A group of complex metal halogen compounds

J. Inorg. Nucl. Chem.. 1961, Vol. 19. pp. 69 to 72. Pergamon Press Ltd. Printed in Northern Ireland

A G R O U P OF COMPLEX METAL H A L O G E N COMPOUNDS A. G. GALINOS* Departments of Chemistry and Chemical Engineering, New York University Heights (Received 9 September 1960; in revisedform 8 December 1960)

Abstract A general method of preparation and some properties are reported for (a) the preparation of salts with pyridine of the strong complex simple and mixed halogen acids of the metals Sb, Cd, Zn, of n

lit

the formula (Py... H . . . Py)+ (MeX3)- or (MeXD . (b) the preparation of complexes with the pyridine molecules inside the co-ordination sphere of the above simple and mixed acids. (c) the study of the infra-red spectra, and X-ray analysis, and other reactions are also reported. THE existence of etherated mixed and simple complex halogen acids of the metals, Zn, II

III

Cd, Sb of the type (MeX3) and (MeX4)("2'a) [(CzHs)20__H__O(C2Hs)2 ] ~, has given rise to the expectation that corresponding compounds involving protonated organic bases might be produced. Such compounds would be similar to the salts of organic bases with the common inorganic acids. In the following we report the preparation of salts of these complex halogen acids with pyridine. Complex compounds formed by combination of metallic halides with pyridine or quinoline have been known for over one hundred years. Since the advent of the Werner theory, many authors have worked systematically to classify these salts in accordance with the requirement of the theory. They reported the preparation of compounds with pyridine and quinoline of many metals including Cd, Zn, Hg, Cu, etc. 14 s~ They also prepared double salts with more than two molecules of pyridine, referring to them as di-, tri-, tetra-, penta- and hexa-pyridinium salts. GROSSMAN, as part of his extensive work, reported the existence of complex halides and thiocyanates of cadmium containing at most two molecules of pyridine per atom of cadmium in the case of the chlorides, and up to as many as six for the bromides and iodides. All these compounds decomposed to some extent when heated above their melting points. PFEIFFERand SCHNEIDER(91 have referred to analogous compounds containing antimony. HIEBER and REINDL~t°) have measured the heat of formation of these salts. General method of preparation. A weighed quantity of freshly prepared and dried etherate of the complex halogen acid was placed in a three-necked flask equipped with a separatory funnel, a stirrer, and a vapour exit tube connected to a vacuum pump by * Present address: Polytechnical University, A t h e n s - G r e e c e . ~11 A. G. GAIANOS, Z . Angew. Chem. 69-507 (19571. izl A. G. GALINOS, J. Amer. Chem. Soc. 82, 3032 (19601. tat A. G. GALINOS, I . M . Tsangaris Chimika Chronika 25, 163 (19601. 14~ p. GROXH, Lieb Ann. 105, 339 (1859). ~J T. ANDERSON, J. Chem. Soc. (2) 7, 406 (18691. IGt A. HESEKIt:L, Ber. Dtsch. Chem. Ges. 18, 309 (18851. /71 H. GROSSMAN, Z. Anorg. Chem. 37, 568 (19041. 18~ F. HONSELER, Z . Anorg. Chem. 46, 301 (19051. /~) p. PFEIFFER and K. SCHNEIDER, Ber. Dtsch. Chem. Ges. 68 B, 50 (1935). I101 W. HEIBER and E. REINDL, Z. Elektrochem. 46, 556 (19401. 69

70

A.G. GALINOS

way of a weighed dry-ice acetone trap and a trap cooled by liquid nitrogen. With the use of cold water to cool the flask and with stirring, an excess of liquid pyridine was added dropwise to the contents of the flask and a reaction vigorous almost to the point of explosion ensued. Stirring was continued to the end of reaction, all vapors evolved being collected in the traps. Analysis of the contents of the traps showed the presence only of ethyl ether in amount equal to that computed as present in the complex acid. The contents of the flask were kept in a vacuum desiccator over sulphuric acid for a period as long as seven or more days to remove the excess of pyridine. The residue, in the form of crystals of various colours was analyzed. Precautions were always taken to exclude moisture during the preparation procedure. Methods of analysis. Because of their sparing solubility in water, it was necessary to form solutions of these compounds in nitric acid before analysis. Standard analytical methods were used to determine the metal and halogen. The pyridine content was obtained by difference, and the H + was taken always as one (see Table 1). Generalproperties. All these compounds are crystalline and of various colors (see Table 1). They smell of pyridine and are insoluble in most of the common organic solvents, and only sparingly in water. They are soluble in acetone and especially so in a mixture of acetone with fuming concentrated hydrochloric acid. If H2S is passed into such a solution no precipitate is noted. Dilution with much water and saturation with HaS produces first a turbidity and then, on 10--12 hr standing, a precipitate of sulphide. In contact with concentrated H~SOa the compounds are inert. Their melting points are not very high. On heating to temperatures sufficiently above their melting points, they are chemically transformed but not decomposed, a molecule of pyridine probably entering the co-ordination sphere and displacing one of the halogen atoms. Details of these last phenomena are given in the next section. Preparation of complexes with the pyridine in the co-ordination sphere. The thermal behaviour of the compound, HCdBr3"2Py (Py = pyridine) was investigated. It was found to melt at 105°C and, on further heating, at 222-225°C to solidify, and form needle-like crystals easily observable with the naked eye and magnifying glass, with no observable evolution of vapour, odour of HBr or pyridine, and with no change in weight or apparent volume. These needles then melted sharply at 235 ° and were stable down to room temperature with no transformation to the original compound. The analytical results for the transformed product were the same as those for the starting compound. Behaviour toward organic solvents, water, H~S, and H~SO4 was similar to that of the original complex salt. In general, the two compounds differed not in observable chemical properties but only in physical properties such as melting point, crystal structure and in particular, odour and colour. The high melting compounds are without odour. Other similar thermally transformed compounds were studied (Table 1). In the case of zinc complexes, heating significantly above the first melting point has been observed to give rise to a glue-like material which, on cooling to room temperature crystallizes only after an hour or more. These crystals have a melting point different from that of the original complex. From the study of the infra-red spectra of all these compounds, there is evidence that the low temperature form of the metalhalide-pyridine complex has an N - H

A group of complex metal halogen compounds

71

TABLE 1

(L) Formula

Analysis

(H) m.p

Colour

(°C) H(SbCl4)2Py

(L) 1:1 :4.05:2.07 (H) 1:0.98:4.01:2.

