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Vibrational Spectra ofDimethyldithiophosphinateAnion: (CH3)2PS2Claudio A. Téllez S. a , Sergio G. de la Riva a ,Eduardo Hollauer b , Ionel Haiduc c & Cristian S.Silvestru ca Departamento de Química , Pontificia UniversidadeCatólica do Rio de Janeiro , PUC-Rio. Rua Marquésde S. Vicente 225, Gávea., Cep: 22453-900, Rio deJaneiro, RJ, Brazilb Departamento de Físico-Química , UniversidadeFederal Fluminense (UFF) , Morro do Valonguinho s/n. Niterói, Centro, Cep: 24210-150, Rio de Janeiro,Brazilc Chemistry Department , Babes-Bolyai University ,R-3400, Cluj-Napoca, RomaniaPublished online: 20 Aug 2006.

To cite this article: Claudio A. Téllez S. , Sergio G. de la Riva , EduardoHollauer , Ionel Haiduc & Cristian S. Silvestru (1998) Vibrational Spectra ofDimethyldithiophosphinate Anion: (CH3)2PS2 , Spectroscopy Letters: An InternationalJournal for Rapid Communication, 31:7, 1469-1483, DOI: 10.1080/00387019808001653

To link to this article: http://dx.doi.org/10.1080/00387019808001653

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SPECTROSCOPY LETTERS, 31(7), 1469-1483 (1998)

VIBRATIONAL SPECTRA OF DIMETWLDITHIOPHOSPHINATE ANION: (Cr4hB:

Claudio ATeUez S.'., Sergio de la Riva G.', Eduardo HoUauer2, Ionel Haiduc3 and Cristian S.Sivestru

' Departamento de Quimica. Ponti6cia Universidade Catolica do Rio de Janeiro. PUC- Rio. Rua Marques de S.Vicente 225, Givea. Cep: 22453-900 Rio de Janeiro. RJ. B d .

Departamento de Fisico-Quimica. Universidade Federal Fluminense (UFF).

MOKO do Valonguinho s/n.Nitdi Centro. Cep: 24210-150. Rio de Janeiro. Brazil.

Chemistry Department, Babes-Bolyai University. R-3400, Cluj-Napoca, Romania.

ABSTRACT

The infrared and Raman spectra of dimethyldithiophosphinate anion (CH&!PSi were

measured and the vibrational modes for the anion complex were assigned. A Normal

Coordinate Analysis in the Modified General Valence Force Field (MGVFF)

approximation was carried out assuming Ca symmetry. Ab Initio Calculations at RHF and

MP2 level were also carried out for the anion geometry as well as for its frequencies,

intensities and force constants.

(*) Author to whom correspondence should be addressed.

1469

Copyright 0 1998 by Marcel Dekker, Inc. www.dekker.com

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1470 TELLEZ ET AL.

INTRODUCTION

Spectroscopic studies of compounds containing the dimethyldithiophosphe anion

are of great interest since correlations of the attributable vibrational fiequencies of the -

PS2 groups and those of the coordinated compounds with these ligands could be done

[1,2]. The i n h e d spectrum of (CH3)2PSi was earlier reported by Dumitrescu and

Haiduc [3], and a n o d coordinate analysis (NCA) for a simplified model M2PSi

(M = CH3) anion in the Urey-Bradley force field approach was carried out. Dumitrescu

and Haiduc [3] assigned the 740.0 and the 726.0 cm-' wavenumbers to the vI(pC) and

to the vXpC) normal modes, and the 600.0 and 497.0 cm-' infked wavenumbers to

the v&S) and v,(CS) respectively. Although in the IR spectrum the assymmetric P-C

stretching band is assigned at 740 cm-' , it is lower in intensity than the symmetric P-C

stretching assigned at 726.0 cm-'. We do not have any other experimental confirmation

on the assignment of these wavenumbers such as the Raman depolarization ratio. The

assignments of these bands are only sustained by a NCA of a reduced model of

(CH&PSi anion and perhaps could lead to a wrong interpretation. To avoid this

problem, the present study include: i) The Raman spectrum of (CH&PSi , u) a

General Modified Valence Force Field for the whole ligand without considering the -

CHI groups as point masses and iii) Geometrical parameters were obtained through ab

initio calculations using a basis set of double-zeta quality at Restricted HartrwFock

(RHF) and RHF/MP2 level (Moller-Plesset Perturbation Theory ) [4].

