Metal complexes with some 3-aryl-1,2,4-oxadiazoles

Specrrochunica km,

Vol. 4lA. No. 12. pp. 1433-1436,

1985. 0

Printed I” Great Britain.

0584-8539/85 53.00 + o.o!l 1985 Pergsmon Press Ltd.

Metal complexes with some 3-aryl-1,2+oxadiazoles MARCELLA MASSACESI,*GEROLAMO DEvoTot and GIOANNAGELLIS di Chimica Generale, Inorganica ed Analitica, Universim, 09100 Cagliari, Italy, tCattedra di Chimica A, Facolm di Medicina e Chirurgia, Universim, 09100 Caghari, Italy and $Istituto di Chimica Organica, Universim, 09100 Cagliari, Italy *Istituto

(Receiued in revisedform 1 April 1985)

Abstract-Complexes of empirical formula M(L),X, were synthesized and characterized, where L = 5methyl-3-(2,4,6-trimethoxiphenyl)-1,2,4-oxadiazole (topho), M = Zn(II), Cu(I1). Co(II), Pd(II), Pt(II), X = Cl, M = Pd(II), Pt(II), X = Br, M = Zn(II), X = I; L = S-methyl-3-(3,5dichloro,2,4,6-trimethyl-phenyl)1,2.4-oxadiazole (ctpho), M = Cu(II), Co(II), X = Cl; L = 5-methyl-3-(2,4,6-trimethylphenyl)-1,2,4-oxadiazole (tpho), M = Cu(II), X = Cl. Magnetic, spectral, conductivity and elemental analysis data indicate that the ligands always act as monodentate, N-bonded. The Pd(I1) and Pt(I1) complexes are square planar and all the other derivatives are tetrahedral Infrared spectra were recorded in KBr pellets (4CQ@400cm- ‘) and Nujol mulls supported between polyethylene plates (400-100 cm-‘) using Perkin-Elmer 983 and 180 spectrophotometers, calibrated for frequency with polystyrene film and with the far i.r. bands of water, respectively. Electronic spectra were recorded on a Beckman Acta MIV spectrophotometer by the diffuse reflectance technique with BaSO. as reference sample. Magnetic susceptibilities were found the Gouy method using Hg[Co(NCS),] as a standard and diamagnetic corrections were applied.

INTRODUCTION

The ligands [l] together with their abbreviations and formulae are shown below. X X= -0Me

Y=

x=

--Me

Y = -CL

ctpho

X=

-Me

Y=-H

cpho

-H

topho

RESULTS AND DISCU8SION

All the compounds were prepared by refluxing the metal salts and the ligands in chloroform solution in the required stoichiometric ratio for about 24 h. The complexes obtained were washed with chloroform and petroleum ether and dried over P40i0.

We have isolated compounds having the general formula M(L)2X2, where M = Co(II), Cu(II), Pd(II), Pt(II), Zn(II), L = topho, X = Cl; and also the compounds Pd(topho)lBr,, Pt(topho)lBrz, Zn(topho)A, Co(ctpho)zCll, Cu(ctpho)zCll and Cu(tpho)K12. The analytical and physical data are reported in Table 1. The most important far i.r., electronic bands and the magnetic data, at room temperature, are listed in Table 2. The compounds are powders, variously coloured and diamagnetic, with exception of the Cu(I1) and Co(I1) derivatives. They all melt or decompose between 1052OO”C, are soluble in DMF, sparingly soluble or insoluble in other common solvents. They are non-conductors in DMF at 25°C although some dissociation is observed in the case of Zn(topho),I,. The i.r. spectra (4OOO4OOcm- ‘) of the compounds are very similar to those of the ligands, however the shift (5-10 cm- ‘) of the v(CN) bands supports coordination of the ring nitrogen atoms to the metal ion [2]. The v(N0) and v(C0) does not change on passing from the ligands to the complexes, thus excluding the participation of the oxygen atom of the oxadiazole ring in metal coordination [3].

Physical measurements

(topho) complexes

Carbon, nitrogen and hydrogen were determined using a Perkin-Elmer 240 analyser. Melting points were uncorrected and determined by a- capillary &ctrothermal apparatus. Conductivitv measurements were carried out with a WTW (Wiss.-Tech;. Werkstatten) LBR/B conductimeter at 25°C for 10-s M solutions in DMF.

Most of the complexes are obtained with this ligand. The far i.r. spectra (400-100 cm-‘) of the Pd(I1) and Pt(I1) complexes show new intense bands at 365, 354 cm- ’ and 358, 342cm-’ assigned to v(Pd-Cl) and v(Pt-Cl) where the ligand does not

Since they contain nitrogen and oxygen as donor atoms, these ligands may form complexes with various metal ions. It is therefore interesting to investigate the nature of these complexes in order to throw light on the stoichiometries and structures which ring substitution can impose on donor atoms. The synthesis and structural aspects of the derivatives of Co(D), Cu(II), Pd(II), Pt(I1) and Zn(I1) halides with (topho), (ctpho) and (tpho) are reported. EXPERIMENTAL Preparation

of the ligands

The (topho), (ctpho) and (tpho) ligands were prepared by reacting aryl nitrile oxides with acetonitrile, as reported in Ref. [ 11. Preparation

of the complexes

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MARCELLA MASSACESI et al.