164 182

(L) . (H) White

H(SbBr4)'2Py

1:1.03:3.97:2.04 1:1.04:4-04:2.1

205 226

(L) (H) Yellow

H(SbCI3Br)2Py

1:1 :3.02:0-97:1.96 1:0.96:3.01:1.04:1.98

200 226

(L) White (H) Yellow

H(SbBr3Cl).2Py

1:1 :2'93:0'96:2.07 1:0.97:3.08:0.94:2.07

182 209

(L) Pale yellow (H) Deep yellow

H(SblsCl)2Py

I:1.02:3'04:0.97:2.08 1:1 :2-95:1.1:2-I

190 215

(L) Yellow (H) Deep yellow

H(SblaBr)2Py

1:1.03:3.05:0.98:2.03 1:0.97:2.90:t.1:2.1

155 205

(L) Yellow

1:1.02:3.03:1.96 1:1.01:3.05:1-98

102 280

(L) Yellow

H(CdBrs).2Py

1:1"05:3-02:1.94 1:1.04:2.95:2.1

105 235

(L) Pale yellow (H) Yellow

H(CdCI~Br)-2Py

1:1.04:2.1:0.95:1.94 1:1.04:1-98:1.04:2.1

155 222

(L) White (H) Gray

H(CdBr,CI).2Py

1:1"02:2-08:0.93:1.98 1:1"05:2.02:0.98:2.1

110 236

(L) Orange

1:1.03:1.97:1.02:2.05 1:1'08:2.03:0.95:2

115 238

(L) Red

H(CdI2Br).2Py

1:0.98:1.96:1.05:2.06 1:I'01:2-02:0.99:2.1

100 226

(L) Yellow (H) Pink

H(ZnCls)'3Py

1:1 1:1

:3.01:3.03 :3.01:3.06

145 160

(H)

H(Znars).3Py

1:1.02:3.04:2.97 1:1 :3 :2.98

109 158

(L) Pale yellow (H)

H(ZnCI~Br).3Py

1:1.03:2.05:0.98:3.06 1:1 :2-03:0.99:3

114 142

(L) White

H(ZnBr2CI)-3Py

1 : 1 02 : 1-97 : 1-04 : 3.01 1 : 1-02:2.03:0.95:3

125 165

(L) Pale vellow (H)

H(CdCls)-2Py

H(CdI2CI)'2Py

(n)

(H) Orange

(n)

(H) Deep red

(L) White

72

A.G. GALINOS

vibration frequency close to that of the pyridinium halides, hence suggesting that the pyridi,le is outside the co-ordination sphere of the central metal ion. The high temperature form, on the other hand, shows evidence of a different N - H vibration in the 3.1-3.2p regions, which is at a significantly higher frequency. This is good evidence that there are two different bonds to pyridine species, one within the co-ordination sphere and the other outside it. In the case of the zinc compounds, which contain three moles of pyridine per mole of metal the spectra correspond identically to those of the Cd and Sb compounds which contain two moles of pyridine. We suggest that high melting form contains only one molecule of pyridine inside the co-ordination sphere. The appearance of pyridine molecules outside the co-ordination sphere is expected on the basis of the equation, H(MeXa).2EtzO -q- 2Pyr-*(PyrN--H--NPyr) + q- (MeXa)- q- 2Et20. It may be presumed that the hydrogen ion establishes a bridge between the nitrogen of the pyridine molecules as diagramed in the formula (CsHsN--H--NCsHs) + (MeXa)This bridge should be similar to the hydrogen bridge as usually formulated and should provide a certain amount of stabilization energy to the crystal. In the case of complexes with high melting points, there probably takes place a migration of a molecule of pyridine H(MeX3) 2Py---~PyH+(MeX2Py)X-°. L H It is also possible that there may have been a change in the co-ordination number. It seems probable that the low melting forms of the compounds of Zn, Cd, Sb have the molecules of pyridine outside the co-ordination sphere. The exact change in co-ordination between the low melting and the high melting forms is unknown, but many possibilities are involved, on the basis either of change in co-ordination number or of exchange between co-ordinated and non-co-ordinated groups. X-ray powder photographs of the compounds H(CdClzBr)2Pyr, H(CdBr3)'2Pyr, H(ZnC12Br).3Pyr show that the high and low temperature forms are distinct phases. In an attempt to distinguish between halogen inside and outside the co-ordination sphere, an acetone solution of AgCIO4 was added to a solution of a weighed sample of H(CdI~C1).2Py of high melting point in the same solvent. A turbidity first formed and in a few seconds a precipitate of AgCI and AgI. The precipitate was filtered rapidly and was found to contain all the halogen of the compound. While there may have been a stepwise precipitation of the halide the speed of total precipitation presented separation of the steps.

Acknowledgement--The work

reported in this paper was done while the a u t h o r held a fellowship o f the N a t i o n a l A c a d e m y o f Sciences of the U n i t e d States o f A m e r i c a u n d e r the visiting scientists' research p r o g r a m . * L = Low temp. form.

H = high temp. form.