spect~bimica A&, Vol. 278. pi. 1845 to 1848. Perssmon Press 1971. prfntad In Northern Ireland

Low frequency infrared spectra of complexes of 2-methylthioanilene with palladium II,

platinum n, nickel II and copper II

M. IKUM and D. B. POWELL School of Chemical Sciences, University of East Anglia

Norwich, NOR 88C

(Received 20 October 1970)

Al&r&-Low frequency infrared spectra of metal complexes of 2-methylthioanilene of the general formula M(mta)& (X = Cl or Br), show that for Nickel II and Copper II the com- plexes are octahedral, with mte acting as a bide&&e ligand and the halogens also coordinated. With Palladium II, mta also acts as a bidentate ligand but the halogens are not coordinated whereas with Platinum II the ligand is only coordinated through the NH9 group, the other two coordirmtion positions being occupied by halogens.

A NUMBER of metal complexes of 2-methylthioanilene (mta) have been reported of the type M(mta),X, (X = Cl or Br), and their infrared spectra studied in the region 4000-400 cm-l [l]. In the present work we have examined the low frequency infrared spectra of a series of these complexes and have found evidence for structural differences for complexes of the same general formula with different metals. The infrared spectra from 400 to 80 cm-l of these complexes are shown in Figs. 1 and 2,

and the observed frequencies below 400 cm-l given in the table. The spectra of the complexes of palladium II, Pd(mta),Cl, and Pd(mta),Br,

show a marked similarity in the region from 160 to 400 cm-l [Fig. l(a) and (b)]. Since bands due to metal-chlorine and metal bromine stretching vibrations should occur in this region (%+&cl 270-360 cm-l and Itpd__Br 180-240 cm-l), it follows that neither of these complexes contsin coordinated halogen atoms and their structure can be represented as [Pd(mta),]X,, with mta acting as a bide&s&e ligand.

In contrast the corresponding complexes of platinum II show strong bonds in the regions associated with platinum-bromine rend platinum-chlorine stretching vibrations (240 and 326 cm-l respectively [Fig. l(c) and l(d)]. Consequently the platinum complexes must contain coordinated halogen atoms, and since platinum II normally has a coordinrttion number of four, mta must be acting as a monodentate ligsnd. Evidence for the coordination being through nitrogen rather than sulphur is given by the N-H stretching frequencies which are lowered in frequency from 3440 and 3340 cm-l in the free ligand, to below 3100 in these complexes. This lowering of frequency is observed for all the complexes studied here and characteristic of a coordinated -NH, group. There is insufficient evidence from the infrared spectra to say whether these planer complexes have the cis or trans cotigurstion, but the frequencies observed for vp’Pt__haiogen are in the region reported for cis com- plexes. Furthermore the shoulder st 336 cm-l in the chloride complex could arise from the symmetric stretching vibration (infrared inactive in the bans isomer) whereas the stronger and broader band at 325 cm-r can be assigned to the asymmetric

[I] N. DUNSIU and T. H. CRAWEORD, J. Imwg. Nucl. Chem. 81, 2073 (1969).

22 1846

1846 111. IKRAM and D. B. POWELL

I

120 4

200 280 360

cm“

(a) Pd Br,(mta), lb) Pd Cl,(mta),

(c) Pt Br,(mta), (d) PtCl,(mta),

Fig. 1. Infrared spectra of complexes of 2-methylthioanilene.

stretching. A further difference from the palladium II complexes shown by the spectra of the platinum bromide complex is the disappearance of the high frequency component of the pair of bands which occur for the bidentate palladium complexes at 328 and 360 cm-l (marked L in the figure). It is probable that this difference arises from the change in configuration of mta when it acts as a monodentate ligand.

The spectra of the nickel II and copper II complexes Fig. 2(b) and 2(c)] are compared with that of Pd(mta),Br, [Fig. 2(a)]. These support the octahedral structure, with trans chlorine atoms, previously suggested for the nickel II complex

Low frequency iufrared spectra of complexes of 2-methylthioanilene 1847

(b)

A 1

120 200 280 360

cm-’

(of Pd Br,fmta& fb) Ni Cl2(mtal,

(c) Cu Ci,(mtal,

Fig. 2. Infrared spectra of complexes of 2-methylthioauilene (Ni II, C?u II).

Table 1. Abso~tion frequeneks of complex6s (400-80 cm-l) (mta = rnethylt~o~ile~e)

PdCL+% PbBr$m@ PtC4mta, PtBr,mt% ~%mt% NiC&mt%

360 s 360 vs 335 sh 345 m 345 m 335 VB 328 vs 325 s 292 m 290 w 302 s 300 8 280 8 280 s 280 m 282 w 295 m

270 m 256 m 270 w 270 m 216 m 222 m 230 mb 230 m 255 s

245 s 220 m 235 m 182m 182m 180b 235 m 200 w 220 m

220 m 192w 200 m

160m 150 m 160m I60m 142 8 130m 135 m 125m 130m 100 w 106 s 100 m

96 8 82s

1848 M. IKRAM and D. B. POWELL

by LIVINQSTONE [2] and similar to that proposed by DnMsxr for the corresponding co- balt II complex on the basis of magnetic susceptibility measurements. Both complexes show a pair of bands corresponding to those which it is suggested are associated with the presence of the bidentate ligand in the case of the palladium complexes. In addition bands associated with metal-chlorine stretching vibrations occur near 220 cm-l for the nickel II complex and near 300 cm-i for the copper II complex. These are the regions where the asymmetric stretching vibration of tram? Cl atoms in such octahedral complexes are usually found in the infrared spectrum.

EXPERIMENTBL

Complexes of 2-methylthioanilene were prepared as described by DUNSKI and CRAWFORD [l]. Satisfactory analyses were obtained in all cases.

Low frequency infrared spectra were obtained as mulls in liquid paraffin on an RIIC FS720 spectrometer, and spectra from 4000 to 400 cm-l on a Perkin-Elmer 126 spectrophotometer.

[Z] S. E. LIVINUSTONE, Quurt. Rew. 19, 386 (1966).