Characterization and structure determination of ammonium bismuth oxalate hydrate, Bi(NH(4))(C(2)O(4))(2).xH(2)O.

From on-line coupled TGA-MS and TGA-FTIR measurements, in combination with a quantitative chemical analysis, it was deduced that the chemical formula for an unknown bismuth oxalate compound had to be Bi(NH(4))(C(2)O(4))(2).3.71(6)H(2)O. Solution of the crystallographic structure on the basis of X-ray powder data proved this formula to be correct. The diffraction pattern was indexed by a tetragonal unit cell [a and c respectively 11.6896(2) and 9.2357(3) A; M(20) = 195 and F(30) = 302; Z(calc) = 4], from which the space group I4(1)/amd (No. 141) was derived. Direct methods were applied to solve the structure. The initial structural model was subsequently refined by means of the Rietveld method (R(B) = 8.0%, R(wP) = 14.0%). Bi is 8-fold coordinated by oxygen from the oxalate anions. Since these BiO(8) polyhedrons do not share any edges or vertexes, an open framework is formed with water and ammonium molecules between. As a result, water can easily be removed, which is clearly indicated by the instant weight loss in the TGA upon heating. Moreover, as shown by HT-XRD, this process of water exchange is reversible as long as the heating temperature does not exceed 100 degrees C.

A new design of lead amalgam/lead sulphate electrode for potentiometric measurement of sulphate.

A new lead amalgam/lead sulphate electrode has been developed which is easy to handle and can be used in a simple measuring cell. Its electrochemical characteristics have been tested in two different cell systems. The potentials obtained were very stable, and reproducible within +/-0.04 mV. The electrode exhibited a Nernstian response to sulphate and its calculated standard potential (-350.68 +/- 0.13 mV) agreed very closely with that recorded in the literature.

Potentiometric investigation of the stability of silver(I) complexes of some N-methyl substituted 4-H-diethylenetriamines in aqueous solution.

By means of potentiometric pH and pAg measurements, the stability constants and the stoichiometric composition of the silver(I) complexes of some N-methyl-substituted 4-H-diethylenetriamines, in aqueous medium of ionic strength 1.3 and at a temperature of 25.00 degrees , have been determined. In addition to mononuclear and polynuclear complexes, together with their protonated forms, some hydroxo complexes are formed. The values of the stability constants are discussed in terms of possible structures.

A potentiometric study of the complexes formed between Ni(II) and Zn(II) and 3-mercaptopropionic acid.

The composition and stability constants of the complexes formed between Ni(2+) and Zn(2+) and 3-mercaptopropionic acid (3-MPA) were studied by a potentiometric method at 25 degrees and in 0.5M KNO(3). For the system Zn(2+)/3-MPA. a mixture of the mononuclear complex BA(2) and the polynuclear complexes B(3)A(4). and B(4)A(6) was found (B means the metal ion and A the ligand). The system Ni(2+)/3-MPA can be represented by the complexes B(5)A(10), B(6)A(11) B(6)A(9) and B(6)A(12). In this series the last two complexes are predominant.

The thermodynamics of ethylene-diamine complexes of silver.

The silver(I)-ethylenediamine system has been investigated and the existence of AgHL(2+) AgH(2)L(3+)(2), AgHL(2+)(2), AgL(+)(2) and Ag(2)L(2+)(2) with stability constants 10(2.33), 10(4.88), 10(6.47), 10(7.64) 10(13.13) has been demonstrated.

Graphical analysis of the formation function-II: the pseudo cross-over point.

In a further attempt to enhance the possibility of interpreting the formation function, a number of special shapes of the formation function are discussed, which give rise to a pseudo cross-over point. It is shown that under certain conditions a pseudo cross-over point can be found in the following cases: (1) two series of homonuclear complexes, (2) a mixture of a series of homonuclear and polymeric complexes, (3) a series of mononuclear complexes and two polynuclear complexes with nearly the same composition, (4) a system which gives a real cross-over point, and one or more polynuclear complexes, (5) a system of two polynuclear complexes. The conditions are mainly discussed in terms of the composition of the complexes. Calculated curves illustrate the different possibilities.

NMR determination of the microscopic constants of diprotonated diamines in aqueous solution.

The microscopic acidity constants of the diprotonated asymmetric N-methyl-substituted ethylenediamines and N-methylpiperazine were determined by using the change of the chemical shift of the methyl protons with varying acidity. The determination was carried out at 25 degrees in aqueous solution and in an ionic medium of 1M KNO(3). The basicity of the amino-functions follows the expected sequence: secondary > primary 2 > tertiary. The influence of the substituent on the basicity of the end-group is primary > secondary 2 > tertiary.

Graphical analysis of the formation function-I The real cross-over point.

From a mathematical treatment, it has been proved that a family of formation curves shows a real cross-over point in the following cases: (a) a mixture of mononuclear complexes BA, BA(2) ... BA(N) and polynuclear complexes of general formula (B(q)A(p))(n), provided that p/q < N; (b) a mixture of homonuclear complexes B(Q)A(p), where Q is constant, and mononuclear complexes shows at least one cross-over point if the maximum value for p is smaller than NQ and at least two cross-over points if NQ lies between the minimum value and the maximum value for p. Curves calculated for three different examples are in perfect agreement with the theory.