1434

Table 1. Analytical Compound

Melting

Colour

and physical

point C( %)

Pd(topho)#, Pd(topho),Br, Pt(topho),CI, Pt(topho),Br, Cu(topho),CI, Co(topho),Cl, Zn(topho),Cl, Zn(topho),I, Cu(ctpho),Cl, Co(ctpho),CI, Cu(tpho),Cl,

Yellow Yellow Pale yellow Brown Pale green Sky-blue Pale pink Ivory Brown Sky-blue Brown

191 170 200 195 185 162 160 168 105 140 115

dec. dec.

dec. dec. dec.

42.5 37.5 37.6 33.7 44.4 43.2 44.3 33.1 41.5 43.8 52.4

data*

Found(calc.) I-U %)

N( %)

AMtin DMF (cm*R- ‘molU ‘)

4.1 (4.3) 3.7 (3.8) 3.6 (3.6) 3.3 (3.3) 4.4 (4.2) 4.5 (4.4) 4.4 (4.3) 3.4 (3.2) 3.6(3.5) 4.0 (4.1) 5.2 (5.6)

8.3 (8.3) 7.3 (7.6) 7.3 (7.1) 6.5 (6.4) 8.8 (8.7) 8.6 (8.4) 8.8 (8.6) 6.8 (6.6) 8.3 (8.1) 8.3 (8.1) 9.0 (8.9)

6 6 2 2 21 27 4 84 32 18 28

(42.5) (38.0) (37.2) (33.2) (44.3) (43.0) (43.9) (33.3) (41.4) (44.0) (52.3)

*The names of the ligands listed above are: 3-(2,4,6-trimethoxyphenyl)-5-methyl-1,2,~oxadi~ole (topho); 3-(3,5-dichloro-4,6-trimethylphenyl)-5-methyl-1,2,4-oxadiazole (ctpho) and 3-(2,4,6trimethylphenyh-5-methyl-1,2,4_oxadiazole (tpho). tThe reference values in DMF, under the same conditions, are 70-90 for 1: 1 electrolytes and 14&150 for 1 :2 electrolytes [16].

Table 2. Solid-state Complex

Absorption

electronic

absorption

maxima

maxima (cm- ‘), far i.r. .bands (4WlOO v(M-X)

v(M-L)

Other

cm- ‘) and magnetic

data

bands (I?.)

topho Pd(topho),CI, Pd(topho),Br, Pt(topho),CI, Pt(topho)ZBr, Cu(topho),CI, Co(topho),Cl,

379w, 224vw 365vs, 354~s 252vs 358s 342s 229~s 346s 3 14vsbr 340mbr, 320m

275m 278m 257m 246m 264s 240mbr

386m, 359m, 368sh, 33Ow, 364w, 301 w,

35Ovsbr. 3 13s 219~s 198mw

254~ 264m

332m, 276~ 351mw

32 270, 27 790, 12 700, 20000, 18620, 1786Osh. 16OCO 15100, 145OOsh, 11800,847O 7300, 6910,669O

340m 349m. 321m

245~ 247s

252w, 221 wbr 274mw, 232~s

35600, 32000,

346vsbr, 317vw

244s

36400, 31550, 26700 32 790, 23 000 36 100,27 320sh 37 050, 28 570 35210, 31250, 1748Osh, 14300 20000, 18600, 17400, 15950 15 3OOsh, 11360, 8450, 7350, 6900, 6720

Zn(topho),Cl, Zn(topho),I, ctpho Cu(ctpho),CI, Co(ctpho),CI,

tpho Cu(tpho),CI,

327sh, 296w, 257~ 329wbr, 295~ 316w, 304~. 286~ 317~. 304w, 290m 218m 276sbr

1.74 4.55

398vw 1.76 4.34

38Ovw. 331~~. 280w 1515Osh, 13500

absorb. These bands are indicative of cis square planar C,, stereochemistry with a terminal halide [4]. The new intense bands at 252 and 229 cm- ‘, diagnostic for trans square planar complexes, are attributed to v( Pd-Br) and v(Pt-Br), respectively. The bands at 346, 3 14 cm- ’ and 340, 320 cm- ’ in the copper(I1) and cobalt(I1) complexes are assigned to a v(Cu-Cl) and v(Co-Cl) terminal, respectively. The bands at 350,313 and 219,198 cm-’ in the two zinc complexes, which are typical of Zn-X terminal vibrations, are assigned to v(Zn-Cl) and v(Zn-I), respectively. The value of 0.63 found for v(ZnCl)/v(Zn-I) agrees with literature data for tetrahedral complexes [5]. For all these complexes the new intense band in the range 278-244 cm- ‘, which is absent in the free ligand, can be attributed to the v(M-N) ring vibration [6]. The electronic spectra for the Pd(I1) and Pt(I1)

