP/6-311G** level (in Å4/amu); T.W., this work; the relative intensities are given in

parentheses; n.m, not measured; m, stretching; d, in-plane bending; c, out-of-plane bending; D, in-plane ring deformation; C, out-of-plane ring deformation; s, torsion; , inpolyethylene; *, in CCl4 solution; |, different scale below 600 cm�1; #, different scale below 200 cm�1.

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to E species. The corresponding band in the metal complexes ofacetylacetone occurs in the 1260–1300 cm�1 range [11,21,26–28]. Junge and Musso [11] assigned this band solely to msC C C.

The 1199 cm�1 band is assigned to the CAH in-plane bending.However, Junge and Musso assigned this band to dCAH + ma C O.It seems that the corresponding frequency for metal complexesof acetylacetone occurs in the 1190–1199 cm�1 range [11,21,26–28]. The strong IR band at 1021 cm�1 is assigned to the symmetricMgAO stretching coupled to one of the ring deformation modes.However, Junge and Musso [11] assigned this band to qCH3.

4.2.2.4. Below 1000 cm�1. In this region, one expects to observeCACH3 and MgAO stretching, CH out-of-plane bending, and in-plane and out-of-plane ring deformation modes. The infrared spec-trum shows two bands at 942 and 928 cm�1. According to the the-oretical calculations, we assigned the band at 942 cm�1 to theCACAC bending which is coupled to the CH3 rocking. This bandis not assigned by Junge and Musso. The corresponding Ramanband, which belongs to A1 species, occurs at 938 cm�1. The928 cm�1 band is assigned to the asymmetric CACH3 stretchingcoupled to the in-plane ring deformation. However, Junge andMusso considered this band as a complicated mode.

The IR spectrum of Mg(acac)2 indicates a weak band at781 cm�1 which, according to the theoretical calculations, belongsto E species of the CHa out-of-plane bending. The 664 cm�1 band isassigned to the B2 species of symmetric MgAO stretching. Jungeand Musso assigned this band to the CACAC out-of-plane bending.The corresponding band in Be(acac)2 occurs at considerably higherfrequencies (826 cm�1). This difference is partly caused by the Mgheavier than the Be, since in this vibration the central atom is alsomoving, and is partly caused by the difference in the strength ofmetalAoxygen bond in these two complexes. However, the A1symmetric species of MAO stretching, in which the central metalis not moving in this vibrational mode, can directly reflect thestrength of the MAO bond. This band is only Raman active and ob-served at 414 and 480 cm�1 in the Raman spectra of Mg(acac)2 andBe(acac)2 [22] complexes, respectively. Therefore, it may con-cluded that the MAO bond in Be complex is considerably strongerthan in Mg complex. This is in agreement with the stability con-stant results for these two complexes [29]. Starý and Liljenzin[29] reported the stability constants of 6.28 � 1010 and14.6 � 1010 for Mg and Be acetylacetonates, respectively.

According to the calculation results, the weak band at 569 cm�1

is assigned to the asymmetric MgAO stretching, and the strongband at 549 cm�1 is assigned to the C C O in-plane bendingmodes.

The 345 cm�1 Raman band is assigned to the OAMgAO bendingmode (B2). The corresponding frequency in the Raman spectrum ofBe(acac)2 has been reported to occur at 441 cm�1 [21].

The very strong infrared band at 426 cm�1 is assigned to the Especies of CACH3 in-plane bending coupled to the in-plane ringdeformation. The corresponding band in the IR spectrum of Be(a-cac)2 occurs at about the same frequency as in Mg(acac)2,420 cm�1. The infrared band at 144 cm�1 and the Raman band at146 cm�1 are assigned to the OAMgAO out-of-plane bending andOAMgAO torsion, respectively.

5. Conclusion

The structural parameters of Mg(acac)2 were calculated at theDFT level using B3LYP functional with 6-31G*, 6-311G**, and 6-311++G** basis sets. For comparison, these calculations were alsoperformed at the MP2/6-31G* level. A good agreement between

Wavenumbers (cm -1)

%T

600800100012001400160018000

20

40

60

80

100

in KBrin CH2Cl2in CH3CN

Fig. 2. Infrared spectra of Mg(acac)2 in CH2Cl2 (. . .. . ..), in CH3CN (————), and inthe solid state (—).

20040060080010001200140016000

20

40

60

80

Raman shift (cm-1 )

Inte

nsity

Fig. 3. Raman spectrum of Mg(acac)2 in the solid phase.

800100012001400160018000.0

0.5

1.0

1.5

2.0

Wavenumbers (cm-1)

Abs

orba

nce

Fig. 4. The deconvoluted IR spectrum of Mg(acac)2 in the CH2Cl2 solution.

Table 4Calculated and observed isotopic frequency shifts. a

FScal FObs 2,4-13C 2-13C Ref. [9]

1582 1612 �43 �18 �191522 1519 �18 �9 �81370 1360 0 0 �11264 1263 �37 �17 �161199 1198 �8 �5 �21024 1020 �4 �2 0924 926 �8 �4 �1788 788 0 0 �1

a FScal and FObs are scaled calculated and observed frequencies (cm�1).

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calculated geometry and the gas-phase electron diffraction resultsare obtained.

The vibrational frequencies were calculated at a variety of pop-ular DFT levels using 6-31G*, 6-311G**, and 6-311++G** basis sets.The predicted frequencies were compared with the experimentaldata in the solid state and in solution. A satisfactory reproductionof the experimental frequencies and isotopic frequency shifts isobtained.

Appendix A. Supplementary data

Supplementary data associated with this article can be found, inthe online version, at doi:10.1016/j.molstruc.2009.09.006.

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