Mercury halide complexes

The stereochemical transformation of the mercury halide complexes in the course of the stepwise complex formation could also be followed by means of X-ray examinations [Ga 68]. The results at times cast doubt on the correctness of the conclusions derived from the equilibrium data. In the case of mercury halides, the stability of the third stepwise-formed complex is much higher than that of the fourth, and the value of X3/X4 is therefore large. This would indicate that the former complex already has tetrahedral symmetry. According to the X-ray examinations, however, the reason for the anomalous stability sequence is that the second complex is linear, the third is pyramidal and only the fourth has tetrahedral symmetry [Ga 68]. 

The structures of two ruthenocene-mercury halide complexes have been reported at an early stage of refinement (2 >0.22), The complex [(ii-C5H5)2Ru]HgBr2 is dimeric (15) with distorted tetrahedral co-ordination... 

We begin by considering the stability constants for the formation of halide complexes with zinc(ii) and mercury(ii) (Table 9-2)... 

A huge number of studies have been done in the past on cadmium and mercury halides and their complexes, and there is still research interest in the field, sometimes yielding surprising results. And simple-looking systems, on closer inspection, turn out to be rather complex. 

Mercury(II) complexes of two t5T>es have been prepared (6) from pent-4-enyl diphenyl phosphine and mercuric halides. These complexes are of the formulae [LHgX2]2(X = Cl, Br, I) and LaHgXg (X = Br, I). In no case is the olefin coordinated to the metal. 

Ligand exchange reactions have been used to prepare mercury(II) trialkylarsine complexes.202 Reaction of AgN03-AsMe3 with mercury halides gave the mercury arsine and silver halide (equations 10 and 11). The silver nitrate complex was not characterized. 

Both 1 1 and 2 1 complexes of Af,.ZV-diethyl- and N,iV-dimethyl-thiourea with zinc, cadmium and mercury halides have been prepared. The 2 1 complexes are either monomeric and tetrahedral or polymeric and halogen-bridged with octahedral metal coordination the 1 1 complexes also possess a polymeric, halogen-bridged structure, but with tetrahedral metal coordination.894 5... 

The reaction of dithiooxamide and its tetramethyl and tetraethyl derivatives with zinc, cadmium and mercury halides leads to complexes of stoichiometry MLX2 (M = Zn, Cd or Hg X = C1, Br or I).900,9 1 M—S bonding is involved IR spectra show that the zinc and mercury complexes are four-coordinate, while the cadmium complexes are octahedral with halogen bridges. 

The stability constants in melts of NH4N03- H20 of ZnX+, ZnX2 (n = 1-3 X = Cl or Br), CdX+, CdX2 (n = 1.5-3 X = Cl or Br) and HgX HgX2 (n = 2.5 X = Cl or Br) have been determined.950,931 The behaviour of zinc is peculiar if the Ki and K2 values are compared with those of cadmium and mercury. The stability constants increase with temperature and the bromide is more stable than the chloride, trends which are opposite to those normally observed for the halide complexes of most metals in anhydrous or aqueous melts. The data also show... 

Following the preparation of 4.79, a number of other cyclic mercury crown compounds have been synthesised, which do exhibit halide complexation behaviour. Compound 4.80, forms a 1 1 polymer with bromide in the solid state in which the Hr anions perch above the Hg3 plane. The Hg—Br distances of 3.07-3.39A are considerably longer than normal Hg—Br covalent bonds (about 2.54A).61 The compound also binds SCN- with similarly long bonds as shown in Figure 4.34.60 The analogous chloride complex has a 3 2 stoichiometry suggesting a triple-decker sandwich of type [4.80 Cl 4.80 Cl 4.80]2. ... 

The 2,2 -bipyridylamine complexes of some zinc, cadmium, and mercury salts have been reported.29 All the metal halide complexes isolated are of the stoicheiometry MLX2 (M = Zn, Cd, or Hg X = Cl, Br, or I), and are assigned a monomeric, tetrahedral structure on the basis of i.r. evidence. The complexes ML(SCN)2 (M = Zn, Cd, or Hg) are also monomeric. Only mercuric cyanide reacts to give the monomeric HgL(CN)2, whereas zinc sulphate forms 1 1 and 1 1.5 complexes which possess highly polymeric structures. Zinc and cadmium acetates form 1 1 complexes having pseudo-octahedral structures with bidentate, symmetrically chelating acetates. Cadmium also forms a 1 3 complex which is best formulated as [CdL3] [OAc]2. 

Complexes of several S-donor ligands have also been reported. The reaction of dithio-oxamide and its tetramethyl and tetraethyl derivatives with zinc, cadmium, and mercury halides leads to complexes of stoicheiometry MLX2 (M = Zn, Cd, or Hg X = Cl, Br, or I).64,65 M—S bonding is involved i.r. spectra show that the zinc and mercury complexes are four-co-ordinate, while the cadmium complexes are octahedral with halogen bridges. The complexes [ML3][C104]2 have also been prepared and do not contain co-ordinated perchlorate. The complexes ZnL (H2L = dithio-oxamide, NiV-dimethyl- and IVA -dicyclohexyl-dithio-oxamide) have been isolated,66 and consist of linear chains containing four-co-ordinate zinc. 

Mercury(II) halide complexes of the phenotellurazine precipitated when solutions of the mercury halide in ethanol were mixed with solutions of the heterocycle in diethyl ether. 

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