36Oinw, 269s

1.86

complexes in the solid state (Table 2, Fig. 1) suggest a square planar geometry [7-91. The d-d absorption maxima at 28 57&23OOOcm-i assigned to the ‘A,, + ‘B,, transition confirm this geometry. In the U.V. region there are strong absorptions below 30 000 cm- ’ due to an L -+ M charge transfer. By assuming a value F2 = 10 F, = 6OOcm-i for the Slater Condon interelectronic repulsion parameters [lo], we can derive A1 = vi + 3.5 F2 from the first spin-allowed dd transition. These values lie in the range 30 670-25 100 cm- i. The i.r. spectra and conductivity data of these complexes confirm the square planar stereochemistry around the metal ions. The solid state electronic spectrum for Co(topho),Cl, (Fig. 3) is typical of distorted tetrahedral chromophores of the type CoN,X, [ll, 123. intense absorptions in the range The 18 600-l 5 950 cm-i are ascribed to the spin-allowed

3-Aryl-1,2,4-oxadiazole complexes

v(103cm-‘) 30

I

25

16

20

I

I

1435

(Fig. 2): p = 1.74 B.M. chemistry.

agrees

with

this

stereo-

(ctpho) complexes

I

I

I

I

300

400

500

600

WurQ Fig. 1. Diffuse reflectance spectra of: Pd( (topho),Cl, (a), Pt (topho),Cl, (b), Pd (topho), Br, (c) and Pt (topho),Br, (d).

v3 transition 4Az + 4T, (P) in Td symmetry, whereas the three strong bands in the near i.r. region have their origin in the splitting of the v2 transition 4A, + 4Tl (F) due to distortion from Td symmetry.

The magnetic moment (4.55 B.M.) falls in the range usually observed for such stereochemistry. The electronic spectrum of Cu(topho)sCls, in the solid state, is suggestive of distorted tetrahedral geometry. In fact the broad d-d absorption band centered at 14000 cm-’ is typical of complexes with distorted tetrahedral CuN,Cl, chromophores [13]

Only two complexes are obtained with this l&and: Cu(ctpho)lCl, and Co(ctpho)&l,. The far i.r. spectra show two bands, at 304cm-’ and 349, 321 cm-‘, absent in the free ligand, and which are attributed to v(M-Cl) in the Cu(II) and Co(I1) derivatives for terminal halides in tetrahedral stereochemistry [ 141. The ligand acts as monodentate N-bonded [v(M-N) = 245, 247 cm-i]. Their electronic spectra resemble those of (topho) complexes (Figs 2, 3). The Cu(ctpho)&12 complex has a strong band at 12 500 cm- 1 while the spectrum of Co(ctpho),Cl, is similar to that of Co(topho),Cls, except for increased splitting of the v2 absorption indicating a deviation from regular geometry (Figs 2, 3) [ll, 121. The magnetic moment values are in agreement with this assignment typical of distorted tetrahedral complexes. (tpho) complexes Cu(tpho)< is the only complex obtained with this ligand. On the basis of the i.r. electronic spectra and pvalues, we can assign a distorted tetrahedral geometry to this complex. In the far i.r. spectrum we found the v(Cu-Cl) band at 346, 317cm-’ which is indicative of terminal chlorides, and we ascribed the band at 244 cm- ’ to v(Cu-N) for metal complexes with nitrogenous heterocyclic ligands [lS]. The electronic spectrum (Fig. 2) is similar to that of the copper complexes of the two other ligands studied. The magnetic moment value (p = 1.86 B.M.) is in agreement with the assigned stereochemistry. CONCLUSION

A comparison of the numbers and stereochemistries of the complexes obtained with each ligand used

Fig. 2. Diffuse reflectance spectra of: Cu(topho),Cl,

(a), Cu(ctpho),Cl,

(b) and Cu(tpho),Cl,

(d).

1436

MARCELLA MASSACES] et al.

500

600

800

1000

1200

1400

1600

A (n4

Fig. 3. Diffuse reflectance spectra of: Co(topho),CI,

suggests that the nature of the X and Y substituents in the phenyl group, in position 3 of the oxadiazole ring, affect the donor capacity of the ligands and the stereochemistry of the complexes.

[l]

[2] [3] [4]

[5] [6]

(a) and Co(ctpho),CJ,

(b).

c71R. PINNA, G. PONTICELLI,C. PRETI and G. Test,

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