Complexes containing five metal ions

In contrast, 1 2 complexes contain one metal ion and two dye ligands and tend more towards dyeing the surface. This system is characterized by five- or six-membered rings, with the metal in the center of the octahedral structure. Metals are the trivalent, six-coordinated chromium, cobalt, and iron ions. Today, the principles underlying the structure and syntheses of metal-complex dyes are well known. Examples are C.I. Acid Blue 193, 15707 (1 2 Chrome) [12392-64-2] (11) and C.I. Acid Yellow 151, 13906 (1 2 Chrome) [12715-61-6] (12). 

EthylenediaminetetraaceticAcid. Ethylenediaminetetraacetic acid (EDTAH has six potential donor groups two nitrogen atoms and four carboxylate groups. If EDTA 4— acts as a hexadentate ligand to a metal, the resulting complex contains five five-membered chelate rings and has a charge that is four less than that of the metal ion. 

Fig. 3a-d. A diagrammatic representation of double-stranded helicates (23, 34] containing (a) two, (b) three, (c) four, and (d) five 2,2 -bipyridine subunits [23], The Cu(I) ions function as a template around which the helicates can assemble. Furthermore, this assembly process exhibits (i) self-self recognition in the preferential pairing to the same ligand in the presence of others in the reaction mixture, and (ii) positive cooperativity in which the complexation of one metal ion facilitates the binding of the next... 

As an example, let s consider an octahedral d] complex, such as one containing a Ti3+ ion. In a free Ti3+ ion, all five 3d-orbitals have the same energy and the d-clec-tron is equally likely to occupy any one of them. However, when a Ti3+ is dissolved in water, six H20 molecules surround it and form a [Ti(H20)h 31 complex. The six point charges representing the ligands lie on opposite sides of the central metal ion along the x-, y-, and z-axes. From Fig. 16.25, we can see that three of the orbitals (dxy, d, and d,x) have their lobes directed between the point charges. These three d-orbitals are called f2g-orbitals. The other two d-orbitals (dz2 and dx, y2), have lobes... 

Most commonly, metal ions M2+ and M3+ (M = a first transition series metal), Li+, Na+, Mg2+, Al3+, Ga3+, In3+, Tl3+, and Sn2+ form octahedral six-coordinate complexes. Linear two coordination is associated with univalent ions of the coinage metal (Cu, Ag, Au), as in Ag(NH3)2+ or AuCL Three and five coordination are not frequently encountered, since close-packing considerations tell us that tetrahedral or octahedral complex formation will normally be favored over five coordination, while three coordination requires an extraordinarily small radius ratio (Section 4.5). Coordination numbers higher than six are found among the larger transition metal ions [i.e., those at the left of the second and third transition series, as exemplified by TaFy2- and Mo(CN)g4 ] and in the lanthanides and actinides [e.g., Nd(H20)93+ as well as UC Fs3- which contains the linear uranyl unit 0=U=02+ and five fluoride ligands coordinated around the uranium(VI) in an equatorial plane]. For most of the metal complexes discussed in this book a coordination number of six may be assumed. 

Most of the nickel compounds in the solid state and almost all in aqueous solution contain the metal in the oxidation state +2, which, by consequence, can be considered the ordinary oxidation state for nickel in its compounds. The electronic structure and stereochemistry of nickel(II) were reviewed in 1968.6 The most stable electronic configuration of the free Ni ion is [Ar]3d8 which is also the ground state configuration in its complexes. The overwhelming majority of nickel(II) complexes have coordination numbers of four, five and six. Complexes with coordination numbers of three, seven and eight are still quite rare. 

The first pentagonal bipyramidal complex of zinc, ZnLCl2 3H20, was reported in 1973, where L is the planar five-coordinate 2,6-diacetylpyridinebis(semicarbazone).346 The crystal structure determination shows the complex to contain the [LZnG(H2Q)]+ cation, with three bland two O-donor atoms forming a slightly distorted planar pentagon around the metal ion and the chlorine and water in axial positions. 

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