EXPERIMENTAL

NaS2PMe.2HzO was synthesized according the method described by Higgins and

Vogel [S]. The infrared spectrum was measured on a FT-IR spectrometer using a

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VIBRATIONAL SPECTRA 147 1

deuterated triglycine sulfate (DTGS) detector. Infiiued data were obatined in two

different ranges: in the 4000.0 to 350.0 cm-' region using KBr pellets and a resolution

of 4.0 cm-' and in the 700.0 to 30.0 cm-' region using pellets of the sample mixed with

polyethylene powder and a 1 .O cm-' resolution. The wavenumber reading in the lower

region was checked by running the spectrum of a polyethylene pellet as a blank. No

significative absorption bands were found between 700.0 and 70.0 an-'. In both cases

the number of scans was 120. The Raman spectra of the solid sample and in aqueous

solution were run on a Nicolet FT-Raman 980 spectrometer with a Ge detector, using

1064.0 nm radiation kom a Nd-YAG laser and a 2.0 an-' resolution. Infrared and

Raman spectra are illustrated in figure 1.

RESULTS AND DISCUSSION

Kbrational spea?a. a) -CHI group and framework couplinp or rock& modes. The

infrared and Raman data of dimethyldithiophosphinate anion are presented in Table 1,

together with the assignments. Band assignments of the -CH3 methyl groups were

done in the usual manner [6 1. IR wavenumbers at 3000,O and at 2902.0 cm-' were

assigned as v.,(C-H) asymmetrical stretching modes. The v,(C-H) symmetrical

stretching were assigned at 2923.0 and at 2915.0 cm". The Raman spectrum shows

Raman shifts at 2994.2 and at 2917.0 cm" which were assigned to the v,,(C-H) and

vXC-H) normal modes, respectively. The bending vibrational frequencies of the -CH3

group are also considered as characteristic kequencies and its assignments are

straightforward . Our assignments of these modes are listed in Table 1. The rocking

p(CH3) vibrational modes were assigned at: 946.0(IR, bl), 942.w ,bl), 915.0(IR, b),

913.m a2); 853.0(m al), 850.1(R, al) cm-'.

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1472 TELLEZ ET AL.

3500 ooo 2500 1DI 1500 IDDO 500 Wavenumbers (cm-1)

7 0

a s - so -

4 s - 4 0 -

IT " L 3.0

I

3500 - 2500 1500 laa so0

Rnman Shift (cm-I)

Figure 1.: Infhred and Raman spectra of dimethyldithiophosphinate anion: (CH3)zPSi .

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VIBRATIONAL SPECTRA 1473

b) Framework or skeletal vibrations. As was earlier pointed out by Silaghi,

Dumitrescu and Haiduc [3], the P-C stretching wavenumbers are expected to

appear between 780.0 to 620.0 cm-'. Although this assignment was confirmed by us

attention should be called since the v a C ) is lower in intensity compared to the

vXpC) found at 726.0 cm-'. In the Raman spectnus the Raman shift at 720.0 cm-'

was correlated with the 726.0 cm-' found in the infrared spectrum. The vXpC) in

the Raman spectrum is very weak in intensity but it has higher intensity than the

vl(pC) found at 738.0 cm-'. The Raman polarized spectrum shows that the Raman

shift at 720.0 cm-' is polarized confirming the previous assignment of the vl(pC)

and vXpC) vibrational modes reported by Haiduc et al. [3].

The Raman spectra in aqueous solution in the region of 840 - 640 cm-' are

depicted in figure 2.

The Raman spectrum in aqueous solution showed an intense Raman band at

501 .O cm-' which was assigned to the vXpS). In this Raman spectrum, the v&'C) was

not observed. In the infiared spectrum the assignments of the P-S stretching were:

v a S ) at 495.0 an'' and vXpS) at 375.0 cm-'. The skeletal bending vibrational modes

were assigned to the following wavenumbers: 375.0(IR), 208.0(IR), 282.0(IR), 228.0

(R), 222.0(R) and 284.0(R) cm-' . Details of the IR and Raman spectra in the 1000 -

350 cm-' region are illustrated in figure 3.

Optimization of the geometrical parameters: Ab initio calculations employing the

Dunning-Huzinaga double-zeta basis set was canied out at RHF and MP2 level. As

expected, the calculations showed similar results in an acceptable agreement with the

estimated geometrical parameters of [3]. The major observed difference is concerned to

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1474 TELLEZ ET AL

Table 1.Infnred and Raman soectra of (CH~IPS;.

