M r=365.54, monoclinic, P2 Jn, a= 5.922(2), b=16.589(12), c=6.722(3)A, fl= 104.52 (3) ° , V=639.3(6) A 3, D x=1.899Mgm -3, F(000)=360, Z=2, MoKa, 2=0.71069A, ~t= 1.5934 mm -~, room temperature, final R = 0.045,

We describe in this paper thethermal decomposition in air of several complexes of palladium(lI) chloride with imidazole and N-methylimidazole. Although the final process of the decomposition gives (PdCI~) n which 'then decomposes to pa ladium which oxidizes to PdO, there are interesting differences in the initial decomposition path. The reasons for these differences appear to be related to the trans-effect and to the presence in the imidazole complexes of .hydrogen bonds which break down at temperatures of around 220 ~ . This paper is the first of a series dedicated to the study of several complexes of palladium(II) chloride with imidazole and N-substituted imidazole. We describe here the thermal decomposition of some of this complexes in air. No attempt was made to obtain kinetic data, our main interest being to determine the existence of new species formed during the process of decomposition. Although the thermal decomposition of palladium complexes is a fertile area of study [1 ], there are, to our knowledge, no previous reports of the thermal behaviour of palladium imidazole complexes. The only example refering to complexes of this kind with elements of the nickel group refer to nickel(II) complexes [2] which, as expected from the general trends in the chemistry of nickel, palladium and platinum [3], differ considerably from those studied here. ExperimentalAll the complexes were obtained as described in reference [7]. The thermoanalytical curves were obtained on a Mettler 181 thermoanalyser. Samples of ,-, 10 mg were placed on uncovered platinum crucibles located on top of the thermocouple. The heating rate was standarized at 10~

The crystal data of cis-and trans-dichlorobis(imidazole)palladium(II), Pd(C3H4N2)2C12, C6HsC12N4Pd, have been determined from X-ray powder diffraction patterns. The compounds are triclinic, a = 10.197 (9), b = 9-107 (7), c = 8.034 (8) A, ~=110.06 (7), /3=95.12 (8), ;'=91.22 (7)

X‐ray diffraction patterns show that the isomers cis and trans[Pd(NMeIm)2Cl2] have a triclinic unit cell, with a = 16.594 (2), b = 10.440 (4), c = 8.757 (1) Å, α = 64.99 (1), β = 83.73 (1), γ = 80.41 (1)°, for the cis complex and a = 11.030 (9), b = 9.393 (7), c = 7.239 (5) Å, α = 101.14 (1), β = 94.43 (1), γ = 98.39 (1)°, for the trans complex.

The compounds [Pd(ImH) (7), c= 7.253 (3) ,~,, ~=93.46 (5),/3=89.83 (6), ~/=98.34 (4) °, for the imidazole compound and a=8-63 (1), b=7.74 (1), c=8-27 (1) A, ~=73-1 (1),/3=63-1 (1), ~=73-9 (2) °, for the N-methylimidazole compound. X-ray powder diffraction data are reported.