Composition of Complex Ions

Colon of copper complexes. When ammonia is added to 0.2 MCu2. the [Cu(NH3)4]2+ complex ion forms. The ammonia-containing ion is an intense deep blue, almost violet. The hydrated copper complex ion [Cu(H20)4]2+ is light blue. 

The nitrogen atom of each NH3 molecule contributes a pair of unshared electrons to form a covalent bond with the Cu2+ ion. This bond and others like it, where both electrons are contributed by the same atom, are referred to as coordinate covalent bonds. 

The Cu(NH3)42+ ion is commonly referred to as a complex ion, a charged species in which a central metal cation is bonded to molecules and/or anions referred to collectively as ligands. The number of atoms bonded to the central metal cation is referred to as its coordination number. In the Cu(NH3)42+ complex ion— 

Complex ions are commonly formed by transition metals, particularly those toward die right of a transition series (MCr — 3oZn in the first transition series). Nontransition metals, including Al, Sn, and Pb, form a more limited number of stable complex ions. 

Cations of these metals invariably exist in aqueous solution as complex ions. Consider, for example, the zinc(II) cation. In a water solution ofZn(N03)2, the Zn(H20)42+ ion is present. Treatment with ammonia converts this to Zn(NH3)42+ addition of sodium hydroxide forms Zn(OH)42-. 

When ammonia is added to an aqueous solution of a copper(II) salt, a deep, almost opaque, blue color develops (Figme 19.1). This color is due to the formation of the Cu(NH3)4 + ion, in which four NHj molecules are bonded to a central Cu ion. The formation of this species can be represented by the equation 

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The type of complex present in each solution depends on the acidity of the solution. In particular, HF solutions with concentrations lower than 25% contain niobium only in the form of NbOF52 complexes, whereas significant amounts of NbF6 ions are found in solutions containing 35% HF and higher. Table 44 shows the composition of complex ions in solutions of different concentrations, as found by Keller [171]. 

Composition of complex ions Instab stab / instab i, °C... 

Bredig [21] presumed that in a mixture of molten salts the variation of the interaction parameter X [see Eq. (8)] makes evident the formation of complex ions. Thus, in the KCl-CdCl2 and RbCl-MgCl2 systems it is observed variations of the X parameter and with the composition of the melt, and the minimum points of those variations correspond to the composition of complex ions. However, the most convincing data on the formation of complex ions can be obtained from measurements of the enthalpy of mixing [22],... 

Bloom et al. [62] showed that the composition of complex ions in melts can differ from that of minimum conductivity, because the complex ions are in equilibrium with the simple ions, so that the maximum negative deviation from the additive conductivity would not correspond to the stoichiometry of the complex ions. Other researchers [63,64] found that the stoichiometry of complex ions is influenced by the maximum value of the activation energy. In any case, the electrical conductivity data must be correlated with other physicochemical data, such as phase diagrams, Raman spectra, minimum thermodynamic activities, to obtain the composition of complex ions. 

Composition of complex ions instah stab / instab t, °c... 

The Compositions of Complex Ions from Transference Data. In... 

Spectrophotometry is a valuable tool lor discovering the Composition of complex ions in solution and lor determining their formation ci)iisianis (K values),... 

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