IRlsolid) Ramadsolid) Raman(aa.sln) Calculated Approximate description

3000.0

2984.0

2971.0

2915.0

2902.0

1459.0

1412.0

1407.0

1290.0

1283.0

1083 .O

946.0

915.0

853.0

739.0

678.0

600.0

522.0

496.0

475.0

3000.1

2983.8

2969.8

2917.0

2902.6

1421.7

1409.3

1294.0

942.4

913.0

850.1

738.6

594.7

547.3

497.1

472.2

2994.2 3023.6

2984.0 2997.9

2897.9

2922.3

2.904.3

1427.3

1414.6 1433.0

1390.9

1303.6

1283 .O

1080.9

943.5

915.0

875.8

733.5 739.9

597.4

553.3

497.4 498.0 V(p-S)@3

600 -122 = 478

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VIBRATIONAL SPECTRA 1475

Table 1. Continued

372.4

295.5

281.6 28 1.6

227.8 228.9

208.2 218.0

363.7 G(bework)(al)

290.0 G(framewurk)(&

283.0 276.0 G ( b w a k ) @ i )

225 7 227.9 G(framework)(b2)

217.5 204.6 G(framework)(at)

i 69.7 torsion

lattice

lattice

122.2 126.5 lattice

159.2 153.7

145.1

a general elongation observed for all bands from RHF to MP2 level. The calculations

pointed out a Ch. symmetry in which two C-H bonds share the CPC plane pointing its

methylenic hydrogens atoms outwards the main C2 axes. This conformer show a

staggered configuration of the Newman projections along the Me-P bonds. A second

conformer showing two planar methylenic hydrogen pointing inwards has been

identified as a conformational transition state, performing through proper force

constant calculations at RHF and PR2 level. As far as we are concerned, no

experimental data of dimethyldithiophosphinate anion have already been reported.

Althoough approximations were made, our calculated results seemed to be better

accurated than those of reference [3]. The results for the most significant geometncd

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0.25 0.240

0.230

0.220

0,210

0.20 I 0.100

0.1w

o.cm

0.1M

0.15 0.140

0.130

\

800 760 720 680 640 Raman Shift (cm-1)

Figure 2. Polarized Raman spectra of (CH&PSi in aqueous solution

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VIBRATIONAL SPECTRA 1477

Wavenumbera (em-1)

1000 900 800 700 600 500 400 h m a n Shift (em-1)

Figure 3.: Raman spectrum of (CH&PSi in the 1000 to 350 cm-' region.

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1478

parameters are:

TELLEZ ET AL.

dPC (A)

dp-s (A)

&-H (A)

L s-P-s

L c-P-c

DZV/HF DZVMP2 Ref[3 ]

1.8593 1.8866 1.86

2.1667 2.1723 2.00

1.0816 1.1031 1.09

123.47 124.07 109.47

128.57 129.11 109.47

Normal coordinate analysis.

The 3n-6 = 27 vibrational modes of (CH3)*PS;

following irreducible representation of the point group Cx:

can be classified according to the

= Sa,(lR,R) + 4az(R) + 7bl(lR,R) + 5bz(lR,R).

The approach in the NCA is based on the assumption that vibrational modes may be

separated into ligand vibrations, ligand-framework coupling vibrations and framework

vibrations [7,8,9]. In this sense, as shown below, we have made the following set of

symmetry coordinates by assuming a C a overall structure. The structure and definition

of the internal coordinates are given in figure 4.

For the al species:

S I = % 43 A ( 2r1 - r2 - r3 + 2r4 - r5 - ra), S2= % 43 A ( 2al - a2 - a3 + cq - as -as )

S , = 1/46 A ( rl + r2 + r? + r4 + rs + r6 )

S 4 = 1/412 A ( a1 +a2 + a3 - P I - pz - P3 + cq + as +as - P d - PJ - 0 6 )

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VIBRATIONAL SPECTRA 1479

2

10 JA 11

Figure 4.: Structure and definition of internal coordinate for (CH3)2PSi .

S9= % 43 A ( 2y + 28 - s1 - EZ - E~ - E ~ )

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1480 TELLEZ ET AL.

for the b2 species,

Szl = !h A ( r2 - r3 - r5 + r6 ), S U = !h A ( a 2 - a3 - a5 +as )

Szl= !h A ( P 2 - p 3 - PJ + Pb), S z d = 1/42 A ( R-I - R-2)

S25 = % A (-€I - €2 + €3 + ~4 )

where the torsion n o d modes were excluded. This vibrational representation can be

subdivided as: rK= al + bl , = a1 + b2,

I-@ 2al+ a2+ 2bl + b2, To=2al +a2 + 2b1 + b2,

l-, = a1 + a2 + bl + b 2 , r, = a1 and re= al

As the normal modes of the -CH3 groups are considered to be characteristic, the

normal coordinate analysis was performed following the Cyvin’s rule [7] i.e., the off

diagonal force constants pertaining to different blocks between a) -CH3 - group and

rocking vibrations, b) -CHI group and skeletal vibrations and c) skeletal and rocking

vibrations were all constrained to zero.

The final set of symmetry force constants was obtained by an iterative least square

method [lo] and the values are listed in Table 2. Valence force constants deduced

from the analytical expressions [ 1 1,121 of the symmetry force constants are given in the

same table. The agreement between observed and calculated frequencies were within

1.0%. The potential energy distribution of force constants indicates the existence of

coupling between the different normal modes such as of the ligands, coupling ligand-

framework and those of the framework. According to the calculated values, in the a1

symmetry types, we found a mixture of the v.(CH) and v&H) normal modes and a

mixture between the bending and rocking of the -CH3 groups. Stark coupling was

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VIBRATIONAL SPECTRA

at Symmctry Force h Symmetry coordinates wauaats coordioata

1481

Fora WlKlanIs

I L.54

y 44 , Fa'O.11

I

Fn = 0.72 * ilj

I fR = slpc) = & = m) = WlWaUtS 4.7739.07 2.79 f 0.22 I 3.14 f 0.23

~~

The units are: stretching force constants in mdyn/A , bending force constants in mdyd, Stretch-bend interaction in mdyn units.

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1482 TELLEZ ET AL.

found between the stretching P-C and P-S and between the 8(CPS) and v,(PS)

vibrational modes. The potential distribution of force constants is given by request from

the authors.

In order to study the bond properties, some important internal force constants

were calculated from the set of symmetry force constants and the following trends were

observed: The value of fR = t;pc, = 2.79 f 0.22 mdy-td-’ and fR- = fms) = 3.14 f 0.23

md&’ agree with the informed values f&)= 2.97 mdyk’ and b. s)= 2.98 md&’

[14] and &-Q= 3.03 mdyd-’ and &,..s) 3.07 mdyd-’ [15], where 4 P-S) means the

mean values between &s) and f&) , confirming the hypothesis of II electron

d e l o d i t i o n in the PS; group.

Acknowledements

Claudio Tellez and Eduardo Hollauer thanks the financial support of FINEPRADCT

(project No 65.95.0381.00) and to CNPq for the research grant.

REFERENCES

1. I.Sdaghi-Dumitrescu, RGreca, L.Silaghi-Dumitrescu and I.Haiduc.,Studia

Univ.Babes-Bolyai,Chemia, 1989,XXXIV,1,97-10 1,

2. 1.Sdaghi-Dumitrescu and Ionel Haiduc; Rev.Roum.Chim., 1980,25(6),823-830

3. 1.Silaghi-Dumitrescu and Ionel Haiduc; Rev.Roum.Chim.,l976,25(6),815-821.

4. T.H.Dunning and P. J.Huy; ‘Modern Theoretical Chemistry” Plenum Press,New

York. 1976.

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VIBRATIONAL SPECTRA 1483

5 . W.A.Higgins, P.W.Vogel and W.G.Craig; J.Am.Chem.Soc.,1955,77, 1894.

6. C.Tellez ; Acta Sud Am.Chem., 1982,2, 59-71.

7. S.J.Cyvin, B.N.Cyvin and R.Andreassen.,J.Mol.Struct.,1975,25,141.

8. C.Tellez and G.Diaz.,J.Mol.Struct.,1981,77,213.

9. C . Tellez., Spectroscopic Letters., 1 98 8,2 1,87 1.

10. Y.Hase and O.Sala., “Computer Programs for Normal Coordinate

Analysis”.Universidade de S b Paulo,Brazil. 1973.

1 1 . K.Shimizu and H.Murata., J.Mol.Spectry.,1960,4,214

12. C.A.Te1lez.S. and L.Davila Cruspeire.,Can.J.of AppIied.Spectroscopy,1990,35(5),

105-109.

Date Received: April 16, 1998 Date Accepted: June 3, 1998

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